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A study examining air-entrainment in fly ash concretes combined with different Portland cements (PCs) is described. Tests were carried out (using five PCs, ten fly ashes and a standard chemical reagent (to entrain air)) on paste suspensions (foam index), mortar and concrete to quantify the material effects. Preliminary tests indicated that the foam index increased with the fineness (specific surface area (SSA) (by nitrogen adsorption Brunauer-Emmett-Teller (BET) method)) of the PC used (varied by grinding) with fly ash. Reductions in the property were found with increasing alkali content in the paste suspensions (by sodium hydroxide addition), which tended to be slightly greater with higher SSA/lower alkali content fly ash. Tests on the wider range of PCs and fly ashes gave a strong correlation between their combined SSA and foam index, with their combined alkali content having less effect on the latter. The influence of fineness was again apparent in the mortar tests, which also showed that when PC and fly ash were of comparable SSA, a change in either material had a similar effect on air-entrainment. However, fly ash had an increasing influence as the difference in this between materials became greater. The results also suggest that air losses after mixing tend to increase with the SSA of PC + fly ash (and hence admixture dose). Similar effects were generally noted in the tests made on concrete. A possible approach to controlling air-entrainment in fly ash concrete may therefore be to ensure that its SSA is similar to that of the PC with which it is used. A test method to enable this to be evaluated is suggested. [ABSTRACT FROM AUTHOR]

A study examining damaging alkali-aggregate reaction (AAR) in concretes containing recycled aggregate is described. This considered masonry units, concrete, demolition waste, road planings, slate and plasterboard. Alkali release tests indicated that masonry units tended to release more alkali than recycled concrete (with higher levels generally obtained from recently produced materials), with slate and plasterboard giving least. Accelerated mortar expansion (reactivity) test results suggested there was a low risk of AAR for the materials. Concrete tests were then made using BS 812-123 exposure conditions. The concretes were proportioned (i) following the standard mixes (NaO = 7·0 kg/m) with recycled materials replacing fine or coarse aggregate in a low-reactivity aggregate combination and (ii) at high alkali level (NaO = 5·4 kg/m) with the materials as fine aggregate in a normal-reactivity aggregate combination. The tests for (i) gave results for the recycled materials indicating low reactivity, with classifications of non-expansive or probably non-expansive to BRE Digest 330. For (ii), expansions for the materials were mainly similar/slightly higher than those found for (i). However, recycled concrete that previously exhibited damaging AAR had greater expansions. Selected concretes were exposed at an external site for up to 8·5 years, during which observations by microscopy were carried out. These gave general agreement with the laboratory tests. The practical implications of the study are reviewed. [ABSTRACT FROM AUTHOR]