Unconventional tools for the study of the flow properties of concrete equivalent mortar based on recycled concrete aggregates

Abstract

The self-compacting concrete (SCC) mix design is much more complex than that of ordinary concrete. Increased testing on fresh concrete and a substantial volume of materials is consequently needed. The concrete equivalent mortar (CEM) method proposes an approach that simplifies and speeds up the experimental testing programmes. This paper seeks to establish the relationships between the rheological properties of SCC and the corresponding CEM mixes. Another aim is to validate the unconventional tools used to test the flow properties of CEM relative to the procedures applied for SCC. Different series of SCC and CEM mixes, based on natural and recycled aggregates, with various superplasticizer contents were tested. The flow behaviour of SCC was tested in line with procedures recommended by EFNARC; that of self-compacting concrete equivalent mortar (SC-CEM) was carried out with unconventional tools (mini-slump cone, slump flow time T 250 , mini L-Box, 2.5-mm sieve, and mini LCPC Box), described in detail in this paper. A rheometer equipped with vane geometry was also used to show the close relationship between SCC and the SC-CEM yield stress. The experimental results indicate that the fresh properties of the mixture series are congruent with the acceptance criteria of SCC, but they are affected when increasing the superplasticizer dosage and further impacted when recycled coarse aggregates (RCAs) replace natural coarse aggregates (NCAs). The slump flow test appears to be a good practical means for predicting the yield stress of SC-CEM. The cross-referencing results reveal significant relationships between SCC and the corresponding SC-CEM, particularly for filling ability and passing properties. Reasonable correlation coefficients from 0.70 to 0.85 were found.Keywords Recycled concrete aggregates • Concrete equivalent mortar • Self-compacting concrete • Fresh properties

Hammer rebound index as an overall-mechanical-quality indicator of self-compacting concrete containing recycled concrete aggregate

“…As rejected concrete components are crushed to obtain RCA [33], the coarse fraction is Natural Aggregate (NA), generally siliceous, with adhered mortar [34], while the fine fraction is a mixture of NA particles and mortar [35]. The workability of concrete containing RCA rather than NA decreases, because the water absorption levels of the former are higher [36]. Moreover, the increased porosity and adhesion problems caused by RCA in the interfacial transition zones of concrete [37] worsen its mechanical behavior [38] and increase concrete deformability [39].…”

Full Characterization of Self-Compacting Concrete Containing Recycled Aggregates and Limestone

“…Several current studies aim to find the appropriate mix design of low-carbon selfcompacting concretes based on recycled gravel, obtained by adding a superplasticizer whose excess can lead to segregation and by incorporating mineralogical additives and recycled aggregate at relatively high rates [20], without the latter adversely affecting the mechanical and rheological performance of the concrete [21]. Therefore, extensive research and testing are required to optimize the mix design of low-carbon self-compacting concretes based on recycled aggregate [22].…”