Hydration Of Pastes Research Articles

Exploring the Influence Factors of Early Hydration of Ultrafine Cement.

This work intends to contribute to the understanding of the influence factors of early hydration of ultrafine cement by focusing on the different fineness, different kinds of hardening accelerators, and different curing temperatures. Isothermal calorimetry, thermogravimetry, and X-ray diffraction (XRD) were performed to compare the hydration and chemical evolution of pastes containing accelerators with different fineness and curing temperatures; meanwhile, mechanical properties and water absorption were tested. The results showed that the cement fineness had a significant effect on the early hydration process; the smaller the cement particle size, the higher the early compressive strength. The 24 h compressive strength of ultrafine cement with a particle diameter of 6.8μm could reach 55.94 MPa, which was 118% higher than the reference cement. Water absorption test results indicated that adding 1% Ca(HCOO)2 to ultrafine cement can effectively reduce the water absorption, and it was only 1.93% at 28 d, which was 46% lower than the reference cement. An increase in curing temperature accelerated the activation of ultrafine cement in terms of the strength development rate, and the content of Ca(OH)2 in the ultrafine cement paste could reach 13.09% after being mixed with water for 24 h, which was 22% higher than that of the reference cement.

An Efficient Approach of Predicting the Elastic Property of Hydrating Cement Paste

Although elastic properties of hydrating cement paste are crucial in concrete engineering practice, there are only a few widely available models for engineers to predict the elastic behavior of hydrating cement paste. Therefore, in this paper, we derive an analytical model to efficiently predict the elastic properties (e.g., Young’s modulus) of hydrating cement paste. Notably, the proposed model provides the prediction of hydration, percolation, and homogenization of the cement paste, enabling the study of the early age elasticity evolution in cement paste. A hydration model considering the mineral composition and the initial w/c ratio was used, while the percolation threshold was calculated adopting a phenomenological semi-empirical method describing the effects of the solid volume fraction and the w/c ratio. An efficient mixing rule based on the degree of solid connectivity was then adopted to calculate the elastic properties of the hydrating cement paste. Moreover, for ordinary Portland cement, a simplified model was built using Powers’ hydration model. The obtained modeling results are following experimental data and other numerical results available in the literature.

Long-term performance and hydration of cement mortars with hydroxyethyl methyl cellulose cured at 5℃ low temperature

As one of the special curing regimes, low temperature environment is considered to be crucial to the development of various properties of cementitious materials. This work focuses on the long-term performance and hydration of cement mortars with hydroxyethyl methyl cellulose (HEMC) cured at 5℃. The results show that the mid-late flexural and compressive strengths decrease with the HEMC content increasing, to get the lowest values at 1% HEMC. Afterwards, with the HEMC content increasing to 3%, the above strengths gradually increase, still being lower than those of the control. The tensile bond strength increases with the HEMC content increasing, to reach the maximum value at 0.3–0.5% HEMC, and then decreases with the HEMC content increasing to 3%, which is still much higher than that of the control. The drying shrinkage presents a significant increase with the HEMC content increasing. Moreover, HEMC significantly retards the early hydration of cement pastes. But the final hydration degree of cement pastes with HEMC tends to be close to that of the control. In addition, macro pores and the total porosity increase with the HEMC content increasing at 0–1%, and then decrease to some extent at 3% HEMC. Obviously, due to its better long-term properties at 5℃, the cement mortars with HEMC are still applicable at low temperatures.

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.

Durability of a New Thermal Aerogel-Based Rendering System under Distinct Accelerated Aging Conditions.

The widespread application of innovative thermal enhanced façade solutions requires an adequate durability evaluation. The present work intends to assess the durability of a new aerogel cement-based rendering system through the adaptation of different accelerated aging cycles, such as heating–freezing, freeze–thawing, and heat–cold. Several mechanical properties and also capillary and liquid water absorptions were tested for uncoated and coated specimens. A decrease in the mechanical strength, especially after freeze–thaw cycles, was observed. However, the water action promoted the late hydration of the cement paste contributing to the densification of the matrix and, consequently, the increase of the adhesive strength. Additionally, a decrease in the dynamic modulus of elasticity and an increase in the Poisson’s ratio were observed after aging, which indicates a higher capacity of the render to adapt to substrate movements, contributing to a reduction of cracking.

Rheological behaviour of low-heat Portland cement paste with MgO-based expansive agent and shrinkage reducing admixture

The combined use of low heat Portland cement (LHC), MgO-based expansive agent (MEA) and shrinkage reducing admixture (SRA) is beneficial to reduce the cracking risk of concrete. In this study, the effects of MEA and SRA on the rheological behaviour of LHC paste were investigated using dynamic and static shearing tests. The response surface methodology was used to estimate the effects of MEA, SRA, and superplasticizer on dynamic rheological parameters, while the zeta potential, calorimetric, and solid phases tests were conducted to explore the mechanisms of time-dependent rheological behaviour. Results indicate that MEA contributes to higher dynamic yield stress and plastic viscosity, while the effect of SRA is dependent on its dosage. MEA promotes the static yield stress development for accelerating the hydration of blends and the formation of Mg(OH)2. SRA retards the hydration of LHC and blended paste and reduces the number of main hydration products. However, the static yield stress is further increased by SRA, showing a consistent changing trend with the surface area of hydrated particles.

Investigation of hydration and setting process in nanosilica-cement blended pastes: In situ characterization using low field nuclear magnetic resonance

In order to characterize the effect of nano-SiO2 addition on early properties of Portland cement paste, low-field nuclear magnetic resonance (NMR) was used to monitor the hydration process and microstructure evolution. The relaxation signals of low-field NMR can provide the information about the water molecules status and corresponding content, thus indirectly revealing the microstructure evolution of cement paste. Based on the relaxation signals, new applications of low-field NMR in predicting the strength and setting time of cement were developed. The results indicate that the increasing nano-SiO2 addition as well as decreasing water-to-cement ratio can accelerate the early hydration process of cement and densify its microstructure, thus shortening the setting time and enhancing the early compressive strength. The effectiveness of low-field NMR in predicting the strength and setting time of cement was confirmed by the results of compression test and Vicat needle test, respectively. Due to the non-destructive and non-invasive characteristics of low-field nuclear magnetic resonance technology, this method shows special advantages in characterizing the influence of nano-silica on the early performance of cement paste.

Effect of direct carbonation routes of basic oxygen furnace slag (BOFS) on strength and hydration of blended cement paste

Mineral carbonation of alkali solid wastes is envisaged to be an effective method to sequester CO2 and turn the wastes into more valuable end products. Steel slag generated from the steel-making industry contains a high content of calcium oxide, which is a potential medium to sequestrate CO2 via the carbonation process. In this paper, the influence of reaction parameters including solid to liquid ratio, CO2 flow rate, temperature, volume of water and carbonation time on aqueous carbonation of basic oxygen furnace slag (BOFS) in maximizing CO2 sequestration was determined. The structural and mineralogical changes of carbonated BOFS were also analyzed using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Using an optimized aqueous carbonation condition, about 16.35% of CO2 can be sequestered, which was obviously higher compared with dry carbonation (about 4.91%) at ambient conditions. Subsequently, the effect of replacing cement with carbonated BOFS (either by aqueous or dry route) on the micro-mechanical properties and hydration characteristics of blended cement paste was studied. The results demonstrated that as a small ratio of aqueous carbonated BOFS (10%-20%) blended in the cement paste they can accelerate the rate of early heat evolution during the first 24 h. On the contrary, as the carbonated BOFS ratio increased, the overall heat of hydration and mechanical strength were decreased. In comparison, BOFS carbonated by aqueous method is found to perform better in blended cement paste than its counterpart carbonated by dry method at the same replacement ratio due to the presence of a greater calcite content (acting as nucleation sites) in the aqueous carbonated BOFS.

Effects of Nano-CSH on the hydration process and mechanical property of cementitious materials

Nanomaterials are widely used in cement to improve the various properties of cement-based materials. Nano-CSH is considered as an effective accelerator for the hydration of cement. This paper studied the effects of nano-CSH on the hydration behavior and compressive strength of cementitious materials with various mineral admixtures. Isothermal calorimetry test was used to study the early hydration of cement paste. Thermogravimetric and X-ray diffraction tests were used to study the evolution of hydration product and unhydrated mineral phases in the hydrated cement paste. The presentation of compressive strength can evaluate the influence of nano-CSH on the property of cement-based material at the macro level. The obtained results show that the used nano-CSH can promote the hydration of tricalcium silicate (C3S), and is more active on the hydration of tricalcium aluminate (C3A) in the samples with GGBFS. The presence of nano-CSH can definitely accelerate the secondary hydration reaction of mineral admixtures.

Hydration and microstructural characterization of early-age cement paste with ultrasonic wave velocity and electrical resistivity measurements

Various non-destructive monitoring methods have been proposed to evaluate the early-age characteristics of cement paste, including the setting time and hardening, but the corresponding microstructural approach has not been reported in investigations of hydration products with non-destructive approaches. This study evaluates the microstructural evolution for 24 h in fresh cement paste through two types of non-destructive measurements, namely, ultrasonic wave velocity and electrical resistivity, compared with setting time by Vicat needle test. Observable non-destructive parameters can reflect the generated cement hydrates and change the tortuous path in the porous material including setting time, but the results of both methods provide different critical times of obtained parameters. To identify the formed hydration products at specific points, XRD and TG analyses are performed around the setting time. As a result, calcium hydroxide occurred after solid percolation mainly induces decreasing porosity and water depercolation, and these physicochemical changes were discussed with the measured non-destructive parameters.

The Effect of Fine-Ground Glass on the Hydration Process and Properties of Alumina-Cement-Based Composites.

This paper discusses studies regarding the impact of fine-ground glass additives on the hydration and properties of alumina cement pastes and mortars. Fine-ground glass was added to pastes and mortars instead of high-alumina cement and calcium aluminate cement in quantities of 5% and 10%. The findings are inconclusive as to the impact of glass on the properties of tested alumina cement types. The effect produced via the addition of glass instead of cement depends on the type of alumina cement used. Adding fine-ground glass to high-alumina cement enhances the paste’s density while improving paste and mortar strength. Using the same additive for calcium aluminate cement reduces its density and strength. The addition of glass to high-alumina cement adversely affects its strength at higher temperatures.

Hydration and Microstructure of Nano Modified Cement Paste

Hydration of cement systems modified by nano additives requires the understanding of its mechanisms. The present research is focused on the investigation of hydration processes in cement pastes modified by multi-walled carbon nanotubes (MWCNTs) suspension. The ultrasonication method was used for homogenization of MWCNTs in the volume of an aqueous suspension. The hydration of cement pastes was assessed by the calorimetry test. The prolongation of cement hydration in case of modification by MWCNT suspension was observed. The microstructure observation by scanning electron microscopy (SEM) was performed for identification of MWCNT's dispergation in hardened cement pastes and for the observation of cement hydration products. The compressive and flexural strength were tested to evaluate the effect of MWCNT on mechanical properties of hardened cement paste.

Synergistic use of sodium bicarbonate and aluminum sulfate to enhance the hydration and hardening properties of Portland cement paste

A novel composite admixture (N-A admixture) including sodium bicarbonate (NaHCO3) and aluminum sulfate (Al2(SO4)3) was developed for the in situ generations of calcium carbonate (CaCO3) nano-reinforced particles in Portland cement paste. The effect of N-A admixture dosage (0%, 1%, 2%, 3%, 4%, 5%) on the hydration and hardening properties of Portland cement paste such as setting time and compressive strength was systematically investigated. The enhancement mechanism of the N-A admixture was also revealed by using XRD, TGA, SEM, MIP, and ICC. The results indicated that the N-A admixture can effectively accelerate the hydration reaction process of Portland cement paste and shorten its setting time. When the N-A admixture was added at 3%, the compressive strength at 1 day was 86.9% higher than that of the control Portland cement paste, and there was no inversion of strength at 90 days. N-A admixture promoted the formation of more hydration products. At the early stage of hydration, in situ CaCO3 with a grain size ranging from 25.53 to 42.98 nm was generated, the amount of which increased with the addition of N-A admixture. Moreover, the in situ CaCO3 also reacted with the aluminum phase to form mono-carbonate (Mc) in the late stage, which effectively reduced the proportion of large pores, resulting in a dense microstructure of the hardened Portland cement paste. The results of this work provide a novel and facile method for the generation of in situ CaCO3, which can be used to greatly improve the performance of cement concrete.

Photocatalytic Concrete Blocks Nanomodified with Zinc Oxide for Paving: Mechanical Performance and Microstructural Characteristics

Abstract Concrete block pavement is considered an ideal substrate for the application of photocatalyst materials. In the paving area, titanium dioxide (TiO2) has been the most widely used semiconductor because of its properties. However, zinc oxide (ZnO) has been recently used as an alternative material to TiO2 in heterogeneous photocatalysis, being applied mainly for the treatment of liquid effluents. In this perspective, the aim of this study was to evaluate the capacity of concrete blocks nanomodified with ZnO in the degradation of nitrogen oxides (NOx) as well as the impact of the nanomaterial on the mechanical properties and microstructural characteristics of concretes. For this purpose, concretes were produced with ZnO incorporation of 3 %, 6 %, and 9 %, being submitted to photocatalytic tests, simple compressive strength, flexural strength, and dynamic Young’s modulus, as well as mercury intrusion porosimetry tests and image evaluations using scanning electron microscopy. Together, evaluation of the influence of nano-ZnO on cement paste hydration reactions was carried out. It could be concluded that the addition of ZnO to concrete provides photooxidative capacity to the material; however, it impairs the mechanical performance and the development of the cementitious matrix microstructure.

Surface properties of clay brick powder and its influence on hydration and strength development of cement paste

Replacing part of cement with recycled clay brick powder (CBP) can ease the environmental impact caused by construction waste disposal and cement production. This research studied the surface properties of CBP and its effect on the hydration and strength development of cement paste at the micro and sub-micro scales. Zeta potential measurement was applied to study the surface chemical properties of CBP. Based on it, the interactions between the main ions in the cement paste solution and the surface of CBP were discussed. Then the effect of CBP on the nucleation and growth of hydrates, and CBP/hydrates interfacial strength was investigated. The results show that CBP has similar surface properties as quartz powder (QP), even though the chemical compositions of them are different. Silicate is the main phase at the surface of CBP. The interactions of CBP’s surface with Ca2+ are due to an electrostatic force, which has an important effect on the nucleation and growth of hydrates (mainly C-S-H) on the surface of CBP, and the adhesion between CBP and the hydrates. The morphology of hydrates on the CBP particles is similar to that on the QP particles. It suggests that the effect of CBP particles on the early hydration of cement is mainly due to its physical properties, rather than the chemical activities. The interface between CBP and hydrates is very weak, and the chemical reaction of CBP in the cement paste is rarely presented. The main role of clay brick used in this study playing in cement paste is a filler, similar to quartz particles.

Accelerated Early Age Hydration of Cement Pastes Blended with Sulphoaluminate Expansive Agent

Accelerated Early Age Hydration of Cement Pastes Blended with Sulphoaluminate Expansive Agent

Pozzolanic activity of mechanochemically and thermally activated coal-series kaolin in cement-based materials

The shortage of good quality supplementary cementitious materials (SCMs) for producing cement concrete eagerly demands an alternative pozzolan material. Thanks to the rich silica-alumina contents and large reserves in China, coal-series kaolin (CK) (a by-product of coal mining) is promising to be used as an effective SCMs in cement-based materials. This study investigated the effectiveness of using thermally activated CK coupled with mechanical grinding in ordinary Portland cement paste and mortar. The mineralogy, physicochemical structures, thermal decomposition, pozzolanic reactivity of this novel treated CK were evaluated and compared with two water-washed high-purity kaolinitic clays. The results showed that the large change of Al coordination environment in the thermally activated CK at a relatively low temperature (650 °C) rendered a high pozzolanic reactivity. The high content of kaolinite and reduced particle size by mechanical treatment were beneficial to enhancing the reactivity of thermally activated CK. With the use of thermoactivated CK, the early hydration of cement paste was significantly accelerated. The high degree of dihydroxylation, large specific surface area and high pozzolanic reaction of thermoactivated CK contributed to refining the pore structure and improving the compressive strength of blended mortar. The results of this study provided an implication of using treated CK as an alternative SCMs.

Physical and Chemo/Mechanical behaviors of fly ash and silica fume belite cement pastes- Part I

Physical, chemical and mechanical properties of high belite cement (HBC) blended with high pulverized fly ash (HPFA) with stable ratio of silica fume (SF) in comparison with Portland cement (OPC) were investigated. Results showed that the water of consistency and setting times (Initial and final) tended to increase with the increase of HPFA content. The bulk density and compressive strength were also improved and enhanced with the increase of HPFS content at all hydration times, but only up to 15 % HPFA, and then decreased with further increase. However, the total porosity slightly decreased, but started to increase with further increase of >15 % HPFA. The free lime content of the pure OPC and HBC gradually were increased as the hydration times progressed up to 90 days, while those of blended cements increased only up to 7 days and then decreased onward. The results were confirmed by measuring the heat of hydration and ultrasonic pulse velocity for the optimum cement pastes comparing with those of both OPC and HBC. The heat of hydration of the optimum cement pastes was decreased at all hydration times and become lower than those of OPC and HBC. The ultrasonic pulse velocity test (USPV) proved that the uniformity and quality of the matrix of the hardened cement pastes are good with no cracks.

Long-term thermal performance of oil well cement modified by silica flour with different particle sizes in HTHP environment

The high temperature and high pressure (HTHP) cementing environment results in strength retrogression and structure degradation of oil well cement sheath. Silica flour is commonly incorporated in cement paste as a high-temperature stabilizer to enhance the thermal stability. This work investigated the long-term thermal stability of cement pastes modified by silica flour with different particle sizes. The compressive strengths of cement pastes cured at 80 ℃ × 0.1 MPa and 260 ℃ × 21 MPa for 1, 7, 28, 90, 300 and 400 d were tested. The phase evolution and microstructure development of cement pastes were characterized by XRD, TGA, MIP and SEM. The results showed that the oil well cement pastes incorporated with 200-mesh silica flour had the highest compressive strengths after HTHP curing. The pastes with 1000-mesh silica flour exhibited lower thermal stability, because more calcium-rich hydration products were formed in the matrix after the thermal exposure. The dissolution of silica flour under HTHP conditions was not the main factor controlling the hydration of cement pastes. The 1000-mesh silica flour released more Si4+ than the 200-mesh one. This reduced the diffusion rate of Ca2+, resulting in a decrease in the rate of hydration. This affected the compressive strengths of cement pastes modified by silica flour in HTHP environment.

Early assessment of hydration and microstructure evolution of belite-calcium sulfoaluminate cement pastes by electrical impedance spectroscopy

In this paper, the interconnectedness among the electrical resistivity, the calorimetric heat and the chemical shrinkage of high Belite calcium sulfoaluminate (BCSA) cement are discussed. Microstructure analyses by using XRD, NMR, ICP-MS and SEM are applied to further demonstrate the relationship among the microstructure, the compositional variation and the electrical resistivity of the hydrated cement paste. Two distinctive hydration stages can be differentiated from the BCSA cementitious materials. First stage is mainly controlled by hydration process of both the ye’elimite and the gypsum, and the second stage is mostly controlled by the formation of AFm and amorphous phases as a secondary hydration process. According to the classic equation depicted the hydration degree of cementitious materials, a specific mathematical equation combining not only traditional parameters but also the electrical resistivity is proposed for the BCSA.