A comparison of stress-strain behaviour of conventional and high strength concrete

Strength performance of concrete is characterized by its compressive strength, elastic modulus, stiffness and energy absorption capacity. Stress strain behaviour of concrete encompasses information on all these parameters, and is thus one of the most vital data to assess its overall performance. The present study utilizes the stress strain response, as a tool, to compare the relative variation in performance of conventional and high strength concrete. Two set of mix compositions (viz., M40 and M80 grade concrete) have been designed. The designed compositions are checked for their target strength by performing load controlled tests on 28 day cured cube specimens. M40 grade concrete comprises of cement and water as binding material, and fine and coarse aggregates as filler. High strength concrete (M80 grade) is designed with cement, mineral admixture and water as binding material; while the fine and coarse aggregates contribute to the filler material. For high strength concrete, super plasticizer has been added in required proportion to ensure adequate workability. Displacement control tests, with controlled strain rate, have been performed on 28 day cured cube specimens. Variability in pre-peak and post-peak stress strain response is analysed for both conventional and high strength concrete. An average of response over atleast four samples is computed for both the M40 and M80 grade concrete. In present study, the characteristic response is normalized with respect to peak strength to obtain a common reference basis and compared. The comparison is summarized in terms of change in pre-peak response and post-peak ductility. The observed results enable quantification of relative change in performance for M40 and M80 grade of concrete. The results are significant for benchmarking performance of high strength concrete structures with those of conventional concrete structures.