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

Influences of nano-TiO2 on the properties of cement-based materials: Hydration and drying shrinkage

Green concrete: Prospects and challenges

Disposal of fly ash (FA) resulting from the combustion of coal-fired electric power stations is one of the major environmental challenges. This challenge continues to increase with increasing the amount of FA and decreasing the capacity of landfill space. Therefore, studies have been carried out to re-use high-volumes of fly ash (HVFA) as cement replacement in building materials. This paper presents an overview of the previous studies carried out on the use of high volume Class F FA as a partial replacement of cement in traditional paste/mortar/concrete mixtures based on Portland cement (PC). Fresh properties, mechanical properties, abrasion resistance, thermal properties, drying shrinkage, porosity, water absorption, sorptivity, chemical resistance, carbonation resistance and electrical resistivity of paste/mortar/concrete mixtures containing HVFA (⩾45%) as cement replacement have been reviewed. Furthermore, additives used to improve some properties of HVFA system have been reviewed.

A brief on high-volume Class F fly ash as cement replacement – A guide for Civil Engineer

An investigation of the microstructure and durability of a fluidized bed fly ash–metakaolin geopolymer after heat and acid exposure

Effects of nano-Al2O3 on early-age microstructural properties of cement paste

An experimental investigation has been carried out to study the physical and mechanical property of high volume fly ash cement paste. Ordinary portland cement was replaced by 0, 20, 30, 40, 50, 60 and 70% class F fly ash (by weight). Water- binder ratio in all mixture was kept constant at 0.3. Cube specimens were compacted in table vibrator. As expected bulk density decreases with fly ash increment in the mixture. Apparent porosity and water absorption value increases with replacement of cement by fly ash. Results confirm the decrease in compressive strength at 3, 7 and 28 day with fly ash addition and it is more prominent in case of more than 30% fly ash content mixes. Ultrasonic pulse velocity test results indicate that the quality of the paste deteriorate with increase of fly ash content in the mixture.

Study on the physical and mechanical property of ordinary portland cement and fly ash paste

An experimental investigation was carried out to compare the compressive strength of zero slump and high slump concrete with high volume fly ash. 40% to 70% replacements of OPC (by weight) with class F fly ash have been incorporated. Superplasticizer was added at 1% of binder (cement + fly ash) to the zero slump mixture to get a slump in the range of 140 to 180mm and cubes were cast without compaction. The results showed that the apparent porosity and water absorption were higher for zero slump concrete than high slump concrete. Zero slump concrete showed better compressive strengths than superplasticized concrete with 40 to 60% fly ash addition for all curing times tested (3,7 and 28 days). Ultrasonic pulse velocity results categorized all mixes as of ‘EXCELLENT’ concrete quality. Based on the present experimental investigation, it can be concluded that high volume fly ash concrete is suitable for general construction applications.

Comparative study on physical and mechanical properties of high slump and zero slump high volume fly ash concrete (hvfac)

Direct stress and sub-stress caused by fire, temperature variation and external loading in a structure are most important for the development of cracks. The chemical reactions of natural healing in the matrix was not been established conclusively. The most significant factor that influences the self-healing is the precipitation of calcium carbonate crystals on the crack surface. The mechanism which contribute autogenic healing are: (a) Continued hydration of cement at cracked surface as well as continued hydration of already formed gel and also inter-crystallization of fractured crystals; (b) blocking of flow path by water impurities and concrete particles broken from the crack surface due to cracking; (c) expansion of concrete in the crack flank (swelling) and closing of cracks by spalling of loose concrete particle are also reported as the sealing mechanism by researchers. The recovery of mechanical as well as physical property was discussed by different researchers. An experimental investigation was carried out to study the autogenic healing of fire damaged fly ash and conventional cementitious mortar samples subjected to steam followed by water curing at normal atmospheric pressure. The micro cracks are generated artificially by heating the 28 days aged mortar samples at 800 Deg. C. The effect of fly-ash replacing ordinary Portland cement by 0 and 20% was studied. Recovery of compressive strength and physical properties i.e. apparent porosity, water absorption, ultrasonic pulse velocity and rapid chloride ion penetration test confirm the self-healing of micro cracks. Such healing is more prominent for fly ash mortar mix. Optical as well as scanning electron microscopy With EDAX analysis and X-ray diffraction study of the white crystalline material formed in the crack, confirms formation of calcium carbonate. Self-Healing Properties of Conventional and Fly Ash Cementitious Mortar, Exposed to High Temperature

Self-Healing Properties of Conventional and Fly Ash Cementitious Mortar, Exposed to High Temperature

S tress (compression/tension) leads to generate micro cracks in concrete matrix, which eventually forms visible cracks. Such formation of cracks is common and causes failure of structures. An experimental investigation was carried out to compare the self healing of partially cracked con ventional mortar (prepared with ordinary Portland cement) and cement - fly ash mortar. 20 % OPC has been replaced by class F fly ash for cement - fly ash mortar. All mortar specimens were prepared with 1:3 binder to sand ratio (by weight) and with fixed 0.5 water/binder ratio. After curing in normal tap water for 28 days, specimens were subjected to direct compression (50% of corresponding 28 days compressive strength) to generate micro cracks in it. Healing environment was made (a) curing in normal tap water for 120 days and (b) curing in normal air for 120 days separately. The compressive strength, ultrasonic pulse velocity, water absorption and rapid chloride ion permeability test on mortar specimens (with/without fly ash) confirm self healing of cementitious composites in terms of recovery of its properties and the self healing property is more prominent for fly ash mortar. FES EM with EDAX and XRD of the white deposition in the crack opening was found to be calcite.

Shaswata Mukherjee

Papers

Effects of nano-Al2O3 on early-age microstructural properties of cement paste

Study on the physical and mechanical property of ordinary portland cement and fly ash paste

Comparative study on physical and mechanical properties of high slump and zero slump high volume fly ash concrete (hvfac)

Self-Healing Properties of Conventional and Fly Ash Cementitious Mortar, Exposed to High Temperature

Comparative Study on Self Healing of Fly Ash and Conventional Cement Mortar