Alkali-activated concrete (AAC) is a focal point in green building material research due to its low carbon footprint and superior performance. This study seeks to enhance the impact resistance of recycled aggregate concrete (RAC) by elucidating the synergistic mechanisms of alkali activation, nano-modification, and fiber reinforcement. To this end, four mix designs, incorporating NaOH and NaOH-Na2SiO3 systems with 2 % nano-SiO2(NS), were developed and assessed through setting time, compressive strength, drop hammer impact tests, and XRD/ SEM analyses. The NaOH-Na2SiO3 system exhibited a 23.5 % increase in compressive strength over NaOH, achieving 28.41 MPa, while NS refined pore structures, elevating strength to 32.2 MPa; XRD/SEM analyses confirmed mechanisms of pore refinement and interfacial enhancement. In the optimized system, the NT12-C5 formulation, incorporating polypropylene fiber (PPF) and recycled carbon fiber (RCF), exhibited superior impact resistance, with NS enhancing interfacial bonding between carbon fiber and the matrix, resulting in a 47.8 % increase in initial crack impact energy. The Weibull model validated the reliability of impact performance. Furthermore, life cycle assessment revealed that Soil Solidification Rock Recycled aggregate concrete (SSRRAC) substantially reduced carbon emissions compared to ordinary Portland cement (OPC), while maintaining competitive economic costs. This study's innovations include: (1) synergistic optimization of low-carbon AAC performance using NaOH-Na2SiO3 and NS; (2) optimized PPF/RCF formulations promoting the reuse of waste carbon fiber; and (3) application of the Weibull model to overcome conventional statistical constraints. Collectively, these findings establish a theoretical and practical foundation for the global development of sustainable building materials.

Red mud, a by-product generated during the extraction of aluminium from bauxite ore, poses challenges to the alumina industry due to its inherent sodicity, alkalinity and heavy metal content. Consequently, studies related to its bulk utilization and valorization have gained attention in the construction sector to promote sustainability. However, utilization of red mud in stabilization of expansive soils using alkali activation is seldom explored. Therefore, this study focuses on improving the geotechnical properties of an expansive soil (black cotton soil, BCS) through chemical stabilization by using blends of two distinct industrial wastes, viz. red mud and GGBS, termed as GGRM, activated with sodium hydroxide (NaOH) solution. The strength, stiffness and durability characteristics of these compacted blends were assessed based on a series of laboratory investigations like unconfined compressive strength, ultrasonic pulse velocity and wet-dry cycles tests. Leachate analysis was also performed to assess the geo-environmental issues of soil ameliorated with blends of alkali-activated GGRM blends. These blended specimens were moulded with different molar concentrations of NaOH solutions (i.e. 2, 5 and 10 M). Further, microstructural studies were carried out through XRD, SEM-EDS and FTIR analysis. The results show that heavy metal contents in alkali-activated specimens are within the permissible limits of USEPA guidelines. Based upon the assessments of strength, durability and P-wave velocity after 28 days of curing period, 25 and 30% binder contents of GGRM100:00, GGRM70:30 and GGRM50:50 corresponding to 5 M and 10 NaOH, were found suitable for subgrade applications in accordance with IRC 37 guidelines.

In order to solve the problem of low comprehensive utilization rate of industrial solid waste, this article focuses on the three problems of slag, which are steel slag, reuse of silica fume, and the strength enhancement and microscopic mechanism of slag-steel slag-silica fume composite material; analyzes the macro strength of the mixture under different curing ages from the two indexes of unconfined compressive strength and splitting tensile strength; and conducts microscopic tests such as X-ray diffraction, scanning electron microscopy, and Fourier transform infrared. The internal mechanism of hydration product formation and strength change of slag and steel wollastonite cementitious material under the excitation of sodium hydroxide and sodium silicate mixed solution as alkali activator was discussed. The strength results show that when the optimum mixture ratio of slag: steel slag: silica fume is 6:3:1, the modulus of lye is 1.2, the content of lye is 6 %, and the compressive strength of slag-steel slag-silica fume base polymer reaches 2.44 MPa under the standard curing condition of 28 day. The results show that the hydration products of geopolymer mainly consist of calcium-silicate-hydrate (C-S-H) gel and a small amount of ettringite (AFt) crystal. The addition of slag reduces the calcium/silicon ratio and increases the aluminum/silicon ratio, which makes the gel polymerization degree increase. C-S-H gel can be formed by the reaction of calcium hydroxide and silicon dioxide produced by steel slag hydration. Silica fume can provide highly reactive silicon for the system, and its seed effect and pozzolanic effect can accelerate the hydration process of the system.

Extensive research interest on lunar construction materials, represented by lunar geopolymers, has been driven by the worldwide programs of in-situ lunar exploration. This study comprehensively investigates different combinations between diverse lunar regolith simulants and activators at various curing temperatures, and their effects are revealed by the mechanical properties, microstructure, and composition of resulting lunar geopolymers. This study proposes that glass-rich lunar regolith should be activated by sodium hydroxide to ensure the aluminosilicate dissolution and form dense zeolitic products, whereas sodium silicate is more suitable for glass-free lunar regolith to assist the generation of amorphous products. Additionally, the temperature for the thermal curing of lunar geopolymers should exceed 60-80 degrees C for applicable 24-hour strength. Based on experimental characterizations and statistical analysis of existing data, three determinants of lunar geopolymer synthesis can be emphasized including the compatibility between activator and regolith activity, the calcium and alkali content of regolith, and the temperature of sealed thermal curing. These principles provide valuable guidance on the selection of regolith and activators along with the establishment of curing protocols towards future lunar constructions.

The weak mechanical properties of dredged soil can be improved by using cementing agents. Comprehensive investigation of the efficacy of stabilizing methods, including Portland cement (PC) and alkali-activated ground granulated blast-furnace slag (CaO-GGBS), cementing agent content from 12% to 16%, and curing methods in different initial moisture content of soils, organic matter content, and soil types was carried out. Experimental results showed that dredged soils have stronger properties using CaO-GGBS than PC. Maximum strength was found by using the highest CaO-GGBS content of 16%. The increase of organic matter content can weaken the enhanced properties of dredged soils stabilized by CaO-GGBS. The highest shear strength of specimens stabilized by CaO-GGBS occurred in dredged soils with 20% sand while the greatest yield strength in e-log p ' space was found in dredged soils with 30% sand. A modified constitutive model based on the framework for cemented geomaterials proposed by Gens and Nova has been developed. The ability of the model to reproduce the mechanical behavior capturing strength development with curing period was explored.