# Experimental and 3D Simulation Research on the Mechanical Properties of Cold-Bonded Fly Ash Lightweight Aggregate Concrete Exposed to Different High Temperatures

## TL;DR

This paper studies how eco-friendly fly ash concrete behaves under high temperatures and finds it retains strength better than regular concrete up to 500°C.

## Contribution

The study introduces a validated 3D mesoscale model to explain the mechanical behavior of cold-bonded fly ash concrete after high-temperature exposure.

## Key findings

- LWC-CB retains about 6% more strength than ordinary concrete below 500°C.
- Failure shifts from aggregate-based shear to mortar and ITZ damage after high-temperature exposure.
- Numerical simulations align closely with experimental results, with deviations under 15%.

## Abstract

Cold-bonded (CB) fly ash aggregate, an eco-friendly material derived from industrial by-products, is used to fully replace natural coarse aggregate in producing lightweight concrete (LWC-CB). This study systematically investigates the post-high-temperature mechanical properties and damage mechanisms of LWC-CB. Specimens exposed to ambient temperature (10 °C) and elevated temperatures (200 °C, 400 °C, 600 °C) underwent cubic compression tests, with surface deformation monitored via digital image correlation (DIC). Experimental results indicate that the strength retention of LWC-CB is approximately 6% superior to ordinary concrete below 500 °C, beyond which its performance converges. Damage analysis reveals a transition in failure mode: at ambient temperature, shear failure is governed by the low intrinsic strength of CB aggregates, while after high-temperature exposure, damage localizes within the mortar and the interfacial transition zone (ITZ) due to mortar micro-cracking and thermal mismatch. To elucidate these mechanisms, a three-dimensional mesoscale model was developed and validated, effectively characterizing the internal multiphase structure at room temperature. Furthermore, a homogenization model was established to analyze the macroscopic thermo-mechanical response. The numerical simulations show strong agreement with experimental data, with a maximum deviation of 15% at 10 °C and 3% after high-temperature exposure, confirming the model’s accuracy in capturing the performance evolution of LWC-CB.