The Effects of Polypropylene Fibers on Mechanical Properties and Permeability of Concrete

In recent years, using of various fibers in concrete mix is growing and each type creates some specific property in concrete. Polypropylene (PP) fiber is a new type fiber with significant advantages in mechanical properties of fibrous concrete. In this research two series of concrete mix were made (without fibers - control concrete - and with PP fibers in length of 6 and 12 mm and in 0.2, o.4, and o.8 percent of cement content) by local aggregates(sand and gravel), Portland cement, silica fume (as pozzolan), and superplasticizer (as admixture with polycarboxilic base). The specimens were cured for 3, 7 and 28 days and tested for compressive and flexural strength. The specimens elected for measuring the permeability depth were tested under 5 atm. water head after 28 days curing and permeability index was calculated by Valenta equation. Results showed that early compressive strength of fiberous specimens was less than control specimens but by increasing the age of specimens, the strength will be increased and maximum compressive strength was for 28-d specimen with 0.8 percent of PP fiber but the flexural strength of fibrous specimens were more than normal specimens at all ages and the maximum flexural strength was for 28-d specimen with 0.4 percent of PP fiber. Permeability of fibrous specimens was less than normal specimens and the minimum value belongs to specimen with 0.4 percent of PP fiber.