M R NIVITHA
Articles written in Sadhana
Volume 44 Issue 5 May 2019 Article ID 0128
This investigation reports the influence of processing condition (air rectification and component blending) on ageing and stress relaxation behaviour in bitumen. FTIR spectra were recorded on two samples of bitumen at unaged, short-term aged and long-term aged conditions. Indices such as aliphaticity, aromaticity,carbonyl and sulphoxide calculated from the FTIR spectra were used in the analysis. It was seen that the ageing compounds in the air-rectified bitumen were higher at the end of the production process compared with theblended bitumen while the rate of oxidation compounds formed during short-term and long-term ageing was higher in the blended bitumen. In addition, a stress relaxation test was performed at 25°C in the unaged, shorttermand long-term ageing conditions. Since the formation of ageing compounds leads to change in ‘stiffness’ and hence a change in the stress relaxation behaviour of the material, it is seen that the stress relaxation results are in line with the material behaviour as seen from the FTIR tests.
Volume 46 All articles Published: 12 August 2021 Article ID 0163
Whitetopping technique for rehabilitation of bituminous pavements has been considered as a costeffective 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 theeffect 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%) andsilica 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 axleloads 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.
Volume 47 All articles Published: 5 April 2022 Article ID 0071
In India, the axle loads have increased substantially in the recent decades and a majority of such overloaded vehicles are expected to have increased tire pressure. Increased tire pressures have a significant impact on the performance of the pavement as the load is applied over a concentrated area. Very little data is available related to the magnitude of tire pressures currently observed in India and its impact on the rutting (Nr) and fatigue (Nf) life of bituminous pavements. This study aims at quantifying such information for India. A field survey was conducted at five weighbridges for 100 vehicles to measure the tire pressures and the corresponding axle loads. Considering all the rear axles, it was observed that the mean tire pressure was 833 kPa and about 50% of the vehicles operated with a tire pressure greater than 800 kPa. To illustrate the combined influence of axle load and tire pressure, pavement sections available in IRC: 37-2018 were chosen and evaluated for their rutting and fatigue performance. For instance, for 10% CBR and 50 Million Standard Axles (MSA) traffic, when the tirepressure was increased from 500 kPa to 1200 kPa, it was observed that Nf reduced by 41% and Nr reduced by 5%. The fatigue life of the surface layer is seen to be more sensitive to variation in tire pressure. Moreover, the magnitude of influence exerted by the tire pressure depended on the axle load to a large extent.