Freeze–Thaw Performance of Fly Ash–Stabilized Materials and Recycled Pavement Materials

A comprehensive research was conducted to study the performance of a variety of stabilized geomaterials against the freeze–thaw (F–T) cycling process. Also included were unstabilized recycled materials, i.e., recycled asphalt pavements (RAP) and recycled concrete aggregates (RCA). Stabilized geomaterials used in this study included natural coarse-grained and fine-grained soils and reclaimed pavement materials (RPM). The stabilizers (binders) included self-cementitious fly ashes (i.e., class C and off-specification fly ashes). Resilient modulus ($M_r$) performances of geomaterials and geomaterials stabilized by binders were evaluated under a number of F–T cycles. This article also compares the F–T performances of different geomaterials including, stabilized coarse-grained versus fine-grained geomaterials, stabilized natural soils versus stabilized RPMs versus unstabilized RAP versus RCA. Additionally, the impact of fly ash type and fly ash content on F–T performance of stabilized geomaterials was also investigated. Moreover, correlations between the physicochemical properties [CaO, $\mathrm{CaO}/{\mathrm{SiO}}_2$, $\mathrm{CaO}/{\mathrm{Al}}_2{\mathrm{O}}_3$, $\mathrm{CaO}/({\mathrm{Al}}_2{\mathrm{O}}_3+{\mathrm{SiO}}_2)$, $D_{60}$, $D_{30}$, gravel-to-sand (G/S) ratio and fines content] of these stabilized and unstabilized geomaterials and their resilient modulus were explored under F–T cycling. $M_r$ decreases (7–50%) in response to F–T cycling and then levels off in approximately 1–5 cycles. Fly ash stabilized coarse-grained geomaterials provided 5% less drop in initial $M_r$ compared to the fly ash stabilized fine-grained soils. RPMs stabilized with fly ash performed better (average reduction of 25%) against F–T cycling than the unstabilized RAP materials (average reduction of 33%) and natural fine-grained soils (average reduction of 29.5%) stabilized with fly ash. No correlations were found between the fly ash types/fly ash contents and $M_r$ performance of fly ash stabilized geomaterials under F–T cycling process. Fly ash stabilized coarse-grained geomaterials with higher $D_{60}$, $D_{30}$, G/S ratio, and fines content tend to lose more stiffness at higher number of F–T cycles. Such correlations could also be determined for RCA and RAP except G/S ratio. Stabilized fine-grained and coarse-grained geomaterials with fly ashes having higher $\mathrm{CaO}/{\mathrm{SiO}}_2$, $\mathrm{CaO}/{\mathrm{Al}}_2{\mathrm{O}}_3$, and $\mathrm{CaO}/({\mathrm{SiO}}_2+{\mathrm{Al}}_2{\mathrm{O}}_3)$ ratios experienced lower loss in $M_r$ during F–T.