STUDY ON STRENGTH CHARACTERISTICS OF COMPOSITE PAVEMENT SLABS

Abstract

A variety of conventional construction practices have been adopted by construction agencies in respect of cement concrete pavement construction. Plain cement concrete is a brittle material with low tensile strength. Yet, it is a popular construction material because of its ability to be moulded to any shapes. The low tensile strength is made good by putting steel reinforcing bars. This, however has a poor area utilisation, low ductility, fatigue and resistance to shocks. In reinforced cement concrete the strength makes up in the direction of reinforcing bars. In pavement construction where tensile stresses are omnidirectional, the reinforcing becomes difficult and expensive. Therefore, attempts have been made to develop composite materials for their application to such constructions. The recent research have established the performance and economics of various types of constructions such as Steel fibre reinforced concrete, Ferrocement, Ferro-fibrocrete, Flyash concrete, Roller compacted concrete. Study shows that when composite materials are used in pavement construction in place of plain or conventionally reinforced concrete section, the thickness requirement is appreciably reduced. Under the present investigation an attempt has been made to study the load carrying capacity, cracking behaviour and crack patterns of three combinations of composite pavement slabs, viz. PCC-SFRC, PCC-Ferrocement and PCC-Ferro-Fibrocrete. The material properties evaluated are namely - compressive strength, flexural strength, impact strength and modulus of elasticity for these composites. The size of PCC-SFRC composite slab was kept as 1.8m x 1.8m x 0.12m composed of 40mm SFRC (0.5% fibre content by volume of concrete with a dia of 0.45mm and aspect ratio 80) over 80mm PCC. The PCC-Ferrocement slab was 1.8m x 1.8m x 0.10m composed of 20mm Ferrocement (1.92% wire mesh reinforcement by volume of mortar, consisting of 2 layers of size 5mm x 5mm, 22 SWG, wire mesh with a dia of 0.82mm embedded in the cement sand mortar) over 80mm PCC. The PCC-Ferro-fibrocrete slab was 1.8m x 1.8m x 0.10m composed of 20mm Ferro-fibrocrete over 80mm PCC. In Ferro-fibrocrete, 0.5% steel fibre and 1.92% wire mesh reinforcement by volume of mortar was used. The study shows that the compressive strength is increased by 14 to 35% in different composites. The flexural strength is increased by 23 to 44% in such composites. However, increase is found to be more predominant in case of PCC-Ferro-fibrocrete composite. The impact resistance is increased by 6.5 to 21.0 times. The modulus of elasticity value of 2.97 x 104 N/mm2 was the highest with PCC-Ferro-fibrocrete composite. The PCC-Ferrocement and PCC-Ferro-fibrocrete composite slabs exhibited multiple cracking mechanism and low crack widths with cracks distributed over a larger surface area of the pavements, with significant reduction in damage. The crack initiation in the PCC-Ferro-fibrocrete composite pavement took vi place at higher loads than the other two composite slabs. The Ferro-fibro combination in the matrix helped in maintaining the cracks tightly closed due to crack arrest properties. The cost of PCC-Ferro-fibrocrete composite slab is about 13% more than the cost of PCC-SFRC and PCC-Ferrocement slab. But the load carrying capacity under corner loading condition works out to be 1.33 and 1.20 times than PCC-SFRC and PCC-Ferrocement composite slabs. Whereas absence of cracking under central loading condition at a 180KN load and reduced crack width and crack propagation in comparison to other two slabs demonstrated the structural, adequacy of the PCC-Ferro-fibrocrete composite slab. The laboratory study and the study of structural behaviour of composite pavement slabs under static plate load tests established that the composite pavements may be recommended for heavily trafficked highway pavements, intersections, bridge decks and runway pavements. The additional cost of such an alternative may be offset due to reduced thickness, improved performance under loading and thereby increased life expectancy of the pavements.