Multiple recycled aggregate properties analysed by X-ray microtomography

Abstract

The increasing production of construction and demolition waste (C&DW) and the ever-greater consumption of natural resources is forcing society to search for alternatives in order to reduce both. Fortunately, many studies have analysed the possibility of producing recycled aggregates (RA) using old concrete from C&DW [1-6], precast industries [7-10] and industry wastes [11-13]. However, the use of RA against the use of natural aggregate (NA) for structural concrete on material performance, environmental benefits and financial viability of the studies conducted so far do not fully demonstrate the choice of production of recycled aggregate concrete (RAC) with a significant advantage [14]. RA influences the physical and mechanical properties of RAC. The direct influence of the quality of RA on the durability is analysed in [7,15] showing that RA coming from precast-structural concretes is one of the most adequate in order to produce RAC. In terms of durability, the incorporation of recycled aggregate was responsible for worse results but did not compromise their use in structural concrete [16,17]. The properties of the interfacial transition zone (ITZ) have a significant impact on the macro mechanical properties of concrete [18]. X-ray computed axial tomography (CT) provides cross-sectional views of materials, components, and assemblies for non-destructive evaluation [19]. It can be used to examine concrete [20] and the high-resolution X-ray micro-CT allows modelling the permeability of cementitious materials [21]. On the one hand, the irregular surface of the old adhered mortar of the RA contributes to the improvement of the physical bond between the old and new cement matrix [22]. On the other hand, the lower mechanical resistance due to the adhered mortar contributes to reduce the compressive strength [15] and significantly so in the case of dynamic rather than static loading [3,23-25] but no significant influence of the recycled aggregate content on the durability performance of concrete exposed to aggressive environments is detected after years [26]. Multiple recycled aggregate properties analysed by X-ray microtomography C. Thomas a, ⁎

Micro- and macro-porosity of dry- and saturated-state recycled aggregate concrete

“…Traditionally open porosity has been obtained by water saturation, although saturation is a slow process and is influenced by the size and shape of the specimens. Modern methods such as microtomography (Thomas et al, 2018) allow access to the open and close porous network without affecting the material but only in very small samples. In addition, image analysis by backscattered electron images of polished sections were used to characterize the concrete (Hu, 2004, Lange et al, 1994.…”

Mechanical and Durability Properties of Concrete with Coarse Recycled Aggregate Produced with Electric Arc Furnace Slag Concrete

“…It is also known that the use of CRA but also the new cement paste affect the fatigue behaviour of concrete, reducing the fatigue limit and fatigue life [40,41]. Other authors have shown that the multi-recycling of the concrete that contain CRA is limited and that after three recycling cycles, CRA are mostly composed of mortar and new NA are needed in the mix design [42].…”

High-Frequency Fatigue Testing of Recycled Aggregate Concrete

“…Innovative techniques, such as micro computed tomography (micro- CT) have also been used to analyze the behavior of concrete at fatigue, both in compressive fatigue [12] and bending fatigue [17]. Moreover, some micro-CT studies, which is a technique able to analyse the pores and cracks on concrete [18,19], had been developed to understand the concrete damage fatigue micromechanism [20,21]. In general, fatigue is known to lead to microcracks in concrete growing at lower loads than in static tests, which can lead to concrete failure earlier than expected [22].…”