Influence of the Mix Proportion and Aggregate Features on the Performance of Eco-Efficient Fine Recycled Concrete Aggregate Mixtures

Abstract

Most of the previous research on recycled concrete aggregates (RCA) has focused on coarse RCA (CRCA), while much less has been accomplished on the use of fine RCA particles (FRCA). Furthermore, most RCA research disregards its unique microstructure, and thus the inferior performance of concrete incorporating RCA is often reported in the fresh and hardened states. To improve the overall behaviour of RCA concrete advanced mix design techniques such as equivalent volume (EV) or particle packing models (PPMs) may be used. However, the efficiency of these procedures to proportion eco-efficient FRCA concrete still requires further investigation. This work evaluates the overall fresh (i.e., slump and rheological characterization) and hardened states (i.e., non-destructive tests, compressive strength and microscopy) performance of sustainable FRCA mixtures proportioned through distinct techniques (i.e., direct replacement, EV and PPMs) and incorporating different types of aggregates (i.e., natural and manufactured sand) and manufacturing processes (i.e., crusher fines and fully ground). Results demonstrate that the aggregate type and crushing process may influence the FRCA particles’ features. Yet, the use of advanced mix design techniques, particularly PPMs, may provide FRCA mixes with quite suitable performance in the fresh (i.e., 49% lower yield stress) and hardened states (i.e., 53% higher compressive strength) along with a low carbon footprint.

Influence of recycled aggregate on the compressive strength and absorption percentage of Lima 2020 pedestrian pavers

“…However, in both cases the use of recycled aggregate is valid. In addition, [11] mentions that the results of his background suggest that the recycled mixtures that contain 100% Residue can produce 35% more drying shrinkage along with 30% and 50% less compressive strength.…”

Influence of Recycled Concrete Aggregate Type on Rheological Behaviour of Mixtures Proportioned Using the Equivalent Volume Method

“…Moreover, work has shown that the EV method produces suitable concrete despite the type of RCA used [11]. Furthermore, the EV method was further used while incorporating FRCA which showed an overall better performance compared to using the DRM [12][13][14]. Figure 2, therefore, illustrates the volumetric comparison of concrete proportioned through the EV method using CRCA and FRCA along with its companion CC.…”

“…Previous studies on concrete made with CRCA show that the higher the RM content, the lower the RCA concrete mechanical properties for mixtures proportioned with the DRM [20][21][22][23][24][25][26] yet, the quality of the RM also plays an important role in the recycled concrete's mechanical properties [10]. Moreover, recent studies have been conducted to improve and evaluate the performance of concrete made with FRCA [12][13][14]27]. Indeed, the multi-phase nature of FRCA is influenced by its crushing procedure where a more severe crushing sequence results in a lower RCP content which in turn influences the concrete's properties and performance.…”

“…Moreover, four 100% FRCA (i.e., 35 MPa with distinct fine aggregate types) were also proportioned through the EV method with a companion CC having a w/c of 0.35 and combined with crushed coarse limestone. One may note the reduction in the w/c for the FRCA mixtures which was required to achieve the targeted strength of 35 MPa [12,13]. Noticeably, the amount of cement is lower than that of CC to account for the RM/RCP in the new concrete.…”

“…As such, mixture proportioning techniques (i.e., Equivalent Mortar Volume -EMV, its modified version EMV -mod and Equivalent Volume -EV) developed specifically for RCA which account for the presence of RM/RCP have shown to improve the overall performance of coarse RCA [6][7][8][9][10] while also reducing the new cement content. Among those, the EV method [10] is the most recent and optimized technique used in various studies [11][12][13][14]. Yet, the rheological behaviour of distinct recycled mixtures designed through the EV must be evaluated to better understand their further applications in the field.…”