Hydration Of Pastes Research Articles

Study on the damage resistance and deterioration behavior of GO concrete under the harsh environment.

To exploretheeffects of physical, mechanical, anti-deterioration properties of graphene oxide (GO) on cement-based cementitious materials, GO sheet dispersions areprepared by the improved Hummers method and ultrasonic dispersion method. The influence of theGO content on the compressive and flexural strengths of cement paste is investigated, and the penetration process of chloride ions in graphene oxide concrete is discussed by the electric accelerated erosion method. Combined with the rapid freeze-thaw test, the deterioration of graphene oxide concrete ismethodically analyzed. Theobtained results reveal that an appropriate amount of GO improves both the compressive and flexural strengths of cement pastev. In the chloride environment, the chloride diffusion coefficient of 0.03% GO concrete is 18.75% less than that of ordinary concrete.Under the action of freeze-thaw cycles, with the increase of salt freezing times, the deterioration mode of GO concrete is a combination of mortar shedding, micro-crack expansion, denudation, and block shedding; The stress-strain curve of the specimen tends to be flat with the growth of salt freezing times. The peak stress gradually lessens, the peak strain gradually grows, and the elastic modulus remarkably reduces. Compared with ordinary cement paste, theGO is capable of promoting the growth of cement paste hydration crystals, changing the size and shape of crystals, and realizingthe regulation of cement paste microstructure. Incorporating an appropriate amount of theGO could promote the cement hydration process and enhance the chemical water-binding amount in the cement paste. The optimal GO content is reported to be 0.03% of the cement mass.

New insights into the impact of inorganic salt on cement pastes mixed with alkali free liquid accelerator in low temperature

Alkali-free liquid accelerators are crucial components of sprayed concrete, and their performance is affected by low environmental temperatures. Therefore, the setting time of the paste is prolonged and the early strength is reduced. In this study, the effect of different types and amounts of inorganic-salt early strength agents on the performance of cement paste mixed with an alkali-free liquid accelerator at low environmental temperatures, was investigated. The results showed that mixing Ca(NO3)2, NaNO3, CaBr2, and NaBr improved the performance of the pastes at low temperatures. Using 1.5% CaBr2 in the mixture showed the most significant improvement in 1 d compressive strength, increasing it from 0.5 MPa to 3.2 MPa and shortening both initial and final setting times. Analysis of the paste hydration products confirmed that nitrate-AFm and bromide-AFm primarily promoted the mixing of an alkali-free liquid accelerator in a low-temperature environment. Therefore, a mechanism for synergetic improvement of nitrate and bromide was proposed.

Application of layer double hydroxide in cementitious matrices for the improvement of the double Barrier Technique in the immobilisation of lead waste

This research deals with the immobilisation of lead-contaminated waste by means of the Double Barrier Technique. Specifically, the integral treatment of lead-contaminated water is studied by incorporating Layer Double Hydroxides (one calcined and two uncalcined) into cement monoliths. The three Layer Double Hydroxides were composed of MgAl in the layer, the calcined with carbonate in the interlayer, and the other two with nitrate or meso-2,3-dimercaptosuccinic acid, respectively. In the first stage of research, the influence of Layer Double Hydroxides and lead on the heat of hydration in cement pastes was analysed. Subsequently, mortars were produced to evaluate compressive strengths, mineralogy and leaching behaviour in monolithic and granular state. The interaction of sulphate ion played an important role in delaying the first stage of hydration. However, the presence of Layer Double Hydroxides counteracted the detrimental effect of lead on the cementitious materials. The compressive strength was modified by Layer Double Hydroxides and lead, less than 5 MPa in all cases, being in line with the heat of hydration. The mineralogical study determined the formation of the same mineral phases in all cementitious systems (with and without Layer Double Hydroxides). Mortars were environmentally classified as “Inert” in monolithic state. Mortar with MgAl in the layer and meso-2,3-dimercaptosuccinic acid in the interlayer was classified as “Non-Hazardous” in granular state reducing the mobility of lead to the medium by 50% with respect to the lead-doped mortar without Layer Double Hydroxides content. The results obtained in this research show the sustainability of the Double Barrier Technique as it achieves an immobilisation of lead-contaminated water while maintaining the criteria of release levels below the established limits.

Hydration, mechanical performance and porosity of Portland cement pastes with functionalized nanosilica with APTES

This study reports on the microstructure of Portland cement pastes with nanosilica (NS) and amino-functionalized nanosilica (NSF). For this, NSF dispersion was prepared in a two-phase reaction system, consisting of an aqueous dispersion with dichloromethane, using 3-aminopropyltriethoxysilane (APTES):NS molar ratio 1:28.62. Cement pastes were analyzed in the fresh state by consistency and in the hardness state by compressive strength, conduction calorimetry, X-ray diffraction (XRD), thermal analysis (TGA), infrared spectroscopy (FTIR) and mercury intrusion porosimetry (MIP). It was verified that the functionalized nanoparticles affected the hydration kinetic properties, indicating the extension of the induction period. Through microstructural analysis, it was observed that NSF increased the amount of the main mineralogical phases generated during Portland cement hydration or the pozzolanic reaction. Therefore, the NSF improves the Portland cement hydration and contributes to the densification of the microstructure of the cement pastes at 28 days.

Influences of Carbonated Recycled Concrete Fines on Cement Hydration

The preparation of recycled concrete aggregate generates a lot of fines, which are obstacles for implementing the recycled concrete aggregate. In this work, carbonation treatment is applied to improve the properties of recycled concrete fine, and the influences of carbonated recycled concrete fine (CRCF) on cement hydration process are evaluated. Both fresh and hardened properties of the cement paste samples replacing 0 to 30% of the CRCF are measured. The results reveal that the addition of CRCF obviously accelerates the hydration process of cement, especially during the early stage, and the initial and final setting times of the cement paste containing 30% CRCF are both reduced by approximately 25% compared to the control. The CRCF improves the strength gain of cement, and that influence becomes obvious with longer curing; the relative compressive strength of cement paste containing 30% CRCF is increased by 18% relative to the control after being cured for 28 days. At the same time, the early hydration of cement paste is accelerated with the addition of CRCF and the total hydration heat after 48 h of cement paste is significantly decreased with the addition of CRCF. Specifically, the total hydration heat after 48 h of cement paste with 30% CRCF is less than 50% of that with 0% CRCF. Besides that, CRCF consumes CH in cement paste and improves the pore structure of hardened cement paste. The morphology of hydrated samples shows that the shape of ettringite formed within the control sample with 0% CRCF is longer than those of the other ones formed in cement paste with CRCF, and the length decreases as the CRCF contents increase. In addition, the sample containing 30% CRCF does not show the particles, which means that CRCF reduces the ettringite forming in hardened paste samples. Thus, the findings from this work provide a better understanding of the field of waste concrete reuse.

An NMR study of the role of coir fibers in the hydration and drying of cement paste at early age

Natural fibers such as coir fibers have been increasingly explored as reinforcement in the cementitious composite to promote sustainable and economical construction. However, the in-situ application of this composite presents challenges due to the complex interplay of water behaviors, involving the hydrophilicity of natural fibers, the hydration of cement and the evaporation due to drying. Although these water-related processes play a crucial role in achieving the desired properties, they have been relatively underreported in the literature. This study aims to investigate the role of coir fibers in the water distribution and pore size distribution during the early age (initial 3 days) of cement paste hydration under drying conditions. Accordingly, Nuclear Magnetic Resonance (NMR) methods involving the moisture profiling and transverse relaxation are used to monitor the water distribution and pore size distribution in time but also in space. The samples are made by adding water-saturated coir fibers to the cement paste at different dosages (0, 1%, 2% and 4%). The effects of drying and coir fiber dosages on the samples are evaluated. The results show that drying leads to a moisture gradient and a larger transverse relaxation time T2, i.e., a coarser pore structure near the drying surface. By adding the saturated coir fibers, the moisture gradient caused by drying is decreased and spread out along the sample. As the coir fiber content increases, the water content along the sample and the total water content of the sample increase. As a result, the samples with coir fibers exhibit a lower T2, i.e., a denser pore structure near the drying surface. Coir fibers are shown to eliminate the adverse effect of drying on cement hydration through three effects, including the internal curing, improved water transport and crack control. The results from this study reveal the promising potential of coir fibers for in-situ construction applications.

Synergistic effect of recovering hardened cement powder and aluminum sulfate alkali-free liquid accelerator for enhancing the hydration and hardening of cement paste

The hardened cement powder (HCP) produced by the concrete waste disposal process can have a significant impact on the environment. How to effectively use HCP is the focus of current researchers. In this work, the synergistic effect of the treated hardened cement powder (T-HCP) and accelerator (ASS) was studied. The synergistic mechanism was studied by apparent porosity, hydration heat, XRD and SEM. Results demonstrated that the T-HCP can be used together with aluminum sulfate alkali-free liquid accelerator to improve the strength of cement. The main reason is T-HCP contains cement clinker mineral phase and fine CaCO3 crystals, in which the clinker mineral phase can be rehydrated, and the fine CaCO3 crystals can be used as nucleation sites to accelerate the generation of hydration products. Besides, adding T-HCP can improve the performance of cement mortar and save cost considering the economic aspects.

Evaluation of pozzolanic activity and environmental assessment of cement composites with lubricating oil re-refining ash

Lubricant oil is considered a hazardous waste, and its disposal in the environment represents a high risk of damage to ecosystems. The purpose of this work is to study the feasibility of using lubricating oil re-refining ash (LORR) as a pozzolanic material in mortar composites with 0–40% of cement replaced by LORR, and determining the optimal content. Systematic experiments were performed to investigate the effects of LORR on the cementitious material properties, including workability, mechanical and flexural strength and water absorption. Furthermore, the hydration of the cement pastes was analyzed using thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The results showed that LORR has high pozzolanic reactivity, increasing portlandite consumption, contributing to the additional formation of calcium silicate hydrate gel. Up to 30% LORR replacement resulted in similar mechanical properties to the control mortar. The leaching test showed that the raw LORR release 9 hazardous substances, including 6 heavy metals. The mortar proved to be effective for encapsulating all substances studied, in addition to contributing to the reduction of hazardous waste deposition in industrial landfills, and reducing the cost (less than24%) and embodied energy (less than29%) of eco-friendly cementitious materials. Therefore, the potential of lubricating oil re-refining ash for application in civil construction was demonstrated.

The Influence of Temperatures on the Hydration of Cement Paste at the Early Age, and Behaviour of Cement Paste with the Addition of Triethanolamine (TEA) and Triisopropanolamine (TIPA)

This paper intends to examine the influence of temperatures on the early age of cement paste hydration, as well as the setting time and the compressive strength of cement paste with the addition of Triethanolamine (TEA) and Triisopropanolamine (TIPA); hence, the mechanisms of TEA, and TIPA at different curing temperatures were explored. The outcomes show that adding 0.05% and 0.1% TEA, and 0.05% and 0.1% TIPA retarded the setting time of cement pastes; however, this retardation depended on both the dosage and the curing temperature. At 23°C curing temperature, both TEA and TIPA could be used as a hardening accelerator at the dosage of 0.05% by cement weight. Adding 0.05% TEA into the cement paste strongly accelerated the hydration of C3A and increased the early compressive strength, which was more efficient than adding 0.05% and 0.1% TIPA, especially after 8 hours of curing. However, at 50°C curing temperature, as TIPA strongly accelerated the formation of AFt, AFm, CH, using TIPA was more effective than using TEA to enhance the cement paste's compressive strength. These results can offer theoretical direction for the application of cement-based materials adding TEA and TIPA under hot and standard curing temperatures.

Alkali activation of paper industry lime mud and assessment of its application in cementless binder

This study revealed that the application of lime mud (LM) aids in construction materials that is sustainably economical, energy-efficient, and environmentally beneficial. A 2 M NaOH solution composed of 70% LM and 30% NaOH dissolved LM, and formed more reactive calcium hydroxide and carbonates, like thermonatrite and Pirssonite. It was confirmed with XRD, FTIR, and TGA of activated LM. Activated LM and untreated LM were used to prepare blends with ground granulated blast furnace slag (GGBFS) and silica fume. Activated LM was found to be compelling in the improvement of the reactivity of binder paste for all substitution extents and resulted in superior compressive quality in comparison to binder with untreated LM. Mineralogical analysis and an isothermal calorimeter showed the development of more hydration products and heat of hydration in binder pastes with activated LM. The leaching test and life cycle analysis also highlight the effectiveness of the proposed method.

The investigation of early hydration and pore structure of Portland cements containing waste dolomite powder based on 1H NMR

Waste dolomite powder (WDP) is being actively investigated as the additive of Portland cement (PC) for lowering the energy consumption and carbon emission of PC. In this work, 1H low-field nuclear magnetic resonance (1H NMR) was used to analyze the impacts of WDP on the hydration and pore structure of PC pastes at the early age. Meanwhile, the compressive strengths of blended cements containing 5–20% WDP were also measured. The results show that the T2 average value and evaporable water content of all the pastes decrease dramatically from 0 to 24 h, and the reduction rate slows down after 24 h. Adding 5% WDP can decrease further the T2 average value and evaporable water content attributed to its nucleating and filler effect, resulting in the compacted pore structure and the higher strength. However, adding more than 5% WDP degrades the pore structure and lowers the compressive strength.

Sustainable approach to simultaneously improve the pozzolanic activity of sugarcane bagasse ash and the vinasse fertilization potential

The purpose of this study was to evaluate the viability of sugarcane bagasse ash as a sustainable supplementary cementitious material and its association with improving the fertilizing properties of vinasse, used as a leaching agent. Thus, a bagasse ash with low quartz contamination was divided into three parts: one kept in natura, one submitted to citric acid leaching and the third to vinasse leaching. After production, which was concluded with re-calcination and ultrafine grinding, the three ashes were characterized according to their chemical and mineralogical composition, particle size, porosity, density, and pozzolanic activity. Paste hydration with 20 wt% cement replacement by each ash was assessed in isothermal calorimetry and chemical shrinkage tests. The elemental and oxide composition of vinasse before and after leaching was also obtained. The results showed that vinasse leaching promoted an increase in specific surface area and pozzolanic activity of ash, comparable to that observed for citric-acid leaching procedure. Tests with pastes containing vinasse-leached ash confirmed the improvement in cement hydration. In addition, after leaching, vinasse exhibited a decline in heavy metal concentration, increased pH (neutralization) and macronutrient concentration. Thus, vinasse leaching improved the pozzolanic characteristics of ash, making vinasse a more environmentally friendly fertilizer.

Roles of carbonated recycled fines and aggregates in hydration, microstructure and mechanical properties of concrete: A critical review

CO2 mineralisation by recycled concrete is a novel approach of carbon capture and utilisation to improve the sustainability of concrete products, which has attracted increasing attention in recent years. This paper presents a comprehensive review on carbonation mechanisms related to CO2 mineralisation and hydration, microstructure and multiscale mechanical properties of concrete containing carbonated recycled concrete fines and aggregates, with special focus on the chemistry-microstructure-property relationships. The carbonation kinetics of recycled fines in aqueous environment exhibit a typical particle size effect, while the high pozzolanic reactivity of carbonated recycled fines can facilitate the nucleation and stabilization of hydration gels and contribute to the rapid hydration of cement paste. Carbonated recycled aggregates are favourable in enhancing the micro-mechanical properties of interfacial transition zone in concrete through the synergic effects of physical interlocking and chemical bonding. Compared to concrete with plain recycled aggregates, up to 33.0%, 12.1% and 28.7% rises in compressive, splitting and flexural strengths of concrete can be achieved under 100% replacement of carbonated recycled aggregates. Due to the Stefan effect, concrete with carbonated recycled aggregates has higher dynamic peak stress but lower strain-rate sensitivity of elastic modulus than concrete with plain recycled aggregates. The global CO2 mitigation capacity of recycled concrete varies from region to region and thus reasonable transportation network and high-efficient carbonation process are essential to ensure a balance between the environmental and economic benefits. This review summarises the recent advances in the field and discusses some future research opportunities to develop low-carbon concrete with recycled concrete as a carbon sink.

A quantitative approach to determining sulfate balance for LC3

Achieving the correct sulfate balance in limestone calcined clay cements (LC3) to control aluminate hydration is critical for early hydration and property development, but the role of the calcined kaolin (metakaolin) fraction relative to other compositional variables has not been previously well-explored. In addition, little published research has investigated the influence of water-to-solid ratio (w/s) and superplasticizers in this context. This study assesses the influence and quantifies the relative significance of compositional predictors on the sulfate balance and cumulative heat evolved by 24 h for LC3 through a stepwise regression model. Sulfate balance was defined as the time difference between the sulfate depletion point and the time of maximum of alite peak obtained from a time derivative of data obtained through isothermal calorimetry. A methodology based on Kernel smoothing was used to precisely identify these events. The first 24 h of hydration of some LC3 pastes was also monitored via in-situ X-ray diffraction to develop linkages between LC3 composition and hydrated phase assemblage. The statistical analysis identified the metakaolin fraction as particularly significant for the sulfate balance. The results suggest that the metakaolin fraction influences the sulfate balance of LC3 both directly and through its interactions with other constituent materials such as limestone.

Co-utilization of aqueous carbonated basic oxygen furnace slag (BOFS) and carbonated filtrate in cement pastes considering reaction duration effect

It is generally agreed that aqueous carbonation of basic oxygen furnace slag (BOFS) is a promising and effective strategy to sequestrate CO2 and enhance the slag properties for use as a construction material. However, the handling of wastewater produced in the aqueous carbonation route is still a challenge. This work investigates the impact of co-utilizing carbonated BOFS as a partial cement replacement and carbonated filtrate as a mixing solution on the fresh and mechanical properties as well as the hydration and microstructural characteristics of cement paste. The carbonation duration of BOFS via the aqueous route (0, 10, 20, 30, 40, 80, and 120 min) was studied, and it was found that calcite was the dominant CaCO3 polymorph with different crystal shapes depending on the concentration of Mg ion in the slurry solution. The early-age compressive strength of blended cement pastes improved with the addition of 15% BOFS slurry carbonated for 40 min compared to as-received BOFS since the in-situ produced fine CaCO3 particles in the former could promote nucleation sites for cement hydration. However, the strength of pastes containing BOFS slurry carbonated for a longer duration was decreased due to the inhibited hydration reaction induced by the nesquehonite (MgCO3∙3H2O). At later ages of hydration, the nucleation effect was less obvious and the strength of cement paste was limited by the lower cement content. Moreover, the volume expansion issue caused commonly by f-CaO/MgO in BOFS can be improved through the precipitation of CaCO3 and nesquehonite.

Influence of direct electric curing on the hydration and microstructure of cement paste excluding ohmic heating

A modified apparatus based on isothermal calorimetry was employed to determine the influence of direct electric curing (DEC) on the hydration of cement paste other than ohmic heating effect. In addition, the effects of DEC on the microstructure of cured cement pastes were investigated by TG, XRD, NMR, SEM and MIP. The results show that the heat release of DEC samples at early-age is increased significantly due to the electrical power. However, the hydration and microstructure of DEC samples in the isothermal environment are familiar with the normal curing sample. This indicates that, other than OH effect, the impact of DEC on the hydration process and microstructure of cement is negligible. Moreover, a theoretical model for predicting the electric power evolution related to porosity, free water content, hydration degree and initial electric power per unit mass was established which is matched well with the actual measurement results.

Effect of using grounded coral sand on hydration and strength development of portland cement paste: Experimental and GEMS modelling investigation

The use of coral sand is mainly focusing on how to use it as aggregate in marine areas, much fewer studies have been conducted to investigate its usage as SCM (supplementary cementitious material) after being grounded into powder. In this context, the influence of CSP(coral sand powder), used as SCM, on the hydration and strength development of Portland cement paste was investigated. In order to describe the hydration process, Experiments including Isothermal calorimetry, XRD and TG analysis were used, along with the GEMS modelling system. The effect of CSP content, curing temperature and w/c were investigated in this study. The result shows that coral powder plays a nucleus effect in the process of cement hydration, which promotes the early age hydration of cement. Low coral powder substitution rate of no more than 10% can enhance the strength development of CSP concrete. However, with the increase of age and replacement rate, the coral powder shows a dilution effect which would slower the exothermic rate of the cement system. As to the hydraulic products. The results shows that the form of aluminum-containing hydration products in the coral powder-cement-based system is closely related to the content of coral powder. Apart from these, the increase of the w/c ratio is conducive to increase the hydration rate and hydration product content of coral powder-Portland cement systems. And with the increase of hydration temperature, the hydration rate of the cement system and the generation rate of hydration products are accelerated, although the main type of hydration product is not changed.

Fresh properties of limestone-calcined clay-slag cement pastes

Formulation of quaternary blended system containing ordinary Portland cement or clinker, slag, limestone and calcined clay (LC2) appeared to be a viable approach to developing low-clinker cements without severely sacrificing mechanical performance at later ages. This paper investigates the effect of two material parameters, i.e., LC2-to-slag ratio and gypsum content, on fresh properties, hydration, and compressive strength of quaternary blended cement pastes (about 65 wt% of LC2 and slag in the binder). Results show that the increase in LC2 proportion decreased flowability and increased water retention capacity, yield stress, and plastic viscosity, as well as accelerated the evolution of stiffness with time (G′ growth). On the other hand, the addition of 2–4 wt% gypsum had little effect on most of the fresh properties. A new metric, the free water indicator, was proposed to describe the effect of free water content and the total specific surface area of binding materials. It correlated strongly with the growth of structural build-up metrics. Finally, adding gypsum delayed the aluminate peak and enhanced compressive strength only at 3 days, whereas increasing slag content reduced accumulated heat of hydration (7 days) but improved 28-day compressive strength. Therefore, adjusting LC2-to-slag ratio of the quaternary blended cement is a feasible way to meet requirements for fresh properties and compressive strength.

Effect of Class C and Class F Fly Ash on Early-Age and Mature-Age Properties of Calcium Sulfoaluminate Cement Paste

To promote the sustainable development of eco-efficient calcium sulfoaluminate (CSA) cements through the partial replacement of the CSA clinker with supplementary cementitious waste products, the effects of coal fly ashes on the early-age and mature-age properties of a calcium sulfoaluminate (CSA)-based cement paste were investigated. The impacts of both Class C and Class F fly ashes on the rheological properties, hydration kinetics, and compressive strength development of CSA cement paste were studied. Rheology-based workability parameters, representing the rate of loss of flowability, the rate of hardening, and the placement limit, were characterized for the pastes prepared with fixed water-to-cement (w/c) and fixed water-to-binder (w/b) ratios. The results indicate a slight improvement in the workability of the CSA paste by fly ash addition at a fixed w/b ratio. The isothermal calorimetry studies show a higher heat of hydration for the Class C fly ash-modified systems compared to the Class F-modified systems. The results show that fly ash accelerates the hydration of the calcium sulfoaluminate cement pastes, chiefly due to the filler effects, rather than the pozzolanic effects. In general, ettringite is stabilized more by the addition of Class F fly ash than Class C fly ash. Both fly ashes reduced the 1-day compressive strength, but increased the 28-day strength of the CSA cement paste; meanwhile, the Class C modified pastes show a higher strength than Class F, which is attributed to the higher degree of reaction and potentially more cohesive binding C-S-H-based gels formed in the Class C fly ash modified systems. The results provide insights that support that fly ash can be employed to improve the performance of calcium sulfoaluminate cement pastes, while also enhancing cost effectiveness and sustainability.

Utilization of Steel Micro-fiber and Carbon Nanotubes in Self-compacting Lightweight Concrete

In this research, the engineering characteristics of self-compacting lightweight concrete (SCLWC) containing carbon nanotubes and steel micro-fiber were evaluated. The variables included the amount of carbon nanotubes (0, 0.02, 0.04, and 0.06% by weight of cement) and steel micro-fiber (0, 0.5, and 1% by volume). Lightweight expanded clay aggregate was used as lightweight aggregates. The experimental tests were self-compacting tests, compressive, splitting tensile, and flexural strengths, ultrasonic pulse velocity, electrical resistivity, water penetration depth, and scanning electron microscope. Adding 0.02 to 0.06 percent of carbon nanotubes to SCLWC reinforced with steel micro-fiber increases the compressive strength by about 33 to 64 percent. The use of 0.06% carbon nanotubes and 1% steel micro-fiber increased the splitting tensile strength by 36%. The use of carbon nanotubes and steel micro-fiber has the effect of influencing the filling of empty spaces and reducing concrete porosity. This can be attributed to the growing process of cement paste hydration and the filling of pores and capillary pores with the products of cement reactions, resulting in concrete compaction. Adding 0.02% carbon nanotubes to SCLWC samples containing 0.5% and 1% steel micro fibers increased the 28-day compressive strength by 36%, 34% and 33% respectively.