| dc.description.abstract | The work presented in this thesis deals with the development of self-consolidating high performance concrete (SCHPC) incorporating rice husk ash (RHA) as a supplementary cementing material. Various SCHPCs were produced using the water-binder (W/B) ratios of 0.30, 0.35, 0.40 and 0.50, and RHA content in the range of 0 to 30% of cement by weight. In addition, a number of pastes and mortars formulated from the concretes were prepared and tested for the filling ability. The paste and mortar filling abilities were tested with respect to flow time and flow spread, respectively, at various dosages of high-range water reducer (HRWR). Also, the mortars were tested for the air content at various dosages of air-entraining admixture (AEA). It was observed that the flow time of the pastes increased with lower W/B ratio and higher RHA content, whereas the flow spread of the mortars decreased with higher W/B ratio and greater RHA content. Both paste and mortar filling abilities increased with higher HRWR dosages. In addition, the air content of the mortars decreased with lower W/B ratio and higher RHA content for given AEA dosages.
The fresh SCHPCs were tested for filling ability, passing ability, air-void stability, segregation resistance, unit weight and air content. The filling ability was determined with respect to slump and slump flow, inverted slump cone flow time and spread, and orimet flow time and spread. The passing ability was measured with regard to slump and slump flow with J-ring, inverted slump cone flow spread with J-ring, and orimet flow spread with J-ring. The air-void stability in several fresh SCHPC mixtures was investigated with respect to re-mixing of concrete and subsequent measurement of air content at different test stages.
The test results obtained for the fresh properties showed that the inverted slump cone and orimet flow times increased with lower W/B ratio and greater RHA content. In addition, the slump flow, inverted slump cone flow spread, and orimet flow spread with and without J-ring increased considerably with lower W/B ratio and greater RHA content. However, the increases in slump with and without J-ring at lower W/B ratio and higher RHA content were not significant. The unit weight of concrete slightly decreased with higher W/B ratio and greater RHA content, and with higher air content. Achieving the target air content required greater AEA dosages for lower W/B ratio and higher RHA content. However, the presence of RHA had no adverse effect on the air-void stability of concrete.
The segregation resistance of various SCHPCs was investigated by visual inspection of concrete in mixer pan, and during and after different flow tests. Slight bleeding and a thick layer of paste were noticed in mixer pan for several concretes. The dynamic segregation in the form of discontinuity or blockage of flow did not occur during the orimet and inverted slump cone flow tests for any concrete. No aggregate pile appeared in the slump flow, and orimet and inverted slump cone flow spreads of any concrete. But minor to severe mortar halos were noticed in the periphery of the flow spread of several concretes, particularly in the presence of high RHA content. The results of visual inspection suggest that both lower W/B ratio and greater RHA content improved the dynamic segregation resistance of concrete. In contrast, the higher RHA content resulted in a lower static segregation resistance, which was overcome in the presence of viscosity-enhancing admixture (VEA).
The static segregation resistance of several SCHPCs was quantitatively determined by sieve and column apparatus. The segregation index given by the sieve increased with lower W/B ratio and higher RHA content, thus indicating a reduced static segregation resistance. In contrast, the segregation factor given by the column apparatus decreased with lower W/B ratio suggesting an increased static segregation resistance. However, the segregation factor increased with higher RHA content, and thus revealed a reduction in static segregation resistance. In the presence of VEA, both segregation index and segregation factor decreased significantly, indicating an improvement in the static segregation resistance of concrete.
The hardened SCHPCs were tested for compressive strength, ultrasonic pulse velocity, water absorption, total porosity and electrical resistivity. Test results revealed that the compressive strength, ultrasonic pulse velocity and true electrical resistivity increased, whereas the water absorption and total porosity decreased with lower W/B ratio and higher RHA content. The entrained air-voids decreased the compressive strength, ultrasonic pulse velocity, water absorption and total porosity, but slightly increased the electrical resistivity of concrete. In general, the hardened properties indicated good durability of the concretes.
The empirical models for the filling ability (slump flow) and compressive strength of SCHPC were derived and verified with test data from this study and other data taken from the literature. The slump flow and compressive strength computed from the models were coherent with the measured values. Both filling ability and strength models were useful to develop a mixture design method for SCHPC with and without RHA. | en |
