Microsilica modified concrete for bridge deck overlays : construction report.

PDFTech ReportFHWA Experimental Features OR 89-03A, OR 89-03B, OR 89-03CSilica fumeBridge decksConcrete overlaysLatex modified concretePortland cement concreteCrackingDelaminationMix designPouringCostsOregonOregon. Department of Transportation. Materials and Research SectionMiller, BoOregon. Department of Transportation. Materials and Research SectionUS Transportation CollectionThe 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 Portland cement concrete (PCC) bridge decks at three sites.At each site the first MC pours had the most problems,as the contractors had no experience with the product. Most of the later pours went smoothly.On most of the problem pours, the mixes were either too stiff as delivered or they started to lose slump too early in the placement and finishing process. Consequently, the MC was hard to finish and a poor quality overlay resulted. Solutions to this problem were: using mixes with higher slumps, delivery of consistent mix to the jobsite, adding most the superplasticizer at the jobsites rather than at the batch plant, and streamlining jobsite testing and mix adjustment.If the mix was workable, the overlay could be mechanically finished. Otherwise, it was hand finished. Fogging was always needed.Delamination and/or cracking was seen on some decks after several months of traffic. The cause of this distress is not known.In conclusion:1) Although the long-term durability of MC deck overlays in Oregon is not presently known, MC overlays were constructed in this study that had adequate strength, a smooth uncracked surface, and minimal delamination, the same as LMC. Many of the problems observed in this study may be prevented by using the February 1990 or later specifications. Consequently, further use of MC is recommended as an alternative to LMC.2) Unlike LMC that requires mobile mixers at the jobsite and priming of the old deck; MC can be produced in an off-site normally used for conventional PCC. In some cases this may be an advantage over LMC.3) The combined cost of furnishing and placing MC and LMC are similar, based on experience with the overlays in this study. The lower cost of furnishing MC is offset by higher construction costs.4) MC overlays have higher initial skid resistances than typical LMC surfaces