The scarcity and cost of high-quality construction materials have resulted in their use being reserved for the construction of structures that experience relatively high stress, such as roads with high traffic volumes. Consequently, mechanically improved abundant marginal materials are common in relatively low stress construction applications such as landscaping, low-volume paved roads and fill material for flood embankments. In clays, mechanical improvement is commonly achieved through the addition of chemical stabilizers such as lime, bitumen, cement, and fly ash. However, these chemical stabilizers are associated with high cost and a large carbon footprint. Here, we present the first research demonstrating that clays can be mechanically improved through the addition of mica. Mica wastes are generated in significant volume as a by-product from the mining of relatively valuable materials. This paper explores the use of mica to improve the ultimate limit state of marginal clays for use as construction material. Kaolin clay was prepared with muscovite sand and muscovite silt in variable fractions (0%, 2.5%, 10% and 30% muscovite fraction). The hydraulic and mechanical response of the composite materials were investigated through one-dimensional compression and direct shear testing. The most notable finding is that, at very low normal stresses (≤100 kPa), a relatively small fraction of mica is sufficient to shift the angle of shearing resistance of the composite, from the value for pure clay (Φ’~17°) towards the value for pure muscovite (Φ’~26°). X-ray computed tomography scans of the consolidated and sheared samples show that the relatively high strength of the mica clay composite at low normal stress is due to a fold-like mode of deformation observed in shearing. This mechanism appears to be suppressed at high stresses with the shear band likely developing through the clay matrix. As a result, the composite exhibits the same friction angle of the clay alone at high stresses.
|Journal||Construction and Building Materials|
|Publication status||Accepted/In press - 12 Jun 2021|
- shear strength
- circular economy
- marginal clay
- hydraulic conductivity