Impact of different types of modification on low-temperature tensile strength and Tcritical of asphalt binders

The introduction of the Superpave((R)) asphalt binder specification provided the asphalt industry with a useful guideline for choosing appropriate materials to meet the requirements of a specific climate. Acid, alkaline, and polymer modification are just some of the ways to modify asphalt to meet the Superpave specification. The direct tension test (DTT) technique was applied to study the low-temperature properties of modified asphalt in terms of DTT failure stress values and the critical cracking temperature (T-critical). The bending beam rheometer (BBR) usually failed to detect improvement in low-temperature performance in polymer-modified asphalt (PMA). DTT results show that elastomeric polymer modification improves the low-temperature performance of PMA. In some PMAs, the failure stress value was higher than 9.5 MPa. The DTT technique for PMA was also reviewed. The effect of acid and alkaline modifiers on asphalt materials was studied. Acid or alkaline modification of asphalt was found to be only temporary and to be reversible. Acid modification of asphalt can be reversed by reaction with alkaline materials such as lime or antistripping agents. Alkaline modification of asphalt can be reversed by reaction with acidic materials such as carbon dioxide. Alkaline also can be washed away by water. Even though the BBR suggested a slight improvement in the low-temperature performance in acid- or alkaline-modified asphalt, the DTT failure stress values and Ti-critical did not confirm this improvement. A relatively simple procedure that allows detection of acid or alkaline modification of asphalt materials is described.