This paper presents an experimental study on the spalling resistance of normal strength concrete with different mixing sequences of polypropylene (PP) fibers subjected to fire. The mixing sequences of PP fibers in concrete mixture investigated are: (1) mixing PP fibers with fresh concrete; (2) mixing PP fibers with coarse aggregates; and (3) mixing PP fibers with fine aggregates. According to the test results, the degree of concrete spalling is reduced for specimens containing PP fibers at 0.2% by volume in the concrete mixture. The beneficial effect on spalling resistance is maximized when the PP fibers are mixed with fresh concrete and when the PP fibers are mixed with fine aggregates. The results are confirmed using scanning electron microscope (SEM) to investigate the dispersion of PP fibers in hardened concrete. In the case of mixing PP fibers with fine aggregates, smaller amount of superplasticizer is needed to obtain the target slump, and it is therefore recommended for practical use.

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The performance of precast concrete load-bearing walls exposed to fire is investigated using 3-D thermal and structural models. The thermal model is validated by comparing the predicted temperatures with results from the fire tests carried out in the present study, previous experimental studies, and Eurocode 2. The structural model is validated by comparing the predicted displacements and crack patterns with results from the fire tests carried out in the present study. It is found that the results obtained from the thermal model and the structural model are in line with the experimental data and Eurocode 2 results. The validated 3-D model of precast concrete load-bearing walls is used to study the effect of load level, slenderness ratio and boundary conditions on the fire performance of the walls. The results show that the fire resistance rating of load-bearing walls decreases with increasing load level and slenderness ratio, while the fire resistance rating of the walls increases when rotational restraints are imposed at the ends of the walls. Finally, equations are presented for estimating the fire resistance rating of the walls with different support conditions.

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