Evaluating residual compressive strength of post-fire concrete using Raman Spectroscopy

Area of Science:

• Materials Science
• Civil Engineering
• Analytical Chemistry

Background:

• Concrete strength relies heavily on the calcium silicate hydrate (CSH) phase.
• High temperatures, such as those in fires, can decompose CSH, reducing concrete's compressive strength.
• Assessing fire damage in concrete is crucial for structural integrity and safety.

Purpose of the Study:

• To investigate the use of Raman spectroscopy for evaluating thermal decomposition in concrete.
• To correlate specific Raman spectral features with concrete compressive strength after heat exposure.
• To demonstrate a non-destructive method for assessing fire-damaged concrete.

Main Methods:

• Utilizing Raman spectroscopy to analyze concrete samples, focusing on bands indicative of CSH and CaCO3 at 1083, 709, and 276 cm⁻¹.
• Calculating the ratio of Raman bands at 1083/709 cm⁻¹ to assess CSH phase changes.
• Correlating the band ratio with measured compressive strength and developing a predictive model.
• Applying the method to a case study of fire-damaged concrete from a warehouse in Kingston, Jamaica.

Main Results:

• A critical peak ratio of 8.78 in the 1083/709 cm⁻¹ Raman bands indicated a rapid decline in compressive strength.
• A residual compressive strength of 0.62 was observed at this critical ratio, following a polynomial curve.
• The study successfully correlated Raman spectral changes with concrete compressive strength loss due to thermal decomposition.
• The developed Raman spectroscopy tool provided an indirect evaluation of the temperature exposure.

Conclusions:

• Raman spectroscopy is a viable tool for non-destructive, in-situ assessment of fire-damaged concrete.
• The 1083/709 cm⁻¹ Raman band ratio effectively quantifies thermal degradation and predicts residual compressive strength.
• This technique offers rapid and accurate evaluation of concrete's structural integrity after fire incidents.