Effect of temperature reduction, foaming water content, and aggregate moisture content on performance of foamed warm mix asphalt

A laboratory study was conducted to evaluate the effect of temperature reduction, foaming water content, and aggregate moisture content on the performance of foamed warm mix asphalt (WMA). Two asphalt binders (PG 70-22 and PG 64-28), two aggregate types (limestone and crushed gravel), and two nominal maximum aggregate sizes (12.5 mm and 19.0 mm) were used in this study. The foamed WMA mixtures were produced using three production temperatures (30 °F, 50 °F, and 70 °F (16.7 °C, 27.8 °C, and 38.9 °C) lower than the traditional hot mix asphalt), three foaming water contents (1.8%, 2.2%, and 2.6%) by weight of the asphalt binder), and three aggregate moisture contents (0%, 1.5%, and 3%). The asphalt pavement analyzer (APA) test was utilized to evaluate the rutting resistance, and the indirect tensile strength (ITS) and the Modified Lottman (AASHTO T 283) tests were utilized to evaluate the moisture sensitivity of the asphalt mixtures. In general, comparable performance was obtained for the HMA and the foamed WMA prepared using 30 °F temperature reduction, 1.8% foaming water content, and fully dried aggregates. The test results revealed that reducing the production temperature of foamed WMA may result in increased susceptibility to permanent deformation (or rutting) and moisture-induced damage, while increasing the foaming water content (up to 2.6% of the weight of the asphalt binder) may not have a negative impact on the foamed WMA performance. It was also found that using moist aggregates may result in inadequate aggregate coating leading to concerns with regard to moisture-induced damage and long-term durability. Therefore, it is critical to use fully dried aggregates to ensure satisfactory foamed WMA performance.