Experimental investigation of mechanical and microstructural properties of re-cemented clay

Abstract

Considerable amounts of cemented mixtures are generated during the construction of deep cement mixing piles. Recycling these generated cemented soils as fill material using re-cemented method can reduce waste transfer to landfills and reduce the use of natural gravel fill resources. However, the properties of these re-cemented materials remain unclear. To fill this research gap, in this study, cement-treated Hong Kong marine deposit (CT-HKMD) was ground into powders and used as a reused material for the second-round cement treatment, named recycled cement-treated Hong Kong marine deposit (RCT-HKMD). The influences of cement content and curing period on the unconfined compressive and tensile strengths, modulus, point load strength index and phase assemblage of CT-HKMD and RCT-HKMD were investigated through unconfined compression (UC) tests, Brazilian tests, point load tests and thermogravimetric analysis (TGA). The results reveal that the unconfined compressive strength (UCS), splitting tensile strength and point load strength index of RCT-HKMD are 1.3–2.6 times greater than those of CT-HKMD within the same cement content and curing period. This is due to denser microstructure and the formation of calcium (alumino) silicate hydrate (C–(A–)S–H) and ettringite to fill into the small pores and improve interparticle bonding, observed from the results of TGA and scanning electron microscopy-energy-dispersive spectrometer (SEM–EDS). Furthermore, different initial cement contents of CT-HKMD powders were used to prepare RCT-HKMD specimens with 10% newly cement content. All test results show that the initial cement content of CT-HKMD has no effect on the UCS, splitting tensile strength and point load strength index of RCT-HKMD specimens as the original bonding structures of the CT-HKMD have been destroyed after crushing and sieving process. All the findings have practical implications for the reuse of waste cemented soil locally and even globally.