Corresponding Author

Walid E. Elemam

Subject Area

Civil and Environmental Engineering

Article Type

Original Study


The purpose of this research is to investigate the impact of hybrid micro and macro polypropylene fibers (PPFs) on the mechanical characteristics and microstructure of high performance concrete (HPC). Seven concrete mixes with different contents of hybrid polypropylene fibers were tested. The tests included the slump test, compressive and flexural strength, resistance to elevated temperatures, and concrete microstructure. Compared to the control mixture, introducing macro and micro polypropylene hybrid fibers to HPC mixes dramatically enhanced the flexural and compressive strength of concrete while lowering workability. HPC compressive and flexural strengths decrease as temperature rises, nevertheless, the strength loss rate was lowered with the use of hybrid PPFs. In addition to increasing the compressive strength by 14.6%, 14.28%, and 11.4% at ages 7, 28, and 56 days, respectively, the combination of 0.75 kg/m3 micro and 5 kg/m3 macro PPFs also raised the flexural strength by 41.9% at age 56 days, and the highest residual compressive and flexural strength of concrete after being exposed to 200, 400 and 800 °C was achieved, the residual flexural and compressive strength up to 45.6%, and 64.3%, respectively, of the initial strength after exposure to 800 oC. The network structure generated by macro and micro polypropylene fibers in the matrix has been well demonstrated by microstructural analysis. The incorporation of hybrid polypropylene fibers prevents capillary cracks in concrete and probable disintegration between aggregate and cement paste.


High performance concrete, elevated temperature, polypropylene fibers, flexural strength, compressive strength, concrete microstructure.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.