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STRENGTH DEVELOPMENT AND HYDRATION PROGRESS OF A
CEMENT-BASED SOLIDIFYING AGENT USED IN CEMENT-
TREATED SOIL CONTAINING VOLCANIC MINERAL
COMPONENTS
Izuru Segawa (1), Yuya Takahashi (1) and Go Igarashi (1)
(1) Department of Civil Engineering, The University of Tokyo, Japan
Abstract
This study investigates the relationship between the strength development and hydration
progress of cement-based solidifying agents (CBSAs) in cement-treated soil with volcanic
mineral components. A CBSA is a cement-based material used as a soil stabilizer. It is known
that the strength development of cement-based materials is inhibited by volcanic mineral
components, e.g., allophane, and CBSAs are specially controlled against hydration inhibitions.
Previous studies showed that allophane might be the governing factor for the inhibition of
cement hydration, and its response to the hydration properties should be investigated.
In this study, cement-paste and cement-treated–soil specimens are made with three types of
binder (ordinary Portland cement, blast-furnace slag cement, and a CBSA) to investigate the
hydration progress and strength development. Uniaxial compression tests were conducted,
and the strength development was measured with the different binder types. It was found that
the strengths of the cement-paste specimens at day 28 were almost the same with the three
binders, while they differed in the mortar specimens that contained allophane. X-ray
diffraction/Rietveld analyses were conducted to measure the hydration properties. From the
results, it was supposed that, owing to the lack of Ca(OH)2, the pozzolanic reaction was
stagnant. Considering the ion concentration of the pore water in the solidified materials,
quantitative estimations of the strength development affected by allophane should be possible
in the future. Keywords: Cement-based solidifying agents, cement-treated soil, XRD Rietveld, ettringite,
allophane
1. INTRODUCTION
A cement-based solidifying agent (CBSA) is a material for soil improvement. Components
that are effective for hardening soil are added to the base cement material. The CBSA
composition is designed to produce the appropriate amount of ettringite during its hydration.
Ettringite should improve the ground through its capacity to absorb large amounts of water
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and decrease the moisture content in the ground; it also acts like a bridge to firmly connect the
soil particles.
CBSAs are widely used in various places for structure-foundation stabilization, roadbed
improvements, etc. About 8-million tons of CBSAs are used annually in Japan. However,
when soil containing volcanic ash is treated, the strength is often lower than in other soil cases.
Because volcanic-ash soils are distributed all over Japan, understandings of the mechanism
and future prediction models are anticipated in the engineering field.
Allophane, a mineral contained in volcanic-ash soil, is thought to be one of the main
causes of the insufficient strength development in cement treatments. Allophane is the
weathered phase of volcanic glass or pumice, and its chemical composition can be represented
as (SiO2)n・Al2O3・(H2O)m, where n = 1.3–2.0 and m = 2.5–3.0. The amorphous phase of
allophane in the soil inhibits the cement-solidification reaction by adsorbing the calcium ions.
Experiments by the Japan Cement Association showed a correlation between the amount of
allophane and the uniaxial compressive strengths of cement-treated soils, as well as a
correlation between the amount of allophane and a reduction in the calcium-hydroxide
solution concentrations [1]. It was assumed that the strength development was inhibited
because of the insufficient hydration progress. However, no studies have been conducted to
quantify the hydration progress against the solidification inhibition.
Thus, in this study, the degree of solidification inhibition by allophane in cement-treated
soil was investigated by preparing cement-treated soil specimens and quantitatively
measuring the clinker consumption and the hydrate production. The study attempts to clarify
the contribution of each hydrate to the strength development.
2. EXPERIMENTAL SETUP
Cement-paste and cement-treated–soil specimens were prepared and subjected to
compressive-strength tests, X-ray diffraction tests (XRD), and thermal gravimetric analysis
tests (TGA). Three types of binder were used: ordinary Portland cement (OPC), blast-furnace
slag cement (type B in accordance with Japanese Industrial Standard JIS R 5211 [2]) (BB),
and a cement-based solidification agent (CBSA).
Table 1 shows the physical properties and clinker compositions of the binders. Cement-
paste specimens were prepared at two water-to-binder ratios (W/B): 0.5 and 1.0. For the
cement-treated soil, the particle sizes of commercial sand from Kanuma, Japan (Kanuma-soil)
were adjusted and used in this study.
Table 2 shows the physical properties of the soil. The allophane content in the soil was
estimated by XRD. It should be noted that the estimated allophane content includes other
inorganic amorphous materials. Table 3 shows a series of cement-treated soil specimens. The
cement-treated soil was prepared according to the method in the Japanese Geotechnical
Society's JGS 0821-2009 [3].
Table 1: Binder properties
Binder
type
Ig. Loss
(%)
Chemical composition (mass %) Density
(g/cm3)
Specific surface
area (cm2/g) SiO2 Al2O3 Fe2O3 CaO MgO SO3
OPC 2.47 13.89 3.74 3.47 75.12 0.97 1.94 3.15 3550
BB 1.88 19.63 7.27 1.76 62.99 3.30 3.27 3.02 3800
CBSA 1.38 22.23 7.13 2.01 55.77 2.61 6.87 3.06 3630
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Three cylindrical specimens (φ5 × 10 cm) were prepared for each cement-paste or cement-
treated–soil case. The top surface of each specimen was covered with plastic wrap until the
test-material age after casting (sealed curing), and the specimens were placed at a constant
temperature of 20 °C.
The specimens were subjected to uniaxial compression tests at their material ages of 1, 3, 7,
and 28 days. After the compression tests, some specimen pieces were collected and subjected
to XRD and TGA tests. The test pieces were pulverized to about 5 mm and immersed in
isopropanol for one week to stop their hydration. Next, one week of vacuum drying was
applied. They were pulverized again and sieved to 100-μm particle sizes for the TGA and
XRD tests.
The TGA measurements were conducted with an STA 2500 Regulus thermal analyzer
(NETZSCH) under nitrogen-flow conditions with a temperature-increase rate of 15 °C/min.
The ignition-loss (Ig. Loss) value is defined as the value of the mass lost from 105 °C to
950 °C divided by the mass at 950 °C. XRD analyses were conducted using the LabX XRD-
6100 X-ray differential system (Shimadzu). The hydrated and dried powder samples were
analyzed under the following conditions: The X-ray source is Cu-Kα, the tube voltage is 40.0
kV, the tube current is 30.0 mA, the scanning range is 2θ = 5–70°, the step width is 0.02°, and
the scanning speed is 2.0°/min.
XRD Rietveld analyses were conducted on the XRD results with SIROQUANT software
ver. 3.0. The following phases were considered in the quantifications as cement minerals or
hydration products: C3S, C2S, C3A, C4AF, MgO, CaO, CaCO3, CaSO4・2H2O (gypsum),
CaSO4 ・ 0.5H2O (basanite), CaSO4 (anhydrite), Ca(OH)2 (CH), C3A ・ 3CaSO4 ・ 32H2O
(ettringite), C3A・CaSO4・12H2O (monosulfate), 3CaO・Al2O3・0.5Ca(OH)2・0.5CaCO3・12H2O
(hemicarbonate), 3CaO・Al2O3・CaCO3・11H2O (monocarbonate), and α-Al2O3. α-Al2O3 of 10
wt% of the samples was mixed as the internal standard.
For the cement-treated–soil specimens, albite, anorthite, and quartz were added to the
phases for the quantifications. The amorphous-substance content was calculated according to
Eq. (1) from the quantified value of the internal standard α-Al2O3 [4]. The amounts of
unhydrated clinkers and hydrated products in the samples were calculated by correcting the
quantitative values obtained from the XRD Rietveld analyses with the Ig. Loss and the
amorphous content, according to Eq. (2).
where A is the amorphous-material content, S is the mixing ratio (%) of α-Al2O3, SR is the
quantified value of α-Al2O3 (%), QR is the quantitative value of each phase (%), and L is Ig.
Loss.
Table 2: Physical soil properties Table 3: Mix proportions of cement-treated soil specimens
Moisture
contentDensity
Amount of
allophane
26.1% 2.7 g/cm3
82%
Gravel Sand Clay& Silt
12% 87% 1%
W/B S/BUnit (kg/m
3)
W B S
1.75 2.50 585 334 835
2.33 3.33 601 257 858
3.50 5.00 617 176 882
W/B S/BUnit (kg/m
3)
W B S
1.13 2.50 475 422 1056
1.50 3.33 491 328 1092
2.25 5.00 509 226 1131
A = {100 × (SR - S)}/{SR × 100 - S) / 100} (1)
Q = QR × (100 - A) / (100 - L), (2)
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3. EXPERIMENTAL RESULTS OF CEMENT-PASTE SPECIMENS
Figure 1 shows the results for the compression tests of the cement-paste specimens. The
legend in the figure represents the (Binder Type)-(W/B). From the results in Fig. 1, BB and
CBSA showed strengths similar to OPC at day 28, while their initial strength developments
were slower than OPC in both the 0.5 and 1.0 W/B cases.
Table 4 and Figure 2 show the phase compositions of the mass calculated by the XRD
Rietveld analyses. The W/C 0.5 cases of the OPC and CBSA specimens are displayed in Fig.
2. There was no significant difference in the C3S hydration rate between OPC and CBSA,
which is considered to contribute the most to the strength in the early ages. Regarding the
other clinkers, CBSA had a slower hydration rate than OPC. In CBSA, anhydrite was
consumed at almost the same rate as C3S, and an accordingly large amount of ettringite was
produced.
Figure 2: Calculated mass of phase compositions
Using the density of each cement mineral and the hydrate phase from previous research [4,
5] (Table 5), the phase compositions in the volume basis were calculated [5, 6]. Figure 3
shows the calculated volume of the phases of the cement-paste specimens. The volume of
ettringite in the CBSA case is larger than that of the OPC case. In addition, the theoretical
porosities of the cement pastes were estimated from the calculated phase volumes. The
porosities of the cement-paste specimens (Φcp ) were calculated by Eq. (3):
where Vpore is the volume of free-water and blank spaces and Vtotal.ini is the volume of the
cement paste at day 0.
Figure 1: Strength development of paste
Table 4: Mineral composition of binders
C3S C2S C3A C4AF
OPC 68 12.2 10.2 5.3
BB 57.3 13.9 6.6 4.4
CBSA 56.1 10.7 5.4 5.9
BassaniteAnhydriteGypsum Others
OPC 0.4 0.1 0.5 3.3
BB 1.9 0.5 3.7 11.7
CBSA 0.7 14.3 2.1 4.8
OPC-0.5 case CBSA-0.5 case
Φcp = Vpore / Vtotal.ini, (3)
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Table 5: Density of each phase in kg/m3
phase C3S C2S ettringite monocarbonate portlandite anhydrite gypsum
density 3150 3310 1778 2175 2251 2968 2311
phase C3A C4AF calcite hemicarbonate monosulfate amorphas water
density 3030 3740 2710 1985 2015 2410 1000
Figure 4 shows the estimated porosities of the cement-paste specimens. A correlation
between porosity and strength was shown in previous research [7]. However, in this study, the
CBSA and OPC cases showed almost the same porosity decrease rates, while the strength
developments were different, as shown in Fig. 1.
From these results, the following process can be assumed for the strength development of
CBSA. In the early stage, large quantities of ettringite are produced, owing to the extensive
anhydrite content. Because the cement-paste skeletons are not very stiff yet, the cement paste
itself expands or is destroyed, due to the expansion pressure of the ettringite. Hence, the
strength of CBSA can be lower than the strength of OPC at the early stage. A similar
tendency was observed in previous research [8].
After the paste has stiffened, the ettringite formation can contribute to the strength, as well
as other hydrates. Previous research has shown that the expansion pressure changes,
depending on the shape of the ettringite, and the shape changes depend on the Ca2+
concentration in the pore solution [9]. In this study, neither the expansion nor the void
distribution was measured. Measuring the volume changes or pore-size distributions can help
researchers better understand the CBSA hydration characteristics.
OPC-0.5 case CBSA-0.5 case
Figure 3: Calculated volume of the phase compositions
Figure 4: Theoretical porosity of the cement-paste specimens
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4. EXPERIMENTAL RESULTS OF CEMENT-TREATED–SOIL SPECIMENS
Figure 5 shows the compressive strengths of the cement-treated–soil specimens. The
strength-development tendencies in the early stages vary, depending on the W/B. The OPC
and CBSA cases have almost the same strength transitions at higher W/Bs (more than 2.25);
these are an available mix-proportion range in actual soil-improving methods. On the other
hand, for lower W/B specimens, the CBSA specimens initially have a higher strength than the
OPC, while the OPC specimens have a higher strength at day 28. The tendency of the cement-
treated–soil specimens is different from the cement-paste specimens. The BB specimens have
significantly lower strength than the rest of the series.
Figure 5: Strength development of cement-treated–soil specimens
Figure 6 shows the XRD profiles of the cement-treated–soil specimens. Each result is a
profile of a corundum mixture. The data for day 0 show the results of Kanuma-soil that does
not contain cement, and the other charts show the results of the cement-treated–soil specimens
of the W/B 1.75 cases for the OPC and CBSA cases. A gentle broad peak around 20–30°,
which is unique to allophane, is observed; however, the height of this peak decreases in the
cement-treated–soil specimens.
In OPC, peaks for hemicarbonate and monocarbonate are observed around 10.7 ° and
11.7 °, respectively. In CBSA, ettringite peaks are observed at around 9.1 °, for example. In
both the OPC and CBSA cases, no CH peaks can be observed.
Previous studies have reported that ettringite can be produced by adding Ca(OH)2 and
gypsum to allophane [10]. It is supposed that the following reaction occurs between allophane
and the cement system in cement-treated soils:
These reactions are assumed to be pozzolanic reactions, and they might be effective for
long-term strength development. With these reactions, large amounts of CH, which are
generated by clinker hydration, are almost completely consumed.
(SiO2)n・Al2O3・(H2O)m + 3Ca(OH)2 + 3(CaSO4・2H2O) + (23-m)H2O
→ 3(CaO・Al2O3)・3CaSO4・32H2O + nSiO2
(4)
2SiO2 + 3Ca(OH)2 + H2O→3CaO・2SiO2・4H2O. (5)
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Figure 7 shows the calculated masses of the phases in the cement-treated–soil specimens,
based on the XRD results. Regarding the clinkers' consumption rates, there is no significant
difference between the cement-treated soil specimens (Fig. 7) and the cement-paste specimens
(Fig. 2).
From these results, the following strength-development mechanisms for CBSA in cement-
treated soil containing allophane can be assumed. Large amounts of ettringite are produced in
the early stage and absorb the moisture. Then, the moisture content in the soil decreases and
the connection between the soil particles can be strengthened, which can contribute to an
increase in strength, as opposed to the OPC case.
On the other hand, after the early stage, because a large amount of gypsum is present, a
large amount of CH is consumed to produce ettringite, and the allophane's pozzolanic reaction
does not occur sufficiently. In addition, CBSA produces only about half of the CH that OPC
does in cement paste. As a result, the amount of calcium-silicate-hydrate (C-S-H) in the
CBSA case is less than that in the OPC case. These phenomena could be the cause of the
strength-development slowdown in the CBSA case. This assumption can also explain the
lowest strength of the BB case. The calcium concentrations in the pore water decrease in the
presence of allophane, and the reaction of the blast-furnace slag can stagnate.
In this research, it was not possible to separate the allophane-derived amorphous phase and
the cement-derived C-S-H amorphous phase in the XRD results. By studying the clear-phase
composition and the theoretical porosity, a strength prediction should be achieved in the
future. In addition, it is thought that the mechanism's hypothesis can be confirmed by
measuring the ion concentrations of the pore solutions to discuss the phase equilibrium of the
pore water and hydrates.
OPC-1.75 case CBSA-1.75 case
Figure 6: XRD profiles of cement-treated–soil specimens
OPC-1.75 case CBSA-1.75 case
Figure 7: Calculated mass of phase compositions of cement–treated–soil specimens
Day 0
Day 3
Day 7
Day 28
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5. CONCLUSIONS
To investigate the hydration characteristics of CBSA, cement-paste specimens and cement-
treated soil specimens were prepared, and uniaxial compression, TGA, and XRD tests were
conducted. The relationships between the compressive strengths and the quantitative values of
the hydrate phases were investigated.
The early-stage strengths of the CBSA cement pastes were smaller than those of OPC. A
large amount of anhydrous gypsum was present and a large amount of ettringite was produced
in CBSA. After the stiffness development of the cement-paste systems, it is supposed that the
ettringite contributes to the strength, as other hydrates do.
The early-stage strengths of the CBSA cement-treated–soil specimens were almost equal to
or slightly higher than those of OPC. On the other hand, the subsequent strength of CBSA did
not increase much. In the early-stage strength development, a large amount of ettringite can
contribute to changing the moisture state of the soil, which can increase the initial strength.
The subsequent slow strength developments can be explained by the stagnation of the
pozzolanic reaction, due to the lack of Ca(OH)2.
ACKNOWLEDGMENTS
This study was financially supported by JSPS KAKENHI grants numbers 17H01284 and
18KK0120.
REFERENCES
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look.’ Cement and Concrete Research 13(3) (1983) 401–406.
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