The
requirement to quickly reopen highways in North Carolina has motivated the
increased use of rapid-setting concrete in overlays. The addition of polymer latex to the material
has been used to increase the service life of the overlays. The latex modified
very early strength concrete (LMC-VES), however has been reported to exhibit
cracking early on after opening the road to traffic. To address this, this
report investigates the early-age behavior and the use of non-metallic fiber
reinforcement in LMC-VES. A state-of-the-art
literature review is provided, an extensive experimental program is conducted,
a review of current construction practice is presented, and findings and
recommendations are reported.
Results from the experimental program indicate
that, due to the expansive nature of rapid setting cement used in this
research, restrained shrinkage cracking is not the primary cause of cracking in
rapid-setting latex modified concrete overlays. Experimental investigations also confirmed
that plastic shrinkage cracking is not a contributing factor to cracking of the
material since, when proper mixture proportioning and placement processes is
used, a meniscus does not form at the surface of the material. Potential sources of cracking were concluded
to result from i) over-finishing in the plastic state, ii) using non-saturated
or non-rewetted burlap during curing, iii) temperature effects in large
geometries due to the high heat of hydration, iv) settlement cracking during
rapid hardening, v) other uncontrolled construction procedures, and vi)
excessive vibration of the bridge deck during or shortly after placement. Since plastic and restrained shrinkage
cracking did not occur in the materials, the use of fiber reinforcement was
deemed unnecessary and was not required.
However, the use of fiber reinforcement to mitigate cracking due to
settlement, improper finishing and curing procedures, and temperature effects
may be effective but requires further investigation.
