It has been suggested that the freeze-thaw behavior of concrete can be related to the rate at which the concrete absorbs water and reaches a critical degree of saturation. After the critical degree of saturation is reached and frozen the sample begins to crack and the stiffness degrades rapidly. This mechanism was suggested by Fagerlund and then expanded by research completed under pooled fund - TPF-5-297. Despite these advancements, there is still more work that is needed. Current design practices for freeze thaw durability are not based on actual weather conditions and are instead based on artificial conditions created in ASTM C 666 testing of concrete. While these conditions seem to have been conservative, a better answer could be obtained if there was more information about how concrete wetted and dried in different environments. This research will use a novel way to measure this by combining low-cost data loggers to measure the moisture and temperature changes in a concrete sent to a number of different environments. This information will be combined with new models that account for the rate that concrete reaches a critical degree of saturation. This work will create specifications that are tailored for different weather conditions and also create a useful forensic tool that could be used to determine the loss in the life of a structure if a substandard concrete is placed. Freeze thaw damage can be suppressed by casting a small and well distributed bubble system in the concrete. The Super Air Meter (SAM) is a new method to measure the size and spacing of these bubbles while the concrete is still fresh by using sequential pressures. Under pooled fund TPF-5-297 the validity of the SAM was established in the lab and the field as well as several new tools were developed to improve the accuracy of the method. Testing was then done to investigate how different construction methods impact the air void system such as pumping. This work will aim to continue to develop the SAM and how different construction practices impact the air void system in fresh concrete.

The ultimate goal of this work is to build on previous research efforts to produce improved specifications and advance existing test methods; while, improve the underlying understanding of freeze thaw damage. This work will specifically focus on construction practices and the impact of weather.

The objectives of the proposed pooled funded study are as follows: 1. Quantify how different weather conditions impact the freeze thaw performance of concrete with low-cost data loggers. This work has been started under this existing project but these samples should be distributed in the field and used to quantify the combination of saturation and freeze thaw cycles in different states. 2. Investigate the freeze thaw performance of existing structures in different climates with different air void qualities. In combination with quantifying the weather in different environments, structures should be found in these structures with different quality of air void systems to determine how they perform. This will provide true case studies of field performance in a quantified exposure. 3. Expand the freeze thaw model to a larger range of mixtures to see if the trends still hold. 4. Further evaluation of the accuracy of the modeling predictions for determining the matrix saturation and the relationship between the secondary sorption and formation factor. 5. Better understand the damage propagation after critical saturation is reached. 6. Extension of this work to include salts such as those that result in calcium oxychloride to further improve the computational modeling predictions. 7. Determine how air void filling impacts the durability of concrete from freeze thaw cycles. 8. Develop freeze thaw specifications based on concrete quality, air void system, and local weather conditions. 9. Determine how construction methods such as pumping, mixing time, paving vibration, and hand held vibrators impact the air void spacing within concrete 10. Improve the SAM by making the measurement more consistent through developing a semi-automated testing procedure and improving reliability prediction. 11. Further refine a rapid test method that measures the uptake and fluid and resistivity of the concrete to determine the freeze thaw durability of concrete Deliverables: This proposed work will answer a number of important questions and will create several new tools to help determine the freeze thaw durability of concrete. Further, this work will create new specifications for DOTs based on their local weather conditions and quality of their concrete. These new efforts will create a new level of understanding and produce practical tools and guidance that will help DOTs change their specifications and consistently produce more durable concrete.

It is recommended that each state commit to the study for three years at $20,000 per year making a total commitment of $60,000 per state. To start the study it is recommended that at least eight states commit to the study. This study will be lead by Dr. Tyler Ley at Oklahoma State University.