The North Carolina Department of Transportation (NCDOT) has constructed a number of concrete bridge decks using lightweight aggregate, with construction of the first lightweight concrete bridge deck completed approximately 40 years ago. Use of lightweight concrete in bridge decks can significantly reduce the deadload of the structure, allowing for longer spans and reduced sizes of other structural members. Some research has suggested that use of lightweight concrete in bridge decks can offer advantages in addition to those directly related to the reduced weight. These possible advantages included reduced cracking tendency and lower permeability. If this is true, enhanced durability performance could result in lightweight concrete bridge decks being a more economical choice than normalweight concrete bridge decks for some applications. In this study, field evaluations were performed on bridge decks constructed of both normalweight and lightweight concrete. For each lightweight concrete bridge deck selected for inclusion in this study, a companion normalweight bridge deck of similar age, traffic loading, and environmental exposure was selected. Field evaluations included visual surveys and several field tests. Using the results of the field evaluations and testing, along with laboratory testing or concrete core samples and powder samples, the field performance of the lightweight concrete bridge decks was evaluated and compared to the performance of the normalweight concrete bridge decks.
Although some differences in the performance of lightweight and normalweight concrete bridge decks were observed in field and laboratory tests, a distinct difference between the overall durability performance of lightweight bridge decks and normalweight bridge decks included in this study was not readily evident. This finding differs from those of a number of studies that have indicated that lightweight concrete can provide enhanced durability performance, and therefore, additional laboratory-based studies of lightweight and normalweight concrete bridge deck mixtures using local materials are recommended. Damages induced by factors such as structural characteristics and external loads may have played a significant role in observed distresses, as well as in results of field and laboratory tests. Additionally, it is possible that that there has not been ample time for distinct differences in performance between lightweight and normalweight concrete decks included in this study to become evident during field observations, or measurable during field or laboratory tests. Regional trends in performance were observed for some durability tests, however, and this information could be utilized by NCDOT.
