This dissertation work is devoted to solving the important scientific and technical problem of obtaining concrete of strength classes C12/15, C16/20, C20/25 with coarse aggregates of recycling origin.
In the conditions of a large amount of destruction caused by military actions there is a need to reuse significant volumes of construction waste after appropriate processing. Among the total mass of demolition waste a significant share is concrete scrap, which after grinding and fractionation can be used as coarse aggregate for concrete. Thus the question arises of taking into account the features of that aggregate when mix designing and choosing the composition of concrete with given properties.
In the first chapter the sources of concrete and reinforced concrete waste have been analyzed. Based on the study of existing regulatory and technical and declarative documents in Ukraine it has been established that during the dismantling of individual building structures, demolition of buildings and structures, new construction design and construction companies are required to implement measures aimed at maximizing the reuse of construction waste, after appropriate processing if necessary. The global experience of researching the properties and applications of recycled aggregates since the 1970s has been considered.
Based on the analysis of data from literary sources the peculiarities of recycled concrete aggregates (RCA) and the characteristic properties of concrete with RCA have been determined. It has been established that overall, the physical, mechanical, and operational properties of RCA and concrete with RCA are somewhat inferior compared to natural aggregates (NA) and concrete with NA. However, depending on the content of RCA, grinding methods, quality and thoroughness of sorting and fractionation of RCA, it is possible to achieve the specified properties of concrete with RCA, sometimes with slight deterioration. At the same time the cost of such concrete is significantly lower compared to concrete with NA.
RCA is obtained by crushing and processing of used concrete. Accordingly, RCA consists of two main phases – natural aggregate and residual mortar. Therefore, concrete with RCA is a more complex system due to the presence of additional phases – residual mortar and the interfacial transition zone (ITZ) between it and the NA. These phases define the characteristics of RCA and concrete with RCA. Existing methods of mix design of concrete with RCA have been analyzed. It has been found that these methods currently tend to be more theoretical and are quite time-consuming.
The common in Ukraine calculation-experimental method of mix design of heavy concrete, which is the basis of national standards, has been reviewed. It has been determined that existing approaches do not adequately account for the peculiarities of RCA and the regularities of the formation of concrete structure with RCA. Based on this, a scientific hypothesis has been proposed regarding the possibility of incorporating the features of RCA when mix designing and choosing the composition of concrete by introducing some experimentally determined adjustments that account for the origin and physical and mechanical properties of RCA. Also, the limitations adopted in this work have been established in the chapter regarding the production of heavy concrete with RCA for some types of structures operating in compression and bending.
In the second chapter, characteristics of the local materials used during the research are given, along with a description of methods for experimental investigations into the properties of RCA and concrete containing RCA. The grain composition of natural aggregates is given, the chemical and mineralogical composition of Portland cement PC II/B-Sh-400 (CEM II/B-S 32.5 N) produced by Heidelbergcement, Kryvyi Rih, and the normal density of cement dough are determined. It has been determined that the grain composition of NA in its natural state does not meet the requirements of national standards, necessitating corrections. The compositions of the concretes, the samples of which were to be crushed, were designed, and the method, tools and equipment used for crushing were described.
The third chapter presents the results of physical and mechanical tests of RCA obtained after crushing concrete samples aged 28 days, 90 days and 180 days. It has been established that the grain composition of fractions (fine and coarse) formed after grinding does not meet the requirements of DSTU B V.2.7-75-98 due to the excessive volume of fractions 10...20 mm and 0…5 mm. At the same time the grain composition of coarse fractions, which is actually RCA, generally meets the requirements of regulatory documentation.
