Metallurgical sludge as sand replacement and constituent of crushed concrete aggregate

Abstract

Wastes are indispensable part of human existence. In 2017 in Poland, as much as 90.5% (113.8 million Mg) of all wastes were those related to economic activity. Already for years, the largest group of industrial waste are those from the mining, energy and metallurgical industries. Numerous scientific studies have shown possibilities of using metallurgical waste for the production of concrete and aggregates. What's more, their use can significantly reduce the negative impact on the environment, such as acidification, eutrophication, greenhouse effect or photochemical potential of ozone formation. The aim of the following research is to assess the possibility of using mixture of sludges from the metallurgical industry as a partial replacement for natural aggregates in order to reduce the negative impact on the environment as well as reduce the consumption of natural resources in accordance with the Circular Economy concept. Concrete samples containing 33% of dried and ground sludge as a substitute for sand and concrete containing crushed aggregate from concrete containing this sludge as a substitute for natural coarse aggregate in the amount of 25 and 50% and rounded aggregate from recycled concrete mix containing this sludge as a substitute for natural coarse aggregate in quantities 25 and 50%. The tests of air content, consistency and density of concrete mix as well as compressive strength tests after 2, 7 and 28 days of curing, permeability and water absorption after 28 days of curing were carried out. The sludge as partial sand replacement deteriorates the consistency of concrete mixtures, increases the air content and the density of the concrete mix. Use of recycled concrete aggregates containing sludge also deteriorated the consistency and increased the air content, but at the same time slightly reduced the density of the concrete mix. The use of sludge as a substitute for sand or recycled concrete aggregate as a replacement of natural aggregate affected the absorption of concrete. It is impossible to determine the correlation of absorbability and aggregate replacement level. The use of sludge as a sand replacement has increased the permeability of concrete to the greatest extent. The use of rounded aggregate from recycled concrete mix also but to a lesser extent, and the use of crushed recycled concrete aggregate from did not affect the permeability of concrete. In comparison of compressive strength results of reference concrete, an increase in strength by about 20% for concretes with recycled aggregate and about 40% for concrete with sludge as sand replacement was found. In addition, the conducted research has shown that it is possible to make concrete with the use of metallurgical sludge as a 30% replacement of sand, and then to create aggregate from the resulting composite.