Early Cement Hydration Research Articles

Dynamic characteristics and microscopic mechanism of graphene oxide modified coastal soft soil under small strain

Graphene oxide (GO) has been shown to improve the static mechanical properties of cement soils. However, the dynamic mechanical properties of GO-modified cement soils are rarely investigated. Therefore, in this study, the effects of different confining pressures, GO contents, and curing ages on the small-strain dynamic shear modulus (G) and damping ratio (D) of GO-modified coastal cement soil (GOCS) are investigated via resonant column tests. The results show that the G of GOCS increases with the confining pressure, GO content, and curing age, whereas D decreases. Moreover, the GOCS indicate the highest stiffness improvement when 0.05 % GO is used as a modifier. The variation patterns of the maximum dynamic shear modulus and maximum damping ratio with the increase in the confining pressure, GO content, and curing age of the GOCS are consistent with the measured results. Microstructural analysis shows that the incorporation of GO can promote the early cement hydration of GOCS and increase its internal calcium-silicate-hydrate gel as well as its crystal types and numbers. The filling and bridging effects of GO not only enhance the stiffness of GOCS, thus increasing its G value, but also effectively reduce the energy consumption of the vibration wave in the sample, thus reducing its D value. The results of this study can provide important references and guidance for the design and construction of coastal soft-soil roadbed projects.

Effect of Stöber Nano-SiO2 Particles on the Hydration Properties of Calcined Coal Gangue-Blended Cement.

This study focuses on the calcined coal gangue (CCG)-blended cements containing Stöber nano-SiO2 (SNS) particles. The effects of SNS particles on the workability, hydration behaviour, mechanical properties and microstructure evolution of the blended cements were comprehensively investigated at curing ages ranging from 1 to 28 d. The hydration behaviour was studied via isothermal calorimetry test, X-ray diffraction (XRD) and thermogravimetric (TG) tests. The microstructural evolution was studied using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The results show that the incorporation of SNS led to a significant reduction in fluidity, particularly at an SNS content of 3%. The SNS significantly increased the compressive strength of the CCG-blended cement at all curing ages, and the optimum SNS content was found to be 2%. SNS significantly accelerated not only the early cement hydration but also the pozzolanic reaction of CCG at later curing ages, resulting in a decrease in portlandite, as evidenced by the isothermal calorimetry, XRD and TG analysis. Microstructural analysis shows that the incorporation of SNS effectively refined the pore structure of the CCG-blended cement, resulting in the formation of a dense microstructure. All these beneficial effects of SNS provides advantages in the development of the compressive strength of the CCG-blended cement at all curing ages.

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Decoupling the physical and chemical effects of silica fume in ultra-high performance concrete (UHPC)

Silica fume (SF) has practically become an essential phase in ultra-high performance concrete (UHPC) proportion due to its superior physical effect (filler effect) and chemical effect (pozzolanic reaction effect). However, the decoupling of these two effects was rarely investigated, which prevents a deeper comprehension of SF’s role in UHPC system. Accordingly, titanium dioxide (TD), an inert filler with similar particle size and shape to SF was selected as a comparison. Results showed that the preferential adsorption of SF on PCE molecules can shorten the induction period of UHPC pastes, and simultaneously benefited from the SF’s seeding effect, both of which can increase the cumulative heat release of UHPC pastes and promote the early cement hydration. In the later stage, SF has the possibility to reduce cement hydration, always exhibiting a lower promoting effect compared to TD. However, the pozzolanic reaction of SF dominates the sustained compressive strength development of UHPC by consuming CH to generate extra C-S-H with lower Ca/Si ratio, which reduces the non-homogeneity and connectivity of UHPC pores.

Towards a further understanding of cement hydration at the early-age stage in the presence of hydrophobic silane IBTEO

Hydrophobic silane hinders internal water penetration by tuning the surface wettability of concrete. The presence of hydrophobic groups in the silane was observed to adversely influence early cement hydration. This study employs a combination of calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma optical emission spectroscopy (ICP-OES), and total organic carbon (TOC) analysis to investigate the effects of hydrophobic isobutyl-triethoxysilane (IBTEO) on cement hydration. The results demonstrate that the silicate reaction integral to cement hydration slows as the concentration of hydrophobic silane increases. The nucleation of hydration products, such as calcium silicate hydrate (C–S–H), exhibits heightened sensitivity to the presence of hydrophobic silane. Although hydrophobic silane marginally impacts the initial dissolution of cement particles, it significantly decreases ion dissolution after 60 min. This reduction in hydration rate and the consequent delay in the emergence of the second exothermic peaks in hydration are attributable to the negative impact of the hydrophobic functional groups on the silicate reactions and the formation of hydrogen bonds. These findings offer new perspectives on the impact of hydrophobic silanes on cement hydration, potentially guiding the development of silane-cement systems towards enhanced superhydrophobicity and improved permeability.

High temperature calcined red mud-cement mortar: Workability, mechanical properties, hydration mechanism, and microstructure

To efficiently utilize red mud (RM) in cement-based materials, this study employed high-temperature calcination to enhance RM's pozzolanic activity. Calcined RM replaced cement in RM-cement mortar, examining the effects of different calcination temperatures and RM addition amounts on the workability and mechanical properties of the mortar. Additionally, XRD, FTIR, SEM-EDS, TAM-Air, and TG were used to explore the hydration mechanism and microstructure of RM-cement mortar. Research showed that as the calcination temperature increased, minerals like Calcite, Hematite, and Cancrinite in RM began to decompose, and the glassy structure increased. At 800 °C, the serrated and amorphous diffraction peaks significantly increased. Calcined RM positively influenced the setting and hardening of cement mortar but negatively affected its fluidity. The optimal calcination temperature for RM was 800 °C, with an optimal addition amount of 10%. The compressive strengths of RM-cement mortar at 3, 7, and 28d, with optimal conditions, are 9.62, 29.94, and 40.12 MPa, respectively, showing increases of 4.25, 1.72, and 1.39 times over untreated RM-cement mortar. When RM was calcined to 800 °C, the diffraction peak intensities of Portlandite, C–S–H, and Ettringite in the RM-cement paste were the highest, and the hydration products interwove to form a dense microstructure. Adding calcined RM extended the induction period of cement, increased the rate of heat release, shortened the acceleration period, and further accelerated the rate of heat release. Nevertheless, the alkaline components in calcined RM pose a certain hindrance to the later stages of cement hydration. In summary, calcining RM to 800 °C enhanced its pozzolanic activity, improved the workability, early hydration, and early strength of cement, and reduced cement consumption and CO2 emissions.

Influence of Nano-Activated CaCO3-Metakaolin on Early Strength and Microstructure of Cement

The early strength, microstructure, and structure of cement mortar under low-temperature curing conditions were investigated through compressive strength tests, scanning electron microscopy, x-ray diffraction, synchronous thermal analysis (thermogravimetric analysis coupled with differential scanning calorimetry), and nuclear magnetic resonance tests. The study focused on the impact of the single addition of nano-activated CaCO3 (NAC) and the simultaneous addition of metakaolin (MK) on cement mortar. The results indicate that the addition of NAC accelerated the early hydration of cement. At a 1% dosage, the compressive strength increased by 6.84%, 14.77%, and 18.58% at 1 day, 3 days, and 7 days, respectively. When 5% MK was co-added, the compressive strength increased by 15.16%, 27.85%, and 21.66% at 1 day, 3 days, and 7 days, respectively. The combination of NAC and MK accelerated the hydration of cement, refined the products, reduced the porosity, improved the microstructure, and enhanced the early compressive strength of cement-based materials.

The influence of low temperature rise polymer on early cement hydration from the point of view of hydration kinetics and thermodynamics

The key to studying the influence mechanism of additives on the cement hydration process lies in revealing the influence process of admixtures on the evolution of chemical driving forces of relevant phases in the cement hydration process. This study is the first to adopt the Krstulovic-Dabic (K-D) kinetic model to investigate the hydration mechanism and kinetic parameters of a cement system with a low-temperature polymer (CAMC). Gibbs Energy Minimization Selektor (GEMS) was used for pore solution composition analysis of cementitious system and calculation of saturation index. The results show that the exponent and reaction rate constant of the (K-D) model decrease with the increase of hydration age and CAMC content, with K1 significantly greater than K2 and K3 being the smallest. The saturation index of calcium hydroxide (CH) and ettringite (AFt) is greater than 0, indicating that both phases are supersaturated in all samples. The transition time from supersaturation to undersaturation of gypsum is delayed, confirming the delayed consumption of gypsum by CAMC. This provides new insights into the effects of admixtures on cement hydration and the mechanisms of cement hydration.

Influence of silica fume addition and content on the early hydration of calcium aluminate cement – The role of soluble silicon

Hydration of a commercial white calcium aluminate cement (CAC) at 23 °C was modified by silica fume (SF) addition in varying amounts. The process was followed by heat flow calorimetry, quantitative in-situ XRD analysis and Gillmore needle experiments supplemented by pore solution analysis, thermodynamic modelling, and 1H-TD-NMR measurements. Lower SF/cement ratios accelerate the hydration of CAC. Higher ratios trigger an intermediate heat flow event, which is correlated to increased setting rates. This intermediate event (IE) initiates an induction period of constant duration, which appears later with increasing SF/cement ratios. Results show the IE is caused by an initially hindered CA dissolution, in which dissolved silicon provided by SF plays a crucial role. Increasing the [Si] concentration in the pore solution leads to a further retardation of the IE and eventually prevents the entire hydration reaction if a critical amount is reached. A detailed model explaining the observed behavior is proposed.

Early hydration of hot-stuffy steel slag-cement composite pastes: isothermal calorimetry and phase evolution

Hot stuffy self-disintegration has become an advanced and popular steel slag treatment method in recent years, presenting numerous advantages. Hot-stuffy steel slag (HSS) obtained by self-disintegration treatment technology with waste heat has different compositions and properties compared with ordinary steel slag (OSS). Although the properties of OSS as a mineral admixture have been reported by numerous articles, few researches focus on HSS, especially its effect on early cement hydration. In this paper, the early hydration of HSS-cement composite pastes is investigated from the insights of isothermal calorimetry and phase evolution. Effects of HSS on the setting time, hydration heat, reaction product, reaction degree, microstructure, and pore solution were systematically studied and compared with those of OSS. Results show that, unlike OSS, HSS hardly ever retards the early hydration of cement. This is caused by the differences in the composition of HSS and OSS due to the diversity in their production treatment processes. During the hot stuffy self-disintegration, the key retarding component in OSS, such as C12A7, reacts with water and their contents in HSS are reduced. It is found that hot stuffy self-disintegration is an effective method to mitigate the retardation effect of steel slag on the early hydration of cement. This study provides a better understanding of HSS, which is crucial for its utilization in cementitious materials.

Hydration of Portland cement in the presence of triethanolamine and limestone powder: Mechanical properties and synergistic mechanism

The study systematically examined the hydration and strength development patterns within ordinary Portland cement (OPC) when triethanolamine (TEA) and limestone (LS) powder were introduced, with a particular emphasis on unraveling their synergistic effects. The findings reveal that 0.02 % TEA addition has a beneficial impact on the early strength of OPC while diminishing later strength. However, the co-incorporation of LS powder effectively eliminates the detrimental effect of TEA on later strength while maintaining the growth of strength. In addition, the concurrent addition of TEA and LS powder reduces the overall cement porosity as well as modulates the pore size distribution, increasing the proportion of non-harmful pores. Through monitoring the hydration process of the OPC, a notably positive synergistic effect between TEA and LS powder is revealed. Firstly, the complexation of TEA indirectly enhances the dilution impact of LS powder, leading to a substantial enhancement in early cement hydration. Secondly, the nucleation effect of LS powder effectively counteracts the inhibitory influence of TEA on C3S, thus eliminating the associated drawbacks. Most significantly, the synergistic effect between TEA and the chemical effect of LS powder accelerates the hydration of C3A and C4AF while preserving ettringite, ultimately resulting in reduced porosity of the samples.

Hydration characteristics and kinetic analysis of polyacrylamide (PAM) anti-dispersion cement-based materials

Abstract Through phase analysis and quantitative calculations of the hydration process, the inclusion of polyacrylamide (PAM) in Anti-dispersion Water Paste affects its hydration characteristics is discovered. Specifically, the presence of PAM reduces early reactivity while accelerating progress in the middle to late stages of hydration. By employing K-D hydration kinetic analysis, it is confirmed that the use of PAM results in the formation of a multi-nucleation homogeneous point system within the cement slurry. This system prolongs the NG (nucleation and growth) process time, increases the hydration degree during the transition from NG to I (induction) process, and inhibits the heterogeneous precipitation of hydration products. Consequently, the early hydration of cement is hindered. As the hydration reaction advances, the microstructure of the product under multi-nucleation points increases the specific surface area. This gradual breakthrough of the hydration threshold barrier shortens the duration of the phase boundary reaction process and reduces the hydration degree during the I and D (diffusion) processes. Consequently, the late-stage hydration rate is accelerated.

Evolution of early hydration in mortar by using waste dolomite powder as a micro-aggregate

The evolution of early hydration in cement – based material is always one of important issues for investigating their engineering application. This study investigated the early hydration reaction of mortars containing different waste dolomite powder (WDP) contents. Compared to the reference sample (WDP0), the hydration process, hydration products, pore structure and mechanical properties of samples prepared by WDP were studied at the early stage. For the hydration process, the 1H low – field nuclear magnetic resonance (NMR) and chemical shrinkage testing results indicated that the process of early hydration of cement could be significantly accelerated by incorporating WDP. Meanwhile, the quantities of hydration products (Portlandite and calcite) in samples with WDP have a significant variation by X-ray diffraction results and thermogravimetric analysis. In addition, the WDP40 has denser pore structure and higher mechanical properties than WDP0. After curing 3 d, the pore volume of WDP40 has a reduction of 17.84 %, the flexural and compressive strength of WDP40 were increased by 6.6 % and 18.06 %, respectively. Based on the mechanism analysis, the filling effect and nucleation effect of WDP in mortars contributed to the improvement of early cement hydration. This study is meaningful to evaluate the impact of WDP on the evolution of early cement hydration, which is expected to offer a reliable reference for the application of inert materials in cement – based materials.

Effect of Wet Grinding Concrete Slurry Waste on Hydration and Hardening Properties of Cement: Micro-Nano-Scale Modification.

The concrete slurry waste (CSW) produced by concrete mixing plants is a type of hazardous waste that is difficult to handle. To better recycle the CSW separated from the aggregates, this study uses a variety of wet-grinding processes to refine the solid in it, replaces some of the cement with the solid particles in wet grinding concrete slurry waste (WCSW), and investigates the properties of WCSW and its effect on the hydration and hardening properties of cement. The results show that a suitable wet-grinding process can ensure that the particle size in WCSW is less than 10 μm, the particle morphology is more flat, and the degree of hydration is higher. The WCSW particles can promote early cement hydration; after adding WCSW, the heat release peak of cement hydration appears earlier and more early hydration products are produced, and with the increase in the substitution amount, the promoting effect on early cement hydration will be more significant. The WCSW particles have a great effect on improving the strength of mortar, especially in the early stage. At 1 d, when the substitution amount is 7.5 wt.%, the compressive and flexural strength is increased by 43.67% and 45.04%; this is related to the filling of matrix pores and the improvement of the interface transition zone by micro- and nanoparticles. After the wet grinding of CSW, fine WCSW particles are obtained, which can improve the performance of cement-based materials by replacing cement.

Microstructure, mechanical properties and interaction mechanism of seawater sea-sand engineered cementitious composite (SS-ECC) with Glass Fiber Reinforced Polymer (GFRP) bar

With increasing demand for sustainable and long-lasting materials, seawater sea-sand engineered cementitious composite (SS-ECC) has emerged as a promising alternative to conventional concrete in near-ocean construction projects. Glass fiber reinforced polymer (GFRP) bar with excellent corrosion resistance is an ideal choice for these applications. This study evaluated the bond performance of GFRP bars embedded in normal-strength ECC with polyvinyl alcohol (PVA) fibers and high-strength ECC with polyethylene (PE) fibers through pull-out tests. Additionally, tests were conducted on GFRP bars in pristine ECC made with freshwater and river sand for comparison. Further investigation explored the structural properties and uncovered load transfer mechanisms. Results indicated that saline content facilitated early cement hydration of normal-strength ECC, resulting in finer pore structure (10.5% lower porosity and 12.5% lower sorptivity), slightly enhanced compressive performance (1.2% higher compressive strength and 8.3% higher elastic modulus), denser microstructure at GFRP-ECC interface (13.7% lower porous transition zone thickness, 19.2% narrower transition zone and 19.7% higher Ca/Si ratio), and superior bond performance (28.3% higher bond strength and 22.6% higher fracture energy). Conversely, saline content imposed a limited impact on the mechanical properties of high-strength ECC, primarily attributed to the ultra-fine microstructure and early strength characteristics exhibited by the silica fume (SF)-based cementitious binder.

Use of coal chemical industry by-product coal gasification fine ash as supplementary cementitious materials in cement: Chemical excitation, hydration and hardening characteristics

In order to realize the resource utilization of coal gasification fine ash (CGFA) in cement fields, a key is to solve the problem of low activity of CGFA. This paper studied the performance of CGFA as supplementary cementitious materials in cement. Furthermore, to enhance the activity of CGFA, targeted chemical activators were employed, with triethanolamine (TEA) and simulated high salinity wastewater (SHSW) chosen as representatives of organic and inorganic agents, respectively. It was found that CGFA had a synergistic effect with cement at a low dosage, while the inhibition effect on cement hydration was dominant at a high dosage. TEA promotes the strength development of the CGFA-cement system by promoting early hydration of cement and dissolution of active minerals in CGFA. However, the promoting effect of TEA on cement hydration will change to an inhibiting effect with the development of time, which will have an adverse effect on the development of strength. In general, the optimal dosage of TEA is 0.03 %, which can increase the 28-day activity index of CGFA from 69.1 % to 75.6 %. SHSW accelerates the strength development of the CGFA-cement system by promoting the hydration of cement and facilitating the dissolution and hydration of active minerals in CGFA. In addition, X-ray diffraction results show that a new hydration product, Friedel’s salt, is formed under the excitation of SHSW. But this new hydration product will gradually dissolve as the pH decreases. The 28-day activity index of CGFA can be increased to a maximum of 83.3 % under the excitation of 2 % SHSW.

Investigation on the early proceeding of cement hydration containing dispersed nano Calcium Silicate Hydrated (CSH) seeds

Steam curing process is a traditional method for accelerating the progression of cement hydration to satisfy the rapid development of compressive strength in precast concrete industry. However, steam curing would release significant amount of CO2 into the atmosphere. In order to avoid the serious environmental pollution caused by the steam curing process, Calcium Silicate Hydrate (CSH) dispersed by comb-like polycarboxylate superplasticizer (PCE), shorted as dispersed nano CSH seed, was utilized to promote the early cement hydration at normal temperature. This investigation aims at disclosing the hydration process of cement and the microstructure evolution of cement paste in the presence of dispersed nano CSH seed during the early stage via setting time, ultrasonic pulse velocity (UPV), compressive strength, conductivity, pH, thermogravimetric (TG), 29Si NMR and nitrogen adsorption/desorption. The results demonstrated that with the dispersed nano CSH seed increasing, the setting process of cement paste was shortened dramatically, the compressive strength and UPV of cement mortar increased significantly especially at 12 h. The variation of conductivity and pH of cement suspension indicated that the ion dissolution process was promoted by dispersed nano CSH seed, which therefore conducive to the precipitation of cement hydration products. TG curves exhibited that the formation of cement hydration products, including CH (Calcium Hydrated), AFt and CSH gel were accelerated by dispersed nano CSH seed. The 29Si NMR (Nuclear Magnetic Resonance) and nitrogen adsorption/desorption results validated that the incorporating dispersed nano CSH seed promoted considerably the polymerization of CSH gel. The aforementioned results are correlated well with the fast formation of microstructure and in turn the rapid development of compressive strength at early age.

Comparison of the effects of carbon-based and inorganic nanomaterials on early cement hydration

This study delves into the impact of nanomaterials on early cement hydration, aiming to elucidate their mechanism of action. Four nanomaterials were selected, including carbon-based nanomaterials (multi-walled carbon nanotubes (CNT) and graphene oxide (GO)) and inorganic nanomaterials (nano-SiO2 and nano-CaCO3). Initially, the zeta potential was employed to examine nanomaterial adsorption on relevant ions in simulated solutions. Subsequently, SEM NMR, XRD, and TGA were utilized to assess the influence of different nanomaterials on hydration product morphology, content, and structure. Utilizing the Krstulovic-Dabic model, the hydration kinetics based on the heat of hydration in cement paste containing nanomaterials was simulated. Results revealed nanomaterials exhibited stronger Ca2+ ion adsorption than cement particles, with CNT and GO particles displaying weaker adsorption relative to SO42- ions. Conversely, nano-SiO2 and nano-CaCO3 particles exhibited a stronger adsorption capacity for Ca2+ ions than SO42- ions. This robust adsorption facilitated hydration product generation, yielding fine and regular C-S-H particles in carbon-based nanomaterial-containing cement pastes, contrasting with coarse and irregular particles in inorganic nanomaterial-containing pastes. Nanomaterial introduction increased polymerization and the average chain length of hydration products. Furthermore, it heightened exothermic peak intensity and total exothermic amount, while reducing the induction period and exothermic peak length. Hydration kinetics, simulated through the Krstulovic-Dabic model, aligned with the nucleation and growth (NG)-phase boundary reaction (I)-diffusion (D) process. In the NG stage, nanomaterials accelerated hydration by reducing reaction stages (n) and increasing the rate constant (K1'). In the I stage, hindered Ca2+ ion migration led to decreased K2', slowing hydration. Stage D witnessed a rapid decline in K3'.

Effect of Limestone Powder Mixing Methods on the Performance of Mass Concrete.

Using limestone powder (LP), the by-product of manufactured sand, to replace part of fly ash (FA) or manufactured sand could not only turn waste into treasure and decrease the price of concrete, but could also enhance the performance of concrete and reduce environmental pollution. However, the impact of various LP incorporation methods on the performance of mass concrete was inconsistent. In this paper, the effects of LP on the workability, compressive strength, constrained expansion rate, hydration temperature and impermeability of mass concrete were studied by replacing FA or manufactured sand alone and replacing FA and manufactured sand simultaneously. The results showed that the impact of LP on the performance of mass concrete was equal when it replaced FA alone and FA and manufactured sand at the same time. When the replacement amount was 20%, the workability, expansibility and early strength of concrete were improved, but the later strength and impermeability were slightly reduced. The workability, compressive strength, expansibility and impermeability of mass concrete were improved when manufactured sand was replaced alone, and the optimal dosage was 10%. The LP, moreover, reduced the hydration temperature peak of concrete in three kinds of mixing methods, but the temperature peak appeared earlier. At lower dosages, LP optimized pore structure and promoted the early hydration of cement through filler effects and nucleation effects. When LP replaced manufactured sand, the microstructure of concrete was more dense, so the replacement of manufactured sand had a better effect on the improvement of concrete properties. A reference value for the use of LP in mass concrete is provided in this study.

A new hydration kinetic model based on boundary nucleation and growth mechanism with time-dependent growth rate: Application to quantitively characterize the influence of alkali on the early hydration of cement

In this study, a boundary nucleation and growth model with a time-dependent growth rate was proposed to quantitively characterize the precipitation of CSH. The newly constructed model was typically applied to quantitively analyse the influence of alkali content on the growth of CSH, and the value-taking equations of the time-dependent growth rate of CSH in various alkali content systems were proposed and verified. The experimental and simulation results proved that a high soluble alkali content stimulated early hydration (within the initial several hours) and inhibited the late growth of CSH (>20 h) in cement paste. The time-varying ion concentrations in cement solutions were the main driving force for the change in the growth rate of CSH with time. Likewise, the variation in the aqueous phase properties of cement pastes also explains the influence of alkali content on the growth rate of CSH, i.e., the high initial pH of the solution with high soluble alkali led to the high supersaturation degree and high growth rate of CSH, consuming large amounts of calcium ions and in turn reducing the later supersaturation degree and growth rate. The newly constructed model is also expected to precisely characterize the factors that have a significant influence on the precipitation of cement hydrates.