Thermal Cracking of Mass Concrete Bridge Footings in Coastal Environments

Abstract

The North Carolina Department of Transportation (NCDOT) identified several mass concrete footings in coastal bridges with cracking that needed to be assessed in the context of current North Carolina mass concrete specifications. Cracked concrete in coastal environments is of particular concern due to the higher potential for corrosion damage. Site visits were made to assess the extent of the cracking observed in mass concrete footings of three different bridges. A finite-element model was developed and used to analyze the footings and assess them for their early age thermal cracking potential. Finite-element model results showed that reasonably sized mass concrete footings that followed typical NCDOT control plans did not have a high likelihood of significant cracking from thermal stresses. However, a much larger mass concrete footing had a distinctly higher risk of significant cracking even when typical NCDOT control plans are followed. Further, cracking was even more likely when formwork was removed early. The model results correlated well with observations from the field. A comparison with temperature rise results from the Schmidt method, as implemented in the design of the mass concrete structural elements, shows the Schmidt method’s limitations in predicting temperature differences for very large mass concrete footings.