Recycling of End of Life Concrete Fines into Hardened Cement and Clean Sand

Abstract

One of the massive by-products of concrete to concrete recycling is the crushed concrete fines, that is often 0 -4mm. Although the construction sector is to some extent familiar with the utilization of the recycled coarse fraction (>4 mm), at present there is no high-quality application for fines due to its moisturized and contaminated nature. Here we present an effective recycling process on lab scale to separate the cementitious powder from the sandy part in the crushed concrete fines and deliver attractive products with the minimum amount of contaminants. For this study, a lab scale Heating-Air classification system was designed and constructed. A combination of heat and air classification, resulted in a proper separation of finer fraction (0 -0.250 mm), from coarser fractions. Heating of the materials was followed by ball milling to enhance the liberation of the cementitious fraction. Experiments were carried out at different heating temperatures and milling durations. Experimental results show that by heating the materials to 500˚C for 30 seconds, the required time of ball milling is diminished by a factor of three and the quality of the recycling products satisfies well the market demand. In addition, the removal of contaminants is complete at 500˚C. The amount of CaO in the recovered finer fraction from the recycling process is comparable with the amount of CaO in low-quality limestone. By using this fraction in the cement kiln as the replacement of limestone, the release of the chemically bound CO2 could be reduced by a factor of three.

Decarbonizing the cementitious materials cycle: A whole‐systems review of measures to decarbonize the cement supply chain in the UK and European contexts

“…Use of untreated end‐of‐life binder in a cement kiln has produced a clinker with a mineralogical composition close to PC clinker and with ∼33% less process emissions from pyro‐processing (Gastaldi et al., 2015). However, technological improvements are generally required to enhance the quality of secondary NPCMs and kiln feed (i.e., to reduce contamination) produced from end‐of‐life CMs (Bakker et al., 2015; Lofti & Rem, 2016). Additionally, implementing these measures at the industrial scale requires changes to demolition practices, including increased collection rates, and improved separation of construction and demolition waste into distinct material types (Material Economics, 2019).…”

Cluster-based identification algorithm for in-line recycled concrete aggregates characterization using Laser-Induced Breakdown Spectroscopy (LIBS)

“…The gap between supply and demand for concrete will lead to the consumption of large amounts of resources, and the over-mining of raw materials for concrete also adds to the damage to the environment. EoL concrete accounts for the vast majority of C&DW (Lotfi and Rem, 2016), and the most viable solution for EoL concrete is recycling or upcycling. The conventional linear approach to recycling needs to be upgraded to a circular process, that is, secondary raw materials are obtained from EoL concrete for a green and sustainable solution (Cossu and Williams, 2015).…”

Recycling-Oriented Characterization of Post-Earthquake Building Waste by Different Sensing Techniques

“…can dramatically influence the possibilities of their correct reuse as recycled aggregate. Concerning RA, previous studies have demonstrated the possibility of evaluating building waste by HSI, assessing the presence of contaminants in RA, and classifying end-of-life construction materials [ 41 , 42 , 43 , 44 ]. However, few studies have been carried out on the monitoring of tiles coming from post-disaster building waste and on their possible reuse as RMA, despite their high presence in earthquake-damaged structures.…”