Optimizing the Design of High-Volume Fly Ash (HVFA) Cementitious Materials: Enhancing the Performance with Clinoptilolite Zeolite Modification

Fulfilling the ambition for maintaining global carbon neutrality, utilizing alternative low-carbon resources is becoming more essential in the design of building materials. Recently, high-volume fly ash (HVFA) cementitious materials have been gaining attention in the industry due to their low environmental impact in terms of carbon dioxide (CO₂) emissions and resource efficiency. However, applications are limited because of major material-related problems, such as increasing setting time and low early strength development. This study aims to overcome the challenges in the material system by modifying HVFA mortars with clinoptilolite zeolite. The HFVA mortar designs were established using 70%, 60%, and 50% F-type fly ash. A portion of fly ash (5 and 10%) was replaced with reactive clinoptilolite zeolite. The influence of zeolite replacement on the performance of HFVA cementitious materials was evaluated by compressive strength and initial setting time. The rheological analysis assessed the impact of zeolite addition on the yield stress and thixotropy of HVFA pastes. The results show that adding clinoptilolite zeolite reduced the delay in initial setting time in HFVA mortars and increased the yield stress and thixotropy of cementitious pastes. On the other hand, incorporating zeolite into the mix resulted in a lower compressive strength than neat HFVA mortars without any zeolite. Therefore, clinoptilolite zeolite has the potential to be used as a viscosity-modified agent in HVFA cementitious materials instead of chemical admixtures.