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.

Determining in-place properties of mass concrete placements is elusive, and currently, there are minimal to no test methods available that are both predictive and a direct measurement of mechanical properties. This paper presents a three-stage testing framework that utilizes common laboratory equipment and laboratory scale specimens to quantify the thermal and mechanical properties of mass high-strength concrete placements. To evaluate this framework, four mass placement of varying sizes and insulations were cast where temperature histories were measured at several locations within each placement where maximum temperatures of 107 to 119°C were recorded. The laboratory curing protocols were then developed using this mass placement temperature data and the three-stage testing framework to cure laboratory specimens to represent each mass placement. Laboratory curing protocols developed for center and intermediate regions of the mass placements reasonably replicated thermal histories of the mass placements, while the first stage of the three-stage framework reasonably replicated temperatures near the edge of the mass placements. Additionally, there were statistically significant relationships detected between calibration variables used to develop laboratory curing protocols and measured compressive strength. Overall, the proposed three-stage testing framework is a measurable step towards creating a predictive laboratory curing protocol by accounting for the mixture characteristics of thermo-mechanical properties of high-strength concretes.

In marine structures, concrete requires adequate resistance against chloride ion penetration. As a result, numerous studies have been conducted to enhance the mechanical properties and durability of concrete by incorporating various pozzolans. This research has investigated the curing conditions of samples including zeolite and metakaolite mixed with Micro nanobubble water in artificial seawater and standard conditions. The results indicated that incorporating zeolite and metakaolin mixed with Micro nanobubble water, which was cured in artificial seawater conditions, compared to similar samples that were cured in standard conditions, improved the mechanical properties and durability of concrete samples. The compressive strength of 28 days concrete samples containing 10% metakaolin mixed with 100% Micro nanobubble water and samples consisting of 10% zeolite blended with 100% Micro nanobubble water cured in seawater in comparison to the control sample cured in the standard condition indicated an increase of 25.06% and 20.9%, respectively. The most results were obtained with a compound of 10% metakaolin, and 10% zeolite with 100% Micro nanobubble cured in seawater (MK10Z10NB100CS) which rose significantly Compressive, Tensile and Flexural Strength by 11.13, 14, and 9.1%, respectively, in comparison with to the MK10Z10NB100 sample cured in the standard condition. Furthermore, it decreased considerably 24-hr water absorption and Chloride Penetration at 90 days by 27.70 and 82.89%, respectively, in comparison with the control sample cured in standard conditions.

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 since such mixture under 3 days of moist curing exhibited low total shrinkage of 360 µε at 56 days and compressive strength of 135 MPa (19,580 psi) at 56 days and flexural strength of 18 MPa (2,610 psi) at 28 days. This mixture subjected to 3 days of moist curing also 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.

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.