Mechanical properties and micro-mechanisms of marine soft soil stabilized by different calcium content precursors based geopolymers

Abstract

Soil stabilization has long been a scientifically and technologically challenging topic to address. It is essential to develop cementitious materials with a “low carbon footprint” by replacing ordinary Portland cement (OPC) with industrial waste based geopolymers. This concept is regarded as a greener approach to soil stabilization technology development. This study compared the mechanical properties and microstructure of marine soft soil stabilized by low-calcium content geopolymers, high-calcium content geopolymers and OPC via unconfined compressive strength (UCS) testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Low-calcium content and high-calcium content geopolymers were produced by alkali-activated coal-bearing metakaolin (CMK) and ground-granulated blast furnace slag (GGBS), respectively. The results indicated that a relatively high alkaline activator/precursor (A/P) ratio, Na2SiO3/NaOH ratio, and NaOH concentration were beneficial to the strength development of CMK-treated samples but were unfavorable for that of GGBS-treated samples. The optimum A/P ratio and Na2SiO3/NaOH ratio for the CMK-treated samples were 1.5 and 75:25, and those for the GGBS-treated samples were 1.0 and 25:75. The recommended NaOH molarity for practical applications was 12 M. At the same precursor content, the CMK-treated samples showed a lower strength than the OPC- and GGBS-treated samples because of their low reactivity at ambient temperature. The GGBS-treated samples showed a higher strength than the OPC-treated samples when the precursor content was higher than 20 wt%. As the curing time increased, the strength of the CMK-treated samples increased linearly, while the strength of the OPC- and GGBS-treated samples increased logarithmically, and a reduction was found in the strength of the GGBS-treated samples at later stages of curing. Increasing the temperature accelerated the formation of cementitious products and shortened the curing time, especially for the CMK-treated samples. The stabilization effect of CMK, GGBS, and OPC on marine soft soil was mainly attributed to the formation of the dense three-dimensional gel network structure. The hydration products of the OPC-treated samples were C-S-H gels, ettringite (AFt), and Ca(OH)2, whereas C-(A)-S-H gels were observed in the GGBS-treated samples, and N-A-S-H gels were observed in the CMK-treated samples.