Assessment of the resistance of concrete with recycled aggregate to freeze-thaw cycles

Abstract

The object of research is a concrete mix in which 50% of the natural coarse aggregate is replaced with recycled aggregate (RA) obtained by crushing demolished buildings and structures. This research was aimed at assessing the compressive strength and freeze-thaw resistance in a 5% NaCl solution of C30/37 concrete in which 50% of the natural coarse aggregate in the 4–8 and 8–16 mm fractions was replaced by RA from two regions of Ukraine.

The research problem concerns the recycling of construction and demolition waste into new building materials that can meet strength and durability requirements. This approach enables the broader use of RA without compromising the performance characteristics of concrete produced with its incorporation.

Two concrete mixes were prepared using RA from different regions: TN-218 (Kharkiv, Ukraine) and TN-249 (Mykolaiv, Ukraine). Both mixtures used CEM II/A-M (S-LL) 42.5 R cement and had the same water-cement ratio (w/c ≈ 0.43). A superplasticizer and an air-entraining admixture were added to the mix.

The resulting concrete mixes demonstrated stable technological properties: the slump corresponded to class S5; the air content was 5.5–5.7%; and the density of compacted fresh concrete was 2444 kg/m³. The 28-day compressive strength of both mixes exceeded 54 MPa, confirming that the regional origin of the RA did not significantly affect strength parameters.

Freeze-thaw resistance was evaluated using an accelerated method in a 5% NaCl solution. Both mixes achieved frost-resistance grade F200: the loss of compressive strength after freeze-thaw cycles was 4.04% for TN-218 and 4.35% for TN-249, while mass change remained minimal – 0.14% and 0.29%, respectively.

The results confirm the feasibility of using 50% RA in the production of C30/37 strength-class concrete intended for exterior exposure to freezing and chloride environments, provided that the aggregate grading, RA water absorption, and air-entrainment level are properly controlled. In practice, such mixes can be recommended for the manufacture of concrete and reinforced concrete products without prestressing, intended for use in environments subject to repeated freezing and thawing.