Green concrete using 100% fly ash based hydraulic binder
Raj Patel1, Fred Kinney2, and Glenn Schumacher3
1
Director of Engineering Research, CeraTech Inc, 3501 Brehms lane, Suite D, Baltimore, MD.
21213, email:raj.patel@ceratechinc.com
2
Vice President of R&D, CeraTech Inc, 3501 Brehms lane, Suite D, Baltimore, MD. 21213,
email:fred.kinney@ceratechinc.com
3
Sr. Scientist, CeraTech Inc, 3501 Brehms lane, Suite D, Baltimore, MD. 21213,
email:glenn.schumacher@ceratechinc.com
Abstract
Fly ash based hydraulic binder (FAHB) is comprised of 90 to 95% fly ash and 5 to 10%
proprietary Activators; Activator 1 (A1) and Activator 2 (A2). FAHB, a zero carbon footprint
binder can be used for making Green Concrete (eGC) with similar or better mechanical and
durability properties than Portland cement concrete (PCC). This paper presents the preliminary
data for making eGC using FAHB as the binding material. A blend of liquid activators (A1 and
A2) is used to activate fly ash and control set time of FAHB. The set time of eGC can be
controlled in a range of 30 minutes to 15 hours by adjusting the blend of two activators; A1 and
A2. Unlike geopolymer cement based concrete, eGC using FAHB does not need elevated
temperature for curing or highly caustic and health hazardous activators. The activators used in
the FAHB are non caustic. This concrete can be placed and air cured at 10C (50F) to 45C
(114F) without any special consideration for mix proportioning, making, placing, and curing.
This paper presents the mechanical properties of eGC such as compressive strength, flexural
strength, splitting tensile, and modulus of elasticity for various binder levels from 297 kg/m3 (500
lbs/y3) to 534 kg/m3 ( 900 lbs/y3). The compressive strength vs. Water-to-Binder ratio (W/B) is
developed to facilitate eGC mix design with FAHB in future. One PCC mix (Binder content 445
kg/m3 (750 lbs/y3)) as a control mix and nine eGC mixes with FAHB (Binder content 297 kg/m3
(500 lbs/y3) to 534 kg/m3 (900 lbs/y3) are presented in this paper. The relation between
compressive strength and other mechanical properties such as flexural strength, MOE and split
tensile strength are established and compared with various Portland cement concrete models of
similar nature. The result shows that the eGC using 100% FAHB has equal or better plastic and
mechanical properties than Portland cement concrete and this new green binder technology will
open a practical avenue for truly green and sustainable concrete.
Key words: Green cement, Green concrete, Sustainable concrete, fly ash, eGC
2012 International Concrete Sustainability Conference 1 ©National Ready Mixed Concrete Association Introduction
Concrete has played significant role in the key development of the world for last one and half
century. Concrete became widely popular material due to its versatility, excellent resistance to
water, low cost, and availability of ingredients across the world (Mehta 2006). Global warming
is a key challenge for our planet and reducing the amount of energy intensive building materials
such as Portland cement in the concrete is desirable as the Portland cement industry is one of the
largest producers of carbon dioxide (Penttala 1997). The production of one ton of Portland
clinker produces approximately one ton of carbon dioxide. The use of fly ash from the
combustion of coal as a partially replacement of Portland cement can offset the emission of
green house gas (Malhotra 2006). Extensive research on the replacement of Portland cement by
fly ash has been conducted worldwide. In the last fifteen years, many researchers investigated the
use of High Volume Fly Ash (HVFA) in concrete to decrease the level of green house gases and
to promote sustainability in concrete construction (Mehta 2009). The basic drawback to use of
HVFA (fly ash replacement exceeding 40%) in concrete is the prolonged time of set and very
slow strength development. At lower temperature, this drawback becomes more pronounced
(Dodson 1981). The same drawback may be eliminated by effectively using certain chemical
admixtures. This approach is more expensive and requires highly engineered mix designing skill.
As a result, the use of fly ash is limited to between fifteen percents to thirty percents.
In past years, geopolymer cement was proposed for making green and sustainable concrete.
Geopolymer cements are pozzolanic materials, essentially fly ash, that are activated with a
second component(s), often which are very hazardous (high pH or caustic). Typically, concrete
made with geopolymer cement also require elevated curing temperatures (60°C to 150°C) for
initial few days (Davidovits 1988, Davidovits 1991). As a result, geopolymer cement concrete
has limited acceptance in the construction industry.
This paper presents 100% fly ash based binder system (FAHB) for green concrete (eGC)
production. The FAHB requires two powders (ASTM class C fly ash and ASTM class F fly
ash), which are activated at the ready-mix producers’ facility with two non-caustic activator
liquids (A1 and A2). This provides a flexibility to tailor the performance to suit the application
needs. Nine non-air entrained eGC mixes with FAHB as binder in a range of 297 kg/m3 (500
lbs/y3) to 534 kg/m3 (900 lbs/y3) are presented in this paper along with one non-air entrained
PCC mix with Portland cement content 445 kg/m3 (750 lbs/y3). The results of mechanical
properties for all mixes such as compressive strength, flexural strength, splitting tensile strength,
modulus of elasticity are presented. The relation between Water to Binder ratio (W/B) and
compressive strength is established for eGC mixes and compared to Abram’s Portland cement
W/C ratio theory. The eGC samples are air cured at 23 ±2oC (72 ±3oF) while PCC samples are
wet cured per ASTM C 192 guidelines until the test.
2012 International Concrete Sustainability Conference 2 ©National Ready Mixed Concrete Association Materials Properties
Table 1: Chemical compositions fly ash and physical properties of fly ash and Activators.
Fly ash used in eGC ASTM Specifications ASTM C ASTM C 618 class 618 Class F C Class C Fly ash Class F Fly ash SiO2 (silicon dioxide), % 32.82 52.98 Al2O3 (aluminum oxide), % 18.28 28.96 Fe2O3 (iron oxide), % 5.54 8.24 SiO2 + Al2O3 + Fe2O3, % CaO (calcium oxide), % MgO (magnesium oxide), % 56.6 29.09 5.5 90.18 1.46 0.91 50 Min 70 Min SO3 (sulfur trioxide), % 2.26 0.03 5.0 Max 5.0 Max Na2O (sodium oxide) 1.95 0.14 K2O (potassium oxide), % Moisture content, % Loss On Ignition (LOI), % Physical analysis 0.32 0.06 0.39 2.57 0.05 2.54 3.0 Max 6.0 Max 3.0 Max 6.0 Max Fineness, amount retained on #325 sieve, % Variation, points from average Specific gravity Variation from Average, % 16.6 1.74 2.73 0.04 18.45 34 Max 34 Max Strength activity index with Portland cement at 7 days, % of Portland cement control at 28 days, % of Portland cement control Water requirement % of cement control Soundness, autoclave expansion, % Properties of Activators 94 96 93 0.06 78.8 80.8 97.1 0.01 75 Min 75 Min 105 Max 0.8 Max 75 Min 75 Min 105 Max 0.8 Max Specific gravity 1.355 1.328 pH 8.4 8.12 Chemical analysis Activator 1 Activator 2 2.31 FAHB consists of ASTM class C fly ash, ASTM Class F fly ash, and two activators (A1 and
A2). ASTM C 618 class C ash with a CaO content of 29.09%, SiO2 content of 32.82%, and
Al2O3 content of 18.28% was used. ASTM Class F fly ash with CaO content 1.46%, SiO2
2012 International Concrete Sustainability Conference 3 ©National Ready Mixed Concrete Association content 52.98%, and Al2O3 content of 28.96% was used. Physical and chemical properties of
class C and class F fly ashes are presented in Table 1.
The activators used in FAHB are intellectual property hence chemical composition is not
disclosed. A1 has specific gravity of 1.355 and pH of 8.4, while A2 has specific gravity of 1.328
and pH of 8.12. Both the activators are made out of green renewable materials. The property of
activators is presented in Table 1.
ASTM # 57 crushed limestone and ASTM C33 natural sand are used as coarse and fine
aggregate respectively. The coarse aggregate have specific gravity of 2.78 and moisture
absorption of 0.92%, while the fine aggregate have specific gravity of 2.74, moisture absorption
of 1.92%, and fineness modulus of 2.61. The physical test results and grading of aggregates are
presented in Table 2. ASTM type I/II Portland cement with specific gravity of 3.15 was used in
one control mix
Table 2: Physical test results and grading of Aggregates.
Sieve size 25 mm ( 1 inch) 19 mm (3/4 inch) 12.5 mm (1/2 inch) 9.5 mm (3/8 inch) 4.75 mm (No 4) 2.36 mm (No 8) Coarse Aggregate, % Passing 99 78 38 23 5 3 Fineness Modulus NA Fine aggregate , % Passing 100 98 82 66 55 29 9 4.5 2.61 1571 2.78 1650 2.74 Dry loose bulk density, Kg/m3 Specific gravity‐ SSD Moisture absorption, % Sieve size 9.5 mm (3/8 inch) 4.75 mm (No 4) 2.36 mm (No 8) 1.18 mm (No 16) 600 micron (No 30) 300 micron (No 50) 150 micron (No 100) 75 micron (No 200) 0.92 1.92 .
Mixture Proportion and tests of eGC
Mix proportion of one PCC mix (control mix) and nine eGC mixes were designed in accordance
with ACI absolute volume mix design method are presented in Table 3. All the concrete mixes
presented are non-air entrained mixes. PCC mix (control mix) was designed with 445 kg/m3 (750
lbs/y3) cement level and no chemical or mineral admixtures were used for the PCC mix. The
binder levels of nine eGC mixes were varied from 297 kg/m3 (500 lbs/y3) to 534 kg/m3 (900
2012 International Concrete Sustainability Conference 4 ©National Ready Mixed Concrete Association lbs/y3). The binder of eGC (FAHB) is sum of class C fly ash (82.16%), class F fly ash (13.83%)
and solid part of two activators (4.01%). The total water presented in Table 3 for nine eGC mixes
is sum of added water to the concrete and liquid portion of the activators. All the concrete mixes
were designed for 75 ±10 mm slump.
All the concrete mixes were prepared in a rotary laboratory concrete mixer. PCC (control mix)
samples made and cure per ASTM C 192 guidelines. After casting, PCC samples were covered
with plastic sheets and left at room temperature for 24 hours. They were then de-molded and
immersed in the water tank saturated with calcium hydroxide until required for the testing.
The eGC mixes were prepared in a same rotary laboratory mixer. First, coarse aggregate and fine
aggregate added to the mixer with approximately half the design water. The mixer was run for
half minutes and both the liquid activator added to the mixer. Second, blend of class C fly ash
and class F fly ash was added to mixer followed by the rest of mixing water. The eGC mixes
were mix for 7 minutes. After casting, these samples were kept at room temperature without
covering with plastic sheet. They were then labeled and air cured at 23 ±2oC (72 ±3oF) until
required for the testing.
Table 3: Mix proportioning of Portland cement concrete (PCC) and Green concrete (eGC) mixes
Liquid Activators Solid Class of Total C liquid fly Class Portland acti ash A 2, Mix cement, Ash, F ash, A 1, no Kg/m3 Kg/m3 kg/m3 kg/m3 kg/m3 kg/m3 kg/m3 1 445 0 0 0 0 0 0 2 0 243.7 41 14.88 3.22 11.9 284.7 3 0 268.1 45.1 16.36 3.54 13.1 313.2 4 0 292.6 49.2 17.8 3.81 14.2 341.8 5 0 316.7 53.3 19.4 4.2 15.6 370 6 0 341.2 57.4 20.8 4.5 16.7 398.6 7 0 365.6 61.5 22.3 4.8 17.9 427.1 8 0 389.8 65.6 23.8 5.2 19.2 455.4 9 0 414.3 69.7 25.3 5.5 20.3 484 10 0 438.7 73.8 26.8 5.8 21.5 512.5 Note: 1 kg/m3 = 1.6855 lbs/y3
Aggregate Total Total Coarse Fine Binder Water, Agg, Agg, kg/m3 kg/m3 kg/m3 kg/m3 445 193 1170 578 296.6 118.6 1170 851 326.3 113.8 1170 835 356 112.3 1170 809 385.6 102 1170 806 415.3 102.3 1170 776 445 99.1 1170 755 474.6 99.5 1170 725 504.3 99.8 1170 695 534 102.5 1170 658 The slump test on all freshly mixed concrete mixes was conducted in accordance with ASTM C
143 procedure. Thermal set time was determined with Grace Adiacal, a semi-adiabatic
calorimeter. The final set time was defined with “fraction” method. This method defines final set
time at half of the ΔT value (Solidus 2006, Wang 2007). For example, in a Temperature-time
curve of Adiacal chart, if initial temperature is 20oC and temperature peaks at 40oC, the final set
2012 International Concrete Sustainability Conference 5 ©National Ready Mixed Concrete Association time considered at temperature 30oC (Wang 2007). One 75 mm x 150 mm cylinder was prepared
for each mix and immediately placed in a Grace Adiacal for determination of final set of each
concrete mix.
The compressive strength of concrete was determined as per ASTM C 39 using unbounded caps
as per ASTM C 1231 guidelines. The compressive strength was measured at 1, 3, 7, and 28 days.
The flexural strength was measures at 1, 7, and 28 days as per ASTM C 78 (using simple beam
with third-point loading). The spitting tensile strength of cylindrical concrete specimens was
measured at 1, 7, and 28 days as per ASTM C 496. The modulus of elasticity (MOE) was
measured at 1, 7, and 28 days per ASTM C 469.
Results and Discussions
Test results of slump, time of set, compressive strength, and flexural strength are presented in
Table 4. While test results of splitting tensile and modulus of elasticity (MOE) are presented in
Table 5.
Table 4: Test results for fresh properties, compressive, and flexural strength
Mix no 1 2 3 4 5 6 7 8 9 10 slump, mm 65 75 75 75 70 70 75 75 75 75 Final set, Min 510 450 465 480 520 600 610 615 600 600 Compressive Strength, MPa W/B 0.43 0.4 0.35 0.32 0.26 0.25 0.22 0.21 0.2 0.19 1 day 4.6 2.32 3 4.6 6.6 9.2 9.8 15.9 16.9 18.6 3 day 19.3 11.52 14.6 19.2 30.2 33.9 34.7 39.3 40.2 42.8 7 day 30.5 15.32 20.8 26.4 34.5 40.5 42.8 48.2 48.8 50 28 day 40.3 21.4 26.2 35 42.1 47.7 51.3 53.6 55.6 57.9 Flexural strength, MPa 1 day NA 0.75 0.9 1.2 1.5 1.8 2 2.4 2.6 2.7 7 day 4.4 2.2 3.1 3.2 3.9 4 4.5 4.7 4.6 4.9 28 day 5.5 2.6 3 3.8 4.2 4.2 5 5 5.3 5.4 Note: 1 MPa = 145 Psi
Water demand of PCC was 193 kg/m3 for 75 ±10 mm slump. While eGC water demand ranges
from 100 to 118 kg/m3 for similar slump (Table 3). The lower water demand of eGC is due to
use of 100% fly ash as binder and one of the activator in FAHB is providing plasticizing effect.
It is well established in literature that for the same workability, as amount of fly ash increases in
PCC mixes, water demand decreases (Naik 1990).
2012 International Concrete Sustainability Conference 6 ©National Ready Mixed Concrete Association Table 5: Test results on splitting tensile strength and MOE
Mix no 1 2 3 4 5 6 7 8 9 10 W/B 0.43 0.4 0.35 0.32 0.26 0.25 0.22 0.21 0.2 0.19 Splitting Tensile strength, MPa 1 day 7 day 28 day 0.8 3 4.7 0.8 2.1 3 0.9 2.6 3.5 0.9 3 4.3 1.2 3 4.6 1.4 3.3 4.6 1.5 3.8 4.8 2 3.9 5 2.4 4 5.3 2.6 4.3 5.3 Modulus of Elasticity (MOE), MPa 1 day 7 day 28 day NA 26827 30966 14710 23240 28482 15200 25720 30160 16690 28724 33172 17050 28814 33210 17210 30240 33810 17100 30140 33724 18222 31356 33580 19556 32242 35150 20552 32070 34210 The design total activator (A1 + A2) liquid weight of eGC is approximately 6.1% of the total
binder by weight. The eGC time of set can be easily controlled at a concrete mixing facility by
just changing blend of A1 and A2. The A1/A2 blend was kept 82%/18% in presented all eGC
mixes. In real field applications, the time of set of concrete is affected by ambient weather
conditions such as temperature, humidity, and direct sunlight. The time of set of concrete may be
affected with minor variability of ash reactivity as well. For higher time of set in summer season,
the blend of activator can be changed to 85%/15%, 90%/10%, 95%/5% etc. While in winter cold
season, blend can be change for right window of time of set of eGC to 80%/20%, 75%/25%,
70%/30% etc. PCC needs additional retarder or accelerator admixtures at concrete mixing
facilities to accommodate ambient weather conditions at field. While eGC mixes need simple
change in the blends of two activators at concrete mixing facility without any additional cost.
Strength Curves of eGC
The compressive strength development of eGC mixes at 1, 3, 7, and 28 days are illustrated in Fig
1. The lower binder content mixes, 297 kg/m3 (500 lbs/y3), 326 kg/m3 (550 lbs/y3), and 356
kg/m3 (600 lb/y3) provided 28-day compressive strength of 21 MPa, 26 MPa, and 35 MPa
respectively and can be used for general purpose concrete. The eGC mixes with binder contents
415 kg/m3 (700 lbs/y3) to 534 kg/m3 (900 lbs/y3) exhibited high early compressive strength at 1
day (9 MPa to 19 MPa) and 3 days (34 MPa to 43 MPa). These concrete mixes can be used for
quick-returns-to service applications.
Under laboratory ASTM wet curing condition, typical PCC develops 3-day compressive strength
about 45 to 50% of 28-day compressive strength and 7-day compressive strength often estimated
to be about 75% of 28-day compressive strength (Lange 1994, Kosmatka 2002). While eGC has
2012 International Concrete Sustainability Conference 7 ©National Ready Mixed Concrete Association developed high early strength at air cured conditions. The 1-day strength of eGC mixes found 11
to 32% of 28-day strength. The 3-day and 7-day strength found 53 to 73% and 71 to 89% of 28day strength respectively.
60
3
900 lbs/y
55
3
850 lbs/y
50
3
800 lbs/y
3
750 lbs/y
Compressive Strength, MPa
45
3
700 lbs/y
40
35
3
650 lbs/y
30
3
600 lbs/y
297 kg/m3
326 kg/m3
356 kg/m3
386 kg/m3
415 kg/m3
445 kg/m3
475 kg/m3
504 kg/m3
534 kg/m3
25
3
550 lbs/y
20
15
3
500 lbs/y
10
5
0
1
0
3
7
14
21
28
Age, days
Fig. 1: eGC strength development over a time for various binder levels
Comparison of Portland cement concrete and ekkomaxx green concrete
Fig 2 demonstrates the compressive strength development of PCC mix (mix 1) and eGC mix
(mix 7). These mixes had same binder contents of 445 kg/m3 (750 lbs/y3) and same workability
of 75 mm (3 inches) slump. The compressive strength of eGC mix with air cure condition is
much higher at all ages than PCC mix at ASTM wet cure and Air cure conditions.
eGC W/B theory
A relationship between PCC strength and water-to-cement ratio was discovered by Duff Abrams
in 1918 as follow (Abrams 1918):
f
A
B /
2012 International Concrete Sustainability Conference (1)
8 ©National Ready Mixed Concrete Association Where,
f
w/c
A and B
= Strength of concrete
= Water-to-cement ratio
= Empirical parameters
The empirical parameters, “A” and “B” are function of units, type of cement, aggregates, and
admixtures used, method of making, curing, and testing of specimen, and age of testing. This law
helps understanding the inverse exponential relation between the strength and w/c. Every
concrete may has different pair of “A” and “B” value (Popovics 1967).
Fig 3 illustrates the Water-to-Binder ratio (W/B) to compressive strength curves at 3-day, 7-day,
and 28-day for eGC mixes. This chart follows the patterns of Abrams’ law for PCC. The
equations derived from the W/B and strength charts of eGC for 3-day, 7-day, and 28-day
strength are as follow:
.
f 3d
.
W/B
(2)
Where,
f 3d
= Compressive strength of eGC at 3-day
W/B
= Water-to-Binder ratio
Abrams’ law empirical parameter “A” = 152.13 and “B” = e 6.476
f 7d
.
.
W/B
(3)
Where,
f 7d
= Compressive strength of eGC at 7-day
W/B
= Water-to-Binder ratio
Abrams’ law empirical parameter “A” = 152.13 and “B” = e 5.686
f 28d
.
.
W/B
(4)
Where,
f 28d
= Compressive strength of eGC at 28-day
W/B
= Water-to-Binder ratio
Abrams’ law empirical parameter “A” = 146.95 and “B” = e 4.76
2012 International Concrete Sustainability Conference 9 ©National Ready Mixed Concrete Association 60
All Concretes with 445
3
kg/m binder and similar
workability
50
Compressive strength, MPa
eGC (Air cure)
40
PCC (ASTM wet
cure)
30
PCC (Air cure)
20
PCC (ASTM wet cure)
PCC (Air cure)
10
eGC (Air cure)
0
0
7
14
21
28
Age, days
Fig 2: Comparison of Portland cement concrete (PCC) and Green concrete (eGC)
60
7 day
28 days
3 days
Expon. (7 day )
Expon. (28 days)
Expon. (3 days)
55
50
Compressive strength, MPa
45
40
35
30
4.76W/B
f 28d = 146.95/e
2
R = 0.9828
25
6.476W/B
f 3d = 152.13/e
2
R = 0.9839
20
5.686W/B
f 7d = 154.45/e
2
R = 0.9887
15
10
0.15
0.17
0.19
0.21
0.23
0.25
0.27
0.29
0.31
0.33
0.35
0.37
0.39
0.41
0.43
Water to Binder ratio (W/B)
Fig 3: eGC W/B vs. Compressive strength
2012 International Concrete Sustainability Conference 10 ©National Ready Mixed Concrete Association The relation between the flexural strength and compressive strength of eGC
The flexural strength is used for the design of various concrete pavements and other slabs on the
ground. Compressive strength is relatively easier to measure than the flexural strength and often
used as an index of flexural strength by structural engineers (Mehta 2006). Wood (1982)
established the relation between flexural strength and compressive strength of PCC samples ages
from 1-day to 5-years. The flexural strength of normal concrete can be estimated as 0.6 to 0.8
times the square root of compressive strength in MPa ( Wood 1992, Kosmatka 2002).
The relation between flexural strength and compressive strength of all eGC mixes is indicated in
Fig 4. Except for few outliers, most of the results fall in between 0.6 to 0.8 times the square root
of compressive strength in MPa.
7
Lower Flex
Higher flex
eGC
Power (Higher flex)
Power (Lower Flex)
6.5
6
Flextural strength, MPa
5.5
FS=0.8x sq root
of comp
Strength
5
4.5
4
3.5
3
FS = 0.6x sq
root of Comp
Strength
2.5
2
1.5
1
5
10
15
20
25
30
35
40
45
50
55
60
65
Compressive strength, MPa
Fig 4: Relation between flexural strength and compressive strength of eGC mixes
The Relation between MOE and Compressive strength of eGC
Many researchers have established relation between MOE and compressive strength of PCC.
Carrasquillo et. al (1981) and ACI committee 363 (1984) suggested following relation.
Ec = 6.9 + 3.32
2012 International Concrete Sustainability Conference (5)
11 ©National Ready Mixed Concrete Association Baalbaki (1991) proposed simple relationship
EC = K0 + 0.2 f’c
Where,
EC
f’c
K0
(6)
= MOE in GPa
= Compressive strength in MPa
= Factor based on type of aggregate (19 for granite and 22 for limestone)
Based on the results presented in this paper, the following relation is established for MOE and
compressive strength of eGC
EC (eGC) = 26.34 + 0.15 f’c(eGC)
Where,
Ec (eGC)
f’(eGC)
(7)
=MOE of eGC at 28-day in GPa
=Compressive strength of eGC at 28-day in MPa
All the eGC mixes were prepared with limestone coarse aggregate hence eGC MOE and
compressive strength relation equation is closed to the Baalbaki (1991) proposed equation for
PCC with limestone aggregate.
The relation between Splitting Tensile strength and Compressive strength of eGC
Concrete structures are designed to resist the compressive stresses but not the tensile stresses.
Usually steel re-bars in the concrete are accommodate the structural tensile stresses developed in
the concrete elements. However, tensile stresses can not be ignored altogether in the concrete as
tensile failure in concrete can be caused by shrinkage in restrained conditions and may result in
cracking leading to failure in concrete (Mehta 2006). As compressive strength of concrete is
relatively easy to measure compared to splitting tensile strength, many researchers developed a
simple relationship models for PCC as follow:
Carrasquillo (1981) suggested relationship for PCC strength ranging 21 to 81 MPa
fsp
= 0.54 f’c0.5
(8)
ACI Committee 363 (1984) suggested relationship for PCC strength ranging 21 to 83 MPa
2012 International Concrete Sustainability Conference 12 ©National Ready Mixed Concrete Association fsp
= 0.59 f’c0.55
(9)
Ahmad (1985) suggested relationship for PCC strength less than 84 MPa
fsp
= 0.462 f’c0.55
(10)
Burg (1992) suggested following equation for moist cured PCC strength ranging from 85 to 130
MPa
fsp
= 0.61 f’c0.5
(11)
Based on the splitting tensile strength and compressive strength results presented in Table 1 and
Table 2, two equations developed for eGC for predicting splitting tensile strength from the
compressive strength of the eGC
fsp(eGC)
= 0.57 f’c(eGC) 0.55
(12)
fsp(eGC)
= 0.69 f’c(eGC) 0.5
(13)
Where,
fsp
f’c
fsp (eGC)
f’c (eGC)
= Splitting tensile strength of PCC
= Compressive strength of concrete
= Splitting tensile strength of eGC
= Compressive strength of eGC
The splitting tensile strength and compressive strength relation developed for eGC (equation 12
and 13) are very close to the existing splitting tensile and compressive strength models
developed by various researchers for PCC (equation 8 to 11).
Conclusion
This study of eGC with 100% FAHB showed promising results and may open new doors for
green and sustainable concrete. The following conclusions are drawn from the study made with
eGC mixes for various binder levels.
1. Unlike Geopolymer cement concrete, eGC concrete does not need elevated temperature for
curing and high caustic health hazardous activators.
2. Unlike PCC, eGC does not require wet curing.
3.. eGC follows Abrams’ law of W/C and W/C to compressive strength chart developed in this
study (Fig 3) can be used for mix design of the eGC mixes.
2012 International Concrete Sustainability Conference 13 ©National Ready Mixed Concrete Association 4. The time of set of eGC can be easily controlled by simply adjusting the blend of A1 and A2 at
concrete mixing facility. No need to use any additional chemical admixture for retardation and
acceleration of time of set due to ambient weather conditions in the field.
5. For a given binder content and given workability, eGC exhibited higher compressive strength
than PCC mix at all ages.
6. The correlation between compressive strength and other mechanical properties such as MOE,
flexural strength, and splitting tensile strength of eGC are similar like respective correlation
models of PCC. Like PCC, flexural strength, MOE, and splitting tensile strength of eGC can be
easily predicted from the simple compressive strength results using equations presented in this
paper.
References
Abrams, D. A., (1918), “Design of Concrete Mixtures”, Bulletin No 1, Structural Materials
Research Laboratory, Lewis Institute, Chicago, Dec 1918, PP. 20
ACI Committee 363, (1984). “State –of-the-art report on high-strength concrete, ACI Journal,
Proceeding 81(4), July-August, pp. 364-411
Ahmad, S.H. and Shah, S.P., (1985). “Structural properties of high strength concrete and its
implications for precast pre-stressed concrete”, PCI Journal, 30(6), November-December 1985,
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