The effect of polypropylene fibres and coconut coir on restrained shrinkage and compressive strength of concrete

This paper investigates the comparative effects of the use of polypropylene fibres and coconut coir on restrained shrinkage and compressive strengths of concrete. Polypropylene fibres and coconut coir were cut (20 and 40 mm lengths) using 0.05 and 0.1% volume fraction of cement and were added to the concrete mix to cast 27 concrete prisms each for the two restrained shrinkage tests (100 mm × 100 mm × 300 mm). 108 Samples of concrete cubes (100 × 100 × 100 mm) containing 0, 0.05 and 0.1% volume fractions of polypropylene and coconut coir (20 mm and 40 mm in length) were also cast for compressive strength test. Concrete substrates and 8 mm mesh reinforcements were separately used to provide restraints for the concretes prepared for shrinkage tests. The shrinkage tests were monitored for 18 h and compressive test were carried out after 7, 14, 21 and 28 days of moist curing of concrete cubes. The results showed that prisms with substrates containing 0.1% polypropylene fibres and coconut coir reduced shrinkage by 31% and 15%, respectively. For wire mesh-reinforced prisms, 0.1% polypropylene and coconut coir decreased shrinkage by 16% and 7%, respectively. The compressive strength results also showed that polypropylene exhibited better strength performance than coconut coir.