Hydration Process Of Cement Paste Research Articles

Insight into the early hydration characteristics of Portland cement with hydroxyethyl methyl cellulose highlighted by 1H low-field NMR

1H low-field nuclear magnetic resonance (1H NMR) as a non-destructive test method can effectively capture the water state changes in cement pastes. The water changes can in turn reflect the early hydration characteristics of cement pastes. Hydroxyethyl methyl cellulose (HEMC) with different viscosities affects the hydration characteristics of cement by acting on the water in different states. The following experimental results are obtained by testing hydration of cement pastes with HEMC by using 1H NMR test. Incorporating 0.1–3% HEMC with different viscosities all can effectively control the bleeding water phenomenon. HEMC can absorb a part of the water in the cement pastes. Incorporating 2–3% HEMC significantly delays the enrichment of the gel pores water and interlayer water. When the content of HEMC increases from 0% to 3%, the hydration degree of cement pastes tends to decrease. Besides, HEMC with higher viscosity of 15000–40000 mPa·s obviously delays the hydration process of cement pastes compared to HEMC with lower viscosity of 400 mPa·s.

Hydration mechanism and photocatalytic antibacterial performance of cement-based composites modified by hydrophilic nano-TiO2 particles

In this paper, the hydration process of cement paste with hydrophilic nano-TiO2 particles was studied by microcalorimeter and electrochemical impedance spectroscopy, and the hydration mechanism was explored based on Krstulovic-Dabic kinetic model. Meanwhile, the photocatalytic activity and antibacterial properties of TiO2-modified cement pastes were investigated by ultraviolet spectrophotometer and enzyme activity analyzer respectively. The results show that TiO2 nanoparticles can promote the hydration rate of cement in the acceleration stage, increase the cumulative heat release of early hydration, but delay the hydration process in the later stage. The Krstulovic-Dabic model can effectively simulate the hydration process of cement pastes with TiO2. Nano-TiO2 helps to increase the hydration rate of the crystal nucleation and growth process (NG) and shorten the duration of phase boundary reaction process (I), but has a negative impact on ion diffusion process (D). The functional relationship between the resistivity ρ of TiO2 cement-based composites and the hydration kinetic parameters was established: ρ(t)=−1k1ln[β1+t50t−t0].The degree of hydration of cement can be assessed by electrochemical in-situ non-destructive monitoring of the sample. In addition, the photocatalytic oxidation rate of TiO2-modified cement-based composites was up to 69.4%. Compared with the control sample without nano TiO2, the antibacterial ability was increased by 72.35%. In this paper, nano-TiO2 was applied to cement system, which provided a new idea for the preparation and application of photocatalytic antibacterial cement-based composites.

Impact of Particle Size on the Setting Behavior of Tricalcium Silicate: A Comparative Study Using ISO 6876 Indentation Testing and Isothermal Induction Calorimetry.

This study examines the impact of particle size on the setting behavior of tricalcium silicate powders. The setting behavior was evaluated using ISO 6876 indentation testing and isothermal induction calorimetry techniques. The objective was to compare the outcomes obtained from these methods and establish a correlation between particle size and setting characteristics. The cement pastes were manually mixed with a water-to-solid ratio of 0.66 for conducting indentation tests according to ISO 6876, while calorimetry measurements were performed using isothermal (conduction) calorimetry at room temperature. The findings demonstrate a significant influence of smaller particle sizes on accelerating the hydration process of cement pastes, resulting in a reduction of setting time by up to 24%. Moreover, the final setting times obtained through the indentation method closely approximate the inflection points of the acceleration curves acquired by calorimetry, with time deviations of less than 12% regardless of particle size.

Enhancement in toughness of cement pastes by chitosan modified with polyacrylic acid (CS/PAA): Microstructure evolution and molecular dynamics

This paper presents the preparation and utilization of chitosan modified with polyacrylic acid (CS/PAA), which possesses abundant hydroxyl, carboxyl, and amide functional groups, to examine its impact on the mechanical properties and hydration process of cement paste, as well as the morphology of hydration products, particularly portlandite.The results show that the addition of CS/PAA can extend the induction period of C3S hydration by facilitating the complexation between Ca2+ and carboxyl, which is not noteworthy due to the competitive adsorption between CS/PAA and C3S, C3A in cement pastes. Furthermore, the (001) crystal plane of calcium hydroxide (CH) can undergo a transformation from hexagonal columnar crystals to lamellar crystals through the oriented adsorption of CS/PAA. These lamellar crystals can serve as local strengthening zones, aiding the cement paste in achieving higher flexural strength without compromising compressive strength. Hopefully, the regulation mechanism of CS/PAA on the morphology and stacking of CH can make a guidance for the application of CS/PAA in cement based materials with high compressive strength and toughness.

Achieving energy savings and early-ages strength enhancement of prefabricated cement components: Combined application of direct electric curing and sodium sulphate

Accelerated curing regimes are widely used to produce prefabricated concrete elements to improve construction quality and reduce time costs. A new accelerated curing regime, direct electric curing (EC), is proposed, and its effect on the performance of cement paste and energy consumption is discussed and compared with the common accelerated curing regime (steam curing). The results show that EC can significantly accelerate the early-ages hydration process of cement paste and increase its 1-d content of hydration products. The compressive strength (1–28 d) of the electro-cured specimen is higher than of the standard-cured sample, but its sorptivity coefficient and drying shrinkage value increases slightly due to the coarsening of the pore structure. EC can greatly improve the energy utilization efficiency in the process of curing cement sample, and its 1-d energy consumption per cubic meter of sample per MPa is only 3.65% of that in steam curing. In order to further improve the energy efficiency of EC, sodium sulphate (SS) is incorporated to the cement paste as a hardening accelerator. Incorporation of SS can further improve the early-ages strength of cement sample, making its 8-h compressive strength (1.5–2% SS) surpass the 1-d strength of steam-cured and electric-cured plain pastes. This means that the combined application of EDS and SS can not only shorten the demoulding time (saving time cost), but also further improve the energy utilization efficiency. The 8-h energy consumption (kWh/m3⸳MPa) of electro-cured cement sample after incorporating 1% SS is only 1.18% of that of steam curing and 35.8% of that of single EC. Under the synergistic acceleration of SS and EC, the energy consumed by curing prefabricated components is significantly reduced, which could lead to an energy revolution and promote sustainable development in building engineering.

Effects of curing temperature on cement-stabilized soils

Curing temperature is widely known for its effects on the strength of various cementitious-based civil engineering materials, including in stabilized soils. Curing materials at different temperatures can cause negative or positive impacts on the mechanical properties of these materials due to the effect of temperature on hydration behavior, hydration rate, and ion exchange. This paper aims to better understand these factors in geoengineering applications. In particular, the discussion focuses on the effects of curing temperatures ranging from below freezing to 50 °C on the hydration process of cement paste (i.e., hydration rate, mineral dissolution, compressive strength) and the hydration process and strengthening mechanism of cement-stabilized soils. Finally, an informative table listing the advantages and disadvantages of the influences of each temperature level on these materials is provided as a summary of the findings from the literature.

Effect of recycled brick powder on the hydration process of cement paste

Using recycled brick powder (RBP) in blended cement is beneficial to energy saving and emission reduction. The hydration process of blended cement containing RBP is significant for the mechanical property and durability of concrete. The hydration mechanism of blended cement containing recycled brick powder (RBP) has been investigated through hydration heat, hydration degree, and hydration products of the pastes to reveal the effect of RBP on hydration and the reaction mechanism of RBP. The results show that the addition of RBP reduces the heat release during the hydration process, but its nucleation and dilution effects promote cement hydration. The inclusion of RBP also decreases the amount of Ca(OH)2 in the system. The content of the amorphous phase in the system continuously increases with hydration time, and after 28 days of hydration, the amorphous phase is derived from both cement hydration and the pozzolanic reaction of RBP. Between 28 and 90 days of hydration, the reactivity of RBP significantly increases.

Improvement of shrinkage reducing performance of polycarboxylate superplasticizer by butyl acrylate and its mechanism

AbstractA series of polycarboxylate superplasticizers (PCEs) with different molecular structures and shrinkage reducing performance were synthesized by modifying PCE with butyl acrylate (BA), and their molecular structures were characterized. The influence of BA on the dispersion and shrinkage reducing performance of PCEs and the influence of PCEs grafting different ration of BA on the hydration of cement were investigated in detail. Furthermore, the mechanisms of BA improving PCE shrinkage reducing performance were emphatically analyzed. The results showed that: (1) BA was successfully grafted into the molecular structures of PCEs and the expected molecular structures were obtained by polymerization. (2) BA has little effect on the dispersion of PCEs, but it will affect the hydration process of cement paste mixed with PCEs and significantly improve the shrinkage reducing performance of PCEs. (3) After grafting BA monomer into PCE, the surface tension of PCE solution decreased and the evaporation rate of alkaline solution mixed with PCE also significantly slowed down. Moreover, the retention capacity of pore water of cement paste mixed with PCE was improved. These three reasons were considered to be the main mechanisms of BA improving the shrinkage reducing performance of PCE.

Study the impedance spectroscopy of early-age cement paste hydration process using Electrodeless impedance analyzer (EIA)

Electrodeless Impedance Analyzer (EIA) --- a new non-contacting electrodeless impedance spectroscopy (IS) measurement device was recently invented to monitor and interpret the hydration process of cement pastes with different water to binder ratios and composites. A perfect arc was observed in the Nyquist plot, and cement pastes seem to have an inductive behavior which has never been recorded before. In order to trace back to the sources of the complex resistivity behavior of cement-based materials, electrolyte, the major conductive phase inside the composite matrix, was detected together with cement pastes. An equivalent circuit model for impedance spectroscopy (IS) of cement paste has been proposed which seems quite different with previous models.

The influence of calcium sulphoaluminate cement on the hydration process of cement paste mixed with alkali free liquid accelerator

Sulphoaluminate cement is considered green cement, which has the characteristics of rapid setting and high early strength. The partial substitution of sulphoaluminate cement (CSA) for ordered portland cement (OPC) was investigated in the system mixed with alkali free liquid accelerator. The hydration process and products were analyzed by hydration heat exothermic curve, XRD, TG and SEM. The results showed that CSA could promote the early hydration of pastes mixed with alkali free liquid accelerator and delay the later hydration. In addition, combined with the analysis results, the hydration conceptual model of CSA for paste mixed with alkali free liquid accelerator was proposed. The sulphoaluminate cement OPC composite cement is used in shotcrete for the first time. Combined with hydration heat, XRD, and TG tests, the theoretical hydration model of CSA-OPC composite cement is proposed. The application of environment-friendly sulphoaluminum cement in shotcrete is realized.

The influence of calcium nitrate/sodium nitrate on the hydration process of cement paste mixed with alkali free liquid accelerator

• The reaction models of CN/NN with C 3 A-H 2 O and C 3 A-Gp-AF-H 2 O were proposed. • It is proved that the formation of new phase is the main reason to promote the early strength of mortar. In this paper, the effects of calcium nitrate (CN) and sodium nitrate (NN) on the setting time and mortar strength of cement paste mixed with an alkali-free liquid accelerator (AF) were investigated. The results showed that the dosage of 1.5% CN/NN can shorten and improve the early strength of cement paste and mortar mixed with AF. Combined with the reaction of CN/NN with C 3 A, the reaction mechanism of CN/ NN in the CN/NN-C 3 A-H 2 O and C 3 A-Gp-AF-H 2 O system was revealed by XRD and Raman: the formation of a new phase 3CaOAl 2 O 3 ·0.83Ca(NO 3 ) 2 ·0.17Ca(OH) 2 ·9.5H 2 O (nitrate-AFt) was the main reason for the improvement of the strength. At the same time, the reaction model of CN and NN in pastes was proposed. Thus, it provided a reference for investigation the influence of inorganic salt-AF on cement hydration.

Preparation of alkali free liquid accelerator for shotcrete with fluorosilicic acid waste liquid and its accelerating mechanism

At present, the waste liquid of fluorosilicic acid produced by phosphate fertilizer plants in China creates serious problems of resource waste and environmental pollution. In view of this, a kind of alkali free liquid accelerator (FSA-AF) for shotcrete was prepared herein by using fluorosilicic acid waste liquid, which can realize the purpose of resource utilization and clean production. After testing the performance of FSA-AF, it was found that the addition of FSA-AF greatly shortened the setting time of cement paste, and it had no significant negative influence on early and late compressive strengths of mortar specimens. The results confirmed that FSA-AF was an alkali free liquid accelerator with excellent coagulation promoting property. Moreover, in order to elucidate the accelerating mechanism of FSA-AF, the early hydration process of cement paste, C3A paste and C3S paste with FSA-AF was measured by isothermal calorimetry, and the phase composition and micro morphology of their hydration products were investigated thoroughly by XRD and SEM analyses. Based on these results, the early hydration models of C3A and C3S in the presence of FSA-AF were proposed.

Effect of Nitrate/Bromide on the Hydration Process of Cement Paste Mixed with Alkali Free Liquid Accelerator at Low Temperature

The effects of different inorganic salt accelerators (CaBr2, NaBr, Ca(NO3)2, NaNO3) and an alkali-free liquid accelerator were researched at a low temperature of 10 °C. The results showed the effects of 1.5% NaBr and 1.5% NaNO3 inorganic accelerator were pronounced. The 1-d compressive strengths of the mortar with these two inorganic salts were increased by 185.8% and 184.2%, respectively, and the final setting times were shortened from 7.74 to 6.08 min and 6.12 min, respectively. The hydration temperatures at 10 °C were measured, and the promotion effects of the inorganic accelerators were calculated: the relationship between the hydration degree was αAS + NN > αAS + NB > αAS + CB > αAS + CN > αAS. In addition, the reaction of C3A with NaBr and NaNO3 was used to analyze the products in an ettringite phase, i.e., Ca4Al2O6Br210·H2O, 3CaOAl2O3Ca(NO3)2X·H2O. The formation of these phases was detected in the hydration products of the cement paste hydration for 12 h, 24 h, and 28 d. Combined with the mass loss of the ettringite phase at 90–120 °C, determined using TG/DTG, the synergetic acceleration mechanism of the inorganic accelerators was comprehensively inferred.

Effects of cement particle distribution on the hydration process of cement paste in three-dimensional computer simulation

This study investigated the influences of cement particle distribution on the hydration process of cement paste using three-dimensional computer simulation. The pre-hydrated models of cement paste were generated by using both the correlation function (CF) method based on SEM images and the random distribution (RD) method. The hydration process of cement paste was simulated using the model based on the CEMHYD3D. The RD method was simpler and required less time in generating a pre-hydrated model than the CF method. In addition, the simulation results of the RD method were similar to those of the CF method in the properties of cement paste using the cement 133 with water-to-cement ratio of 0.3. Although the simulation results of the RD method was in good agreement with those of the CF method, authors highly recommended that the cement particles larger than a critical diameter (13 µm) in the simulation contain multiple cement crystalline phases whereas the other ones smaller than the critical diameter should contain a single phase. The proposed RD method was validated by using the previously reported experimental results using ordinary Portland cement as well.

Early-age hydration process and autogenous shrinkage evolution of high performance cement pastes

This paper presented a comprehensive study on the early-age hydration process and autogenous shrinkage evolution of high performance cement pastes. The early-age hydration process of cement pastes was analyzed by combining 1H nuclear magnetic resonance relaxometry (1H NMR) with isothermal calorimetry. The hydration degree was contrastively analyzed by using 1H NMR and thermogravimetry analyses (TGA). Moreover, the relationship between the free water consumption process and autogenous shrinkage for cement pastes was revealed. Results showed that a magnetism-heat (M − H) model could be established according to the correspondence between free water consumption rate and hydration exothermic rate, which divided the early-age hydration process of cement pastes into four periods. The initial setting time was the onset that free water signal fraction started to drop, after this moment, the consumption rate of free water was increased and more hydration products were generated. After about final setting time, the weighted mean relaxation time of the free water sharply decreased, and the pore structure of cement pastes was gradually refined. The hydration degree (α) of cement calculated by 1H NMR and TGA showed good agreement, with the error of α values less than 2% after initial setting time. Furthermore, cement paste with a lower water/cement ratio showed higher autogenous shrinkage and lower free water signal fraction, but they did not show a good linear correlation with each other throughout the hydration process.

Influence of Submicron Fibrillated Cellulose Fibers from Cotton on Hydration and Microstructure of Portland Cement Paste.

This paper reports the influence of submicron hydrophilic fibers on the hydration and microstructure of Portland cement paste. Submicron fibrillated cellulose (SMC) fibers was prepared by the acid hydrolysis of cotton fibers in H2SO4 solution (55% v/v) for 1.5 h at a temperature of 50 °C. The SMC fibers were added into cement with a dosage of 0.03 wt.%, and the effect of SMC on the hydration and microstructure of cement paste was investigated by calorimeter analysis, XRD, FT-IR, DSC-TG, and SEM. Microcrystalline cellulose (MCC) fibers were used as the contrast admixture with the same dosage in this study. The results show that the addition of SMC fibers can accelerate the cement hydration rate during the first 20 h of the hydration process and improve the hydration process of cement paste in later stages. These results are because the scale of SMC fibers more closely matches the size of the C-S-H gel compared to MCC fibers, given that the primary role of the SMC is to provide potential heterogeneous nucleation sites for the hydration products, which is conducive to an accelerated and continuous hydration reaction. Furthermore, the induction and bridging effects of the SMC fibers make the cement paste microstructure more homogeneous and compact.

Influence of liquid accelerators combined with mineral admixtures on early hydration of cement pastes

The main purpose of this paper was to investigate the influence of different liquid accelerators (AR, liquid accelerator based on sodium aluminate; AS, liquid accelerator based on aluminum sulfate; AF, liquid accelerator based on fluoroaluminate) and mineral admixtures (fly ash, slag and silica fume) on the setting time of cement pastes and compressive strength of mortar. In addition, the early hydration process of cement pastes with different mineral admixtures in the presence of AR, AS and AF was explored by isothermal calorimetry, and the crystals composition and micro morphology of hydration products were analyzed by XRD and SEM. The results indicated that in the presence of 7.0% AF, the initial and final setting time of cement pastes with 10% and 5% silica fume are 0.67 min and 1.47 min, respectively. In the presence of 4.0% AR, the mortar with 10% silica fume reaches the highest value of 16.8 MPa. In addition, when the dosages of AF and silica fume are 7.0% and 10%, the first exothermic peak value of paste is 87.79 mW/g. Furthermore, in the presence of liquid accelerators, different mineral admixtures also have great influence on the morphology and crystals composition of hydration products.

Effect of pre-introduced sodium chloride on cement hydration process

Chloride-based accelerators are widely used to accelerate cement hydration; however, there is no focus on the effect of the interaction between Cl− and SO42− on cement hydration. Hence, the interaction effect between initial gypsum and sodium chloride (NaCl) in the cement hydration process was investigated. Isothermal calorimetry, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and inductively coupled plasma spectroscopy were used to evaluate the hydration process of cement paste. Moreover, a thermodynamic model and boundary nucleation and a growth model were applied to calculate the hydration products and describe the hydration process, respectively. It is clear that sodium chloride can accelerate cement hydration, but as the incorporated sodium chloride increases, the acceleration effect is weakened. The incorporation of chloride salts will promote the dissolution of minerals and increase the growth rate. In the early stage of hydration, the formation of ettringite precedes formation of Friedel's salt, owing to the fact that tricalcium aluminate (C3A) favours binding with SO42−, which can be demonstrated by the change in ion concentrations and the evolution of hydration products. The formation of Kuzel's salt depends not only on the chloride concentration but also on the hydration time.

Effects of slag on cement hydration by electrical resistivity characterization

Non-contact resistivity measurement was used to characterize the early hydration characteristics of cement paste with different contents of slag, combined with other traditional methods such as hydration heat, compressive strength. The results show that the maximum compressive strength of sample P0.4SL20 was 34.4 MPa and 45.2 MPa at 3 d and 7 d, respectively. The addition of slag could reduce the hydration heat of slurry, which makes the second hydration exothermic peak shift to the left. The characteristic points on electrical resistivity differential curve with different slag contents had good correspondence with the corresponding characteristic points on hydration heat release curve of samples with different slag contents. A good linear relationship between electrical resistivity and compressive strength was shown as f c(3d) = 5.23992P(3d)-12.31066. The electrical resistivity method can be used to characterize the influence of slag on the hydration process of cement paste and predict its compressive strength.

Study of the Hydration Kinetics of Cement Paste by Measuring Electrical Conductivity

The hardening cement paste is a highly concentrated polyelectrolyte that changes over time. From this point of view, the main electrochemical characteristics of the hydration process of cement paste can be the electrical conductivity and electrode potentials of metals lowered into cement pastes. In the process of setting and hardening of cement dough, complex physical and chemical processes of interaction of clinker minerals with water occur. In this case, new chemical compounds are formed, the concentration of Ca2+, Mg2+, A13+, Si4+, Na+, H+, OH− ions in the liquid phase changes, and the amount of free water decreases. Therefore, the electrical conductivity of the cement paste will change during the hydration of Portland cement minerals. The kinetics of hydration of cement paste is studied by measuring the electrical conductivity depending on the water-cement ratio and in the presence of additives SP C-3 and PDO-M. The parameter of electrical resistance of cement paste was studied using a digital voltmeter of type B7-27A/1. In experimental studies, we used additive-free sulphate-resistant Portland cement with an activity of 41.0 MPa with a normal density of 0.24 and pure clinker minerals – C3S и β-C2S. After preparation, the cement paste was placed in the assembled cell and compacted by vibration. Graphs of changes in the complex electrical resistance of cement pastes are obtained, which show that the curves have an oscillatory character. It was found that with an increase in the water-cement ratio, the vibrational nature of the interaction of water with Portland cement minerals weakens. When the water-cement ratio is equal to 0.42, there are no fluctuations in electrical conductivity. This can be explained by the fact that when the amount of water in the cement paste increases, the influence of cations on the degree of its ordering decreases. Curves of changes in the electrical conductivity of cement pastes obtained at W/C=0.26, without additives, as well as in the presence of SP C-3 and PDO-M additives. It can be seen that in the presence of SP C-3, fluctuations in electrical conductivity are weakly expressed. It can be assumed that SP C-3 has a disordering effect on the water in the cement paste. The addition of PDO-M, on the contrary, orders the structure of water, there are fluctuations in electrical conductivity. It is shown that in the CaO–SiO2–H2O system, a state of instability develops at certain ratios of the rate constants of individual stages of the hydration process. SP C-3, adsorbed on the adsorption centers of polysilicon acid, slows down some processes, which accelerates others, and the difference between the speed constants of individual stages increases.