Polyurea reinforcement of disintegrated mudstone embankments and the underlying mechanism

Abstract

Disintegrated mudstone (DM) is often discarded during highway constructions because of its potential continuous disintegration and large wet deformation. The purpose of this study is to improve DM so that it can be used to fill highway embankments. The chemical reinforcement method based on polyurea (PU) was selected to reinforce disintegrated carbonaceous mudstone (DCM) and disintegrated red-bed mudstone (DRM). Tensile strength (TS) tests under various temperature-humidity conditions, and then contact angle tests, unconfined compressive strength (UCS) tests under cyclic wet-dry conditions were carried out on PU modified disintegrated mudstone (PU-MDM). The hydrophobicity and mechanical characteristics of PU-MDM were studied. In addition, a series of microscopic tests including scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR) were conducted to examine the curing mechanism of PU from a microscopic perspective. The results show that PU modified disintegrated carbonaceous mudstone (PU-MCM) is insensitive to temperature and high humidity when it is modified into a hydrophobic material. The TS and contact angle increase gradually with increasing PU content and component B, and they tend to be stable after the PU content and dosage ratio reach 5 wt% and 1:4, respectively. The stabilized TS is 2.42 MPa, and the corresponding contact angle is 94.84°, indicating that the material is modified to be hydrophobic. At natural temperature (30 °C), the specimen with a PU content of 5 wt% and a dosage ratio of 1: 4, the TS value can reach 77% of the maximum after curing for 1 d. PU-MDM with 5 wt% PU shows a good resistance to wet-dry cycles. After 10 wet-dry cycles, the UCS of PU-MDM is still significantly higher than that of DM specimens without wet-dry cycles. The microscopic results indicate that PU can effectively enhance the cementation of soil particles, which leads the soil structure to be denser and exhibit a certain hydrophobic effect. It is found that PU is not only environmentally friendly but also effective and fast in modifying DM.