Study on optimization of hydration process of blended cement

In this study, the effect of nano-SiO2 on the mechanical properties, microstructure, and hydration process of cementitious materials incorporating hydrophobic admixture (CM-HA) was studied through mechanical strength and hydration heat tests, x-ray diffraction (XRD), a scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP). The results showed that the addition of hydrophobic admixture reduced the compressive strength of cement paste by about 18% in 28 days, and the addition of nano-SiO2 increased the strength of cement paste incorporating hydrophobic admixture by about 20% after 7 days, which indicated that the mechanical properties and strength development of CM-HA could be significantly improved by nano-SiO2 due to the nucleus effect, hydration activity, and nano-filling function, although hydrophobic admixture was not beneficial for the strength development due to the delay for hydration process. Results also indicated that nano-SiO2 could significantly accelerate the hydration rate and reduce the porosity of cement, especially the porosity of macropores. This study provided a new research method for alleviating the adverse effects of hydrophobic admixture on the mechanical properties and durability of concrete and implemented the application of nano-materials in hydrophobic materials.

Influence of LiAl-layered double hydroxides with 3D micro-nano structures on the properties of calcium sulphoaluminate cement clinker

Effect of TiO 2 on the hydration of tricalcium silicate

Hydration properties and kinetic characteristics of blended cement containing lithium slag powder

Fly ash has been widely used as supplementary cementitious material in concrete industry. Hydration mechanism of composite binder containing fly ash is much more complicated due to the mutual effect of the hydration of cement and the pozzolanic reaction of fly ash. This paper involves the hydration kinetics of composite binder containing up to 65 % of fly ash and comparison of the results with data on composite binder containing slag that are previously published. The hydration heat evolution rate and cumulative hydration heat of composite binder containing fly ash were measured at 298, 318 and 333 K with an isothermal calorimeter. Based on the hydration kinetics model, three hydration processes, namely nucleation and crystal growth (NG), interactions at phase boundaries (I) and diffusion (D) were characterized, the relationship between the hydration rate and hydration degree was discussed at different stages, and kinetics parameters, n, K and Ea, were calculated and analyzed. Results show that the hydration heat evolution rate and cumulative hydration heat of composite binder obviously decrease with increasing the replacement ratio of fly ash. Elevated temperatures promote the hydration process, especially for composite binder containing high amount of fly ash. The kinetics model could simulate the hydration process of composite binder containing no more than 65 % of fly ash, whose hydration process sequence is NG → I → D at 298 and 318 K, but it becomes NG → D at 333 K. Fly ash has relatively smaller effect on the overall reaction of composite binder than slag. The reaction rates of composite binder containing fly ash at different stages are higher than those of composite binder containing slag at the same replacement ratio. The value of Ea for the overall reaction of composite binder decreases first and then increases with increasing the content of fly ash, and it is lower than that of composite binder containing slag at the same replacement ratio.

Mechanical activation as an innovative approach for the preparation of pozzolan from iron ore tailings

Fluids capable of transporting proppant with the least formation and fractures contamination are one of the most relevant areas of the technological development of hydraulic fracturing treatment. In the world in recent years, there has been a tendency to switch from cross-linked guar-based fracturing fluids to synthetic ones. Highly viscous friction reducers find wider application in the new concept of modern industry development. Unlike traditional guar-borate-based fluids, these fluids have a number of advantages - they provide higher residual fracture conductivity, are less sensitive to the mineral composition and temperature of the water source, contain fewer chemical elements in the working formulation and, as a rule, are less demanding of equipping a hydraulic fracturing fleet. Also, in addition to the above features, note the possibility of making changes to an engineering solution immediately in the work process, ensured by the simplicity of fluid making-up and high hydration rate. Despite the obvious advantages in using synthetic fluid systems over standard guar-based systems, until now they have not been widely used in conventional reservoirs. This is supported by poor knowledge of the practical application associated with proppant transport and the absence of selection criteria based on the system rheological properties which significantly affect the hydraulic fracturing success rate. The paper describes a set of rheological studies, including building viscosity and elasticity profiles, as well as an assessment of the fluid system thermal stability. The viscosity behavior was also studied in a wide range of shear rates. The effects of elastic moduli were studied by conducting vibrational-shear tests in a spectrum of various frequencies. Quantitative and qualitative comparative measurements were carried out to study the settling rate of proppant, as well as its viscoelastic properties in a flow. The result of the study is generalized analytical findings on synthetic fluid systems confirmed by practical application in real conditions of conventional reservoirs in West Siberia. This paper will help to understand the key factors affecting the choice of fracturing fluid formulations based on high-viscosity friction reducers and, in the future, may become the basis for creating a methodology for testing synthetic gels.

A non-contact electrical resistivity measurement device was employed to indicate the early hardening process of cement asphalt emulsified mortar (CA mortar). It was found that this process was analogous with the hydration process of cement and could be categorized into three parts: dissolving period, induction period and setting period. The mortar resistivity first decreased and then increased with the elapsed time. The effect of water/cement ratio (W/C), asphalt emulsified/cement ratio (A/C), cement types were also explored. Results indicated that the increase of W/C, dosages in SF (Silica fume) extended the induction period; replacement of Portland cementII with sulfoaluminate cement in CA mortar markedly increased the electrical resistivity and advanced the onset of setting period by 5∼6 h, making it possible to prepare CA mortar with high early strength, which can preventing distress such as peeling and bleeding during construction in winter and conformance to requirements in acceptance standard.

Estimation of non-traditional supplementary cementitious materials potential to prevent alkali-silica reaction using pozzolanic reactivity and bulk resistivity

Enhanced pozzolanic reactivity in hydrogen-form zeolites as supplementary cementitious materials

Calcined clay limestone cements (LC3)

Partially replacing cement clinkers with activated clays is one of the most promising routes to decarbonise the cement industry and tackle the climate change crisis. This study systematically investigated the impact of mechanochemical activation on the physicochemical properties of kaolinite, muscovite and montmorillonite clays, including particle size distributions, morphologies, bulk and surface chemical structures. The results suggest that mechanochemical activation treatment is particularly efficient for improving the pozzolanic activity of 2:1 clays (i.e. muscovite and montmorillonite), which are difficult to effectively activate through thermal treatments and therefore not previously been extensively used as supplementary cementitious materials (SCMs). In addition to dehydroxylation and amorphisation, mechanochemical milling also leads to surface aluminium enrichment and reduction in binding energies of both Si and Al elements, all contributing to the enhanced pozzolanic reactivity. The outcome from this study represents a step-change in scientific knowledge and extends frontiers of developing new SCMs from sustainable resources.

Influence of foreign ions on calcium silicate hydrate under hydrothermal conditions: A review

This study investigates the effects of soaking method (ultrasound-assisted soaking (UAS) and conventional soaking (CS)), soaking solutions with varying pH (distilled water (W), citric acid (CA), and sodium bicarbonate (SB)), and soaking times (4, 8, and 12 h) on anti-nutritional factors (phytic acid (PA) and trypsin inhibitor (TI) contents), moisture absorption, and hardness of chickpeas, beans, and soybeans. Additionally, the study examined changes in soluble solids content (SSC), pH, turbidity, and color of the soaking solutions. While the soaking method and solution significantly (p < 0.05) affected TI content in seeds, they had no notable impact on PA content. The most notable reductions in PA were observed following 12 h of CS: 27.0% in chickpeas and 38.9% in soybeans soaked in water, and 30.5% in beans soaked in sodium bicarbonate. Sodium bicarbonate was more effective than citric acid and water in reducing TI. UAS generally led to greater TI reductions compared to CS, although its effectiveness was reduced in sodium bicarbonate. UAS resulted in higher hydration rates across all solutions. Chickpeas and beans soaked in citric acid for 4 h and soybeans soaked in citric acid for 12 h exhibited the lowest hardness values. UAS notably increased SSC, turbidity, and pH changes in the soaking solutions compared to CS.

Filling and nucleation are the mechanisms of modifying cement paste with nanomaterials, as investigated by previous studies, and are difficult to reflect the different effects of nanomaterials, especially on the changes of cement clinker and hydration products in the cement hydration process. In this study, the mechanisms of modifying cement paste with nano-calcium carbonate (NC), nano-graphene oxide (NG), nano-silica (NS), and nano-titanium dioxide (NT) were investigated by determining the mechanical properties of cement paste treated with nanomaterials and analysing the changes in the cement clinker (tricalcium silicate and dicalcium silicate), hydration products (portlandite and ettringite), and microstructure through many micro-test methods. The results indicate that the incorporation of nanomaterials could improve the early strength of cement paste specimens due to more consumption of cement clinker. Meanwhile, different nanomaterials promote the formation of different hydration products at early ages. C–A–S–H gel, flower-like ettringite, and C–S–H seeds are widely distributed in the cement paste with the incorporation of NC, NG, and NS, respectively. NT exhibits insignificant nucleation effect and has inhibitory effect on portlandite precipitation. This study provides key insights into the mechanism of nanomaterials from the perspective of cement hydration, which may promote the further research and application of nanomaterials in the cement and concrete industries.