Cement Hydration Research Articles

Experimental Evaluation of Concrete Blended with Eco-Friendly Bio-Sulfur as a Cement Replacement Material

Bio-sulfur (BS), extracted from landfill bio-gas via microbial methods, was examined herein as a potential cement replacement material. The study developed five modified BS variants through limestone incorporation processes (sulfur-to-limestone ratios of 1:0.5, 1:1, 1:1.5, 1:3, and 1:5). The study revealed that modified BS with higher limestone ratios demonstrates significant workability and strength reductions of over 50% with increased content, leading to the adoption of a sulfur-to-limestone ratio of 1:1. The concrete specimens exhibited compressive strength improvements of up to 12% with increased BS content, while the UPV showed proportional increases with increased BS content that remained independent of the water/binder (W/B) ratio. Statistical analysis confirmed significance with p-values below 0.05. XRD analysis identified initial cement hydrate peaks at 3 d that evolved into distinct Mg-S hydrate and Ca-Al-S hydrate formations in the BS-containing specimens by 28 d.

The shard test and nanoporomechanics reverse classical paradigm of cement hydration being contractive

Le Chatelier in 1887 and Powers in 1947 demonstrated that the volume of nanoscale C-S-H (calcium silicate hydrate) particles formed during hydration is smaller than the combined volume of the reactants-the anhydrous Portland cement and water. Hydration has thus been considered as contractive. An experiment shows that the opposite is true above the nanoscale. The porous skeleton of cement paste expands as the growing C-S-H particles push each other apart, similar to crystal growth pressure. This is significant for high-performance concretes (HPC) with low water-cement ratios (w/c [Formula: see text] 0.4), where chemical self-desiccation lowers pore relative humidity by 40%, compared to just 1% in traditional concretes (w/c [Formula: see text] 0.5). Standard American Society for Testing and Materials (ASTM) C1608 tests, using 10 mm thick water-immersed specimens, show large shrinkage because the half-time of water ingress is many decades, unable to offset shrinkage-causing self-desiccation. The present experiment, using a laser microscopy-topography technique, proves the opposite-expansion, evidenced by measuring the length changes of water-immersed HPC shards 0.5 mm thick in which the diffusion halftime, only about one hour, allows continuous resaturation of pores, canceling self-desiccation. The faster diffusion (halftime of one hour) enables continuous pore resaturation, preventing shrinkage. When sealed with paraffin oil, the shards self-desiccate and shrink. These findings align with studies since 2015, showing that models excluding hydration expansion cannot fit test data across various specimen sizes and sealing conditions. The results suggest that standardized ASTM tests for the so-called chemical shrinkage in modern concretes with very low water-cement ratios are misleading and need revision.

Influence of metakaolin on physical and mechanical properties of cement stone heat-resistant binder from mineral-technogenic raw materials of the Aral region

The results of studies of the influence of metakaolin obtained from kaolin of the Khodzhakul deposit on the process of formation of cement stone based on heat-resistant binder from mineral-technogenic raw materials of the Aral Sea region are presented. It has been established that metakaolin allows one to control the processes of hydration, setting and hardening of the cement mass. The high degree of hydration of aluminous cement in the presence of metakaolin provides porosity and sufficiently high compressive strength of the cement stone in the last 14‒28 days of hardening. Increasing the concentration of metakaolin in the cement mixture to 15 % affects not only the process of liquefying the cement mortar, reducing the setting and hardening time of the cement mass, but also increases the compressive strength of the cement stone. New formations of hydration products have been studied.

Impacts of Mg/Al-layered double hydroxide modified with polycarboxylate on the properties of cement paste

Mg/Al-layered double hydroxide (Mg/Al-LDH) has been claimed as a potential hardening accelerator of cementitious materials. The performance of Mg/Al-LDH modified with polycarboxylate superplasticizer (PCE) adopted into cementitious materials was vitally important, which was urgently necessary to be thoroughly revealed. In this paper, the adoption of four kinds of Mg/Al-LDH-PCE into cement paste has been conducted. The rheological performance and hydration process of cement paste have been analyzed. The results showed that LDH-PCE was advantageous for modifying rheological performance of fresh cement paste. With increased content of LDH-PCE, the viscosity and the yield stress of fresh binder decreased gradually. And LDH3-PCE contributed to the lowest yield stress. The adoption of LDH-PCE prolonged the introduction period of cement paste, but contributed to elevated exothermic peak in the acceleration period and enhanced cumulative hydration heat flow, indicating enhanced hydration of silicates. Due to the enhanced cement hydration with the adoption of LDH-PCE, more hydration products formed in the matrix, and contributed to improved compressive strength. Among the four kinds of LDH-PCEs, the application of LDH3-PCE led to the highest compressive strength of cement mortar at 28d, with 15.6% increment compared with the blank sample.

Effect of a novel negative temperature early-strength agent in improving concrete performance under varying curing temperatures

This study investigates the effect of a novel negative temperature early-strength agent (NEA) in enhancing concrete performance under varying curing temperatures, with a discussion on the underlying mechanism through analysis of hydration products and microstructure.The results indicate NEA markedly accelerates early cement hydration, reduces setting time, and enhances compressive strength. Moreover, the efficacy of NEA is more pronounced at lower temperatures. With an optimal dosage of 3%, the incorporation of NEA leads to a remarkable 285.9% increase in compressive strength at 28 days under -5°C curing temperature. Despite accelerating cement hydration can induce increased chemical shrinkage, NEA effectively mitigates early freezing expansion under negative temperature and significantly diminishes chloride ion permeability. Higher temperatures facilitate early cement hydration but also compromise long-term hydration continuity. Consequently, the highest hydration degree and loweast porosity are observed at 28 days under 5°C curing temperature. NEA's air-entraining component introduces numerous superfine pores into the paste, augmenting early pore volume while optimizing pore structure. As the early-strength component fosters hydration, these pores undergo further filling and refinement, ultimately reducing the total pore volume at 28 days. This study provides insights into optimizing concrete performance in cold environments.

CaCO3 coating of off-specification fly ash for upcycling in cementitious materials

To address this challenge of shortage of specification-grade fly ash(SGFA) and recycling of off-specification fly ash(OSFA), this research proposes a novel approach of coating OSFA with nano-CaCO3. This improves the surface characteristics of the particles and creates nucleation sites that enhance cement hydration, thus potentially improving the fundamental properties of cementitious materials incorporating OSFA. The first step in this process involves optimizing the quantity of nano-CaCO3 coating on OSFA to achieve the best mechanical properties for concrete applications. Subsequently, experimental investigations were conducted to compare the mechanical properties of cementitious pastes prepared with original OSFA, OSFA and nano-CaCO3 powders, and coated OSFA. Isothermal calorimetry and pore structure analyses indicated that the coating treatment transformed OSFA from a detrimental additive to a beneficial one for concrete. This coating significantly strengthened the OSFA particles and promoted cement hydration, consequently enhancing the mechanical properties of cementitious composites containing OSFA. This innovative method offers a promising solution for addressing the fly ash shortage in the concrete industry while minimizing the need for land disposal of OSFA.

Study on sewage erosion resistance of nano titanium modified coral concrete

Sewage environments can significantly erode and degrade coral concrete, impacting its structural longevity. Moreover, the curing water environment greatly influences coral concrete's resistance to sewage erosion. This study investigated the modification of coral concrete with nano TiO2 to enhance its sewage erosion resistance. Concrete specimens with four different mass fractions of nano TiO2 were prepared and cured in three environments. Tests for compressive strength, flexural strength, and mass loss were conducted before and after 180 days of sewage exposure, and a corrosion coefficient was defined to evaluate resistance to sewage corrosion. While nano TiO2 significantly improved the mechanical properties and sewage erosion resistance of coral concrete, oxalic acid and seawater environments had adverse effects. Furthermore, increasing the nano TiO2 mass fraction initially enhanced and then reduced strength and resistance, while mass loss rates first decreased and then increased. The optimal nano TiO2 dosage of 4% resulted in a maximum increase of 22.2% in compressive strength, 33.2% in flexural strength, a 0.06 increase in the compressive corrosion resistance coefficient, and a 0.1 increase in the flexural corrosion resistance coefficient. At this dosage, compressive strengths of coral concrete cured in oxalic acid and seawater were 97.8% and 93.9% of those in freshwater, while flexural strengths were 97.8% and 94.4%, respectively, with slight decreases in corrosion resistance coefficients, accompanied by higher mass loss rates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that nano TiO2 promotes cement hydration, forming a dense structure by filling matrix pores. However, oxalic acid reacts with Ca(OH)2 to form calcium oxalate, slowing cement hydration, while MgCl2 in seawater reacts with Ca(OH)2, forming expansive Mg(OH)2, which increases internal concrete pores.

Effect of sodium metasilicate on the early-age hydration and setting behavior of alkali-activated common cements containing slag

Effect of sodium metasilicate on the early-age hydration and setting behavior of alkali-activated common cements containing slag

Hydration, Hardening Properties, and Microstructure of Magnesium Phosphate Cement–Emulsified Asphalt Composites across Various Stoichiometries

Hydration, Hardening Properties, and Microstructure of Magnesium Phosphate Cement–Emulsified Asphalt Composites across Various Stoichiometries

Early age hydration of cements containing ye’elimite (YCC) produced with spent catalyst (SFCC)

Resumo Diante dos impactos ambientais associados à produção do cimento Portland convencional, o estudo de cimentos especiais de reduzido impacto ambiental tem sido uma tendência. Neste contexto, os cimentos contendo ye’elimita (YCC) se destacam devido à baixa emissão de CO2. Apesar das vantagens ambientais, a alta demanda por alumínio limita economicamente a produção destes cimentos. Uma alternativa para viabilizar a sua produção é o uso de matérias-primas residuais como fonte de Al2O3, a exemplo do SFCC (catalizador gasto do craqueamento catalítico de leito fluidizado). Diante disso, este trabalho tem como objetivo avaliar a hidratação na idade inicial de cimentos YCC produzidos a partir do coprocessamento do SFCC. Para isso, foram produzidos seis clínqueres com diferentes teores de ye’elimita, com e sem SFCC. Estes foram caracterizados por DRX/Rietveld. As pastas foram avaliadas por TG/DTG e DRX/Rietveld para compreender o mecanismo de hidratação em idade inicial destes cimentos. Foi possível sintetizar as principais fases dos YCC, nos clínqueres com e sem SFCC. Além disso, na idade avaliada, as pastas com e sem SFCC apresentaram composição de fases comparáveis indicando o potencial de coprocessamento do SFCC neste tipo de cimento.

Research on the Durability of Composite Epoxy Resin Modified Repair Mortars Based on Water-Oil Gradient Phase Change: From Macroscopic to Nanoscopic Scales

With the rapid pace of urbanization, global demand for concrete is increasing, shifting focus from construction to repair and maintenance. Traditional cement-based repair materials generally suffer from brittleness and poor durability, failing to meet the growing demand for durable repair solutions. We developed a water-oil gradient composite epoxy resin (CEP) modified cement-based repair mortar (MCEP) using self-synthesized water-based epoxy resin (WEP) and oil-based epoxy resin (EP). Durability tests showed that CEP-modified cement mortar exhibited improved resistance to solution penetration, shrinkage, acid corrosion, and freeze-thaw cycles, with increased CEP content positively affecting mortar durability. Notably, the addition of CEP not only enhanced the interface bonding strength between MCEP and old concrete but also maintained good bonding stability under moisture erosion. X-CT and SEM microstructural tests revealed that CEP is evenly distributed in the cement paste, forming a cement-polymer interpenetrating network structure, which improves crack resistance and reduces solution penetration in MCEP. Molecular dynamics simulations explored the adsorption of CEP on calcium aluminate hydrate (AFt), a key cement hydration product, and the moisture transport mechanisms in AFt and CEP-modified AFt nanopores. Results indicated that CEP molecules adsorb onto AFt via ionic and hydrogen bonds, demonstrating good stability. During moisture penetration, CEP reduced water transport efficiency in the nanopores. CEP modification improved the crack resistance and durability of cement repair mortars, providing valuable insights into molecular-scale enhancements in water permeability resistance. This study aims to contribute to the design and practical application of water-oil gradient epoxy resins and other polymer-modified cement-based repair materials.

Sustainable utilization of feldspar powder from lithium extraction byproducts as road construction material

In order to reduce the storage cost and avoid environmental hazards of feldspar powder waste from lithium extraction byproducts, this work investigated the feasibility of ordinary silicate cement-stabilized feldspar powder-lateritic clay (FP-LC) composite as road construction material. Firstly, preliminary mix design of the new material was conducted to determine the optimum moisture content and maximum dry density. Subsequently, the effects of ratio of FP to LC on the mechanical properties of the composite were investigated through unconfined compressive strength (UCS), California bearing ratio (CBR) and shear strength tests. Finally, the strength formation mechanism of the FP-LC mixture was analyzed in combination with SEM and XRD testing. The results indicate that the UCS after 14 d curing, CBR and cohesive strength of FP simply stabilized by 6% cement is 0.95MPa, 87.3% and 140.64 kPa, respectively, which can meet the requirements for subgrade materials. The addition of LC significantly improves the mechanical properties of the composite. The mass ratio of 40% FP to 60% LC results in the optimal UCS after 14 d curing, CBR and cohesive strength with 1.6MPa, 164.1% and 250.16 kPa, respectively, which makes it applicable as subbase materials for medium-light traffic levels. The particle closest packing analysis and SEM and XRD characterization demonstrated that the enhancement of UCS, CBR and shear strength comes from compact arrangement of FP and LC particles and the bonding effect of cement hydration products between them. This work proposes an eco-friendly and sustainable utilization approach of feldspar powder from lithium extraction byproducts as road construction material, which are important to overcome the challenges of both waste management and resource shortage for new energy and highway industries, respectively.

Microbial self-healing cement-based materials co-reinforced by Mg2+: using recycled aggregates as carriers

Microbial self-healing cementitious materials have attracted widespread attention due to their targeted repair of cracks, but their practical application is limited by cost. In this study, self-healing mortar was prepared using recycled concrete fine aggregate as a cementitious material to investigate the effect of magnesium ions on crack repair, to explore the compatibility of self-healing components and cement, and to assess the cost and environmental impact of this self-healing mortar. The results showed that the mineralization efficiency was the highest at 31.1% with a Ca/Mg molar ratio of 3, and the 28 d crack repair rate reached 97.8%; yeast and peptones in the self-repairing system slowed down the rate of cement hydration, whereas magnesium chloride and calcium lactate facilitated the hydration reaction. The use of recycled concrete fine aggregate (RCA) reduces the cost of the self-repairing material and the CO2 emission, and improves the application of microbial self-healing cementitious materials potential.

Effect of CO2 wet mineralized steel slag-granulated blast furnace slag composite admixture on mechanical properties and chloride corrosion resistance of mortar

Given the global emphasis on environmental issues, addressing the substantial quantities of steel slag and greenhouse gases produced by the steel industry has garnered significant attention from researchers worldwide. This research investigates the application of wet CO2 mineralization for the treatment of steel slag. The microstructure and phase composition of steel slag are analyzed and compared before and after the mineralization process using SEM, XRD, TG-DTA, and particle size analysis. Composite mineral admixtures were prepared by mixing steel slag and granulated blast furnace slag to replace 50% cement. The study examined the influence of varying quantities of mineralized steel slag in the admixture on the mechanical properties, chloride permeability and autoclaved stability of mortar. The effects were elucidated through the application of SEM, XRD, TG-DTA, FTIR and early hydration heat testing. The results show that a layer of mineralized shell is formed on the surface of steel slag following wet mineralization treatment, which strengthens the mechanical adhesion between cementitious materials. The calcite produced by the mineralization reaction acts as a nucleation agent and micro-aggregate in the cement hydration process, leading to a significant enhancement in the early strength of mortar. When the mineralized steel slag content is below 30%, it positively impacts the strength of mortar. When the content is below 20%, it has little effect on the chloride ion permeability of mortar.

Controllable fabrication of the luminescent photocatalytic material AgB/SMSO for application in cement: Optimization of doping strategies and all-weather degradation of pollutants

This paper presents an innovative luminescent photocatalytic material, Ag3PO4/BiVO4/Sr2MgSi2O7:(Eu2+, Dy3+) (AgB/SMSO), which overcomes a pivotal limitation of photocatalysts—dependence on a light source—and effectively remediates pollutants and augments cement-based composite properties. The efficient carrier separation facilitated by Ag3PO4, in conjunction with the broad spectral response of BiVO4, enables AgB/SMSO to harness the internal luminescent properties of SMSO as a persistent light source, achieving continuous degradation of pollutants, which reveals the exceptional afterglow characteristics and photocatalytic activity of AgB/SMSO. At a 1:1:40 ratio, AgB/SMSO maintained its catalytic efficacy for over 8 h in the dark (methylene blue degradation rate of 70.43%), surpassing the 3-hour limit of current luminescent photocatalysts. Furthermore, the impact of integrating AgB/SMSO with cement on early-stage cement hydration, morphology, and micromechanical properties was comprehensively assessed. Ultimately, the overall photocatalytic capability of the derived AgB/SMSO cement-based composites was evaluated through experiments, revealing the synergistic mechanisms involved. This study not only enriches the theoretical understanding of photocatalysis but also provides a robust technical foundation for the innovation of environmentally friendly building materials and the advancement of sustainable urban development.

Application of porous luffa fiber as a natural internal curing material in high-strength mortar

This study explores the potential of renewable plant fibers as internal curing (IC) materials, analyzing their potential in high-strength mortar (HSM) applications. Experiments involving the incorporation of different volumetric ratios of luffa fiber into concrete assessed impacts on autogenous shrinkage (AS), mechanical properties, and microstructure. The research found that the addition of luffa fibers extended both the setting times of the mixture, and after final setting, continued the hydration reaction by releasing internally stored water. Compared to the control group, luffa fibers significantly reduced AS by up to 56.87%, primarily due to their high-water absorption capacity (211%), which mitigates the internal capillary pressures during the cement hydration process. Moreover, the inclusion of luffa fibers significantly affected the concrete's mechanical properties: a 1% luffa addition enhanced the compressive strength at 28 days by 7.6% over the control; concrete with 2% luffa fiber exhibited the highest flexural strength at 28 days, showing a 9.4% increase over the control. Microstructural analysis revealed that luffa fiber not only promoted continued hydration but also increased the content of hydration products and enhanced the compactness of the cementitious matrix. Overall, luffa fibers effectively reduce HSM’s AS and enhance its mechanical properties and microstructure, showing potential to improve concrete performance.

Rheological properties of cement paste with in-situ polymerization of sodium acrylate: Roles of polymerization and hydration

In-situ polymerization modified cement paste shows a great potential in 3D concrete printing (3DCP) due to its enhanced rheological properties. Unlike direct adding conventional polymer, how in-situ polymerization and cement hydration synergistically regulate the rheology of cement paste with different monomer dosages remains unclear. Here, we investigate the rheological properties of in-situ polymerization modified cement paste with different dosages of sodium acrylate (SA) to reveal the roles of cement hydration and polymerization. When the monomer dosage is lower (1 % and 3 %), the polymerization inhibits the cement hydration without providing sufficient contribution to the structural development of cement paste, resulting in the decreased rheological properties, such as static/dynamic yield stress and structural build-up rate. On the contrary, once the monomer dosage reaches a higher level (5 % and 7 %), the resultant polymers can gradually form a network interwinding within the cement particles, thus leading to enhanced rheological properties, regardless of the more severely inhibited cement hydration.

Corrosion and carbonation resistance of mortars incorporating rice husk ash

The Rice Husk Ash (RHA) was obtained by incinerating Rice Husk with a temperature of 300℃, 500℃, 700℃, and then added into control mortars as replacement of cement to prepare modified mortars. The microstructure of RHA was characterized by FT-IR test, then the corrosion and carbonation resistance of mortars were investigated. Additionally, the microstructure of cement mortars was revealed using the SEM test. Researched results indicated that the cement hydration is improved and the mezzanine structure of RHA at 700℃ is compact, while the mezzanine of RHA at 300℃ is composed of crisscross plates. Moreover, the incorporation of RHA improves the corrosion and carbonation resistance of mortars.

The mechanism of accelerator types on calcium leaching in shotcrete

In regions characterized by abundant water, the surrounding rock exhibits a high water content, which leads to calcium leaching in the shotcrete of the tunnel. This poses a significant hazard to the safe operation of the tunnel. The experimental design focuses on three commonly used accelerators in the market and investigates the leaching process of samples under accelerated leaching conditions. By integrating XRD, TG, and SEM-EDS testing, the calcium leaching mechanism of shotcrete was elucidated. Results revealed that sodium aluminate-based liquid accelerator exhibits the highest detrimental effect on mortar resistance against calcium leaching, followed by fluoroaluminic acid-based liquid accelerator. Additionally, an appropriate amount of aluminum sulfate-based liquid accelerator can effectively mitigate performance degradation during leaching processes in shotcrete. The addition of aluminum sulfate reduces CH content and C-S-H Ca/Si ratio of hydration products, leading to wrapping AFt generated by cement hydration with C-S-H and thereby slowing down solid calcium-containing substance dissolution in hydration products. A moderate accelerator can enhance shotcrete porosity so that corrosive products like CaCl2 accumulate in existing pores first, reducing shotcrete performance deterioration rate.

Study on improving the performance of engineered cement-based composites by modifying binder system and polyethylene fiber/matrix interface

In this study, cement, rice husk ash (RHA), silica fume, mineral powder and fly ash were used as multi-component cementing materials, and the polyethylene (PE) fiber was modified by cellulose nanocrystal (CNC) to develop an Engineered Cementitious Composites (ECC) with high ductility and strength. The hydration heat and X-ray diffractometer (XRD) results indicate that RHA delays the early hydration of cement, its pozzolanic effect refines the internal porosity of hydration matrix and improves the compactness of ECC samples. Moreover, RHA increases the interfacial properties between fiber and cement matrix, reduces the first cracking strength and significantly improves the tensile strain rate of ECC. With the increasing content of RHA, its reinforcement effect becomes more obviously. The strain rate of ECC samples that uses RHA to replace 40 % of cement can reach 6.81 %. However, once the content of RHA is too high, the quality of cement involved in hydration will be significantly weakened, which reduces the amount of hydration products and has a negative impact on the compressive strength. By CNC coating, the active groups can be coated to the fiber surface to improve the fiber’s wettability. Which has promoted the growth of hydration products on the fiber surface, enhancing the fiber/matrix interface properties, and improved the ductility of ECC. CNC coating can also make up for the loss of compressive strength caused by RHA. The molecular dynamics simulation results show that unmodified PE fiber hardly to form a stable bond with C-S-H. However, CNC can adsorb with C-S-H through hydrogen and Ca-O bonding, and can also interaction with PE fiber by hydrogen bonding. Herein, CNC acts as an intermediate to connect PE and C-S-H, increase the interface stability of fiber/cement matrix, improve the interface bonding, and thus enhance the ductility of ECC. Developing multi-binder system and reinforced fiber/interface can significantly reduce the amount of cement used in ECC, and understanding the enhancement mechanism is beneficial to guide the optimal design of ECC.