The majority of residents in Latvia live in standard multi-storey residential buildings, which were constructed between 1950 and 1992. At present, these buildings are obsolete; besides, in the course of construction process the durability and reliability levels were planned to be insufficient. In Riga, residents of standard multi-storey residential buildings do not support building renovation and are passive, despite the availability of the EU and government support as well as co-financing of building renovation projects. The majority of the respondents assume that the apartment is the most significant asset of the family. Moreover, 34 % - 69 % of the participants have renovated their apartment and save resources within their apartment boundaries. Only some respondents evaluate the technical condition of communal property, but most respondents do not have information concerning resource supply and energy accounting as well as are not interested in resource saving possibilities within the building in general, and do not understand the importance of technical maintenance of the building.

This study determined the elastic properties of “green” concrete with cement partially replaced by oil shale ash (OSA) and reinforced with short basalt integral fibers (BIFs). Commercially available Deutsche Basalt Faser (DBF) GmbH Turbobuild Integral basalt fibers were used. There is currently a high demand both for strengthening concrete and applying ecological approaches with respect to circular economy. Oil shale ash is the byproduct of oil shale combustion. Basalt fiber is produced by melting basalt rock. Both BIF and OSA are used as additives in concrete. Cement replacement by OSA non-linearly changes the concrete’s strength properties, and the addition of BIF improves them. An experimental investigation was conducted using four-point bending tests and cube sample compression tests. Theoretical methods such as Voigt and Reuss boundaries, the Halpin–Tsai method, and the Mori–Tanaka method were used to predict the elastic properties of the fabricated samples. The theoretical models can provide useful information, although they may not fully capture the real properties observed experimentally. The results show that BIFs protect against instant brittle destruction. The experiments demonstrated an optimal OSA concentration for a fixed amount of BIF, resulting in the highest load-bearing capacity of the concrete. The addition of either 15% OSA only or 20% OSA and CBF can increase the stiffness of the concrete. This article provides guidance to the construction sector on using OSA and CBF together.