The applications of alkali-activated slag (AAS) face challenges such as poor workability, rapid setting, and high autogenous shrinkage, which require chemical admixtures (CAs) to adjust the performance of AAS. Unfortunately, there are limited specific CAs available to tune AAS properties. To address this gap, this study proposes using a ubiquitous, naturally occurring compound, L-ascorbic acid (LAA), as a multi-functional performance-enhancing additive for AAS to overcome the major challenges of AAS. The findings showed that LAA can function as a retarder, plasticizer, strength enhancer, and autogenous shrinkage reducer for AAS. When 0.5% LAA was added, the compressive strengths of AAS mortars at 3d and 28ds increased by 28.9% and 19.6%, respectively, and the 28d autogenous shrinkage decreased by 43.1%. Both surface adsorption and ion complexation have been confirmed as the working mechanisms of LAA in hydrated AAS.

In this study, low-carbon ultra-high-performance concrete (UHPC) was designed by adding fly ash-based mineral admixtures (SD-FA). The improved Andreasen & Andersen model was used to obtain SD-FA, which was then used to replace part of UHPC cement, to achieve the effect of low-carbon emission reduction. The effects of the composition and dosage of cement-based materials, the water-cement ratio, the composition of sand, the steel fiber content, and the lime-sand ratio on the properties of UHPC were studied, and the design of the batches was optimized. On this basis, the performance changes were analyzed at the micro level. The results show that when the 1~3 grade fly ash content after screening treatment is quantitative, the densest stacking is theoretically reached. The SD-FA optimized design improves the bulk density of UHPC and realizes the dense microstructure of UHPC. Under the optimal mixing ratio, its processability is guaranteed and the mechanical properties are enhanced.

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 με and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.

A comprehensive laboratory testing program, field-testing program, numerical analysis, and life-cycle cost analysis were conducted to evaluate the beneficial effects of incorporating shrinkage-reducing admixture (SRA), polymeric microfibers (PMFs), and optimized aggregate gradation (OAG) into internally cured concrete (ICC) mixtures for rigid pavement applications. Results from the laboratory program indicate that all the ICC mixtures outperformed the standard concrete (SC) mixture. All the ICC mixtures showed a decrease in drying shrinkage compared to the SC mixture. Based on the laboratory program, three ICC mixtures and one SC mixture were selected for the full-scale test and subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixtures incorporating SRA, PMFs, and OAG can be beneficially used in pavement applications to achieve increased pavement life.

Successful implementation of extrusion-based three-dimensional (3-D) printing requires the development of print materials with adapted rheology. In this study, filtration characteristics coupled with rheological properties of mortar mixtures are investigated to characterize the extrudability of print materials and establish a “printability window” (that is, the acceptable range of material properties for successful extrusion and shape stability). The extrudability was measured as the maximum force needed for the ram extrusion of the material. The fluid filtration rate was assessed in terms of desorptivity of the fresh mixture under pressure. The yield stress, plastic viscosity, and desorptivity were varied by changing the water-cement ratio (w/c), high-range water-reducing admixture (HRWRA) dosage, and welan gum (WG) content. Regression analysis indicated that during extrusion-based printing, the yield stress and desorptivity values can exhibit a more significant effect on extrudability than plastic viscosity.