SHRP PRODUCT 2035A:
Rapid Bridge Deck Rehabilitation Manual
Michael Sprinkel

Product Summary
Product Use and Evaluation
Contacts/Champions
Reference List of Project Use
Guidelines for the Use of Rapid Set® Cement in Latex-Modified Concrete Overlays

Guidelines for the Use of Rapid Set^® Cement in Latex-Modified Concrete Overlays

Materials
Rapid Set^® Cement should be manufactured by CTS Cement Manufacturing Company, Cypress, California, phone (800)929-3030. Material should be of recent manufacture (within 1 year) and free from lumps.

Sand should be clean and conform to the requirements of ASTM C 33 for concrete sand.

Coarse aggregate should be clean, sound, crushed stone or gravel meeting the general requirements of AASHTO M 80. The maximum size particle should not be larger than 1/2 the depth of the section to be placed.

Latex emulsion should be DOW Modifier A as manufactured by DOW Chemical Company, Midland, Michigan, phone (800)447-4369. Modifier A is a styrene butadiene polymeric emulsion in which the polymer comprises 47.05% - 49.0% of the total emulsion. Stabilizers and an antifoam agent have been added at the point of manufacture. Emulsion should weigh approximately 8.5 lb per gallon.

Water used in the production of the latex-modified concrete should be clean and free from: salt, acid, oil, organic matter, or other substance injurious to the finished product.

Citric acid (food grade) can be used as a retarder to lengthen working time. Food grade citric acid should be dissolved into a solution with water. Solution should be added to the admixture tank, not containing latex emulsion, and dispensed as an admixture.

Mix Design
(Typical formulation, consult your local CTS Representative for correct proportions for job application).

Batching
Accurate proportioning and thorough mixing are crucial requirements of a mixer of Rapid Set^® latex-modified concrete (RSLMC). To assure the inspector and owner that the concrete being delivered to the deck is of proper and uniform composition, the following guidelines are suggested:

1. The capacity of the mixer and bulk materials handling system should be such that a minimum of 6 cubic yards per hour can be accurately proportioned, mixed, placed, and finished properly.
2. A cement meter with ticket printout is a desirable feature to assure uniformity of composition. Alternate techniques may be available but should be approved by the owner.
3. All ingredients should be accurately and positively proportioned by weight with an approved scale.
4. Mixing should be done with equipment that will not be aggravated by residual buildup of concrete. Ready mix trucks are not recommended.
5. Mixed material should be discharged on the deck in sufficient time for the finishing operations to be completed. The working time of RSLMC is largely dependent on temperature and as with regular portland LMC it can be as short as 10 minutes in hot, windy, dry weather.

Equipment
Continuous Mixers

1. Calibration of mobile mixers should be checked every 100 yards for proper proportioning. The yield will be required to be within tolerance of 1.0% according to the following tests: 2. With the cement meter set at zero, and all controls set for desired mix. Discharge mix material into a square container measuring 36" x 36" x 9". When the container has been filled, and struck level, the cement meter should read an amount equal to the cement desired for 1/4 of a cubic yard.
2. They should have available fluid tanks to separate water and latex as well as any admixtures that will be used.
3. They should provide positive control of the flow of water, latex, and admixtures into the mixing chamber.
4. They should have provisions to prevent foreign matter or objects from entering the cement hopper during the loading process.
5. If citric acid is used in the RSLMC, it should be introduced to the auger through an on board admixture tank.

Surface Preparation
Surface should be sound, clean, and free of any laitance. This is generally done with mechanized equipment such as scarifiers and shot blasters or with high-pressure water from hydrodemolition equipment. This should be done within 24 hours to placing the RSLMC. Immediately prior to placement, the clean surface should be thoroughly wetted for a period of not less than 1 hour.

Placing and Finishing

1. Shovels and brooms are used for placing and brushing-in freshly mixed modified concrete and for distributing it to approximate correct level. Hand operated vibrators and screeds should be used to place and finish small areas.
2. A self propelled finishing machine, capable of forward and reverse movement should be used for finishing large areas of work.
3. A suitable, portable, lightweight work bridge should be used behind the finishing operation for any brooming or tining.
4. Metal trowels are recommended for any hand finishing required at scuppers, gutters, and along edges.

Construction Method
Placing and Finishing
RSLMC or slurry should be brushed into the moist substrate just ahead of the pour. Care should be exercised to cover all vertical surfaces as well as horizontal surfaces with an even coating. Stones that accumulate from the brushing operation should be discarded.

The RSLMC should be placed as soon as possible over the brushed surface to prevent its drying out. The finishing machine should proceed over the pour as the material is placed. Deep sections should be vibrated with a spud vibrator. Edges will need to be finished by hand. Final finishing should be completed before the material has reached a final set. Water should not be applied to the surface to aid finishing. Working time can be extended by adding citric acid solution to an admixture tank. Do not add citric acid directly to Dow Modifier A.

Curing
The surface should be covered promptly after final finishing with a single, clean layer of wet burlap. Immediately following the covering of wet burlap, a layer of polyethylene (preferably white) film should be placed over the wet burlap. The coverings should remain until the RSLMC has reached a strength desired for initial traffic loading. Depending on temperatures and specified strength this will usually be within 1 to 6 hours after the pour. The surface of the RSLMC should remain wet for this time period. Additional water may need to be applied to the burlap during the curing, as the surface of the concrete will tend to dry out under the wet burlap.

Limitations
Traffic Loading
No vehicular traffic should be permitted on the RSLMC until an early bearing strength has been achieved. This can be verified by making field cast test cylinders, and protecting them from adverse temperatures. An unheated foam curing box is recommended during a cold weather pour.

Cold Weather (Below 50 F Degrees)
RSLMC should not be placed if temperatures will not be above 45 F degrees for the duration of the pour and initial curing period. Provisions will have to be made to ensure that the RSLMC has an initial temperature above 60 F degrees. During the curing phase, the covering of polyethylene should be replaced with an approved insulation blanket. All other aspects of the curing section should be followed. Also see ACI 306, Recommended Practice for Cold Weather Concreting for further guidance.

Hot Weather (Above 80 degrees F)
During periods of hot weather, RSLMC can be mixed with citric acid to extend working time. Consult your local CTS Representative for appropriate doses. When daytime conditions produce temperature in excess of 85 degrees F, or when daytime conditions of temperature, wind, and humidity cause an evaporation rate greater than 0.15 lbs/sf/hour, consideration should be given to night placement. Also see ACI 305, Recommended Practices for Hot Weather Concreting for further guidance.

Health Hazard for Rapid Set 7 Cement
Rapid Set^® Cement is a cementitious material. Cementitious materials can cause skin, eye, and respiratory irritation. Avoid contact with skin whenever possible. If cementitious material contacts eyes, rinse immediately and thoroughly with water and get prompt medical attention. See the MSDS SHEET for more detailed information.

Consult DOW Literature for information on Modifier A.

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