Alkali-Activated Materials from Industrial Solid Waste

Alkali-activated materials harness the latent cementitious properties of industrial by-products by triggering chemical reactions with alkaline solutions. Common precursors include ground granulated blast furnace slag, fly ash and soda or carbide residues, each rich in silica, alumina or calcium. When activated by sodium or calcium hydroxide, silicate or aluminate species dissolve and reorganise into binding gels such as calcium silicate hydrate (C-S-H) or sodium aluminosilicate hydrate (N-A-S-H). This approach transforms waste streams into low-carbon binders, offering equivalent compressive strength to ordinary Portland cement while reducing greenhouse gas emissions and landfill burdens. Applications span structural concrete, soil stabilisation, mine backfill and durable mortars, with performance governed by precursor composition, activator type, water content and curing conditions. Global interest has surged as regulators and industry seek sustainable construction alternatives that valorise solid wastes and close material loops.

Research from Nature Portfolio

Recent studies have evaluated calcium carbide residue and coal fly ash as complementary binders for soil stabilisation, identifying an optimal CaO:(SiO₂+Al₂O₃) ratio of 1.5 to maximise long-term compressive strength in paste and mortar systems. Mineralogical analyses reveal the formation of mixed C-S-H and calcium aluminate silicate phases that enhance binding efficiency. Application to loess soil at dosages between 10 and 25 wt % demonstrated consistent unconfined compressive strength through multiple wet-dry cycles, with only minor reductions after extended cycling due to microcracking. These findings underscore the potential of finely tuned industrial blends to deliver durable ground improvement with a markedly lower carbon footprint than conventional stabilisers.

Alkali-Activated Materials from Industrial Solid Waste publication trend

The graph below shows the total number of articles in alkali-activated materials from industrial solid waste across all publications each year (not limited to Nature Index journals).

Technical terms

Alkali-activated material: A binder formed by the reaction of an aluminosilicate precursor with an alkaline solution, producing cementitious gels.

Geopolymer: An inorganic polymer formed by polycondensation of dissolved aluminosilicate species under high pH, resulting in a three-dimensional Si–O–Al network.

Pozzolanic reaction: A chemical process where silica or alumina from a precursor reacts with calcium hydroxide to form cementitious hydrates.

Ground granulated blast furnace slag (GGBFS): A glassy by-product of iron production, rich in calcium, silica and alumina, activated by alkalis to yield C-S-H gel.

Calcium carbide residue (CCR): The alkaline by-product of acetylene production, primarily composed of Ca(OH)₂, used as a solid alkali activator.

Soda residue: Also known as waste lime, a highly alkaline industrial by-product of sodium carbonate manufacturing, containing Ca(OH)₂ and various soluble salts.

C-S-H gel: Calcium silicate hydrate, the principal binding phase in many cementitious systems, providing strength and cohesion.

N-A-S-H gel: Sodium aluminosilicate hydrate, the main binding phase in low-calcium geopolymer systems, contributing to mechanical integrity and durability.

References

1. Evaluation of calcium carbide residue and fly ash as sustainable binders for environmentally friendly loess soil stabilization. Scientific Reports (2024).
2. Utilization of Calcium Carbide Residue as Solid Alkali for Preparing Fly Ash-Based Geopolymers: Dependence of Compressive Strength and Microstructure on Calcium Carbide Residue, Water Content and Curing Temperature. Materials (2022).
3. Properties and Hydration Mechanism of Soda Residue-Activated Ground Granulated Blast Furnace Slag Cementitious Materials. Materials (2021).