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Article

Comparative Study on the Calcium Leaching Resistance of Low-Heat Cement, Moderate-Heat Cement, and Ordinary Portland Cement Pastes

by
Chunmeng Jiang
1,2,*,
Shihao An
1,2,
Shuangxi Li
1,2,
Yingjie Chen
1,2 and
Jian Liu
1,2
1
College of Hydraulic and Civil Engineering, Xinjiang Agricultural University, Urumqi 830052, China
2
Xinjiang Key Laboratory of Hydraulic Engineering Security and Water Disasters Prevention, Urumqi 830052, China
*
Author to whom correspondence should be addressed.
Materials 2025, 18(1), 212; https://doi.org/10.3390/ma18010212
Submission received: 5 December 2024 / Revised: 27 December 2024 / Accepted: 2 January 2025 / Published: 6 January 2025
(This article belongs to the Special Issue Sustainable and Advanced Cementitious Materials)
Browse Figures
Figure 1
<p>Schematic diagrams showing the exposure conditions and testing.</p> "> Figure 2
<p>Mass loss rates of specimens exposed to NH<sub>4</sub>Cl solution.</p> "> Figure 3
<p>Porosity of the specimens exposed to NH<sub>4</sub>Cl solution.</p> "> Figure 4
<p>Leching depths of specimens exposed to NH<sub>4</sub>Cl solution.</p> "> Figure 5
<p>Compressive strength loss rate of the specimens exposed to NH<sub>4</sub>Cl solution.</p> "> Figure 6
<p>Vickers hardness of the different cement pastes under calcium leaching.</p> "> Figure 7
<p>Ca/Si ratio versus mass loss of cement specimens under calcium leaching.</p> "> Figure 8
<p>XRD patterns of the cement pastes (<b>a</b>) before calcium leaching and (<b>b</b>) after being exposed for 180 days.</p> "> Figure 9
<p>TG-DTG curves of the cement pastes (<b>a</b>) before calcium leaching and (<b>b</b>) after being exposed for 180 days.</p> "> Figure 10
<p>Morphology of the OPC specimens exposed to NH<sub>4</sub>Cl leaching.</p> "> Figure 11
<p>Morphology of the MHC specimens exposed to NH<sub>4</sub>Cl leaching.</p> "> Figure 12
<p>Morphology of the LHC specimens exposed to NH<sub>4</sub>Cl leaching.</p> ">
Versions Notes

Abstract

:
Hydraulic structures are frequently subjected to soft-water or acidic environments, necessitating serious consideration of the long-term effects of calcium leaching on the durability of concrete structures. Three types of common Portland cement (ordinary Portland cement, moderate-heat cement, and low-heat cement) paste samples widely applied to hydraulic concrete were immersed in a 6 mol/L NH4Cl solution to simulate accelerated calcium leaching behavior. The mass loss, porosity, leaching depth, compressive strength, and Ca/Si ratio of the three types of pastes were measured at different immersion stages (0, 14, 28, 56, 91, 140, and 180 days). The Vickers hardness index was employed to compare cement samples subjected to erosion for 30 and 180 days. The microstructure and composition of the mineralogical phases of the leached samples were also determined by X-ray diffraction, thermogravimetric analysis, and scanning electronic microscopy. Accordingly, the time-varying behavior and deterioration mechanism of the different cements subjected to leaching were contrastively revealed. The results showed that the calcium leaching resistance of the low-heat cement was the best, followed by the moderate-heat cement and ordinary Portland cement, proving that the content and structure of Ca(OH)2 and C-S-H gels were closely related to the leaching performance of the cement. The less Ca(OH)2 and more aggregated C-H-S gels produced by C2S led to better calcium leaching resistance in the cement. Therefore, the leaching performance of Portland cement could be effectively improved by reducing the content of C3S and increasing the content of C2S, and the dissolution rate of calcium ions under leaching could be reduced by controlling the low initial calcium content in cementitious materials. This paper offers theoretical guidance for mitigating the long-term effects of calcium leaching on hydraulic concrete structures by conducting a comprehensive comparative analysis of the damage behavior and deterioration mechanisms of various types of Portland cement under identical erosion conditions.

1. Introduction

The calcium leaching of hydraulic concrete consists of a process in which cement-based materials are exposed to soft water for long periods of time. Consequently, the equilibrium state between solid calcium in the hydration products and calcium ions in the pore solution will be destroyed due to the concentration difference, resulting in a diffusion loss of the calcium phase in the pore solution and the decalcification dissolution of hydration products, leading to concrete failure [1]. The content of calcium hydroxide (Ca(OH)2) and hydrated calcium silicate (C-S-H) gels produced by the hydration of the tricalcium silicate (C3S) and dicalcium silicate (C2S) of the cement serves as the main factor affecting damage caused by calcium leaching from cementitious materials [2,3]. Currently, scholars have extensively studied the erosion performance and hydration characteristics of ordinary Portland cement (OPC), moderate-heat Portland cement (MHC), and low-heat Portland cement (LHC), with a primary focus on their erosion degradation behavior, mechanical properties, and erosion mechanisms [4,5,6]. For instance, lv et al. [7] found that the leaching resistance coefficient of low-heat cement was higher than that of ordinary Portland cement, and the compressive strength and flexural strength of low-heat cement samples were higher than those of ordinary Portland cement at the same leaching age. Following a 29Si NMR test, Wang et al. [8,9,10] found that the porosity of low-heat cement under complete hydration was significantly lower than that of ordinary Portland cement, and the average molecular chain length of C-S-H gel in the low-heat cement paste was longer than that in the ordinary Portland cement. Wang et al. [11] compared the basic physical properties of low-heat cement and ordinary cement, revealing that the large amount of C-S-H gel produced through the hydration of the low-heat cement dominated by C2S was the primary factor leading to a high-strength dense cement-stone structure.
The differences in the contents of calcium silicate (C3S) and dicalcium silicate (C2S) were the primary factors contributing to the distinct hydration behaviors of the three cement types, ultimately resulting in variations in their calcium leaching performance. [12,13]. Most studies on different types of Portland cement primarily investigate their chemical properties, crack behavior, and strength development [14,15]. Conversely, comprehensive comparative studies on the damage mechanisms of ordinary Portland cement, moderate-heat cement, and low-heat cement under identical erosion conditions, particularly from the perspective of mineral composition, remain relatively scarce [16]. The advantages of the high C2S content and low C3S content of low-heat cement compared to moderate-heat cement and ordinary cement involve reduced amounts of the hydration product Ca(OH)2 and more C-S-H gel, with the hydration equations shown in Equations (1) and (2) [17]. It is generally believed that the leaching resistance of cementitious materials can be effectively improved by reducing the C3S content and increasing the C2S content. By comparing the mechanical performance of Portland cement with different compositions in 5% sodium sulfate solution, Cao et al. [18] found that cement specimens with low C3S and tricalcium aluminate (C3A) concentrations exhibited good leaching resistance. Wang et al. [19] found that the early hydration rate of C2S was very slow; however, this process could be conducive to the generation of a physically well-structured C-S-H gel. Thus, the internal pore size and the distribution of hydration products in low-heat cement were more homogeneous than those in ordinary cement. He et al. [20] showed that the average chain length and degree of polymerization of hydrated calcium silicate after the full hydration of low-heat cement were higher than those of ordinary Portland cement, which could reduce the decalcification of hydrated calcium silicate due to the exhaustion of Ca(OH)2 depletion during the leaching process.
2 C 3 S + 11 H → C 3 S 2 H 8 + 3 CH
2 C 2 S + 9 H → C 3 S 2 H 8 + C H
To simulate long-term calcium leaching within a short period and predict the long-term performance of cementitious materials in low-concentration environments, this study employed a 6 mol/L NH4Cl solution to accelerate the erosion of ordinary Portland cement, moderate-heat cement, and low-heat cement samples. Macroscopic indicators, including the mass loss rate, porosity, leaching depth, compressive strength, Vickers hardness, and Ca/Si ratios, were measured for the three types of cement samples. The microstructural morphology and phase composition of the cement samples before and after calcium leaching were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) to understand the erosion mechanisms involved. By analyzing the calcium leaching characteristics of three types of silicate cement and incorporating microscopic testing, this study examined how variations in mineral compositions and hydration products influenced the calcium leaching damage mechanism of the cement matrix. This comparative analysis provided theoretical guidance for optimizing cement material applications in soft-water or acidic environments. Among the tested cements, the low-heat cement exhibited superior anticalcium leaching performance, underscoring its potential as a sustainable and high-performance material.

2. Materials and Methods

2.1. Materials and Sample Preparation

Low-heat Portland cement, moderate-heat Portland cement (GB/T 2000-2007 [21], namely ASTM C150 (2018) [22] type IV Portland cement), and P.O 42.5 ordinary Portland cement (GB 175–2023 [23], namely ASTM C150 (2018) type I Portland cement) were used in this study to explore the impact of compositions on their calcium leaching performance. Chemical and mineral compositions, as well as the physical–mechanical properties of the three types of Portland cement, were supplied by Sichuan Jiahua Cement Plant, China. Detailed values are presented in Table 1 and Table 2.
According to the commonly used proportioning scheme for hydraulic concrete, three types of cement paste specimens were designed for Portland cement, denoted as OPC, MHC, and LHC. Cylindrical specimens with 50 mm diameters and 100 mm heights were cast and stored in a standard curing environment (20 °C and 98% relative humidity) for 24 h before demolding. Subsequently, all samples were cured in saturated limewater (Westlong Science & Technology Co., Ltd., Shantou, Guangdong Province, China)at 20 °C until reaching an age of 90 days, followed by accelerated leaching tests in a NH4Cl (Westlong Science & Technology Co., Ltd., Shantou, Guangdong Province, China) solution.

2.2. Sample and Exposure Conditions

Prior to the immersion test, epoxy resin (Evergrande New Material Technology Co., Ltd., Huizhou, Guangdong Province, China) was uniformly applied to both ends of the specimens to ensure that the calcium leaching process proceeded in the diameter direction. Then, the specimens were transferred to several sealed boxes filled with 6 mol/L of the NH4Cl solution for the full immersion test, as shown in Figure 1a, and all sealed boxes were kept at a constant temperature of 20 °C. During the test, the NH4Cl solution was replaced every 30 days to ensure that the concentration of the test solution was stable.
To test the indicators at different immersion stages (0, 14, 28, 56, 91, 140, and 180 days), prior to measuring the test indicators, the samples were sectioned using an HQP-150 concrete core slicing machine (China Construction Instrument and Equipment Co., Ltd., Cangzhou, China). The specimens were cut into small specimens with a diameter of 50 mm and different heights. The porosity, compressive strength, leaching depth, Vickers hardness, and Ca/Si ratio were determined, as shown in Figure 1b. In addition, an electronic balance (0–1 kg range, 0.01 g accuracy) manufactured by Shanghai Puchun Metrology Instruments Company (Shanghai, China) was utilized throughout the experiment. Specific intact cylinders were used throughout the test to determine the mass loss under different leaching ages. Three samples were prepared for each test, and the average value of three data points was used as the result.

2.3. Methods

2.3.1. Mass Change and Porosity Tests

Mass loss and porosity serve as important indicators in evaluating the durability of cement paste [24]. The relative mass loss (W) and porosity (P) of the samples over a certain exposure duration were calculated using Equations (3) and (4):
W = M 0 − M t M 0
P = m t − m 0 V
where M0 and Mt are the weights of the same cylinder specimens before and after calcium leaching, which were air-dried to a constant value in the laboratory before measurement, in g; mt is the saturated surface dry mass of the subsample (see Figure 1b) in g; m0 is the mass of this cylinder after drying at 60 °C for 24 h in g; and V is the sample volume measured using the drainage method in cm3.

2.3.2. Leaching Depth Test

Leaching depth serves as an important indicator for detecting the speed and extent of the calcium leaching process, providing a way to determine micro-leaching behavior from a macro-phenomenon [25]. Cement specimens at the specified immersion stage were removed and split along the diameter using a cutting machine. The residual cement paste on the specimen’s cross-section was rinsed with clean water, and excess surface moisture was dried using absorbent paper. The specimen was then sprayed with 1% alcohol phenolphthalein reagent (Shentai Chemical Reagent Co., Ltd., Tianjin, China), and the distance from the cylinder edge to the discoloration demarcation line was measured as the leaching depth using vernier calipers when the leached specimens appeared obviously colorless with pink demarcation lines [26].

2.3.3. Compressive Strength Test

Compressive strength is considered a fundamental and important mechanical property, as well as a direct index used to quantify the deterioration of specimens [27]. After the cement samples reached the designated calcium leaching stage (0, 14, 28, 56, 91, 140 and 180 days), compressive strength experiments were performed with an electronic universal testing machine at a path-controlled speed of 0.1 mm/min. The strength loss rate ( Δ σ t ) was calculated according to Equations (5) and (6):
σ t = F t A
Δ σ t = σ 0 − σ t σ 0 × 100 %
where Ft is the failure load in kN; A is the cross-sectional area of the cylindrical specimen in m2; σ t is the strength of damage of the sample exposed to NH4Cl solution for t days in MPa; and σ 0 is the initial compressive strength in MPa.

2.3.4. Vickers Hardness Test

Hardness testing serves as an effective approach for locally and immediately estimating microstructural changes in materials [26]. The Vickers hardness at different leaching depths was measured and combined with the compressive strength loss rate to determine the mechanical property degradation characteristics of cement-based materials under calcium leaching. Prior to testing, all tested sections of the cut subsamples (Figure 1b) were manually polished using 400-, 800-, and 1000-grit sandpapers (Gerde Industrial Technology Co., Ltd., Shanghai, China) with water as a lubricant and then dried in the laboratory for 24 h. The hardness was measured every 0.5 mm from the outer layer of the cement pastes to the interior along the diffusion direction, and the resulting values consisted of the mean values of eight testing points with the same radius. The measurements were carried with a micro-Vickers hardness tester with 0.9807 N of force applied to the surface for 15 s.

2.3.5. Calcium–Silicon Ratio Test

To quantify the changes in the hydration products of the three types of cement pastes with different degrees of leaching, the cylindrical specimens were cut into thin disks with a thickness of 1.5 mm, the calcium ion content of the solution was tested by using the EDTA complexometric titration method, and the Ca/Si of the entire specimen was accordingly determined [28]. To calculate the calcium content of the leached specimens and to obtain the Ca/Si ratio of the disks in the leaching solution, we subtracted the calcium content in the leaching solution from the calcium content of the initial disk.

2.3.6. Mineralogical, Morphological, Thermal, and Microstructural Analyses

After leaching in NH4Cl solution for 180 days, several typical samples were collected from the outer layer of the damaged specimens by cutting and artificially breaking off the specimens. We then conducted X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electronic microscopy (SEM) assessments. The samples at the designated erosion stage were ground into powder with a particle size smaller than 80 μm and then dried in a glass vessel with a desiccant at room temperature until the XRD and TGA measurements were performed. The XRD analysis was performed using a Rigaku SmartLab SE (Rigaku Corporation, Tokyo, Japan) diffractometer with a 40 kV operating voltage, a scanning speed of 10°/min, and a scanning range of 10–50° to assess changes in the specimens’ crystal compositions during the erosion process. The thermogravimetric analysis (TGA) was performed using a NETZSCH STA 449F3 synchronous thermal analyzer (NETZSCH-Gerätebau GmbH, Selb, Germany) under a nitrogen atmosphere, with a temperature range of 30–600 °C and a heating rate of 10 °C/min. Moreover, the obtained fracture surfaces of the flake samples maintained their original micro-morphology, and they were subsequently coated with a 5 nm thick gold film and observed with a TESCAN MIRA LMS-type scanning electron microscope (TESCAN ORSAY HOLDING, a.s., Brno, Czech Republic).

3. Results and Discussion

3.1. Mass Loss Rate

Figure 2 shows the change in the mass loss rate of the three types of Portland cement specimens in the 6 mol/L NH4Cl solution. The results show that the mass loss rates of the OPC, MHC, and LHC specimens subjected to accelerated leaching with the NH4Cl solution all increased with increasing immersion time. After 180 days of leaching, the mass loss rates of the OPC specimen was greater than that of the MHC and LHC, with values of 8.17%, 8.03%, and 7.39%. For the OPC specimen, the mass loss rate was higher than that of the other two specimens during the 180-day leaching period. Therefore, it could be assumed that under the same leaching conditions, the resistance to calcium leaching of the ordinary cement was weaker than that of the moderate-heat and low-heat cements and that the latter, by having a decreased content of C3S and increased content of C2S, effectively reduced the generation of hydration products of Ca(OH)2 and reduced the loss of the calcium phase from its cement specimens in the process of calcium leaching.

3.2. Porosity

The porosity development of the OPC, MHC, and LHC specimens subjected to the NH4Cl solution is shown in Figure 3, where the continuous depletion of the calcium phase in the hydration products was the main reason for the increase in porosity. The porosity of the cement specimens eroded over 180 days followed the order of OPC > MHC > LHC, from large to small. In addition, the porosity of the ordinary cement specimen showed the highest increase of 11.19% throughout the leaching process, followed by 10.23% for the moderate-heat cement specimen and the smallest increase of 10.16% for the low-heat cement specimen. The slower growth in porosity of the MHC and LHC specimens compared to the OPC specimen under accelerated leaching with the 6 mol/L NH4Cl solution was consistent with the change in the mass loss of all three cement types. This could be attributed to the effect of the hydrated calcium silicate gel produced through silicate cement hydration on the structural densification aspect, while the low-heat cement had the highest C2S content and formed the greatest amount of C-S-H gel and the pore structure of its cement specimens was denser [29,30].

3.3. Leaching Depth

Calcium leaching behavior is a process that occurs from the outside to the inside, and the leaching depths of the eroded specimens subjected to the NH4Cl solution are shown in Figure 4. The leaching depths of the three types of cement pastes increased with the immersion time, and the leaching depths of the OPC specimens at each leaching stage were the largest, followed by those of the MHC specimens, and the leaching depths of the LHC specimens were the lowest. The reason for this was consistent with the change in porosity, where the higher C2S content of the low-heat cement specimens generated a large amount of C-S-H gel and a smaller amount of Ca(OH)2, which allowed the polymerization and hinge system of the LHC paste to provide a better combination, making it difficult for NH4+ to enter the interior of the specimen.

3.4. Compressive Strength

The results for the compressive strength and loss rate of the three types of Portland cement eroded by the NH4Cl solution (0, 14, 28, 56, 91, 140, and 180 days) are shown in Figure 5. These results demonstrate that the compressive strength loss rate of all the cement specimens showed a significant decrease in the first period, followed by a slow decrease. Specifically, OPC, MHC, and LHC exhibited a significant decrease in compressive strength loss rate after 30 days of accelerated leaching, mainly due to the consumption of a large amount of solid-phase Ca(OH)2, and subsequently, when the solid-phase Ca(OH)2 was almost completely dissolved, a small amount of calcium in the C-S-H gels started to decompose and replenish the local chemical equilibrium, until finally, only SiO2 gel remained [31]. The loss rates of compressive strength for the OPC, MHC, and LHC were 58.43%, 55.51%, and 51.4% following the 180-day leaching process, indicating that the more calcium hydroxide produced by the hydration of C3S and C2S in the cementitious materials, the more serious the deterioration damage to the specimens under calcium leaching. Calcium hydroxide is the component with the highest hardness in cement hydration products, which may be an important reason for the decrease in mechanical properties of cement-based materials [32,33].

3.5. Vickers Hardness

Figure 6 depicts the trend in hardness with depth for the three types of cement specimens subjected to the NH4Cl solution for 30 and 180 days. The results show that the Vickers hardness gradually increased from the outer to the inner layers of the specimen and then tended toward a stable value. The Vickers hardness of the LHC specimen in the intact zone was greater than that of the MHC and OPC specimens, which proved that the densification and strength of the hydration products of the low-heat cement with a high C2S content were greater than those of the hydration products of the moderate-heat cement and ordinary cement under the same conditions. In addition, the hardness of the three types of specimens in the leaching zone was greatest for the low-heat cement, followed by the moderate-heat cement and then the ordinary cement. The OPC specimens demonstrated the highest loss of the calcium phase and the most serious damage to the internal structure after leaching. Combined with the index of the loss of compressive strength, the mechanical properties also showed that the low-heat cement demonstrated better resistance to calcium leaching.

3.6. Ca/Si Variations with Mass Loss

A relationship between the Ca/Si ratio and mass loss was established, as shown in Figure 7. The figure reveals that the Ca/Si ratios of the ordinary Portland cement (OPC), moderate-heat cement (MHC), and low-heat cement (LHC) specimens followed a two-stage linear relationship with mass loss. The slopes of the fitting lines and the inflection points varied among the three types of cement. The Ca/Si ratio decreased as mass loss increased, with a significantly steeper decline in the first stage than in the second stage. The rates of decline in the Ca/Si ratio for the OPC specimen was 0.144 and 0.057 in the first and second stages, respectively, exceeding the rates of 0.139 and 0.051 for the MPC specimen and 0.131 and 0.037 for the HBC specimen. In addition, at the inflection point of the two phases, the OPC corresponded to a transverse mass loss rate of 10.34%, at which point the Ca/Si value was 1.67, while the MHC and LHC corresponded to a decrease in the transverse mass loss rate and Ca/Si ratio at the cutoff point, with values of 10.09% and 1.53 and 8.30% and 1.48.
We inferred that the C3S content was higher in the first stage of the OPC and MHC, with more calcium hydroxide produced by hydration, and that Ca(OH)2 could easily decompose during the calcium leaching process. Thus, the mass loss and calcium loss were greater than those of the low-heat cement. When Ca(OH)2 was almost completely dissolved, following the second phase, the calcium phase in the C-S-H gel started to decompose to maintain the local chemical equilibrium, until finally, only the SiO2 gel remained. Due to its high content of C2S, the LHC produced less calcium hydroxide from hydration and more hydrated calcium silicate gels, resulting in a lower rate of calcium leaching. Incidentally, this was reflected in the relationship between mass loss and the Ca/Si ratio, as shown in Figure 7, which was also consistent with the law studied by Chen et al. [34].

3.7. XRD

The compositions of the mineralogical phases of the three types of cement before calcium leaching are shown in Figure 8a. Strong diffraction peaks are shown at 18.1°, 34.2°, and 47.5°, which were observed in the range of 10–50° before the leaching effect of the cement pastes, corresponding to the diffraction peaks of calcium hydroxide [35]. The Ca(OH)2 peaks of the three types of cement demonstrated the highest trend for the OPC, followed by the MHC, and the lowest trend for the LHC, which was mainly due to the fact that the C3S content of the LHC was the lowest among the three cements and the calcium hydroxide content in the LHC paste was significantly lower than that in the OPC and MHC pastes. The diffraction peaks at 16.0° and 28.9° correspond to those of ettringite (AFt) [36]. The mineralogical phase compositions of the three types of Portland cement after 90 days of calcium leaching are shown in Figure 8b. In the XRD plots of 10–50°, the wider dispersion peaks originated from the amorphous phases of C3S and C2S [37], which slightly decreased with the onset of the calcium leaching process, indicating that their amorphous phases were consumed during the calcium leaching process. A comparison with the Ca(OH)2 diffraction peaks before calcium leaching clearly showed that the calcium hydroxide consumption of the OPC was the greatest after leaching, followed by that of the MHC, and the lowest was observed for the LHC, and these trends were consistent with the Ca/Si ratio.

3.8. TGA

Figure 9 shows the TG-DTG curves of the OPC, MHC, and LHC specimens before and after calcium leaching. As shown in Figure 9, the heat absorption peak in the range of 80–100 °C is mainly related to substances such as the C-S-H gel and AFt, indicating that the LHC specimens before calcium leaching had the highest content of hydrated calcium silicate and calcite from hydration, followed by the MHC and OPC. Based on the porosity and compressive strength indicators before dissolution, along with the high-density characteristics of the calcium silicate hydrate microstructure [38], it was concluded that the formation of abundant calcium silicate hydrate effectively filled the pores in the cement matrix, disrupted pore connectivity, and enhanced the density of the LHC specimens. In addition, the heat absorption peak in the range of 400–480 °C was caused by the dehydration of calcium hydroxide [39], with the Ca(OH)2 content following the order of OPC > MHC > LHC, from highest to lowest. With accelerated leaching caused by the NH4Cl solution, we found that Ca(OH)2 in the range of 400–480 °C was almost completely consumed, while the peaks of the C-S-H gel and AFt in the range of 80–100 °C in the cementitious material showed less change. This indicated that the cementitious material system lost a large amount of Ca2+ during the leaching process, and the Ca2+ loss was mainly related to the depletion of calcium hydroxide, indicating that Ca(OH)2 was the first to be consumed under calcium leaching, followed by calcium phases such as the C-S-H gel [40], which was consistent with the conclusion that the calcium leaching process was divided into two phases, namely the decomposition of calcium hydroxide and that of hydrated calcium silicate, as indicated by the Ca/Si test.

3.9. SEM

The micro-morphologies of the three types of Portland cement pastes before and after calcium leaching were compared using SEM at 2000×, as shown in Figure 10, Figure 11 and Figure 12. The microstructural images of the cement samples before dissolution revealed that, after complete hydration, their hydration products were relatively intact. The OPC sample predominantly consisted of plate-like calcium hydroxide, the moderate-heat cement exhibited denser amounts of C-S-H gel, and the low-heat cement featured high-density C-S-H gel with a more uniform and compact microstructure. This trend was similar to the mechanical properties of the LHC, which demonstrated improved durability compared to the MHC and OPC. After 90 days of calcium leaching, we observed that on the surface of the three types of specimens, the hydration products were significantly reduced, the internal pores significantly increased, and the OPC and MHC specimens were the most seriously damaged, with a significant increase in black pores. The reason for this phenomenon was that the cement specimens under leaching consumed a large amount of solid-phase calcium, such as Ca(OH)2 and C-S-H gel, and the cement specimen pores continued to increase, which further increased calcium leaching. Furthermore, in this process, the tricalcium aluminate (C3A) inside the concrete specimen generated flaky Friedel’s salt with CaCl2 and water. However, the C3A content of the OPC was the highest, and this flaky Friedel’s salt possibly had a negative effect on the stability of the internal structure of the specimen, causing expansion damage to the cemented specimen, which was possibly one of the factors that led to the weaker resistance to solvency of the OPC than the MHC and LHC in the NH4Cl solution.

4. Conclusions

The macro-properties and micro-indices of the ordinary Portland cement, moderate-heat cement, and low-heat cement pastes exposed to the 6 mol/L NH4Cl solution were contrastively determined to reveal their calcium leaching behavior and deterioration mechanisms. The following conclusions were drawn based on this work.
(1)
The content of Ca(OH)2 in the low-heat cement paste cured for 90 days was significantly lower than that of the ordinary Portland cement and moderate-heat cement, with the largest generation of C-S-H gel being observed in the low-heat cement. Therefore, the internal pore structure of the low-heat cement was the most dense out of the three types of Portland cement after complete hydration.
(2)
The macroscopic performance deterioration of the low-heat cement specimens under accelerated leaching was consistent with that of the ordinary Portland cement and moderate-heat cement specimens, and its comprehensive resistance to calcium leaching was the highest, followed by the moderate-heat cement and the ordinary Portland cement.
(3)
The large amount of C-S-H gel produced by the hydration of C2S and C3S in the low-heat cement could have improved its calcium leaching resistance, and it could be considered that the leaching resistance of Portland cement could be effectively promoted by decreasing its content of C3S and appropriately increasing its C2S content.
(4)
The Ca/Si ratio of the low-heat cement and its leaching rates in both the Ca(OH)2 dissolution stage and C-S-H gel decomposition stage were the lowest out of the three cement types. This was due to the low initial Ca(OH)2 content in the LHC, leading to a lower diffusive dissolution rate of calcium ions, and the C-S-H gel in the LHC pastes exhibited a higher degree of polymerization, which made it relatively more difficult to decompose.

Author Contributions

Conceptualization, C.J.; data curation, S.A. and S.L.; funding acquisition, C.J.; investigation, S.A.; methodology, C.J.; project administration, C.J.; supervision, S.L.; validation, Y.C.; writing—original draft, S.A.; writing—review and editing, C.J., Y.C. and J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Science Foundation of the Xinjiang Uygur Autonomous Region (2022D01B104) and the “Tianchi talent” Introduction Program for the talent development fund of the Xinjiang Uygur Autonomous Region. And The APC was funded by the Natural Science Foundation of the Xinjiang Uygur Autonomous Region.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Conflicts of 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.

References

  1. Sugiyama, D.; Fujita, T. A thermodynamic model of dissolution and precipitation of calcium silicate hydrates. Cem. Concr. Res. 2005, 36, 227–237. [Google Scholar] [CrossRef]
  2. Yokozeki, K.; Watanabe, K.; Sakata, N.; Otsuki, N. Modeling of leaching from cementitious materials used in underground environment. Appl. Clay Sci. 2003, 26, 293–308. [Google Scholar] [CrossRef]
  3. Hou, P.; Zhang, R.; Cai, Y.; Cheng, X.; Shah, S.P. In situ Ca(OH)2 consumption of TEOS on the surface of hardened cement-based materials and its improving effects on the Ca-leaching and sulfate-attack resistivity. Constr. Build. Mater. 2016, 113, 890–896. [Google Scholar] [CrossRef]
  4. Pustovgar, E.; Mishra, R.K.; Palacios, M.; Lacaillerie, J.; Flatt, R.J. Influence of aluminates on the hydration kinetics of tricalium silicate. Cem. Concr. Res. 2017, 100, 245–262. [Google Scholar] [CrossRef]
  5. Jennings, H.M. A model for the microstructure of calcium silicate hydrate in cement paste. Cem. Concr. Res. 2000, 30, 101–116. [Google Scholar] [CrossRef]
  6. Garrault, S.; Nonat, A. Hydrated layer formation on tricalcium and dicalcium silicate surfaces: Experimental study and numerical simulations. Langmuir 2001, 17, 8131–8138. [Google Scholar] [CrossRef]
  7. Lv, P.F.; Wu, Y. Research and application of high belite cement (LHC) performance test. Yangtze River 2010, 41, 67–70. (In Chinese) [Google Scholar]
  8. Wan, L.; Dong, Y.; Zhou, S.H.; Chen, E.; Tang, S.W. Energy saving benefit, mechanical performance, volume stabilities, hydration properties and products of low heat cement-based materials. Energy Build. 2018, 170, 157–169. [Google Scholar]
  9. Wang, L.; Yang, H.Q.; Zhou, S.H.; Chen, E.; Tang, S.W. Hydration, mechanical property and C-S-H structure of early-strength low heat cement based matenials. Mater. Lett. 2018, 217, 151–154. [Google Scholar] [CrossRef]
  10. Wang, L.; Yang, H.Q.; Zhou, S.H.; Chen, E.; Tang, S.W. 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. 2018, 187, 1073–1091. [Google Scholar] [CrossRef]
  11. Wang, J.; Wen, Z.J.; Sui, T.B.; Zhang, Z.L.; Fan, L. Study on the properties and hydration mechanism of high belite cement. Dev. Guide Build. Mater. 2004, 1, 45–49. [Google Scholar]
  12. Bullard, J.W.; Jennings, H.M.; Livingston, R.A.; Nonat, A.; Scherer, G.W.; Scrivener, K.L.; Thomas, J.J. Mechanisms of cement hydration. Cem. Concr. Res. 2011, 41, 1208–1223. [Google Scholar] [CrossRef]
  13. Thomas, J.; Ghazizadeh, S.; Masoero, E. Kinetic mechanisms and activation energies for hydration of standard and highly reactive forms of beta-dicalcium silicate (C2S). Cem. Concr. Res. 2017, 100, 322–328. [Google Scholar] [CrossRef]
  14. Zeng, H.; Jin, M.; Li, W.; Gao, C.; Ma, Y.; Guan, Q.; Liu, J. Performance evolution of low heat cement under thermal cycling fatigue: A comparative study with moderate heat cement and ordinary Portland cement. Constr. Build. Mater. 2024, 412, 134863. [Google Scholar] [CrossRef]
  15. Li, L.; Pan, L.; Lu, X.; Wang, Y.; Xu, W. Comparative study on the properties of low-medium heat cement and ordinary silicon cement. Cem. Concr. Prod. 2021, 3, 9–11. (In Chinese) [Google Scholar]
  16. Ma, Y.; Jin, M.; Tang, J.; Li, W.; Liu, J. Degradation mechanism of moderate-heat Portland cement paste under corrosion action. J. Chin. Ceram. Soc. 2024, 52, 3351–3360. (In Chinese) [Google Scholar]
  17. Lea, F.M. Chemistry of Cement and Concrete, 3rd ed.; Edward Arnold Ltd.: London, UK, 1970; pp. 257–266. [Google Scholar]
  18. Cao, H.T.; Bucea, L.; Ray, A.; Yozghatlian, S. The effect of cement composition and pH of environment on sulfate resistance of Portland cement and blended cement. Cem. Concr. Compos. 1997, 19, 161–171. [Google Scholar] [CrossRef]
  19. Wang, K.L. Fracture toughness of High-Belite cement concrete. J. Chin. Ceram. Soc. 2014, 42, 1409–1413. (In Chinese) [Google Scholar]
  20. He, Y.J.; Lu, L.N.; Struble, L.J. Effect of calcium-silicon ratio on microstructure and nanostructure of calcium silicate hydrate synthesized by reaction of fumed silica and calcium oxide at room temperature. Mater. Struct. 2014, 47, 311–322. [Google Scholar] [CrossRef]
  21. GB/T 200-2017; Moderate Heat Portland Cement, Low Heat Portland Cement China. China Standards Press: Beijing, China, 2017.
  22. ASTM 2018 ASTM C 150; Standard Specification for Portland Cement. ASTM International: West Conshohocken, PA, USA, 2018.
  23. GB 175-2023; Common Portland Cement. China Standards Press: Beijing, China, 2023.
  24. Yan, X.; Jiang, L.; Guo, M.; Chen, Y.; Song, Z.; Bian, R. Evaluation of sulfate resistance of slag contained concrete under steam curing. Constr. Build. Mater. 2019, 195, 231–237. [Google Scholar] [CrossRef]
  25. Nguyen, V.H.; Colina, H.; Torrenti, J.M.; Boulay, C.; Nedjar, B. Chemo-mechanical coupling behaviour of leached concrete Part I: Experimental results. Nucl. Eng. Des. 2007, 237, 2083–2089. [Google Scholar] [CrossRef]
  26. Yang, H.; Jiang, L.; Zhang, Y.; Pu, Q.; Xu, Y. Predicting the calcium leaching behavior of cement pastes in aggressive environments. Constr. Build. Mater. 2012, 29, 88–96. [Google Scholar] [CrossRef]
  27. Sumer, M. Compressive strength and sulfate resistance properties of concretes containing Class F and Class C fly ashes. Constr. Build. Mater. 2012, 34, 531–536. [Google Scholar] [CrossRef]
  28. Wang, X.C.; Liu, L. Study on microstructure evolution of cement mortar under dissolution based on disc method. Mater. Rep. 2016, 30, 124–129. (In Chinese) [Google Scholar]
  29. Brouwers, J.H.; Chen, W. Dependence of compressive strength on phase assemblage in cement pastes: Beyond gel-space ratio - Experimental evidence and micromechanical modeling. Cem. Concr. Res. 2014, 56, 75–83. [Google Scholar]
  30. Shen, X.; Guo, S.H.; Li, W.W.; Lu, C.; Zhang, K.Y.; Wang, M.; Wen, Z.J. Research Status on Hydration and Properties of Low-Heat Portland Cement. Bull. Chin. Ceram. Soc. 2023, 42, 383–392. (In Chinese) [Google Scholar]
  31. Carde, C.; Francois, R. Effect of the leaching of calcium hydroxide from cement paste on mechanical and physical properties. Cem. Concr. Res. 1997, 27, 539–550. [Google Scholar] [CrossRef]
  32. Murthy, M.S.; Raghavendrachar, P.; Sriram, S.V. Thermal decomposition of doped calcium hydroxide for chemical energy storage. Sol. Energy 1986, 36, 53–62. [Google Scholar] [CrossRef]
  33. Ramachandran, V.S. Influence of triethanolamine on the hydration characteristics of tricalcium silicate. J. Appl. Chem. Biotechnol. 1972, 22, 1125–1138. [Google Scholar] [CrossRef]
  34. Chen, J.J.; Thomas, J.J.; Jennings, H.M. Decalcification shrinkage of cement paste. Cem. Concr. Res. 2006, 36, 801–809. [Google Scholar] [CrossRef]
  35. Xiao, Y.; Zhang, X.Y.; Shi, X.; Zhang, L.; Lu, G.H. X-ray diffraction analysis of the hydration process of calcium silicate. J. Yi Li Norm. Univ. (Nat. Sci. Ed.) 2015, 9, 38–40. (In Chinese) [Google Scholar]
  36. Stepkowska, E.T.; Aviles, M.A.; Blanes, J.M.; Perez-Rodriguez, J.L. Gradual transformation of Ca(OH)2 into CaCO3 on cement hydration - XRD study. J. Therm. Anal. Calorim. 2007, 87, 189–198. [Google Scholar] [CrossRef]
  37. Lee, S. Performance of mortars exposed to different sulfate concentrations. KSCE J. Civ. Eng. 2012, 16, 601–609. [Google Scholar] [CrossRef]
  38. Zarzuela, R.; Luna, M.; Carrascosa, M.L.; María, P.Y.; Inés, G.L.; Teresa, M.; Miguel, A.; José, M.; María, J. Producing C-S-H gel by reaction between silica oligomers and portlandite: A promising approach to repair cementitious materials. Cem. Concr. Res. 2020, 130, 106008. [Google Scholar] [CrossRef]
  39. Villagrán-Zaccardi, Y.A.; Egüez-Alava, H.; Buysser, K.; Gruyaert, E.; Belie, N. Calibrated quantitative thermogravimetric analysis for the determination of portlandite and calcite content in hydrated cementitious systems. Mater. Struct. 2017, 50, 179. [Google Scholar] [CrossRef]
  40. Butcher, E.; Borwick, J.; Collier, N.; Williams, S. Long term leachate evolution during flow-through leaching of a vault backfill grout. Mineral. Mag. 2012, 76, 3023–3031. [Google Scholar] [CrossRef]
Materials 18 00212 g001
Figure 1. Schematic diagrams showing the exposure conditions and testing.
Figure 1. Schematic diagrams showing the exposure conditions and testing.
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Materials 18 00212 g002
Figure 2. Mass loss rates of specimens exposed to NH4Cl solution.
Figure 2. Mass loss rates of specimens exposed to NH4Cl solution.
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Materials 18 00212 g003
Figure 3. Porosity of the specimens exposed to NH4Cl solution.
Figure 3. Porosity of the specimens exposed to NH4Cl solution.
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Materials 18 00212 g004
Figure 4. Leching depths of specimens exposed to NH4Cl solution.
Figure 4. Leching depths of specimens exposed to NH4Cl solution.
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Materials 18 00212 g005
Figure 5. Compressive strength loss rate of the specimens exposed to NH4Cl solution.
Figure 5. Compressive strength loss rate of the specimens exposed to NH4Cl solution.
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Materials 18 00212 g006
Figure 6. Vickers hardness of the different cement pastes under calcium leaching.
Figure 6. Vickers hardness of the different cement pastes under calcium leaching.
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Materials 18 00212 g007
Figure 7. Ca/Si ratio versus mass loss of cement specimens under calcium leaching.
Figure 7. Ca/Si ratio versus mass loss of cement specimens under calcium leaching.
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Materials 18 00212 g008
Figure 8. XRD patterns of the cement pastes (a) before calcium leaching and (b) after being exposed for 180 days.
Figure 8. XRD patterns of the cement pastes (a) before calcium leaching and (b) after being exposed for 180 days.
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Materials 18 00212 g009
Figure 9. TG-DTG curves of the cement pastes (a) before calcium leaching and (b) after being exposed for 180 days.
Figure 9. TG-DTG curves of the cement pastes (a) before calcium leaching and (b) after being exposed for 180 days.
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Materials 18 00212 g010
Figure 10. Morphology of the OPC specimens exposed to NH4Cl leaching.
Figure 10. Morphology of the OPC specimens exposed to NH4Cl leaching.
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Materials 18 00212 g011
Figure 11. Morphology of the MHC specimens exposed to NH4Cl leaching.
Figure 11. Morphology of the MHC specimens exposed to NH4Cl leaching.
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Materials 18 00212 g012
Figure 12. Morphology of the LHC specimens exposed to NH4Cl leaching.
Figure 12. Morphology of the LHC specimens exposed to NH4Cl leaching.
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Table 1. Chemical composition and mineral composition of cement (wt.%).
Table 1. Chemical composition and mineral composition of cement (wt.%).
Sample CodesChemical CompositionMineral Composition
CaOSiO2Al2O3Fe2O3MgOSO3* R2OLOIC3SC2SC3AC4AF
LHC58.7422.823.554.284.992.430.391.3628.743.92.113.0
MHC60.2722.184.014.495.072.040.461.0637.535.53.013.6
OPC62.8320.505.613.841.703.071.311.5948.022.98.411.7
Note: * R2O = Na2O + 0.658K2O; C4AF: tetracalcium aluminoferrite.
Table 2. Physical and mechanical properties of cement.
Table 2. Physical and mechanical properties of cement.
Sample
Codes		Density
/(g·m3)		SSA
/(m2·kg−1)		Setting Time/minSoundnessCS/MPa
InitialFinal7d28d90d
LHC3.21332233343Pass25.453.669.8
MHC3.22325227332Pass30.751.465.0
OPC3.22356125277Pass41.557.165.3
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Jiang, C.; An, S.; Li, S.; Chen, Y.; Liu, J. Comparative Study on the Calcium Leaching Resistance of Low-Heat Cement, Moderate-Heat Cement, and Ordinary Portland Cement Pastes. Materials 2025, 18, 212. https://doi.org/10.3390/ma18010212

AMA Style

Jiang C, An S, Li S, Chen Y, Liu J. Comparative Study on the Calcium Leaching Resistance of Low-Heat Cement, Moderate-Heat Cement, and Ordinary Portland Cement Pastes. Materials. 2025; 18(1):212. https://doi.org/10.3390/ma18010212

Chicago/Turabian Style

Jiang, Chunmeng, Shihao An, Shuangxi Li, Yingjie Chen, and Jian Liu. 2025. "Comparative Study on the Calcium Leaching Resistance of Low-Heat Cement, Moderate-Heat Cement, and Ordinary Portland Cement Pastes" Materials 18, no. 1: 212. https://doi.org/10.3390/ma18010212

APA Style

Jiang, C., An, S., Li, S., Chen, Y., & Liu, J. (2025). Comparative Study on the Calcium Leaching Resistance of Low-Heat Cement, Moderate-Heat Cement, and Ordinary Portland Cement Pastes. Materials, 18(1), 212. https://doi.org/10.3390/ma18010212

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