Effect of rice husk ash properties on the early age and long term strength of mortar

This paper presents an experimental study on the effect of chemical composition and physical properties of rice husk ash (RHA) on the strength of mortar. The aim of this investigation was to establish the optimal RHA replacement levels as blending component in cement. Four different types of RHA (A, B, C and D) were used of which RHA-C and D had the highest content of amorphous silica. Compressive and tensile strength and workability of the mixes were compared with control OPC samples. Results show that the early age (7days) strength of RHA blended mortar samples was lower than the compressive and tensile strength of the OPC control samples. However, the 28 day strength of samples with up to 20% RHA-C and RHA- D was higher than that of the control samples. The 90 day strength of all blended samples with up to 40% RHA was higher than that of the control samples. RHA-D performed best in the experiments with a compressive strength increase of 16% at 20% RHA replacement and an increase of compressive strength of 8.6% at 40% RHA replacement. The results at 90 days show that cement could be replaced with up to 50% RHA with only a small reduction in strength compared to OPC mortar. From the results it was found that the content of amorphous silica has the biggest influence on the strength of the mortar samples while the workability was higher for samples with finer grained RHA

Strength assessment of lightweight concrete

Available from British Library Document Supply Centre- DSC:DX171648 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Progressive Collapse Analysis Of Flat Slab Buildings With Post-Punching Effect

The reinforced concrete flat slab is one of the types of floor systems used to construct residential, office and parking buildings. Because of the direct transfer of floor loads to columns, flat slabs are susceptible to punching failure in slab-column connections. The punching failure in one column can initiate failure in adjacent columns and cause progressive punching shear failures resulting in the progressive collapse of the entire structure. Using the post-punching capacity of the connections can prevent or minimize the likelihood of such failures. The post-punching resistance of slab-column connections in the absence of shear reinforcements is provided by the dowel action and vertical component in flexural and integrity bars when they deflect after punching. Most studies of flat plate performance were attended to punching shear failure and the post-punching behaviour of flat slabs is ignored. This can reduce accuracy in progressive collapse analysis.This paper validates analytical methods previously proposed by the authors to simulate post-punching behaviour a multi-panel flat plate system. Then, the progressive collapse potential of a three-story flat slab building was evaluated using the proposed analytical model. The effect of factors such as column removal position, structural member damage due to previous seismic loads on subsequent failures, floor load intensity, and boundary conditions (slab expansion around the building) on flat slab structural behaviour were investigated. The analysis results showed that the building internal column removal would cause the punching failure in the adjacent slab-column connections, but due to the post-punching resistance of the connections, overall failure did not occur. Therefore, ignoring the effect of post-punching resistance on slab-column connections can lead to an error in the evaluation of the progressive failure potential of flat slab structures. The analysis results revealed that the internal column removal of the building is the most critical. In the structure, with the slab expansion around the building, the removal of the edge column is the most critical scenario. The Dynamic Amplification Factor (DAF) was calculated by comparing static and dynamic vertical displacements for model structures. The analysis results showed that DAF could be greater than 2 in the flat plate slabs