INVESTIGATIONS ON LOAD CARRYING CAPACITY OF THIN SFRC PAVEMENTS OVER WBM BASE

Abstract

With the advent of composite materials such as Steel Fibre Reinforced Concrete (SFRC), Ferrocement and Ferrofi-brocrete, throughout the world, the recent research emphasis has been on the construction of thinner pavement sections which are longer lasting and have better performance and could bear the heavy traffic and repetitions of modern vehicles. It has now been well established that SFRC is such a composite material which offers the possibility of placement as pavement slabs directly on stronger subgrades. Also, for thin SFRC pavement sections in locations where the subgrades are of poor quality, the provision of sub-base or base becomes necessary. Under the present investigation, an attempt has been made to study the load carrying capacity, cracking behaviour and crack patterns of two thin SFRC pavement slabs with varying percentage of fibre content of 0.5% and 1.25% by volume of concrete when laid over WBM base course. The load carrying capacity, cracking behaviour and crack patterns of a comparatively thicker PCC pavement slab over WBM base has also been studied to make a comparision with SFRC pavement slabs. The size of SFRC-1 (0.5% fibre content by volume of concrete) and SFRC-2 (1.25% fibre content by volume of concrete) were kept as 1.8mx1.8m x .06m SFRC over 150mm WBM base. In the present study two fibre contents of 0.5% and 1.25% are taken in view of the fact that the optimum fibre content for SFRC is reported as 1.25% by volume of concrete, but fibre being a costly material, commonly 0.5% fibre contents are generally used in field conditions. iv The investigations establish that the load carrying capacity of thin SFRC pavement slabs is increased considerably when placed over WBM bases. With the provision of WBM base the load carrying capacity of SFRC pavement slabs has been increased 2.5 times over that of SFRC pavementslab of same thickness when laid directly over subgrade. Also the load carrying capacity of thin SFRC slabs over WBM base is increased by 1.55 and 2.00 times over WBM-PCC pavement under edge loading condition for 0.5% and 1.25% fibre contents respectively. Under corner loading conditions the corresponding improvements are 1.5 and 1.833 times over WBM-PCC. The absence of cracking under central loading condition at 180KN load and reduced crack width and crack propagation in comparison to PCC slab demonstrated the structural adequacy of the SFRC slabs over WBM base. The life expectancy studies of the three types of pavement slabs established that, the expected service life of SFRC pavements may be up to 9 times more than that for PCC pavement and the reduction in thickness may be more than 30%. The semi-full scale testing of these slabs in laboratory under static plate load test recommends their use in heavily loaded areas even with the subgrades of poor quality. The increase in cost of these pavement slabs can be justified in favour of reduced thickness and cracking, lower maintenance cost, better serviciability and enhanced life cycle. The thin SFRC pavement slabs laid over WBM base course thus offer the possibility of pavements which are longer lasting and expected to give better overall performance.