Vlastimir Radonjanin

Recycled Aggregate Concrete for Structural Use – An Overview of Technologies, Properties and Applications

By the end of the twentieth century generation of huge amounts of waste became one of the biggest environmental problems in the majority of the world. Construction and demolition waste (C&D) makes almost half of the total industrial waste. On the other hand, consumption of natural aggregate as the largest concrete component is constantly and rapidly increasing with the increase in the production and utilization of concrete. Recycling represents one way to convert a waste product into a resource. It has the potential to reduce the amount of waste disposed of in landfills and preserve natural resources while limiting environmental disturbance. This paper presents a review of traditional and advanced production technologies that make recycling of concrete in a completely closed loop technically feasible. The specific features of recycled aggregate concrete (RAC) mix proportioning methods affected by the recycled aggregate (RA) properties are presented. The mechanical, rheological and durability properties of RAC based on up-to-date research are discussed from the point of the potential of its utilization in structural concrete. The current state of technical rules and standards in this area is briefly presented. The future research and necessary actions in facilitating the more extensive use of RAC in concrete structures are also pointed out.

Life-cycle assessment (LCA) of concrete with recycled aggregates (RAs)

This chapter focuses on the life-cycle assessment (LCA) of aggregates obtained by recycling of demolished concrete - recycled concrete aggregates (RCA), and concrete made with such aggregates - recycled aggregate concrete (RAC). It includes methodological aspects, such as the treatment of allocation in the case of concrete recycling. The results of LCA case studies on two different RCA applications - as aggregate in structural RAC concrete and as material for road base, are presented. The potentials and limitations of LCA in comparing different waste management scenarios are discussed based on the published research. Recommendations regarding future research are given.

Optimization of UHPFRC beams subjected to bending using genetic algorithms

AbstractUltra high performance fibre reinforced concrete (UHPFRC) is cementitious composite with very high strength, and when compared with ordinary concrete it is a more superior material both in terms of its mechanical properties and its durability. In order to predict the behaviour of UHPFRC beams, first of all, experiments were carried out to investigate the mechanical properties of composites containing 2% and 4% of steel fibres. Following this, four beams of 2 m in length were tested by subjecting to four point bending. Two beams contained only micro steel fibres, while the remaining two contained conventional steel bar reinforcement. On the basis of experimental studies and recommendations by the AFGC for UHPC, the behaviour of the beams was modelled and optimization was carried out using genetic algorithms (GA) according to the criterion of minimum price. In this paper, the prices of individual UHPFRC beams are also shown in comparison with beams, which contain steel bars or prestressed reinforcement.

Comparative Analysis of Axially Loaded Composite Columns

Experiments on square and circular steel columns filled with light-weight concrete and high strength concrete have been conducted to investigate the contribution of these types of concrete to load bearing capacity of short composite columns. The aim of this research was to determine the effect of two types of concrete filling on behaviour of the composite columns. Thirteen specimens were divided in two groups: steel tubes filled with different type of concrete, with or without reinforcement and RC columns with same dimensions and shape, made of same type of concrete. Comparison was made between load bearing capacity of the steel tubes filled with light-weight concrete, and high strength concrete (with and without reinforcement). All specimens were tested by axial compression until to the failure state realization. Factors which influence the behavior and failure mode, ultimate strength, deflections and stress-strain relation were discussed.

Compressive Strength Improvements of Cement-Based Composites Achieved with Additional Milling of Metakaolin

Kaolin from a Serbian deposit, having a high content of mica and quartz, disordered kaolinite and a high specific surface area, was used to prepare metakaolin (MK). The calcination at temperatures of 700 °C or 750 °C for 30 to 180 min resulted in MK having high pozzolanic activity, but also significant aglomeration of particles. In order to disperse aglomerates, MK was milled, which resulted in increased pozzolanic activity and reduced particle size. The effects of MK and additionally milled metakaolin (MKmill) on the composite strengths and microstructure of the pastes were compared. We prepared and investigated composites in which ordinary Portland cement (OPC) was replaced with 10% to 50% of MK or MKmill, as well as the representative samples of paste for determination of microstructure.

Properties of the Cement-Based Composites with High Content of Metakaolin

Environmental concerns and sustainable development require increased replacement of cement. Most of previous studies have shown that the compressive strength of cement-based composites is maximized with a 20% content of metakaolin. We investigated composites prepared by replacing ordinary Portland Cement (OPC) with 30 to 50% of metakaolin (MK) and addition of appropriate amount of hydrated lime, which were ordinary cured for 2, 28 or 90 days. Hydration products and microstructure of the pastes were determined by X-ray diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG) and mercury intrusion porosimetry (MIP). MK was produced by calcination of kaolin from a Serbian deposit, which contained a high level of impurities.