In the Netherlands, beside cement replacement with more green cement types, there is also an urgent need for alternative materials for natural sand in new concrete in order to make it circular. Furthermore, the recyclers have raised questions regarding upscaling and the potential of fine recycled concrete aggregates (fRCA) in structural concrete elements since the availability of recycled construction rubble is increasing. The variations in their chemical and physical properties and lack of standards for their quality evaluation is the main reason for not yet using fRCA in new concrete. In this paper, an in-depth characterization of different fRCA is performed in order to define their chemical properties. The properties can be eventually related to concrete mix design and performance (next step), so that fRCA can be classified as a material that can be used in more advanced applications. This is achieved with a multi-level chemical characterization of individual and total fractions (0-0.25 mm, 0.25-4 mm and 0-4 mm) for finding type and content of the original sand and cement phases and potential contamination of selected fractions. The tests include quantification of element composition with X-ray fluorescence (XRF), qualitative and quantitative phase analysis with X-ray diffraction (XRD) and Rietveld method. In addition, cement paste content, chlorides and sulfates of each type of fRCA was measured in order to evaluate contamination of studied material. It was shown that fRCA from different origins have similar chemical and mineralogical composition and contain comparative chloride content. The chemical composition testing can provide a first line control regarding composition and potential contamination of fRCA. After that, it can be decided which additional tests are necessary to be done in order to evaluate the suitability of fRCA for replacement of primary natural fine aggregates in new concrete.@en

This paper discusses the state-of-the-art of the fine recycled concrete aggregates (fRCA), focusing on their physical and chemical properties, engineering properties and durability of concretes with fRCA. Based on the systematic review of the published literature, it is impossible to deduce without any further research the guidelines and tools to introduce the widespread application of the fRCA in new concrete whilst keeping the cement contents at least the same or preferably lower. Namely, what is still missing is knowledge on key physico-chemical properties and their relation to the quality of the concrete mix and the concrete performance. This paper sets the foundations for better understanding the quality of fRCA obtained either from parent concrete specifically produced in the laboratory, with controlled crushing and sieving of the recycled aggregates or from field structures. By comparing properties of fRCA with properties of fine natural aggregates, the key limiting properties of fRCA are identified as the high water absorption of fRCA, moisture state of fRCA, agglomeration of particles and adhered mortar. As such, continuous quality of fRCA is hard to be obtained, even though they may be more continuous in terms of chemistry. Advanced characterization techniques and concrete technology tools are needed to account for limiting properties of fRCA in concrete mix design.

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In circular concrete design, beside cement replacement with more environmentally friendly cement types, there is also an urgent need for sand replacement with fine recycled concrete aggregates (fRCA). The variations in physical and chemical properties of fRCA and lack of standards for their quality evaluation are the main reasons for not yet using fRCA in new concrete. In this study, an in-depth characterization of different Dutch fRCA is performed in order to examine suitability of fRCA as an alternative material for river sand and define indicators for fRCA quality. These indicators eventually can be related to concrete mix design and performance, so that fRCA can be classified as a material that can be used in structural concrete elements. This is achieved with physical, chemical and mineralogical characterization of individual and total fractions (0–0.250 mm, 0.250–4 mm and 0–4 mm). The physical properties such as grading, density, surface area, water absorption and cement paste content of fRCA were tested. The chemical analyses include quantification of element composition with X-ray fluorescence spectrometry (XRF) and carbonate content with thermogravimetry and mass spectrometry (TG-MS). Potential contamination (chlorides and sulfates) and reactivity of selected fractions were evaluated. In addition, qualitative and quantitative phase analyses with X-ray diffraction (XRD) combined with Rietveld refinement method were performed and supported by optical polarizing-and-fluorescence microscopic (PFM) study. Based on combined experimental approaches, characteristic quality indicators were defined for fRCA. These indicators showed that fRCA were uncontaminated and nonreactive. Despite fRCA were from different origins, they had similar chemical and mineralogical composition and contained comparative chloride content. In contrast, the content and surface area of fine fraction (0–0.250 mm) and particle size distribution of fRCA varied with the source. With this it can be assumed that fRCA will have different effect on the properties of the new concrete.

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Many standardised durability testing methods have been developed for Portland cement-based concretes, but require validation to determine whether they are also applicable to alkali-activated materials. To address this question, RILEM TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ carried out round robin testing of carbonation and chloride penetration test methods, applied to five different alkali-activated concretes based on fly ash, blast furnace slag or metakaolin. The methods appeared overall to demonstrate an intrinsic precision comparable to their precision when applied to conventional concretes. The ranking of test outcomes for pairs of concretes of similar binder chemistry was satisfactory, but rankings were not always reliable when comparing alkali-activated concretes based on different precursors. Accelerated carbonation testing gave similar results for fly ash-based and blast furnace slag-based alkali-activated concretes, whereas natural carbonation testing did not. Carbonation of concrete specimens was observed to have occurred already during curing, which has implications for extrapolation of carbonation testing results to longer service life periods. Accelerated chloride penetration testing according to NT BUILD 443 ranked the tested concretes consistently, while this was not the case for the rapid chloride migration test. Both of these chloride penetration testing methods exhibited comparatively low precision when applied to blast furnace slag-based concretes which are more resistant to chloride ingress than the other materials tested.

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Extreme wintercondities, zoals vorst-dooi, kunnen tot veel schade leiden in allerlei materialen. Bij zeer open asfalt (ZOAB) kan vorstschade leiden tot rafeling maar op dit moment is geen betrouwbare vorst-dooi test voor handen om de gevoeligheid voor dit type schade vast te stellen. ZOAB is dusdanig uniek met zijn open poriestructuur en lage bitumengehalte, dat de bestaande vorst-dooi proeven voor steenachtige materialen of dicht asfalt niet zomaar overgenomen kunnen worden en geen voorspellende waarde hebben voor de vorst-dooi bestendigheid. InfraQuestwerkt daarom aan een pragmatische vorst-dooi test voor ZOAB om een beeld te vormen van de parameters die van invloed zijn op het vorst-dooi gedragen uiteindelijk om te voorspellen of een materiaal bestand is tegen vorst-dooi cycli.Daarbij worden bestaande vorst-dooi testen omgebouwd om specifiek rekening te houden met enerzijds de open structuur van ZOAB mengsels en anderzijds de dichte structuur van de bitumen component daarin. Verschillende zoet – en zoutwaterbelastingen worden vergeleken voor een welbepaald cyclisch temperatuurregime. In deze paper wordt de proefmethode in detail beschreven en worden daarna de resultaten weergegeven van een eerste testserie van 3 mengsels. Samengevat komt uit dit onderzoek naar voren dat deze pragmatische vorst-dooi proef onderscheidend is voor ‘goede’ versus ‘slechte’ ZOAB mengsels en dus een goede basis vormt voor verdere ontwikkeling. Op basis van de huidige resultaten kan niet uitgesloten worden dat het mechanisme dat de proefstukken in de test verzwakt heeft, gekoppeld is aan watergevoeligheidop zich, al dan niet in combinatie met temperatuurs- en zoutbelasting. De resultaten van de indirecte treksterkte (ITS) beoordelingsmethode blijken gevoelig voor heterogeniteit en geven mogelijk een vertekend beeld, met name voor verouderde, stijve proefstukken. Op basis van de huidige resultaten wordt voorgesteld in de toekomst watergevoeligheid als een aparte variabele mee te nemen, alsook het effect van temperatuurcycli en mechanische belasting tijdens de vorst-dooi proef. De beoordelingsmethode mag niet worden beperkt tot ITS en uitbreiding met microscopie wordt voorgesteld op basis van een verkennende analyse van microscopiefoto’s.@en