A large number of bridge deck rehabilitations are performed each year in North Carolina. Latex Modified Concrete (LMC) and LMC–Very Early Strength (LMC-VES) are frequently used in these rehabilitations because these materials provide reasonable installed performance and allow for a rapid return to service. Over the last 5 years, the NCDOT has completed an average of about 25 overlays per year using LMC or LMC-VES materials.
The vast majority of these projects are highly successful. However, despite comprehensive NCDOT guidelines and specifications (such as PSP003 and PSP004), substantial cracking is sometimes observed in these overlays shortly after installation. Prior research funded by NCDOT has indicated that if placement and curing follows proper construction procedures, then the primary causes of cracking (such as shrinkage and plastic shrinkage) in LMC and LMC-VES materials are unlikely to develop. However, other secondary mechanisms can potentially cause cracking, including vibration of the structure during casting and curing, temperature changes during casting, and slight differential settlement/deflection of supporting decks as overlay placement progresses across a bridge. These suspected secondary causes of cracking are difficult (or impossible) to mitigate in practice. In practice, it can also be difficult to completely enforce proper construction procedure, which can lead to some shrinkage cracking. For example, fogging above fresh LMC-VES is allowable, but allowing water to accumulate on the material during placement and finishing is not – the distinction is sometimes difficult to monitor and enforce in the field.
It is proposed to study whether the use of non-metallic fibers in LMC and LMC-VES materials for bridge deck overlays will reduce the occurrence of cracking in these overlays due to the secondary effects described and improve field performance. Fibers mixed into the concrete should be effective at controlling cracking, especially in cases where potential crack-generating mechanisms such as vibration cannot be otherwise controlled. Fibers may also be useful for controlling shrinkage cracking in cases where ideal construction practice is not followed.