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The 16th International Congress on the Chemistry of Cement 2023 (ICCC2023)
“Further Reduction of CO2 -Emissions and Circularity in the Cement and Concrete Industry”
September 18–22, 2023, Bangkok, Thailand
Variation of Fluidity of Calcined Clay Limestone Cements by Power
Ultrasound and Gypsum Addition
C. Rößler1, J. Kocis2, M. Heinemann1, F.Kleiner1, T. Sowoidnich1 and H.-M. Ludwig1
1 Bauhaus-University, Weimar, Germany
Email: christiane.roessler@uni-weimar.de, melanie.heinemann@uni-weimar.de,
thomas.sowoidnich@uni-weimar.de horst-michael.ludwig@uni-weimar.de
2 Friedrich-Schiller-University, Jena, Germany
Email: jackson.robert.kocis@uni-jena.de
ABSTRACT
The substitution of Portland cement clinker with a combination of limestone, calcined clays and set
regulator (calcium sulphates) is a promising way to reduce CO2 emissions of concrete. These cements are
described as Limestone Calcined Clay Cement (LC3, https://lc3.ch/). Calcined clays are known to have a
high specific surface area, which results in an increased water demand and thus reduced workability of
mortars and concretes made from them. In practice, the reduced workability, among other things, means
that these cements are rarely used. The advantage of calcined clays is their pozzolanic reactivity, so they
contribute to hydration and thus to strength development. Previous work has shown that the amount of set
regulator has significant effects on workability and strength development. For Portland cement, it is known
that a brief exposure to power ultrasound during the mixing process improves workability and accelerates
setting.
Here we show how power ultrasound affects the fluidity of LC3 cements. This is compared with the effect
of gypsum on the cement fluidity by measuring the slump of cement suspensions. The dispersing effect of
ultrasound in cements is imaged in the scanning electron microscope (SEM) using high pressure frozen
samples, that are sectioned using a focused ion beam (FIB). This allows to visualize agglomeration and
deagglomeration of sub-micron scaled particles in a close-to native state. Result show that PUS strongly
de-agglomerates LC3 cements leading to a significantly increased specific surface area. Furthermore, the
very early hydration (≤ 5 h) of cements is monitored by in-situ X-ray diffraction. The effects of sonication
on hydration and particle dispersion on fluidity of cements pastes are discussed.
KEYWORDS: calcined clay cements, fluidity, power-ultrasound, cryo-FIB-SEM
1. Introduction
It is no surprise that climate change has influenced the course of scientific research towards the development
of low(er)-carbon solutions for sources of anthropologically generated carbon emissions.
Born of this realization, researchers from Cuba, India, and Switzerland began development in the late
2000’s of a low-clinker cement not reliant on industrial waste. This research would eventually result in
what are known as Limestone Calcined Clay Cements, or LC3 for short (https://lc3.ch/). LC3s function by
replacing 50% of the clinker with a mixture of hydraulically active calcined clay (30%, usually metakaolin),
ground limestone (15%), and gypsum (5%) while obtaining similar engineering performances as Ordinary
Portland cement (Sharma et al. 2021).
These cements are made from globally abundant materials (clays, limestones) and can, in comparison to
Ordinary Portland cement (OPC), reduce emissions associated with production by up to 40% while
maintaining comparable long-term strength, costs, while sometimes even exceeding the lifespans of OPCs,
depending on the application (Scrivener et al. 2022, Scrivener et al. 2019, Pillai et al. 2019, Nguyen et al.
2020). These benefits are however checked by the generally poorer, and unpredictable rheology LC3
concretes exhibit (Tregger et al. 2010, Mousavi et al. 2021). Workability is amongst the most crucial factors
to consider when laying, casting, or pouring cement products and is naturally of particular importance to
the construction sector who steadfastly rely on uniform and predictable rheological outcomes from their
cements.
The application of Power Ultrasound (PUS) has been shown in previous studies to improve the rheological
behaviour, increase early strength gain, and accelerate setting time in OPC mortars and concretes (Peters
2016, Remus et al. 2018).
In preliminary tests PUS was shown however to greatly worsen the rheology in pure, metakaolin based
LC3s. The present work is therefore targeted on trying to understand the origin of the loss in workability
experienced by LC3s when given PUS treatment. In addition, it will be evaluated whether to what extent
additions of gypsum might stymy this process or whether it can be used towards a more predictable
rheological outcome.
2. Materials and Methods
2.1 LC3 cement
The LC3 Reference (Ref) is used as a bulk standard for the Deutsche Forschungsgesellschaft (DFG) funded
project “Opus Fluidum Futurum” (https://www.spp2005.de/), which seeks to build a foundation for
rheology-based design of cements as well as the development of sustainable construction materials. The
Ref LC3’s preparation was done by project partner Heidelberg Materials. The LC3 Ref contains 52.0 wt.-
% CEM I, 30.0 wt.-% calcined clay, 15.6 wt.-% limestone and 5.0 wt.-% of set regulator (C$ = anhydrite
+ gypsum + hemihydrate). Samples LC3 Ref +C$ and ++C$ contained 5.7 respectively 6.7 wt.-% C$.
Further details on LC3 Ref properties can be found elsewhere (Pott et al. 2023).
The uncalcined clay contained 5.6 wt.-% calcite, 18.6 wt.-% quartz, 7.5 wt.-% muscovite, 31.9 wt.-% illite,
32.0 wt.-% kaolinite and 4.4 wt.-% montmorillonite. After calcination the amorphous content of the
calcined clay was approximately 45 wt.-%.
2.2 Slump test and Setting time
The production of mortars (w/c 0.5) tested for their slump bases itself on DIN 196-1 but deviates from the
norm in several ways to accommodate the extra step of applying PUS to the cement pastes while
maintaining the highest degree of comparability. The measurement of slump itself follows DIN EN 1045-
3. The slump of each mortar, with and without the addition of PUS, was measured 20 minutes after the
initial addition of water. The determination of setting time was carried out using an automatic Vicat device
(RatioTEC) following DIN 196-3. Measurements were made every 10 minutes over the course of 15 hours.
2.4 Power Ultrasound
Sonication proceeded using an ultrasound processor and generator (UIP1000hd, Hielscher) connected to an
amplifier (Booster B2-2.2, Hielscher) and Sonotrode (BS2d34, Hielscher). The maximum amplitude was
set at 42.4 μm for all experiments. To ensure all treated sample received the same amount of energy, a
voltmeter (Energy-Check 3000, Voltcraft) was first used to determine the amount of energy delivered to
samples.
2.5 XRD and SEM
In-situ XRD measurements were performed (D8 diffractometer, energy-dispersive Sol-X detector Siemens)
using Cu radiation at 40 kV and 30 mA. The scanning was set at a step width of 0.015° 2θ over an angular
range from 8° to 56° 2θ with 19.2 s counting time per step. The samples were sealed with a Kapton foil and
placed on a Peltier-cooled sample holder to maintain a stable reaction temperature of 25°C. After mixing
with water the sample was immediately placed and sealed on the XRD sample holder. The first XRD scan
was taken approximately 5 min after water addition and following after every hour.
Cryo-SEM on 20 min hydrated cement suspensions was carried out using a high-pressure freezing (HPM
100, Leica) procedure as described elsewhere (Holzer et al. 2007). For obtaining a section and recording of
backscattered electron images (BSE) a high-resolution scanning electron microscope equipped with a
focused ion beam (SEM-FIB, Helios G4 UX, ThermofisherScientific) was used.
3. Results
Results in Figure 1 show that PUS worsened workability
across all C$ levels. Important to note as well, is that
additional C$ did only improve the slump for the sonicated
sample. Interestingly the error bars in the sonicated sample
are reduced compared to the non-sonicated LC3 Ref.
The second effect of sonication is an acceleration of setting
of cement pastes as shown by results in Table 1. These
findings furthermore reveal that additional C$ has a minor
influence on this acceleration effect.
The phase formation during early (≤ 5 h) hydration of the
sonicated and non-sonicated LC3 samples were
investigated by in-situ XRD (Figure 2). Results show that
within the investigated hydration time sonication does not
introduce other phases (AFm for example) or accelerates
gypsum consumption and that the intensities of the
ettringite and gypsum reflections are very similar. This indicates that sonication does not alter the LC3
phase assemblage to a verifiable extent.
To further unravel the cause of the fluidity reduction caused
by sonication of cement suspensions, cryo-SEM
investigations on 20 min hydrated LC3 pastes have been
carried out. In order to view LC3 particle distribution in the
aqueous phase without the necessity to sublimate the
sample, the high-pressure frozen suspension was sectioned
in the SEM using a focused ion beam. Results are shown in
Figure 3. The BSE images in Figure 3A and B clearly show
that in the sonicated sample the particles are dispersed and more homogenously distributed within the
amorphous ice. To analyse the particles, images were segmented (Figure 3C & D) and particle size
distributions were determined (Figure 4). As indicated by the images in Figure 3, the sonication leads to a
dispersion of particles, and thus to a shift in particle size distribution towards smaller particles (Figure 4).
In the non-sonicated LC3 reference sample these particles are probably agglomerated.
4. Conclusions
Results of the investigation show:
1. Sonication of LC3 cement leads to a slump
reduction, which is in contrast to
observations with OPC.
2. Nevertheless, sonication leads to an
acceleration of LC3 setting.
3. Phase assemblage investigated by in-situ
XRD is mostly unaffected by sonication.
4. Cryo-FIB-SEM imaging revealed that
sonication caused a dispersion of particles
shifting the particle size distribution to
smaller sizes. This is consistent to OPC.
However, the dispersion of particles is
associated with improved slump in OPC,
whereas in LC3 a reduction was shown.
Figure 2: Stacked in-situ X-ray diffractograms for
2 θ range from 7.8-17.5°. reflections labels: Ett-
ettringite, C$-gypsum, A) LC3 Ref, B) LC3 w. PUS.
Figure 1: Slump of mortars in
dependence of sonication and gypsum
(C$) content.
5.1% C$ 5.7% C$ 6.7% C$
120
130
140
150
160
170
155,5
160
157
123
135,5
141
slump (mm)
C$ content (wt%)
LC3 Ref w.o. US LC3 Ref w. US
Table 1: Set times of cement pastes (Vicat).
w.o. PUS
w. PUS
LC3
480 min
360 min
LC3++C$
480 min
360 min
References
Holzer L., Gasser P., Kaech A., Wegmann M., Zingg
A., Wepf R., Muench B., Cryo-FIB-nanotomography
for quantitative analysis of particle structures in
cement suspensions, Journal of Microscopy, 227
(2007) 216-228.
Mousavi S.S., Bhojaraju C., Ouellet-Plamondon C.,
Clay as a Sustainable Binder for Concrete —A
Review, Construction Materials 1 (2021) 134–168.
Nguyen Q.D., Kim T., Castel A., Mitigation of alkali-
silica reaction by limestone calcined clay cement
(LC3), Cement and Concrete Research 137 (2020)
106176.
Peters S., The Influence of Power Ultrasound on Setting
and Strength Development of Cement Suspensions: Doctoral Dissertation, Bauhaus-Universität Weimar, 2016
https://doi.org/10.25643/bauhaus-universitaet.2744
Pillai R.G., Gettu R., Santhanam M., Rengaraju S., Dhandapani Y., Rathnarajan S., Basavaraj A.S., Service life and
life cycle assessment of reinforced concrete systems with limestone calcined clay cement (LC3), Cement and
Concrete Research 118 (2019) 111– 119.
Pott, U., Crasselt, C., Fobbe, N., Haist, M., Heinemann, M., Hellmann, S., ... & Stephan, D. (2023). Characterization
data of reference materials used for phase II of the priority program DFG SPP 2005 “Opus Fluidum Futurum–
Rheology of reactive, multiscale, multiphase construction materials”. Data in Brief, 108902.
Remus R., Rößler Ch., Ludwig H.-M. "Power Ultrasound-Assisted Concrete Production—Workability, Strength
Development, and Durability." ACI Special Publication 330 (2018): 135-150.
Scrivener K.L., Laffely J. D, Favier A., Cement Plant Environmental Handbook 3rd Edition: LC3 – Limestone
Calcined Clay Cement, Tradeship Publications Ltd, UK, 2022.
Scrivener K., Avet F., Maraghechi H., Zunino F., Ston J., Hanpongpun W., Favier A., Impacting factors and properties
of limestone calcined clay cements (LC 3 ), Green Materials 7 (2019) 3–14.
Sharma M., Bishnoi S., Martirena F., Scrivener K., Limestone calcined clay cement and concrete: A state-of-the-art
review, Cement and Concrete Research 149 (2021).
Tregger N.A., Pakula M.E., Shah S.P., Influence of clays on the rheology of cement pastes, Cement and Concrete
Research 40 (2010) 384–391.
Figure 3: Cryo-SEM images of high-pressure frozen, FIB sectioned LC3 cement suspension (w/c = 0.5,
20 min hydrated): A, Reference B, Sonicated. C, D) segmented particles (Image width 46.3 µm resp.
44.8 µm).
Figure 4: Particle size distribution determined from
segmented images and Fig. 3C & D.
0.001 0.01 0.1 1
0.0
0.2
0.4
0.6
0.8
1.0
particle area in µm²
frequency
LC3 Ref w.o. US LC3 Ref w. US
