Early-age shrinkage cracking has been observed in many concrete bridge decks in Washington State and elsewhere around the U.S. The cracking increases the effects of freeze-thaw damage, spalling, and corrosion of steel reinforcement, thus resulting in premature deterioration and structural deficiency of the bridges. In this study, the main causes of the early-age cracking in the decks are identified, and concrete mix designs as a strategy to prevent or minimize the shrinkage cracking are evaluated. Different sources (eastern and western Washington) and sizes of aggregates are considered, and the effects of paste content, cementitious materials (cement, fly ash, silica fume, slag), and shrinkage reducing admixture (SRA) are evaluated. A series of fresh, mechanical and shrinkage property tests were performed for each concrete mix. The outcomes of this study identify optimum concrete mix designs as appropriate mitigation strategies to reduce or eliminate early-age shrinkage cracking and thus help minimize shrinkage cracking in the concrete bridge decks, potentially leading to longer service life.

Early-age shrinkage cracking has been observed in many concrete bridge decks in Washington State and elsewhere around the U.S. The cracking increases the effects of freeze-thaw damage, spalling, and corrosion of steel reinforcement, thus resulting in premature deterioration and structural deficiency of the bridges. In this study, the main causes of the early-age cracking in the decks are identified, and concrete mix designs as a strategy to prevent or minimize the shrinkage cracking are evaluated. Different sources (eastern and western Washington) and sizes of aggregates are considered, and the effects of paste content, cementitious materials (cement, fly ash, silica fume, slag), and shrinkage reducing admixture (SRA) are evaluated. A series of fresh, mechanical and shrinkage property tests were performed for each concrete mix. The outcomes of this study identify optimum concrete mix designs as appropriate mitigation strategies to reduce or eliminate early-age shrinkage cracking and thus help minimize shrinkage cracking in the concrete bridge decks, potentially leading to longer service life.

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.