Latex-modified Concrete Overlay Containing Type K Cement

About the report:

Hydraulic cement concrete overlays are usually placed on bridges to reduce the infiltration of water and chloride ions and to improve skid resistance, ride quality, and surface appearance. Constructed in accordance with prescription specifications, some overlays have performed well for more than 30 years whereas others have cracked and delaminated before the overlay was opened to traffic. Shrinkage of the concrete is the most common cause of cracking in overlays. The use of Type K (expansive) cement should increase the probability that concrete overlays with minimal cracks will be constructed. This report describes the Virginia Department of Transportation's first experience with the use of Type K cement for the construction of a latex-modified concrete overlay. One lane of the overlay was constructed with traditional Type I/II cement, and the other lane with Type K cement. With the exception of the cement, the requirements for the overlays were the same. The evaluation of the overlays included measurements for slump, temperature, air content, compressive strength, permeability to chloride ion, shrinkage, and bond strength. As expected, the shrinkage of the concrete containing Type K cement was much less than that of the concrete containing Type I/II cement. Other properties were similar. The use of Type K cement is estimated to increase the cost of the concrete approximately 2.6 percent, or about $1/sq. yd. for an overlay 1.5 in thick. This is much less than the cost to seal the shrinkage cracks in an overlay: $10/sq. yd. Greater savings can also come from the longer service life of a crack-free overlay. To gain more experience, the Virginia Department of Transportation should construct additional latex-modified concrete overlays using Type K cement.

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