Hydration Process Of Cement-based Materials Research Articles

Unraveling the molecular freezing behavior of water on a calcium silicate hydrate matrix.

The hydration process of cement-based materials primarily results in the formation of calcium silicate hydrate (CSH), which is crucial in deciding how long concrete will last. This study utilizes molecular dynamics simulation technology to explore the freezing behavior of pure water solutions within various calcium silicate hydrate (CSH) matrices. The investigated matrices encompass four different Ca/Si ratios. According to the simulation, as ice crystals develop close to the surface of CSH, the CSH matrix strengthens its hydrogen and ionic interactions with water molecules, which effectively prevents water molecules from crystallizing and nucleating. Consequently, these molecules compose an unfrozen water film structure that bridges between ice crystals and the CSH matrix. The research also reveals an intriguing relationship between silica chain behavior on the Ca/Si ratio and the CSH surface. Surface flaws arise as a result of the silica chains of CSH breaking into shorter segments as the Ca/Si ratio increases. These surface defects manifest as grooves on the matrix's surface, effectively capturing and retaining specific water molecules. The CSH matrix's hydrogen bonds with water molecules are weakened as a result of this process, facilitating their participation in the crystallization process, and leading to a thinner unfrozen water film thickness with an increased Ca/Si ratio. This study contributes to a greater knowledge of the performance and dependability of cement-based products by offering molecular-level insights into the freezing actions of liquids in gel pores.

Micro-nano bubble water process: Effect of micro-nano bubble water as mixing water on volume stability of shotcrete

As a kind of active water, micro-nano bubble water (MBW) can promote the early hydration of cement paste and improve the early mechanical strength of shotcrete. However, accelerating the hydration process of cement-based materials will increase their shrinkage deformation to a certain extent at early age. Therefore, this paper mainly studies the effect of MBW combined with aluminum sulfate alkali-free accelerator (AL) on the volume stability of cement-based materials within 180d. The results show that MBW as mixing water can reduce the autogenous and drying shrinkage of cement-based materials with AL, and also has a certain mitigation effect on water loss rate and internal humidity (IH) drop under dry conditions. It can also reduce the ring constraint shrinkage cracking time and crack width. MBW can reduce the cement paste pore size distribution of 10–50 nm, and reduce the surface tension of the aqueous solution, thereby reducing the capillary tensile stress. This paper provides some theoretical guidance for micro-nano bubble water in practical engineering applications.

Effect of acid activation on the mechanical and shrinkage properties of cement-based materials

Effect of acid activation on compressive strength, shrinkage, microstructure and hydration process of cement-based materials is studied by adding acid activator to them. The strengthening mechanism of acid activation on the mechanical properties and shrinkage resistance of cement-based materials is proposed based on the effects of acid on cement particles, fresh paste and hardened paste, combined with multi-level analysis by microscopic means. The results show that acid activation can significantly improve the compressive strength and shrinkage resistance of cement-based materials. The reason for this is that the acid activator has the effect of refining cement particles, increasing the particle concentration of fresh paste, and densifying hardened paste microstructure.

Nondestructive Monitoring Hydration of Belite Calcium Sulfoaluminate Cement by EIS Measurement.

In this study, the impact of water-to-cement (w/c) ratios of belite calcium sulfoaluminate cement (BCSA) on the hydration kinetics and the electrochemical impedance spectroscopy (EIS) parameters is studied. According to the analysis of classic hydration measurements, such as calorimetry tests, chemical shrinkage content, and chemically bound water content, it can be concluded that a higher w/c ratio clearly accelerates the hydration of BCSA cement paste. The electrical resistivity of BCSA0.35 cement paste is more than 4.5 times that of BCSA0.45 and BCSA0.5, due to the gradually densified micropore structure blocking the electrical signal transmission rather than the free charged-ion content. The porosity of BCSA0.5 is 27.5% higher than that of BCSA0.35 and 7.8% higher than that of BCSA0.45, which proves the resistivity is clearly related to the variation in microstructure, especially for the porosity and pore size distribution. The novelty of this study is the linear regression with logarithm terms of electrical resistivity and classic hydration parameters such as chemical shrinkage, cumulative hydration heat, and chemically bound water is established to extend the classical expression of cement hydration degree. It indicates that the electrochemical impedance spectroscopy can be taken as a nondestructive testing measurement to real-time monitor the cement hydration process of cement-based materials.

Calorimetric Study of High-Volume Fly Ash-Cement Paste Hydration at Different Temperatures

The study on the hydration process of cement-based materials is of significance since it determines the development of the macro-properties. The hydration process of high-volume fly ash (FA)-cement based materials is quite special and needs systematic study. In this study, the hydration heat release of cement paste with high volume FA were measured with isothermal calorimetry at different temperatures. The full-width at half-maximum (FWHM) value of the exothermic peak and the cementitious index (CMI) of FA were used comprehensively to evaluate the influence of FA on cement hydration. It was found that increasing the FA content and water-binder ratio retarded the hydration process for paste but did not show obvious effects on the hydration of cement. The CMI values show that raising the temperature intensified the retarding effect of FA on cement hydration during the induction period, but promoted the subsequent hydration process. According to the normalized heat release to cement, and the change of CMI values with temperature, new evidence was found that FA may not act as nucleation sites during the hydration process of cement. The result can be better explained by the topochemical reaction mechanism.

Effect of Bacillus mucilaginosus on hydration and microstructure of hardened pastes of C3S at early age: Simulation and experiment

The application of microbial mineralization in cement-based materials has broad prospects, especially in strengthening the surface layer, improving the microstructure, and healing the cracks. This paper mainly studies the interaction between the mineralizing process by Bacillus mucilaginosus fixing CO2 from air and the hydration process of cement-based materials after addition of microorganisms. The coupling model described the interaction of the hydration of C3S and the microbial mineralization is established. This model is used to predict the contents of hydration products, the microbe induced bio-CaCO3 and the porosity distribution in hardened pastes of C3S. The calculated results revealed that the hydration degree of C3S, the contents of C-S-H gel and bio-CaCO3 increased and the remained C3S, the content of Ca(OH)2, the porosity decreased in certain depth of the surface layer of the hardened pastes of C3S after the addition of microorganisms. Moreover, the calculated results are in good agreement with the experimental.

Effect of Nano-Magnesium Oxide on the Expansion Performance and Hydration Process of Cement-Based Materials.

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence of nano-MgO on the long-term consistency, fluidity, expansion stability, hydration, and mechanical properties of 30% fly ash cement-based materials and improves research into nano-MgO as an expansion agent. Expansion performance, flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were employed to study their hydration process and microstructure. The results showed that nano-MgO had an obvious effect on the consistency, fluidity and expansion performance of cement paste. After curing in water for 365 days and autoclaving thereafter, the hydration of nano-MgO was relatively complete. The volumetric expansion pressure of the magnesium hydroxide (Mg(OH)2) crystals and the crystallization pressure generated after their continuous precipitation were the main reasons for the expansion of the slurry. Nano-MgO improved the microstructure of cement paste and significantly enhanced its long-term flexural strength and compressive strength. When the content of nano-MgO was less than 10%, the cement with 30% fly ash had good long-term stability with the potential to compensate for the shrinkage of large-volume concrete.

Influence of the aerogel/expanded perlite composite as thermal insulation aggregate on the cement-based materials: Preparation, property, and microstructure

Aerogel/expanded perlite composite (AEP) provide an effective approach for low cost application of aerogel in building materials. AEP cement-based composites (AEPC) was prepared based on the three kinds of cement-based materials. The influences of AEP on the workability, physical and mechanical property, and microstructure of AEPC were studied. The results shown that the negative influence of the hydrophobic AEP on the workability of the AEPC fresh mixture were improved by adopting the reasonable cement-based binders, and combing with the method of KH550 modifying AEP or adding HPMC in the cement-based binders. However, the KH550 and the HPMC inhibited the hydration process of cement-based materials. The AEPC had been prepared with the dry density of 524–951 kg/m3, the compressive strength of 3.79–14.47 MPa, and the thermal conductivity of 0.1063–0.1953 W/(m·K). The AEP were able to stably exist in the AEPC without generate new hydration products in the cement matrix. Because of the stability of aerogel in the AEP and AEPC, the thermal conductivity of AEPC decreased by 10.8%~28.5% compared with the expanded perlite cement-based composites.

Analysis on Electrochemical Impedance Spectroscopy of the Hydration Process of Cement-based Materials with a Large Amount of Mineral Admixture

High-performance concrete with a large amount of mineral admixtures is more and more preferred by research scholars. The pozzolanic activity and chemical constituents of mineral admixture directly affect the secondary hydration reaction time, and ordinary microscopic test means cannot reflect the continuity of chemical reaction process. In this paper, slag, fly ash and silica fume were used as mineral admixture to explore the electrochemical impedance spectroscopy change of mixing amount and curing age of a large amount of mineral admixture on the hydration process of cement-based materials, and the influence of mineral admixture ratio on electrochemical impedance spectroscopy was studied, the research results showed that the secondary hydration reaction of fly ash mainly occurs at the age of 42d-60d, while the secondary hydration reaction of slag mainly occurs at the age of 21-42d. The micro-aggregate effect of fly ash plays a role in increasing the electrochemical impedance of the cement slurry from the early stage of mixing, while the slag increases the electrochemical impedance of cement slurry due to the secondary hydration reaction. This paper continuously tested the hydration process of fly ash, slag and silica fume on cement-based materials.

Characterization Methods for the Effect of Microbial Mineralization on the Microstructure of Hardened C3S Paste

Microbial mineralization has a significant effect on the hydration process of cement‐based materials. This paper mainly studied the characterization methods for hydration degree and hydration product of C3S in hardened paste under microbial mineralization. Quantitative X‐ray diffraction (QXRD), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FT‐IR), and electron backscatter diffraction (EBSD) were used and compared. The results showed that microbial mineralization increased the hydration degree of T‐C3S. QXRD and EBSD could be used to characterize the content of C3S, and there were few differences between the two methods. TG could accurately characterize the content of Ca(OH)2 and CaCO3 at different depths of the sample, and FT‐IR could qualitatively characterize the presence of Ca(OH)2 and CaCO3.

Characterising the hydration process of cement slurry system based on low-field NMR

As a non-destructive and non-invasive technique with high stability and continuity, low-field nuclear magnetic resonance (low-field NMR) was used to characterise the initial hydration process of cement slurry systems based on grade G oil well cement, which is widely used in various cementing operations, and microfine cement, which is playing an increasingly important role as a reinforcing material, especially in the field of low-temperature cementing. The initial hydration process of the cement slurry systems was investigated using the Carr–Purcell–Meiboom–Gill (CPMG) technique. This method was used as it has the advantage over other spin echo techniques in that it allows rapid multiple accumulations of the echo train signal, which is an important issue in increasing detection sensitivity at low fields. The transverse relaxation time (T2) distribution curve and CPMG echo train of the cement slurry systems were first obtained. Then, the initial hydration process of grade G oil well cement and microfine cement was characterised by using the peak area and the value and distribution of T2. The results showed that the low-field NMR has great potential in the characterisation of the hydration process of cement-based materials.

The Role of Various Powders during the Hydration Process of Cement-Based Materials

The role of various powders including glass powder (GP), limestone powder (LP), and steel slag powder (SSP) during the hydration process of cement-based materials was investigated by using X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and strength tests. GP has adverse impact on early strength, but the pozzolanic reaction at later stage enhances the strength development greatly. LP can significantly improve early strength. SSP has a good contribution to the early and later strength of the paste when its content is less than 15%. GP has little effect on the kind of hydration products but relatively large effects on the quantity. Calcium hydroxide (CH) content of GP paste decreases over curing age gradually, which is different from pure cement paste because its pozzolanic activity consumes more CH than that generated from the cement hydration. SSP and LP mainly play a role of filling effect at early stage. Nucleating effect of LP also promotes the early hydration of cement. The hydration of LP occurs at later stage and forms the calcium carboaluminate hydrates. The hydration of SSP is relatively slow, which generates CH at later stage and is effective in the strength development.

Hydration process of cement-based materials by AC impedance method

AC impedance is a new method to study the changes of pore structure and the hydration degree during the hydration and hardening process of cement paste by the change of the electrochemical parameters. Employing AC impedance method, we studied the hydration and hardening process of cement paste with fly ash and slag, and analyzed the influence of different hydration age, water-binder ratio and mineral admixture on the impedance parameters. Moreover, we compared the results with those by the conventional porosity testing method and X-ray diffraction method. The results showed that AC impedance could be taken as a new technology in cement and concrete research.

Research of Electrical and Hydration Behavior of Phosphoaluminate Cementitious Material

Electrodeless resistivity and impedance spectroscopy measurement are reliable equipments of test online for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process and impedance spectroscopy characteristics of PAC with different dosage of retarder were investigated. According to the test, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC, which indicates the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration. Impedance spectroscopy can reflect the change of micro-structure and ion concentribution of PAC matrix by resistance and capacitance.

Resistivity Study on Early Hydration Process of Phosphoaluminate Cementitious Material

An electrodeless resistivity measurement system developed recently can provide a reliable method for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process of PAC with different dosage of retarder was investigated by the electrodeless resistivity equipment. According to resistivity-time curve, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC. Heat evolution of PAC was also measured. The hydration mechanism and structure formation were studied according to these results. Depending on the dosage of retarder, the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration.

Hydration monitoring of cement-based materials with resistivity and ultrasonic methods

Two test setups, the electrical resistivity and ultrasonic techniques, were used to monitor the hydration process of cement-based materials. In the electrical resistivity method, a non-contacting device was used. In the ultrasonic method, a wave was transmitted and measured by the embedded piezoelectric ultrasonic transducers, which had good coupling with the surrounding materials. The focus of the study was to detect the setting and hardening behaviors of cement paste during the first 7 days of hydration using the above techniques. Immediate after placing the cement paste into the mould, the measurement started and continued throughout the hydration process. The obtained resistivity and ultrasonic data were used to interpret the hydration process of the specimens. The correlation of two techniques was also studied. The results illustrated that both electrical resistivity and ultrasonic techniques were effective to accurately monitor the hydration of cement pastes. The resistivity method was able to study both the chemical reaction and physical change during hydration, while ultrasonic method was sensitive to physical change of cement only.