September 9, 2022
By Jaclyn Ferraro and Simonida Grubjesic, Ph.D.
When fire impacts a structure, concrete may be the only component that’s left standing. To understand the extent of the damage, the structural engineer’s upfront involvement plays a critical role in determining the integrity of the structure. Time is of the essence: owners need to recover as quickly as possible and insurance adjusters are eager to understand the extent of repairs needed to get back online.
On-site assessments can reveal a good amount of information about the concrete’s condition, but evidence like surface crazing, spalling, popouts, and color variations can make the structural integrity of the concrete come under question. Various laboratory testing methods go beyond the surface to provide a thorough analysis. Getting an accurate diagnosis from a reputable laboratory can save time, especially when time is of the essence.
Microscopy takes a methodical approach in determining fire or heat-related damage to concrete, and is in general accordance with ASTM C856, “Standard Practice for Petrographic Examination of Hardened Concrete.” The fire and heat can cause expansion and contractions, as well as mineralogical changes, within the concrete. To observe these changes and find out the depth and extent of damage, microscopy evaluation begins with making initial visual observations of the concrete sample’s exterior surface(s) exposed to the fire or heat.
Microscopy shows fire damage in concrete, revealing a coarser grain structure within a limestone particle from recrystallization due to fire exposure.
The exterior surface(s) of the sample may show soot deposits, charring, have other various melted materials adhered, and/or exhibit surface crazing or spalling, among other possible observations. At depth, the near exterior surface may show paste softening, desiccation, and discoloration, and/or aggregate discoloration, physical changes, and recrystallization.
Deeper into the body of the concrete, microscopy notes loss of bond to steel reinforcement and cracking/crack patterns. Specific changes in the concrete are linked to the temperature in which the concrete was exposed. Through visual, stereomicroscopic, and thin section analysis observations, petrographers can determine the depth and extent of fire or heat-related damage.
Along with microscopy, complimentary analytical chemistry techniques may be utilized in evaluating fire damaged concrete. Other techniques generally are used supplementally to microscopy and to obtain specific information on the extent of degradation to specific concrete constituents or to quantify the amount of degradation to specific components.
Analytical techniques might include thermoluminescence (to qualify aggregate condition), thermogravimetric analysis or thermal dilatometry (to determine the amount of water loss within the concrete depth), x-ray diffraction (XRD) could also be used to qualify the damage to aggregate or paste in the concrete while Fourier-transform infrared spectroscopy (FTIR) would be used to identify organic surface compounds (soot deposits, charring, etc.) and to identify changes in elastomeric materials as well as the absence of organics with the concrete (such as admixtures, etc.).
Evaluation of Reinforced Concrete Components Damaged During Refinery Fire
An explosion and fire occurred in the Isocracker Battery of a Refinery. CTLGroup was retained by the Owner to perform an evaluation of certain reinforced concrete components located within the heat-affected area. CTLGroup’s scope of work included both field evaluation and laboratory examination of material samples.
When fire strikes, understanding the extent of damage as quickly as possible is critical. CTLGroup’s experts are well-versed in the nuances of fire damage and can advise on which testing methods can provide critical information needed to make the right decisions. Contact our team to learn more.
About the Authors:
Jaclyn Ferraro is Senior Petrographer and Group Director at CTLGroup. Ms. Ferraro oversees the firm’s petrography, concrete, and mortar laboratories. She can be reached at jferraro@ctlgroup.com.
Simonida Grubjesic, Ph.D. is Senior Scientist and Laboratory Manager, Analytical Chemistry. Dr. Grubjesic oversees CTLGroup’s chemistry laboratory and is a consultant with CTLGroup’s Materials Practice. She can be reached at sgrubjesic@ctlgroup.com.
