Investigation of Curing and Strength Characteristics of Cold-Mix Asphalt with Rice Husk Ash–Activated Fillers

Presently, the application of cold-mix asphalt (CMA) in structural layers of pavement is limited due to the slow curing rate and low early-life strength. This study attempts to achieve the reduction in curing period and improvement in strength development of CMA by using nonconventional fillers (NCFs) such as fly ash, ground granulated blast-furnace slag (GGBS), rice husk ash (RHA), and fly ash and GGBS activated with RHA. Curing rate was evaluated using moisture loss monitoring of mixture and compacted specimens of CMA. Strength development was evaluated using indirect tensile strength testing and wheel tracking testing. Laboratory investigations revealed that curing period and temperature have a significant impact on the rate of moisture loss and strength gain. Mechanical strength increased with the increase in curing period and temperature for cold mixes with NCFs. CMA with GGBS activated using RHA exhibited higher curing rates than conventional CMA and substantially higher early-strength development among all the mixes considered. This is due to the combined effect of moisture loss and accelerated hydration process. Statistical analysis also indicated that the improvement was significant. Thus, the use of GGBS with RHA as activator by partial replacement of mineral filler is a potential solution to prolonged curing period and weak early-life strength of CMA.

Cold-mix asphalt is a sustainable paving mix with economic and environmental advantages. All the steps involved in the construction of the road using a cold mix are done at ambient temperature. Increasing the application of cold-mix asphalt is highly essential. The long time required for curing and the low early strength deter the extensive use of cold mixing in the field. This study suggests that the use of cold mixes in which ground granulated blast-furnace slag with rice husk ash are incorporated as filler helps in resolving these issues by increasing the curing rate and early strength of cold mixes. The study recommends using 25% stone dust, 50% ground granulated blast-furnace slag, and 25% rice husk ash as filler. Because ground granulated blast-furnace slag and rice husk ash are industrial and agricultural waste materials, respectively, using these materials is a sustainable way of resolving the problems of cold mixing. Also, as these materials are easily available, and the modified mix can be easily produced; this can be conveniently implemented in the field. This can pave the way to the use of cold mixing in the top layer of heavily trafficked roads as well.