ترجمه مقاله روش طرح اختلاط برای واحدهای بلوک های بتنی

The use of concrete masonry units for high-rise load bearing construction has created a need for concrete block with high compressive strength. To achieve high strength levels, block producers generally define concrete mixtures by a trial and error process. The most common procedure is to produce some trial mixtures possessing different cement content using the equipment available in the block plant and test the strength of blocks. This approach is costly, time consuming and generally leads to expensive solutions for using large amounts of cement. Besides, it makes difficult to test new combinations of aggregates and admixtures once disturbs very much the plant routine. In this paper is presented a mix design procedure for structural concrete blocks based on laboratory tests. Initially a reference mixture is studied. In this phase it is possible to vary the type and proportion of aggregates, admixtures and water content in order to achieve a suitable face texture with lower energy of compaction. After that, several mixtures are produced varying the cement content and density. Cylindrical specimens was produced with these mixtures and tested in compressive strength. With the results, it is elaborated a mix design chart where the desired compressive strength can be obtained by varying the aggregate/binder ratio and density. The last phase is testing some selected mixtures in actual block machine, determining both density and compressive strength. With the results it is possible to make the final adjustments in the mix proportions. The application of this procedure in a block plant of the south of Brazil led to satisfactory results showing that is possible to forecast of the mechanical resistance of the concrete blocks starting from laboratory studies in cylindrical specimens and also demonstrated the importance of the control of several parameters related to the productive process for the compressive strength of the units.