Effect of Rice Husk Ash Blending of Portland Cement on Compressive Strength of Gap-Graded Concrete

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Title: Effect of Rice Husk Ash Blending of Portland Cement on Compressive Strength of Gap-Graded Concrete

Author(s): D. D. Bui and P. Stroeven

Publication: Special Publication

Volume: 171

Issue:

Appears on pages(s): 297-308

Keywords: Admixtures; blending cements; high-strength concrete; pozzolans.

Date: 8/1/1997

Abstract:
Rice husk ash (RHA) is a very reactive pozzolanic material. It has been succesfully used as a mineral admixture in concrete. Rice husks are readily and in large quantities available in Vietnam. Hence, it would be of economic interest to study the use of RHA for the production of high-strength and durable concretes based on indigenous raw materials. This con-cept should also encompass the aggregates, with coarse-grained crushed rock (granite) and very fine river sand as natural candidates. The particle size distribution of this sand violates the building code, however. Since blending with coarse (imported) sand would be too expensive, this study focused on gap-graded mixtures. For the binder an ASTM Type I portland cement was employed, being the only quality produced in the region in Vietnam. RHA with a significant carbon content was obtained after burning rice husks at temperatures below 75OOC. The ash was thereupon finely ground in conjunc-tion with a naphtalene-based superplasticizer. The application of the RHA in conjunction with this superplasticizer in the gap-graded concretes with very fine sand made it possible to produce high consistency and cohesive mixtures with a relatively low sand content. 28-days compressive strengths values of 70-90 MPa were obtained for mixtures with slumps of 140-225 mm and water to binder ratios of 0.40-0.33. For stiff mixtures, with water to binder ratios of 0.35-0.27, the 28-days compressive strength values were in the range of 60-100 MPa.