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Synthesized nanocalcium-silicate-hydrate (C─ S─ H) was successfully employed as an accelerator in portland cement. C─ S─ H nanomaterials were produced in this study utilizing a process that used separate nucleation and growth steps with varied solvent compositions. The effects of the water/alcohol volume ratio (W/A) in the combined solvent on the calcium silicon ratio, particle size, morphology of C─ S─ H nanomaterials, and compressive strength of portland cement were studied. The results reveal that when the W/A ratio decreased, the calcium to silicon (Ca/Si) molar ratio reduced, and the morphology of the C─ S─ H nanomaterials turned from micalike to mixed lamellar and granular, then to granular with a wrinkled surface, and finally to foillike. When the W/A was 3∶1 , the small particles (100 nm) of C─ S─ H nanomaterials had the highest W/A, whereas the large particles (>200 nm) had the highest W/A. C─ S─ H nanomaterials offered calcium silicate hydrate nucleation sites, altered C─ S─ H gel development modes, and enhanced the number of hydration products. The composition, particle size, and shape of C─ S─ H nanomaterials all influenced the compressive strength of the cement paste. [ABSTRACT FROM AUTHOR]

Delaminated MXene was incorporated into cement to improve the properties of cement composites, and its effects on the hydration process, microstructures, and mechanical properties were investigated, respectively. The investigation results showed that delaminated MXene was well-dispersed in the cement matrix and significantly reinforced the compressive strength of cement, especially when the addition is 0.01 wt%. Meanwhile, the total hydration heat of cement hydration and the quantity of hydration products were increased with the addition of delaminated MXene. In addition, the formation of HD C-S-H gel was promoted, and the microstructure of hydrated cement became more compact. [ABSTRACT FROM AUTHOR]

Abstract: Fineness is one of the key factors in determining the hydration activity factor of slag. The present research investigates the effect of particle size distribution (PSD) of slag on water requirement, setting time, and compressive strength. For this purpose, a reference and 17 cement samples containing different blast furnace slag are made and the properties are tested. When slags with proper PSD are prepared the cement properties can be better than the reference. [Copyright &y& Elsevier]

Sintering red mud (SRM) is an industrial alkaline waste residue generated from the sintering process in alumina production, which is often directly discarded and causes environmental issues. In this study, an innovative magnesium-modified wet carbonation method was proposed to convert sintering red mud to valuable calcium carbonate whiskers using CO 2 -containing flue gas. The effects of carbonation conditions including temperature, MgCl 2 concentration, and duration on the composition, microstructure, and morphology of carbonated products were systematically investigated. It was found that a high whisker content of 60% with an aspect ratio of ∼6 could be obtained under the optimal conditions of 80 °C, 0.4 M MgCl 2 , and 2 h reaction time. Besides the formation of whiskers, amorphous aluminosilicate gel was also generated during SRM carbonation. The effects of the as-prepared whisker-rich materials as partial cement replacement on the mechanical properties of cement paste were evaluated with 5 wt% replacement, the 28 d compressive strength was significantly improved by 20.5% compared to the control specimen. The effective reinforcement was ascribed to the fibrous whiskers and enhanced interfacial bonding. This method enables high-value utilization of SRM waste and CO 2 fixation, providing a green and low-cost approach to producing high-performance cementitious materials. [ABSTRACT FROM AUTHOR]

The influence of limestone powder (primarily composed of calcite) on hydration and properties of concrete has been extensively researched. However, there is limited understanding of how different calcium carbonate (CC) polymorphs affect cement hydration due to the difficulty in formation of vaterite. Therefore, preparing calcite and vaterite from solid waste carbide residue (CS) by wet carbonation and examining influence of these two CC polymorphs (0–20 %) on cement hydration and properties are comprehensive investigated in the paper. The results reveal that pure cubic calcite can be obtained through CS carbonation, while high-purity spherical vaterite can be synthesized using glycine as a regulator. The specific surface area (SSA) of spherical vaterite (15.47 m2/g) is approximately three times that of calcite (4.8 m2/g) with a comparable particle size distribution (PSD). The addition of calcite reduces the flowability of cement, whereas vaterite enhances it. The cement mortar with calcite demonstrates a lower compressive strength, while the incorporation of vaterite results in a higher or comparable compressive strength in contrast to control sample. Compared with control cement hydration, new hydration products, like monocarbonate aluminate and hemicarbonate aluminate, are formed with the addition of both calcite and vaterite. The metastable vaterite exhibits increased reactivity. The research presents a novel approach for the valorisation of solid wastes through CO 2 sequestration, offering insights into the preparation of highly added-value products. [ABSTRACT FROM AUTHOR]

• Influence of LCFA on the properties of cement-based materials was investigated. • Appropriate LCFA is positive to the strength and chloride resistance of cement-based materials. • Early strength of cement-based materials with LCFA can be increased by WG. • LCFA can fill the coarse pores and make the pore structure more compact. To enhance the utilization of circulating fluidized bed fly ash in construction materials, this study investigated the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the properties of cement-based materials. In addition, an alkali activator was added to improve the properties of cement-based materials mixed with LCFA and the synergistic effect was also investigated. The results show that an appropriate amount of LCFA can improve the compressive strength of cement-based materials in underwater curing conditions. The addition of LCFA can improve the physical properties and carbonization resistance of cement-based materials. Whereas, the addition of water glass (WG) can appropriately shorten the setting time and effectively increase the compressive strength of cement mixtures with LCFA. In addition, adding WG can effectively improve the resistance of chloride ion penetration and carbonation. It is speculated that adding appropriate amount of LCFA enhanced the amount of hydration products generated, filled the coarse pores, and made the pore structure of samples more compact. Appropriate addition of LCFA and WG increases the concentration of hydroxyl groups in the system, accelerates the rupture of Si-O and Al-O bonds on the surface of LCFA particles, and forms free and unsaturated active bonds on the surface of LCFA, which is easier to react with Ca(OH) 2 to form hydration products such as C-S-H and C-A-S-H. At the same time, gelatinous hydration products migrate and diffuse with the change of ion concentration in the system, and gradually fill and compact the internal structure. [ABSTRACT FROM AUTHOR]

A normal weight porous aggregate (NWPA), with the saturated surface dry density of 2.3 g/cm 3 , was prepared. Impact of NWPA on performance of mortar with water to cementitious materials ratio of 0.3 was presented in this paper. The results show that NWPA has smaller pores and higher water absorption speed than expanded clay, but lower desorption speed. Strength of mortar accompanying NWPA is higher than or close to that of a plain one. Mortar containing NWPA expand less than that with expanded clay under sealed condition, which suggests the lower internal curing efficiency of NWPA. However, still it could diminish the shrinkage of low w/c mortar and be used as internal curing agent. Variation of water absorption and dynamic modulus from top to bottom of mortar with NWPA is similar to that of plain one, and lower than that of expanded clay mortar, which certifies that NWPA could promote the uniformity of internally cured mortar. [ABSTRACT FROM AUTHOR]

Understanding the doping behaviors of impurity ions in mineralogical compositions is of great significance for optimizing the quality of sulphoaluminate cement (SAC) clinker as well as its performance in engineering utilizations. The key issue is determining the exact existing state of these impurity ions. Here, combined with experiments and density functional theoretical (DFT) simulations, we systematically studied the substitution preference of chromium in the three main composed phases of SAC clinker, i. e, C 4 A 3 S̅, C 2 S and C 4 AF. The formation energies indicate that Cr ions prefer to enter C 4 AF by substituting Fe ions followed by incorporating into C 4 A 3 S̅ with replacement of S ions. The results from X-ray diffractions of single phase show the successful incorporations of Cr ions into both individual mineral, C 4 AF and C 4 A 3 S̅. The dominant content of C 4 A 3 S̅ in SAC clinker is well illustrated from Rietveld refinement. Further proof of the doping preference is from the difference in relative amounts of Cr(III) and Cr(VI) in SAC clinker samples with lower dosages. More in-depth analyses from both electron contributions and bond order-bond length distributions show that the substitution preference follows the "electronic structure matching" principle, which ensures the effective substitution by forming stronger bonds between guest ions and oxygen atoms. The doping preference provides a possibility of controlling the valence state of Cr ions by tuning the mineralogical compositions of SAC clinker, thus is essential in guiding the synthesis of SAC-based materials by utilizing Cr-bearing solid waste. [Display omitted] • The substitution preference of Cr ions in SAC clinker phases is studied by experiments and DFT simulations. • Cr ions prefer to incorporate into the composed mineral C 4 AF by substituting Fe ions. • Cr ions can also enter into the dominant mineral C 4 A 3 S̅ by substituting S ions. • The preference can be attributed to similar electron contributions between Cr and Fe ions. [ABSTRACT FROM AUTHOR]

The alinites and calcium chloroaluminates are main minerals of ecocement. In this paper, the alinite and calcium chloroaluminate minerals are synthesized. Analytical reagents are mixed into the raw meals of alinite and calcium chloroaluminate that are burnt under different temperatures. Through the content of f-CaO detection and XRD analysis, we have confirmed the firing condition. Especially, the scanning electron microscope SEM-EDS analysis are used to test and analyze the composition and hydration mechanism of the minerals. [Copyright &y& Elsevier]