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A numerical model to simulate the impact of high temperature on the behavior of conventional concrete under chemoplastic framework is developed and validated. The model is based on new formulation of a constitutive law with new chemoplastic potential. By overlaying the chemoplastic potential on the modified Etse and Willam yielding surface, both defined on the Haigh-Westergaard coordinates, it was found that the two curves do not undergo similar stress state at the same strength parameter. For an adequate evaluation of normal vectors, each surface is forced to pass through the current stress state. Keeping the loading surface unchanged, the calculation of the plastic potential need to be modified. The proposed constitutive model is validated by comparing predicted and experimental data. The model is shown to be accurate to predict different stress states of concrete under different temperature levels.

The purpose of this paper is to evaluate high strength concrete (HSC) containing polypropylene fibers (PP-fibers) at high temperature under a compressive load.

The use of PP fibers in HSC is known to reduce and at times eliminate the risk of spalling. HSC containing 0, 1 and 2 kg/m³ of PP-fibers were subjected to various temperatures from 20°C to 150°C, 300°C and 450°C and evaluated in a “hot condition”. One group of specimens was in a non-stressed condition during heating (unstressed hot), while a second group was subjected to an initial preload of 40 per cent of the room temperature compressive strength during the heating (stressed hot).

Results showed that stressed concrete containing PP-fibers had lower thermal gradients (the temperature difference between the surface and center temperatures as a function of radial distance) and a decrease in relative porosity. However, the compressive strength of stressed specimens was improved with or without fibers as compared to that of the unstressed HSC. The increased stress levels due to concrete expansion at elevated temperature were also reported. The PP-fibers did not have a significant effect on the compressive strength of stressed concrete as compared to the unstressed state.

This paper reports the compressive strength of PP-fibers in HSC at elevated temperature with and without a pre-load.