Ivan Ignjatović

Comparative environmental assessment of natural and recycled aggregate concrete

Constant and rapid increase in construction and demolition (C&D) waste generation and consumption of natural aggregate for concrete production became one of the biggest environmental problems in the construction industry. Recycling of C&D waste represents one way to convert a waste product into a resource but the environment benefits through energy consumption, emissions and fallouts reductions are not certain. The main purpose of this study is to determine the potentials of recycled aggregate concrete (concrete made with recycled concrete aggregate) for structural applications and to compare the environmental impact of the production of two types of ready-mixed concrete: natural aggregate concrete (NAC) made entirely with river aggregate and recycled aggregate concrete (RAC) made with natural fine and recycled coarse aggregate. Based on the analysis of up-to-date experimental evidence, including own tests results, it is concluded that utilization of RAC for low-to-middle strength structural concrete and non-aggressive exposure conditions is technically feasible. The Life Cycle Assessment (LCA) is performed for raw material extraction and material production part of the concrete life cycle including transport. Assessment is based on local LCI data and on typical conditions in Serbia. Results of this specific case study show that impacts of aggregate and cement production phases are slightly larger for RAC than for NAC but the total environmental impacts depend on the natural and recycled aggregates transport distances and on transport types. Limit natural aggregate transport distances above which the environmental impacts of RAC can be equal or even lower than the impacts of NAC are calculated for the specific case study.

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.

Radiological and material characterization of high volume fly ash concrete

The main goal of research presented in this paper was the material and radiological characterization of high volume fly ash concrete (HVFAC) in terms of determination of natural radionuclide content and radon emanation and exhalation coefficients. All concrete samples were made with a fly ash content between 50% and 70% of the total amount of cementitious materials from one coal burning power plant in Serbia. Physical (fresh and hardened concrete density) and mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of concrete were tested. The radionuclide content (226Ra, 232Th and 40K) and radon massic exhalation of HVFAC samples were determined using gamma spectrometry. Determination of massic exhalation rates of HVFAC and its components using radon accumulation chamber techniques combined with a radon monitor was performed. The results show a beneficial effect of pozzolanic activity since the increase in fly ash content resulted in an increase in compressive strength of HVFAC by approximately 20% for the same mass of cement used in the mixtures. On the basis of the obtained radionuclide content of concrete components the I -indices of different HVFAC samples were calculated and compared with measured values (0.27-0.32), which were significantly below the recommended 1.0 index value. The prediction was relatively close to the measured values as the ratio between the calculated and measured I-index ranged between 0.89 and 1.14. Collected results of mechanical and radiological properties and performed calculations clearly prove that all 10 designed concretes with a certain type of fly ash are suitable for structural and non-structural applications both from a material and radiological point of view.

Experimental Setup for Measuring Long-Term Behavior of Green Reinforced Concrete Beams

The behavior of reinforced concrete under long-term loading is an important topic when designing concrete structures. Creep and shrinkage of concrete and long-term deflections of concrete structures, mainly reinforced concrete beams, have been studied for many decades but because of the long-term nature of these tests, existing experiments are relatively scarce. More importantly, there are significant challenges when carrying out these tests. These include achieving optimal beam design to ensure a realistic stress distribution with a developed cracked state, measuring deflections from self-weight, adequately measuring elastic deflections and strains, and instantaneously applying the imposed load. The problem is exacerbated with the advent of sustainable structural concretes containing recycled and waste materials—green concretes; they possess specific properties and experimental results for these concretes are even scarcer.