The primary aim of this study was to investigate the boron leaching process from alkali-activated ludwigite ore. Initially, the ore underwent activation through roasting at 1050 °C for 60 min with 20% sodium carbonate. Subsequently, the study examined the influence of leaching parameters, including temperature, time, liquid-to-solid ratio, and particle size, using the activated ore as the raw material. Additionally, water leaching characteristics of the residues and boron kinetics were analyzed. The results demonstrated that boron leaching efficiency reached 93.71% from the reduced ludwigite ore under specific conditions: leaching temperature of 180 °C, leaching time of 6 h, liquid-to-solid ratio of 8:1, and feed particle size of 52.31 μm (average particle size). Leach residue characteristics indicated the dissolution of minerals during the process. The boron behavior during water leaching followed the Avrami Equation, and the kinetics equation was derived by fitting the leaching data. Moreover, the activation energy (Ea) value for boron leaching was determined to be 8.812 kJ·mol-1 using the Arrhenius Equation, indicating that the leaching process is controlled by diffusion.

Cement production contributes significantly to carbon dioxide emissions. Alkali-activated materials offer an environmentally friendly alternative due to their comparable strength, durability and low-carbon emissions while utilizing wastes and industrial by-products. Wood ash is a waste material that shows promising results as a partial replacement for Portland cement and precursors in alkali-activated systems. The aim of this study was to examine the effect of ground wood ash on the mechanical properties of alkali-activated mortars. Wood ash was incorporated as a 0 wt%, 10 wt% and 20 wt% partial replacement for ground granulated blast furnace slag (GGBFS). The wood ashes were ground in a planetary ball mill for 10 and 20 min. Sodium silicate (Na2SiO3), sodium carbonate (Na2CO3), and sodium hydroxide (NaOH) were used as alkali activators. The results demonstrated that ground wood ash improved the mechanical properties of alkali-activated systems compared to untreated wood ash. However, the incorporation of wood ash increased the porosity of the binder matrix.

A growing interest in alternative cements has emerged with the sole purpose of reducing the environmental footprint associated with cement production. One of the promising alternatives is to use non-carbonate materials such as alkali-activated materials. They have demonstrated to have a similar performance as traditional Portland cement and have the potential to significantly reduce CO2 emissions. This paper reviews the main relevant technologies that are already available in the construction industry and explains how to consider them for alkali-activated cement and concrete production. This includes aluminosilicate pre-treatment methods (drying, grinding, and calcining) to increase the precursor\'s reactivity and degree of amorphization, alkali activation by two-part or one-part mix, as well as, mixing and casting fresh alkali-activated concrete ensuring low porosity and adequate strength development. This review also presents an overview of the alkali-activated cements market, providing examples of commercialized products, estimating related CO2 and costs, as well as future considerations for standardization and commercialization. Most of the commercialized alkali-activated materials are two-part mixes despite their limitations for in-situ applications. CO2 emissions can be reduced by more than 68% when compared to Portland cements. However, they have been estimated to be 2 to 3 times more expensive and the cost is primarily dependent on the aluminosilicate and alkali activators source.

Titanium-extracted tailing slag (TETS) has high activity, but the content of chloride ions is high. To effectively bind the chloride ions, CaO was used to activate the TETS, and the solidified cementitious material of CaO-activated TETS was prepared. The effects of CaO content and curing age on the strength of solidified samples, chloride binding capacity, and chloride binding mechanism were studied. By means of XRD, FTIR, SEM, and EDS, the hydration reaction products, microstructure, morphology, and micro-components of the solidified sample were characterized. The results show that the chloride ions can be effectively bound by using CaO to activate TETS with higher mechanical strength. When the CaO content is 10 wt%, the strength of the 28-day-cured body can reach more than 20 MPa, the chloride ion binding amount is 38.93 mg/g, and the chloride binding rate is as high as 68%. The new product phases of the solidified sample are mainly Friedel\'s salt (FS) and calcite, in which the amount of FS production and the degree of crystal development are affected by the CaO content and curing age. The chloride binding ions in the solidified sample are mainly the chemical binding by FS. The FS diffraction peak strength increases with the increase of CaO content and curing age, but the calcite diffraction peak strength is less affected by them. FS mainly accumulates and grows in the pores of the solidified sample. It can optimize the pore structure of the solidified sample and improve the strength of the solidified sample while binding chloride ions. The results can provide useful information for the resource utilization of chlorine-containing TETS, the improvement of durability of Marine concrete, and the application of sea sand in concrete.

Different ecological binders have been used to minimize the negative effects of cement production and use on the environment. Wood ash is one of these alternative binders, and there has been increasing research related to this topic recently. The wood ash utilized in the literature primarily originates from power plants and local bakeries, and predominantly wood fly ash is used. This review paper examines the use of wood ash as an ecological binder in two different applications: as a cement replacement and as an alkali-activated material. Studies have shown that while increased wood ash content in concrete and mortars can have negative effects on strength and durability, it is still a promising and developable material. Depending on the chemical composition of the wood ash, the strength and durability properties of concrete might be slightly improved by utilizing wood ash as a replacement for cement, with an optimal replacement level of 10-20%. However, there is a need for more research regarding the effects of wood ash on the durability of cement-based materials and its use in alkali-activated materials. Overall, this review provides a comprehensive overview of the properties of wood ash and its potential applications in conventional concrete and mortars, as well as in alkali-activated materials.

Current research into the production of sustainable construction materials for retrofitting and strengthening historic structures has been rising, with geopolymer technology being seen as an advantageous alternative to traditional concrete. Fiber reinforcement using this novel cementitious material involves a low embodied carbon footprint while ensuring cohesiveness with local materials. This study aims to develop fly ash-based geopolymers reinforced with six different types of fibers: polyvinyl alcohol, polypropylene, chopped basalt, carbon fiber, and copper-coated stainless steel. The samples are produced by mixing the geopolymer mortar in random distribution and content. Twenty-eight geopolymer mixes are evaluated through compressive strength, split-tensile strength, and modulus of elasticity to determine the fiber mix with the best performance compared with pure geopolymer mortar as a control. Polyvinyl alcohol and copper-coated stainless-steel fiber samples had considerably high mechanical properties and fracture toughness under applied tensile loads. However, the polypropylene fiber source did not perform well and had lower mechanical properties. One-way ANOVA verifies these results. Based on these findings, polyvinyl alcohol and stainless-steel fibers are viable options for fiber reinforcement in historical structures, and further optimization and testing are recommended before application as a reinforcement material in historic structures.

Blast furnace slag is one of the largest solid wastes in the world. The slag-based geopolymer obtained by alkali activation has many advantages, such as a high strength, a good corrosion resistance, low carbon and environmental protection. Existing studies have shown that the mechanical properties of slag-based geopolymers are related to the combined effects of many factors, but there is still a lack of reliable conclusions on the primary and secondary influence degree of each factor, which greatly affects the scientific preparation and application of slag-based geopolymers. In order to solve this problem, we choose to proceed from the two perspectives of the mix ratio of the alkali activator and the elemental composition of raw materials. Through the orthogonal analysis method, this paper studies the influence of the modulus of the alkali activator, the solid-to-liquid ratio of the activator, the water-cement ratio and the metakaolin replacement rate on the uniaxial compressive strength of a slag-based geopolymer. The results show that when the solid-liquid ratio is about 0.25, the modulus of the alkali activator is 1.3~1.5, the water-cement ratio is about 0.4 and the samples with higher strength can be prepared. With the addition of metakaolin, a new gel phase NASH was formed in the system, which significantly promoted the late strength and toughness growth of the sample. The research results comprehensively analyze the influence of different factors on the mechanical properties of the slag-based geopolymer, which can provide a valuable reference for the engineering application of alkali-activated slag materials.

The 7d unconfined compressive strength tests of alkali-activated tungsten tailings and the microscopic characteristics tests of scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were conducted to investigate the effect of alkali-solid ratio on the properties of alkali-activated tungsten tailings. The test results indicate that the unconfined compressive strength of alkali-activated tungsten tailings increased with the alkali-solid ratio. However, the strength decreases slightly when the alkali-solid ratio is 12%. The microstructures of the gels generated in the alkali-activated tungsten tailings are affected by the alkali-solid ratio. The details are as follows: the microstructure is honeycomb in low alkali-solid ratio (7%, 8% and 10%), with N-A-S-H as its primary form, and flocculation in high alkali-solid ratio (14% and 15%), mainly in the form of C-A-S-H. When the alkali-solid ratio is at the medium level (12%), the microstructure is a small round bead, and the N-A-S-H is equivalent to the C-A-S-H. The more C-A-S-H content, the greater the strength. This study can provide a scientific basis and technical reference for the resource utilization of tungsten tailings.

This paper presents the preparation of alkali-activated red mud (RM) light material by an ultra-high liquid-solid ratio (1.98) based on the super water absorption characteristic of RM particles. Compressive strength, dry density, and water absorption are analyzed over time. Besides, the characteristic distributions of porosity and pore size are measured by mercury injection tests, and the microstructure is further analyzed by scanning electron microscopy. The results show that the ultra-high liquid-solid ratio can be used to prepare light samples with superior mechanical properties, low water absorption, reasonable pore distribution, and fine microstructures compared with light samples prepared with a foaming agent. The reason is that the significant increase in the free water does not change the dense microstructure of samples and effectively limits the increase in the detrimental pores. This effectively alleviates the sudden decrease in compressive strength and limits the increase in water absorption.

Alkali-activated materials (AAM) are recognized as potential alternatives to ordinary Portland cement (OPC) to limit CO2 emissions and beneficiate several wastes into useful products. Compared with its counterparts involving the concentrated aqueous alkali solutions, the development of \"just add water\" one-part alkali-activated materials (OP-AAM) has drawn much attention, mainly attributed to their benefits in overcoming the hazardous, irritating, and corrosive nature of activator solutions. This study starts with a comprehensive overview of the OP-AAM; 89 published studies reported on mortar or concrete with OP-AAM were collected and concluded in this paper. Comprehensive comparisons and discussions were conducted on raw materials, preparation, working performance, mechanical properties, and durability, and so on. Moreover, an in-depth comparison of different material pretreatment methods, fiber types, and curing methods was presented, and their potential mechanisms were discussed. It is found that ground granulated blast-furnace slag (GGBS) provides the best mechanical properties, and the reuse of most aluminosilicate materials can improve the utilization efficiency of solid waste. The curing temperature can be improved significantly for precursor materials with low calcium contents. In order to overcome the brittleness of the AAM, fiber reinforcement might be an efficient way, and steel fiber has the best chemical stability. It is not recommended to use synthetic fiber with poor chemical stability. Based on the analysis of current limitations, both the recommendations and perspectives are laid down to be the lighthouse for further research.