Construction and Building Materials 250 (2020) 118807
Contents lists available at ScienceDirect
Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat
Comparison between the effects of phosphorous slag and fly ash on the
C-S-H structure, long-term hydration heat and volume deformation of
cement-based materials
Lei Wang a,b,⇑, Fanxing Guo a, Yuqiang Lin c, Huamei Yang b, S.W. Tang d,⇑
a
College of Materials Science and Engineering, Xi’an University of Architecture and Technology, Xi’an, China
College of urban construction, Wuchang University of Technology, Wuhan, China
National Dam Safety Research Center（Yangtze River Scientific Research Institute), Wuhan, China
d
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, China
b
c
h i g h l i g h t s
The addition of 30 wt% PS reduces the 180-day hydration heat by about 9.2%.
The addition of 30 wt% PS reduces the 180-day shrinkage by about 9.0%.
FA is more conductive to reducing the long-term hydration heat and shrinkage.
PS reacts with CH and produces lots of C-S-H with high polymerization degree.
FA increases the polymerization and Al content of C-S-H more noticeable than PS.
a r t i c l e
i n f o
Article history:
Received 4 June 2019
Received in revised form 14 February 2020
Accepted 20 March 2020
Keywords:
Phosphorous slag waste
Fly ash
C-S-H
Long-term
Hydration heat
Volume deformation
a b s t r a c t
Fly ash (FA) has been widely used in hydraulic projects. The utilization of phosphorous slag (PS) to partially or completely replace FA in hydraulic concrete has gained much attention in China in recent years.
In this study, the effects of PS and FA on C-S-H structure, long-term hydration heat, hydration products,
mechanical properties and volume deformation of cement paste/concrete were investigated and compared via 29Si NMR nuclear magnetic resonance (29Si NMR), X-ray diffraction (XRD), scanning electron
microscopy (SEM), thermal analysis and the dissolution method. The retarding effect of PS at early age
hinders the generation of C-S-H, whereas the pozzolanic reaction of PS largely occurs at middle and late
age. More than half of the Ca(OH)2 content in cement paste is consumed and lots of C-S-H gels with high
polymerization degree are produced at middle and late age, leading to a dense microstructure of cement
paste. FA has a more noticeable effect on the enhancement of the polymerization degree and Al content of
C-S-H than PS. There is a reduction of 25.3% and 18.6% in the cement hydration heat within 3 days and
180 days when 30 wt% FA is blended. By contrast, PS is more helpful for lowering the hydration heat at
early age, the incorporation of 30 wt% PS reduces the 180-day hydration heat by about 9.2%. Additionally,
after the first few days, PS concretes possess stronger mechanical properties in comparison with FA ones,
confirming PS has a higher pozzolanic activity than FA. The adiabatic temperature rising of plain cement
concrete at 28 days was reduced by 4–5 ℃ due to 30 wt% PS incorporation. The addition of 30 wt% PS
reduces the early autogenous shrinkage significantly and declines the 180-day drying shrinkage and
autogenous shrinkage by about 7.2%-9.0% and 8–11%, respectively. However, FA is more effective in
reducing the adiabatic temperature rising, long-term autogenous shrinkage and drying shrinkage of concrete than PS. The results in this study could provide useful experience for the utilization of PS in hydraulic projects.
Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction
⇑ Corresponding authors at: College of Materials Science and Engineering, Xi’an
University of Architecture and Technology, Xi’an, China (L. Wang).
E-mail addresses: 535250684@qq.com (L. Wang), tangshengwen1985@163.com
(S.W. Tang).
https://doi.org/10.1016/j.conbuildmat.2020.118807
0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.
Hydropower is regarded as a renewable, clean and cheap
energy. Currently a series of world-famous hydropower stations,
2
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
such as Baihetan (installed capacity of 14 000 MW), Xiluodu (13
860 MW) and Wudongde (8 700 MW), etc., are being built in the
southwest of China. The temperature rising and volume deformation are particularly important to hydraulic mass concrete projects,
in which cracking may occur due to the temperature gradient or
shrinkage [1,2]. It is generally recognized that cracks could weaken
the performance and durability of concrete and even jeopardize
the integrity of concrete structure [3].
Fly ash (FA), a by-product of the coal power plants, comprises mostly of SiO2 and Al2O3 within an assemblage of
alumino-silicate glassy phases, with minor quantities of crystalline
phases such as quartz (SiO2), mullite (3Al2O32SiO2) and magnetite
(Fe3O4) [4–9]. The influences of FA on properties of concrete have
been widely studied. The spherical shape and fine size of FA particles could be beneficial to improve the fluidity and workability of
the fresh concrete [8,10–12]. Besides, FA is widely used to reduce
the temperature rising and the cracking risk of hydraulic mass concrete [13–15], since the addition of FA can decrease the hydration
heat of cement and internal temperature rising of concrete due to
its dilution effect and very low pozzolanic reactivity at early ages
[14,16,17]. Moreover, addition of FA could decrease the autogenous shrinkage and drying shrinkage of concrete at different
replacement levels, thus reducing the potential cracking of concrete [10–12,18,19]. It is widely reported that FA incorporation
can refine the pore structure and improve the long term compressive strength and durability of concrete due to the filler effect and
pozzolanic effect of FA, which could consume Ca(OH)2(CH) and
generate more secondary calcium silicate hydrate (C-S-H) at late
hydration time [4,8,20–22]. However, FA resources are relatively
scarce in southwestern China [23,24], especially in the regions of
Jinsha River, Yalong River and Dadu River, where hydropower
resources are quite abundant [25]. Therefore, the utilization of
other alternative mineral admixtures such as limestone powder
[26], phosphorous slag (PS) [27] and natural pozzolans [23] to partially or completely replace FA in hydropower projects, has gained
much attention in China in recent years.
Phosphorous slag (PS) waste is an industrial by-product during
the production of yellow phosphorus. It is estimated that producing 1 ton of yellow phosphorus generally generates 7 tons of PS,
and the annual production of PS is>8 million tons in China
[24,28]. PS is usually considered as a landfill waste, which causes
serious environmental pollution in southwestern China. PS is considered to be mainly composed of CaO and SiO2 with small
amounts of Al2O3 and P2O5 [5,29,30]. The glassy phase content of
PS is higher than 90% by weight, illustrating that PS has a potential
pozzolanic reactivity [24,27,29,31].
The utilization of PS in construction of hydropower projects is
beneficial for solving the accumulation issue of industrial PS
wastes and the problem of FA shortage in southwestern China.
However, PS has not been widely used in hydraulic mass concretes,
since the residual phosphorus in the form of P2O5 can postpone the
cement setting time and decrease the early concrete strength, consequently the engineering construction progress could probably be
delayed [27,32,33]. Besides, insufficient content of Al2O3 in PS
could weaken the early mechanical properties of concrete
[24,32,34]. Some thermal, chemical and mechanical activation
techniques are widely used to improve the pozzolanic reactivities
of PS [24,28,33,35]. Some chemicals, such as NaOH or water glass
solution, are used to activate the pozzolanic reactivity of PS. Shi
and Li [36] have reported that the chemically activated PS system
could achieve a 28 day-compressive strength of 120 MPa due to the
generation of lots of C-S-H in the activated system. Thermal treatments or elevated curing temperature can also improve the
strength of PS blended cement-based materials especially at early
age [28]. Moreover, the early reactivity of finely ground PS produced by mechanically grinding can be largely improved due to
the increase of specific surface area. The chemically or mechanically activated PS can be used to produce high content PS blended
cement [28,31–33,36–38], mass concrete [30] and even ultra-high
performance concrete [24]. The appropriate addition of PS could
also improve the mechanical property and durability of concrete
such as the resistance to aggressive ion erosion or to freeze–thaw
[5,24,29,30,33,37,39]. Similar to FA, PS consumes CH and produces
additional C-S-H during the pozzolanic reaction, resulting in the
refinement of the microstructure of cement matrix and improvement of the mechanical properties of concrete [5,29,32–34,40]. In
addition, it was widely reported that PS incorporation could reduce
the hydration heat of cement and decrease the internal tensile
stress of concrete at early age when the mechanical properties of
concrete were relatively weak, which was particularly beneficial
to prevent the early cracking of mass concrete [27,30,40]. Moreover, Chen et al. [27] and Yang et al. [33] have reported that the
autogenous shrinkage and drying shrinkage of mortar decreased
in the presence of PS.
Due to the high calcium content, PS could largely participate in
the pozzolanic reaction at middle and late hydration time
[5,24,28,30,33,40], which would inevitably produce additional
hydration heat and probably affect the final volume stability of
concrete. However, to our best knowledge, the influence of PS addition on long-term hydration heat of cement and volume deformation of concrete has not been fully studied. A full understanding of
the effects of PS on the hydration heat at different stages would
provide more information about the hydration kinetics of PS
blended cement-based materials. In addition, there is still a lack
of information about the effects of PS on the microstructure of CS-H, which constitutes approximately 70% of the total volume of
hydrated Portland cement paste and contributes significantly to
the macro performance of concrete [6,41–44].
The main focus of this study was to assess and compare the
long-term hydration heat, hydration products and C-S-H in PS
blended cement pastes and in FA blended cement pastes, by using
X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis and 29Si magic angel spinning (MAS) nuclear magnetic
resonance (NMR) techniques. Then the properties of fresh concrete,
mechanical properties, adiabatic temperature rising and long-term
volume deformation (drying and autogenous shrinkage) of concretes containing PS and FA were investigated and compared.
2. Materials and methods
2.1. Raw materials
In the present work, Portland cement (CEM I 42.5) complying
with the Chinese national standard GB175 for Common Portland
cement [45] and mineral admixtures (FA and PS) were adopted.
The finely ground PS with mean particle size (d50) of 13.5 lm
was provided by a phosphoric acid plant in Guizhou province,
China. The ground PS was obtained by mechanical grinding the
raw granulated electric furnace phosphorous slag through a high
energy mill in this phosphoric acid plant. The FA used in the current study was obtained from the combustion of anthracite coal
in a power station in Yunnan province, China. The total SiO2,
Al2O3 and Fe2O3 content of this FA is 85.5% (the minimum value
of this content for Class F FA should be 70% [9]). This kind of FA
can be classified as Class F type conforming to ASTM C618 (Standard specification for coal fly ash and raw or calcined natural pozzolan) [46] and Chinese national standard GB/T 1596 (Fly ash used
for cement and concrete)[47]. The chemical compositions of these
raw materials in terms of major oxides, as determined by X-ray fluorescence (XRF), and the basic physical characteristics of them are
shown in Table 1. The specific surface area of Portland cement, FA
3
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 3
Mix proportions and notations of paste specimens.
Table 1
Physical characteristics and oxide compositions of PC, FA and PS by XRF.
Oxide
CaO
SiO2
Fe2O3
Al2O3
MgO
SO3
P2O5
R2O*
Loss on ignition (%)
Physical Properties
Specific gravity
Blaine specific surface area (m2/kg)
Fineness (% retain in 45 mm)
Strength activity index
*
Oxide constituents (wt%)
Notation
FA (wt%)
PS (wt%)
W/B ratio
CEM I PC
FA
PS
62.72
20.32
4.46
4.42
3.92
2.37
0
0.41
1.04
2.94
54.54
10.18
24.78
2.94
0.37
0
1.04
2.18
47.23
40.12
1.45
2.20
2.16
1.64
2.31
1.24
1.85
PC paste
FA paste
PS paste
0
30
0
0
0
30
0.3
0.3
0.3
3.22
332
8.4
–
2.32
386
6.8
78
2.88
391
6.5
88
Alkali content (R2O) = Na2O + 0.658K2O
and PS were tested using the Blaine method according to GB/T
8074 [48]. Other physical characteristics such as specific gravity,
fineness and strength activity index were tested in laboratory conforming to the GB/T 1596 [47] and DL/T 5387 (Technical specification for phosphorous slag powder use in hydraulic concrete) [49].
The fine aggregate used was the crushed limestone with a fineness modulus of 2.71 and a maximum particle size of 5 mm. The
coarse aggregate used was also a crushed limestone, ranging in size
from 5 mm to 40 mm. The measured specific gravity of fine and
coarse aggregates was 2.70. The sieve analysis of aggregates was
conducted conforming to Chinese standard DL/T 5151 (Code for
testing aggregates of hydraulic concrete) [50] and the results were
presented in Table 2. It should be noted that the test results are
within the limits of Chinese standard DL/T 5144 (Specifications
for hydraulic concrete construction) [51]. It should be noted that
the aggregates used in hydraulic concrete should be in saturatedsurface-dry (SSD) condition, as specified in DL/T 5144. The SSD
condition of the aggregates is defined by DL/T 5151 as the state
that the open pores in the aggregate particles are filled with water
while the surface of the aggregates does not contain any free water.
Aggregates in SSD condition will not adsorb mixture water or
release excess water to the concrete mixture, and therefore will
not change the water to binder (W/B) ratio of concrete. The moisture content of the aggregates in SSD condition is defined as the
SSD water absorption and the SSD water absorption tested using
DL/T 5151 is 1.1% and 0.5% for fine and coarse aggregates,
respectively.
2.2. Mixture proportion design
In the present study, cement paste with a W/B ratio of 0.30 was
casted for hydration heat tests and microstructural analysis and
the concretes were prepared at two W/B ratios of 0.30 and 0.50
for the compressive strength, adiabatic temperature rising and vol-
ume deformation (drying and autogenous shrinkage) tests. The
mixture proportions for casting the cement paste and concrete
specimens in this study are shown in Tables 3 and 4, respectively.
FA and PS were added to pastes and concretes at 30 wt% replacement level of cement. After casting, the paste and concrete specimens were cured under laboratory conditions. After 24 hours, the
specimens were demolded and cured in a foggy room at 20 ± 1 °C
and RH > 95% until tested.
The W/B ratios in the range of 0.3–0.5 are generally used to
design the hydraulic concrete. The W/B ratio of 0.3 is usually used
for high-strength concrete, and the W/B ratio of 0.5 is used for low
strength concrete for dam body or foundation. The maximum W/B
ratio used for concrete of hydraulic projects is limited to 0.5 or 0.55
(depending on the environmental conditions) according to Chinese
standard SL 191(Design code for hydraulic concrete structures)
[52]. In addition, cement paste with a W/B ratio of 0.5 is too fluid
and easy to segregate. In the present work, the W/B ratios of 0.3
and 0.5 were adopted for concretes and a W/B ratio of 0.3 was chosen to prepare cement pastes.
The concrete mixture proportion was designed in this study
based on the volume method according to Chinese standard DL/T
5330 (Code for mix design of hydraulic concrete) [53]. The volume
method is also adopted in other literature [54,55]. The basic principle of this method is that the volume of the concrete mix is equal
to the sum of the absolute volume of each component and the air
content of the concrete mix. The designed slump of concrete mixtures and air content were 50–70 mm and 4%, respectively. The
optimal fine aggregate to total aggregate ratio of 33%-34% by volume and the optimal water content of 117–118 kg/m3 were determined firstly and used in all concrete mixtures, then the mass of
each concrete component can be calculated following the volume
method. A polycarboxylate based superplasticizer was used to
minimize the optimal water content in concrete mixtures so as
to reduce the binder content. The dosage of superplasticizer was
fixed at 0.6–0.7%, by weight of binder.
It should be noted that this study intents to evaluate the possibilities of the application of PS in hydraulic projects to replace FA in
southwestern China. The arch dams, which generally consume less
concrete and are less costly than other types of dam such as gravity
dam, are mostly adopted and built in southwestern China, e.g., Baihetan, Wudongde, Jinping and Xiluodu arch dams, etc. The maximum replacement level of PS for cement in normal concrete
(relative to roller compacted concrete) for arch dam is limited to
30% or 35% (depending on the type of cement used) according to
Chinese standard DL/T 5387 (Technical specification for phospho-
Table 2
Sieve analysis of fine and coarse aggregates.
Fine aggregates
Coarse aggregates
Sieve size (mm)
Percent passing (wt%)
Requirement in DL/T 5144(wt%)
Sieve size(mm)
Percent passing (wt%)
Requirement in DL/T5144(wt%)
5
2.5
1.25
0.63
0.315
0.16
Fineness modulus
99.9
80.6
64.2
48.9
25.1
10.04
2.71
>95
–
–
–
–
6–18
2.4–2.8
40
20
5
–
–
–
–
100
55
1.3
–
–
–
–
>95
–
less than5
–
–
–
–
4
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 4
Mix proportions and notations of concrete specimens.
Notation
W/B ratio
PC3
PC5
PSC3
PSC5
FAC3
FAC5
0.3
0.5
0.3
0.5
0.3
0.5
Mix proportions (kg/m3)
water
cement
FA
PS
sand
Coarse aggregate
Super plasticizer
118
117
118
117
118
117
393
234
275
164
275
164
0
0
0
0
118
70
0
0
118
70
0
0
631
696
627
694
618
689
1341
1414
1333
1409
1314
1398
2.75
1.40
2.75
1.40
2.75
1.40
rous slag powder use in hydraulic concrete)[49]. Therefore, the PS
replacement level of 30 wt% is selected in this work. Accordingly,
the reference paste and concrete with 30 wt% FA replacement level
are prepared.
denote a SiO4 tetrahedron connected to 0, 1, 2, 3, and 4 SiO4 tetrahedra, respectively, whereas Qn(0 Al), Qn(1 Al), Qn(2 Al), Qn(3 Al)
and Qn(4 Al) correspond to SiO4 tetrahedron connected to 0, 1, 2,
3 and 4 AlO4 tetrahedra, respectively.
2.3. Test methods
2.3.1.5. Hydration heat tests. The hydration heat tests are conductive to comprehensively understand the impacts of FA and PS on
the hydration kinetics of cement pastes. The hydration heat of
cement pastes containing FA or PS during the first 72 h was determined by an 8-channel isothermal calorimeter (TA Instruments, U.
S.A.) at 20 ± 0.5 °C. During the test, the binder (plain cement or
cement with FA or PS) and water with a W/B ratio of 0.3 was mixed
for 2 min. After that about 6 g of the paste sample was extracted
and placed in a sealed glass tube immediately. Then the glass tube
was placed into the calorimeter to test the heat release behavior.
The heat flow was recorded every 15 s up to 72 h during the tests.
The long-term hydration heat of cement pastes with FA or PS up
to 180 days was determined by the dissolution method according
to GB/T 12,959 [58]. During the long-term hydration heat tests, a
SHR-2 hydration heat meter system that includes a 60 L water
bath, a 0.65 L vacuum bottle, and a beckman differential thermometer was used. The testing procedure was as follows: firstly,
approximately 410 g of nitric acid solution (2 mol/L) and 8 mL of
hydrofluoric acid solution (22.4 mol/L) were mixed together and
put into the vacuum bottle. Secondly, the vacuum bottle was
placed into the water bath maintained at 20 ± 0.1 °C. Thirdly, the
cement paste specimen was ground and about 10 g of the powder
sample was put into the vacuum bottle quickly. Finally, the values
obtained by the thermometer were recorded. The hydration heat
released by the testing sample is calculated by subtracting the dissolution heat of the tested hydrated cement paste directly from the
total dissolution heat of anhydrous cement. The hydration heat
was tested at different curing time (1, 3, 5, 7, 14, 21, 28, 40, 56,
70, 80, 90 and 180 days). Two samples were tested for each cement
paste.
2.3.1. Cement paste testing
2.3.1.1. XRD. The raw materials, plain cement paste and pastes
added with FA and PS were investigated mineralogically by using
a D8 advance X-ray diffractometer (XRD, Bruker, Germany) with
CuKa radiation source. The XRD measurements were performed
at a step of 0.02° per 0.2 s and in the range of 2h 5°-60°.
2.3.1.2. Thermal analysis. In this study, the thermal analysis were
performed by a thermo gravimetric-differential thermal analyzer
(TG-DTA) conducted on a TA SDT 2960 (TA Instruments, U.S.A.)
to approximately determine the content of CH in cement pastes.
The CH content in plain cement paste and pastes containing FA
or PS were measured and compared at various hydration ages
(i.e., 3, 28 and 180 days). During the tests, the paste specimens
were ground into fine powders, after that about 30–40 mg of the
powder sample was heated up from 50 °C to 1000 °C with an
increasing rate of 10 °C per minute in an atmosphere of nitrogen
gas with a flow rate of 100 mL/min.
2.3.1.3. SEM. The SEM images of PS and FA particles, as well the
plain cement paste and pastes with FA and PS were obtained by
conducting a JEOL JSM6300 scanning electron microscope (Oxford
instruments, Japan) at an accelerating voltage of 5–20 kV, depending on the magnification needed. The samples were coated with a
thin layer of gold in vacuum conditions before tests in order to
reduce the effects of electric charge.
2.3.1.4. 29Si MAS NMR. To evaluate the effects of PS and FA addition
on the microstructure of C-S-H in cement pastes, a solid-state NMR
spectrometer (Varian VXR600) was performed to analyze the raw
materials, as well the plain cement paste and pastes with FA and
PS at ambient temperature. The 29Si MAS NMR spectra were collected operating at a spinning speed of 9 kHz with a pulse width
of 2.0 ls and a relaxation delay of 5 s, under a magnetic field of
14.5 T. The hardened cement pastes were ground into powders
and filled into 3.5 mm zirconia rotors, then the rotors were placed
into the spectrometer and the tests began. Each paste sample was
scanned and accumulated for a minimum of 2500 times. The
chemical shifts are referenced to tetramethylsilane (TMS) as an
external reference. Because the 29Si MAS NMR spectrum often consists of overlapped peaks caused by Si atoms with different chemical surroundings, the commercial solid-state NMR software is
usually used to divide the spectrum into individual signal for quantification analysis. The fundamental theory of the quantification
analysis is that the integrated intensities of NMR Qn signals are
directly proportional to the relative amount of silicon in each kind
of Qn site [56,57]. It should be noted that Q0,Q1, Q2, Q3 and Q4
2.3.2. Concrete testing
2.3.2.1. Fresh concrete properties. The slump, air content and setting
time of concrete were determined immediately after mixing in
accordance with DL/T 5150.
2.3.2.2. Mechanical property. The compressive strength of concrete
was determined in accordance with DL/T 5150 [59], using an electronic universal testing machine with a load capacity of 300 KN.
The concrete specimens (150 mm 150 mm 150 mm) were
cured in a foggy room under temperature 20 ± 2 °C before they
were tested at 3, 7, 28, 90 and 180 days. Three specimens of each
concrete mixture were used to test the compressive strength at
various ages.
2.3.2.3. Adiabatic temperature rising. The adiabatic temperature rising of concrete containing FA/PS was obtained by performing a
MIT-686-0-01 automatic thermal performance test machine (Shimadzu Corporation, Japan). The test machine used is shown in
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Fig. 1. Adiabatic temperature rise reflects the real temperature evolution inside the mass concrete structures since the test conditions
are possibly close to the real adiabatic situations of mass concrete.
The test methods, which are specified in DL/T 5150, are as follows:
during the test, about 120 kg of freshly prepared concrete was cast
into an insulated cylindrical box with a size of U
500 mm 600 mm. Then a thermocouple that could accurately
probe the temperature change of concrete, was embedded in the
center of the fresh concrete sample. The box was placed into the
test machine after it was sealed carefully. The temperature rising
of the sample was continuously recorded every 0.5 h until to
28 days with an accuracy of 0.1℃.
2.3.2.4. Volume deformation. Autogenous volume change and drying volume change are two main components of volume deformation [10,60]. In this work, the autogenous shrinkage was
determined and calculated according to DL/T 5150. The test procedure is provided in the following: firstly, three cylindrical steel barrels with the size of U 200 mm 500 mm were prepared for each
concrete mixture. Secondly, a strain meter was fixed in the center
of each barrel vertically, after that the fresh concrete was cast into
the two barrels and compacted using a vibration table. During casting and vibration, any damage to the strain meters should be
avoided. Thirdly, the barrels were covered, then the gaps between
the barrels and covers, as well the outlets of each strain meter
cable were sealed and welded to prevent any moisture loss from
the concrete sample. Finally, the sealed barrels were stored in a
room maintained at 20 ± 2 °C. The data transferred from the strain
meters were recorded four times during the first day and thereafter
twice a week during the first 14 days, after that they were recorded
twice a month up to 180 days. Then the autogenous shrinkage (Gt)
of concrete was determined based on the measured strain data following Eqs. (1) and (2), according to DL/T 5150.
Gt ¼ f ðZ Z 0 Þ þ ðb eÞðT T 0 Þ
ð1Þ
T ¼ a0 ðR R0 Þ
ð2Þ
-6
where Gt was the autogenous shrinkage of concrete, 10 ; f was the
strain sensibility of the strainometer, 10-6/(0.01%); Z was the measured resistance ratio, 0.01%; Z0 was the initial reference value of
resistance ratio, 0.01%; b was the temperature compensation coefficient of the strainometer, 10-6/°C; e was the linear expansion coefficient of the tested concrete, 10-6/°C; T0 was the initial value of
temperature, °C; T was the measured temperature during the test,
°C; a’ was the temperature sensibility of strainometer, °C/X; R
was the measured resistance value, X; R0 was resistance at 0 °C, X.
Fig. 1. The automatic thermal test machine for adiabatic temperature rise.
5
Drying shrinkage was investigated on concrete prisms of
515 100 100 mm conforming to DL/T 5150. The initial length
and length changes of the prisms placed in a drying room (20 ± 2 °C
and 50 ± 5% RH) were recorded to calculate the drying shrinkage
till to 180 days.
3. Results and discussion
3.1. PS and FA characterization
3.1.1. XRD
The mineralogical phases of the PS and FA, as determined by Xray diffraction (XRD) technique, are given in Fig. 2. From Fig. 2, the
PS diffractogram has no obvious crystalline peaks but a broad halo
over the range between 25° to 35°(centered at 30° 2h), which is
similar to XRD results of PS reported by other authors [24,30,40].
So, it is confirmed that PS used in this study predominantly consists of amorphous phases and trace number of crystalline phases
such as calcite. Fig. 2 also shows that the strong peaks corresponding to quartz and mullite and some minor peaks belong to magnetite can be found in the FA diffractogram, where the peak
intensity of quartz seems much stronger than those of other crystalline phases. Many researchers have reported the similar XRD
results of FA [7,8,17,61–63]. Comparison of the XRD results in
Fig. 2 indicates that glassy phases in the PS are dominant while
FA contains a small amount of crystalline phases that could yield
strong diffraction peaks.
3.1.2. SEM
The particle morphology of PS and FA by using SEM are indicated in Fig. 3. It can be clearly observed from Fig. 3 that the morphology of PS differs significantly from that of FA. Fig. 3 indicates
that FA particles are comprised primarily of regular smooth
spheres with different sizes. These spheres are commonly known
as cenospheres [7,8,62]. The morphology of FA is closely associated
with the rapid cooling process during its production [6,8]. On the
contrary, PS particles consist dominantly of fragmented and irregular polygonal particles, with inhomogeneous particle size distribution and relatively smooth surface. The mechanical grinding
process, which promotes the pozzolanic activity of PS, may result
in this morphology.
3.1.3. 29Si MAS NMR
The 29Si MAS NMR spectra for anhydrous PC, PS and FA are
shown in Fig. 4. From Fig. 4(a), both PC and PS exhibit a sharp
Fig. 2. X-ray diffraction (XRD) patterns of PA and FA.
6
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Fig. 3. SEM micrographs of (a) PS and (b) FA.
Fig. 4.
29
Si NMR spectra of anhydrous PC, PS and FA.
and strong resonance centered at 72 ppm, which is associated
with Q0 site. It is well known that Q0 denotes the individual silicate
tetrahedron presented at the unhydrated C3S and C2S [6,41,43,64–
66]. Different from PC and PS, FA presents a wide signal from
90 ppm to 115 ppm. This wide signal consists of a series of individual signals that can be assigned to mullite (Q3 located between
90 ppm and 95 ppm), quartz (Q4 at-108 ppm) and glassy phases
[6,42,67]. The significantly broadened NMR spectrum of FA compared with that of PC or PS is due to the presence of iron in FA
(10.18 wt% represented as Fe2O3 in Table 1). As revealed by Refs.
[6,57], the resonance widths increased with increasing the level
of iron in the samples. The similar NMR observation of FA has been
reported by other researchers [42,67–69]. Additionally, it can be
found that the chemical surroundings of Si sites in PS are similar
to those in Portland cement which are monomeric (Q0 site), and
much different from those in FA which are present in network
structure (Q3 and Q4 sites).
3.1.4. Strength activity index
It can be found from Table 1 that the strength activity index of
PS is 88%, which is approximately 10% higher than that of FA.
According to Chinese standards [47,49], the strength activity index
is a ratio between the 28-day compressive strength of mortar (water: binder: sand = 1:2:6) with cement replacement level of 30% by
FA or PS and that of the plain cement mortar. The methods specified in Refs. [47,49] for testing the strength activity index are similar with those in ASTM C311(Standard test methods for sampling
and testing fly ash or natural pozzolans for use in Portland-cement
concrete) [70]. This index essentially reflects the pozzolanic activity of PS and FA. GB/T 1596 [47] specified the strength activity
index of Class F fly ash should be higher than 70%. Similarly,
according to DL/T 5387 [49], the PS with a strength activity index
higher than 60% can be used in hydraulic concrete.
Based on a review of the current literature, many mineral materials have the same Q3 and Q4 sites with FA. For instance, the silica
fume [6,65] and nano SiO2 [69] have Q4 Si sites, while the biomass
wastes [65] have Q3 and Q4 Si sites. It should be noted that all these
materials have a much stronger reactivity than FA. So the Si sites
determined by NMR technique are most likely not associated with
the activity of mineral materials. The pozzolanic activity of mineral
materials are probably mostly related to their fineness and compositions. Moghaddam et al.[22] reported that the strength activity
indexes were 72%, 83% and 107% for the FA with specific surface
areas of 302, 368 and 495 m2/kg, respectively. The strength activity
index was observed to increase with increasing specific surface
area. A similar trend has been also reported by Allahverdi et al.
[31], who found that the compressive strength of mortar containing PS with different fineness significantly increased with increasing in Blaine fineness from 205 to 450 m2/kg. As concluded by Yang
et al.[33], Peng et al.[29] and Yang et al.[67], a higher specific surface area of PS or FA meant more lattice distortions and chemical
bonds breakages on the particle surfaces, leading to a higer pozzolanic reactivity. It should be noted from Table 1 that PS has
almost the same Blaine specific surface area (391 m2/kg) as that
of FA (386 m2/kg), and thus, the higher strength activity index of
PS compared with FA could be attributed to the difference in their
mineralogical phases. In other words, the high amorphous phase
content of PS is believed to result in a high pozzolanic activity.
3.2. Cement paste testing results
3.2.1. XRD analysis
The XRD patterns of PC paste, PS paste and FA paste at 3, 28 and
180 days are presented in Fig. 5. From Fig. 5, it is found that the
strong peaks belong to the clinker phases C3S (at about 29.5°,
32°–33°, 34°, 41.3° and 51.7°) [71–74] and C2S (at about 32°–33°
and 41.3°) [73–75] decrease in intensity with hydration time for
the three kinds of pastes, indicating the continuous hydration of
cement. As the main hydration product in Portland cement pastes,
C-S-H cannot be clearly identified in Fig. 5, since it is almost amorphous and has no obvious diffraction peaks, which is consistent
with previous XRD results [5,41].
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
7
pozzolanic reaction at early age. The BSE image analysis conducted
by Zhang et al. [40] revealed that the reaction degree of PS was
5.7% at 3 days in a cement paste containing 30 wt% PS. So the
reduction in CH peak intensity at 3 days is perhaps due to the dilution effect of FA and PS, which reduces the cement content and
consequently leads to a reduction in the amount of hydration products especially at early age. Besides, it should be noted that PS
retards the cement hydration in the early stage, which can further
inhibit the generation of CH and result in a more prominent reduction in CH peak intensity for PS paste. These results are in agreement with the findings by other researchers [40].
At 28 days, the CH peak intensity of PS paste is obviously
weaker than that of FA paste and PC paste. This trend is more obviously at 180 days. In addition, form Fig. 5(c) the halo of PS centered
at 30° that could be identified at 3 days cannot be observed at
28 days. These phenomena can be explained by the pozzolanic
reaction of PS which continuously consume CH at middle and late
age. It was reported that PS could react with CH significantly at
middle and late ages [39,40]. Similarly, the reduction in the intensity of CH peak for FA paste compared to PC paste at 180 days can
also be observed, which is most likely due to the pozzolanic reaction between the glassy phases in FA and CH at late age. However,
the quartz phase of FA can be clearly observed at various hydration
ages as expected, indicating the quartz phase is unreactive even at
late age. A similar trend was obtained by Walkley and Provis [6],
who reported that the crystalline phases present in FA, such as
quartz and mullite, were relatively unreactive compared with the
aluminosilicate glassy phases.
The quantitative information of CH content in these pastes will
be further studied in Subsection 3.2.2.
In addition, form Fig. 5(c) the halo of PS centered at 30° could
not be identified clearly at 3 days, which can be explained by the
following two aspects: 1) the content of PS of the binder (30 wt
%) in this study is not very high compared with the cement content,
so the weak halo is further inhibited. 2) The PS halo appears within
the range of 2h 25°-35° may overlap with the strong peaks of
cement minerals and CH. Therefore, the halo of PS cannot be seen
as a good indicator of the pozzolanic reaction.
3.2.2. Thermal analysis
TG-DTA curves of PC paste, PS paste and FA paste at 3, 28 and
180 days are indicated in Fig. 6. As observed from Fig. 6, the major
weight loss between the region of 440–550 °C corresponds to the
decomposition of CH, while the minor weight loss between 600
and 800 °C corresponds to the decarbonation of CaCO3, which
results from the slight carbonation during the experimental
processes.
The content of CH and CaCO3 in a paste sample can be calculated by using the weight losses due to the CH decomposition
and CaCO3 decarbonation, respectively, using the following Eqs.
(3) and (4) [63,79,80]:
Fig. 5. XRD patterns of PC paste, PS paste and FA paste at 3, 28 and 180 days.
Fig. 5 also shows that, at 3 days, the addition of PS and FA
reduces the intensity of CH peak at 2h 18.0°, 34.0° and 47.2°
[17,33,63,74], and the reduction effect of PS is more prominent.
It is considered that the reactivity of FA is very low at early age,
independent of the fineness, particle size distribution, glass content and replacement ratio [7,18,22,76,77]. Termkhajornkit et al.
[78] have reported that the reactivity degree of FA in a FAcement binary paste was no>5% at 3 days. Similarly, in a study conducted by Gao et al. [39] it was reported that even an ultrafine PS
with a fineness beyond 600 m2/kg could hardly participate in the
CH content ðwt:%Þ ¼ Weight loss of CH 74=18
ð3Þ
CaCO3 content ðwt:%Þ ¼ Weight loss of CaCO3 decarbonation
100=44
ð4Þ
where 74, 18, 100 and 44 are the molar masses of CH, H2O, CaCO3
and CO2, respectively.
Moreover, the CaCO3 portion of the cement pastes in this study
originates from the carbonation of CH, so the carbonated CH content can be calculated based on the CaCO3 content, by using the
Eq. (5) as follows [80]:
Carbonated CHcontent ðwt:%Þ ¼ CaCO3 content 74=100
ð5Þ
8
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
a ¼ CHcontent=25 wt:% 100
Fig. 6. TG-DTA curves of cement pastes.
As a result, the total CH content of a specimen could be calculated by summing up the contents of CH before and after carbonated. The CH and CaCO3 content, as well as the total CH content
determined are listed in Table 5.
Table 5 indicates that the CH content increases with increasing
the hydration time, from 10.66 wt% at 3 days to 18.50 wt% at
180 days, the trend of these data corresponds well with the XRD
results above.
The content of CH present in a Portland cement paste can be
used to trace the hydration progress of cement, and the hydration
degree of cement (a) can be calculated by Eq. (6) proposed by Refs.
[80,81]:
ð6Þ
where a is the hydration degree of cement, %; CH content is the
content of CH in PC paste at a given hydration time, wt%; 25 wt%
is the CH content in a fully hydrated cement paste proposed by previous references [80–82].
It can be calculated that a of PC were 42.6% at 3 days, 58.2% at
28 days and 74.0% at 180 days. The calculated value was higher
than the value of 54.6% at 28 days (W/B = 0.24) reported by Poon
et al. [21], and a little lower than those reported by Sabine [83]
and Sun et al. [84], who found a were 81.1% and 60.1% for plain
cement pastes with W/B ratios of 0.45 and 0.35 at 28 days, respectively. Zhang [85] proposed that a was in the range of 55–80% at
28 days, depending on the W/B ratio used, and a higher W/B ratio
generally led to a higher a. However, this method is unable to estimate the a of a cement paste containing FA, because in such a binary system cement produces CH while at the same time FA
consumes CH [78,80]. The a and reaction degree of FA (b) in such
a binary system can be determined by the NMR method, as will
be discussed in Subsection 3.2.4.
From Table 5, it is found that the 3-day total CH contents in PS
paste and FA paste are 4.95 wt% and 6.95 wt%, respectively, which
are smaller than that in PC paste (10.66 wt%) at the same hydration
time. As discussed above, the dilution effects of FA and PS lead to a
reduction in CH content in cement pastes. Moreover, the addition
of PS could inhibit the cement hydration and consequently further
reduce the amount of hydration products including CH at early age
compared with that of FA. So, the relatively low CH content in PS
paste at early age is mainly associated with the low cement content and relatively low degree of cement hydration.
It can be found from Table 5 that the CH contents in FA and PS
ones increase during the first 28 days, after which a reverse trend is
observed for FA paste up to 180 days, while for PS paste the CH
content stays fairly constant up to 180 days. Moreover, Table 5
shows that the CH content in PS paste and in FA paste are about
6.71 wt% and 10.24 wt% at 28 days, respectively, which are reduced
by 53.9% and 29.6% compared with that in PC paste (14.54 wt%) at
28 days, while the CH content are reduced by 63.5% and 56.4% at
180 days, respectively. These phenomena can be explained by
the continuous pozzolanic reactions of FA and PS with CH at middle and late ages. The pozzolanic reaction would consume CH and
produce secondary C-S-H, which filled the pores and enhanced the
microstructure of hardened pastes [29,33].
Table 5 also illustrates that CH content in PS paste (6.71 wt% at
28 days and 6.76 wt% at 180 days) is obviously lower than that in
FA paste (10.24 wt% at 28 and 8.07 wt% at 180 days) at the same
hydration age. The lower CH content in PS paste than in FA paste
indicates that PS has a higher pozzolanic reactivity compared with
FA, which consumes more CH [33]. The findings correspond well
with the XRD results above, confirming that PS possesses a higher
pozzolanic activity than FA at middle and late age.
3.2.3. SEM analysis
Fig. 7 gives the SEM images of PC paste (a-c), FA paste (d-f) and
PS paste (g-i) at 3, 28 and 180 days. From Fig. 7(a), it can be found
that the needle-like C-S-H (less than 1 lm in length) precipitates
mostly around cement grains, and the large CH and AFt crystals
about 5 lm in size are also observed to form in the voids of paste
at 3 days. At the same time, most FA particles are observed to be
covered with C-S-H needles (Fig. 7d), which is consistent with
the results observed by others [20,22,76,86], who reported that
the secondary C-S-H often grew on the surface of FA particles during cement hydration. In addition to the filler effect, FA acts as
nucleation site and favors the precipitation of C-S-H gel, as
Moghaddam et al. [22] claimed. By contrast, as for the PS paste
at 3 days, the smooth surfaces of PS particle seem to be unaffected
9
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 5
The total CH content in hydrated cement pastes.
Notation
Curing time (days)
PC paste
3
28
180
3
28
180
3
28
180
FA paste
PS paste
Content (wt%)
Total CH
CH
CaCO3
(wt%)
9.86
13.45
16.68
5.53
8.89
7.13
4.21
5.64
5.93
1.08
1.48
2.46
1.92
1.82
1.26
0.99
1.45
1.12
10.66
14.54
18.50
6.95
10.24
8.07
4.95
6.71
6.76
Fig. 7. SEM images of PC paste (a-c), FA paste (d-f) and PS paste (g-i) at 3, 28 and 180 days.
by the cement hydration, and the hydration products such as C-S-H
and tiny CH crystals are observed to deposit in the voids of paste
(Fig. 7g).
At 28 days, C-S-H is observed to exist more noticeably in pores
of the hardened paste (Fig. 7b, e and h) and the microstructures of
the pastes are denser compared with those at 3 days. It is illustrated from Fig. 7h that the texture of PS particle surfaces is
strongly corroded, and the edges of PS particles are poorly defined,
revealing the reaction occurs predominantly at PS particle surfaces.
Besides, few CH crystals could be found in PS paste at 28 days,
implying the consumption of CH by the pozzolanic reaction of
PS. On the contrary, many FA particles with smooth surface are
found clearly in Fig. 7e, suggesting the hydration degree of FA is
not very high at 28 days.
As hydration proceeds, PS particles and CH crystals are difficult
to be identified at 180 days (Fig. 7i), suggesting most PS has reacted
with CH at late age. Besides, the unreacted PS particles are found to
be densely embedded in hydration products and therefore few
pores were observed compared with those at 28 days. Therefore,
the microstructure of the PS paste could be densified, due to the
10
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
pozzolanic reaction of PS with CH at middle and late age [39]. As
for the FA paste (Fig. 7f), a few unreacted FA spheres embedded
in the paste are observed, implying parts of FA particles may act
as inert filler to enhance the packing density of the pastes. The similar observation has been reported by Moghaddam et al. [22].
As can be seen in Fig. 8, the chemical surroundings (Qn sites) of
FA, PC and hydration products are different, so it is possible to
determine the hydration degree of cement (a) and the reaction
degree of FA (b) in FA paste according to Eqs. (9) and (10) based
on the relative integral intensity of Qn sites. The same method
has also been adopted in other studies [64,88,89].
3.2.4. 29Si MAS NMR analysis
29
Si MAS NMR spectra for unhydrated cement mixtures (70%
PC + 30% FA and 70% PC + 30% PS) and hardened cement paste samples (PC paste, FA paste and PS paste) cured for 3, 28 and 180 days
are presented in Fig. 8. From Fig. 8(a), the peaks associated with CS-H are assigned for Q1 site near 79 ppm, Q2 site centered at
82 ppm and Q2(Al) site near 85 ppm. It is widely considered
that C-S-H has chain-like structures, Q1 denotes the silicate tetrahedra presented at the ends of C-S-H chains while the Q2 and
Q2(Al) sites denote the tetrahedra appear in the middle chain of
C-S-H [6,41–43,56,64,66,69,87–89].
The mean silicate (alumino) tetrahedra chain length (MCL) and
molar ratio of aluminum to silicon (Al/Si) ratio in C-S-H are two
factors dominating the structures and compositions of C-S-H
[6,43,63,87,90]. MCL and Al/Si ratio of C-S-H in this study can be
determined according to Eqs. (7) and (8) proposed by Refs.
[6,41–43,63,64,87–89]:
a = 1I(Q 0 )/I0 (Q 0 )
MCL = 2 + 2I(Q 2 ) /I(Q 1 ) + 3 I(Q 2 (Al)) /I(Q 1 )
ð7Þ
Al/Si ratio = 0.5I(Q 2 (Al)) /[I(Q 1 ) + I(Q 2 ) + I(Q 2 (Al))]
ð8Þ
where I(Qn) denotes the integral intensity of Qn site in hydrated
cement pastes(%).
b = 1I(Q 3 + Q 4 )/I0 (Q 3 + Q 4 )
ð9Þ
ð10Þ
where I0(Qn) denotes the integral intensity of Qn site in unhydrated
‘‘100%PC” or cement mixture ‘‘70% PC + 30% FA”. However, the Q0
signals of PC and PS appear together at 72 ppm, as shown in
Fig. 4, therefore the unhydrated cement mixture ‘‘70% PC + 30%
PS” presents a sharp overlapped Q0 signal that cannot be divided,
so a and reaction degree of PS cannot be determined using the
NMR method.
The values of MCL, Al/Si ratio in C-S-H, a and b are summarized
in Table 6.
Fig. 8 demonstrates that I(Q0) decreases with the hydration
time for the three types of pastes. In the meantime, the intensities
of Q1, Q2, Q2(Al) signals and MCL of C-S-H enhance with increasing
the hydration age. These phenomena can be ascribed to the continuous cement hydration, and the generation and polymerization of
C-S-H with the increase of hydration time, as reported by others
[63,72]. As shown in Table 6, a of PC paste are 39.4%, 57.5% and
78.4% at 3, 28 and 180 days, respectively, which are comparable
to the values of a determined by TG-DTA (42.6%, 58.2% and
74.0%, correspondingly).
Fig. 8. 29Si NMR spectra of (a) unhydrated cement mixtures (70% PC + 30% FA and 70% PC + 30% PS) and hardened cement paste samples cured for (b) 3 days, (c) 28 days and
(d) 180 days.
11
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 6
MCL and Al/Si ratio of C-S-H, hydration degree of cement (a) and the reaction degree of FA (b) in hydrated pastes.
Notation
Age
(days)
I(Q0)
I(Q1)
100%PC
PC paste
0
3
28
180
0
3
28
180
0
3
28
180
100
60.6
42.5
21.6
49.1
27.1
20.5
9.5
100
67.5
34.8
18.6
–
32.3
46.3
59.5
–
15.8
23.7
32.8
–
27.4
47.9
58.3
70%PC+30%FA
FA paste
70%PC+30%PS
PS paste
I(Q2)
I(Q2(Al))
I(Q3 + Q4)
MCL
Al/Si ratio
a
b
3.3
5.3
10.3
3.8
5.9
8.6
39.4
57.5
78.4
–
–
–
2.9
8.4
12.5
2.56
2.61
2.78
–
3.20
3.89
3.83
0.05
0.05
0.05
5.1
9.8
11.3
0
0
0
50.9
49.1
37.6
33.9
0.06
0.10
0.11
44.8
58.2
80.7
3.5
26.1
33.4
2.5
12.9
15.6
2.6
4.4
7.5
0
0
0
2.47
2.81
2.92
0.04
0.03
0.05
–
–
–
–
–
–
As for the unhydrated cement mixture ‘‘70% PC + 30% FA” indicated in Table 6, the integral intensities of Q0 site belongs to PC and
(Q3 + Q4) sites belong to FA are 49.1% and 50.9%. Considering that
the SiO2 contents in PC and FA are 20.32 wt% and 54.54 wt%
(Table 1), it is calculated that in the mixture ‘‘70% PC + 30% FA”
the relative contents of silicon from PC (Q0) and FA (Q3 + Q4) are
about 46.5% and 53.5%. It is observed that the calculated value by
NMR technique is very close to the values expected for this mixture. From Table 6 and Fig. 8, the weakening trend of I(Q3 + Q4)
is found in FA paste, indicating the continuous pozzolanic reaction
of FA, which is in accordance with others [42,67,69,88,91]. Besides,
Table 6 shows that the 3-day value of b is 3.5%, 28-day value is
26.1% and 180-day value is 33.4%. It should be noted that the errors
of calculated b determined by 29Si NMR cannot be ignored, because
the broad FA signals (Q3 + Q4) and their low intensity especially in
the FA pastes may cause an unneglectable deviation. But the calculation accuracy of b can be improved to a certain extent by multiple
iterative calculations. The results of b support the XRD, DTA and
SEM findings above that the FA reactivity is weak at early age,
but is activated to a certain content at late age.
The reaction degrees of FA (b) determined by the selective dissolution method or NMR method conducted by other researchers
are listed in Table 7. The results in Table 7 indicate that b is less
than 5% at 3 days, and within the range of 9–28% at 28 days, 17–
36.2% at 90 days and 26–29% at 180 days. So, the values of b calculated in this study are generally within the range reported by other
literature. Nevertheless, it is found that some values in Table 7 are
somewhat scattered, as revealed by Ref. [18], b is significantly
affected by the quality of FA. Many researchers [8,22,77] proposed
that the quality of FA varied widely and the reactivity of FA was
influenced by many factors, such as the glass content, chemical
compositions, fineness, changes in temperature, duration of combustion and quenching during the manufacturing process, etc.
Furthermore, from Table 6, a in the FA paste is 5.4% higher than
that in the PC one at 3 days, confirming the nucleation and accel-
eration effects of FA at early age, which corresponds well the 3day hydration heat and SEM results. Table 6 also shows that MCL
in FA paste is the longest among the three type of pastes at all
hydration age in this study. The incorporation of FA could enhance
the polymerization degree of C-S-H. It should be noted that the Al/
Si ratio in C-S-H increases from 0.06 at 3 days to 0.10 at 28 days,
and to 0.11 at 180 days in the presence of FA. These phenomena
are closely related to the high Al content in FA. As shown in Table 1,
the Al2O3 content of FA is about 24.78 wt%, nearly 6–12 times larger than those of PS and PC. The effects of Al content on MCL and
Al/Si ratio in C-S-H may be explained by two mechanisms. On the
one hand, the alumino-silicate framework in the glassy phases of
FA is destroyed during the pozzolanic reaction, a large number of
Al and Si tetrahedra are released into the pore solution, which
could participate in pozzolanic reaction to form additional C-S-H
and increase the polymerization of alumino-silicate chains in CS-H [63,69,93]. On the other hand, the high Al content in FA
blended cement paste or in synthesized C-S-H system could largely
enhance the polymerization of C-S-H, because Al tetrahedra usually act as bridging sites to link short silicate chain segments
[41,42,56].
Although the a and reaction degree of PS cannot be determined
based on the NMR technique, as mentioned above, many interesting findings could be obtained. Fig. 8(b) and Table 6 present that, I
(Q2) and MCL in PS paste are relatively weaker and shorter than
those in PC paste and FA paste at 3 days, indicating that the
amount and polymerization degree of C-S-H in PS paste are lower
in comparison to those in PC one and FA one. These phenomena
could be caused by the retarding effect of PS at early age, which
could hinder the generation of C-S-H and its polymerization
degree. In addition, as shown in Fig. 8(c), I(Q2) and MCL in PS paste
are stronger and longer than those in PC paste at 28 days, implying
that PS begins to react with CH and produces plenty of C-S-H with
high polymerization in PS paste at middle age. The same phenomenon is also observed in Fig. 8(d), demonstrating that the poz-
Table 7
The reaction degrees of FA (b) obtained from other references.
Methods
W/B ratio
Specific surface
area(m2/kg)
FA content (wt%)
29
0.3
–
0.38
0.24
1.0
0.4
0.33
0.30
386
2550 (BET)
–
386
376
406
596
279
426
30
30
30
25
25
20
40
25
Si NMR
Selective dissolution method
Reaction degrees of FA (b) at different ages
References
3-d
7-d
28-d
60-d
90-d
180-d
3.5%
–
–
–
4％
0
–
–
–
–
0.84%
–
5.7%
–
–
16.5%
15%
21%
26.1%
23.1%
–
13.9%
9%
13%
28%
22%
23%
–
–
23.3%
–
–
–
–
–
–
–
–
–
22.6%
–
17%
36.2%
–
–
33.4%
–
–
–
29%
–
–
26%
28%
This study
Ref.[88]
Ref.[89]
Ref.[21]
Ref.[78]
Ref.[77]
Ref.[92]
Ref.[18]
12
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
zolanic reaction of PS largely occurs at 180 days in PS paste, which
is in good agreement with the decrease in CH content and peak
intensity as revealed by TG-DTA and XRD techniques. As a result,
a large amount of C-S-H in PS paste is produced compared with
that in PC paste at long-term hydration time.
Understanding the relationships between C-S-H structure and
material macro-performance is an important but challenging task,
since the features at nanoscale are closely associated with the
properties of the material at macro-scale level. Many studies
reported that the long MCL of C-S-H commonly facilitated the
improvement of compressive strength of cement-based materials
[64,94]. A hypothesis could be provided here that the increase in
MCL of C-S-H in the presence of PS may lead to an enhanced
strength of cement-based materials at medium and late age. Nevertheless, further research should be carried out to support this
claim.
3.2.5. Hydration heat
3.2.5.1. Early hydration heat within 72 h. Fig. 9 depicts the releasing
rate of hydration heat and cumulative hydration heat curves for
plain cement paste and pastes with 30 wt% FA or PS within 72 h.
As observed in Fig. 9(a), all the samples exhibit the similar heat
releasing behavior that includes five distinct stages: preinduction stage, induction stage, acceleration stage, deceleration
stage and hardened stage, which on the whole corresponds well
with the Portland cement hydration heat results reported by others
[17,19,72,74,95].
The pre-induction stage begins within the first few minutes
after mixing cement with water, when the C3S phase in cement
quickly reacts with water and sulphate [22], releasing large
amount of heat immediately and yielding a sharp and
instant exothermic peak, as was shown in Fig. 9(a). Moghaddam
et al.[22] reported that the early hydration heat of C3A may be
failed to collect since the mixing of cement with water was conducted several minutes before the test. Hu et at.[19] found that
the mixing and stirring processes of the samples may cause fluctuation or inaccuracy to the measured heat results in this stage.
Therefore, the first exothermic peak was not included for
discussion.
From Fig. 9(a), it is evident that the incorporation of 30 wt% PS
prolongs the induction stage about 4.3 h and 3.2 h in comparison to
those of PC and FA pastes, respectively.
In addition, during the acceleration period, the maximal heat
releasing rate of PS paste (1.49mW/g at 14.8 h) is considerably
reduced and postponed in contrast to those of PC one (2.43 mW/
g at 10.3 h) and FA one (1.87 mW/g at 12.1 h), as observed in
Fig. 9(a).
These results are consistent with the findings of others
[24,27,28,30,96]. There are two explanations for this strong negative retarding effect of PS: firstly, the PO34 anion released from PS
reacts with Ca2+, inhibiting the nucleation and precipitation of
CH and C-S-H phases [30,96]. Secondly, phosphoric acid can form
due to the presence of residual phosphorus in PS, which inevitably
decreases the pH value of pore solution in cement paste and consequently hinders the cement hydration [27,28]. By contrast, the
less noticeable retarding effect of FA on cement hydration could
be observed. Many studies [22,30,97]revealed that the retarding
effect of FA was mainly associated with its dilution effect and weak
pozzolanic activity. Other studies [98–100] have reported that FA
could absorb some calcium ions from the solution, which
decreased the Ca2+ concentration in the first few hours and postponed the formation of CH and C-S-H, thus retarding the hydration
of C3A and C3S at early hours. Comparison of the data in Fig. 9
clearly indicates that PS possesses a stronger negative influence
on early cement hydration than FA, which is consistent with the
findings of others [30].
Fig. 9(b) also indicates that, the cumulative heat of hydration
within 72 h of PS paste and FA paste is 140.1 J/g and 167.5 J/g,
respectively, which is 37.7% and 25.5% lower compared with those
of PC paste (224.9 J/g) in this study. As mentioned above, FA and PS
present inert characteristics and could hardly react with CH at
early age[19,22,39,40], so the reduction in hydration heat after
PS or FA addition is mainly caused by the dilution effects [22,40].
Hu et al.[19] showed that, the hydration heat of cement pastes
was mainly controlled by the cement content. It worth noting that
the difference in hydration heat between the FA paste and PC paste
is about 25.5%, which is lower than the FA replacement ratio of
30 wt%. This is because the weak retarding effect of FA on the
cement hydration disappears after the first early hours of mixing,
and thereafter FA acts as nucleation sites and favors the formation
of hydration products, as demonstrated by the SEM results above,
thereby accelerating the cement hydration process and producing
more hydration heat. There results are consistent with the findings
reported by others [100,101], who found the nucleation effects
could accelerate the cement hydration after the induction stage.
In contrast to FA, the reduction effect of PS on cumulative heat
within 72 h is more prominent, which is attributed to the stronger
retarding effect of PS on the early cement hydration [30,40]. There-
Fig. 9. The releasing rate of hydration heat and cumulative hydration heat of cement pastes within 72 h by using the isothermal calorimeter.
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
fore, the incorporation of 30 wt% PS declines the heat releasing rate
and 3-day hydration heat of cement by about 37.7%, which is helpful for lowering the thermal cracking risk of mass hydraulic concrete at early age.
3.2.5.2. Long-term hydration heat within 180 days. In the concrete
dam, the internal temperature changes dramatically during the
first month after concrete pouring because of the intense hydration
heat of cement, thereafter the internal temperature cools down
very slowly from the highest temperature to the steady temperature, which normally takes several decades or hundreds of years
[102]. Although the temperature peak of concrete appears within
the first month, long-term hydration heat will accumulate inside
and increase the thermal stress, and thus increasing the cracking
risk of concrete [102]. Therefore, it is necessary to study the effect
of PS on the hydration heat in the long-term period.
The results of long-term hydration heat of PC paste, FA paste
and PS paste, as determined by the dissolution method within
180 days are presented in Fig. 10. As can be seen from Fig. 4, it is
clear that the hydration heat of three types of cement pastes
increases sharply during the first 28 days, after which it increased
gradually up to 180 days.
From the comparison between Figs. 9 and 10, it can be observed
that the hydration heat during the first 72 h measured by the dissolution method are nearly equivalent to those determined by
using the isothermal calorimeter. For instance, the hydration heat
within 72 h by the dissolution method is 221,165 and 136 J/g of
binder for PC, FA and PS paste, respectively, which are almost
equivalent with those (224.9, 167.5 and 140.1 J/g of binder, correspondingly) obtained by the isothermal calorimeter.
As for FA paste, there is a reduction of 25.3% in the hydration
heat within 3 days when 30 wt% FA is blended, while it is 23.7%
at 28 days and 18.6% at 180 days. As mentioned above, the reduction in early hydration heat is caused by the dilution effect and the
inert characteristic of FA at early stage. In addition, the hydration
heat gap between the PC paste and FA paste decreases with the
hydration process. It is widely known that the pozzolanic reaction
of FA becomes dominant after 28 days[21]. NMR results in this
study also reveal that about 26.1% and 33.4% FA have reacted at
28 and 180 days, respectively. As a result, additional hydration
heat is produced by the reaction of FA with CH, reducing the hydration gap between the two pastes.
As for PS paste, the hydration heat of PS paste develops slowly
during the initial 7 days compared with that of FA paste because of
the retarding effect of PS. After the first 7–14 days, PS paste exhi-
Fig. 10. Long-term hydration heat of cement pastes by the dissolution method.
13
bits higher hydration heat than that of FA one, and the difference
of hydration heat between them becomes larger with time. For
instance, the 28-day hydration heat of PS is 7.0% higher than that
of FA paste (255 J/g), and this value increases to 11.6% at 180 days,
demonstrating PS has a higher pozzolanic activity than FA. Besides,
the retarding effect of PS can be considered as negligible after the
first two weeks, other researchers considered that PS had no retardation effect at middle and late ages [27,40].
Moreover, the hydration heat gap between the PC paste and PS
paste tends to decrease with the prolongation of hydration time.
The total hydration heat of PS paste (345 J/g) within 180 days is
only 9.2% lower than that of PC one (380 J/g). These phenomena
can also be explained by the pozzolanic reaction between PA and
CH at middle and late age, which will inevitably generate additional hydration heat. As evidenced by the XRD and TG-DTA results
in this study and the findings of Refs. [33,39,40], PS participates
significantly in pozzolanic reactions in the middle and late stage.
Zhang [40] reported that the hydration degree of PS could accelerate the late hydration of cement.
From the findings above, it can be concluded that FA is more
beneficial for reducing the long-term hydration heat compared
with PS, and the incorporation of 30 wt% PS can also decrease
the 180-day hydration heat by about 9.2%.
3.3. PS and FA effects on the concrete properties
3.3.1. Fresh properties and setting time of concrete
The fresh properties and setting time of plain cement concrete
and concretes with PS and FA are presented in Table 8. It is clear
from Table 8, the addition of PS can slightly improve the slump
value of concrete. There are two reasons responsible for this
improvement. Firstly, due to the dilution effect, the effective W/B
ratio of concrete with PS is relatively increased and the excessive
water could increase the slump of concrete [24]. Secondly, the fine
PS particles act as a dispersing agent to improve the fluidity of concrete, which has been also reported by Gao [39]. However, the
improvement effect of PS on slump was less noticable than that
of FA. The main reason for this phenomenon could be the difference in the morphology between PS and FA. The spherical FA particles (as Fig. 3 indicated) would lead to a ball bearing effect that
can improve the fluidity of concrete. Another possible reason is
that the lower density of FA relative to PS and PC results in a higher
volume of paste at the same binder and water content, which facilities the fluidity of concrete [22,103].
Additionally, Table 8 presents the addition of PS and FA can
delay both the initial and final setting time of concrete, while the
retarding effect of PS is more significant. For instance, the initial
and final setting of PS5 concrete (W/B ratio of 0.5) are 16 h
35 min and 21 h15 min, which are postponed about 4h10min
and 3h30min compared with those of PC5 respectively. These
results are in line with the hydration heat data, this is due to the
PS retarding effect on cement hydration. In fact, this phenomenon
has been widely reported by many researchers [24,27,31,32], who
also revealed the retarding effect of PS on concrete setting and proposed that this negative effect would increase with the PS content,
or decrease with the PS fineness for normal-strength concrete.
3.3.2. Mechanical property of concrete
Fig. 11 exhibits the compressive strength of PC concrete (PC3
and PC5), PS concrete (PSC3 and PSC5) and FA concrete (FAC3
and FAC5) at 3, 28 and 180 days. It can be noted form Fig. 11,
the compressive strength of all the concrete specimens generally
increases with the curing age, or the decreasing W/B ratio. It can
be clearly seen form Fig. 11 that the W/B ratio has a profound effect
on the concrete strengths. Besides, the increasing rate before
28 days in Fig. 11 is obviously larger than that after 28 days,
14
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 8
Fresh properties and setting time of PC concrete, PS concrete and FA concrete.
Notation
W/B ratio
Water (kg/m3)
PC3
PC5
PSC3
PSC5
FAC3
FAC5
0.3
0.5
0.3
0.5
0.3
0.5
118
117
118
117
118
117
FA content
PS content
(wt.%)
(wt.%)
0
0
0
0
30
30
0
0
30
30
0
0
Slump (mm)
52
60
58
65
62
68
Setting time (h:min)
Initial
Final
8:30
12:25
11:20
16:35
9:20
13:45
12:50
17:45
15:40
21:15
14:05
19:00
Fig. 11. The compressive strength of PC concrete, PS concrete and FA concrete.
demonstrating that cement in concrete hydrates rapidly during the
first 28 days, after that it hydrates slowly, which is in good agreement with the 29Si MAS NMR and hydration heat results reported
in Sections 3.2.4 and 3.2.5 and Ref.[102].
It could be noted from Fig. 11 that the inclusion of FA in concrete declines not only the early compressive strength but also
the late one. For instance, the compressive strength of FAC3 (W/
B = 0.3) is reduced by 28.0%, 23.2% and 17.0% at 3, 28 and 180 days,
respectively, compared with that of PC3 concrete. As for the FAC5
concrete, the reduction in strength is 28%, 22.7% and 15.9% at 3, 28
and 180 days, respectively. It can be seen clearly that the differences between the PC concrete and FA concrete become small with
prolongation of hydration time, suggesting the pozzolanic reaction
between FA and CH become dominant at middle and late age. As
can be noted from the XRD, TG-DTA and NMR results in this paper,
the increased reaction degree of FA with CH minimizes the
strength differences between the PC concrete and FA one. However, a controversy exists regarding whether the long-term
strength of concrete with FA exceeds that of concrete without FA.
The long-term strength results of concrete with 20–40 wt% FA
obtained from other studies were listed in Table 9. It can be
observed in Table 9, Oner et al. [4] and Poon et al. [21] reported
that the long-term compressive strength of concrete with 25–
30 wt% FA was either similar or superior to those of concrete without FA. However, other authors [104,105] found that FA concrete
exhibited much lower long-term strengths compared with the concrete without FA, even a superfine FA with fineness of 510 kg/m2
was used. Siddique and Khan [9] have shown that the addition of
Class F FA (low-calcium) may have a negatively effect on the compressive strength while the addition of Class C FA (high-calcium)
may have a positive effect. In this study, the concrete with 30 wt
% FA has lower strength than the ones without FA, indicating the
pozzolanic reactivity of this FA is slightly weak. Comparison of
the results in Table 9 indicates that the chemical compositions
and fineness of the FA listed are more or less the same. As discussed above, in addition to the composition and fineness, the
reactivity of FA is influenced by many other factors.
From Fig. 11, PS concrete shows decreases of 25% and 21% in 3day compressive strength compared with those in PC concrete and
FA concrete, respectively. This negative effect on concrete mechanical property at early age could be explained by the retarding effect
of PS, which can inhibit the cement hydration and consequently
reduce the early mechanical property of concrete. These results
correlate well with the XRD and hydration heat results above, as
well as the data reported by others [5,24,27,30,40].
It can be also observed from Fig. 11 that after the first 7 days, PS
concretes possess stronger mechanical property in comparison
with that of FA ones, confirming PS has a much higher pozzolanic
activity than FA at middle and late age. These results are similar
with those of Wang et al. [30], who have also compared the
strength difference between PS concrete an FA one.
In Fig. 11, the strength increasing rates of PS concrete are higher
than those of FA concrete and PC one. For instance, the 180-day
compressive strength of PSC3 is 64.1 MPa, which is increased by
about 96.6% compared with that at 7 days. By contrast the strength
increasing rates of PC3 and FAC3 are 64.8% and 79.9% during the
same hydration period. The similar trend is also found for the concrete with a W/B ratio of 0.5. These results could be also explained
by the strong pozzolanic reaction between PS and CH at middle
and late age. It is accepted that the pozzolanic effect of PS facilitates the improvements of the microstructures and long-term
mechanical properties of concrete [24,30].
Furthermore, Fig. 11 exhibits that PS concretes have comparable
compressive strengths with those of PC ones at 180 days. The longterm strength of PS concrete reported by other researchers is also
listed in Table 9. It can be found from Table 9 that the effects of
15
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 9
The long-term strength of concrete with 15–40 wt% FA or PS in this study and other references.
Type
Class
Class
Class
Class
Class
PS
PS
PS
F
F
F
F
F
FA
FA
FA
FA
FA
Content (wt%)
Specific Surface area (kg/m2)
30
20
40
25
20
387
335
–
386
300
510
391
–
657
30
15
30
15
30
Chemical compositions (wt.%)
Long-term compressive strength (Mpa)
SiO2 + Al2O3 +Fe2O3
CaO
90-d
180-d
360-d
89.5
89.2
85.9
90.0
–
2.9
2.1
5.6
less than3
–
43.8
49.9
47.2
40.1
45.1
41.6
60.5(49.6)*
–
38(33)
114.5(123.6)
84.8(74.5)
84.8(81.4)
60.5(59.4)
65 (66)
65 (67)
57(58)
57(52)
64.6(53.6)
26.6(26.7)
–
–
–
–
64.6(64.1)
–
–
–
–
–
–
42.5(38)
–
–
–
–
–
–
58(61)
58(56)
Refere-nces
In this study
[4]
[104]
[21]
[105]
In this study
[40]
[5]
*The values in parentheses are the strengths of concrete added with FA, while those out of the parentheses are the strengths of plain cement concrete.
PS on long-term strength in this study and in other literature are
similar. For example, Hu et al. [5] found that the strength of concrete with 15–30 wt% PS at 90 days and 360 days was more or less
the same as those of concrete without PS. Zhang et al. [40] reported
the same strength trend of PS concrete with 15–30 wt% PS.
3.3.3. Adiabatic temperature rising of concrete
According to Ref. [102], the internal temperature changes significantly in hydraulic concrete during the first month after concrete placement. Besides, the concrete specimen in test system is
hard to be completely adiabatic over a very long time span because
of the possible experimental error. The adiabatic temperature rising of concrete was tested until 28 days.
Fig. 12 presents the adiabatic temperature rising development
of PC concrete (PC3 and PC5), PS concrete (PSC3 and PSC5) and
FA concrete (FAC3 and FAC5) within 28 days. From Fig. 12, it could
be observed that the adiabatic temperature rising of the three
types of concretes increases with the hydration age.
It can be noted from Fig. 12, PS concrete shows an obviously
slower temperature rising rate compared with those of PC and
FA one before 14 days, regardless of W/B ratios, which is also
related to the retarding effect of PS. Thereafter, the temperature
rising of PS concrete increases gradually and exceeds that of FA
concrete beyond 14 days, illustrating higher pozzolanic activity
of PS in comparison with FA. This trend is in good agreement with
the hydration heat results in Fig. 10 and the results reported by
Wang et al.[30], who have also compared the temperature rising
difference between the PS concrete and FA concrete.
As observed from Fig. 12, the 28-day temperature rising of PC3,
FAC3 and PSC3 concrete are 50.1℃, 40.0℃ and 44.7℃, while the
ones for PC5, FAC5 and PSC5 concrete are 44.1℃, 35.6℃ and
39.5℃. This sequence in the temperature rising value of these concretes is in line with that of the long-term hydration heat results in
Fig. 10.
The results of adiabatic temperature rising of concrete obtained
in this study and from other references were listed Table 10.
Table 10 shows that, the addition of 50 wt% FA can reduce the adiabatic temperature rise by 12–13 °C [1,14], while in this study, the
adiabatic temperature rise was reduced by 8–10 °C after the incorporation of 30 wt% FA. Besides, Ref. [30] found that the adiabatic
temperature rising of concrete with 50% PS was 2.4℃ higher than
that of concrete with 50% FA, while in this study, this difference
was within the range of 2.9–4.7℃ between the concrete with 30%
FA and the concrete with 30 wt% PS. Therefore, a trend is summarized from Table 10, that is, the addition of FA is more conducive to
reducing the adiabatic temperature rise than that of PS. Nevertheless, Table 10 shows that the adiabatic temperature rising of concrete is reduced by 4–5 ℃ due to 30 wt% PS incorporation. As
discussed above, a relatively low internal temperature rising favors
Fig. 12. Adiabatic temperature rising of PC concrete, PS concrete and FA concrete.
the reduction in thermal stress and crack risk of mass hydraulic
structures.
3.3.4 vol. deformation
3.3.4.1. Autogenous shrinkage. Fig. 13 shows the development of
autogenous shrinkage of PC, PS and FA concrete, respectively. Autogenous shrinkage of concrete originates from the self-desiccation
and the shrinkage of cement paste caused by the water consumption during the hydration process under sealed conditions, without
any change in weight [10,33,60]. It can be observed from Fig. 13
that there is a rapid increase in autogenous shrinkage during the
16
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
Table 10
The results of adiabatic temperature rising of concrete obtained in this study and other references.
Binder content in 1 m3 concrete (kg)
PC
393
275
275
234
164
164
400
200
430
215
210
210
FA
0
118
0
0
70
0
0
200
0
215
210
0
PS
0
0
118
0
0
70
0
0
0
0
0
210
Peak temperature
References
50.1℃
40.0℃
44.7℃
44.1℃
35.6℃
39.5℃
55℃
42℃
57℃
35.2
37.2
39.6
In this study
[14]
[14]
[1]
[1]
[30]
[30]
Fig. 13. Development of autogenous shrinkage of PC concrete, PS concrete and FA concrete.
first 28 days, indicating the rapid cement hydration before 28 days.
Thereafter, the increasing rate of autogenous shrinkage tends to
slow down up to 180 days for all concretes, suggesting the formation of the structure helps to restrict the deformation. This trend
correlates well with the long-term hydration heat in Subsection
3.2.5.
Fig. 13 (a) and (b) show that both the W/B ratio and type of mineral admixture have a pronounced influence on the autogenous
shrinkage development of concrete.
In this work, concrete with a lower W/B ratio produces a higher
autogenous shrinkage and vice versa. For instance, as for the PC
concrete, a reduction of W/B ratio from 0.5 (PC5) to 0.3 (PC3)
increases the autogenous shrinkage from 80 to 106 micro strains
at 180 days. The same trend can be also found for PS concrete
and FA concrete. These phenomena can be explained by the following three points. Firstly, the high cement content in concrete due to
the low W/B ratio was probably the main reason. The cement content in concrete has been considered as a predominant role determining the autogenous shrinkage [12]. For example, cement
content in concrete in PC3 is 393 kg/m3,which is 159 kg/m3 higher
than that in PC5, while the water content of PC3 and PC5 are
almost the same (117–118 kg/m3), as shown in Table 3. It was
reported that the increase in cement content could lead to the
shortage of water in concrete and decrease the capillary water content, therefore, the reduction in relative humidity caused by the
cement hydration may be more significant for concretes with high
cement content or low W/B ratio, leading to the formation of high
self-desiccation and large autogenous shrinkage [19,24,106]. Secondly, as Tongaroonsri and Tangtermsirikul [107] have concluded,
the decrease of W/B ratio could partly prevent the movement of
mixture water into fine pores and lead to a significant increase in
self-desiccation and consequently increase the autogenous shrinkage of concrete. Another possible reason could be the enhancement
of the constraint effect in concrete with larger content of aggregate. For instance, the total aggregate content in PC3 is 1972
kg/m3, which is 139 kg/m3 smaller than that of PC5. Hawreen
et al. [108] proposed that the restriction effect on free shrinkage
of concrete is mostly provided by the aggregate skeleton. Similarly,
Rao [109] found that the final shrinkage of mortar decrease with
increasing the aggregate size and proportion because of the
restraining action of the aggregate on the mortar. Obviously, aggregate particles with higher content will restrict the shrinkage of the
mortar or concrete to a greater extent.
Moreover, it is interesting to notice that the absorption or
release of water by aggregates could also affect the autogenous
shrinkage of concrete, e.g., the utilization of the pre-wetted fine
lightweight aggregate could provide internal water that can help
mitigate autogenous shrinkage in concretes [60]. However, the
aggregates used in this study have no such effects, because they
were in saturated-surface-dry (SSD) condition and would not
adsorb mixture water or release excess water to the concrete
mixture.
Fig. 13 also indicates that the autogenous shrinkage obviously
decreases with the incorporation of PS or FA. Previous studies
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
[12,19] proved that the autogenous shrinkage of concrete went
down linearly with increasing the FA content. Similarly, some
authors [24,33] reported that the increase in PS content generally
led to a considerable reduction in autogenous shrinkage of concrete. It is generally accepted that the reactivity of PC is much
higher than the mineral admixtures such as FA and PS, therefore,
PC has a more noticeable impact on the water consumption and
self-desiccation during the hydration process [18,19,33]. As discussed above, the reduction in cement content could reduce the
autogenous shrinkage of concrete. Therefore, the reduction effect
on autogenous shrinkage due to PS or FA incorporation is mainly
caused by the dilution effect when cement is partially substituted.
It can be found that the reduction effect of PS on autogenous
shrinkage is more prominent in comparison to that of FA under
the same W/B ratio level during the first 2–3 weeks. This is can
be attributed to the retarding effect of PS, which could decelerate
the early cement hydration, thereby mitigating the selfdesiccation and shrinkage of concrete. After the first 2–3 weeks,
the autogenous shrinkage of PS concrete increases progressively
and surpasses that of FA concrete up to 180 days. The 180-day
autogenous shrinkage strains are reduced by 18–20% and 8–11%
due to the incorporation of 30 wt% FA and 30 wt% PS, respectively.
This trend is consistent with the results of the long-term hydration
heat, compressive strength and adiabatic temperature rising of
concrete above. The high pozzolanic reactivity of PS could explain
this phenomenon, PS with high reactivity would accelerate the
water consumption and self-desiccation inside the concrete, and
thus increasing the autogenous shrinkage. This mechanism is similar to the that reported by Yang [33], who revealed that the mortar
containing ultra-fine PS (mean particle size d50 of 2.2 lm) with
much higher pozzolanic reactivity exhibits larger autogenous
shrinkage than the mortar containing raw PS (mean particle size
d50 of 38.3 lm).
Form the results above, it can be found that FA is more conductive to reducing the long-term autogenous shrinkage of concrete
compared with PS. However, PS could reduce the early autogenous
shrinkage effectively and the 180-day autogenous shrinkage strain
could be lowered by 8–11% in the presence of 30 wt% PS.
3.3.4.2. Drying shrinkage. Fig. 14 shows the development of drying
shrinkage of PC, PS and FA concrete, respectively. The drying
shrinkage of concrete develops rapidly during the first 14 days,
subsequently it gradually increases for the rest of the time up to
180 days. This trend agrees well with the studies by others
17
[27,33,110]. Besides, comparison of the results in Fig. 14 (c) and
(d) indicates that, before 14 days, the drying shrinkage is almost
equivalent for the three types of concretes under the same W/B
ratio. It is generally agreed that the drying shrinkage of concrete
usually results from the evaporation of internal free water from
the internal connected-pores [10,60]. As stated by Kristiawan and
Aditya [12], the early pore characteristics were mainly governed
by the water content in the concrete mixtures. It should be noted
that the water contents of the concrete mixtures are nearly the
same (117–118 kg/m3), as shown in Table 3. So, the rapid evaporation and release of the internal free water in concrete can probably
explain the fast development and similar trend of drying shrinkage
at early age.
The results in Fig. 14 show that W/B ratio also possesses a
strong effect on the drying shrinkage of the three types of concretes. As for the PC concrete in Fig. 14, a decrease in W/B ratio
from 0.5 to 0.3 leads to a reduction in drying shrinkage from 382
to 278 micro strains. The similar phenomenon can be also observed
in Fig. 14(b). These results can be explained by two possible reasons. Differences in cement content are considered to be the first
reason for this effect. For instance, Table 3 shows that PC3 concrete
has a similar water content but a much higher cement content
compared with PC5 one. As revealed by Tao et al. [111], a higher
binder content could restrict the water evaporation from the internal pore networks, resulting in a decreased drying shrinkage. The
second possible reason could be the high loss of internal water in
concrete with high W/B ratios. As it is concluded by Hu et al.
[25] and Zhang et al. [112], the concretes with higher W/B ratios
possess high porosities and large pore diameters, which could
accelerate the moisture loss and increase the capillary pressure
in the internal pores and therefore increasing the drying shrinkage
of concrete.
In addition, Fig. 14 show that both the incorporation of FA and
PS reduces the long-term drying shrinkage. Specifically, the incorporation of FA decreases the drying shrinkage at 180 days by 15.8%
(44 micro strains) for FAC3 and by 16.2% (62 micro strains) for
FAC5. As for the PSC3 and PSC5, the drying shrinkage is decreased
by 7.2% (20 micro strains) and 9.0% (34 micro strains) due to the
incorporation of 30 wt% PS, respectively. The results are in agreement with other studies [12,110,113], which reported that the drying shrinkage can be effectively lowered in the presence of FA and
the shrinkage strains generally decreased with the FA content,
because the filler and pozzolanic effects of FA at late hydration
age could refine the microstructure and improve the resistance
Fig. 14. Development of drying shrinkage of PC concrete, PS concrete and FA concrete.
18
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
to concrete shrinkage. As for the effects of PS, the results in this
study are in agreement with those found by Chen et al.[27], who
have reported that the addition of 20–60 wt% PS can reduce the
drying shrinkage of mortars, and the drying shrinkage decreased
progressively with the increase in PS content. On the contrary,
Yang et al. [33] have observed that the drying shrinkage value
increased with the increase in ultra-fine PS content from 20 wt%
to 60 wt%. The seemingly conflicting results are due to the significant difference in the fineness of PS. It can be noticed that the mean
particle size (d50) of the ultra-fine PS is 2.2 lm in Ref. [33], while
the specific surface area of PS in Ref. [27] is 400 kg/m2 , which is
almost the same as that of PS in this study (391 kg/m2 and d50
is 13.5 lm). There is a general agreement that the drying shrinkage
strains of concrete increase significantly with the fineness of mineral materials (e.g., PS, silica fume and ground granulated blast furnace slag, etc.) [27,109,114]. In this study, the minor discrepancy in
fineness between PS and FA can be neglected.
Moreover, through the comparison of the results in Fig. 14, the
reduction effect of FA on the long-term shrinkage is more noticeable than that of PS. Amoudi et al. [84] reported that the type of
binder is a critical factor in determining the drying shrinkage,
because the difference in reaction degree may affect the final
shrinkage. Yang et al. [77] found the shrinkage under drying conditions to be a function of the hydration degree of the binder. So the
high drying shrinkage of PS concrete at middle and late age may be
attributed to the high reactivity of PS, which could result in selfdesiccation and a lack of water inside the PS concrete, thus leading
to a high drying shrinkage.
Based on the results above, it has been verified that FA was
more effective in decreasing the long-term drying shrinkage than
PS. Nevertheless, the addition of 30 wt% PS could decline the
180-day drying shrinkage by about 7.2%-9.0% in this study.
4. Conclusion
(1) The incorporation of 30 wt% PS and 30 wt% FA in the cement
paste decreased the CH content by about 53.9% and 29.6% at
28 days, and about 63.5% and 56.4% at 180 days, respectively, compared with those in the plain cement paste, confirming PS has a
higher pozzolanic activity than FA.
(2) The retarding effect of PS at early age hinders the generation
of C-S-H, whereas the pozzolanic reaction of PS largely occurs at
middle and late age. Lots of C-S-H gels with high polymerization
degree are produced at middle and late age, leading to a dense
microstructure. FA has a more noticeable effect on the enhancement of polymerization degree and Al content of C-S-H than PS.
Besides, the hydration degree of cement and reaction degree of
FA have been evaluated by the NMR technique and the results
are compared with those in other studies.
(3) There is a reduction of 25.3% and 18.6% in the cement hydration heat within 3 days and 180 days when 30 wt% FA is blended.
By contrast, PS is more helpful for lowering the hydration heat and
thermal cracking risk at early age. Additionally, the incorporation
of 30 wt% PS reduces the 180-day hydration heat by about 9.2%.
(4) After the first few days, PS concretes possess stronger
mechanical properties in comparison with that of FA ones. PS concretes have comparable compressive strengths with PC ones at
180 days. The adiabatic temperature rising of plain cement concrete at 28 days was reduced by 4–5 ℃ due to 30 wt% PS incorporation. The addition of FA is more conducive to reducing the
adiabatic temperature rise than that of PS. A low internal temperature rising favors the reduction in thermal stress and crack risk of
mass hydraulic structures.
(5) Compared with PS, FA is more conductive to reducing the
long-term autogenous shrinkage and drying shrinkage of concrete.
However, the addition of 30 wt% PS reduces the early autogenous
shrinkage effectively and declines the 180-day drying shrinkage
or autogenous shrinkage by about 7.2%-9.0% and 8–11%, respectively. The results in this study could provide useful experience
for the utilization of PS and FA in hydraulic projects.
CRediT authorship contribution statement
Lei Wang: Conceptualization, Writing - original draft, Supervision, Project administration, Funding acquisition. Fanxing Guo:
Investigation, Writing - original draft. Yuqiang Lin: Investigation,
Writing - original draft. Huamei Yang: Investigation, Writing review & editing. S.W. Tang: Investigation, Writing - original draft,
Writing - review & editing.
Funding
Natural Science Research Project of Shaanxi Provincial Department of Education (WL), China.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgement
This work is financial support by Open funding of National Dam
Safety Research Center (CX2019B12),Talent fund of Xi’an University of Architecture and Technology, NSFC of China (51409016
and 51602229).
References
[1] S.H. Jung, Y.C. Choi, S. Choi, Use of ternary blended concrete to mitigate
thermal cracking in massive concrete structures-A field feasibility and
monitoring case study, Constr. Build. Mater. 137 (2017) 208–215.
[2] Y. Li, L. Nie, B. Wang, A numerical simulation of the temperature cracking
propagation process when pouring mass concrete, Automat. Constr. 37 (2014)
203–210.
[3] T. Yen, T.-H. Hsu, Y.-W. Liu, S.-H. Chen, Influence of class F fly ash on the
abrasion–erosion resistance of high-strength concrete, Constr. Build. Mater.
21 (2) (2007) 458–463.
[4] A. Oner, S. Akyuz, R. Yildiz, An experimental study on strength development
of concrete containing fly ash and optimum usage of fly ash in concrete, Cem.
Concr. Res. 35 (6) (2005) 1165–1171.
[5] J. Hu, Comparison between the effects of superfine steel slag and superfine
phosphorus slag on the long-term performances and durability of concrete, J.
Therm. Anal. Calorim. 128 (3) (2017) 1251–1263.
[6] B. Walkley, J.L. Provis, NMR Solid-state nuclear magnetic resonance
spectroscopy of cements, Mater. Today 1 (2019) 100007.
[7] O. Bouchenafa, R. Hamzaoui, A. Bennabi, J. Colin, PCA effect on structure of fly
ashes and slag obtained by mechanosynthesis. Applications: Mechanical
performance of substituted paste CEMI + 50% slag/or fly ashes, Constr. Build.
Mater. 203 (2019) 120–133.
[8] Rabah Hamzaoui, Othmane Bouchenafa, Sofiane Guessasma, A. Nordine
Leklou, Bouaziz,, The sequel of modified fly ashes using high energy ball
milling on mechanical performance of substituted past cement, Mater. Design
90 (2016) 29–37.
[9] R. Siddique, M.I. Khan, Supplementary cementing materials, Springer-Verlag,
Berlin Heidelberg, 2011.
[10] W. Wongkeo, P. Thongsanitgarn, A. Chaipanich, Compressive strength and
drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement
mortars, Mater. Des. 36 (2012) 655–662.
[11] S. Altoubat, M. Talha Junaid, M. Leblouba, D. Badran, Effectiveness of fly ash
on the restrained shrinkage cracking resistance of self-compacting concrete,
Cem. Conc. Compos. 79 (2017) 9–20.
[12] S.A. Kristiawan, M.T.M. Aditya, Effect of high volume fly ash on shrinkage of
self-compacting concrete, Procedia Eng. 125 (2015) 705–712.
[13] L. Wang, S.H. Zhou, Y. Shi, S.W. Tang, E. Chen, Effect of silica fume and PVA
fiber on the abrasion resistance and volume stability of concrete, Compos.
Part B-Eng. 130 (2017) 28–37.
[14] C.D. Atis, Heat evolution of high-volume fly ash concrete, Cem. Concr. Res. 32
(2002) 751–756.
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
[15] J.H. Ha, Y.S. Jung, Y.G. Cho, Thermal crack control in mass concrete structure
using an automated curing system, Automat. Constr. 45 (2014) 16–24.
[16] L. Wang, H.Q. Yang, S.H. Zhou, E. Chen, S.W. Tang, Mechanical properties,
long-term hydration heat, shinkage behavior and crack resistance of dam
concrete designed with low heat Portland (LHP) cement and fly ash, Constr.
Build. Mater. 187 (2018) 1073–1091.
[17] B. Yin, T. Kang, J. Kang, Y. Chen, L. Wu, M. Du, Investigation of the hydration
kinetics and microstructure formation mechanism of fresh fly ash cemented
filling materials based on hydration heat and volume resistivity
characteristics, Applied Clay Sci. 166 (2018) 146–158.
[18] P. Termkhajornkit, T. Nawa, M. Nakai, T. Saito, Effect of fly ash on autogenous
shrinkage, Cem. Concr. Res. 35 (3) (2005) 473–482.
[19] X. Hu, C. Shi, Z. Shi, B. Tong, D. Wang, Early age shrinkage and heat of
hydration of cement-fly ash-slag ternary blends, Constr. Build. Mater. 153
(2017) 857–865.
[20] K.Y. Liao, P.K. Chang, Y.N. Peng, C.C. Yang, A study on characteristics of
interfacial transition zone in concrete, Cem. Concr. Res. 34 (6) (2004) 977–
989.
[21] C.S. Poon, L. Lam, Y.L. Wong, A study on high strength concrete prepared with
large volumes of low calcium fly ash, Cem. Concr. Res. 30 (3) (2000) 447–455.
[22] F. Moghaddam, V. Sirivivatnanon, K. Vessalas, The effect of fly ash fineness on
heat of hydration, microstructure, flow and compressive strength of blended
cement pastes, Case Studies in Constr. Mater. 10 (2019) e00218.
[23] S. Peng, X. Li, Z. Wu, J. Chen, X. Lu, Study of the key technologies of application
of tuff powder concrete at the Daigo hydropower station in Tibet, Constr.
Build. Mater. 156 (2017) 1–8.
[24] R. Yang, R. Yu, Z. Shui, X. Gao, Low carbon design of an ultra-high performance
concrete (UHPC) incorporating phosphorous slag, J. Clean. Prod. 240 (2019)
118157.
[25] Y. Li, Y.B. Li, P.F. Ji, J. Yang, The status quo analysis and policy suggestions on
promoting China‫׳‬s hydropower development, Renew. Sust. Energ. Rev. 51
(2015) 1071–1079.
[26] Z. He, R. Cai, E. Chen, S. Tang, The investigation of early hydration and pore
structure for limestone powder wastes blended cement pastes, J. Therm. Anal.
Calorim. 229 (2019) 116923.
[27] X. Chen, L. Zeng, K. Fang, Anti-crack performance of phosphorus slag concrete,
J. Wuhan Univ. Technol.-Mater. Sci. Ed. 14 (1) (2009) 80–86.
[28] A. Allahverdi, S. Pilehvar, M. Mahinroosta, Influence of curing conditions on
the mechanical and physical properties of chemically-activated phosphorous
slag cement, Powder Technol. 288 (2016) 132–139.
[29] Y. Peng, J. Zhang, J. Liu, J. Ke, F. Wang, Properties and microstructure of
reactive powder concrete having a high content of phosphorous slag powder
and silica fume, Constr. Build. Mater. 101 (2015) 482–487.
[30] Q. Wang, Z. Huang, D. Wang, Influence of high-volume electric furnace nickel
slag and phosphorous slag on the properties of massive concrete, J. Therm.
Anal. Calorim. 131 (2) (2017) 873–885.
[31] A. Allahverdi, M. Mahinroosta, Mechanical activation of chemically activated
high phosphorous slag content cement, Powder Technol. 245 (2013) 182–
188.
[32] D. Li, J. Shen, L. Mao, Q. Xue, The influence of admixtures on the properties of
phosphorous slag cement, Cem. Concr. Res. 30 (2000) 1169–1173.
[33] J. Yang, J. Huang, X. He, Y. Su, S.-K. Oh, Shrinkage properties and
microstructure of high volume ultrafine phosphorous slag blended
cement mortars with superabsorbent polymer, J. Build. Eng. 52 (29)
(2020) 101121.
[34] X. Chen, K. Fang, H. Yang, H. Peng, Hydration kinetics of phosphorus slagcement paste, J. Wuhan Univ. Technol. - Mater. Sci. Ed. 26 (1) (2011) 142–
146.
[35] H. Mehdizadeh, E.N. Kani, Rheology and apparent activation energy of alkali
activated phosphorous slag, Constr. Build. Mater. 171 (2018) 197–204.
[36] C. Shi, Y. Li, Investigation on some factors affecting the characteristics of
alkali-phosphorus slag cement, Cem. Concr. Res. 19 (4) (1989) 527–533.
[37] A. Allahverdi, M.M.B.R. Abadi, K.M. Anwar Hossain, M. Lachemi, Resistance of
chemically-activated high phosphorous slag content cement against freeze–
thaw cycles, Cold Reg. Sci. Technol. 103 (2014) 107–114.
[38] JC/T 740-2006. Portland phosphorous slag cement, China, China Building
Materials Industry Press, Beijing.
[39] P. Gao, X. Lu, C. Yang, X. Li, N. Shi, S. Jin, Microstructure and pore structure of
concrete mixed with superfine phosphorous slag and superplasticizer, Constr.
Build. Mater. 22 (5) (2008) 837–840.
[40] Z. Zhang, Q. Wang, J. Yang, Hydration mechanisms of composite binders
containing phosphorus slag at different temperatures, Constr. Build. Mater.
147 (2017) 720–732.
[41] G.K. Sun, J.F. Young, R.J. Kirkpatrick, The role of Al in C-S-H: NMR, XRD, and
compositional results for precipitated samples, Cem. Concr. Res. 36 (1) (2006)
18–29.
[42] R.I. Malek, Z.H. Khalil, S.S. Imbaby, D.M. Roy, The contribution of class-F fly
ash to the strength of cementitious mixtures, Cem. Concr. Res. 35 (6) (2005)
1152–1154.
[43] L. Zhang, K. Yamauchi, Z.J. Li, X.X. Zhang, H.Y. Ma, S.G. Ge, Novel
understanding of calcium silicate hydrate from dilute hydration, Cem.
Concr. Res. 99 (2017) 95–105.
[44] E. L’Hôpital, B. Lothenbach, G. Le Saout, D. Kulik, K. Scrivener, Incorporation of
aluminium in calcium-silicate-hydrates, Cem. Concr. Res. 75 (2015) 91–103.
[45] GB 175-2007. Common Portland cement, China, China Standard Press,
Beijing.
19
[46] ASTM C618. Standard specification for coal fly ash and raw or calcined natural
pozzolan, West Conshohocken (PA): ASTM International, 2012.
[47] GB/T 1596-2017. Fly ash used for cement and concrete, China, China Standard
Press, Beijing.
[48] GB/T 8074-2008. Testing method for specific surface of cement-Blaine
method, China, China Standard Press, Beijing.
[49] DL/T 5387-2007. Technical specification for phosphorous slag powder use in
hydraulic concrete, China, China Electric Power Press, Beijing.
[50] DL/T 5151-2014. Code for testing aggregates of hydraulic concrete, China,
China Electric Power Press, Beijing.
[51] DL/T 5144-2015. Specifications for hydraulic conrete construction, China,
China Electric Power Press, Beijing.
[52] SL 191-2008. Design code for hydraulic concrete structures, China, China
Water Conservancy and Hydropower Press, Beijing.
[53] DL/T 5330-2015. Code for mix design of hydraulic concrete, China, China
Electric Power Press, Beijing.
[54] Y. Kim, A. Hanif, M. Usman, M.J. Munir, S.M.S. Kazmi, S. Kim, Slag waste
incorporation in high early strength concrete as cement replacement:
Environmental impact and influence on hydration & durability attributes, J.
Clean. Prod. 172 (2018) 3056–3065.
[55] H.Q. Yang, M.J. Rao, Y. Dong, Influence study of extra-large stone limited size
and content on full-graded concrete properties, Constr. Build. Mater. 127
(2016) 774–783.
[56] J. Schneider, M.A. Cincotto, H. Panepucci, 29Si and 27Al high-resolution NMR
characterization of calcium silicate hydrate phases in activated blast-furnace
slag pastes, Cem. Concr. Res. 31 (2001) 993–1001.
[57] C. MD., G. Goberdhan., 29Si MAS NMR study of the hydration of tricalcium
silicate in the presence of finely divided silica, J. Mater. Sci. 23(11) (1988)
4108-4114.
[58] GB, T,, 12959–2008. Test code for cement hydration heat measurement
method, Standard Press, China, China, 2008.
[59] DL/T5150-2017, Test code for hydraulic concrete, China, China Electric Power
Press, Beijing.
[60] T. Deboodt, T. Fu, J.H. Ideker, Evaluation of FLWA and SRAs on autogenous
deformation and long-term drying shrinkage of high performance concrete,
Constr. Build. Mater. 119 (2016) 53–60.
[61] L. Zhang, Y. Zhang, C. Liu, L. Liu, K. Tang, Study on microstructure and bond
strength of interfacial transition zone between cement paste and highperformance lightweight aggregates prepared from ferrochromium slag,
Constr. Build. Mater. 142 (2017) 31–41.
[62] A.M. Rashad, H.E.-D.H. Seleem, A.F. Shaheen, Effect of silica fume and slag on
compressive strength and abrasion resistance of HVFA concrete, Int. J. Concr.
Struct. M. 8 (1) (2014) 69–81.
[63] B. Ma, H. Li, X. Li, J. Mei, Y. Lv, Influence of nano-TiO2 on physical and
hydration characteristics of fly ash–cement systems, Constr. Build. Mater. 122
(2016) 242–253.
[64] Y.L. Chen, C.J. Lin, M.S. Ko, Y.C. Lai, Characterization of mortars from beliterich clinkers produced from inorganic wastes, Cem. Conc. Compos. 33 (2)
(2011) 261–266.
[65] S. Martínez-Ramírez, M. Frías, E.Y. Nakanishi, H. Savastano, Pozzolanic
reaction of a biomass waste as mineral addition to cement based materials:
studies by nuclear magnetic resonance (NMR), Int. J. Concr. Struct. M. 13 (1)
(2019) 1–8.
[66] J. Roncero, S. Valls, R. Gettu, Study of the influence of superplasticizers on the
hydration of cement paste using nuclear magnetic resonance and X-ray
diffraction techniques, Cem. Concr. Res. 32 (2002) 103–108.
[67] J. Yang, J. Huang, Y. Su, X. He, H.b. Tan, W. Yang, Eco-friendly treatment of
low-calcium coal fly ash for high pozzolanic reactivity: A step towards waste
utilization in sustainable building material, J. Clean. Prod. 238 (2019) 117962.
[68] S.A. Bernal, J.L. Provis, B. Walkley, R.S. Nicolas, J.S.J.V. Deventer, Gel
nanostructure in alkali-activated binders based on slag and fly ash, and
effects of accelerated carbonation, Cem. Concr. Res. 53 (2013) 127–144.
[69] M. Liu, H. Tan, X. He, Effects of nano-SiO2 on early strength and
microstructure of steam-cured high volume fly ash cement system, Constr.
Build. Mater. 194 (2018) 350–359.
[70] ASTM C311/C311M-17. Standard test methods for sampling and testing fly
ash or natural pozzolans for use in Portland-cement concrete.
[71] E.M. Foley, J.J. Kim, M.M. Reda Taha, Synthesis and nano-mechanical
characterization of calcium-silicate-hydrate (C-S-H) made with 1.5CaO/SiO2
mixture, Cem. Concr. Res. 42 (9) (2012) 1225–1232.
[72] L.P. Singh, S.K. Bhattacharyya, S.P. Shah, G. Mishra, U. Sharma, Studies on
early stage hydration of tricalcium silicate incorporating silica nanoparticles:
Part II, Constr. Build. Mater. 102 (2016) 943–949.
[73] B. Liu, S. Wang, Y. Chen, C. Gong, L. Lu, Effect of waste gypsum on the setting
and early mechanical properties of belite-C2.75B1.25A3$ cement, J. Therm.
Anal. Calorim. 125 (1) (2016) 75–83.
[74] J. Sun, H. Shi, B. Qian, Z. Xu, W. Li, X. Shen, Effects of synthetic C-S-H/PCE
nanocomposites on early cement hydration, Constr. Build. Mater. 140 (2017)
282–292.
[75] E.B. da Costa, E.D. Rodríguez, S.A. Bernal, J.L. Provis, L.A. Gobbo, A.P.
Kirchheim, Production and hydration of calcium sulfoaluminate-belite
cements derived from aluminium anodising sludge, Constr. Build. Mater.
122 (2016) 373–383.
[76] F. Deschner, F. Winnefeld, B. Lothenbach, S. Seufert, P. Schwesig, S. Dittrich, F.
Goetz-Neunhoeffer, J. Neubauer, Hydration of Portland cement with high
replacement by siliceous fly ash, Cem. Concr. Res. 42 (10) (2012) 1389–1400.
20
L. Wang et al. / Construction and Building Materials 250 (2020) 118807
[77] E. Sakai, S. Miyahara, S. Ohsawa, S.H. Lee, M. Daimon, Hydration of fly ash
cement, Cem. Concr. Res. 35 (6) (2005) 1135–1140.
[78] P. Termkhajornkit, T. Nawa, K. Kurumisawa, Effect of water curing conditions
on the hydration degree and compressive strengths of fly ash–cement paste,
Cem. Conc. Compos. 28 (9) (2006) 781–789.
[79] D.K. Panesar, M. Aqel, D. Rhead, H. Schell, Effect of cement type and limestone
particle size on the durability of steam cured self-consolidating concrete,
Cem. Conc. Compos. 80 (2017) 175–189.
[80] N. Shafiq, Degree of hydration and compressive strength of conditioned
samples made of normal and blended cement system, Ksce J. Civil Eng. 15 (7)
(2011) 1253–1257.
[81] B.E.I. Abdelrazig, D.G. Bonner, D.V. Nowell, P.J. Egan, J.M. Dransfield,
Estimation of the degree of hydration in modified ordinary portland
cement pastes by differential scanning calorimetry, Thermochim. Acta 145
(1) (1989) 203–217.
[82] S. Mindess, J.F. Young, Concrete(2nd Edition), Prentice-Hall, Murray Hill,
2002.
[83] C. Sabine, Influence of aggregates on chloride diffusion coefficient into
mortar, Cem Concr Res 33 (7) (2003) 1021–1028.
[84] G. Sun, Y. Zhang, W. Sun, Z. Liu, C. Wang, Multi-scale prediction of the
effective chloride diffusion coefficient of concrete, Constr. Build. Mater. 25
(10) (2011) 3820–3831.
[85] S. Zhang, M. Zhang, Hydration of cement and pore structure of concrete cured
in tropical environment, Cem. Concr. Res. 36 (10) (2016) 1947–1953.
[86] G.L. Golewski, An assessment of microcracks in the interfacial transition zone
of durable concrete composites with fly ash additives, Compos. Struct. 200
(2018) 515–520.
[87] I.G. Richardson, The nature of C-S-H in hardened cements, Cem. Concr. Res. 29
(8) (1999) 1131–1147.
[88] D. Jiang, X. Li, Y. Lv, M. Zhou, C. Li, Utilization of limestone powder and fly ash
in blended cement: Rheology, strength and hydration characteristics, Constr.
Build. Mater. 232 (2020) 117228.
[89] B. Ma, T. Zhang, H. Tan, X. Liu, J. Mei, Effect of triisopropanolamine on
compressive strength and hydration of cement-fly ash paste, Constr. Build.
Mater. 179 (2018) 89–99.
[90] E. L’Hôpital, B. Lothenbach, D.A. Kulik, K. Scrivener, Influence of calcium to
silica ratio on aluminium uptake in calcium silicate hydrate, Cem. Concr. Res.
85 (2016) 111–121.
[91] F. Ana, A.G.d.l. Torre, A. Palomo, G. López-Olmo, M.M. Alonso, M.A.G. Aranda,
Quantitative determination of phases in the alkaline activation of fly ash. Part
II: Degree of reaction, Fuel 85(14) (1996) 1960-1969.
[92] Y.M. Zhang, W. Sun, H.D. Yan, Hydration of high-volume fly ash cement
pastes, Cem. Conc. Compos. 22 (6) (2000) 445–452.
[93] F. Zou, C. Hu, F. Wang, Y. Ruan, S. Hu, Enhancement of early-age strength of
the high content fly ash blended cement paste by sodium sulfate and C-S-H
seeds towards a greener binder, J. Clean. Prod. 224 (2020) 118566.
[94] D.S. Wu, Y.N. Peng, The macro- and micro properties of cement pastes with
silica-rich materials cured by wet-mixed steaming injection, Cem. Concr. Res.
33 (9) (2003) 1331–1345.
[95] S.W. Tang, Z.J. Li, H.Y. Shao, E. Chen, Characterization of early-age hydration
process of cement pastes based on impedance measurement, Constr. Build.
Mater. 68 (2014) 491–500.
[96] L. Kalina, J. Vlastimil Bílek, R. Novotný, M. Mončeková, J. Másilko, J. Koplík,
Effect of Na3PO4 on the hydration process of alkali-activated blast furnace
slag, Materials 9 (5) (2016) 395–403.
[97] M. Codina, C. Cau-dit-Coumes, P. Le Bescop, J. Verdier, J.P. Ollivier, Design and
characterization of low-heat and low-alkalinity cements, Cem. Concr. Res. 38
(4) (2008) 437–448.
[98] Y. Halse, P.L. Pratt, J.A. Dalziel, W.A. Gutteridge, Development of
microstructure and other properties in flyash OPC systems, Cem. Concr.
Res. 14 (4) (1984) 491–498.
[99] J.Y. He, B.E. Scheetz, D.M. Roy, Hydration of fly ash-portland cements, Cem.
Concr. Res. 14 (4) (1984) 505–512.
[100] B.W. Langan, K. Weng, M.A. Ward, Effect of silica fume and fly ash on heat of
hydration of Portland cement, Cem. Concr. Res. 32 (7) (2002) 1045–1051.
[101] H.C. Lung, D.-H. Shen, The effects of blast-furnace slag and fly ash on the
hydration of portland cement, Cem. Concr. Res. 21 (4) (1991) 410–425.
[102] B. Zhu, Thermal stresses and temperature control of mass concrete, 1st ed.,
Butterworth-Heinemann, Oxford, 2014.
[103] C.F. Ferraris, K.H. Obla, R. Hill, The influence of mineral admixtures on the
rheology of cement paste and concrete, Cem. Concr. Res. 31 (2) (2001) 245–
255.
[104] R. Siddique, Performance characteristics of high-volume Class F fly ash
concrete, Cem. Concr. Res. 34 (3) (2004) 487–493.
[105] P. Chindaprasirt, J. Chai, T. Sinsiri, Effect of fly ash fineness on compressive
strength and pore size of blended cement paste, Cem. Conc. Compos. 27 (4)
(2005) 425–428.
[106] Y. Ma, G. Ye, The shrinkage of alkali activated fly ash, Cem. Concr. Res. 68
(2015) 75–82.
[107] S. Tongaroonsri, S. Tangtermsirikul, Effect of mineral admixtures and curing
periods on shrinkage and cracking age under restrained condition, Constr.
Build. Mater. 23 (2) (2009) 1050–1056.
[108] A. Hawreen, J.A. Bogas, A.P.S. Dias, On the mechanical and shrinkage behavior
of cement mortars reinforced with carbon nanotubes, Constr. Build. Mater.
168 (2018) 459–470.
[109] G.A. Rao, Long-term drying shrinkage of mortar-influence of silica fume and
size of fine aggregate, Cem. Concr. Res. 31 (2001) 171–175.
[110] X. Hu, Z.-G. Shi, C. Shi, Z. Wu, B. Tong, Z. Ou, G. de Schutter, Drying shrinkage
and cracking resistance of concrete made with ternary cementitious
components, Constr. Build. Mater. 149 (2017) 406–415.
[111] T. Yang, H. Zhu, Z. Zhang, T. Yang, H. Zhu, Z. Zhang, T. Yang, H. Zhu, Z. Zhang,
Influence of fly ash on the pore structure and shrinkage characteristics of
metakaolin-based geopolymer pastes and mortars, Constr. Build. Mater. 153
(2017) 284–293.
[112] M.H. Zhang, C.T. Tam, M.P. Leow, Effect of water-to-cementitious materials
ratio and silica fume on the autogenous shrinkage of concrete, Cem. Concr.
Res. 33 (10) (2003) 1687–1694.
[113] P. Nath, P. Sarker, Effect of fly ash on the durability properties of high
strength concrete, Procedia Eng. 14 (3) (2011) 1149–1156.
[114] W. Zhang, Y. Hama, S.H. Na, Drying shrinkage and microstructure
characteristics of mortar incorporating ground granulated blast furnace
slag and shrinkage reducing admixture, Constr. Build. Mater. 93 (2015) 267–
277.