Due to their good performance and environmental friendliness, fly ash-based construction materials have great potential as alternatives to ordinary Portland cement. To realize sustainable development and beneficial use of fly ash in the construction industry, this paper presents a comprehensive review of relevant literature to evaluate the properties and performance of fly ash, with a particular focus on recent advances in characterization, compositional understanding, hydration mechanism, activation approaches, durability and sustainability of fly ash as a construction material. Several key aspects governing the performance of fly ash, including chemical composition, activator type and hydrates evolution in concrete, are highlighted. Finally, the important needs, pertinent to the optimal and broad utilization of fly ash as an integral part of sustainable construction materials, are identified for further research and development, where large-scale application studies, further classification of fly ash, advanced characterization tools and technology transfer to biomass fly ash are recommended.

Characteristics and applications of fly ash as a sustainable construction material: A state-of-the-art review

Fly ash and slag

Physicochemical properties of binder gel in alkali-activated fly ash/slag exposed to high temperatures

In this study, the super-fine ground granulated blast furnace slag was obtained by wet grinding (i.e. WGBBS), and an attempt to activate the super-fine ground granulated blast furnace slag by sodium sulfate (SS) and sodium carbonate (SC) was made. SS/SC-activated WGGBS samples were prepared and cured at the room temperature. The compressive strength at the age of 3 d, 7 d, 28 d, and 56 d was tested. Hydration heat was assessed, and micro structure and hydrates were also characterized with XRD, TG-DTG, SEM-EDS, and NMR; the pore structure was assessed with MIP. The results showed that SS and SC efficiently activated the hydration of WGGBS with D50 = 3.87 μm at the room temperature, and such high activating efficiency of SS and SC under room temperature was seldom reported in the literature. The mechanism behind was mainly because of the super-fine particles of slag with greater amounts of hydration points, which were produced in the process of wet grinding. Difference in activating efficiency between SS and SC was mainly because the anionic groups acted as different roles in hydration process: SS could induce the formation of ettringite while SC could induce the formation of calcite. Such results were expected to provide guidance on designing weak base-activated slag system.

Compressive strength and hydration process of wet-grinded granulated blast-furnace slag activated by sodium sulfate and sodium carbonate

Sustainable utilization of red mud waste (bauxite residue) and slag for the production of geopolymer composites: A review

Microstructural and strength improvements through the use of Na2CO3 in a cementless Ca(OH)2-activated Class F fly ash system

Synthesis of structural binder for red brick production based on red mud and fly ash activated using Ca(OH)2 and Na2CO3

This study presented CaCl 2 as a potential additive activator to develop a new strong, price-competitive CaO-activated GGBFS binder blended with fly ash (CAS 4:4:2) to commercially replace ternary blended cements, which generally consist of 40% Portland cement, 40% GGBFS, and 20% fly ash (wt.%) (PC 4:4:2), widely used for concrete production. Despite CAS 4:4:2 having no clinker cement compound, the addition of CaCl 2 not only significantly accelerated reactions of CAS 4:4:2 binders but also largely increased strengths at all curing days. Up to 72 h, the cumulative reaction heat of CAS 4:4:2 with CaCl 2 was also reasonably low. Reaction products and microstructures of hardened CAS 4:4:2 pastes were considerably changed after CaCl 2 addition. The CaCl 2 presence markedly promoted dissolution of the glass phase of GGBFS and fly ash in early days, resulting in more production of reaction products (e.g., C-S-H, hydrocalumite) and pore-size refinement.

Effects of CaCl2 on hydration and properties of lime(CaO)-activated slag/fly ash binder

Properties of quicklime(CaO)-activated Class F fly ash with the use of CaCl2

In this study, barium hydroxide was proposed as a main activator for ground granulated blast-furnace slag (GGBFS) to produce a strong binder, and it was compared to calcium hydroxide in terms of strength development, reaction products, and microstructure. The Ba(OH)2-activated GGBFS (BHAS) achieved a significantly higher compressive strength than Ca(OH)2-activated GGBFS (CHAS), except at 3 days, mainly due to (1) the more formation of hydration products, leading to a notable reduction in pore sizes and volume, and (2) the higher solubility of Ba(OH)2, resulting in a higher dissolution of GGBFS than that of Ca(OH)2. Although calcium silicate hydrate (C-S-H) was a major reaction product in both mixtures, the Ca/Si ratios were much different. In the BHAS, the presence of barium ions prohibited the synthesis of ettringite and monocarboaluminate, which formed in the CHAS mixtures, but it induced Ba-bearing products, stratlingite, and the hydrotalcite-like phase. The removal of ettringite was the cause of the lower strength of the BHAS at 3 days compared to that of the CHAS.

Dongho Jeon

Papers

Microstructural and strength improvements through the use of Na2CO3 in a cementless Ca(OH)2-activated Class F fly ash system

Synthesis of structural binder for red brick production based on red mud and fly ash activated using Ca(OH)2 and Na2CO3

Effects of CaCl2 on hydration and properties of lime(CaO)-activated slag/fly ash binder

Properties of quicklime(CaO)-activated Class F fly ash with the use of CaCl2

Strength development and microstructural characteristics of barium hydroxide-activated ground granulated blast furnace slag