As one of the key factors influencing the hydration process, as well as the microstructure formation and evolution of ultra-highperformance concrete (UHPC), the action mechanism of different curing regimes have been studied to some extent. However, the current knowledge of the underlying mechanisms that control the different effects of different curing regimes is limited. In this study, the composition of hydration products, micromorphology, and migration and evolution of aluminum-phase hydration products of UHPC under three combined curing regimes (standard curing, steam curing + standard curing, and autoclave curing + standard curing) were investigated in depth. Micromorphology observation shows that heat treatment promoted the formation of higher-stiffness hydration products (tobermorite and xonotlite) in UHPC, and the higher the polymerization degree, the higher the Si/Ca ratio of the hydration product. Meanwhile, 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy shows that specimens with higher strength had higher Al[4]/Si and a lower amount of ettringite and AFm at the early curing stage. The elevated curing temperature reduced the formation of ettringite and AFm and allowed more Al3+ to replace Si4+ into the structure and interlayer of the calcium- (alumino)silicate-hydrate (C-(A)-S-H) gel, which increased the mean chain length (MCL) and polymerization degree of the C-(A)-S-H gel. However, the polymerization effect of Al ions is limited, so the provision of the silicon source to improve the Si/Ca ratio of the system is important.

In light of the effort for decarbonization of the energy sector, it is believed that common geopolymer binding materials such as fly ash may eventually become scarce, and new geological aluminosilicate materials should be explored as alternative binders in geopolymer concrete. A novel, tension-hardening geopolymer concrete (THGC) that incorporates high amounts of semi-reactive quarry wastes (Metagabbro) as a precursor and coarse quarry sand (granite) was developed in this study using geopolymer formulations. The material was optimized based on the particle packing theory and was characterized in terms of mechanical, physical, and durability properties (i.e., compressive, tensile, flexural resistance, Young’s Modulus, Poisson’s ratio; absorption, drying shrinkage, abrasion, and coefficient of thermal expansion; chloride ion penetration, sulfate, and salt-scaling resistance). The developed THGC with an air-dry density of 1,940 kg/m³ [121 lb/ft³], incorporates short steel fibers at a volume ratio of 2% and is highly ductile in both uniaxial tension and compression (uniaxial tensile strain capacity of 0.6% at an 80% post-peak residual tensile strength). Using DIC, multiple crack formation was observed in the strain-hardening phase of the tension response. In compression the material maintained its integrity beyond the peak load, having attained 1.8% compressive strain at 80% post-peak residual strength whereas upon further reduction to 50% residual strength, the sustained axial and lateral strains were 2.5% and 3.5%, respectively. The material exhibited low permeability to chloride ions and significant abrasion resistance due to the high contents of Metagabbro powder and granite sand. The enhanced properties of the material, combined with the complete elimination of ordinary Portland cement from the mix, hold promise for the development of sustainable and resilient structural materials with low CO₂j, emissions while also enabling the innovative disposal of wastes as active binding components.

A compressive 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 (PMF), and optimized aggregate gradation (OAG) into an internally cured concrete (ICC) mix for rigid pavement application. Results from the laboratory program indicate that all ICC mixes outperformed the standard concrete (SC) mix. All ICC mixes showed a decrease in drying shrinkage compared to the SC mix. Based on the laboratory program, three ICC mixes and one of the SC mixes were selected for the full-scale test subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixes incorporating SRA, PMF, and OAG can be beneficially used in pavement applications to achieve increased pavement life.

This research focuses on developing a mixture design for highstrength geopolymer concrete (HSGPC) complying with the highstrength concrete criteria mentioned in Indian standards. This study focuses on optimizing the content of alkaline activators and binders proportionately. The compressive strength of different proportions of geopolymer mortar was carried out meticulously to determine the optimal proportions of solution-binder (S/B) and sodium silicatesodium hydroxide (SS/SH) ratios. The aforementioned ratios were optimized using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) analysis for further calculation. The mixture proportions for Grades M70, M80, M90, and M100 were determined and verified through experimental validation. To assess the suggested mixture design, a slump test was conducted to quantify the workability, subsequently followed by the evaluation of compressive strength after 24 hours, 7 days, and 28 days. After achieving the desired workability, promising compressive strength was observed as 76, 89, 93, and 104 MPa at 28 days. Finally, the mechanism of strength increment was investigated using various characterization techniques, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energydispersive spectroscopy (EDS). The SEM/EDS analysis of the HSGPC proves the dense microstructures of different gel formations. The proposed mixture design procedure falls under the target strength-based method category. It has successfully yielded a strength of 104 MPa for ground-granulated blast-furnace slag (GGBS)-based geopolymer concrete incorporating coarse and fine aggregates.

environments during their operation time. The aim of this study is to investigate the effect of sulfuric acid on the mechanical characteristics of PC. In this context, specimens were submerged in 5 and 15% sulfuric acid solutions (named SP5 and SP15, respectively) up to 180 days and then subjected to monotonic and cyclic compressive and tensile loadings. Results demonstrated that the specimens that were immersed in 15 vol% of sulfuric acid (MC15 and MT15) had the greatest losses in compressive and tensile strength, which were 33% and 21% (70 and 8 MPa), respectively, compared to the control specimens. Peak strain, compressive strength, and energy absporption capacity (EA) for MC15 are approximately 1.6, 2, and 1.7 times higher than corresponding values for normal concrete. Corroded PC specimens still have a substantially higher strength and energy absorption capacity than cement-based concrete. Based on the obtained results, stress-strain relationships were proposed for SP5 and SP15 in compression and tension.