Abstract
Concrete itself, and issues relating to the recycling and management of reinforced concrete waste, are highly relevant, especially when urban expansion is being achieved by increased building construction volumes. This research investigates concrete waste and its (re)usage possibilities and resolves several major issues related to the question of how natural materials can be replaced by compounds made from concrete waste, thereby saving natural resources. The experiment was carried out using concrete mixtures, which were combined with natural aggregates and crushed concrete waste (fraction 4/16). The resulting mix of concrete was achieved using natural aggregates, thus replacing natural aggregates with waste, which had partially and fully replaced bulky aggregates with crushed concrete waste. The main aim of the investigation was to investigate how aggregates made from crushed concrete waste impact the properties of concrete. The exothermic effect on the concrete mixture during the hardening process was investigated. Furthermore, a macrostructural analysis of hardened concrete was conducted using scanned sample images; the adhesion zone between newly formed concrete stone and aggregates derived from natural rock from crushed concrete waste was investigated. Using an electron microscope to observe aggregate from crushed concrete waste and the contact zone of hardened cement stone revealed that the aggregate from waste adheres poorly with hardened cement stone. Furthermore, both the mechanical properties of new, hardened concrete and determined resistance to frost indicators are weak. Concrete density and compression strength decreased (by up to 8% and up to 18%, respectively), and absorption increased almost twofold due to aggregates derived from crushed concrete waste, since their cleavage strength indicator was twice as high, while water absorption was four times higher than that of natural aggregate. The results indicate that recycled concrete obtained from demolished buildings is environmentally sustainable and can be recommended for lower quality concrete for use in related engineering projects.
Highlights
The world is intensively attempting to solve concrete waste recycling and re-usage problems.Concrete waste can be used as an aggregate in newly mixed concrete production [1]
Mixture CW2 (15 h 34 min), which has coarse aggregates obtained by crushing concrete waste, had a Tmax of 30.50 ◦ C, while its reaching period lengthened by 1 h 6 min when compared with fresh concrete without waste’s (CW0—14 h 28 min) temperature, for which only natural coarse aggregates were used
By using the standard research method to determine the main aggregate characteristics, it is evident that coarse aggregate obtained from concrete waste differs from aggregate made with natural rock
Summary
Concrete waste can be used as an aggregate in newly mixed concrete production [1]. Scientific research in the examined subject is directed towards appropriate addition and admixture research and how to rationally use concrete waste in new quality product production [3,4,5,6]. To develop concrete waste usage in fresh concrete, scientific research is a must, by choosing the most appropriate fresh concrete compositions or by researching additions. Materials 2020, 13, x FOR PEER REVIEW additions without admixture, which would improve concrete physical and mechanical without admixture, which would improve concrete physical and mechanical properties [7,8].properties This way,. Thiswaste way,can concrete waste can be used in usedconcrete new ecological concrete production technological concrete be used in used new ecological production technological cycles [9,10]. By cycles [9,10]
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