Abstract:
Large number of hot mix asphalt (HMA) pavements fail prematurely even with the perfect mix design. Large temperature differentials, caused by the placement of cooler portion of plant produced HMA into mat, can potentially cause compaction problem that translates into less than the desirable densities. This phenomena leads to the investigation of construction related temperature differentials and the corresponding density differentials. Temperature differential has direct stimulus on the properties of HMA and it can lead to the higher air voids, low density, high permeability and segregation. This research study is focused on investigating the effect of various compaction temperatures on the properties of HMA. Laboratory investigation was conducted over two NHA specified gradations for open graded Mix design of wearing course. The research study evaluated the performance of commonly used gradation and Job Mix formula of HMA in the country for various compaction temperatures. First gradations had 4% bitumen content and 9.5 mm maximum size aggregate while the second had 3.5% and 12.5 mm maximum size of aggregate. The strength and volumetric parameters of HMA were determined using Marshall Method in order to investigate the effect of wide compaction temperature ranges i.e. from 160°C to 70°C. Wheel Tracker equipment was used to test the performance based parameter of permanent deformation i.e. rutting propensity for various compaction temperatures. From the Marshall Test, compaction temperature of 140°C to 130°C was found to be the optimum compaction temperature range regarding the strength and volumetric properties whereas the results of rutting propensity test revealed, compaction temperature of 135°C as suitable temperature for the HMA. A Non linear regression analysis involving Cobb-Douglas functional form was performed to ascertain the rutting propensity of HMA as a function of no. of wheel passes, compaction temperature and gradation type. Also, rut vulnerability nomographs were developed as a function of no. of wheel passes and compaction temperature. The research findings can help the highway agencies/construction firms in temperature differential control regime which can arrest the problems of inadequate compaction, thus increased strength, durability, fatigue life and decreased aging and moisture damage of pavements.
