Embedding magnetic particles into cement paste produces a smart material in which the rheological properties of the resultant paste can be actively controlled through the use of magnetorheological principles. This research investigates the rheological behavior of cement-based MR pastes with and without air entrainment to gain a better understanding of the effects of air-entrained bubbles on MR cement pastes. Such information would be critical for the use of such MR Pastes in 3D concrete printing applications. It is revealed that the incorporation of entrained air results in increasing the MR response and this effect is related to the bubble bridge effect.

This study examines the impact of deicers on the compressive strength and microstructure of concrete at ambient temperature in sub-zero areas. In this study, after seven days of curing in plain water, concrete specimens were exposed to four deicer chemical solutions: sodium chloride, sodium acetate, calcium nitrate, and urea at 3%, 6%, and 9% concentrations, respectively. The specimens were tested for compressive strength after 14 days, 28 days, and 90 days of exposure. All tested deicers, except calcium nitrate, have a propensity to decrease the compressive strength of concrete. Exposure to sodium acetate, which appears to have the most detrimental effect, decreased the compressive strength of concrete by a maximum of 30.79% at a concentration of 9%, whereas exposure to calcium nitrate increased the compressive strength of concrete by 17% at a concentration of 3%. Deicers changed the microstructure of concrete, which was investigated using Field Emission Scanning Electron Microscopy (FESEM). This was followed by X-ray diffraction (XRD) for qualitative analysis of phases present in deicer-treated concrete specimens. The desirability function was used to determine the optimal exposure period and calcium nitrate concentration for concrete in subzero environments, which were respectively 10 to 11 days and 8.8 to 9%.

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.

The attached cement paste in the recycled concrete aggregate leads to its potential reactivity against sulfate ions. Several test methods were evaluated to find a suitable, reliable, and accurate method to evaluate the potential reactivity of aggregates. Different quality recycled concrete aggregates were used to apply those methods. The studies include evaluations of concrete cores drilled from source concrete, recycled concrete aggregates, recycled mortar bars under different exposures, and recycled concrete prisms exposed to external sulfate attack. The concrete core test allowed qualifying source concrete as potentially reactive against sulfate in a short time. Tests on recycled aggregates and recycled mortar bars showed variable sensitivity levels. Results from concrete prisms showed an effective reactivity of recycled aggregates when the replacement is higher.

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.