LMC Installation | LMC Specifications
(Specifications cont'd)
Construction Requirements
Bridge deck repairs and LMC overlays shall be made as soon as practical following the removals of the deck surface, pouring full depth patching, performance of Hydro-demolition as specified and all necessary final deck cleaning. Traffic will not be allowed on any deck surface until final curing is completed in accordance with these specifications.
Deck or Surface Preparation Methods
a. Scarifying: the entire bridge deck surface shall be removed to a minimum of ¼ inch if the bridge deck was constructed under a previous contract. After initial surface removal an additional ¼ inch may be removed as directed. On decks that have received an initial overlay, the entire overlay shall be removed and an additional ¼ inch of the existing bridge deck surface milled or scarified. This operation may be completed in one pass. All surface residual, including water, dust, and concrete must be removed immediately.
b. Hand-chipping: Following cleanup of surface removal operations the entire bridge deck surface shall be sounded for bad concrete. The areas of unsound concrete shall be marked and removed. Unsound areas shall be removed by hand-chipping or hydro-demolition. Jack hammers shall not heavier than the nominal 45lb. class and chipping hammers shall not heavier than the 15lb. class. Only hand-chipping hammers may be used when removing concrete within 1 inch of reinforcing steel. Where the bond between the reinforcing steel and the existing concrete is destroyed the concrete adjacent to the steel shall be removed to a minimum clearance of 1 inch. Several soundings may be necessary to assure removal of the unsound concrete. Cleanup of all areas will be performed prior to resounding.
c. Hydrodemolition: The hydrodemolition machine shall utilize a high pressure water jet system and shall be approved prior to use. The hydrodemolition equipment will be calibrated to only remove unsound concrete and to provide a highly bondable surface for the new overlay. The calibration of the equipment shall be re-performed on each structure. Precautions shall be taken during the hydrodemolition operation to prevent damage to surrounding property and traffic. Do not allow waste water to dry on the bridge deck surface.
Regardless of the removal method being used, the removal operation shall be stopped if it is determined that sound concrete is being removed. Recalibration of equipment or alternative changes in equipment or practice shall be performed before resuming removal operations.
- Blast Cleaning
Before the overlay is placed the entire deck surface and any related vertical surfaces of the concrete curbs, patches, parapets or barrier walls shall be cleaned to one inch above the top surface elevation of the overlay. The deck surface shall be thoroughly blast cleaned by sand-blasting, shot-blasting or high pressure water-blasting of 5,000 psi minimum the preferred method after hydro-demolition. The deck surface shall be clean and free of any laitance, oils, dirt, grease, paint, bituminous matter, rust or any foreign substance prior to the placement of the overlay. Expose the fine and coarse aggregate if pouring on new concrete surfaces.
All debris of any type, including dirty water from water-blasting shall be contained and completely removed or flushed from the entire deck surface. The deck surface shall not be allowed to dry out after water-blasting operation has been completed. Any method which does not consistently produce satisfactory work and conform to the above requirements shall be discontinued and replaced by an acceptable method. The entire surface shall be covered with plastic after cleaning operations have been completed. The Engineer may direct that blasting operations be repeated if the overlay placement is not performed within 36 hours or any part of the deck has dried out at the contractors expense.
Placement and Finishing Limitations
Prior to the placement of the overlay the Engineer shall establish the Contractor’s ability to place the overlay on a continuous basis and to consolidate, finish, texture prior to the formation of the plastic surface film and the commencement of curing procedure. Operations or procedures which are considered to be detrimental to the integrity and durability of the repaired and overlaid bridge deck will not be permitted.
Expansion joints shall be maintained throughout placement of the overlay. A bulkhead equal in thickness to the width of the joint shall be installed to the required grade and profile, prior to placing the overlay. The screed rails for the finishing machine shall be placed and anchored vertically and horizontally to secure the required specification profile. Screed rails shall not be treated with any bond breaking compound.
After the screed rails have been set to proper profile. The finishing machine shall be given a dry run to assure that the specified nominal thickness of the overlay will be attained over the entire deck.
After the surface has been cleaned and prior to the overlay placement the deck surface shall be thoroughly wetted with potable water for a period of not less than one hour or as many as 6 hours if needed to cool the deck temperature in hot weather. Once the deck is wet, cover with plastic to keep clean and prevent surface evaporation. No deck evaporation should be occurring prior or during placement of the overlay. Remove all standing water from the deck surface prior to starting placement. Use vacuums or oil-free compressed air to remove any standing water during the overlay placement.
LMC shall be mixed at the job site in accordance with the specified requirements for the equipment used. The maximum time between mixing and placement shall not exceed 20 minutes. Mixing capability shall be such that the finishing operations can proceed at a steady pace with final finishing completed before formation of the plastic surface film. Keep the wet burlap (non-dripping) within 20-30 feet of the finishing operation and place white plastic over the burlap as soon thereafter as possible. Misting the burlap prior to placing the white plastic is suggested.
The overlay should not be placed unless the ambient temperature is 45 degrees F and rising and predicted temperatures will be over 45 degrees F over the duration of the placement without the written approval of the Engineer. Protection of the overlay shall be made to assure the overlay remains above 45 degrees F for the duration of the cure period prior to opening to traffic or the specified compressive strength whichever comes first. If during wet or dry cure periods the ambient temperatures fall below 45 degrees F, the number of hours that the temperature falls below 45 degrees F will not be considered part of the 96 hour cure period. Also, during the dry cure period if rain occurs to wet the surface for one hour or more the number of hours will not be considered part of the dry cure period. Do not allow the overlay surface to freeze prior to the end of the cure period or until proper compressive strength is achieved.
Placement may be required to be made during early morning hours, late night or other limited time frames when daytime temperatures exceed 85 degrees F. No overlay shall be placed when temperatures or concrete are above 85 degrees F without the approval of the Engineer.
The overlay should not be placed if rain is expected. Adequate precautions should be taken to protect the freshly place overlay material from sudden or unexpected rain. Damaged material will be removed and replaced with no additional payment. A construction dam or bulkhead shall be prepared and placed if delays of one hour are expected. Delays of less than one hour wet burlap shall be placed on the leading edge of the overlay to keep from drying out.
The LMC should be stiffly broomed onto the wet prepared deck surface in a good thick paste just ahead of the overlay placement. All horizontal and vertical surfaces should receive a thorough even coating of LMC. Do not let this material dry out prior to covering with additional material for final placement and grade. Any loose aggregate that has lost its grout paste must be removed from the deck surface and disposed of. Brooming is not necessary on hydrodemolition prepared surface.
All areas that cannot be reached by the finishing machine vibrator shall be spud vibrated. Curb lines, variable depth patches, joints or dams shall be vibrated. Hand finishing with a float will be required along the edge of the placement or in small areas.
Texturing
When pre-cure texturing is specified and a tight uniform surface has been achieved, it shall be textured immediately after finishing and before the plastic film forms. The transverse grooves shall be formed by specified texturing equipment and shall be terminated at a specified distance from the face of the curb or barrier wall. The grooves shall be relatively uniform and smooth, and shall be formed without tearing the surface and without exposing or bringing pieces of coarse aggregate to the surface.
Mechanical grooving is to be completed after the dry cure process or specified cylinder strengths are achieved.
Curing
The surface of the overlay shall be promptly covered with a single layer of clean wet burlap as soon as the surface will support it without deformation usually within 15-20 minutes after placement.
Cover the wet burlap with a layer of white polyethylene film of 4 mil thickness for the entire duration of wet cure.
Keep burlap continuously wet during the length of the wet cure. In hot temperatures soaker hoses shall be used to cool the overlay under the white plastic and an extended wet cure of 24 hours is suggested.
Cure durations: Type I Cement LMC Mix = 24 hrs wet / 72 hrs dry
Type III Cement LMC Mix = 24 hrs wet / 24 hrs dry
Rapid Set Cement LMC Mix = 3 hr wet / = 2,500 psi
Payment
Method of Measurement
Latex Modified Concrete Overlay Using Hydrodemolition (___ inches thick) Latex Modified Concrete Overlay Using Hydrodemolition shall be measured by the square yard based on the theoretical volume required for the overlay shown in the Plans. The accepted quantity of bridge deck overlay (LMC) will be paid for at the contract unit price per square yard, which price will be full compensation for the placement and finishing of the overlay in accordance with the Standard Specifications and for any tools, labor, equipment or incidentals for such placement. This item shall include only the (LMC) for the theoretical plan depth of the overlay. Placement shall also include all labor and equipment to place the variable thickness overlay (since the variable thickness and the constant thickness overlay are placed in one operation).
Latex Modified Concrete, Variable Depth, Material Only Latex Modified Concrete, Variable Depth, Material Only shall be measured by the cubic yard complete in place. The number of cubic yards will be determined by deducting the theoretical volume (plan specified thickness) of bridge deck overlay (LMC) from the total volume (as indicated by the batch quantity tickets) of (LMC) required to obtain the finished grade shown on the Plans or established by the Engineer. Accepted quantities of (LMC) Variable depth will be paid for at the invoice price of the materials delivered to the project plus 15 percent, except in no case shall maximum payment exceed $400 per cubic yard plus 15% where Type I Portland Cement is used, $500.00 per cubic yard plus 15% where Type III Portland Cement is used and $700.00 per cubic yard where Rapid Set Cement is used. All other costs associated with placement of Latex Modified Concrete, Variable Depth, Materials only shall be incidental to the price bid for, Latex Modified Concrete Using Hydrodemolition (___ inches thick).
Basis of Payment
Payment for completed and accepted quantities as measured above will be made at the contract price for:
| Item | Unit | Description |
| Square yard | Latex Modified Concrete Overlay Using Hydrodemolition (___ inches thick) | |
| Cubic yard | Latex Modified Concrete, Variable Depth, Material Only |
Hydrodemolition Surface Preparation
For detailed specifications on hydrodemolition preparation visit the Hydrotech website.
Use ACI 308 and ACI 548.3R-95 as added reference for LMC Overlays.
THIS INFORMATION IS SUPPLIED AS A REFERENCE. COMPILED FROM SEVERAL DOT DEPARTMENTS AND LATEX MAUFACTURER SPECIFICATIONS. IT IS OFFERED IN GOOD FAITH AND WITHOUT WARRANTY OR LEGAL RESPONSIBILITY OF ANY KIND.
THIS INFORMATION FAVORS LMC REQUIREMENTS, PREPARATION, INSTALLATION AND CURING. OTHER CONSTRUCTION GUIDELINES MAY BE NECESSARY.
IF THERE ARE QUESTIONS PLEASE CALL FOR ASSISTANCE.
