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.
A modified foam drainage test protocol for assessing incompatibility of admixture combinations and stability of air structure in cementitious systems
Abstract Unexpected interactions between chemical admixtures and other ingredients in a cementitious systems may occur as cementitious systems become more complex and demands on the systems are more rigorous. Incidents related to use of chemical admixtures in highway concrete have been reported in some states. A common problem was instability of the air void system with air contents changing significantly during handling and placing. The stability of an entrained air void system in fresh concrete can have a profound influence on the potential durability such as freeze/thaw resistance. A technique known as the foam drainage test has been in use to assess the potential stability of air void system in fresh paste samples in the laboratory. However, there has been little reported work on the correlation between the test results and air void system in hardened concrete. In addition, the method, as published, is not rigorous with respect to some factors such as test temperature, and there is no pass/fail limit to evaluate testing results. The work presented here sought to evaluate the effects of variables such as environmental conditions, testing procedures, and admixture dosages on the data obtained. Multiple cementitious combinations with various chemical admixtures, such as air entraining and water reducing agents, were used to propose a pass/fail limit for admixture combinations. In addition, selected combinations were used to prepare concrete specimens and the air void system was evaluated after handling activities were mimicked in the lab.
Low-temperature thermal expansion of PEEK, HTA and some of their composites reinforced with carbon fibres
Abstract The thermal expansion of poly(ether ether ketone), a modification of poly (ether sulphone) and carbon fibre reinforced composites of these polymers has been measured over the range −153 to 27°C with a push-rod diameter. Where other measurements are available for comparison, agreement is obtained within experimental scatter. Some multidirectional composites are tested and the measured values of thermal expansion are explained qualitatively. It is thought that the specimen size has had a significant effect on these results. The longitudinal and transverse coefficients of thermal expansion of Hercules AS4 fibre have been calculated.