Understanding the Impact of Fires on Reinforced Concrete Structures and Methods for Assessment

Fires can cause various damages to reinforced concrete (RC) structures, affecting their surface, chemical composition, and overall integrity. Understanding the mechanisms of fire damage and employing effective assessment methods are crucial for determining the condition of the structure and making informed decisions on repair or demolition.

Fire Damage Mechanisms

1. Surface Cracking

Concrete surfaces may develop a network of fine cracks due to factors like low humidity, thermal incompatibility, and exposure to fire. These cracks, with a depth of 3 mm and grid diameters smaller than 50 mm, can impact the structural properties.

2. Chemical Decomposition

The increase in temperature during a fire can lead to the evaporation of water and dehydration of cement paste, causing chemical decomposition. This process alters the color of concrete, which serves as an indicator of exposure temperature and corresponding damage.
Table 1: Concrete Color and Temperature Assessment

3. Microcracking and Spalling

The rapid change in temperature, such as exposure to fire, can lead to the development of small cracks and subsequent spalling, exposing steel reinforcement. The yield strength of steel can be lost, and spalling can result in partial or complete destruction.

Assessment Methods

1. Preliminary Investigation

1.1 Cleaning

Thoroughly cleaning smoke deposits is essential to reveal spalling and cracks. Methods such as water blasting and chemical washing are preferred to avoid secondary damages.

1.2 Visual Inspection

Recording visible damages, deformations, and exposure of steel reinforcements through a detailed visual inspection.

1.3 Fire Intensity

Estimating fire intensity by observing building contents and post-fire conditions.

1.4 Field Tests

Conducting simple field tests, such as striking hammer and chisel, to assess fire damages.

2. Detailed Investigation

2.1 Non-destructive Tests

Utilizing non-destructive tests like pulse velocity and rebound hammer to specify concrete properties.

2.2 Destructive Test Methods

Performing destructive tests, including coring, in the lab or field to gather detailed information on material properties, depth of fire, and crack locations.
Table 2: Test Methods for Fire-Damaged Concrete

Table 3: Conditions of Materials Useful for Estimating Temperature Attained Within a Structure During a Fire

Conclusion

Understanding the mechanisms of fire damage and employing a comprehensive assessment plan is crucial for making informed decisions on the repair or demolition of reinforced concrete structures.