Abstract
The negative environmental impacts of Portland cement as a binder in the construction industry have created a growing impetus to develop sustainable alternative binders. Various types of clay have been considered as potential cement replacements. The impact of clays as cement replacement depends on the dosage and treatment methods. This paper presents a comprehensive review to determine the effects of different types of clay on the fresh and hardened properties of concrete mixtures by analyzing the experimental database reported by the literature, including raw, calcined, modified, nano, and organo. This study intends to show the process of optimizing the use of clay in concrete, the reason behind converting raw clay to modified types, and research gaps through a comparison study between different types of clays. The present review study shows that clay-based concrete mixtures have higher thixotropy and yield stress values, improving shape stability. This results in lower early-age shrinkage of the concrete. However, the high floc strength of clay-based concrete causes a reduction in flowability. Treatment methods of raw clay, such as calcination and nano-sized clay particles, improve concrete compressive strength. General results of the previous studies highlight that all types of clay investigated positively affect the resistance of concrete to environmental attack.
Highlights
Global demand for cement and concrete has increased significantly in recent years due to the rapid expansion of countries and continued population growth throughout the world [1,2]
The vast majority of the research has shown the reduction effect of raw clay minerals on the compressive strength, while the results reported by Budelmann et al (2006) [141] show different trends than the other investigations
There are three mechanisms attributed to the improvement of strength in nano-clay containing pastes, including: (1) nano-clays can act as a filler due to their nano-sized particles [160,161]; (2) the high amount of SiO2 in nano-clay on its ultra-thin surface can increase the rate of C–S–H [162,163]; and (3) the swelling of tubular nanoclay due to entrapment of water within its layers, which results in expansion of the clay and an enhanced filling effect in the capillary pores [161]
Summary
Global demand for cement and concrete has increased significantly in recent years due to the rapid expansion of countries and continued population growth throughout the world [1,2]. Automation of the manufacturing of lime in modern cement kilns and increased use of alternative and sustainable fuel sources are the key improvements in the cement industry for reducing energy consumption and associated CO2 emissions [11] These initiatives have been outpaced by the dramatic increases in demand, and further developments are required to reduce the environmental impacts and costs. Clays have already been shown to have excellent pozzolanic properties under specific calcination conditions or surface modifications [14,19] For these reasons, clays in their raw, calcined, and modified forms are important cement-replacement alternatives for the development of sustainable concretes with lower costs and environmental impacts. A more comprehensive review is necessary for future works to review the LC3 technology
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