The Air Entertainment of Mortar

The history of air entrainment and of mortar is considered and the current picture with respect to air entrained mortar reviewed. A review is presented of the literature dealing with the mechanisms of air entrainment, the materials used and the effect on the amount and type of air of imposed conditions of procedure and mix design. Methods for determination of air content are reviewed and comparative experimental research reported. The major conclusions are that the current British Standard test methods are insufficient with respect to procedural detail and any assessment of statistical accuracy. Of the two, the density method is the most reproducible. Research into the effect of many variations in mix proportion, material type, plant and procedure on air content is reported. For ‘the air entraining agent tested it was found that the air content generally decreased with mixing time having reached a maximum after two minutes mixing. The reduction in air content was not related to drying or to attrition of the sand and was more marked with increasing fineness of the sand originally used. It was unaffected by silt or clay in the sand. With very high cement contents there was little or no air loss with mixing time. Sand grading, cement fine ness and alkali content affect air content but neither sand particle shape nor composition has any affect.