Currently, when a lot of attention is paid to environmental pollution, the impact of CO2, and the saving of natural resources, new structural solutions and materials are being sought that would be sustainable, long-lasting, energy efficient and competitive in the existing market. When solving these problems, we constantly face extremely strict quality requirements for the materials and technologies used. To date, the technology of shotcrete (spraying of concrete with the help of compressed air) is not very popular in Lithuania due to the high prices of the materials used for this technology. All materials required for filling are imported to Lithuania from other EU countries or Norway. Since there has been no research in Lithuania up to now on shotcrete concrete, the production of which would use local raw materials, this project aimed to popularize our country’s competitive and efficient technology, which would allow us to solve complex engineering problems, promote domestic consumption using local raw materials, and provide an opportunity to improve the technology itself on a global level. By varying the components of shotcrete during the project, the aim was to create constructive, waterproofing and heat-insulating products of shotcrete, which would be easy to process and form the surfaces of constructions with various textures and textures.
The project was carried out together with Incon UAB, which won the “Intelligence” project financed by the European Union in accordance with priority 1 “Promotion of scientific research, experimental development and innovation” of the 2014-2020 European Union funds investment action program. The total value of the project is EUR 1.019,387.98.
KTU’s role in the project was extremely significant, because with its extensive experience in the design of various types of concrete (self-compacting, self-renewing, especially strong, water-conductive, light-conductive concrete) it was able to solve all the tasks set and fulfill the main goal of the project – to create a structural, waterproofing and thermal insulation shotcrete mixture, using local raw materials, to conduct research on these products and provide final data on the basis of which these products were certified. The project was carried out in the field of development of new construction products, creating new practices and possibilities in the installation of multi-purpose constructions (water-insulating or thermal-insulating).
Project funding:
This research project is funded by European Regional Development Fund according to the 2014–2020 Operational Programme for the European Union Funds’ Investments under measure No. J05-LVPA-K “Intellect. Joint Science-Business Projects”
Project results:
During the project, mixes of all possible types (dry, moist, and wet) of sprayed concrete were created. It can be said that each of them is suitable, but a specific technology can be chosen in individual cases according to which properties of sprayed concrete are prioritized. The results showed that the technology of dry and moistened filling in most cases allows to achieve higher compressive strength, but if it is necessary to achieve greater frost resistance, the technology of wet filling is more optimal. In most cases, it was the samples formed in the latter way that showed greater frost resistance. These differences can be explained by the fact that dry or wet sprayed contains less water and, at the same time, a lower water-cement ratio, which helps to achieve higher compressive strength, while in wet shotcrete/sprayed concrete, the closed porosity is visibly formed by pores of the required size, which helps to achieve better frost resistance. During the production of heat-insulating sprayed concrete, it was found that expanded clay fillers double the structural properties of sprayed concrete, i.e. compressive strength and density (compared to foamglass fillers), but it was already known from the research conducted at the initial stage of the project that such a large increase in density (up to 1600 kg/m3) will have a negative impact on thermal insulation properties. Meanwhile, with foam fillers, on the contrary, the density and compressive strength of sprayed concrete decreased depending on the composition (from 753 kg/m3 to 1210 kg/m3 and from 3.1 MPa to 15.1 MPa), which allowed to achieve a relatively low thermal conductivity coefficient ? (<0.2 W/(m·K). In the production of shotcrete, using fractions of blowing agent of light aggregates or mixtures of blowing agent and expanded clay aggregates, samples with very good thermal insulation and mechanical properties were obtained, the value of the thermal conductivity coefficient varying from 0.174 W/(mK) up to 0.322 W/(mK), and the compressive strength ranged from 5.5-8.6 MPa (with foam fillers) to 20.2 MPa (with a mixture of foam fillers and expanded clay fillers). The obtained results show that shotcrete concrete with such properties has high prospects for use in the construction industry to install heat-insulating load-bearing structures, and using a continuous method of installation, after the installation of partitions, it is possible to avoid thermal bridges and increase the fire resistance of existing structures (due to the additional layer). The characteristics of shotcrete concrete samples obtained by dry and wet shotcrete methods are quite similar, but in most cases, shotcrete concrete filling by these two methods was obtained with higher strength (up to 35%) than shotcrete concrete shot wet. The dry shotcrete concrete had the highest strength properties, so it was this mixture that was chosen for commercial use and certification. After carrying out spraying tests of various waterproofing shotcrete concrete compositions, which included a crystalline additive, it was possible to obtain watertight shotcrete concrete (water penetration depth < 20 mm). When developing waterproofing shotcrete products, the wet shotcrete method was chosen, as it was observed that wet spraying results in greater homogeneity, which plays a decisive role in terms of waterproofing. Waterproof shotcrete, recommended for use when installing underground parking lots and stabilizing slopes, where the spraying distance usually does not exceed 35 m from the shotcrete machine. Received W14 waterproof class and depth of penetration of water under pressure up to 20 mm. In order to produce frost-resistant shotcrete, many shotcrete compositions were tested analogously, using in individual cases an air-entraining additive or shredded tire rubber (fr. 0.6/1). Although the use of these admixtures made it possible to achieve frost-resistant shotcrete, but the use of these admixtures reduced the compressive strength of shotcrete to 33%. When evaluating wet and wet spraying methods, in most cases the use of limestone powder in their composition (from 10 to 20% of cement mass) had a particularly positive influence on the frost resistance of shotcrete concrete. After completing all the research and implementing all the tasks, the main goal of the project was achieved - to certify new construction products. Received Kiwa Inspecta certificate No. 04-22-322, 2022-07-29, where it is noted that the products created by Trokret comply with the LST EN 14487-1 standard.
Period of project implementation: 2019-01-03 - 2022-07-30
Project coordinator: UAB Incon
Project partners: Kaunas University of Technology
