Influence of axle load on the fatigue life of thin whitetopping with fibre-reinforced concrete

Whitetopping technique for rehabilitation of bituminous pavements has been considered as a cost-effective solution when the life cycle cost of pavement is considered. Thin whitetopping is a preferred overlay when both the structural and functional capacities of the pavement are required to be enhanced. IRC:SP:76-2015 outlines the procedure for construction of thin whitetopping in India. While IRC:SP:76-2015 suggests that thin whitetopping can be used on rural roads and medium to moderately heavy volume roads, the traffic composition related to the same is not clearly specified. In this study, an attempt was made to specify the limiting traffic characteristics for thin whitetoppings in terms of the axle load and their number of repetitions. To estimate the effect of traffic, the actual traffic data collected from four National Highways in India were used and the whitetopping design was carried out as per IRC:SP:76-2015. To increase the total load carrying capacity of the whitetopping overlay, especially in locations experiencing heavier traffic loads, mixes with different dosages of polypropylene fibres were designed and silica fume was added to enhance the bond between fibres and concrete. Eight different mixes were prepared with different combinations of fibre dosage (0.8%, 1.3% and 1.8%) and silica fume (8% and 13%) in addition to a control mix and a mix with 8% silica fume and no fibres. The mix with 8% silica fume and 1.8% fibres exhibited the highest equivalent flexural strength and the control mix with no fibres and silica fume exhibited the lowest equivalent flexural strength. These two mixes were considered to estimate the effect of axle loads. In most cases, it was seen that thin whitetopping without fibres failed in design for the actual traffic conditions as the fatigue response was highly sensitive to the axle loads. When the axle loads were limited closer to the legal axle loads specified in IRC:3-1983, it was seen that even the mix without fibres was able to sustain the design traffic.