Snežana Marinković

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.

Life cycle assessment (LCA) of concrete made using recycled concrete or natural aggregates

Abstract: This chapter is devoted to comparative environmental assessment of structural concrete made with recycled concrete aggregates and structural concrete made with natural aggregates. The results of life cycle assessment of concretes with three different types of aggregate: natural gravel, natural crushed and recycled concrete aggregate are presented. The influence of the transport phase and CO2 uptake during the life cycle of concrete structures are analyzed. Conclusions on eco-efficiency of recycled aggregate concrete compared to natural aggregate concrete and recommendations for future research are given.

On the selection of the functional unit in LCA of structural concrete

A recently published article by Panesar et al. (2017) presents an analysis of the impact of the selection of functional unit (FU) on the life cycle assessment of green concretes. The authors correctly emphasize that, despite the multifunctional nature of every concrete structure, many previously performed LCA studies were based on a ‘simple’ FU, most commonly equal to the unit volume of concrete. For that reason, the authors investigated the influence of six different FUs (which included volume, compressive strength, durability of concrete, binder intensity and a combination of these) on several impact categories. However, some aspects of this work in my opinion deserve commentary for the sake of scientific fairness and correctness. Firstly, in the part of the article where previous work was analysed, the comment made on the work of Marinković et al. (2010) on comparative LCA of natural and recycled aggregate concrete is not correct. In this work, all compared concrete mixes were designed to have the same 28-day compressive strength andworkability to ensure the same function regarding the strength of a concrete element. To provide for similar durability performance, the analysis was limited to a type of concrete structure for which low-aggressive exposure conditions apply, i.e. with no risk of reinforcement corrosion (such as indoor low air humidity environments of residential and office buildings). The same function was obtained with the same volume (equal to 1 m of concrete) but with different mix designs. So, the comparison of the environmental impacts of the different concrete mixes was made on the basis of a functional equivalency, contrary to the authors’ statement in the article. Panesar et al. (2017) analysed four different concretes with an indication that these specific design mixes are used by the Ministry of Transportation of Ontario in transportation infrastructure. The assessment was performed without specifying the application of concrete—on the ‘material’ level, but from the context of the article it can be concluded that these mixes are intended for structural applications. In my opinion, the function of the concrete is the function of the structure made of it, and it does not exist independently of the structure in which the concrete is applied. If rationales and methodology in (Panesar et al. 2017) are applied to any type of concrete structure, following remarks regarding the FU calculation in this work can be put forward: FUs are not in fact units, but rather measures of the functional performance obtained as ratios of chosen properties of different concrete mixes (they are dimensionless). Final impacts (LCIAresult) of different concrete mixes are obtained by multiplying the ‘raw’ impacts per unit volume (LCIAresultimpactcategory,alternativematerial) with the ratios obtained in such a manner (FU). They are also normalized to the impacts of the base material (LCIAresultimpactcategory,basematerial), according to Eq. (1):

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.