Experimental Investigation of the Impact of Aggregate Chemical Composition on the Mechanical Performance of Zeolite-Modified Concrete under Combined Fire and Carbonation Exposure in Urban Tunnels

Articles in Press

Document Type : Research Paper

Authors

Department of Civil Engineering, Sha.C., Islamic Azad University, Shahrood, Iran

10.22124/jcr.2026.30659.1700

Abstract

carbonation, improving the mechanical performance of concrete is of great importance. This study investigates the effect of the chemical composition of three types of aggregates (silica–alumina, calcium oxide, and calcite) on the mechanical behavior of zeolite-containing concretes subjected to high temperature and accelerated carbonation. Concretes were produced with a water-to-binder ratio of 0.45 and varying zeolite contents (0, 5, 10, 15, and 20%). After mixing and standard curing, the specimens were heated to 800 °C and subsequently exposed to a CO₂-saturated environment for 3, 56, and 90 days. The carbonation depth was determined using a phenolphthalein solution, and microstructural analyses were performed through SEM and XRD techniques to clarify the underlying mechanisms. The results showed that concrete produced with silica–alumina aggregates and 10% zeolite exhibited the highest compressive strength, as the coexistence of silica and alumina contributed to enhanced structural densification. In contrast, concretes with calcitic aggregates were more vulnerable to carbonation, leading to greater strength reduction. The influence of zeolite on tensile strength was limited across all mixes. Microstructural observations confirmed that elevated temperatures caused decomposition of C–S–H gel, increased porosity, and reduced alkalinity, which were consistent with the mechanical test results. Overall, the combination of silica–alumina aggregates with 10% zeolite is recommended as an effective option for producing concretes resistant to the deteriorative conditions of urban tunnels.

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Concrete Research

Articles in Press, Accepted Manuscript
Available Online from 05 January 2026

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