The impact of zeolite on mineralogy changes and compressive strength development of cement-treated sand mixtures through microstructure analysis

The main objective of this research is to study the impact of zeolite on mineralogical changes leading to development of the compressive strength of cemented-sand mixtures. The mixtures consist of Portland cement type II, natural zeolite (Clinoptilolite) and Babolsar sand, and the cement content is chosen to be 8% based on the dry weight of the sand. The experimental program consists of a cement substitute with 0, 35, 60, and 90% zeolite along with the amount of optimal water content obtained from the standard compaction test. The samples were made by an under-compaction process and cured at room temperature for various periods of time (7, 28, and 90 days). The microstructural properties were analyzed using X-Ray Diffractometer (XRD) tests and Scanning Electron Microscopy (SEM) tests equipped with an Energy Dispersive X-ray analysis system (EDX). In addition, an unconfined compression test was carried out for various zeolite percentages in the same curing time. Strong adhesion in the Interfacial Transition Zone (ITZ) resulted in densely compacted mineralogy in the presence of 35% zeolite, which promoted the Unconfined Compressive Strength (UCS). The connection between microstructure and macrostructure clearly showed suitable relations between compressive strength and the intensity of the C-S-H phase.