CO2 Curing of Ca-Rich Fly Ashes to Produce Cement-Free Building Materials

Carbonation and Leaching Behaviors of Cement-Free Monoliths Based on High-Sulfur Fly Ashes with the Incorporation of Amorphous Calcium Aluminate

The high sulfate content in various alkaline wastes, including those from fossil fuel and biomass combustion, and other industrial processes, necessitates careful management when used in cementitious systems to prevent potential deterioration of construction materials and environmental safety concerns. This study explores the under-researched area of high-sulfur fly ash (HSFA) utilization in the production of cement-free monoliths through accelerated carbonation and further examines the effect of niobium slag (NS)-a calcium aluminate-containing slag-as an additive on the strength development and the mobility of SO42-. The methodology involves mineralogical and microstructural analyses of monoliths before and after carbonation, accounting for the effects of accelerated carbonation treatment and NS addition. The findings suggest that accelerated carbonation significantly improves the initial compressive strength of the HSFA monoliths and generally immobilizes heavy metals, while the effect on sulfate immobilization can vary depending on the ash composition. Moreover, the addition of NS further enhances strength without substantially hindering CO2 uptake, while reducing the leaching values, particularly of sulfates and heavy metals. These findings suggest that it is feasible to use calcium aluminate-containing NS in HSFA-based carbonated monoliths to immobilize sulfates without compromising the strength development derived from carbonation. This research contributes to the understanding of how accelerated carbonation and NS addition can enhance the performance of HSFA-based materials, providing valuable insights for the development of sustainable construction materials.

Wood Ash as Sustainable Alternative Raw Material for the Production of Concrete-A Review

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.

Accelerated and natural carbonation of a municipal solid waste incineration (MSWI) fly ash mixture: Basic strategies for higher carbon dioxide sequestration and reliable mass quantification

The carbonation of alkaline wastes is an interesting research field that may offer opportunities for CO₂ reduction. However, the literature is mainly devoted to studying different waste sequestration capabilities, with lame attention to the reliability of the data about CO₂ reduction, or to the possibilities to increase the amount of absorbed CO₂. In this work, for the first time, the limitation of some methods used in literature to quantify the amount of sequestered CO₂ is presented, and the advantages of using suitable XRD strategies to evaluate the crystalline calcium carbonate phases are demonstrated. In addition, a zero-waste approach, aiming to stabilize the waste by coupling the use of by-products and the possibility to obtain CO₂ sequestration, was considered. In particular, for the first time, the paper investigates the differences in natural and accelerated carbonation (NC and AC) mechanisms, occurring when municipal solid waste incineration (MSWI) fly ash is stabilized by using the bottom ash with the same origin, and other by-products. The stabilization mechanism was attributed to pozzolanic reactions with the formation of calcium silicate hydrates or calcium aluminate hydrate phases that can react with CO₂ to produce calcium carbonate phases. The work shows that during the AC, crystalline calcium carbonate was quickly formed by the reaction of Ca(OH)₂ and CaClOH with CO₂. On the contrary, in NC, carbonation occurred due to reactions also with the amorphous Ca. The sequestration capability of this technology, involving the mixing of waste and by-products, is up to 165 gCO₂/Kg MSWI FA, which is higher than the literature data.