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FOR THE CONSTRUCTION INDUSTRY
ABSTRACT 01 | INTRODUCTION 01
CONCLUSIONS 07 | Authors 08
CEM III Cements in Cement Spray Plaster
Abstract
The global emission of carbon dioxide as green house gas, contributing to global warming, has increased much faster than
the forecast of the UN World Climate Council in 1996 had predicted. In 2007 the 25 member states of the European Union
have agreed to reduce the emission of green house gases until 2020 by 20% based on the year 1990. The German
government has an even more ambitious goal of 40% reduction in the same time frame.
The cement industry is one of the targets of this plan due to the high energy intensity of cement clinker production. 7%
of the global CO2 emissions are caused by the production of cement. One possibility to reduce the emission of CO2 is an
increased use of latent hydraulic components in cementitious products.In the past years cements with an increased content
of blast furnace slag and fly ash were not suitable for cement spray plaster as a result of reduced cement setting kinetics
and strength development.
Intensive application tests were done to compare various CEM I, CEM II and CEM III cements in a cement spray plaster
formulation. We evaluated in detail the performance characteristics and the physical properties of these plasters.
Specific hydroxyethyl methylcellulose grades (HEMC) were selected and compared in the different plaster products.
We could optimize the performance profiles of the cement spray plasters. The CEM III based plaster showed some
surprising performance advantages.
INTRODUCTION
According to EN 197-1 cements are segmented in the
following categories: CEM I, CEM II, CEM III, CEM IV and CEM
V. In our investigation we only focused on CEM I, II and III.
Portland cement with a clinker content of >95% is described
by the class CEM I. CEM II cements can be further grouped
depending on their clinker content into categories A (80 –
94%) and B (65 – 79%). They contain other puzzolanic
components like blast furnace slag, micro silica, fly ash
and ground lime stone. CEM III cements are even lower in
the clinker content and are also further split into subgroups:
A (35 – 64% clinker) and B (20 – 34% clinker). Table 1
summarizes the norm requirements for the composition
of the cement types used in this study.
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EN 197-1:2000 examples of cement types
Content (%)
Description
Portland-cement
clinker
Limestone
Blast-furnace slag
Gypsum, other
CEM I
Portland cement
95 – 100
–
–
0–5
CEM II/ B-LL1)
Portland limestone
cement
65 – 79
21 – 35
–
0–5
Blast furnace cement
35 – 64
–
36 – 65
0–5
Table 1: Cement types with different content of cement clinker
1)
LL total organic carbon toC < 0.20 M.%
The different cement qualities have some advantages and
disadvantages for the application. Portland cement CEM I has
always been marketed by the cement industry as a premium
product. The performance advantages are mainly fast strength
development and consistent quality. The cement market has
changed considerably over the past ten years. Secondary fuels
are widely used in the production of cement because they
offer recycling options for many products and help to reduce
production cost. They have a considerable impact on cement
quality which needs to be managed by the applicators. They
have to understand the impact of quality variations and use
intelligent ways to counterbalance the undesirable effects.
The major part of cement is used for ready-mix and precast
concrete applications where performance differences can
be well managed. The dry-mix mortar industry has different
requirements on the cement quality. But their influence on
the cement producers is limited.
In the past, CEM III cements had the disadvantage in spray
plaster applications of slow curing and strength development.
During summer temperatures, the spray plaster applied on
the wall will dry out fast, also caused by the low thickness/
surface ratio. The water evaporates faster than the cement
can hydrate. The plaster will have reduced strength and low
abrasion resistance. We have therefore selected a CEM III
cement in our study with comparable strength build up to
CEM I 42.5R.
Beside the retarded cement hydration kinetics, the
application properties of the formulated spray plaster are
key requirements. They are also strongly influenced by the
cement type used in the formulation. Our investigations have
demonstrated that these cements can have a positive impact
on the workability.
Characterization of Cement Binders
Compared to CEM I Portland cement CEM III/A cement
consists approximately of only 50% cement clinker. The
remaining 50% can be blast-furnace slag or other latent
hydraulic components. The theoretical reduction potential in
CO2 emission in comparison to CEM I is 40-50 %.
Vital for the successful use of CEM III/A in CSP are the
hydration time, the development of strength during the
first 3 days and excellent workability during the application.
In order to relate the performance of the formulated plasters
to the cement quality, it is required to have sufficient
knowledge about their particle size distribution, their detailed
compositions and their chemical-physical properties.
Verteilungssumme Q3 / %
CEM III/ A2)
Partikelgröße /μm
Verteilungsdichte q*(x)
Cement type
Partikelgröße /μm
Figure 1: Particle Size Distributions of different Cement types
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CEM I 42,5 r
CEM II/B-M
(S-LL) 42,5 r
test value
test value
EN 197-1
specific area
(Blaine)
cm 2 /g
3730
5020
–
water demand
%
28,9
30,9
–
min
130
140
> 60
min
180
190
< 720
N/mm2
32
31
> 20
N/mm2
61
59
42.5 – 62.5
setting time,
start
setting time,
finish
compressive
strength 2 days
compressive
strength 28 days
Table 2: Cement CEM I and CEM II chemical-physical Properties
compared to the required standards
Table 2 summarizes the specific surface area of CEM I and
CEM II of our investigation, their setting kinetics and their
strength development. They are compared to the EN 197-1
standards for such cements. The lower content of cement
clinker in CEM II is compensated by a higher Blaine area
resulting in almost identical strength properties after 2
and 28 days.
CEM III/A
CEM III/A
52,5 N
52,5 N
(Producer A) (Producer B)
test value
test value
EN 197-1
specific area
(Blaine)
2
cm /g
5180
6110
–
water demand
%
30,8
31,5
–
min
140
160
> 60
min
190
200
< 720
N/mm2
27,2
28,4
> 20
N/mm2
58
64
> 52,5
%
40
38
36 – 65
setting time,
start
setting time,
finish
compressive
strength 2 days
compressive
strength 28 days
blast furnace
slag
The two CEM III cements have a blast furnace slag content of
about 40%. The product of Producer B has a slightly higher
Blaine specific surface giving also slightly higher strength
properties.
In order to compare the water demand and the resulting
consistencies of the cement slurries, all cements were mixed
with varying water content to achieve a constant flow table
spread of 200 mm. CEM I 42.5 R has the coarsest granulometry
and subsequently the lowest water/cement ratio of 0.51.
CEM II/B-M 42.5 R and CEM III/A 52,5 N of Producer A have
very similar particle size distribution (see Figure 1) and their
water demand is also very close. The finest granulometry of
CEM III/A 52,5 N of Producer B results in the higher water/
cement ratio of 0.66.
consistency (mm)
Figure 1 shows the particle size distribution of various
cement qualities measured by laser diffraction measurement.
The curve illustrates that the 50% mean particle size of the
selected cement qualities varies from 5μm to 10μm. The
strength of the hydrated cement is mainly controlled through
its fineness. The following tables (Table 2 and 3) give an
overview of the detailed composition of the cement grades
used in this study.
Figure 2: Variation of Consistency of Cement Grades
The consistency increase after 5 and 10 minutes are for
all cements very different. CEM II shows a less pronounced
consistency increase compared to the pure Portland cement
CEM I. The consistency development of CEM III of producer
A is very comparable to CEM I and II. The difference in cement
slurry consistency after 5 and 10 minutes in the case of the
CEM III qualities, however, is significant. CEM III of producer
B only shows a flow table spread of 80 mm only 5 min after
mixing and stays then constant. One reason for this
phenomenon could be early and shortened setting as a
result of sub-optimized dosage of the sulfate carrier.
Table 3: Cement CEM III chemical-physical Properties and
the required standards
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cement
11 pbw
lime hydrate
3 pbw
limestone filler
15 pbw
limestone gravel 0,1/0,5mm
25 pbw
limestone gravel 0,5/1,0mm
35 pbw
quartz sand 0,1/0,6mm
10 pbw
air entraining agent
0,035 pbw
Perlite 0/2mm
230 l/Mt
Walocel® cellulose ether
0,095 pbw
The plasters were evaluated to understand the cement setting
kinetics using ultrasonic and heat flow methods. We also
looked at the strength development over a period of 4 weeks
at various temperatures. Finally the application performances
of the plaster formulations were compared.
Ultrasonic Measurement of Cement Setting Rates
We used the ultrasonic device IP8 developed by Prof.
Steinkamp to monitor the increase of sound velocity as a
function of cement setting with time.
The sound velocity in m/s after 3 days correlate with the
compressive strength measured after the same period of
time. The plaster formulation based on CEM I did not show
the fastest increase in sound velocity during the first 24 hours.
However, after this period the setting rate accelerated
significantly. After 3 days both the strength and the sound
velocity were highest. The other three cements performed
very comparable. The ultrasonic test method proved to be
a useful technique to monitor and compare the strength
development of plaster formulations.
Heat Flow Measurement of Cement Setting Rates
Cement setting is an exothermic reaction which can be easily
followed by isotherm heat flow curves. We have been using a
TAM AIR heat flow meter (TA Instruments) for our tests. The
plasters where mixed in the lab prior to testing.
Normalized Heat Flow [mW/g]
CSP Formulation – Cement Spray Plaster
We have been using the following formulation of a limestone/
cement plaster for our investigations:
time t[h]
Sound velocity [m/s]
Figure 4: heat Flow of CSP`s with Different Cements
time t[h]
Figure 3: ultrasonic Monitoring of Plaster Setting (3 days)
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Figure 4 shows the CSP heat flow curves of our cement
formulations during the first 45 hours after mixing. It is
interesting to note that both CEM III cements show fastest
setting during the first seven hours. CEM III of producer A
shows another peak after 18 hours, whereas CEM III of
producer B only indicates a shoulder after 20 hours.
The CEM I and CEM II based formulations have peaks at
17 hours, respectively at 15 hours. CEM II reacts faster than
CEM I. The reason for this is most likely based in its finer
granulometry.
Compressive Strengths of Cement Plasters
In the past there was the general understanding that CEM III
cements only give insufficient early strength after 3 to 7 days
although their final strength properties were comparable.
CEM III cements of our study did not show this deficiency.
Figure 5 gives an overview of the mortar strengths of the four
plaster formulations at 20ºC and 10ºC to illustrate the impact
of cold temperature curing as this is often the case in real
application during autumn and winter.
Application Data
The dry-mix plaster formulations were sprayed onto highly
absorbent brick walls using a PFT G4 spray plaster machine.
Some parts of the wall were made non-absorbent using a
primer to test the sag resistance of the plaster under more
stringent conditions. We evaluated both the spraying
performance and the workability during the first even-out.
The formulation based on CEM I 42.5 R was used as the
reference system. All performance criteria were set at 100%.
The other cement formulations were compared against this
standard and ratings above 100% indicated an improvement,
whereas rating of less then 100% showed inferior
performance.
Figure 5: Compressive Strengths of cement plasters
formulated with various cements at 20ºC and 10ºC
At 20ºC the strength of the mortars after 3 days were in the
range of 0.5 – 0.9 N/mm2. These plasters were prepared in the
lab and had lower fresh mortar densities as compared to the
mortars prepared in the spray plaster machine. This is
the reason why the strength data listen in Figure 3 are higher
(0.9 to 1.5 N/mm2). The mortar strength after 7 and 28 days
of these formulations follow about the same trend with one
exception. The plaster containing CEM III of producer B gives
much higher strength after 28 days.
The strength development at lower temperature is strongly
retarded. The strength of the prisms after three days stored at
10ºC is not measurable in any of the samples. After one week
the mortar prisms break at around 0.5 N/mm2. The long-term
strength after 28 days or more, however, is in the same range
as at 20ºC. CEM III of producer B showed different
performance and almost did not cure at 10ºC. We are further
investigating this phenomenon.
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Table 4: Application assessment with different cement qualities
In Table 4 performances relative to the reference are also
indicated using colors (green for improvement and red for
disadvantages).
The CEM II based plaster formulation had some problems
already during the spraying. The plaster was not uniformly
wetted, but it showed good sag resistance during spraying.
But once the plaster was evened out for the first time, the
sag resistance severely dropped, especially on the nonabsorbent substrate. The plaster was also sticky which
caused difficulties during the even-out working step.
The spraying pattern of the plaster formulated with
CEM III of producer A was the best of all formulations tested.
However, some dry agglomerates could also be observed,
which disappeared after the first even-out. The most obvious
benefit of this formulation was its ease of leveling and its
low stickiness.
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Not all CEM III cements perform the same which became
very obvious with the fourth formulation based on CEM III
of producer B. The spray performance was almost identical
to the reference formulations. But the plaster on the wall
showed strong post-thickening, which negatively impacted
the spreadability of the plaster. This behavior was already
described in Figure 2: Variation of Consistency of Cement
Grades where the time depending consistency of the cement
slurries where illustrated. CEM III of producer B showed the
most pronounced increase in consistency after only 5 min.
Table 5: Application assessment, comparison between different hEMC Walocel grades
Table 5 shows the performance profiles of cement spray
plaster formulations based on the same CEM III cement of
producer A, but using Walocel cellulose ethers of different
modification levels, further adjusting water demand and sag
resistance. The formulation using Walocel MKW 20000 PP 20
was used as the reference system. When increasing the
modification levels (PP 30 and PP 40) the water demand of the
plaster increases and so does the workability. The formulation
based on Walocel MKW 20000 PP 40 showed some post
thickening, but the overall performance was best.
CoNCLuSIoN
The use of CEM III cements, where parts of the clinker
are replaced by other puzzolanic components, in cement
spray plaster can contribute positively to the reduction of
CO2 emissions. In our technical investigations we could
demonstrate that special CEM III cements can be successfully
used in high performance construction applications. Some
of the critical performance requirements for cement spray
plasters can even be improved. CEM III based plasters can
have reduced stickiness, increased sag resistance and shear
stability.
CEM III based cement plasters are a good example
demonstrating that sustainability of construction material,
CO2 reduction and demanding application requirements are
no longer a conflict. Intelligent solutions for this kind
of conflicts are the prerequisite for successful product
innovation.
1
Locher F.W.: Zement - Grundlagen der Herstellung und Verwendung.
Düsseldorf: Verl. Bau und Technik. 2000
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AuthorS
Andreas Hecker, Robert Baumann, Jörn Breckwoldt, Karl-Heinz Schoppa, Björn Giesecke
The Dow Chemical Company
For more information please send your email to
dccinfo@dow.com
or consult our web site
www.dowcc.eu
840-01401-112010