Timely and uniform application of curing compound on concrete pavement
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Concrete curing is a critical stage during construction for volume stability, long-term strength development, and ultimate durability. Poor curing can lead to shrinkage, scaling, and other durability issues. Proper concrete curing maintains sufficient moisture in the concrete and allows continuous hydration. The high surface are-to-volume ratio of concrete pavement is making it difficult to maintain a uniform moisture content throughout the pavement, therefore curing concrete will provide a better environment for concrete to develop uniform and equal hardened properties. While a variety of curing techniques can be used, including wet curing, internal curing, and forced chemical curing, membrane-forming curing compounds (MFCCs) are often the easiest and most cost-effective technique to minimize evaporation for pavements and slabs placed on grade. The application of MFCC has been adopted by States Department of Transportation (DOT). However, achieving a quality curing has been challenging because of the limitations of techniques that can be implemented on field to evaluate the effectiveness of curing compound application on concrete pavement in real time. Some states DOTs rely on the use of the calibrated white paper sheet examination or the experience of the engineer for evaluation of the curing compound application effectiveness. Additionally, most of the evaluation tests are performed on hardened concrete and not applicable or difficult to assess for fresh concrete in the field. This study has developed a test method embedded resistance that can measure curing effectiveness in real-time during the early age of concrete. The embedded resistance as a measure to assess drying behavior of fresh concrete to quantify the effectiveness of curing Embedded resistance is a technique that uses concrete moisture content to assess the effectiveness of curing compound effectiveness on concrete. Concrete goes through phase change from plastic phase to solid during the early age. This transition is mainly caused by the hydration reaction. During the early age of concrete cement reacts with water to produce hydration reaction products and the excess water evaporate due to drying, leading to concrete microstructure development. However, at early age the presence of moisture in concrete makes concrete less resistant to current flow, as the electrical current in concrete moves through the pore spaces. With time more pores spaces in concrete are filled up with hydration reaction products, subsequently concrete becomes more resistant to the current flow, as electrical conductivity ability of concrete depends on the conductivity of the fluids inside the interconnection of pores system, the degree of saturation of the concrete, and the permeability. Therefore, using the resistance technique to trace moisture content in concrete can be an important tool to assess curing compound application effectiveness on fresh concrete. The study evaluated the effect of curing compound applications rates and application time using the embedded resistance technique. Furthermore, this study investigated the effects of curing compound application time on freshly placed concrete, the effect of curing conditions as well on the performance of concrete cured before and after the initial setting time, and lastly the effect of curing compound application rates and uniformity during the application. Tests were indexed against the standard moisture loss testing in addition to a newly developed real-time assessment of moisture loss and curing by embedded resistance. Ultimately with the goal of providing a correlated measure of moisture loss from field measurements. Lastly, surface profile degree of hydration and the maturity curve were performed in this study to under the effect of curing compound application rates on degree of hydration and strength gain. The findings from this study demonstrated that resistance is able to distinguish between samples with and without curing compound and significant differences in drying observed between the surface and relatively shallow depths. Additionally, the testing techniques were able to differentiate between the quality and rate of curing compound application and evaluate performance across a variety of environmental conditions. These findings indicate that a resistance-based approach could be a low-cost and non-destructive technique to evaluate the effectiveness of curing compound applications in real-time. Additionally, the study showed that a correlation can be found between moisture retention test, degree of hydration and the embedded resistance test. Based on the findings the embedded resistance test could be a suitable replacement for moisture loss test the test is much simpler and quicker test to be performed both in the lab and in the field.
Table of Contents
Introduction -- Literature review -- Methodology -- Preliminary investigation into using resistance techniques to assess concrete curing -- Embedded resistance as a technique to monitor concrete curing -- Determination of concrete curing-affected zone using embedded resistance technique -- Conclusion
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Ph.D. (Doctor of Philosophy)