Investigation of the compressive resistance of infilled concrete masonry

Abstract

The compressive resistance of infilled concrete masonry depends on the infill strength, the concrete block strength and their composite action. This study investigates various parameters effecting unit strength for a newly developed block. Compressive resistance analysis and failure mode analysis were undertaken. Three different unit tests were used for the purpose of this investigation: (i) Type 1: to obtain compressive stress results for hollow concrete blocks loaded in compression. (ii) Type 2: to obtain compressive stress results for infilled blocks where the load is taken both by the block and the infill. (iii) Type 3: to obtain compressive stress results for the composite units where only the cores are taking the compressive force. The concrete infills used are CS, C7, ClO, C15, C20 and C25. Hollow blocks averaged a wet and dry compressive stress of 1.79N/mm2 and 2.88N/mm2 respectively. A total of 96 infilled blocks (with samples of 16 blocks per concrete grade) and another 20 hollow concrete blocks were tested. For the infilled blocks, Type 2 and Type 3, an increase in concrete infill grade resulted in an increased ultimate failure load. Comparisons between Type 2 and Type 3 specimens loads indicate that at higher infill grades, the failure loads become closer to each other, meaning that the block's contribution to the overall capacity at high grades reduces. Failure modes for Type 2 blocks are comparable to failure modes of Type 1 and Type 3 blocks when combined. Also, Type 2 blocks resulted in a gradual crack formation, whilst Type 3 blocks exhibited a brittle failure. Variations in strength of mortar could therefore modify the mode of failure. Bond was noticed to be affected by the slump of the concrete infill. Higher slump results in better bond between internal faces of the block and the infill and so a greater shear resistance at the interface.