In a previous study, SD94-04, one aspect of the project was to construct an NMFRC deck overlay for the Vivian Interchange on I-90. Usually, for deck overlays, a plain low-slump dense (LSD) concrete is produced by a mobile-mixer. In this study attempts were made to produce a LSD NMFRC with a mobile-mixer. However, after determining that the mobile-mixer could not meter the fiber addition rate and the mixing chamber could not evenly distribute the fibers, a different means of producing the LSD NMFRC had to be found. With some skepticism, testing was done to produce and deliver the necessary concrete with redi-mix trucks. This test proved that the desired product could be obtained.
Even though a LSD NMFRC deck overlay has successfully been constructed, research is necessary to give the Department additional experience with this method of producing and delivering a LSD NMFRC, to ensure that the desired concrete product is obtained, and to evaluate it's performance over the badly deteriorated structures at Exit 32.
Findings: Because each deck was badly deteriorated, minimal partial depth removal of concrete took place after a typical scarification. Knowing the present condition of these decks, SDDOT decided to enhance its present low-slump dense (LSD) deck overlay concrete by reinforcing it with 3M’s Polyolefin Fibers. Because of previous SDDOT research with these fibers, it was anticipated that the performance of the deck overlays would be enhanced by the fibers. By using Non-Metallic Fiber Reinforced Concrete (NMFRC), cracking, spalling, or delamination should not pose serious problems because the fibers will hold the concrete together, whereas, a plain concrete overlay might not hold together and possibly allow a loss of material from the top side of the deck causing hazards to the traveling public.
As a result of the study, the Department will consider the use of LSD NMFRC not only on badly deteriorated bridge decks, but on a case by case basis for all bridges for the following reasons:
- LSD NMFRC will improve the performance of the deck overlay and reduce the potential for hazards to the public.
- Based on 1997’s average unit bid cost for LSD concrete, the increase in cost due to the addition of fibers for the Exit 32 decks was minimal ($5,040) when compared to the total contract cost ($342,329).
However, for bridges that are some distance from a concrete plant, it may not be advantageous to use LSD NMFRC and SDDOT’s plain LSD concrete should be used. This is true because, plain LSD concrete is supplied by a mobile mixer, whereas, LSD NMFRC is delivered by mixing trucks.
As a result of this study, research study SD98-18 (The Determination of the Permeability, Density, and Bond Strength of Non-Metallic Fiber Reinforced Concrete in Bridge Deck Overlay Applications) has been initiated to study the effect the fibers have on the permeability, bond, and density of the bridge deck overlay concrete.
Assist design personnel in the development of construction plans and notes.
In conjunction with design personnel design the concrete mix. Conduct tests on the mix design to ensure desired properties are obtained.
Attend the preconstruction meeting(s) and recommend NMFRC construction methods.
Observe the construction on both deck overlays and record construction problems, weather conditions, and other construction variables.
Outline inspection procedures used to perform deck overlay condition surveys.
Periodically conduct deck overlay condition surveys to evaluate the performance of the LSD NMFRC deck overlays through one freeze-thaw cycle. Relate the observed deck overlay conditions to the maps supplied by SDDOT which will be obtained by sounding for delaminations and visually observing.