Effect of polypropylene fibers on unrestrained early age shrinkage of concrete and long-term performance subjected to fire

Micro cracks at early age concrete very difficult to avoid although treatments have always been managed. This study focuses on the role of polypropylene fibers of concrete mixtures during first 24 hours after casting. Further investigation has also been carried out to investigate long-term performance of concrete subjected to fire.Size model of 60 mm x 100 mm x 1000 mm was employed investigating the plastic shrinkages,and 50 mm x 200 mm x 350 mm was used to examine concrete micro-cracks. Five polypropylene dosages variations of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% to the mortar volume were applied. Whilst, cylindrical specimen of O150 mm x 300 mm has been conducted with five variations of 0, 1.5, 2.0, 2.5, and 3 kg/m3 polypropylene dosages to investigate concrete performance under various temperatures. Test results indicate the addition of polypropylene fibers play significant role to reduce cracks and plastic shrinkage. The 0.3% of polypropylene fibers reduces shrinkage losses to 90%. Under elevated temperature, the addition of polypropylene has less significant effect on normal concrete but has very significant effect on high-strength concrete. The high-strength concrete with 2.0 kg/m3 polypropylene dosage under temperature of 300OC and 700OC has 90% and 35% residual strength, respectively. Therefore, minimum value of 2.0 kg/m3 polypropylene addition to the concrete mixture is recommended.