Marcela Ondova

Evaluation of the Influence of Specific Surface Treatments of RBA on a Set of Properties of Concrete

High water absorption of recycled brick aggregate (RBA) is one of the most discussed parameters in terms of its application in the production of concrete—its influence on the amount of mixing water and, hence, the quality of the concrete, is usually considered negative. In this paper, different methods of decreasing the absorption of RBA and, consequently, the impact on the properties of concrete, are described. The RBA has been treated to decrease the water absorption capacity by impregnation approach using specific impregnators. Afterwards, the RBA samples have been dried at two different temperatures in the laboratory oven—20 and 90 °C. Concretes using 4/8 fraction of the treated RBA instead of natural aggregate (NA) have been mixed and tested. The effectiveness of the RBA treatments have been evaluated on the basis of their influence on the properties of the hardened concrete; by means of the following tests: flexural strength, compressive strength, capillarity, total water absorption capacity, depth of water penetration under pressure, and frost resistance. The method of ranking by ordinal scale has been used as it is suitable for the comparison of a large set of results, while results have been analyzed in terms of the most important technological parameter that influences the quality of the concrete-effective water content. Out of all the tested surface-treatments of RBA, treatment by sodium water glass has the best potential for reduction of the water/cement (w/c) ratio. When the effective w/c ratio is kept within standard limits, concretes containing treated RBA are possible to be specified for various exposure classes and manufacturing in practice. The experiment confirms that at a constant amount of mixing water, with decreasing water absorption of RBA, the effective amount of water in the concrete increases and, hence, the final properties of the concrete decrease (get worse). As the water absorption of the RBA declines, there is a potential for the reduction of the w/c ratio and improvement in the quality of the concrete.

Environmental Assessment of the Concrete Based on Blast Furnace Slag

The paper deals with the use of blast furnace slag in the production of plain concrete and with its impact on the elements of the environment. The finely ground granulated blast furnace slag with the weight of 10, 20, 30, 40, 50, 60, 80, 95 and 100 % was used as a substitute of Portland cement in ratio 1:1 of weight. The following properties were observed in all prepared experimental mixtures: consistency of concrete mixture, density of fresh concrete mixture, cube and prism strengths, water tightness, frost resistance and static modulus of elasticity. Subsequently, the life cycle assessment as well as the comparison of environmental impact of selected plain concretes by the LCA method was made. They were monitored total environmental impacts in terms of threats to soil, water, air and human health in order to select the most suitable alternative. The comparison of the reference mixture and mixture with 60% wt. of blast furnace slag showed that using secondary raw materials visibly decreased the impact in each category: Abiotic depletion of 56%; Acidification of 52%; Eutrophication of 56%; Global warming of 58%; Ozone layer depletion of 50%; Terrestrial ecotoxicity of 59%; Photochemical oxidation of 50%, Primary energy (non-renewable fossil) of 53% and of 58% for Human toxicity, Fresh water aquatic ecotoxicity and Marine aquatic ecotoxicity, respectively.

Steel Slag as a Substitute for Natural Aggregate in the Production of Concrete

This article presents the results of an experimental research dealing with the use of steel slag as a partial substitute for natural aggregates in the production of concrete composite. Comparative mixture based on natural aggregates was prepared from the fractions of 0/4, 4/8 and 8/16 mm, which were represented in the volume ratio of 40:30:30. During the experimental research, natural aggregates with the fractions of 4/8 mm, 8/16 mm were replaced with steel slag of the same faction. We have tested the input properties of natural aggregates and steel slag for the designed experimental mixtures (grain size, density, specific weight, powder density, absorption capacity, resistance to crushing, shape index). In case of concrete mixture prepared according to the experimental recipes, we have monitored the following characteristics: density of fresh concrete mixture, consistency of concrete mixture, strength characteristics - cube strength after 3, 7, 14, 21, 28 and 90 days, prism strength after 28 days. The research has discovered that substitution of natural aggregates with steel slag of the same fraction in concrete mixture is possible, without significantly affecting the strength properties of the concrete based on steel slag in comparison with the concrete based on natural aggregates.