Effect of specimen size and shape on the compressive performance of high strength engineered cementitious composites at elevated temperatures

This study provides detailed insights into the effect of specimen size on the residual compressive strength of hybrid polyethylene-steel fibre reinforced high strength engineered cementitious composite after exposure to elevated temperatures. A mix design with high residual performance was selected and a total of 120 specimens with different cross-section shape (square and circular), aspect ratio (1 and 2) and sizes (cylinders of 40 mm, 75 mm, 100 mm, 150 mm diameter with height to diameter ratio of 2:1, cubes of 50 mm, 75 mm, 100 mm side and prism of size 75 x 75 x 150 mm) were cast. These specimens were subjected to temperatures ranging from 200 to 800 degrees C and the residual compressive strength and change in microstructure was then analysed after air cooling. Experimental results indicated that cubic specimens experienced less strength loss compared to prism specimens with the same cross-sectional area and the damage was found to decrease with increase in the volume to surface area ratio of the specimens. Furthermore, no spalling occurred in any of the specimens despite the change in specimen size or cross-section. Unlike previous studies that did not present any clear influence of specimen size, the present work established that the residual strength is dependent on aspect ratio and volume to surface area ratio of the specimen. As a result, these findings are valuable for selecting appropriate specimen size in elevated temperature studies and for the development of suitable guidelines to facilitate meaningful comparisons with the existing data.