Study on Mechanical Properties and Microstructure of Fly-Ash-Based Geopolymer Solidified Waste Mud

Abstract Chemical solidification of construction mud is usually used to resolve environmental problems and problematic geotechnical engineering properties. This study investigated the feasibility of solidifying waste mud with fly ash (FA) based geopolymer, which was activated by calcium carbide residue (CCR) and sodium silicate solution (NS). The unconfined compressive strength (UCS) tests were carried out to optimize the CCR/NS ratio at various curing time, in addition, the tests involving water content, pH, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and natural dehydration were also performed. The UCS results show that, when the CCR/NS ratio is 6:4, the optimal 28-day strength reaches 2.2MPa with the ratio of the activator CCR-NS to FA at 1:1. The binder can reduce the water content of the mud in the short term, with the best effect at pH value of 12. The microscopic compositions showed that calcium silicate hydrate (CSH) and aluminosilicate-Na hydrate (NASH) dominated cementitious products filled the pores and bonded with particles for strength development. The dehydrating cracking process of solidified mud and untreated mud was quantitatively analyzed using image processing method. The variation of cracks area ratio and water content during dehydration was studied. The solidified mud is suitable in subgrade projects, which may facilitate the diversion of large amounts of waste mud, industrial by-products CCR and FA from landfills.