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Present research critically investigates drying sensitivity and cement hydration resumption in recycled aggregate concrete (RAC). To determine minimum post-curing time for optimum strength resumption in RAC, a curing ratio (δ) is introduced. Curing ratio is defined as the ratio between post-curing duration and delay time before curing. Drying sensitivity of RAC is observed significantly lower than NAC. The maximum strength loss under drying conditions is 25.9% in RAC (OPC) and 23.2% in RAC (PPC). Strength criteria determine the curing ratios of RAC (OPC) and RAC (PPC) as 2.22 and 0.30. The maximum delay time for RAC (OPC) and RAC (PPC) is determined at 8 days and 21 days with a minimum post-curing for 17.76 and 6.63 days. The longest allowable delay produces ion penetration less than 1000 Coulombs, resistivity greater than 208 ohm-m, superior structural integrity and internal compactness, and sorptivity comparable to RACs cured after a shorter delay. [ABSTRACT FROM AUTHOR]

This study demonstrates an integrated thermomechanical treatment process to produce high quality recycled concrete aggregate (RCA) for structural concrete. RCA is mechanically treated after 90 min of heating at 250 °C in this process. The material properties of RCA produced through 15 combinations of charges and drum revolutions are compared using a statistical method. The highest ranking of an RCA identifies it as a high-quality class. Concrete composed of 100% RCA (recycled aggregate concrete, RAC) has 1.7% higher compressive strength than natural aggregate concrete (NAC). RAC has tensile and flexural strengths of 0.95 and 1.03 in fraction of NAC. RAC meets durability criteria such as UPV greater than 4.4 km/s, rapid chloride ion penetration test (RCPT) less than 1000 C, electrical resistivity greater than 208 Ohm-m, and sorptivity closer to NAC. Water absorption and abrasion resistance are similar to or superior to those of NAC. Coherent and uniform surface morphology of RCA enhances the ITZ microstructure in RAC. [ABSTRACT FROM AUTHOR]

This study outlines a method for identifying high-quality recycled concrete aggregate (RCA) obtained after mechanical treatment. In the present approach, the physical and mechanical properties of RCA are considered as quality parameters. As a first step, mechanically treated (Los Angeles) RCA is produced with 28 combinations of charges and drum revolutions. Twenty-eight sets of mechanically treated RCA are produced, each with different physical and mechanical properties. Furthermore, the 28 sets of RCAs are compared using the performance-based quality optimization approach. The performance index for each set of RCAs is calculated applying a multicriteria decision-making approach named "technique for order of preference by similarity to ideal solution." This approach considers physical and mechanical properties as a response and the combination of charges and drum revolutions as alternatives to obtain the performance index of alternatives. Based on its performance, the leading rankings RCAs are selected for an experimental study to validate the methodology. As a result of RCA's optimized quality, recycled aggregate concrete (RAC) has excellent physical, mechanical, and durability characteristics that agree with natural aggregate concrete (NAC) composed of parent aggregate. The 28- and 91-day compressive strengths of RAC exceed those of NAC by 8.5% and 30.65%, respectively. Flexural strength, split tensile strength, fracture energy, ultrasonic pulse velocity (UPV) values, rapid chloride-ion penetration test values, water absorption, and abrasion resistance are comparable with NAC. The quality optimization approach identifies RCA with superior shape, texture, and elastic properties. An RCA with optimized qualities also strengthens the new interfacial transition zone and old interfacial transition zone as well as RAC's associated properties. The RAC's dynamic modulus of elasticity is superior to the reported values and is 0.95 fractions of NAC. Optimized quality of RCA reduces the sorptivity of RAC compared with the reported values. The RAC may not have equivalent sorptivity to NAC without lowering RCA parts, whether mortar-attached, mortar-covered, or mortar-only type aggregate or applying other treatments that may increase the production cost. This research presents a standard procedure for identifying mechanically treated recycled concrete aggregate with properties (physical properties and mechanical properties) similar to those of the parent aggregate (natural aggregate). The method demonstrated in this study may be adapted to real-life worksite conditions—but not exactly. In Los Angeles abrasion machines, recycled concrete aggregates obtained from a source can be processed by varying drum revolutions and charges. Based on the charges and drum revolutions selected for treatment, treated recycled concrete aggregate can be prepared with different sets of physical and mechanical properties. Based on the present research, the physical and mechanical properties of treated recycled concrete aggregate can be compared between these sets. In this way, recycled concrete aggregates can be produced that resemble their parent aggregates. Using this process, recycled concrete aggregates may be used to replace natural aggregates without compromising the concrete's physical, mechanical, or durability properties. [ABSTRACT FROM AUTHOR]