Rice husk ash as an alternative soluble silica source for alkali-activated metakaolin systems applied to recycled asphalt pavement stabilization

Alkali-activated binders have been shown as a viable alternative do ordinary Portland cement. However, the development of lower carbon emission activators for this process is still a research-gap. The goal of this research was to analyze the stabilization of recycled asphalt pavement (RAP) mixtures with a metakaolin-based binder, alkali-activated by rice husk ash synthetized sodium silicate. Compaction, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were conducted in stabilized RAP mixtures, submitted to different curing periods and temperatures. Also, results were correlated with the porosity/binder content index. Compaction results showed a reduction in dry unit weight as the RAP content increased for non-stabilized mixtures and a non-linear behavior for stabilized ones. For the UCS tests, the increase in binder content led to an increase in strength for all mixtures. High curing temperatures prevented the efflorescence phenomenon, however reduced strength due to crack formation. XRD analyzes showed the formation of minerals rich in silica and alumina, indicating the formation of geopolymerization products. Finally, the porosity/binder index was shown to be a viable dosage method to predict the strength of stabilized RAP mixtures.