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Alkali activated slag ultra-high performance concrete (AAS-UHPC) is a promising low-carbon cementitious material that can effectively utilize industrial solid waste and reduce pollutant emissions during the production of cementitious materials compared with ultra-high performance concrete (UHPC), and it also exhibits excellent mechanical properties. The objective of this study is to conduct a comparative experimental analysis of the workability, mechanical properties and deformation behavior of UHPC and AAS-UHPC. In this study, AAS-UHPC prepared with lower water/cement ratio (w/b) has good flowability, faster setting time and higher strength. Although the early hydration rate of AAS-UHPC was similar to that of UHPC, its cumulative heat of hydration was higher. In chemical shrinkage experiments, the shrinkage value of AAS-UHPC increased with increasing water bath temperature and remained at about twice the strain value of UHPC. The age-early drying shrinkage of AAS-UHPC can be divided into four phases: transient deformation, dormant, accelerated, and slow development. stage, accelerated stage and slow development stage. Self-shrinkage is divided into three stages: dormant stage, accelerated stage and slowly developing stage. Compared with ultra-high performance concrete, AAS-UHPC has a longer dormant phase of early age shrinkage, and the deformation in this phase is mainly plastic shrinkage. Starting from the accelerated stage, the relative humidity decreases rapidly due to the strong occurrence of hydration reaction and shrinkage of pore structure. This leads to a rapid increase in the modulus of elasticity of AAS-UHPC, which results in greater deformation. In the later stages, the rate of shrinkage development slows down due to the basic formation of the concrete skeleton.

Borates are well-known candidates for optical materials, but their potentials in photocatalysis are rarely studied. Ga3+-containing oxides or sulfides are good candidates for photocatalysis applications because the unoccupied 4s orbitals of Ga usually contribute to the bottom of the conducting band. It is therefore anticipated that Ga4B2O9 might be a promising photocatalyst because of its high Ga/B ratio and three-dimensional network. Various synthetic methods, including hydrothermal (HY), sol-gel (SG), and high-temperature solid-state reaction (HTSSR), were employed to prepare crystalline Ga4B2O9. The so-obtained HY-Ga4B2O9 are micrometer single crystals but do not show any UV-light activity unless modified by Pt loading. The problem is the fast recombination of photoexcitons. Interestingly, the samples obtained by SG and HTSSR methods both possess a fine micromorphology composed of well-crystalline nanometer strips. Therefore, the excited e- and h+ can move to the surface easily. Both samples exhibit excellent intrinsic UV-light activities for pure water splitting without the assistance of any cocatalyst (47 and 118 µmol/h/g for H2 evolution and 22 and 58 µmol/h/g for O2 evolution, respectively), while there is no detectable activity for P25 (nanoparticles of TiO2 with a specific surface area of 69 m²/g) under the same conditions. [ABSTRACT FROM AUTHOR]