Forensic Investigation and Petrographic Analysis of Concrete Apron Distresses; A Case Study in Nashville, Tennessee

This study presents a forensic investigation into pavement distress in a concrete apron located in Nashville, Tennessee. The investigation involved detailed engineering observations and a comprehensive pavement condition survey in accordance with ASTM D۵۳۴۰. To identify the underlying causes of deterioration, petrographic examinations were conducted on three concrete cores extracted from the apron, following ASTM C۸۵۶ guidelines. The analysis revealed consistent aggregate distribution, primarily composed of micritic limestone and quartz-based sand, with air content (total of entrapped and purposefully entrained air) ranging from ۳.۹% to ۵.۲% and air void spacing factors exceeding American Concrete Institute (ACI) recommendations for freeze-thaw durability. No carbonation was detected in the cores, but moderate to abundant ettringite, calcium hydroxide, and alkali-silica gel resulting from Alkali-Silica Gel (ASG) were observed lining voids and fractures. The findings indicate that Alkali-Silica Reaction (ASR)-related damage, exacerbated by cyclic wetting and drying, is a primary contributor to the pavement deterioration. Freeze-thaw damage due to inadequate air entrainment was also identified as a contributing factor. Based on the results, recommendations for improving the long-term performance and durability of the concrete apron include using low-alkali cement, selecting better-graded and less reactive aggregates, increasing the percentage of purposefully entrained air to reduce air void spacing and improve freeze-thaw durability, and incorporating supplementary cementitious materials (SCMs) to reduce alkali availability and enhance ASR resistance. We note the use of lithium nitrate has also been proven to mitigate ASR in new concrete. However, the mechanism of mitigation is not fully understood, and the relatively high cost and limited availability of lithium introduces challenges for this alternative. This study underscores the importance of petrographic examination in understanding concrete deterioration mechanisms and developing targeted repair strategies to enhance infrastructure durability.This study presents a forensic investigation into pavement distress in a concrete apron located in Nashville, Tennessee. The investigation involved detailed engineering observations and a comprehensive pavement condition survey in accordance with ASTM D۵۳۴۰. To identify the underlying causes of deterioration, petrographic examinations were conducted on three concrete cores extracted from the apron, following ASTM C۸۵۶ guidelines. The analysis revealed consistent aggregate distribution, primarily composed of micritic limestone and quartz-based sand, with air content (total of entrapped and purposefully entrained air) ranging from ۳.۹% to ۵.۲% and air void spacing factors exceeding American Concrete Institute (ACI) recommendations for freeze-thaw durability. No carbonation was detected in the cores, but moderate to abundant ettringite, calcium hydroxide, and alkali-silica gel resulting from Alkali-Silica Gel (ASG) were observed lining voids and fractures. The findings indicate that Alkali-Silica Reaction (ASR)-related damage, exacerbated by cyclic wetting and drying, is a primary contributor to the pavement deterioration. Freeze-thaw damage due to inadequate air entrainment was also identified as a contributing factor. Based on the results, recommendations for improving the long-term performance and durability of the concrete apron include using low-alkali cement, selecting better-graded and less reactive aggregates, increasing the percentage of purposefully entrained air to reduce air void spacing and improve freeze-thaw durability, and incorporating supplementary cementitious materials (SCMs) to reduce alkali availability and enhance ASR resistance. We note the use of lithium nitrate has also been proven to mitigate ASR in new concrete. However, the mechanism of mitigation is not fully understood, and the relatively high cost and limited availability of lithium introduces challenges for this alternative. This study underscores the importance of petrographic examination in understanding concrete deterioration mechanisms and developing targeted repair strategies to enhance infrastructure durability.

کلیدواژه ها:

Concrete Apron ، Petrographic Examination ، Freeze-thaw Damage ، Alkali-Silica Reaction (ASR) ، Petrographic Analysis