Freeze–Thaw Resistance of Concrete Made with Natural Clinoptilolite Zeolite

Abstract

The utilization of natural zeolite as a supplementary cementitious material to improve the overall performance of concrete has been an interesting practice. However, limited research has been conducted on natural zeolite, which contains approximately 15% void space, to address the freeze–thaw (F–T) impact in a severe environment of cold regions. This study determined the resistance to freezing and thawing of nonair-entrained concrete made with up to 20% by mass natural clinoptilolite zeolite replacement of portland cement for up to 300 alternate cycles per current standards. The influence of clinoptilolite zeolite on the workability and air content of fresh mixes was measured before preparing the concrete specimens. The water absorption, void content, and splitting tensile strength of concrete were assessed 28 days prior to F–T testing. The resistance to freezing and thawing of concretes was monitored through the dynamic modulus of elasticity based on the fundamental transverse frequency, durability factor, and mass loss of beam specimens having a size of 76 × 76 × 406 mm. The chloride ion permeability via surface resistivity of all concrete beams was examined before and after freezing and thawing. Results revealed that using zeolite could entrain (and/or entrap) a slightly higher air content but decrease the workability of concrete. The application of up to 20% clinoptilolite zeolite exhibited a slightly higher water absorption and porosity in both mortar and concrete compared to the control samples. The favorable curing environment and the pozzolanic performance of 5%–15% zeolite produced a dense matrix, leading to a higher dynamic modulus of elasticity, increased frost resistance, and minimal mass loss against freezing and thawing. Using zeolite also led to a moderate level of chloride ion penetrability after 300 F–T cycles. Based on the results, the optimum dosage of clinoptilolite zeolite with the replacement of portland cement was found to be 10% due to the satisfactory resistance to the F–T impact, maintaining the structural integrity for up to 300 cycles. The present study investigated the effect of using natural clinoptilolite zeolite as the supplementary cementitious material in the concrete against the freeze–thaw impact. Typically, the air-entraining admixture is applied to form the air voids in the concrete so that the ice crystal may occupy that void during the freezing environment to reduce the overall hydraulic pressure. However, every 1% volume of entrapped and/or entrained air can reduce the strength of concrete by up to 5%, while the maximum allowable air content is up to 5%–8% in a severe environment. Therefore, applying this strategy could significantly decrease the performance of the concrete. Since zeolite is a highly porous material, it will entrain (and/or entrap) air voids in the concrete where the ice crystal may form during the freezing environment, leading to lower hydraulic pressure. Hence, the use of air-entraining admixtures can be reduced and/or eliminated in the concrete without compromising the strength. Moreover, the pozzolanic activity of clinoptilolite zeolite will increase the strength and enhance the microstructural development, leading to the production of additional hydration reaction products along with finer pore size distribution of concrete microstructure.