Use of glass and nylon fibers in concrete for controlling early age micro cracking in bridge decks

One of the major defects in concrete bridge decks are the formation of early age micro cracking which ultimately reduces its durability. The inclusion of fibers in concrete slabs has showed satisfactory performance with improved mechanical properties and reduced early age micro cracking (EAMC). The relative high compressive strength (CS), achieved by using high cement content, is the main cause of early age micro cracking in concrete. The low tensile strength (TS) also results in less resistance to early age cracking. Other factors causing EAMC include temperature rise, water content and shrinkage strain. The EAMC can be reduced by increasing CS and TS with use of economical materials other than cement. In this work, mechanical properties of glass fiber reinforced concrete (GFRC) and nylon fiber reinforced concrete (NFRC) are determined for the application of concrete bridge decks. The effectiveness of glass fibers (GF) and nylon fibers (NF) in concrete will be checked by comparing mechanical properties of GFRC and NFRC with that of plain concrete (PC). The mix design ratio of PC is 1:3.33:1.67 (cement:sand:aggregate) with a water cement ratio of 0.71. The GF and NF having a length of 50 mm and a fiber content of 5%, by mass of cement, are added in the concrete mixture for the production of GFRC and NFRC. Standard specimens are tested for determining compressive, splitting-tensile and flexural strengths of PC, GFRC and NFRC. Pre-crack energy absorption and toughness indices are also studied for different types of loadings i.e. compressive, splitting-tensile and flexural loadings. There is a decrease in compressive strength and an increase in splitting-tensile and flexural strengths of GFRC and NFRC compared to that of PC. Even though pre-crack energy absorption of GFRC and NFRC is less but their toughness indices are more than that of PC. Thus, GFRC and NFRC are suitable for reducing EAMC in bridge decks.