Abstract
Recycled Concrete Aggregates (RCA) form a significant part of construction and demolition waste and its recycling is crucial for long-term construction sustainability. This study examined the incorporation of various fractions of RCA in Semi-Dense Asphalt (SDA) mixtures. The control SDA aggregates were replaced by RCA in selected fractions of 2/4 mm (coarse) and 0.125/2 mm (sand) at 100% and 50% each, and the filler at 100% of the fraction. The replacement was performed by mass with only one fraction being replaced for any single mixture. The mixtures were evaluated by their volumetrics, indirect tensile strength (ITS), water sensitivity (EN 12697-12), fracture energy and rutting resistance (EN 12697-22), in order to assess the effects of each RCA fraction on the mixture properties. The results showed that RCA coarse aggregates absorb significant amounts of binder and require more energy for compaction, which is not the case for the RCA sand or filler. The ITS results showed increased peak load for the RCA replacement samples but also increased brittleness in terms of resistance to crack initiation and propagation. RCA sand incorporation decreased the fracture energy at a higher rate than the coarse per total amount replaced. The ITSR% was similar to the control for lower amounts of RCA replacement, but significantly lower with higher replacement. The rutting resistance improved with RCA sand and especially coarse aggregate replacement. The study shows some limitations for use of RCA in asphalt mixtures, but also the potential for using them when the replacement rate is limited and replacement by volume is recommended. The RCA filler performance was very similar to the virgin filler, which makes its use in asphalt mixtures especially promising.
Highlights
Some of the greatest challenges to construction sustainability is the production and recycling of waste
The mixtures were evaluated by their volumetrics, indirect tensile strength (ITS), water sensitivity (EN 12697-12), fracture energy and rutting resistance (EN 12697-22), in order to assess the effects of each Recycled Concrete Aggregates (RCA) fraction on the mixture properties
The compactability, expressed as a modified Compaction Energy Index (CEI, Fig. 3) is an indication of the energy needed to compact the mixture to a required density
Summary
Some of the greatest challenges to construction sustainability is the production and recycling of waste. Solutions for using RCA need to consider the ability to incorporate them in high volumes, which makes their use in asphalt pavements, by replacing the virgin aggregates, a potentially fruitful area of study [8]. The primary significance of the experimental program is the observation of the effect of each RCA fraction on the volumetric and mechanical properties of the resulting mixture, potentially helping to take advantage of the benefits of graded RCA fractions economically as well as mechanically. This would allow for the more effective recycling of RCA in new materials, and more acceptance as an alternative material for asphalt. Of secondary significance are the evaluation of RCA in higher porosity asphalt and using fracture energy – calculated through two different methods – in assessing the water sensitivity of the mixtures
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