Enhancing the engineering characteristics of sustainable recycled aggregate concrete using fly ash, metakaolin and silica fume.

The present global environment is facing growing issues linked to production of concrete, mostly due to high consumption of concrete as the dominating construction material globally. In today's climate of environmental sustainability, recycled concrete production using RA (recycled aggregates) requires a more holistic approach. This study examined how recycled aggregate (RA), metakaolin, silica fume and fly ash affect mechanical characteristics (compressive strength, split tensile strength), and durability characteristics (acid resistance, absorption, sorptivity) of concrete. The objective of this investigation is to figure out how the potential of RA based concrete can be improved so that they can be used to their maximum extent. To achieve the desired outcome, the study involved testing three distinct groups of concrete samples, each containing different percentages (25%, 50%, and 75%) of recycled aggregate (RA) with a constant amount of silica fume, (25 kg/m3). The first group was used as the control mix, while the second group incorporated 10% fly ash, and the third group included 15% metakaolin. The findings of this research show that the RA concrete mechanical properties as well as durability can be significantly improved by incorporating 15% metakaolin and 10% fly ash. The investigation involves the examination of all ternary blends within two distinct acidic environments, specifically a 5% hydrochloric acid (HCl) solution and sulfuric acid (H2SO4). Both the ternary mixes (metakaolin and fly ash) with the combination of silica improve all characteristics. The quality assurance, cost analysis and the reduction of CO2 emissions are carried out, utilizing RA (recycled aggregates) as a substitute for NA (natural aggregate). In case of producing superior structural concrete, it is recommended based on results to limit the replacement percentage of recycled aggregate (RA) to a maximum of 50% in presence of 10% fly ash and 15% metakaolin, otherwise the RA replacement percentage should not be more than 25%.

Performance of Porous Asphalt Mixtures Containing Recycled Concrete Aggregate and Fly Ash.

This study investigates the effects of two waste materials from construction and industry, namely recycled concrete aggregate (RCA) and Type C fly ash, on the overall performance of a special type of pavement surface mixture, porous asphalt mixture. Mixtures of different combinations of RCA (for partial aggregate replacement) and fly ash (for filler replacement) were prepared in the laboratory and tested for a variety of pavement surface performance parameters, including air-void content, permeability, Marshall stability, indirect tensile strength, moisture susceptibility, Cantabro loss, macrotexture, and sound absorption. The analysis of the results showed that incorporating RCA or fly ash in a porous asphalt mixture slightly reduced the air-void content, permeability, and surface macrotexture of the mixture. A 10% replacement of granite aggregates with RCA in the porous asphalt mixtures led to a reduction in mixture stability, indirect tensile strength, resistance to raveling, and sound absorption. The further substitution of mineral filler with fly ash in the mixture, however, helped to offset the negative impact of RCA and brought the mechanical properties of the mixture with 10% RCA to levels comparable to those of the control mixture.

Laboratory Evaluation of the Use of Florida Washed Shell in Open-Graded Asphalt Mixtures.

This study investigates the substitution of conventional aggregate with a Florida washed shell in open-graded asphalt mixtures and evaluates the optimal substitution percentage in aggregate gradations of various nominal maximum aggregate sizes (NMASs) (i.e., 4.75, 9.5, and 12.5 mm). Laboratory experiments were performed on open-graded asphalt mixture specimens with the coarse aggregate of sizes between 2.36 and 12.5 mm being replaced by the Florida washed shell at various percentages (0, 15, 30, 45, and 100%). Specimen properties relevant to the performance of open-graded asphalt mixtures in the field were tested, evaluated, and compared. Specifically, a Marshall stability test, Cantabro test, indirect tensile strength test, air void content test, and permeability test were conducted to evaluate the strength, resistance to raveling, cracking resistance, void content, and permeability of open-graded asphalt mixtures. The results show that there is no significant difference in the Marshall stability and indirect tensile strength when the coarse aggregates are replaced with Florida washed shell. This study also found that the optimum percentages of Florida washed shell in open-graded asphalt mixture were 15, 30, and 45% for 12.5, 9.5, and 4.75 mm NMAS gradations, respectively.