Influence of granular fraction and origin of recycled concrete aggregates on their properties

Abstract

Large quantities of construction and demolition wastes are produced each year. In order to make good use of recycled concrete aggregates (RCA) in concrete, it is very important to study the influence of the granular fraction and the origin of RCA on their properties. In this study, RCA from industrial produced blocks (RCA_Blocks) and slabs (RCA_Slabs) were crushed and then separated into four granular fractions (0/2, 2/6.3, 6.3/14, 14/20 mm). Each granular fraction of RCA was physically characterised. Real RCA from recycling plant were also used for comparison. The results showed that recycled sands offered significantly higher cement paste content (higher bound water content) than coarse recycled aggregates. The fine RCA had therefore a higher water absorption coefficient compared to coarser fractions of RCA. The water absorption of finer fraction of RCA could be extrapolated precisely from the relationship between water absorption and cement paste content (or bound water content) of three coarse fractions of RCA. The values of hardened cement paste content obtained for the RCA_Blocks were lower than those measured on the RCA_Slabs, which was due to a smaller amount of initial cement paste content in blocks. The results showed that RCA_Slabs were more angular than RCA_Blocks.

Use of recycled concrete aggregates from precast block for the production of new building blocks: An industrial scale study

“…The water absorption of RCA 2/6.3 mm is 3.43% and its apparent density is 2.51 g/cm 3 (whereas it is 0.37% and 2.7 g/cm 3 for natural aggregate) according to European standard EN 1097-6 (CEN, 2013b). The higher value of water absorption and low value density of RCA are due to the presence of hardened cement paste (which is much porous than natural aggregate) adhering to the natural aggregate for the RCA (Zhao et al, 2018).…”

“…Up to now, most of recycled C&D waste has been used as a base or sub-base material in road construction ("down cycling"), engineering fill or landfill engineering (Barbudo et al, 2012;Poon and Chan, 2006a), while only a small proportion is re-used as recycled aggregates in the concrete industry (high-value application) (Courard et al, 2010;Delvoie et al, 2018;Huang et al, 2002;Zhao et al, 2018).…”

Use of Recycled Fine Aggregates from C&DW for Unbound Road Sub-Base

“…RCA are composed of a mix of natural aggregates and adherent hardened cement paste [ 29 , 30 , 31 , 32 ]. The latter is usually much more porous than natural aggregates [ 33 , 34 ] and leads to a large water demand which makes RCA less easy to recycle into concrete [ 1 , 35 , 36 , 37 ]. Properties of RCA such as water absorption and porosity can deeply influence the fresh properties of concrete as well as mechanical properties and durability of concrete made with RCA [ 16 , 38 , 39 , 40 , 41 ].…”

Microwave Radiation as a Pre-Treatment for Standard and Innovative Fragmentation Techniques in Concrete Recycling

“…The quality of these recycled aggregates is often suboptimal in view of replacing a large fraction of natural aggregates in new structural or non-structural concrete [5,6]. A high content of residual cement matrix in the recycled aggregate fraction results in a high porosity and increased water absorption [7,8], which negatively affects workability, strength and durability of concrete prepared from these aggregates [9,10,11]. As a result, low-grade recycled aggregates produced in Flanders and obtained with current fragmentation technologies, are mostly used in applications with less strict aggregate requirements, e.g., primary foundation and levelling works [3].…”