This study uses neutron radiography (NR) and visual inspection to quantify water penetration in concrete samples exposed to water pressure on one face. It provides experimental data regarding the impact of mixture proportions on the hydraulic permeability of concrete. Specifically, it illustrates the influence of water-to-cement ratio (w/c), curing duration, entrained air content, and coarse aggregate (CA) size and volume on water transport. In addition, this paper quantifies the impact of permeability-reducing admixtures (PRAs) on water transport in concrete. It was observed that decreasing the w/c and/or increasing the curing duration reduced the fluid transport. Liquid and powder PRAs efficiently reduced fluid transport in concrete without impacting the compressive strength. The liquid PRA showed more consistent results, likely due to better dispersion than the powder PRA. Fluid ingress in concrete samples appears to increase with entrained air content due to a lower degree of saturation (DOS) at the start of the test. Increasing the CA volume fraction or decreasing the CA size will increase the fluid transport in concrete due to an increase in the connectivity of the interfacial transition zone. The influence of entrained air content, curing duration, CA volume fraction, and CA size was less noticeable on mixtures with PRA due to the higher density and low permeability of these samples compared to control samples.

Carbonatable calcium silicate cement (CSC) is a promising approach to reducing the carbon footprint associated with concrete production. Carbonatable CSC gains strength by reacting with carbon dioxide (CO2). While the concept of carbonation is well known, more information on the curing process is needed. This study focuses on studying the impact of drying time, carbonation duration, and degree of saturation (DOS) on the carbonation reaction of CSC-mortar. Samples were exposed to different drying durations at controlled environmental conditions to reach various DOS ranging from 100 to 0%. The samples were then exposed to carbonation under the same environmental conditions for different durations. Neutron radiography (NR) is performed on the samples during drying to determine the DOS corresponding to various drying durations. NR was also used during the carbonation period to determine the degree of carbonation (DOC) in real time. The impact of carbonation on the diffusivity of water vapor (Dh) and pore size distribution of CSC-based samples was examined using dynamic vapor sorption (DVS). It was concluded that the carbonation reaction increased as the DOS decreased from 100% to 40%. The carbonation reaction ceased for samples with DOS values less than 6% DOS. It was also concluded that as the DOC increased, the pore structure was refined, which led to a decrease in the Dh of the CSC-mortar samples.

This study proposed using CO₂ as an indirect admixture for calcined clay blended pastes. By injecting CO₂ gas into lime water, solid nano CaCO₃ particles were synthesized and used to partially replace the binder at ratios of 2, 4, and 6%. Various tests and analyses were performed on the calcined clay blended pastes. After adding nano CaCO₃, the strength, ultrasonic pulse velocity, hydration heat, and electrical resistivity were improved, monocarboaluminate and hemicarboaluminate were formed, and the CO₂ emissions were lowered. The electrical resistivity was improved more significantly than the strength. The reduction ratio in CO₂ emission was higher than the replacement ratio of nano CaCO₃. In summary, based on the transformation of gaseous CO₂ to solid nano CaCO₃ particles, the proposed technique shows a similar concept to limestone calcined clay cement (LC3) concrete and can overcome the limitations of carbonation curing.

This paper is aimed at investigating the effects of different fiber inclusion on the mechanical properties of ultra-high-performance concrete (UHPC) by adding mineral admixtures as cement replacement materials to reduce production costs and CO_2 emission of UHPC. Throughout this research, 21 mix designs containing four cement substitution materials (silica fume, ground granulated blast-furnace slag, limestone powder, and quartz powder) and three fibers (steel, barchip, and polypropylene) under wet and combined (autoclave, oven, and water) curing were developed. To investigate the mechanical properties in this research, a total of 336 specimens were cast to evaluate compressive strength the modulus of rupture (MOR), and the toughness index. The findings revealed that at the combined curing, regarded as a new procedure, all levels of cement replacement recorded a compressive strength higher than 150 MPa (21.76 ksi). Furthermore, the mechanical properties of the mix design containing microsilica and slag (up to 15%) were found to be higher than other cement substitutes. Also, it was shown that all levels of the fiber presented the MOR significantly close together and samples made of barchip fibers and steel fibers exhibited deflection-hardening behavior after cracking. The mix design containing microsilica, slag, limestone, and quartz powder, despite the significant replacement of cement (about 50%) by substitution materials, experienced a slight drop in strength. Therefore, the development of this mixture is optimal both economically and environmentally.

In this paper, the Taguchi method was used to identify the optimum mixture proportions of alkali-activated reactive powder concrete (AARPC) by considering the most influential parameters. Five main parameters, including binder content, alkaline activator-binder ratio (Al-binder), binder-fine aggregate ratio, sodium silicate to sodium hydroxide ratio (Na2SiO3-NaOH), and sodium hydroxide (NaOH) concentration, were considered in the mixture design. A total of 18 trial batches were designed according to the L18 array obtained from the Taguchi method. The results showed that the highest average compressive strength was 110.9 MPa (16.08 ksi) and the lowest average compressive strength was 50.6 MPa (7.34 ksi). The test results of the 18 trial batches were then evaluated by the analysis of variance (ANOVA) method to determine the optimum level of each parameter. It was found that specimens with a binder content of 700 kg/m3 (0.025 lb/in.3), Al-binder ratio of 0.3, binder-fine aggregate ratio of 0.8, Na2SiO3-NaOH ratio of 2, and NaOH concentration of 14 M produced the highest 28-day compressive strength (116.77 MPa [16.94 ksi]) at the ambient curing conditions.