Cement Hydration Reaction Research Articles

Study on Strength Development and Microstructure of Cement-Solidified Peat Soil Containing Humic Acid of Dianchi Lake

The disposal of peat soil poses an increasingly difficult problem for actual engineering projects of Dianchi Lake area. This study obtains peat soil from seven areas around Dianchi Lake, and the content of humic acid (HA) in peat soil is between 2.36% and 28.13%. Then, this study simulates the peat soil by adding HA into the cohesive soil and uses cement to solidify it. The effect of cement and HA on the strength development of samples is examined by the unconfined compressive strength (UCS) test. Additionally, the microstructures of typical mixes are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results showed that HA will significantly reduce the UCS of cement soil. The SEM, XRD, and MIP confirmed that cement hydration reaction increases with cement ratio. In addition to the cementitious soil particles, hydration products gradually fill the pores of the soil and effectively reduce the number of large-size (6000∼40,000 nm) pores in cement soil, which makes the soil particle framework stronger. When the cement ratio increases from 15% to 25%, the diffraction peak of CAH and CSH increases faster. Combined with the results of the UCS test, it could be proved that cement ratio greater than 20% weakens the influence of HA on the strength development of cement soil sample.

Effect of abaca natural fiber on the setting behavior and autogenous shrinkage of cement composite

In this study, the effects of abaca fibers on the initial hydration and autogenous shrinkage characteristics of cement were investigated with the aim of using natural abaca fibers as construction materials. Abaca fiber content was chosen as the primary experimental variable and was varied from 0 to 0.25, 0.5, 1, and 2% of the weight of cement for testing. To identify the influence of the fibers on the hydration reaction of cement, the heat of hydration, ultrasonic pulse velocity, and setting time were measured. The internal curing effect of abaca fibers was evaluated using thermogravimetry and microstructure analysis by conducting compressive strength and autogenous shrinkage tests. The results indicate that abaca fibers can be used as internal curing agents owing to their high water absorption rate, which results from the cross-sectional characteristics of their hollow bundle-type tubular structure. Abaca fibers are found to be an effective alternative that can mitigate the risk of cracking by reducing the autogenous shrinkage of high-performance cement concrete products.

EFFECT OF INCINERATED SUGARCANE BAGASSE IN REDUCING HEAT OF HYDRATION IN CONCRETE

Incinerated sugarcane bagasse (ISB) is an agro-based industrial waste material which is rich in silica. It has been observed that it has the potential to reduce the heat that will be generated from hydration reaction. Lower rate of heat release and lesser magnitude of heat production during the hydration reaction of cement are desirable properties in mass concreting and production of concrete in hot weather condition. In this study, the heat evolution and tensile strength development of concrete with and without the inclusion of ISB was examined. A systematic volume-based replacement of cement by ISB was made with ISB amount of 10%, 20% and 30%. The hydration kinetics of cement paste with various percentages of ISB was checked using differential calorimeter. In addition, a concrete made with ISB was prepared and the temperature evolution history was traced in an environmentally controlled chamber. The heat generated from a set of concrete samples were studied under a surrounding temperature of 250 C and 500 C. Results obtained from both the differential calorimeter of cement paste and the concrete in the controlled chamber indicate, with the increase of the ISB replacement, the rate of heat release and the amount of heat generation within the mix decreases. In conjunction, with the increase of ISB up to 20% the early-age tensile strength of concrete increases. These two important attributes of adding ISB to concrete signify reduction in the risk of early age cracking in concrete.

Experimental Investigations on the Mechanical and Microscopic Behavior of Cement-Treated Clay Modified by Nano-MgO and Fibers

Cement is often used to stabilize soft clay; however, it has some limitations in increasing clay strength and improving clay failure mode. To solve this, two different additives, i.e., polypropylene fiber and nano-Magnesium Oxide (MgO), were tested with the purpose of improving the mechanical performance of cement-treated soft clay. Four groups of samples with different mixture ratios of coastal soft clay, cement, fiber, and nano-MgO were first designed. Microscopy tests including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), as well as unconfined compression test was then carried out. XRD and EDS test results show that the cement hydration reaction is the main source of strength increase and the nano-MgO can generate Magnesium Silicate Hydrates (M-S-H) gelation, which helps to fill the pores of the clay and increase clay compactness. The unconfined compressive strength test results show that adding fiber or nano-MgO alone has a poor effect on the strength improvement for cement-treated clay with high water content. However, adding both additives lead to a significant increase in the clay’s unconfined compressive strength, which is verified by the microscopic observation of clay compactness in SEM images. Moreover, the fiber is found to increase the ductility of cement-treated clay based on the observed failure modes of modified samples.

Stabilization nature and unified strength characterization for cement-based stabilized soils

Although extensive studies have been conducted on cement-based stabilized soils (CBS), there is limited research focusing on the effect of water content, sand/silt fraction and particle size distribution of the original clays on the unconfined compression strength (UCS) of CBS. In this study, experimental results were combined with the available data collected from the literatures to clarify the effect of the water content, sand/silt fraction and size distribution on the CBS strength and to develop a generalized predictive strength equation for clays with various gradations, water contents and cement contents. The findings suggest that at a constant cement mass, original dry clay and water, the addition of sand (<80% in this case) has no influence on the UCS. However, at the same cement mass, water, and total soil (e.g., original clay with incorporated sands), the UCS decreases because of less absorbed water and more available water with sand substitution. It can be concluded by the scanning electron microscopy (SEM), that sand acts as hard inclusions within the CBS matrix. Based on the nature of the sand function within the CBS, a modified binder/water ratio (new indicator) was proposed to characterize the UCS by combining the traditional binder/water ratio and the mass ratio of the clay fraction to water. Using the modified binder/water ratio, the strength predictive equation was developed, which is useful as a tool for mix design to attain a target strength. The powerfulness of the equation is confirmed by the prediction results of the available CBS data collected from the literatures. The slope of the equation is found to be dependent on the cement hydration and pozzolanic reaction with clay minerals.

High-temperature CO2 for accelerating the carbonation of recycled concrete fines

Accelerated carbonation of recycled concrete fines (RCF) is one of the effective ways of improving their poor quality for sustainable reuse in the construction industry. Flue gas containing waste heat that is usually discharged into the atmosphere can be reused to enhance the gas-solid reaction of RCF carbonation. Therefore, this study investigates the influence of high temperature (20–140 °C) CO2 (with a concentration of 20%) on the carbonation performance of RCF, whereby it is demonstrated that the carbonation efficiency is greatly enhanced by increasing the temperature optimally up to 100 °C and achieving 21.65% CO2 uptake. Vaterite and calcite are the main carbonation products of the carbonated RCF (CRCF), especially where calcite becomes larger and more stable with a higher temperature of carbonation. The CaCO3 polymorph affects the rate of cement hydration in which the vaterite plays an important role in enhancing the early-age cement hydration reaction, whereas the calcite in the CRCF has less impact due to its more thermodynamically stable characteristic. Overall, it is concluded that the higher carbonation degree of CRCF results in better performance as a cement substitute. Cement paste containing CRCF at 100 °C possesses a shorter setting time, higher heat of hydration, and a comparable 28-day strength to that of pure cement paste.

Effect of alkaline pre-treatment and chemical additives on the performance of wood cement panels manufactured from sunflower stems

This research was performed to investigate the NaOH pre-treatment, chemical additives, and their combined effects on the properties of wood cement panels produced with sunflower stems. The experimental panels were produced with a target density of 1200 kg/m3, a wood/cement ratio of 1:3 and a dimension of 500 mm × 500 mm x 10 mm using the treated/untreated sunflower stem particles as a partial replacement of poplar wood and various chemical additives (CaCl2, AlCl3, MgCl3). The physical, mechanical, thermal, and morphological properties of sunflower stem-based cement panels were evaluated and compared with traditional wood cement panels. In general, the highest mechanical properties were obtained from the panels produced by using the CaCl2 additive and a mixture of pre-treated sunflower stems (40%) and aspen poplar (60%). The panels containing 100% sunflower stem particles-treated with NaOH reached mechanical properties above the minimum standard requirements when CaCl2 was added. The panels’ water resistance, dimensional stability, and mechanical performance were remarkably enhanced by the NaOH pre-treatment of sunflower stems and the chemical additives. Moreover, the addition of sunflower stems led to a marked decrease in the thermal conductivity of the panels. TGA results demonstrated that the sunflower stem adversely affected the cement hydration reaction, whereas the chemical additives and the pre-treatment improved it. In addition, the combined effect of NaOH pre-treatment and chemical additives resulted in more portlandite content in the WCPs compared to their separate use. The SEM observations revealed that the NaOH pre-treatment of sunflower stems and the chemical additives contributed to promoting cement hydration products. It was also observed that the honeycomb structure of sunflower stem pith was crushed and deformed due to the high pressure applied in the manufacture of WCPs.

Study on the Characteristics of Grinding Activation of Fly Ash and Its Influence on Cement Cementitious System

This study takes fly ash of a coal-fired power plant as the research object, the pulverized and activated fly ash was processed by ball milling process. The difference of physical and chemical properties of fly ash before and after pulverized and activated treatment and its influence mechanism on cement cementitious system were studied by a series of characterization analysis methods. The results show that pulverized fly ash activation significantly reduces the particle size of fly ash, increases its specific surface area, and decreases the crystallinity of crystal minerals and anionic polymerization degree of internal silicon aluminate substance in fly ash, thus reaching the deep activation effect of fly ash activity. Fly ash powder can promote the compressive strength of test block more than fly ash original ash, especially the early compressive strength of test block. The experimental results of water absorption and thermogravimetry show that the effect of fly ash powder on test block is mainly to improve the compactness of test block, reduce its porosity. At the same time, accelerating the secondary hydration reaction of cement is bound to produce more C–S–H gel, thus improving the mechanical properties of test block.

Resource utilization from solid waste originated from oil-based shale drilling cutting during shale gas development

With the large-scale development of shale gas, oil-based drilling fluids are widely used, generating significant amounts of solid wastes from oil-based shale drilling cutting (OBSDC). These solid wastes are biologically toxic and are difficult to degrade. The current treatment methods do not meet the requirements for oily sludge. This study begins with pyrolysis of OBSDC in order to use it as an external admixture for preparing cement slurry for resource utilization. The research results showed that when the OBSDC content was increased to 35%, the mechanical properties of developed cement were favourable. Evaluating the cement sheath integrity showed that the OBSDC cement met the subsequent production requirements for a casing with an internal pressure of 50.01 MPa, applicable for cementing surface casings as well as technical casings. The active SiO2 and feldspar in OBSDC after pyrolysis promoted the hydration reaction of cement and accelerated the crystallization of C-S-H, which in turn complemented the cement mechanical properties. When OBSDC was in the proper dosage range, the particle gradation characteristics further optimized the pore structure of the cement matrix and increased the cement strength.

Physical, mechanical properties and durability of cement mortars containing fly ash from the sewage sludge incineration process

Pursuant to European Union regulations, waste generated during municipal sewage treatment should be managed in an environmentally friendly manner. In order to eliminate the risk to human health and to the environment, and also to minimise the volume of the resulting sludge, it is subjected to thermal treatment. The resulting ash contains heavy metals, and thus proper management is required. Since it is known that products of cement hydration reactions have a potential ability to immobilise heavy metals, a preliminary verification was conducted of the possibility of disposing of this type of waste by including it in cement composites. For this purpose, suitable tests were carried out on the mechanical properties and durability of cement binders containing ash from the incineration of sludge produced from municipal sewage (Sewage Sludge Ash – SSA). The tests were conducted for a standard mortar composition based on Portland cement CEM I and on ash obtained on a technical scale in a sewage treatment plant at a temperature of about 850 °C. This mineral addition was used to replace 10%, 20%, 30% and 40% of the cement by weight. The physical and mechanical characteristics were measured, such as compressive and flexural tensile strength after 14, 28 and 90 days of curing as well as durability characteristics such as total porosity, the ability to transport chloride ions and resistance to sulphate ions. The results obtained confirm that replacing 10% of the cement with this admixture has a beneficial effect on the mechanical and durability characteristics, but greater amounts are reflected in a clear deterioration of these characteristics.

Influence of calcination temperature of impure kaolinitic clay on hydration and strength development of ultra-high-performance cementitious composite

Despite the recent considerable interest in sustainable supplementary cementitious materials, the effect of calcined impure clay on ultra-high-performance cementitious composite (UHPC) is insufficiently understood. In this study, three impure kaolinitic clays calcined at 600 °C, 800 °C, and 1000 °C were compared with quartz powder in terms of hydration reaction and strength development of UHPC. As a function of calcination temperature, the clays had different effects on the properties of UHPC. The clays calcined at 600–800 °C increased the initial strength of UHPC (≤3 days) by ∼10–35% but show lower strength by ∼5–9% after 28 days compared to reference sample. It is because the clays accelerated both cement hydration and pozzolanic reaction at an early age of the UHPC, but the premature consumption of water and pore refinement inhibited the long-term pozzolanic reaction. In contrast, the clay calcined at 1000 °C no longer affected the UHPC’s strength after increasing the 1st-day strength by 17%, since it acted as an inert filler after early age (>1 day). However, once heat treatment (at 90 °C for 48 h) was applied to UHPC, all of the clays did not express pozzolanic reactivity because the main initiative for the pozzolanic reaction shifted from metakaolin to silica fume. From these results, it is concluded that the use of calcined clays does not notably reduce the strength of UHPC, as long as impure clays with sufficient kaolinite content (>40%) are used.

Dissolution of Portlandite in Pure Water: Part 2 Atomistic Kinetic Monte Carlo (KMC) Approach.

Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology changes of a hexagonal platelet portlandite crystal. First, the atomistic rate constants of individual Ca dissolution events are computed by a transition state theory equation based on inputs of the computed activation energies (ΔG*) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or , 010 or 00, or , and 001 or 00) are considered, resulting in a total of 16 different atomistic event scenarios. Results of the upscaled KMC simulations demonstrate that dissolution process initially takes place from edges, sides, and facets of 010 or 00 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 0) was computed to be 1.0443 mol/(s cm2); however, 0.0032 mol/(s cm2) for or , 2.672 × 10−7 mol/(s cm2) for 001 or 00, and 0.31 × 10−16 mol/(s cm2) for 100 or were represented in a decreasing order for less reactive facets. Obtained upscaled dissolution rates between each facet resulted in a huge (16 orders of magnitude) difference, reflecting the importance of crystallographic orientation of the exposed facets.

The research on mechanism of C-S-H nanocrystal improving early properties of shotcrete at low temperature by thermodynamic modelling

In this study, the effect of CSH nanocrystals on the performance of shotcrete are investigated in a low-temperature environment. Setting time and early compressive strength were evaluated for mixtures with different dosages of CSH nanocrystal at 5 ℃, 10 ℃, and 20 ℃. The results show that CSH nanocrystal can shorten the setting time of cement paste mixed with the accelerator, improve the 1 d compressive strength of shotcrete. Meanwhile, the typical samples hydration products and microstructure were determined using XRD, TG/DTG, and SEM, indicate that combined CSH nanocrystal and Alkali free liquid accelerator (AS) can accelerate the cement hydration reaction and promote hydration products AFt, CH, and C-S-H. Moreover, the thermodynamic model (GEMS) simulates the composition change of hydration products of cement paste mixed with CSH nanocrystal and AS at 5 ℃, 10 ℃, and 20 ℃; Confirmed that CSH nanocrystal significantly influences the early hydration products CH, AFt, C-S-H at different curing temperatures, which is similar to the experimental results. Therefore, based on the experimental and simulation results, the synergistic effect of CSH nanocrystal and AS was proposed to solve the problems of a weak early performance of shotcrete and provide a reference for the construction of low-temperature shotcrete.

Combined effect of recycled tire rubber and carbon nanotubes on the mechanical properties and microstructure of concrete

The application of recycled tire rubber (TCR) in concrete replacing conventional aggregates offers high recycling potential. However, the poor bonding between the hydrophobic rubber particles and the cement matrix weakens the material's mechanical properties. This study investigated the combined effect of carbon nanotubes (CNTs) and TCR on the mechanical properties of concrete, as well as microstructure characteristics. The different CNTs, surfactants, and ultrasonic dispersion time were subjected to a screening procedure in cement paste. Concrete production and mechanical performance tests are carried out after obtaining the above parameters. The results show that the improvement of the compressive strength of concrete by CNTs is negatively correlated with the content of TCR. The reinforcement behavior of CNTs has no subordinate properties among compressive strength, flexural strength, and splitting tensile strength. The morphological characteristics of CNTs-reinforced crumb rubber concrete (CNTCRC) revealed that CNTs refined the micropores as fillers. Furthermore, the poor interfacial bonding between TCR and cement matrix together with microcracks was modified due to the bridging effect of CNTs. In addition, the working mechanisms of TCR and CNTs in the cement hydration reaction were conceptually explored to help understand the reinforcing mechanism of CNTs on the macro level.

Rice Husk Ash Incorporation in Calcium Aluminate Cement Concrete: Life Cycle Assessment, Hydration and Strength Development

In this research effect of rice husk ash (RHA), as silicate impurities, on the hydration reaction and mechanical strength of calcium aluminate cement (CAC) concrete, as one of the most important non-Portland cements, was investigated. Furthermore, in order to evaluate the environmental performance of mixtures, a lifecycle assessment was performed using the recipe midpoint and endpoint method. Compressive and tensile strength tests were conducted at the ages of 7, 28, and 90 days on specimens containing different contents of RHA (0, 2.5, 5, 7.5, and 10%) substituting for cement at the water-cement ratio of 0.4. Moreover, in order to calculate the hydration reaction of the specimens, thermogravimetric analysis (TGA) was performed at a rate of 10 °C/min to up to 1000 °C. The results revealed that the use of rice husk ash as a partial replacement at a concentration of 5% could reduce CO2 emission and ozone depletion by 18.75% and 31%, respectively. The findings indicate that, at 90 days, the mechanical strength of the mixes containing RHA were higher than those of the control mix, with the maximum improvement occurring at the substitution percentage of 5%. In accordance with TGA analysis the substitution of 5% RHA in CAC concrete led to a higher hydration level, which in turn improved the mechanical properties relative to the specimen without RHA at 90 days.

Evaluating the effect of autoclave curing on the microstructure and compressive strength evaluation of a high strength concrete

High strength concrete is usually cast with low water-to-binder ratio (w/b) in order to produce a compact microstructure with high strength and durability. Autoclave curing can accelerate cement hydration and pozzolanic reactions and further modify microstructure of cement pastes (such as decreasing the Ca/Si ratio and forming crystallized calcium silicate hydrate). The present paper evaluates the effect of w/b ratio, in the range 0.20 – 0.40, on compressive strength, porosity and microstructure of a high strength concrete. Some samples were subjected to autoclave curing in order to evaluate the effect of this process on the parameters evaluated. The microstructure was evaluated using X-ray diffraction and scanning electron microscopy. The results show the porosity decreased when w/b ratio decreased from 0.40 to 0.30 and thereafter the total porosity remained virtually constant while the water permeable porosity increased. An inverse relationship is observed between the porosity and the compressive strength. Autoclave curing affects significantly the phases developed in hardened concrete. It accelerates hydration and pozzolanic reactions, affects the interfacial transition zone and triggers the formation of crystalline C-S-H. These changes reflect in improved compressive strength at a low w/b but its effect is negligible at moderate w/b ratios.

Influence of Early Strength Agent on the Strength and Water Resistance of Cement-Desulfurized Building Gypsum Composite Cementitious System

The test takes the cementing system composed of ordinary Portland cement and desulfurized building gypsum as the research object, and the research is carried out based on the mechanism of the early strength agent that can accelerate the cement hydration reaction in the composite cementing system. In the experiment, the influence of the type and dosage of the early strength agent on the strength and water resistance of the composite gelling system was studied to determine the appropriate type and optimal dosage of the early strength agent. The test results show that sodium sulfate has a poor improvement effect on the sample due to the presence of desulfurized building gypsum in the composite cementing system, while calcium chloride and calcium formate can effectively promote the hydration of the cement in the composite cementing system, significantly improving the compressive strength and softening coefficient of the sample. When the calcium chloride content is 2%, the compressive strength of the sample is increased by 57.0% compared with the reference sample, and the softening coefficient is 0.82. When the calcium formate content is 1%, the compressive strength of the sample is increased by 31.1% compared with the reference sample, and the softening coefficient is 0.80.

Geotechnical and microstructural properties of cement-treated laterites stabilized with rice husk ash and bamboo leaf ash

This study investigated the geotechnical and microstructural properties of cement-treated laterites stabilized with rice husk ash and bamboo leaf ash. In going about the tests, the soil sample was subjected to compaction, California Bearing Ratio (CBR) and preliminary tests; such as specific gravity, particle size distribution and Atterbergs limits to determine its index properties. Thereafter, the soil sample was mixed with cement at varying proportions of 0–12% at 2% intervals and also, separately mixed with bamboo leaf ash (BLA) and rice husk ash (RHA) in proportions of 0–16% at 2% intervals. The mixes at each stage were subjected to compaction, Atterberg limits and CBR tests. The highest values were 66.7% and 54.8% for unsoaked and soaked CBR at 6% cement+8% BLA and 78.5% and 63.8% for unsoaked and soaked CBR at 8% cement+8% RHA. Samples at these optimal CBR values were subjected into Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) tests. Results showed that new compounds were formed and there were changes in the microstructural arrangements. It can therefore be concluded that pozzolanic and cement hydration reactions actually took place in the course of stabilization.

Promoting effect and mechanism of several inorganic salts on hydration reaction of magnesium oxychloride cement at low temperature

In this work, the Magnesium oxychloride cement (MOC) added with five kinds of inorganic salts (CaCl2, Ca(NO3)2, KCl, LiCl, and NH4NO3) were prepared under the low temperature (5 ℃), and the effects of inorganic salts on the hydration reaction and engineering properties were investigated. The results show that the addition of inorganic salt can significantly improve the hydration reaction rate, increase the content of the 5-phase, and shorten the curing time. Compared with pure MOC, the compressive strength of MOC added with CaCl2 increased by about 128% after 7 days of curing. Moreover, the existence of inorganic salts weakened the surface shielding layer [Mg(H2O)6]2+ of active MgO, thereby improving the zeta potential of active MgO and promoting the diffusion rate of Mg2+. Overall, these results could provide valuable information for studying the hydration reaction and engineering performance of MOC at low temperatures.

Study on compatibility of poplar wood and Portland cement

Portland cement particle board is a new type of building decoration material prepared by Portland cement and wood or non-wood shavings as the main raw material. The polarity and compatibility of Portland cement pretreated particleboard are different, which makes it difficult to form poplar Portland cement particleboard. In this paper, the hydration characteristics of poplar and Portland cement were studied by measuring the temperature of poplar and Portland cement, poplar, Portland cement and additive hydration reaction mixture system, and then the compatibility of poplar and Portland cement was studied. Studies have shown that poplar wood contains water-soluble polysaccharides, formic acid and acetic acid. The water-soluble polysaccharide dissolves in water and transforms into sugar acid. The sugar acid reacts with calcium ion of hydration product of Portland cement to form a ball like sugar calcium complex. The calcium sugar acid will be coated on the cement particles to hinder the further hydration of cement and produce a certain anti setting effect on Portland cement. Water soluble carboxyl group will chelate with calcium ion of Portland cement hydration product, which will reduce the concentration of calcium ion in the hydration system, then affect the hydration process of cement, and also have a certain anti setting effect. Calcium chloride and sodium silicate can inhibit the retarding effect of water-soluble polysaccharide and organic carboxylic acid on Portland cement, and improve the compatibility of poplar and Portland cement. Sodium silicate has a better inhibitory effect on the coagulation blocking effect.