Installation of a Latex Modified Concrete Overlay on a Bridge Deck
How do we achieve a good quality LMC Project?
By being prepared and communicating beforehand the essential parts of a LMC Overlay Project that is critical to its success.
What are the essential parts of a LMC overlay?
- Fulfilling mix and specification requirements for the LMC
- Superior bridge deck preparation
- Superior installation of the LMC
- Excellent curing of the LMC
Fulfilling Mix & Spec Requirements
- Utilize the appropriate Latex Modified Concrete product and equipment to meet the needs of the project
- Properly condition and protect aggregate stockpiles from over-saturation by covering with plastic to assure uniform moisture and slumps at least two days prior to use.
Bridge Deck Surface Preparation
- Scarification of bridge deck. Remove existing overlays plus ½” min. existing deck.
- Sounding for bad concrete.
- Removal of deteriorated/unsound concrete – total surface hydrodemolition is the preferred method for longest lasting LMC overlays.
- Thoroughly clean the bridge deck surface by sand-blasting, shot-blasting and / or water-blasting (7,000 PSI minimum preferred method after hydrodemolition) – the entire deck, curb line, new concrete, joints, drains and surfaces the new overlay will contact. Expose fine and coarse aggregate on new concrete surfaces.
- Dry-run of finish machine making sure it is set to proper operation and profile. Make sure machine mounted foggers are working properly.
- Pre-soak burlap and allow to drain prior to placement. New burlap will need to soak for several days.
- Investigate bridge deck for any irregularities; no bond-breakers (paint, oil, dirt, etc.), cracks, unsound concrete, reinforcing steel is not dislodged, longitudinal joint is sound, prior to wet down.
- Wet down deck with potable water 1 hour prior to pour or as many as 6 hours if needed too cool the deck temperature in hot weather. No deck evaporation should be occurring during placement of LMC. Do not allow deck to dry out! Must have adequate potable water supply.
- Remove all standing water from deck surface prior to starting overlay and have the capacity to remove any standing water in depressions with vacuum or oil-free compressed air during pour.
- Cover deck with plastic to keep clean and to prevent evaporation from occurring.
- Provide enough people and equipment to do the job right.
- Through proper bridge deck surface preparation – superior bonding of the overlay will occur – this will lead to the longest lasting Latex Modified Concrete overlays.
Installation of LMC Overlay
- Be conscious of weather conditions – avoid hot, dry, windy weather. Utilize night pours or early AM pours.
Mix is “right” — slump, air and yield.
- Have brooms available to provide a good thick gray/green Latex Paste on the deck surface of a scarified deck. Not necessary for a hydrodemolition prepared surface. Remove all standing water on deck. Keep all water away from mix by vacuum.
- Remove all aggregate that has lost latex paste from the deck area.
- Place variable depth patches and uniform depth overlay in one operation on a hydrodemolition prepared surface.
Finishing machine dry ran prior to pour to make sure it is set properly and vibrator working to consolidate mix. Work quickly during placement.
- For good vibration of entire LMC deck especially along curbs, joints, deep areas and end dams — always use 2 small spud vibrators to work both sides of the overlay.
- When Hydrodemolition surface preparation is used, vibrate the entire deck surface with the small spud vibrators to insure consolidation of the overlay to the roughened base deck.
- Check depth of overlay periodically throughout the pour.
- Tining (or mechanical grooving after cure).
- Keep wet burlap (non-dripping) within 20-30 feet of finishing operation and place white plastic over burlap as soon thereafter as possible. Misting the burlap with a pressure washer prior to placing white plastic is suggested.
- Moved to curing.
A proper installation of a LMC overlay will ensure a high strength bond to the existing deck and will protect the existing concrete with an impermeable (water resistant) structural layer.
Curing of the LMC Overlay
- Cover freshly placed LMC overlay with wet burlap and the white polyethylene plastic to provide an evaporation barrier AS SOON AS POSSIBLE. (20 to 30 feet max. from time of placement).
- In hot weather, use machine mounted foggers to aid in placement and closing surface of overlay.
Keep burlap continuously wet during wet cure period with soaker hoses.
- In hot weather, soaker hoses are highly recommended to reduce chances of cracks occurring by keeping the overlay cool under the white plastic.
- High Performance Type I Cement LMC Mix 48 hours wet / 48 hours dry
- High Performance Type III Cement LMC Mix 24 hours wet / 24 hours dry
- High Performance Very Early Strength LMC Mix 3 hour wet = 3,000 psi
With proper preparation, placement, and curing, Latex Modified Concrete is the only thin bonded overlay specifically designed to withstand harsh freeze-thaw environments with a proven service life of over 30 years.