This research studies the use of microfiber to control cracking in Latex Modified Concrete – Very Early Strength (LMC-VES) for bridge deck overlays. The research investigated fibers and fiber dispensing methods that are commercially available and compatible with the volumetric mixing equipment commonly used for LMC-VES overlays.
Two fibers were recommended for further study in small-scale laboratory experiments, larger scale laboratory experiments, and a full-scale field trial. Small-scale laboratory experiments studied the effects of fiber on the slump, compressive strength, flexural strength, and bond strength to ordinary concrete of LMC-VES.
Casting
and Finishing Laboratory Overlay Slabs
Larger-scale laboratory experiments studied the tendency of LMC-VES overlays to crack when subjected to vibration or sudden temperature changes during curing. Citric acid, commonly used as a retarder in LMC-VES, was found to effect set time, but also to influence LMC-VES workability.
A large-scale field trial applied LMC-VES overlays to three lanes of a bridge in central North Carolina. The first lane used LMC-VES with no fiber and the second and third lanes included fiber in the mixture. Concrete strength and concrete slump were measured at regular intervals across the project for mixtures with and without fiber. The field trial illustrated weaknesses in the current field inspection process for LMC-VES.
In addition, the field trial highlighted difficulties of including fiber in a volumetric mixing process with LMC-VES. Ultimately, the laboratory and field experiments conducted here point to the conclusion that fiber is not necessary in LMC-VES to control cracking. Rather, enforcing proper construction procedure, including curing techniques and control of citric acid usage are likely more effective ways of controlling cracking.
