Experimental investigation of bitumen physical properties on foamability and mechanical properties of foam bitumen stabilized mixes
The use of foamed bitumen stabilization technique is growing rapidly and it is gaining wide acceptance in many different counties. This technique is new to New Zealand and it just has started to achieve some acceptance within the roadway industry. In the first part of this work, bitumens from seven different bitumen sources were collected and examined. Three sources that are currently used in New Zealand, three are from three sources in California in the United States, and one source from Australia. The physical properties of bitumens such as penetration, viscosity and softening point, in addition to foamability tests were carried out on these bitumens samples in order to examine the effect of bitumen source, grade and bitumen rheology on the characteristics of the resulting foam. Mixes with similar gradation were prepared with the foam bitumen resulting from the different grades and sources were subjected to resilient modulus tests to examine the mechanical properties, moisture and temperature susceptibility. Foamed stabilized mixes exhibited a significantly improved moisture resistance as the mixes kept their integrity and strength and they did not deteriorate significantly, even after 5 days of continuous soaking in water. The average index of retained strength (IRS) value of 86% was observed which is reasonably high and comparable with that of the HMA mixes. Temperature susceptibility of foamed stabilized mixes is reasonably low and it was proved that the use of temperature susceptible binders does not have a direct effect on the foaming properties. However, the resulting mixtures are likely to be sensitive to temperature changes. In addition, mechanical properties of mixtures treated with different binders varied noticeably.