COMPERAT1VE STUDY ON MODEL CONCRETE PAVEMENT SLABS

Abstract

Cement concrete pavements maintain a very high recognition among the engineers and road users alike. When considering the whole-life cycle-cost, cement concrete pavement emerges as the most economical since they are practically maintenance free and do not require rehabilitation or strengthening courses, which are essential for Bituminous specifications. Also the vehicle operation cost on cement concrete pavements are much lovr than the Bituminous pavements. As India' s road modernisation programme gathers momentum, the need to construct pavements capable of withstanding heavy loads but economical in the long run has to be examined. Cement concrete pavements in the present context may be an ideal one. Further, among the various types of concrete pavements the type of pavement which will best suit our conditions are to be worked out. It is necet.sary to understand the behaviour of the pavements that directly influence their services. In the work presented here, stul 1:-s have been carried out on three types of concrete slabs, viz, Grouted cement concrete slab, Rolled concrete . slab, and the Roller compacted concrete slab. The materi.al properties evaluated are namely-Compressive strength, tensile strength, modulus of elasticity, flexural strength, and load carrying capacity of the concrete slabs. In the Grouted cement concrete pavement slab the final .of approximate proportion of the materials used works Gut to 1:2:54 (i.e. 1 cement : 2 sand : 54 coarse aggregate by weight). In the Rolled concrete pavement slab the lean concrete mix was used. However in this study it had been adopted for use as wearing course and hence the design strength was adopted at 15 N/rnm2, and the mix proportion worked out to 1:2:31:5.37 (i.e. .1. cement : 2.31 sand : 5.37 coarse aggregate). The Roller compacted concrete is a no slump concrete which is compacted by vibratory rollers. The water content was as per the optimum moisture content for attaining the maximum compacted density as determined by the Modified Proctor's compaction method. The Roller compacted conct ete mix used for the study was of proportion 1:2.31:3.87 (i.e. I cement 2.31 sand : 3.87 coarse aggregate by w eight ), and the design strength wqs 30 N/mm2 at 28 days curing. To sin:late the field conditions in casting the laboratory • specimens, different compaction methods had been tried. The Modified Proctor's Ommpaction was found suitable for both Grouted cement concrete and Rolled concrete. Vibro—compaction method was found suitable for the Roller—compacted concrete. It was observed that in Roller Compacted concrete, even though the water content is not as per water—cement ratio, and the construction was similar to the bituminous construction, the strength and other properties developed were similar with that of the conventional concrete pavements. From the load vs. strain plot it was observed that the strain developed in the Roller compacted concrete slab was lesser than V that of the other two types of concrete slabs at a particular load value. Grouted cement concrete slab cracked at a strain value of 300x106, while the Rolled concrete cracked at a strain value of 260x106. The Roller compacted concrete slab cracked at a strain value of 480x106. The modulus of elasticity value of 2.77x10„4 N/mm2 was the highest with Roller compacted concrete as compared to other two types of concrete. The finished surfaces of the Roller compacted concrete slab and the Grouted concrete slab were rough textured and hence will not be advisible for high speed vehicular traffic unless another wearing course treatment is done on them. However smooth finish could be obtained in the case of Rolled concrete. For a slight variation in the cost of construction, i.e. , 9 percent and 12 percent more than Grouted cement concrete and the Rolled concrete respectively, for the same thickness of slab, the Rolier compacted concrete was found to have much higher load carrying capacity. The load carrying capacity of Roller compacted concrete slab worked out to 1.88 times and 1.41 times the load carrying capacity of the Grouted cement concrete slab and Rolled concrete slab respectively. To arrive at final conclusion about the priorities to be given to the above listed three types of concx ete detail