Analysis of Influencing Factors on Water Stability and Stripping Resistance of Paving Polyurethane Mixture

Abstract

Polyurethane mixtures (PUMs) have excellent deformation resistance and fatigue resistance. However, their inferior water stability and stripping resistance have been hindering their wider application. To better understand the critical factors to PUMs’ stripping resistance and water stability, we investigated the statistical relationships among the stripping resistance, splitting strength, water stability, binder-to-aggregate ratio (BAR), gradation type, and fine aggregate content (FAC). A series of tests, including direct tensile test, binder bond strength test, and water boiling test, were used to study the flexibility and adhesion strength of polyurethane (PU) binder. Three gradation types with different FACs were designed. Three types of tests, namely the Cantabro test, the splitting test, and the water stability test, were employed to study the effects of gradation type, FAC, and BAR on the performances of PUM. The significant factors to water stability and stripping resistance of PUM were identified using a mixed-effects regression model (MERM). The results showed that the unsolidified PU binder has high fluidity and low adhesion strength, and the solidified PU binder has excellent adhesion strength and low flexibility. Increasing the BAR and FAC improved the risk of the PUM specimen’s volume bulge. Dewatering of raw materials of PU binder and aggregates was beneficial to solve the bulging problem. The fine aggregate can prevent the PU binder from flowing away under the gravity action, resulting in the film thickness of the PU binder increasing and the enhancement of stripping resistance and water stability of PUM. The gradation type and FAC affected the failure mechanisms of the PUM specimen in the splitting test. The MERM results indicated that the BAR and FAC significantly affect the stripping resistance, splitting strength, and water stability.