Abstract
Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to evaluate the porosity in the interfacial transition zones. The porosity of the cement paste, the aggregate and the interfacial transitional zones (ITZ) of a PC with recycled coarse aggregates (RCA) and silica fume (SF) is measured by means of image analysis–scanning electron microscope (IA)-(SEM) and by mapping the chemical elements with an SEM-EDS (energy dispersive spectrometer) detector microanalysis linked to the SEM and, as a contrast, the mercury intrusion porosimetry technique (MIP). In the IA process, a “mask” was created for the aggregate and another for the paste, which determined the porosity percentage (for the anhydrous material and the products of hydration). The results showed that using SF caused a reduction (32%) in the cement paste porosity in comparison with the PC with RA. The use of RA in the PC led to a significant increase (190%) in the porosity at different thicknesses of ITZ compared with the reference PC. Finally, the MIP study shows that the use of SF caused a decrease in the micropores, mesopores and macropores.
Highlights
permeable concretes (PC) is a special concrete with a high gap content and high permeable capacity when compared with conventional concrete [1,2]
It was observed that the inclusion of recycled coarse aggregates (RCA) in PC causes a reduction in its mechanical properties of 31% and 30% with regard to natural coarse aggregate (NCA) 100 C
The physical properties evaluated show that using Recycled aggregates (RA) in the PC leads to a reduction in properties when compared to the reference PC (32%, 30% and 6% for compression, flexure and mechanical properties when compared to the reference PC (32%, 30% and 6% for compression, permeability, respectively), as these old aggregates are nearing the end of their life cycle and have less flexure and permeability, respectively), as these old aggregates are nearing the end of their life cycle mechanical strength than natural aggregates
Summary
PC is a special concrete with a high gap content and high permeable capacity when compared with conventional concrete [1,2]. This PC offers several environmental benefits, among which are rainwater runoff control, replenishment of underground water supplies, an improvement in water quality and a reduction in water and subsoil contamination [3]. It is necessary to determine and study the porosity of these areas of interest [5]. The use of natural aggregates is currently widespread in the manufacture of PC [6], but few studies have used RA [7]. As important quantities of construction and demolition waste are contaminating many ecosystems worldwide, it is imperative to recycle them and produce new building materials, Materials 2019, 12, 2201; doi:10.3390/ma12132201 www.mdpi.com/journal/materials
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