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To promote the safe use of MgO expansive agent (MEA) in mass concrete, the influence of fineness and sintering temperature of MEA on the expansion, mechanical properties, and microstructure of fly ash-Portland cement pastes was studied. The results indicate that the agent prepared at 950 °C does not adversely affect the compressive strength of the pastes. Whereas the agent prepared at 1150 °C (MII) has a marked negative impact on the volume stability and strength of the pastes. Furthermore, incorporating MII with coarser particle size results in a larger expansion, greater strength loss, and coarser pore structure. The presence of fly ash delays the hydration of MgO, making more MgO available for the formation of Mg(OH)2 at the late age. Meanwhile, the pozzolanic reaction leads to decreased total porosity, leaving less space available for the accommodation of Mg(OH)2. Consequently, fly ash cement pastes suffer greater strength loss than plain cement pastes when the destructive expansion occurs due to the delayed hydration of MgO. [ABSTRACT FROM AUTHOR]

Highlights • Shrinkage characteristics of self-leveling have been proposed. • Hydration heat and pore structure of self-leveling mortar were investigated. • Drying and autogenous shrinkage are reduced by using superabsorbent polymer for internal curing. Abstract This paper aims at putting forward the shrinkage control measures for evaluating the effect and mechanism of shrinkage compensation of self-leveling mortar by analyzing the shrinkage characteristics of cementitious self-leveling mortar (SLM). The drying shrinkage, autogenous shrinkage and mechanical properties of the self-leveling mortar are analyzed by comparing it with the ordinary mortar. The difference between the two kinds of matrix was explained by the result of hydration and pore structure. The internal curing of self-leveling mortar was carried out by superabsorbent polymer. The variation of drying shrinkage and autogenous shrinkage of self-leveling mortar were tested with the content at 0%wt, 0.2%wt, 0.4%wt and 0.6%wt. The pore structure and pore size distribution were also investigated. The experimental results show that the self-leveling mortar has larger the drying shrinkage and smaller the autogenous shrinkage than those of ordinary mortar. The main reasons for this are the hydration delay and the change of pore structure of self-leveling mortar caused by the addition of organic admixture. The internal curing by using superabsorbent polymer has excellent effect on drying shrinkage and autogenous shrinkage compensation which decrease by 10% and 10.2%, respectively, when the content is 0.4%wt. [ABSTRACT FROM AUTHOR]

Customarily, retarders serve as the setting time regulators of cement-based composites to meet the demands of various construction environments. However, the limited ability to adjust the setting time restricts the application of polysaccharides in special environments. In this study, we reported a naturally high-efficiency retarder, konjac glucomannan (KGM), and studied the mechanism of its effect on the hydration of ordinary Portland cement. Incorporating KGM could significantly prolong cement hydration without strength damage. Furthermore, the active hydroxyl group (−OH, rich in KGM) could chelate with Ca2+ (released from cement hydration) to form a cross-linking network, which is adsorbed on the surface of cement clinker, thereby being conducive to delaying the process of cement hydration and reducing the heat of hydration. The findings of this study are critical to the ongoing efforts to develop polysaccharide-cement-based composite materials for application in various special environments. [ABSTRACT FROM AUTHOR]

Highlights: [•] An analytical model was proposed to acquire the relative resistivity of cement paste and C–S–H. [•] Increasing hydration degree shows an increase with the relative resistivity and a reduction in critical exponent. [•] The relative resistivity of C–S–H and its exponent present constant values of 121 and 1.8. [ABSTRACT FROM AUTHOR]

In this study, a new modification method of waste rubber powder (WRP) was proposed to improve the workability and mechanical properties of rubber cement-based materials (RCM). This method combines mechanochemical action, inorganic powder intercalation, and modified slurry coating to obtain modified rubber aggregates (MRA). The modification mechanism and structure properties of the WRP were measured and characterized by NMR and TG-DSC. The effects of the WRP and MRA on the hydration, workability and mechanical behavior of RCM were further studied by an isothermal calorimeter, and rheometer. The ITZ between rubber and the cement matrix (R-CM) was analysed by SEM, Micro-hardness. The result showed that the porosity of the MRA was reduced (24.68 to 17.87) and the stability is increased (mass loss rate was reduced from 64.8 % to 57.5 %) compared with the WRP. WRP delayed the hydration induction and acceleration periods of cement hydration by 9 h, but MRA was only 0.5 h compared with control groups. The yield stress and plastic viscosity of MCRM were decreased by 356.95 % and 154.65 % respectively, compared with CRM. The compressive and flexural strengths of MCRM increased by 159.0 % and 87.5 % compared with CRM. The voids at the interface of R-CM disappeared after modification, and ITZ thickness decreased from about 160 µm to 80 µm. The interfacial adhesion of R-CM is a key factor in improving the failure model and mechanical behavior of RCM. [ABSTRACT FROM AUTHOR]