Toward Gap-Graded HPC in Vietnam Using Crushed Rock, Very Fine Sand, and RHA Blended Cement


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Title: Toward Gap-Graded HPC in Vietnam Using Crushed Rock, Very Fine Sand, and RHA Blended Cement

Author(s): P. Stroeven, D. H. Dalhuisen, N. T. Quy, D. D. Bui, and A. V. Dong

Publication: Special Publication

Volume: 154


Appears on pages(s): 263-278

Keywords: aggregates; cements; compressive strength; concretes; rice; sands; gap graded aggregate; mortars (material); Materials Research

Date: 5/1/1995

Economic solutions for production of high-strength concrete in Vietnam require use of locally available indigenous resources. Proportioning of gap graded mixtures in Northern Vietnam is therefore based on broken rock and very fine Red River sand. Additionally, normal portland cement blended with fine-grained rice husk ash (RHA) is employed in combination with a superplasticizer. This paper discusses results obtained in a Dutch-Vietnamese research cooperation program. RHA was incinerated in a specially constructed oven under temperatures up to 750 C, yielding amorphous silica with a relatively high carbon content (23 percent). Ash was ground for 18 hours in a laboratory ball mill in combination with or without use of a naphthalene type of superplasticizer. Dutch sand and gravel were used, simulating as closely as possible the Vietnamese aggregate. Particularly promising data was obtained for 19 percent sand content in the aggregate and a paste content of 500 kgf/m 3, in which the RHA content amounted to 100 and 200 kg/m 3 with a corresponding water to paste ratio of 0.3 and 0.35, respectively. RHA ground with the superplasticizer was used in such cases (yielding 75 percent of particles to be smaller that 5 micro-m). Compressive strength was found to exceed 50 MPa at seven days and 70 MPa at 28 days.