The flatbed scanner method for air void analysis of concrete is investigated through a comparison study with the standard ASTM C457 manual and Rapid Air 457 test methods. Air void parameters including air content and spacing factor are determined by image analysis of a large population of scanned samples through contrast enhancement and threshold determination procedures. It is shown that flatbed scanner method is giving comparable results to manual and Rapid Air 457 methods. Furthermore, a comparison of the air void chord length distributions obtained from the two methods of flatbed scanner and Rapid Air 457 has been implemented in this research. The effect of having different settings in the scanning process of scanner method is also investigated. Moreover, a threshold study has been performed that showed the flatbed scanner method can be employed in combination with manual and Rapid Air 457 methods as a time and cost saving strategy.

The flatbed scanner method for air void analysis of concrete is investigated through a comparison study with the standard ASTM C457 manual and Rapid Air 457 test methods. Air void parameters including air content and spacing factor are determined by image analysis of a large population of scanned samples through contrast enhancement and threshold determination procedures. It is shown that flatbed scanner method is giving comparable results to manual and Rapid Air 457 methods. Furthermore, a comparison of the air void chord length distributions obtained from the two methods of flatbed scanner and Rapid Air 457 has been implemented in this research. The effect of having different settings in the scanning process of scanner method is also investigated. Moreover, a threshold study has been performed that showed the flatbed scanner method can be employed in combination with manual and Rapid Air 457 methods as a time and cost saving strategy.

Air entraining admixtures (vinsol or non-vinsol) are used in concrete mixes that will be exposed to freeze-thaw cycles or sulfate attack. Entrained air is intended to improve the durability and resistance of hardened concrete to freeze-thaw cycles. However in many instances a significant loss of compressive strength has been observed in concrete mixes containing non-vinsol admixtures. Mixture forensic analysis has determined air void coalescing to be the main factor in observed low compressive strengths. The result of air void coalescing is the over design of compressive strength to account for the possible lower strengths and decreased confidence in the compressive strengths obtained during the quality control/assurance process.

Master of Science / Department of Civil Engineering / Kyle A. Riding / Air void clustering around coarse aggregate in concrete has been identified as a potential source of low strengths in concrete mixes by several Departments of Transportation around the country. Research was carried out to (1) develop a quantitative measure of air void clustering around aggregates, (2) investigate whether air void clustering can be reproduced in a laboratory environment, (3) determine if air void clustering can blamed for lower compressive strengths in concrete mixes, (4) and identify potential factors that may cause clustering. Five types of coarse aggregate and five different air entraining agents were included in the laboratory study to see if aggregate type or chemical composition of air entraining agent directly relates to air void clustering. A total of 65 mixes were made, implementing the frequently used technique of retempering that has been previously associated with air void clustering around aggregates. Compressive strength specimens as well as samples for hardened void analysis were made. Compressive strength at 7 and 28 days was determined and the automated hardened void analysis (including a new method of clustering evaluation) was performed on all samples. It was found that it is possible to reproduce air void clustering in laboratory conditions. However, the results have shown that retempering does not always cause air void clustering. It was also observed that air void clustering is not responsible for a decrease in compressive strength of retempered concrete as neither aggregate type nor chemical composition of air entraining agent had a significant impact on severity of void clustering around coarse aggregate particles. It was also found that the total air content and an inhomogeneous microstructure and not air void clustering were responsible for lower strengths.

The presence of moisture in hot mix asphalt (HMA) causes loss of strength and durability of the mix, which is referred to as moisture damage. This study deals with the development of experimental methods for measuring total suction in HMA, which can be defined as the free energy state of water in HMA mixes. The total suction is related to the ability of moisture to get into the mix under unsaturated conditions; it is also related to the ability of the mix to retain moisture. Soil suction has been studied extensively. However, suction in HMA as a porous material and its relationship to moisture damage have not been studied. The development of a procedure to measure the total suction in HMA mixes is the first objective of this research. The second objective is to relate suction measurements to physical and chemical properties of the mixtures. The objectives were achieved in two phases. In the first phase, the total suction was measured in HMA specimens with different types of aggregates (limestone and granite), and with different air void distributions and aggregate gradations. The results of this phase showed that the drying test using a 60 oC temperature-controlled room is the proper setup for measuring the total suction in HMA using thermocouple psychrometers. The characteristics of suction-moisture content curves were found to be related to the air void distribution in HMA. In the second phase, total suction was measured in sand asphalt specimens. These specimens had different combinations of aggregates and binders with different bond energies and exhibited different field performance in terms of resistance to moisture damage. The suction measurements in sand asphalt specimens were used to calculate the moisture diffusion coefficient. The results revealed that water diffused into sand asphalt specimens that are known to have poor resistance to moisture damage faster than those that are known to have good resistance to moisture damage

The presence of moisture in hot mix asphalt (HMA) causes loss of strength and durability of the mix, which is referred to as moisture damage. This study deals with the development of experimental methods for measuring total suction in HMA, which can be defined as the free energy state of water in HMA mixes. The total suction is related to the ability of moisture to get into the mix under unsaturated conditions; it is also related to the ability of the mix to retain moisture. Soil suction has been studied extensively. However, suction in HMA as a porous material and its relationship to moisture damage have not been studied. The development of a procedure to measure the total suction in HMA mixes is the first objective of this research. The second objective is to relate suction measurements to physical and chemical properties of the mixtures. The objectives were achieved in two phases. In the first phase, the total suction was measured in HMA specimens with different types of aggregates (limestone and granite), and with different air void distributions and aggregate gradations. The results of this phase showed that the drying test using a 60 oC temperature-controlled room is the proper setup for measuring the total suction in HMA using thermocouple psychrometers. The characteristics of suction-moisture content curves were found to be related to the air void distribution in HMA. In the second phase, total suction was measured in sand asphalt specimens. These specimens had different combinations of aggregates and binders with different bond energies and exhibited different field performance in terms of resistance to moisture damage. The suction measurements in sand asphalt specimens were used to calculate the moisture diffusion coefficient. The results revealed that water diffused into sand asphalt specimens that are known to have poor resistance to moisture damage faster than those that are known to have good resistance to moisture damage

The quantitative nondestructive evaluation (NDE) of cement-based materials is a critical area of research that is leading to advances in the health monitoring and condition assessment of the civil infrastructure. Ultrasonic NDE has been implemented with varying levels of success to characterize cement-based materials with complex microstructure and damage. A major issue with the application of ultrasonic techniques to characterize cement-based materials is their inherent inhomogeneity at multiple length scales. Ultrasonic waves propagating in these materials exhibit a high degree of attenuation losses, making quantitative interpretations difficult. Physically, these attenuation losses are a combination of internal friction in a viscoelastic material (ultrasonic absorption), and the scattering losses due to the material heterogeneity. The objective of this research is to use ultrasonic attenuation to characterize the microstructure of heterogeneous cement-based materials. The study considers a real, but simplified cement-based material, cement paste - a common bonding matrix of all cement-based composites. Cement paste consists of Portland cement and water but does not include aggregates. First, this research presents the findings of a theoretical study that uses a set of existing acoustics models to quantify the scattered ultrasonic wavefield from a known distribution of entrained air voids. These attenuation results are then coupled with experimental measurements to develop an inversion procedure that directly predicts the size and volume fraction of entrained air voids in a cement paste specimen. Optical studies verify the accuracy of the proposed inversion scheme. These results demonstrate the effectiveness of using attenuation to measure the average size, volume fraction of entrained air voids and the existence of additional larger entrapped air voids in hardened cement paste. Finally, coherent and diffuse ultrasonic waves are used to develop a direct relationship between attenuation and water to cement (w/c) ratio. A phenomenological model based on the existence of fluid-filled capillary voids is used to help explain the experimentally observed behavior. Overall this research shows the potential of using ultrasonic attenuation to quantitatively characterize cement paste. The absorption and scattering losses can be related to the individual microstructural elements of hardened cement paste. By taking a fundamental, mechanics-based approach, it should be possible to add additional components such as scattering by aggregates or even microcracks in a systematic fashion and eventually build a realistic model for ultrasonic wave propagation study for concrete.

Field compaction of asphalt mixtures is an important process that influences performance of asphalt pavements; however there is very little effort devoted to evaluate the influence of compaction on the uniformity and properties of asphalt mixtures. The first part of this study evaluated relationships between different field compaction patterns and the uniformity of air void distribution in asphalt pavements. A number of projects with different asphalt mixture types were compacted, and cores were taken at different locations from these projects. The X-ray Computed Tomography (X-ray CT) system was used to capture the air void distributions in these cores. The analysis results have revealed that the uniformity of air void distribution is highly related to the compaction pattern and the sequence of different compaction equipment. More importantly, the efficiency of compaction (reducing air voids) at a point was found to be a function of the location of this point with respect to the compaction roller width. The results in this study supported the development of the "Compaction Index (CI)," which quantifies the degree of field compaction. The CI is a function of the number of passes at a point and the position of the point with respect to the compaction roller width. This index was found to correlate reasonably well with percent air voids in the pavement. The CI calculated from field compaction was also related to the slope of the compaction curve obtained from the Superpave gyratory compactor. This relationship offers the opportunity to predict field compactability based on laboratory measurements. The compaction of longitudinal joints was investigated, and recommendations were put forward to improve joint compaction. The air void distributions in gyratory specimens were related to the mixture mechanical properties measured using the Overlay and Hamburg tests. The second part of this study focused on studying the relationship between air void distribution and moisture diffusion. A laboratory test protocol was developed to measure the diffusion coefficient of asphalt mixtures. This important property has not measured before. The results revealed that the air void phase within the asphalt mixtures controls the rate of moisture diffusion. The measured diffusion coefficients correlated well with the percent and size of connected air voids. The measured diffusion coefficient is a necessary parameter in modeling moisture transport and predicting moisture damage in asphalt mixtures. The last part of this study investigated the resistance of asphalt mixtures with different percent air voids to moisture damage by using experimental methods and a fracture mechanics approach that accounts for fundamental material properties.

The objective of this study is to characterize the properties of typically adopted drainage layer materials in VA, OK, and ID. A series of laboratory tests have been conducted to quantify the volumetric properties, permeability and mechanical properties of the laboratory-compacted asphalt treated and cement treated permeable base specimens. The modified test protocols to determine the dynamic modulus of the drainage layer materials have been provided, which can be followed to determine the dynamic modulus of the drainage layers as level 1 input in Mechanistic-Empirical (M-E) pavement design. The measured dynamic moduli have been used to calibrate the original NCHRP 1-37A model to facilitate its application on drainage layer materials for prediction of the dynamic modulus as level 2 input. The compressive strength of the cement treated permeable base mixture of different air void contents has also been quantified in laboratory. Numerical simulations are conducted to investigate the location effects and the contribution of the drainage layer as a structural component within pavement. The optimal air void content of the drainage layer is recommended for Virginia, Oklahoma and Idaho based on the laboratory-determined permeability and the predicted pavement performances during 20-year service life. / Ph. D.

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