Trade Journals for the Concrete Industry

In Qatar, blast furnace slag, fly ash and micro-silica are permitted additives for utilisation in concretes alongside Portland cement. Blast furnace slag makes up the major proportion of the concrete additives employed in Qatar but is not always available in the amounts needed and hence has to be imported, just like all other concrete constituents with the exception of Portland cement and water. The objective was to test in practice the suitability of locally available fly ash in concrete as compared with blast furnace slag, also available regionally. Test recipes were devised based on selected reference recipes as well as on the QCS 2010 series of standards valid in Qatar, on analyses of source materials and specifications concerning fresh and hardened concrete properties. All recipes were produced and verified by a concrete testing laboratory in Qatar. It was shown that utilising the fly ash available with lower water/binding agent values and slightly less superplasticiser content led to processing properties comparable with the properties of the reference concretes. This was confirmation in this case that fly ash can have a positive effect – independently of temperature – on processing properties. The early strength of concretes containing fly ash is, as expected, lower. This is also usually accompanied by weaker heat development. The results from the investigations carried out into durability show that concretes with fly ash can each be assigned the same durability class according to QCS 2010 as the reference concretes with blast furnace slag.