United States Department of Transportation
i
Microsilica modified concrete for bridge deck overlays : first-year interim report.
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1991-11-01
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By Miller, Bo
[PDF-1.21 MB]
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Abstract:The study objective was to see if microsilica concrete (MC) is a viable alternative to the latex modified concrete (LMC) usually used on bridge deck overlays in Oregon. The study addresses MC overlays placed in 1989 on 7 portland cement concrete (PCC) bridge decks. This report covers the performance of the overlays during the first year of use.
After one year, the only distresses on these overlays were cracking and delamination. There was cracking on all of the overlays. In most cases, the cracking was hairline and random. In heavily cracked areas, the cracks connected to form a map pattern. This cracking may be due to drying shrinkage. Similar problems are seen on Oregon State Highway Division (OSHD) LMC overlays.
In addition, there were delaminations on 5 of the 7 overlays. This distress was not extensive, as the worst deck had only 2.5% of its surface delaminated. In most cases, the delaminations were small, scattered throughout the deck, and covered by uncracked MC. The exceptions were two large delaminations that were under sections of the overlay with severe map cracking, and numerous delaminations adjacent to construction and expansion joints. The delaminations that were repaired were almost always between the overlay and the old deck. The cause of these delaminations is not known. Similar distress is often seen on OSHD LMC overlays.
The wheel-to-pavement friction numbers of these overlays were similar to typical state highway pavements and LMC bridge decks in Oregon.
The only maintenance and repair cost to the OSHD was the sealing of cracks on one deck with methacrylate and sand, at a cost of $4,000. This sealant was effective.
The overlays met 2 of their 3 design objectives after one year's use. They were still adding strength to the deck and providing a smooth and durable wearing surface. However, as they were cracked, it is surmised that they were no longer sealing the underlying deck from the intrusion of chlorides. Experience with a recently placed MC overlay is discussed and recommendations are made.
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