Civil Engineering Association

MITIGATING SHRINKAGE CRACKING OF CONCRETE IN BRIDGE DECKS THROUGH INTERNAL CURING

As the need for durable, long lasting infrastructure increases, new methods and
techniques are being explored to prolong the service life of roads and bridges. One method to
reduce shrinkage and early age cracking in concrete is internal curing. Internal curing supplies
water to concrete, using pre-wetted lightweight aggregate (LWA), as needed throughout the
process of hydration to reduce self desiccation, which leads to cracking. This research project
analyzed two types of coarse LWA, expanded clay and expanded shale. The mixtures were
developed specifically for use in bridge decks and adhered to specifications of the Arkansas State
Highway and Transportation Department (AHTD). The concrete mixtures contained LWA at
rates of 0, 100, 200, and 300 lb/yd3. The research was divided into two phases. The first phase
measured autogenous and drying shrinkage in both plastic and elastic states using embedded
vibrating wire strain gages (VWSG) cast in concrete prisms. The expanded clay LWA mixtures,
with the 300 lb. replacement rate yielding the best results, were most effective in reducing
shrinkage. Compressive strength decreased as the amount of LWA included in the mixture
increased. However, all mixtures surpassed the 28 day compressive strength specified by AHTD.
The second phase of the research project measured plastic shrinkage cracking in thin concrete
test slabs. Methods and materials were investigated to produce consistent plastic shrinkage
surface cracks of the concrete slabs. The extent of plastic shrinkage that occurred was quantified
by measuring the total crack area of the test slabs. Implementation of 300 lb. of expanded clay
LWA did not reduce the crack lengths, but did reduce the average crack widths experienced by
the test slabs due to plastic shrinkage.