Experimental study on mechanical properties of fiber-reinforced and geopolymer-stabilized clay soil

Abstract

Geopolymers are recently regarded as superior sustainable alkali-activated binders (AAB) for soil improvement due to their good bonding properties. In this study, the mixture of sodium silicate (Na2SiO3) and quicklime (CaO) was used as alkali-activator (AA) for preparing AAB employing metakaolin (MK) as a precursor. The unconfined compression tests (UCT) were performed to optimize the material ratio of metakaolin-based geopolymer-stabilized clay soil (GSCS) and explore the optimum content and length of basalt fiber (BF) in GSCS. The optimum mixture was then better characterized by further experiments, including direct shear test, indirect tensile test, diffraction analysis, and microstructural analysis, and compared with other binders such as ordinary Portland cement (OPC) and lime. Results indicate that the unconfined compressive strength (UCS) of GSCS increases first and then decreases with AAB and BF contents and the length of BF. The UCS of BF-reinforced GSCS (FRGSCS) is optimum when the mass ratio of AAB in clay soil (CS) is approximately 15%, and the content and length of BF are 0.4% and 12 mm, in which the mass ratio of MK and AA in AAB is approximately 2: 1, and the mass ratio of Na2SiO3 and CaO in AA is approximately 1: 0.8. Comparison experiments on strength performance indicate that FRGSCS is consistently superior to GSCS, OPC soil (OPCS), lime soil (LS), and CS. The diffraction analysis and the microstructural analysis show that the weak alkalinity of GSCS results in poor geopolymerization of AAB in the early curing age but rapid development of aluminosilicate gels in the later curing age. The contribution of fibers to the toughening mechanisms of GSCS shows that the fiber-matrix interaction would be the dominant effect controlling the strength of FRGSCS. The results of this study provide a parameter basis for the application and popularization of FRGSCS.