Civil Engineering Association

Evaluation, Presentation and Repair of Microbial Acid-Produced Attack of Concrete

The Texas Department of Transportation (TxDOT) has approximately 50,000 bridges in its inventory and the deterioration of concrete under these bridges, most of which are reinforced, has been a critical issue affecting the service condition. Recent research on deteriorated concrete columns on bridges in Texas indicated that microbial colonization might be a factor promoting the surface deterioration of bridge columns continuously exposed to water. Although microbial activities may be involved in the surface deterioration, it is however not clear how severe the deterioration is and whether it is a significant contributor to the deterioration. Field and laboratory investigations are needed to identify the impact of microbial induced deterioration (MID) on TxDOT bridges. To evaluate the severity of the deterioration and determine whether MID is a significant contributor to the deterioration, visual inspection and a number of in situ tests were performed on columns of twelve selected TxDOT bridges. Laboratory tests including microbial, chemical composition, mineralogy and petrographic analyses were performed to investigate the potential cause and extent of the deterioration. Results from this comprehensive study were used to provide evidence of concrete degradation and ascertain the degree of deterioration caused by microbial attack. The study also evaluated the effectiveness and consistency of various measurements used in this study and provided a suggested test procedure to identify microbial attack on concrete and evaluate the integrity of deteriorated concrete due to the attack. In addition, a preliminary evaluation of the microbial attack resistance of commonly used TxDOT mixes was performed through evaluation of resistance of a series of mixes subjected to field and/or sulfuric acid solution exposure.