STRUCTURAL BEHAVIOUR OF FERRO-FIBROCRETE OVERLAYS

Abstract

It is well known that PCC fails in tension due to formation of microcracks in the initial stage and their subsequent propagation. has limited ductility and little resistance to cracking. The microcracks so formed propagate resulting in its low fracture toughness , poor tensile strength and limited resistance to impact and shock loading. The properties most interested to a pavement/highway engineer. Due to above reasons, the thickness requirements of concrete are very high. Traditional resurfacing of concrete pavements by means of PCC often calls for an overlay thickness in excess of 100 mm. This may not be feasible or desirable at certain specific locations where level and drainage constraints exist, especially on city streets, residential roads, bridge deck slabs intersections etc. Therefore, attempts have been made to develop, composite materials as an overlay alternative. The present study is an attempt to examine the feasibility of thin ferro-fibrocrete overlays for resurfacing rigid pavements. Two 25mm partially bonded ferro-fibro overlays were laid over two cracked composite slabs namely PCC-SFRC & PCC-Ferrocement composite slabs of size 1.8m x 1.8m. The structural behaviour, cracking patterns, and cracking behaviour of the two overlaid slabs under various loading conditions was examined. To study the flexural behaviour of overlays, laboratory flexural tests were conducted on overlaid beams. The effect of overlay thickness and bonding characteristics was also examined. All these tests were conducted ever 100x100x500 mm overlaid prizms. iv Two overlay thicknesses 25mm and 40mm, with partially bonded and unbonded condition, were studied. The study suggests that thinferro-fibrocrete overlay is a promising rehabilitation technique for surface deteriorated/cracked concrete pavements. The ferro-fibrocrete overlays exhibited multiple cracking and complete crack control even upto failure loads. The crack initiation was considerably delayed. Ferro-fibrocrete overlays exhibited superior flexural performance than other types regardless of bonding 'conditions. But, the bonding conditions were observed to have significant effect over the performance of the overlay (FF0) under various flexural tests. The additional cost of such an alternative may be offset due to reduced thickness, improved performance under loading and thereby increased life expectancy.