The utilization of locally available concrete waste for producing recycled concrete aggregates is recognized as one of the most sustainable ways of satisfying the growing demand for concrete production. However, the quality of concrete waste depends on its origin and it may significantly differ from one concrete structure to another. Knowing the chemical composition of the parent concrete is crucial for determining or verifying the origin of the raw materials. For this reason, pre-demolition concrete waste streams need to be characterized and classified. Therefore, a new non-destructive method for determining the cement and aggregate type in hardened concrete using handheld X-ray fluorescence (hXRF) analyser is presented in this paper. The method was tested on different raw powders and on concretes containing different types of cements including CEM I 42.5 N (Portland cement), CEM II/B-V 42.5 N (Portland-fly ash cement), CEM III/B 42.5 N (GGBFS cement). Combined desktop XRF and Energy-dispersive X-ray Spectroscopy (EDS) measurements were used for the purpose of validation. The results revealed that the curing of concrete affects the results: a dried concrete surface condition was optimal for measurements since it limits the impact of the concrete surface moisture and efflorescence on characteristic element oxides, such as CaO. The effective measurement duration was 30 s. A CEM III/B 42.5 N (GGBFS)-based concrete surface was distinguished from other concretes using Al2O3, MgO and Fe2O3 as characteristic oxides. The inner layers of concrete were rich in SiO2, the oxide characteristic for the aggregate composition tested in this study. This shows that hXRF is suitable for use in concrete, provided that the concrete surface is dried and the characteristic elements are defined to ensure a distinction between different cement and aggregate types. Direct adoption of such characterization, however, requires field testing across a wide range of concrete compositions and in situ conditions.@en

Demand for high quality recycled concrete aggregates (RCA) to offset the use of primary materials is significantly rising due to circular economy goals and high-value reuse of concrete. The quality of RCA significantly affects their availability for new concrete production due to the variability of parent concrete streams. The optimization of recycling procedures is under development to improve the quality of RCA, however, the costs and energy efficiency of such processes are of practical concern. With this in mind, this paper presents a new framework for reducing the variability of RCA quality by identifying concrete members before their demolition. The goal of identifying demolished concrete members from a structure is to provide groups of concrete members with similar mechanical and chemical properties through a systematic classification of the structural members. The quality assessment of concrete structures and their mechanical and chemical (composition, contamination) properties prior to demolition is generally recognized as challenging due to the absence of guidelines and the lack of easy-to-use in situ characterization techniques. This paper proposes experimental approaches that can non-destructively determine the properties of concrete structures, with a major emphasis on the measurement of the chemical composition of concrete before demolition. Characteristic quality indicators to classify concrete members are first proposed and can be instrumental in setting up future studies. A new method is proposed for in situ chemical composition testing of existing concrete structures; assuming that no records about the parent concrete are available. Next, the challenging parameters for in situ, non-destructive measurements are outlined. The practical application of the proposed method and its uptake in industry can potentially unlock a huge potential for optimized material recovery and contribute greatly to a fully circular construction industry.@en

Momenteel wordt gerecycled beton meestal toegepast als wegfundering en daarmee 'gedowncycled'. Dat komt onder meer doordat er geen informatie beschikbaar is over de kwaliteit van het gesloopte beton. Hoogwaardig hergebruik van gerecyclede toeslagmaterialen in nieuwe betonconstructies vereist een strengere kwaliteitscontrole. Aan de TU Delft wordt nu in samenwerking met Rijkswaterstaat een methode ontwikkeld – een niet-destructieve betonidentificatietechniek gebaseerd op chemische en ultrasone analyse – om ‘gezond’ beton vóór het slopen te karakteriseren en te scheiden van ‘aangetast’ beton. Met die methode kan beton ook worden voorgesorteerd op sterkteklasse en kwaliteit zodat er meer garantie kan worden gegeven voor de kwaliteit van het nieuwe beton. @en

Over the last century, over one hundred crack width formulas have been developed to calculate the width and spacing of cracks in reinforced and prestressed concrete elements. It is unclear which formulas are the most accurate. An extensive comparison study is required to determine which formulas accurately describe the crack patterns, consisting of the crack width and spacing. To make such a study possible, this paper proposes categorizing formulas. The categorization of the formulas is based on their applicability, crack pattern representation, and background. The categorization presents an overview of the different assumptions and application areas for describing crack patterns.@en

Acoustic emission (AE) signal parameters can be used to classify the source type in concrete structures. However, signal parameters are influenced by the wave propagation from the source to the receiver, leading to wrong source classification results, especially for monitoring large concrete structures. This paper experimentally evaluates the influence of wave travel distance on signal parameters on a full-scale shear test of a reinforced concrete beam. The evaluated signal parameters include the RA value, average frequency, peak frequency, frequency centroid, and partial power. The evaluation reveals the limitation of using RA value - average frequency trends in large scale structural concrete members. Based on the evaluation, we propose a new source classification criterion using peak frequency or partial power, which can effectively classify the source type. The new criterion is also validated in a reinforced concrete slab test, which is another structural type. Based on the new criterion, we suggest a sensor layout that is suitable for source classification for large concrete structures. The results of this paper can help developing a reliable solution for real-time source classification for large concrete structures in general.@en

This paper presents the measurement and analysis of energy consumption of a laboratory jaw crusher during concrete recycling. A method was developed to estimate the power requirements of a lab-scale jaw crusher. The impact of material properties on the crusher performance is studied. Eight concrete strength classes (C20/25–C80/95) were considered in the approach. Concrete specimens were cured for 28 days; at which time, concrete properties were obtained through tests such as bulk density, compressive strength, tensile strength, rebound number and ultrasonic pulse velocity. The impact of different aperture size (5 mm and 25 mm) on the energy consumption was also studied. From the experimental results, it is demonstrated that there is a strong dependance of energy consumption on the compressive strength of concrete. Energy of crushing for specimens with a 90 MPa compressive strength was four times higher than the energy needed to crush specimens with a 28 MPa compressive strength. Furthermore, the crushing requires three times more energy when the smaller aperture size is used to process concrete specimens. The results of this study can form a basis for a future large-scale field analysis and a detailed determination of the energy and economic efficiency of concrete recycling.@en