# Shear Performance Degradation of Fiber-Reinforced Recycled Aggregate Concrete Beams Under Salt Freeze–Thaw Cycles

## TL;DR

This study examines how fiber-reinforced recycled aggregate concrete beams degrade in shear strength when exposed to salt and freeze-thaw cycles in harsh environments like northwest China.

## Contribution

The paper introduces a new shear capacity degradation model for FR-RAC beams under composite salt freeze–thaw conditions.

## Key findings

- After 100 freeze–thaw cycles in composite salt solution, cracking load and shear capacity dropped by 39.8% and 22.2%, respectively.
- At 175 cycles, reductions in cracking load and shear capacity reached 56.8% and 36.1%.
- A degradation prediction model showed strong agreement with experimental results.

## Abstract

In saline soil and alpine regions of northwest China, fiber-reinforced recycled aggregate concrete (FR-RAC) beams are subjected to coupled degradation from a chloride–sulfate composite salt attack and freeze–thaw cycling. Existing studies predominantly focus on natural aggregate concrete in freshwater environments or single-salt solutions, with limited documentation on the shear performance of FR-RAC beams after freeze–thaw exposure in chloride–sulfate composite salt solutions. To investigate the durability degradation patterns of FR-RAC beams in Xinjiang’s saline soil regions, two exposure environments (pure water and 5% NaCl + 2.0% Na2SO4 composite salt solution) were established. Shear performance tests were conducted on nine groups of FR-RAC beams after 0–175 freeze–thaw cycles, with measurements focusing on failure modes, cracking loads, and ultimate shear capacities. The results revealed that under composite salt freeze–thaw conditions: after 100 cycles, the cracking load and shear capacity of tested beams decreased by 39.8% and 22.2%, respectively, compared to unfrozen specimens representing reductions 29.6% and 82.0% greater than those in freshwater environments; at 175 cycles, cumulative damage intensified, with total reductions reaching 56.8% (cracking load) and 36.1% (shear capacity). A shear capacity degradation prediction model for FR-RAC beams under composite salt freeze–thaw coupling was developed, accounting for concrete strength attenuation and interfacial bond degradation. Model validation demonstrated excellent agreement between predicted and experimental values, confirming its robust applicability.