The Influence of Heat and Mechanical Treatment of Concrete Rubble on the Properties of Recycled Aggregate Concrete

Abstract

Concrete is a building material commonly used for ages. Therefore, in the result of repairs or demolition of building structures, large amounts of concrete rubble are created, which requires appropriate management. The aim of the realized research was to determine the influence of heat and mechanical treatment of concrete rubble on the properties of recycled aggregate concrete. The research experiment included 12 series, with three variables: X1—roasting temperature (300, 600, 900 °C), X2—time of mechanical treatment (5, 10, 15 min), X3—content of coarse recycled aggregates (20, 40, 60% by volume). Two additional series containing recycled aggregate without treatment and natural aggregate were also prepared. Established properties of individual aggregates have confirmed a positive effect of thermo-mechanical treatment. Then, based on the results of compressive strength, flexural strength, Young’s modulus, volumetric density, water absorption, water permeability and capillarity, the most favourable parameters of heat and mechanical treatment of concrete were determined. The test results showed that appropriate treatment of concrete rubble allows to obtain high-quality coarse aggregate and valuable fine fraction. This was also confirmed by the macro- and microscopic observations of the aggregate and separated cement paste. Works realized on the concrete recycling method resulted in obtaining a patent PAT.229887.

Properties of Concrete with Recycled Concrete Aggregate Containing Metallurgical Sludge Waste

“…This applies to mixtures containing 50% and 100% RCA [23]. Similar results are presented in [24]. The studies described in [25] have shown that mixes containing 50% and 100% RCA and modified with a superplasticizer have reached the same consistency as the reference mix-therefore it is possible to control the consistency of mixes containing even large amounts of RCA.…”

“…The strength of concrete containing 100% RCA is lower by about 8% after 2 days but higher by about 5% after 7 and 28 days [23]. After 28 days a decrease in compressive strength by about 10% was found [24]. Similar relationships were found for mortars containing 25%-100% fine RCA [28].…”

The Properties of Composites with Recycled Cement Mortar Used as a Supplementary Cementitious Material

“…The coarse aggregate (>4 mm) obtained in recycling process can be used in new concrete as a substitute of natural aggregate. The test results of properties of concrete with recycled aggregate were presented in [8].…”

“…Research on the recycling of concrete is mainly devoted to finding the most effective way to obtain recycled aggregates of the best quality, which usually means removing the impurities from the surface of the natural aggregate grains. The recycled aggregate's quality is closely related to the adhered cement paste properties, since the bond between the natural aggregates and the cement paste is usually weak in the interfacial transition zone [5][6][7][8]. It is widely accepted that the presence of cement paste in recycling concrete aggregate causes its worse physical, mechanical and chemical properties compared to natural aggregates.…”

“…The method allows obtaining high-quality secondary aggregate and a fine fraction that can be used as a partial cement replacement. Research on the effect of recycled aggregate on new concrete properties has been described in [8].…”