One of the most voluminous types of modern humanity’s vital activity waste is concrete and reinforced concrete, which is formed as a result of necessity of reconstruction of outdated buildings, imperfection of production technology and accumulation of substandard large construction products at companies, as well as natural phenomena and large-scale military actions.
Undoubtedly, the increasing year by year volume of construction garbage and arising solutions of the environmental protection problem, inevitably would lead to the need of its re-use.
Information search shows that the main target product of concrete waste recycling is the re-used coarse aggregate (10-40mm) applicable for the use of new concrete mixtures as macadam (crushed stone) and, practically, all investigations in this direction are targeted on improvement of the quality of such aggregate and enhancement of such equipment. Moreover, it is noted, that the fine fraction of scattered mass is up to 40% of the total amount of concrete waste and, as an industrial waste, it is used, in general, as a backfilling for various constructions.
It should be noted that this method of recycling refers only to heavy concrete, since in such concrete the strength of a large aggregate is much greater than the strength of the hardened cement stone. As a result, the resulting fine fraction is mainly represented by a crushed cement stone.
The presented project is devoted to the investigations, which directionality is fundamentally different from the known in the literature since it is devoted to more efficient use of both small fraction of crushed mass of used concrete and ground concrete scrap as a whole. The results of the investigations, conducted in the Institute of Mechanics of NAS RA, have become the basis for this purpose.
Since the early 50s of the last century experimental investigations of concrete, ripened and stored in various conditions, have been conducted in the Institute, with the aim to explore the influence of number of factors on the strength and deformational properties of concrete and reinforced concrete with taking into account the material aging. This explains the presence in the Institute of the experimental samples of more than half a century old, unique because of the availability of full information about their origin.
As a result of investigations, conducted in the Institute of Mechanics and devoted to the study of strength properties’ dependence on the duration of water storage of heavy and lightweight concrete of 2 and 23 years of age, an idea of concrete secondary hardening was suggested. Saying hardening we mean the resumption of hydration process of unreacted cement grains, presenting in concrete.
In order to confirm the truth of the suggested assumption the X-ray-phase analysis was done on the perlite-pumice-concrete samples of the age of 57 years and heavy concrete of the age of 39 years. The results of analysis confirm the presence of the significant amount of rough concrete grains in spent concrete.
According to data of some authors the amount of unhydrated Portland cement within concrete in old reinforced concrete structures can reach 50% of the initial Portlandcement, used during these constructions’ production.
The foregoing shows the presence of quite large internal resource in recycled concrete. Scientifically-based use of this resource can help new construction materials to be fabricated without any application of traditional binders (cement, lime, liquid glass). For this purpose in the Institute of Mechanics new construction materials were attempted to be extracted from the crushed mass of concrete samples, which were made in the 50s of the last century. The attempt was successful. Without any application of traditional binders the construction material, which density does not exceed the parent concrete’s density and which compressive strength is significantly greater, was extracted.
The aim of this project is to implement a non-traditional approach to the problem of recycling of construction waste by developing technologies to product new construction materials extraction without addition of binders both from small fraction of spent concrete, which practically is an unrecycled waste for manufacturers, who are interested in recycling concrete and reinforced concrete waste, and from small fraction of crushed mass on the whole.
The notes last approach to solve the problem is more reasonable to apply in the case of utilization of non-load-bearing elements of buildings and structures made of light and fine-grained concretes, which volume forms about 30-40% of the total volume of structures. The application of this approach is also expedient for the utilization of heavy concretes in regions, which are rich with appropriate stone quarries.
We are planning to develop the technology of hydrothermal processing, which is traditional for concrete, as well as the technology of high temperature processing, inherent for ceramic materials. It is expected that materials, extracted by the method of hydrothermal processing, will have a compressive strength of 10 up to 25 MPa and will be used for production of silicone brick and concrete blocks for internal and external building walls. Materials, which will be extracted by the method of high temperature processing, will have a compressive strength of at least 45 MPa and a bent (flexure) strength of 15 up to 25 MPa. It is supposed that it is more expedient to use these materials to produce tiles and ceramic blocs for floors as well as for building walls.
In the case of successful implementation of the project, which final results will become a commercialized product, the following main problems will be solved, having both scientific and practical importance:
· experimental confirmation of expediency of quarry waste application in new building materials and production of some construction materials as ingredients which can stimulate reactivity of non-hydroactive cement grains, presenting in recycled concrete;
· development of practically wasteless technologies of production of new construction materials of various purposes both from small fraction of crushed mass of used concrete and from crushed concrete waste on the whole.
Also the following priority issues, relative to the ISTC, will be solved: provide the scientists, involved in work with armaments, with a peaceful alternative job and involve promising young professionals in studies; resumption and further development of contacts with scientific centers of CIS countries and establishment of new contacts with leading scientific centers; support of development of technologies which promote environmental protection.
The presented project is planned to be implemented in 36 months. It consists of 7 tasks which are divided into 24 subtasks.
The role of foreign collaborators is to exchange the information during the project implementation, to discuss the obtained results and technical reports, to organize joint seminars and to publish joint articles.
The bases of the work, necessary to implement the mentioned project tasks, are mainly the applied investigations and, simultaneously, the technologies development. The technical approach and methodology of these investigations implementation is the following: the determination of necessary physical and mechanical characteristics of initial recycled concrete and appropriate activating ingredients, as well as of developing construction materials, will be conducted according to the current standards.
During the chemical analysis of initial ingredients the methods of silicate and X-ray-phase analysis will be used. Mineral-graphic analysis of materials will be implemented with the help of polarizing microscope (petrographic method). It is planned to conduct the mentioned investigations together with the Georgian institution - Union “Science and Energetics".
The optimal regimens of hydrothermal and high temperature treatment of billet samples will be chosen by the experiment to obtain an appropriate product.
The scientific potential of Defense scientists and experience, gained by the technical staff during the execution of works to construct composite materials with predetermined properties in the framework of already finished projects A-540 “Development of heat-resistant aluminum-oxide vacuum-tight ceramics”, A-892 “Reinforced polymer composite materials of frictional and general-technical purposes” and A-1167 “The new technology for production of better quality perlite filler and materials on its basis”, guarantee success in achieving the goal of the project.
