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.
Molecular diversity of skin mucus lectins in fish.
Among lectins in the skin mucus of fish, primary structures of four different types of lectin have been determined. Congerin from the conger eel Conger myriaster and AJL-1 from the Japanese eel Anguilla japonica were identified as galectin, characterized by its specific binding to beta-galactoside. Eel has additionally a unique lectin, AJL-2, which has a highly conserved sequence of C-type lectins but displays Ca(2+)-independent activity. This is rational because the lectin exerts its function on the cutaneous surface, which is exposed to a Ca(2+) scarce environment when the eel is in fresh water. The third type lectin is pufflectin, a mannose specific lectin in the skin mucus of pufferfish Takifugu rubripes. This lectin showed no sequence similarity with any known animal lectins but, surprisingly, shares sequence homology with mannose-binding lectins of monocotyledonous plants. The fourth lectin was found in the ponyfish Leiognathus nuchalis and exhibits homology with rhamnose-binding lectins known in eggs of some fish species. These lectins, except ponyfish lectin, showed agglutination of certain bacteria. In addition, pufflectin was found to bind to a parasitic trematode, Heterobothrium okamotoi. Taken together, these results demonstrate that skin mucus lectins in fish have wide molecular diversity.