Mirjana Malešev

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.

Monitoring of Water Content in Building Materials Using a Wireless Passive Sensor

This paper describes an innovative design of a wireless, passive LC sensor and its application for monitoring of water content in building materials. The sensor was embedded in test material samples so that the internal water content of the samples could be measured with an antenna by tracking the changes in the sensor’s resonant frequency. Since the dielectric constant of water was much higher compared with that of the test samples, the presence of water in the samples increased the capacitance of the LC circuit, thus decreasing the sensor’s resonant frequency. The sensor is made up of a printed circuit board in one metal layer and water content has been determined for clay brick and autoclaved aerated concrete block, both widely used construction materials. Measurements were conducted at room temperature using a HP-4194A Impedance/Gain-Phase Analyzer instrument.

The assessment of the structure of Novi Sad Open University damaged in a fire

Abstract The fire which spread over the top six floors of the 54 m tall building of the Open University in Novi Sad, caused severe damage to the load-bearing reinforced (RC) concrete structure and the steel facade structure. This paper presents the recorded data on the damage and the assessment of the structure after the fire. All the damage is described and the most characteristic ones are illustrated with photographs. The damages caused by the fire have been classified according to the criteria of the manner and degree to which they are manifested. The authors separate and describe the defects, which occurred as a result of errors made during the construction of the building. The results of the subsequent testing of the quality of the built-in materials are also presented in the paper. It has been concluded that the damage of the elements of the load-bearing RC structure from the 8 th to the 12 th floor has been so severe that the stability and bearing capacity of this part of the structure has been jeopardized, but with appropriate repair measures it can be restored to its previous condition.

Basic Properties of Structural LWAC Based on Waste and Recycled Materials

AbstractThis paper presents results of experimental research on the impact of different types of lightweight aggregates and supplementary cementitious material (fly ash and metakaolin), on basic physical and mechanical properties of structural lightweight aggregate concrete (LWAC). The used aggregates are: lightweight aggregate obtained by firing waste materials (mixture of stone sludge, paper sludge, and fly ash) and expanded recycled glass. The results showed that it is possible to obtain structural LWAC with both types of lightweight aggregates even with substitution of cement with fly ash up to 45% (by mass). LWAC with high amount of active mineral admixtures and low water-binder ratio achieved higher compressive strength and specific strength compared to LWAC made only with portland cement. Comparison of static (Ec) and dynamic (Ed) modulus of elasticity showed that, for everyday engineering practice, static modulus of elasticity of LWAC can be determined using proposed expression Ec=0.65·Ed with hig...