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.

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 standard ASTM C672 de-icer salt scaling resistance test has been found to be overly aggressive to concretes containing slag cement. It was compared to the newly proposed ASTM WK9367 method, based on the Quebec BNQ test, as well as several modifications, including use of an accelerated curing regime developed in Virginia (VADOT). Sixteen concrete mixtures were studied using high-alkali cement, low-alkali cement, grade 100 slag and grade 120 slag with slag contents of 0%, 20%, 35% and 50%. Vinsol resin air-entraining admixture was compared to Micro Air®. Reducing the water cement ratio from 0.42 to 0.38 had the biggest impact on improving scaling resistance of slag concretes. In general, increased slag contents increased scaling regardless of the test method used. The Micro Air® admixture provided a lower air void actor and higher hardened air content compared to Vinsol resin.

The standard ASTM C672 de-icer salt scaling resistance test has been found to be overly aggressive to concretes containing slag cement. It was compared to the newly proposed ASTM WK9367 method, based on the Quebec BNQ test, as well as several modifications, including use of an accelerated curing regime developed in Virginia (VADOT). Sixteen concrete mixtures were studied using high-alkali cement, low-alkali cement, grade 100 slag and grade 120 slag with slag contents of 0%, 20%, 35% and 50%. Vinsol resin air-entraining admixture was compared to Micro Air®. Reducing the water cement ratio from 0.42 to 0.38 had the biggest impact on improving scaling resistance of slag concretes. In general, increased slag contents increased scaling regardless of the test method used. The Micro Air® admixture provided a lower air void actor and higher hardened air content compared to Vinsol resin.