The use of alkaline activator in alkali-activated materials (AAMs) may pose risk of alkali-silica reaction (ASR), and the variations in the mixture design could have great influence on the performance of AAMs system. In this case, this paper investigated the effects of slag fineness (3000–8000 cm²/g) and water-to-binder (w/b) ratio (0.5–0.8) on ASR behavior of alkali-activated slag (AAS) mortars under accelerated mortar testing conditions as specified in ASTM C1260. The length change, mass gain, microstructure and formation of ASR products were examined to evaluate the degradation caused by ASR. It was found for the first time that slag fineness induces a “pessimum effect” in the ASR expansion of AAS mortars. On the other hand, there is a “pessimum effect” in the influence of w/b ratio on ASR expansion in the early-stage (≤14d), and the induced expansion increased with an increase in w/b ratio in the late-stage (>14d). The mechanism governing the effect of slag fineness and w/b ratio is complicated and cannot be explained solely by the properties of ASR products. This work contributes to the understanding of ASR in AAMs system and could provide a basis for the mixture optimization of AAMs.

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Limestone-calcined clay-cement (LC3), as one of the most promising sustainable cements, has been under development over the past decade. However, many uncertainties remain regarding its rheological behaviors, such as the metakaolin content of calcined clay. This study aims to investigate the effect of increasing the content of fine-grained metakaolin in calcined clay on the rheology of LC3 pastes. Rheological behaviors and early-age hydration of studied mixtures were characterized using flow curve, constant shear rate, small amplitude oscillatory shear and isothermal calorimetry tests. Results show that increasing the content of fine-grained metakaolin decreased flowability but promoted structural build-up and early-age hydration. These phenomena can be attributed to the decrease of mean interparticle distance caused by the increased amount of fine-grained metakaolin, which may enhance colloidal interactions, C-S-H nucleation and direct contact between particles. Overall, modifying the fine-grained metakaolin content is a feasible approach to control the rheology of LC3 pastes.

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3D printing of engineered cementitious composites (3DP-ECC) serves as an effective means to enable digital and automated construction while removing the dependence of steel reinforcement typical in normal concrete construction. As generally recognized, process control in 3DP is as crucial as material constituents to the performance of the printed structure. Printing parameters pose direct influence on the micro-structure of material, which further impacts the macro-scale properties of printed ECC. In this paper, the effects of different nozzle standoff distances and nozzle travelling speeds are investigated. It is found that lowering the nozzle standoff distance within a certain range increases the in-plane tensile strength and strain capacity of 3DP-ECC by 39% and 30%, respectively. The tensile performance is also enhanced by a moderate printing speed. In addition, a 141% increase in interfacial fiber bridging force is found with elevated nozzle standoff distance. Furthermore, the micro-structure observed via μ-CT correlates well with the printing parameters, micro-structure and macro-scale properties of 3DP-ECC.@en