A review on the utilization of fly ash

The concrete industry is known to leave an enormous environmental footprint on Planet Earth. First, there are the sheer volumes of material needed to produce the billions of tons of concrete worldwide each year. Then there are the CO2 emissions caused during the production of Portland cement. Together with the energy requirements, water consumption and generation of construction and demolition waste, these factors contribute to the general appearance that concrete is not particularly environmentally friendly or compatible with the demands of sustainable development. This paper summarizes recent developments to improve the situation. Foremost is the increasing use of cementitious materials that can serve as partial substitutes for Portland cement, in particular those materials that are by-products of industrial processes, such as fly ash and ground granulated blast furnace slag. But also the substitution of various recycled materials for aggregate has made significant progress worldwide, thereby reducing the need to quarry virgin aggregates. The most important ones among these are recycled concrete aggregate, post-consumer glass, scrap tires, plastics, and by-products of the paper and other industries.

The greening of the concrete industry

Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume

The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

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A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

Recycled aggregate from C&D waste & its use in concrete – A breakthrough towards sustainability in construction sector: A review

Use of nano-silica to reduce setting time and increase early strength of concretes with high volumes of fly ash or slag

This paper presents results on the physical and chemical properties of rice husk ash (RHA), and deals with the properties of fresh and hardened concrete incorporating the same ash. The properties of fresh concrete investigated included workability, bleeding, setting time, and autogenous temperature rise, and those of the hardened concrete included compressive, splitting tensile, and flexural strengths, modulus of elasticity, drying shrinkage, resistance to chloride ion penetration, resistance to freezing and thawing cycling, and salt-scaling resistance. In addition to the effects of the percentage of RHA and the water-cementitious materials ratio on the properties investigated, the properties of the RHA concrete were also compared with those of the control Portland cement concrete and silica fume concrete.

High-Performance Concrete Incorporating Rice Husk Ash as a Supplementary Cementing Material

Microwave-assisted beneficiation of recycled concrete aggregates

Rice-husk ash paste and concrete: Some aspects of hydration and the microstructure of the interfacial zone between the aggregate and paste

The effects of nano-silica (NS) on setting time and early strengths of high volume slag mortar and concrete have been experimentally studied. Effects of NS dosages, size and dispersion methods on strength development of high volume slag mortars were also investigated. A constant water-to-cementitious materials ratio (w/cm) 0.45 was used for all mixtures. The results indicate that the incorporation of a small amount of NS reduced setting times, and increased 3- and 7-day compressive strengths of high-volume slag concrete, significantly, in comparison to the reference slag concrete with no silica inclusion. Compressive strength of the slag mortars were increased with the increase in NS dosages from 0.5% to 2.0% by mass of cementitious materials at various ages up to 91 days. The strengths of the slag mortars were generally increased with the decrease in the particles size of silica inclusions at early age. Ultra-sonication of nano-silica with water is probably a better method for proper dispersion of nano-silica than mechanical mixing method.

Min-Hong Zhang

Papers

Use of nano-silica to reduce setting time and increase early strength of concretes with high volumes of fly ash or slag

High-Performance Concrete Incorporating Rice Husk Ash as a Supplementary Cementing Material

Microwave-assisted beneficiation of recycled concrete aggregates

Rice-husk ash paste and concrete: Some aspects of hydration and the microstructure of the interfacial zone between the aggregate and paste

Use of nano-silica to increase early strength and reduce setting time of concretes with high volumes of slag