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Summary A modified wellbore simulation chamber (MWSC) apparatus was used to perform a series of gas migration tests to identify the vulnerability period of cement slurries containing three different percentages of CaCl2. In addition, the Virtual Cement and Concrete Testing Laboratory (VCCTL) software was used to establish a correlation between the vulnerability period and the fundamental properties of the hydrating slurry, such as the degree of hydration (DoH) and the volume fraction of hydration products. MWSC test results confirmed that as long as the slurry pressure is higher than the formation gas pressure, gas migration does not take place. However, once the slurry pressure drops below the formation gas pressure, gas migration can occur. The incorporation of CaCl2 affects the vulnerability period in two ways. First, CaCl2 increases the strength gain rate of the slurry, thus shortening the time for the slurry pressure to drop below the formation gas pressure. In addition, the incorporation of CaCl2 shortens the time needed for the slurry to develop sufficient rigidity to withstand gas migration. However, the effect of CaCl2 on the latter is significantly higher. The test results show that for the studied cement slurry, the incorporation of 2% CaCl2 reduces the vulnerability period by approximately 40%. It was also shown that regardless of the percentage of CaCl2, all three mixtures developed sufficient rigidity to withstand gas migration when they reached the DoH of approximately 25%. At this hydration stage, the sum of volume fraction of hydration products for all the mixtures was approximately 24%.

Drying shrinkage and coefficient of thermal expansion (CTE) are key material properties that affect the long-term performance of a concrete pavement. The importance of these two properties will continue to increase as extreme heat events occur more frequently with climate change. Standard laboratory tests performed to quantify these properties do not replicate the in-situ slab conditions such as spatial and temporal variation in moisture levels. As a result, laboratory-determined material property values may not accurately reflect the response of the pavement to changes in temperature. In this research, strain data from a 16-year-old in-service jointed plain concrete pavement was studied with a focus on the variation in drying shrinkage and response to temperature change. Drying shrinkage over time was estimated at different locations within the slab. Additionally, the structural coefficient of thermal expansion (SCTE) was determined as the strain response of the slab to unit changes in temperature. The frequency and amount of monthly rainfall was compared with SCTE results to explain seasonal variation in SCTE values. The results indicate that slab restraint conditions affect both the development of drying shrinkage and the SCTE of the pavement. Additionally, this study shows that both drying shrinkage and SCTE are not constant through the pavement structure, and both parameters are affected by the moisture content of the concrete. The SCTE was up to 23% larger and 22% smaller than the CTE determined through laboratory testing. In addition, only 31% of the laboratory measured ultimate drying shrinkage was realized in the slab.

The debonding mechanism of bonded concrete overlay of asphalt (BCOA) due to fatigue loading was investigated quantitatively based on an accelerated loading test. During the test, a nondestructive technique was deployed to measure the area of interface debonding. In addition, a numerical model incorporating a cohesive-zone based interface was developed to calculate the fracture energy associated with the interface debonding. Finally, the fatigue algorithm of the interface debonding was established by relating the area of debonding to the fracture energy. This fatigue algorithm can be used to predict the degree of BCOA debonding due to repeated traffic loading and the consequent stress increase in the overlay. Its development is of great significance, because it not only represents the physics of BCOA debonding more closely than the other existing models, but can also greatly improve the accuracy of the predicted life of the BCOA when incorporated into the design process.