Q: What is Rapid Set® Low-P™ Cement?
A: Rapid Set® Low-P™ Cement is a specialty formulated Rapid Set cement when incorporated into a concrete, the performance includes very low permeability, high durability and corrosion resistance. These attributes are highly desirable for structural repairs and bonded overlays in exterior and harsh environments (i.e. bridge decks, marine docks and parking garages).
Q: How does Rapid Set Low-P compare to Rapid Set® Latex Concrete (RSLMC), Latex Modified Concrete (LMC), Micro Silica and packaged cement-based high performance concretes?
A: Rapid Set Low-P Cement requires the addition of aggregates, water and in some cases a retarder such as citric acid. The resulting concrete will have the high performance of RSLMC at a cost similar to that of LMC or Micro Silica Fume concrete.
Q: Where can Rapid Set Low-P Cement concrete be used?
A: Rapid Set Low-P Cement concretes can be used in patching structural concrete, replacing/installing elevated deck joints and as wearing surface bonded overlays (bridge decks and industrial slabs).
Q: What is a typical mix design?
A: Rapid Set Low-P Cement has been produced, tested and proven using 572-lb, 611-lb and 658-lb mix designs. For thin bonded wearing surfaces, 3/8” stone should be considered with the stone to sand ratio (45% stone to 55% sand). For patching structural repairs with depths exceeding 2”, a traditional ¾” to 1” top size stone with the mix ratio favoring stone should be considered. Water to cement ratio will range between .42 and .45 with resulting slump range of 6 to 9 inch allowable. Note that the Rapid Set Cement by nature has a high water demand, about a third higher than what Portland cement requires to hydrate.
Q: What is the working time and how can I extend this?
A: Working time will vary depending on ambient temperatures. In cooler ambient temperatures, the working time will be 20 minutes where as in hot temperatures, it will be 10 minutes. Using a retarder such as citric acid can extend working time 20 to 40 minutes. Citric acid will act as a wetting agent and aids in clean-up. Cool water and materials will extend working time while hot water and materials will speed up working time. Do not exceed the designed amount of water to extend working time. This will cause segregation of the concrete.
Q: What is the temperature range that Rapid Set Low-P Concrete can be used?
A: Rapid Set Low-P concrete can be applied in ambient temperatures between 40° F to 95° F. However the existing surface and substrate temperatures must also be considered. In hot weather, cooling the substrate may needed to slow the hydration process. For freezing temperature applications, please contact your local CTS Cement Representative for more information.
Q: Does Rapid Set Low-P Cement concrete require special equipment for mixing, placing and finishing?
A: Rapid Set Low-P can be mixed with conventional equipment, but volumetric mixers are typically used for large placements. Direct deposit, conveyors and buggies can be used. Pumping will require additional retarders and machinery. Placing with roller screeds, hand strikes and self-propelled deck finishers are commonly used. Truss screeds can be used in small area applications. Scrub coating is not required for applications where proper surface preparation has been established. Traditional finishing tools are required.
Q: What surface preparation is required?
A: To establish a mechanical bond, all concrete surfaces need to be prepared with a minimum ICRI profile of #6. For elevated wearing surface overlays, hydro-demolition is highly preferred but sand blasted/shot blasted surfaces have been sufficient to establish a uniform bond profile for Rapid Set Low-P Concrete. Pull off tests can be started at 24 hours after placement, but preferably after 48 hours for better consistency of results.
Q: How do you cure Rapid Set Low-P Cement concrete?
A: Wet cure the concrete for a minimum of 2 hours or until 3,000 psi compressive strength. Wet cure involves maintaining a wet saturated surface starting as soon as it is possible to place burlap on the surface without damaging the finished surface. Wet burlap can be placed sometimes as soon as 10 minutes behind the deck finisher and as long as 25 minutes in cool weather. Other wet cure methods are available but must be approved prior to start of placement.
Q: How do traffic conditions affect the placement of Rapid Set Low-P Cement concrete? When can Rapid Set Low-P Cement concrete be opened for traffic?
A: Due to the fast setting nature of Rapid Set Low-P cement, tensile strength development occurs very rapidly. This will shorten the amount of time that vibrations from adjacent traffic lanes can be a factor to early age stress cracking in the concrete. The 572-lb Rapid Set Low-P Cement concrete mix design has proven to produce 3,000 psi in less than 3 hours. At 3,000 psi compressive strength, many states allow wearing surface overlays and patches on elevated decks to be open for traffic. Refer to your states regulations for conditions for opening to traffic.
Q: How is Rapid Set Low-P Cement packaged and where is it available?
A: Rapid Set Low-P Cement is available in bulk and super sacks. Rapid Set Low-P Cement is produced in Mexico, MO and Nazareth, PA.