# Comparison of Elastic Modulus Calculations in ASTM D7205 and CSA S806 for CFRP Rebar Under Elevated Temperature

## TL;DR

This paper compares two standards for calculating the elastic modulus of CFRP rebars at high temperatures and finds differences in their results and stability.

## Contribution

The study identifies how ASTM D7205 and CSA S806 standards differ in calculating elastic modulus at elevated temperatures and evaluates their prediction accuracy.

## Key findings

- ASTM calculates modulus from the initial linear stress–strain segment, while CSA includes post-transition data.
- ASTM modulus showed lower COV than CSA at temperatures below 325 °C.
- A calibrated model with the lowest average error was identified for predicting modulus under high temperatures.

## Abstract

In this study, the elastic modulus of CFRP rebars under high-temperature conditions was evaluated in accordance with ASTM D7205 and CSA S806, and the differences between the two standards were compared and analyzed. CFRP rebars with diameters of 10 mm and 13 mm were tested, and tensile specimens were prepared following the procedures specified in both standards. Tensile tests were conducted at temperatures ranging from 25 °C to 650 °C using an electric furnace. Fracture morphology before and after testing, as well as microstructural changes, were examined through scanning electron microscopy (SEM). The results revealed that the ASTM standard determines the elastic modulus based on the initial linear portion of the stress–strain curve before the transition point, whereas the CSA standard includes the post-transition segment. At temperatures below 325 °C, the ASTM-derived modulus exhibited a lower coefficient of variation (COV) compared to the CSA-derived values, indicating a more stable performance. By applying the experimentally obtained modulus values to various prediction models, the model with the lowest average error was identified. These findings confirm that the elastic modulus of CFRP rebars can be reasonably predicted under elevated-temperature conditions using calibrated models.