Abstract
This study comparably assessed the pozzolanic effect of silica fume (SF) and ground rice husk ash (RHA) as supplementary cementing materials on the properties of blended cement pastes and concretes. A commonly commercial silica fume (SF) and locally-produced rice husk ash (RHA) samples with two finenesses (one with larger size than cement and the other with smaller size than cement) were used in this study. Material properties of SF and RHA were experimentally characterized. Hydration and mechanical properties of cement pastes incorporating SF and RHA were determined by thermogravimetric analysis (TGA) and compressive strength tests, respectively. Properties of concretes regarding workability, mechanical property, durability, and microstructure were evaluated. Results showed that, although the finely ground RHA used in this study possessed lower SiO2 content and higher particle size compared to SF, it exhibited comparable pozzolanic reactivity with SF due to the nano-scale pores on its each single particle, leading to a higher specific surface area. The optimal replacement levels of SF and RHA were 10% by weight of cement in pastes and concretes. Although addition of SF and RHA led to a significant reduction in slump for the fresh mixtures, inclusion of up to 30% of SF or 15% of ground RHA did not adversely affect the strength of concretes. At the same mix, incorporation of finely-ground RHA in cement composites provided comparable mechanical properties, hydration degree, and durability with SF blended cement composites, owing to the porous structure and high specific surface area of RHA particles. Microstructure morphology analysis of concretes explored by scanning electron microscopy (SEM) further validated the strength and the durability test results.
Highlights
In the manufacture of cement, the clinker production process requires a great amount of energy and emits a large amount of carbon dioxide (CO2 ) into the atmosphere
It can be seen that the paste incorporating CRHA shows the lowest compressive strength at all the testing curing ages, which may be due to the larger particle size and lower surface area of coarse
It is found that chloride permeability of finely ground RHA (FRHA) series is “very low” when FRHA is used at 5%
Summary
In the manufacture of cement, the clinker production process requires a great amount of energy and emits a large amount of carbon dioxide (CO2 ) into the atmosphere. Silica fume (SF) and rice hush ash (RHA) are both siliceous materials They are highly concentrated sources of amorphous SiO2 and possess similar chemical reaction mechanism in cement matrix system. The reactivity of SF and RHA contributes to the strength enhancement of cement-basted materials by pozzolanic reactions between amorphous silica and calcium hydroxide liberated during the cement hydration process. One of the main dimensions of this investigation was to explore the feasibility of RHA instead of SF (which is not economically available even in developed countries) in mortars and concretes This would reduce the environmental problems associated with the current open field burning of the rice husk. The microstructures of concretes were explored through scanning electron microscopy (SEM) analysis
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