Cracked pavement slabs lead to uncomfortable and eventual unsafe driving conditions for motorists. Replacement of cracked pavement slabs can interrupt traffic flow in the form of lane closures. In Florida, the traffic demands are high and pavement repairs need to be carried out swiftly typically using concrete with high cement contents and accelerators to create rapid setting and strength gain. The concrete used in these pavement replacements is usually accompanied by a high temperature rise, making the replaced slabs susceptible to cracking. Cracking is a result of developed tensile stresses in the concrete, which exceed the concrete's tensile strength capacity. This research is being conducted to determine the risk of cracking for pavement slabs with varying dosages of chloride based accelerator used to promote high early strength. To analyze the effect of the accelerator, five different concrete mixtures including a control were assessed in a series of tests with varying accelerator dosages. Experiments included: mortar cube testing, concrete cylinder testing, autogenous deformation measured with a free-shrinkage frame, and restrained stress analysis using a rigid cracking frame. The findings indicate that accelerators are necessary to meet the strength requirements, and that the higher the accelerator dose, the higher the early shrinkage in the first 24 hours determined from the free shrinkage frame. Accidental overdose of the chloride-based accelerator results in the highest cracking potential and the highest shrinkage when tested under field generated temperature profiles.

Due to strict placement time and strength constraints during the construction of concrete pavement repair slabs, accelerators must be incorporated into the mixture design. Since the most common accelerator, calcium chloride, promotes corrosion of concrete reinforcement, a calcium nitrate-based accelerator was studied as an alternative. To replicate mixtures used in the field, commercial accelerators commonly used in concrete pavement repair slabs were used in the current study. Crack risk of different mixtures was assessed using modeling and cracking frame testing. HIPERPAV modeling was conducted using several measured mixture properties; namely, concrete mechanical properties, strength-based and heat of hydration-based activation energies, hydration parameters using calorimetric studies, and adiabatic temperature rise profiles. Autogenous shrinkage was also measured to assess the effect of moisture consumption on concrete volume contraction. The findings of the current study indicate that the cracking risk associated with calcium nitrate-based accelerator matches the performance of a calcium-chloride based accelerator when placement is conducted during nighttime hours.

The industrial concrete floor is a very important part of an industrial building, distribution center, storage or shopping mall, and it must have high quality surfaces for operation. To achieve the high quality we must know the problems and how to treat them. The most important problems on the concrete floors are: (i) cracks which are caused by shrinkage and creep, (ii) curling resulting in a loss of contact between concrete slab and sub-base, and (iii) unevenness In this thesis, it is aimed to investigate the effect of optimizing the concrete mix with and without additional shrinkage reducing agents (SRA) to reduce the crack risk in industrial concrete floors. Four types of concrete recipes are used (A-D) which include a recipe with optimized mix design for minimum shrinkage, a reference recipe (standard mix), an optimized mix with SRA and a fourth recipe with the reference plus SRA. The testing program extended to 224 days of age and comprised e.g. free-shrinkage, restrained shrinkage, weight change, modulus of elasticity, compressive strength, splitting tensile strength and creep of concrete. At early ages, a 28 days, there are large differences in shrinkage-time relations for different mixes. Later than 28 days, the relations are closer. A comparison among shrinkage and creep test results of four recipes shows that recipes A and C have greater crack risk than recipes B and D. The recipe D has also the best result in restrained shrinkage test. These results are because of the aggrega-te graduation, type of cement and shrinkage reducing agents which all have a direct influence on the concrete properties. These tests were done by CBI (The Swedish Cement and Concrete Research Institute) during 2009.