WATER DEMAND OF CONCRETE MIXTURES

Abstract

After summarizing the former methods for evaluating water demand of concrete mixtures [1-17], the author gives some information about his investigations of the last twenty years carried out in Hungarian Institute for Building Sciences, sponsored partly by Ministry for Building (1975-1985), partly by National Organization of Technical Development in Hungary, OMFB, (1989-1992), partly by National Foundation for Scientific Research in Hungary, OTKA (1992-1994). The detailed results came - as by-products - from these investigations, which had the aim to determine possibilities and criteria of making durable concretes. According to the results, the water demand of concretes may be separated into three stages: (a) mixture of water and aggregate with cement content from zero to a relatively small quantity (depending on the aggregate grading up to 150-250 kg/m 3 ), where the necessary water quantity (in kg/m 3 ) for a given workability is constant and depends only on the aggregate grading (from aggregate+water up to lean concrete mixtures), (b) mixture of cement, water and aggregate with cement content from 150-250 kg/m 3 up to 600-700 kg/m 3 , where the necessary water quantity depends on the aggregate grading but increases slowly with increasing cement content (ordinary con- crete mixtures), (c) mixtures from very rich concretes (cement content of about 600-700 kg/m 3) up to cement pastes, where the necessary water content for a given workability depends mainly on cement content (pastes or paste-like mixtures). The paper deals with the calculation method of necessary water quantity depending on cement content and fineness (specific surface), on aggregate grading (type and fineness) and on necessary workability.