Latex-Concrete Overlays on Bridge Decks

Abstract

Visual field inspections and soundings were performed on latex concrete overlays on 24 bridges on I 64 between Milepoint 150 and the West Virginia state line. The inspections were conducted in response to a request from the Kentucky Department of Highways to determine if cracking problems in the overlays were related to workmanship or materials. The field inspections revealed that most of the overlay crack problems were related to 1) reflection cracking caused by pre-existing fractures in underlying concrete bridge decks and 2) “pull-in” cracks in the overlay, caused by belated tyning of the bridge deck. Field diaries, inspection reports, material test reports and the final construction inspection report were reviewed. Correlations were sought among latex brand, cement brand, date of pouring, rain during pouring, pouring temperature, percent entrained air, and slump to determine their effects on overlay cracks. No correlations were detected. Pre-existing deck fractures are related to thermal stresses between the concrete and reinforcing steel and to flexure of the bridge. Those cracking patterns and the extent of cracking have been found to be generally specific to the overall design of the structure. A small number of construction-related bridge-deck flaws such as mudball holes and delaminations were detected. The extent of delaminations detected by the Kentucky Transportation Research Program vas less than that identified by the Department of Highways. This was due to differences in sounding techniques and interpretations employed by the two parties. It is recommended that the contractor be held liable only for patching or treating longitudinal "pull-in” cracks. The contractor also should be held accountable for mudball holes and delaminations. The contractor should not be held accountable for reflection cracks. It is recommended that modifications be made to Kentucky Department of Highways Standard Specifications for Road and Bridge Construction, Section 617, entitled "Concrete Bridge Deck Overlays.” Those changes should mandate 1) timely placing and texturing of the overlay and 2) qualification testing of overlay contractors.