Chemical transformation of rice husk ash for sustainable, constructable, and durable binary cementitious system Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sq87bz85v

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  • The production of cement and concrete results in the production of large amounts of CO₂ emissions which can have significant negative environmental impacts. Using supplementary cementing materials (SCMs) as a cement replacement is an effective solution to reduce these negative environmental impacts, as most SCMs are waste by-products from other industries. Rice husk ash (RHA) is one such by-product material. RHA is produced from the burning of rice husks for the production of electricity. This material consists mostly of amorphous silica and has high potential to be used as a SCM. However, the use of RHA is limited. This is due to its cellular, honeycomb-like morphology. This morphology absorbs mix water and reduces the workability of fresh mixtures containing RHA. Reducing RHA particle size can improve the workability of cementitious systems containing RHA. However, reducing RHA particle size with mechanical grinding is time-consuming and costly. This dissertation evaluates the development of a new chemical transformation method to reduce particle size and to eliminate the RHA cellular, honeycomb-like morphology of the RHA. This dissertation focuses on developing a chemical transformation process for RHA, assessing the performance of systems containing chemically transformed RHA (t-RHA), and evaluating the influence of mixing and transport variables on the characteristics of RHA blended cement systems. Results indicate that using the chemical transformation process can be an alternative method to reduce RHA particle size and eliminate the cellular, honeycomb-like morphology of the RHA. This results in the improved flowability, higher chemical shrinkage, faster set, reduced porosity, and increased early-age strength of blended cementitious systems when compared to the 100% portland cement (PC) system. When mixing time and mixer revolution counts increase, using t-RHA exhibits lower flow reduction rates and lower chloride diffusivity than the 100% PC system. However, the performance of the t-RHA and the as-receive RHA (AR-RHA) system are similar with increasing mixing time and mixer revolutions count.
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