Concrete Pavement Mixture Design and Analysis (MDA): Evaluation of Foam Drainage Test to Measure Air Void Stability in Concrete
The stability of air bubbles in fresh concrete can have a profound influence on the potential durability of the system, because excessive losses during placement and consolidation can compromise the ability of the mixture to resist freezing and thawing. The stability of air void systems developed by some air entraining admixtures (AEAs) could be affected by the presence of some polycarboxylate-based water reducing admixtures (WRAs). The foam drainage test provides a means of measuring the potential stability of air bubbles in a paste. A barrier to acceptance of the test was that there was little investigation of the correlation with field performance. The work reported here was a limited exercise seeking to observe the stability of a range of currently available AEA/WRA combinations in the foam drainage test; then, to take the best and the worst and observe their stabilities on concrete mixtures in the lab. Based on the data collected, the foam drainage test appears to identify stable combinations of AEA and WRA.
Identifying incompatible combinations of concrete materials : volume I, final report.
Unexpected interactions between otherwise acceptable ingredients in portland cement concrete are becoming increasingly common as cementitious systems become more and more complex and demands on the systems are more rigorous. Such incompatibilities are exhibited as early stiffening or excessive retardation, potential for uncontrolled early-age cracking, and unstable or unacceptable air void systems. A number of test methods have been reviewed to assess their usefulness in detecting incompatibility early to help prevent problems with pavements in the field. A protocol has been developed to allow product manufacturers, concrete producers, contractors, and owners to monitor their materials and concrete systems. The protocol is phased to allow relatively simple field tests to provide early warnings of potential problems and then central laboratory tests to support and confirm the field work. This is the first of two volumes. The other volume in this series is: Federal Highway Administration (FHWA) HRT-06-080, "Identifying Incompatible Combinations of Concrete Materials: Volume II—Test Protocol."
ACHIEVING AND VERIFYING AIR CONTENT IN CONCRETE
The objective of this research program was to resolve discrepancies in measurement of concrete air content between fresh and hardened states. It consisted of three phases. In the first phase, data and information related to air content measurement were collected. A database was developed using studies where air contents were determined in the fresh and hardened states on the same batches of concrete. A questionnaire was also circulated in order to gather information from practical applications. In the second phase, a laboratory investigation was conducted to evaluate the effects of air-entraining admixture, cement alkali level, temperature, and retempering on changes in concrete air contents between fresh and hardened states. Following the completion of Phase II, a field-simulation study was conducted in order to examine the influence of field conditions on air content measurements. A statistical analysis was conducted on test results in order to define the significance of each factor affecting air content measurements. This study indicated that none of the factors evaluated have a significant effect on air content discrepancy. Although air content of hardened concrete may differ from air content of fresh concrete measured with the pressure meter, in most cases these differences are insignificant.