Durability, Long-Term, and Environmental Evaluation of Alkali-Activated Alternative Soluble Silica Source for Recycled Asphalt Pavement Stabilization

Abstract

The preservation of natural resources has been gaining considerable space in recent decades, encouraging the use of industrial and civil construction waste. In this work, the recycled asphalt pavement (RAP) from the milling of the pavements was used to replace virgin aggregates for the construction of road base layers. Due to the large amounts of materials involved in road construction, it is necessary to develop alternative binders. Particularly when it comes to alkali-activated materials, the use of residues in the production of sodium silicate has not yet been investigated for RAP stabilization. Therefore, in this study, rice husk ash (RHA) was activated in an alkaline environment, playing the role of an alternative source of silica, for the formation of an alkali-activated binder (AAB). The exposure of these mixtures to seasonal variations in humidity and temperature was evaluated through durability tests from wet–dry cycles and the unconfined compressive strength (UCS) retained in the samples after the cycles. AAB permanence was also verified through long-term mechanical performance and its environmental impact through leaching tests. The results indicated that mixtures with a RAP to AAB ratio = 40:40, 50:30, and 50:40 reached the minimum design strength (2.1 MPa) even after wet–dry cycles; however the mixture with RAP:AAB = 40:40 is potentially superior for better performance in field conditions, possibly without premature failure. In addition, this mixture has no environmental impact because the results of environmental tests did not show any significant risk or hazardous characteristics.