Zoran Grdić

Analysis of carrying capacity of concrete sleepers for switches and crossings under static and dynamic load

The testing of bearing capacity under static and fatigue loading is mandatory in case of prestressed concrete sleepers for switches and crossings. The authors present the static testing required according to EN13230-4:2009, and the optional dynamic testing of sleepers for switches and crossings, which is conducted at the customer’s request only. The criterion for positive evaluation in accordance with the standard is met based on static test results. The determinants from EN13230-2: 2009, with deviations in the number of load cycles, are applied during dynamic testing.Obavezna ispitivanja prednapetih betonskih pragova za skretnice i križišta jesu ispitivanja nosivosti pragova pri statičkom opterećenju i opterećenju na zamor. U radu je prikazano obavezno statičko ispitivanje prema normi EN13230-4:2009 i dinamičko ispitivanje pragova za skretnice i križišta koje nije propisano, nego se provodi isključivo na zahtjev kupca. Na osnovi rezultata statičkog ispitivanja ispunjen je kriterij za pozitivnu ocjenu u skladu s normom. Pri dinamičkom ispitivanju su korištene odrednice EN13230-2:2009, uz odstupanja u broju ciklusa opterećenja.The testing of bearing capacity under static and fatigue loading is mandatory in case of prestressed concrete sleepers for switches and crossings. The authors present the static testing required according to EN13230-4:2009, and the optional dynamic testing of sleepers for switches and crossings, which is conducted at the customer’s request only. The criterion for positive evaluation in accordance with the standard is met based on static test results. The determinants from EN13230-2: 2009, with deviations in the number of load cycles, are applied during dynamic testing.

Environmental Aspects of Red Mud and Its Utilization as a Component of Building Materials

The Bayer process is the main industrial process covering 90 % of global production of alumina. The sintering process deals with the medium and low grades of bauxite resource. During the alumina production process, red mud is generated as a waste rock which consists of: hematite, Goethite, quartz, boehmite, calcite, tricalcium aluminate, zinc and magnesium oxides, sodium hydroxide etc. Due to high viscosity of the mud, prior to transport to the waste industrial water is added in the share of 10–15 % prior to transport to the waste disposal dump so that the pipeline transport would be facilitated. What makes red mud a hazardous pollutant is the alkaline liquid phase (Zlaticanin et al. in Prot Mater 53:292–298, 2012, Paramguru et al. Extr Metall Rev 26:1–29, 2005) [1, 2]. From the aspect of stored quantities, red mud represents a significant environmental problem (Zlaticanin et al. in Prot Mater 53:292–298, 2012) [1]. A large number of methods for sustainable disposal of red mud was developed, however, it a tendency to use the red mud in other production process, up to 20 % of it until 2025. The potential for utilization of red mud is seen making masonry products, ceramic tiles, in replacement of a part of cement or aggregate, as a component in self-compacting concretes, geopolymers. The paper provides a review of the developed methods for storage of red mud, with a goal of sustainability and cost-effectiveness. Simultaneously, the paper provides the review of potential application of red mud as a component of building materials. In the experimental part was considered the usage of red mud as a mineral admixture for making self-compacting concrete.

HYDRO-ABRASIVE RESISTANCE AND MECHANICAL PROPERTIES OF CONCRETE WITH ADDED FLY ASH

The durability of hydraulic engineering structures mostly depends on the resistance of their concrete surfaces to mechanical abrasion. In this paper, we study the hydro-abrasive resistance and mechanical properties of concrete in which cement is partially replaced with fly ash in various proportions. To evaluate these concretes, we measured their compressive strength, flexural strength, static modulus of elasticity, ultrasound velocity through concrete, and sclerometer rebound. The hydro-abrasive resistance of concrete with 15% fly ash was similar to that of reference concrete without fly ash. However, concretes with more than 15% fly ash exhibited lower resistance to abrasive erosion than the reference concrete. Also, the mechanical properties of the concrete deteriorated as the fly ash content increased.