Liberation of original natural aggregates from recycled concrete by abrasion comminution

Recycling of concrete waste into structural concrete reduces the consumption of raw materials, decreases transport and production energy costs, and saves the use of limited landfill space. Since attached mortar is known for lowering the performance of recycled concrete aggregates (RCA) in concrete applications, current recycling involves the use of RCA as a road base material or in non-structural concrete with low strength requirements. Therefore, the application in structural concrete is limited. In general, the applicability of RCA is improved by comminution through various crushing methods. Hereby, the parent particles are cleaved or shattered into a minimum of two particles with a comparable size and a number of much smaller particles. Through this technique, both mortar and aggregates fracture alike, resulting solely in a size reduction. However, to minimise undesirable effects, original natural aggregates (ONA) have to be cleared from attached mortar. Through the use of attrition and shear instead of pressure or impact, surface layers, edges and corners are removed, producing particles both slightly smaller and much smaller than the initial. In this study, ONA liberation through abrasion was investigated

Crushing of MSWI bottom ash towards material purification

Municipal Solid Waste Incineration (MSWI) reduces mass and volume of the waste by about 70% and 90%, respectively. Next to boiler and fly ash, solid MSWI Bottom Ash (hereinafter referred to as bottom ash; BA) makes up for 80% of the remaining material containing unburned matter, glass, ceramics, metals, and minerals. Despite its similar composition to concrete constituents, which suggests their applicability in this field, at present BA is landfilled or used in low-grade applications (e.g. road base material). In order to make a higher end application possible, correlations between physical properties, size fractions and mineralogical composition have been studied. This study looks into the crushing of the materials within BA and how certain fractions are enriched with specific types of material, therefore depleting and purifying other fractions making them better suitable for implementation in concrete

Utilization of recycled concrete aggregates in structural concrete by applying a fraction partitioning model

The recycling of concrete waste into new structural concrete reduces the utilization of raw materials, decreases transport and production energy cost, and saves the use of limited landfill space. Currently, recycling involves the use of recycled concrete aggregates (RCA) as road base material or in non-structural concrete with low strength requirements. Hence, the application in structural concrete is limited. In order to improve the applicability of RCA in structural concrete, a fraction partitioning – other than the norm sand and gravel fractions (0/4mm and 4/32mm respectively) – is advised. In this initial study, the theory is tested on a mortar level, dividing norm sand into sieve fractions towards an optimal particle packing. Subsequently, the obtained fractions are used in a particle packing model to define the quantity of each size fraction to be used in mortar production. With this tool, an optimised mortar particle distribution was created and compared to a standard mortar in terms of mechanical properties

Processing disaster debris liberating aggregates for structural concrete

Worldwide, the removal of debris and reconstruction is requested when natural disasters and conflicts cause damaged or collapsed buildings. The on-site recycling of concrete waste into new structural concrete decreases transport and production energy costs, reduces the utilization of raw materials, and saves the use of limited landfill space. The application of recycled concrete aggregates (RCA) in structural concrete is currently limited, since concrete recycling involves application as road base material or in non-structural concrete with low strength requirements. Applying an optimised crushing method could improve the applicability of RCA in structural concrete. The quality of the initial concrete investigated is unknown, and embedded defects influence the quality of the final concrete made with RCA. Separating the hardened cement paste (HCP) from the aggregates through optimised crushing minimises the influence of the initial concrete on the quality of concrete made with RCA. In turn, the HCP can be extracted, reducing water absorption and minimising workability problems. Through this, optimised crushing makes the application of recycled concrete into new concrete far less troublesome, and therefore widely applicable and highly suitable for post disaster areas. This study primarily looks into the influence of the optimised crushing process on the resulting particles of the produced RCA. For this, concrete demolition waste is passed through the optimised crusher three times. An initial visual assessment of the RCA produced is made and the specific aggregated density measured shows promising results regarding aggregate quality

Detailed characterization of particle size fractions of municipal solid waste incineration bottom ash

Municipal Solid Waste Incineration Bottom Ash (MSWI BA) is of increasing interest as a secondary construction material worldwide. In most cases, MSWI BA is used in isolated conditions. However, according to the Dutch Green Deal B-076 in 2012, by 2020 all MSWI BA should be used in a non-sealed environment in the Netherlands. However, freshly produced. MSWI BA normally does not match environmental legislation due to high leaching of chlorides, sulfates, and potentially toxic elements. Because different particle size fractions of MSWI BA are of interest for designing optimized concrete recipes, it is beneficial to analyze the whole range of MSWI BA fractions in detail. In this study, 14 size fractions of MSWI BA were analyzed to determine the total elemental composition and leaching capacity, mineralogical composition, and shape variety of fine particles. From the point of view of mineralogical composition, 6 particle size fractions ( 22 mm) can be distinguished. All together the analyses showed that almost all fractions of the investigated MSWI BA can be used as secondary building materials. However, because the leaching of fine fractions is 5–10 times higher than of coarse fractions, all these fractions must undergo various treatments to allow them to match the environmental legislation. Thus, to decontaminate MSWI BA from potentially toxic elements, a division into three size groups is suggested: fine (<125 μm), medium (125 μm - 1 mm), and coarse fractions (over 1 mm)