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Highlights • The effect of temperature on the structural buildup of cement pastes with various mineral admixtures was studied. • The hydration kinetics of cement paste was studied by boundary nucleation and growth model. • The relation between hydration kinetics and structural buildup was analyzed. Abstract The temperature dependence of structural build-up is of great importance to some new concrete technologies, such as 3D printing and slip-form casting concrete. In this paper, the structural build-up of cement paste with various mineral admixtures, characterized by the growth of static yield stress, were measured at 10, 20 and 40 °C. They were related with the calorimetric curves of cement paste at various temperatures. Nucleation kinetic (K N) and growth kinetic (K G) were introduced to analyze the hydration dynamics. The results showed that the addition of fly ash and slag were unfavorable for the structural build-up of cement paste at 10 and 20 °C, however, a favorable phenomenon was observed at 40 °C. The additions of nano-CaCO 3 or nano-SiO 2 had positive effect on structural build-up at all temperatures. The incorporation of silica fume had negative effect on structural build-up at 10 °C, while positive effect at 20 and 40 °C. Both the K N and K G played important roles on the structural build-up rate of cement paste. K G contributed more to the temperature dependence of structural build-up than K N. [ABSTRACT FROM AUTHOR]

• The performance of calcined CSMR as a new SCM was corroborated. • Fresh and hardened properties of blended cement-based materials were examined. • Calcined CSMR exhibited higher reactivity than siliceous fly ash. • Cement composites with 20% calcined CSMR showed desired engineering performances. • Adding calcined CSMR reduced the environmental footprints of the final products. Supplementary cementitious materials (SCMs) have been widely used in modern concrete technology to improve the sustainability and performance of concrete, but the concern over the decreasing supply of conventional SCMs in the future raises a need to explore their alternatives. This study aims to corroborate the performance of a calcined solid waste, i.e., cutter soil mixing residue (CSMR), as a new SCM in sustainable cementitious materials. The rheological behaviors, hydration kinetics, pore structures, physico-mechanical properties, and durability of cement paste and mortar blended with calcined CSMR were experimentally investigated. Results showed that the calcined CSMR powders with a lower specific surface area than the cement particles could improve the flowability of the cement paste. The calcined CSMR exhibited higher reactivity than the coal fly ash and could accelerate the cement hydration, create additional hydrates, and refine pore structures. Adding 20% calcined CSMR in the cement mortar had negligible adverse effects on the compressive strength, dry shrinkage resistance, electrical resistivity, and sulfate attack resistance. Meanwhile, the incorporation of 15–30% calcined CSMR reduced the embodied energy and carbon emissions of the cement mortar by around 13–25%. Overall, this research demonstrated the possibility of using calcined CSMR as a new SCM to develop greener cementitious materials without compromising the engineering properties. [ABSTRACT FROM AUTHOR]

Aging of Portland cement, due to its reaction with moisture and atmospheric CO 2 prior to regular use, has the potential to severely impair its hydration reactivity. The effectiveness of using metakaolin to improve the properties of aged Portland cement exposed to a laboratory conditions (RH=65 %, 20 °C) as well as the associated mechanism are studied. The incorporation of 5–10 % metakaolin changes the early-stage hydration kinetics of aged cement obviously by enhancing reactions of both C 3 S and C 3 A through the filler effect at the early hydration stage, thereby mitigating detrimental influences of aging on setting time and early-age strength development (up to 7 days). Metakaolin exhibits significant effectiveness on enhancing 28-day strength of aged cement, and the enhancement arises from the synergic reaction between metakaolin and CaCO 3 , which converts CaCO 3 resulting from aging into carboaluminate phases and produces secondary C-S-H. The incorporation of 5 % metakaolin increases the 28-day compressive strength of the sample with cement aged for one month to a comparable level as that of fresh cement. • Aging leads to relaxation and reconstruction of the cement surface can hinder the activity of the cement. • The filler effect caused by metakaolin promotes the reaction of C 3 S and C 3 A in aged cement. • The synergistic reaction between metakaolin and CaCO 3 formed in aged cement improves the mechanical property. [ABSTRACT FROM AUTHOR]

• Application of steel slag in cementitious materials based on dense packing can achieve high utilization efficiency of both steel slag and cement. • Early age hydration kinetics, fluidity of blends, and properties including strength and water absorption are investigated on paste specimens. • The appropriate amount of gypsum addition can enhance long-term strength through improving the early-age hydration kinetics SS-SPC cementitious systems. • The findings of this research help to valorize steel slag utilization in cement-based materials without sacrificing mechanical property and durability. Steel slag is an industrial solid waste with latent hydration nature, possessing a high potential use in cement and concrete but has not been fully utilized yet. This study reveals an implication approach based on dense packing to achieve high utilization efficiency of both steel slag and cement. Steel slag-based reverse filling approach utilizes higher volume of relatively coarser steel slag particles as micro fillers and a smaller quantity of fine cement grains as the major binding component. Thus, giving an initial compact packing structure and an enhanced strength of the resulting materials. Based on the packing density of various mixes, steel slag-based reverse filling cementitious materials are formulated. Early age hydration kinetics, fluidity of fresh pastes, and properties including mechanical strength and water absorption are further investigated on paste specimens. Results indicated that a maximum packing density of 0.6956 was attained for the blend containing 85 % steel slag with 15 % superfine Portland cement. The compressive strength of formulated mixes reached 96.4 MPa, 105.6 MPa and 123.8 MPa at 180 days for pastes containing 15 %, 25 % and 35 % of superfine Portland cement, respectively. The addition of appropriate amount of gypsum can enhance long-term strength by 8 ∼ 18 MPa through improving the early-age hydration kinetics of the steel slag based cementitious systems. The findings of this research help to valorize steel slag utilization in cement-based materials without sacrificing mechanical property and durability. [ABSTRACT FROM AUTHOR]

To understand the effect of elevated Al concentration on early hydration in Portland cement, hydration heat, the evolution of solid and aqueous composition in paste blended with reactive alumina were investigated in this study. The increase of Al concentration depletes gypsum rapidly with massive precipitation of ettringite during the pre-induction period, resulting in decreased Ca and S concentration in pore solution. The elevated Al concentration passivated the active sites on C 3 S surface, and the decreased Ca concentration inhibited the nucleation of C–S–H and precipitation of portlandite, hence prolonging the induction period. Meanwhile, the reaction of C 3 A has not been accelerated even after the complete depletion of gypsum, which is associated with the lowered undersaturation degree caused by the increased Al concentration. Additionally, the precipitation of large amounts of ettringite and foil-shaped C–S–H reduced available nucleation sites, thus hindering the reaction of both C 3 S and C 3 A during the acceleration period. [ABSTRACT FROM AUTHOR]

The incorporation of steel slag usually leads to retardation on the early-age hydration of cement, which limits its use as supplementary cementitious material in cement or concrete. Aiming to a better understanding of the retarding mechanism, the influences of two representative basic oxygen furnace steel slags on setting behaviour, hydration kinetics, aqueous and solid composition during early age were investigated. Different from the existing mechanisms, this study highlights the role of aluminate phase contained in steel slags in the retardation of hydration. The incorporation of steel slag with high aluminate phases content reduces C 3 S/aluminate phase ratio significantly. This reduction in C 3 S/aluminate phase ratio leads to undersulfation in the system, where aluminate phases react prior to C 3 S, resulting in flash setting, reduced C 3 S reaction, and thus the hindered early-age strength gain. This study also proposes an efficient way to alleviate the retarding effect of steel slag on early-age hydration by increasing the sulfate supply, which allows the system to react in a properly sulfated manner. [ABSTRACT FROM AUTHOR]