Leaching of Pervious Concrete Produced Using Mixed Recycled Aggregates
Brazilian Archives of Biology and Technology
Waste produced by the construction sector is a problem that has grown over the last few years. Construction and demolition waste makes up about 50% by mass of the total solid waste produced in Brazil. One alternative by which to reduce this volume is recycling this material in the form of aggregates. However, it is necessary to analyze the environmental risk that the use of recycled aggregates can entail for adjacent soil and the water table. The purpose of this work was to evaluate pervious
... crete samples that contained recycled aggregates and to subject them to leaching tests. The results were compared with the limits established by the Italian methodology. Aggregates with 10, 25, 50, and 100% ceramic were used, as well as a recycled concrete aggregate and a natural aggregate. With the exception of the 25% ceramic trial, all the treatments introduced chromium to the water in which they were immersed, with accumulated concentrations varying from 0.009 to 0.099 mg L -1 . Cadmium was found in higher quantities, with cumulated concentrations between 0.104 and 0.417 mg L -1 . Sulfate concentrations were higher after 24 h of immersion, with a maximum release of 71.7 mg L -1 . The concrete made with 100% ceramic aggregate leached more chromium and sulfate than the other aggregates. CDW production has become an issue in many countries, leading them to require the allocation of areas for the deposition of these materials. For example, construction waste in Brazil is taken to specific landfills where it is recycled and stored until it can be used  . For this reason, the use of CDW as a recycled aggregate is being studied  . In addition, this would avoid the extraction and grinding process of natural aggregates, resulting in decreased consumption of energy and lower CO2 emissions  . The high availability and low cost of natural aggregates often impede the search for alternative materials  . However, the increasing use of natural resources causes local shortages, leading to the need for the materials to be transported and for a corresponding increase in price. With time, CDW could become a more viable option for recycled aggregate production. Countries like Denmark, Estonia, Germany, and England recycle up to 75% by mass of all CDW produced  . Even though Brazil has an installed capacity to recycle up to 46% of the volume of CDW generated, it is estimated that only 21% is used in aggregate production  . CDW consists of waste generated from construction, demolition, and renovation activities. The vast majority of CDW comes from building demolitions. However, new construction also generates waste  . This waste is mainly composed of concrete fragments, brick, and ceramic materials; however, depending on the type of activity that is being performed and the materials used, different kinds of waste, including wood, glass, plastic, metals, and soils, can be found [9, 10] . CDW can also be used as a recycled aggregate for pervious concrete production. Pervious concrete is a material that has a pore volume of about 15 to 35%, which allows water to drain through its interior [11, 12] . Tennis, Leming and Akers  affirms that because of this property, pervious concrete is an alternative for urban drainage systems. Reduction of runoff, groundwater recharge, and ambient temperature balance are some of the advantages of using this material  . The aggregate used in pervious concrete usually has a uniform particle size distribution, as this property yields a higher pore volume and ensures greater concrete permeability [14, 15] . The grain size of the aggregate can vary. Nonetheless, aggregates with uniformed larger dimensions provide this material with higher permeability [15, 16] . The most commonly used aggregates are those with dimensions between 1.18 and 19 mm, as determined using standardized sieves over a range of mesh sizes  . Results obtained by Ramezanianpour and Joshaghani  show that aggregates with dimensions from 9.5 to 12.5 mm can provide concrete with good permeability and compressive strength. Recycled concrete aggregates (RCAs) and mixed recycled aggregates can release heavy metals because of material leaching when they are used in pavement subbases  . The authors found chromium and sulfate after water passed through the aggregate, thereby simulating rainwater percolation. Jacob, Rocha, Cheriaf and Schaefer  also confirmed the presence of chromium, arsenic, zinc, and cadmium in leached water from conventional concrete made with recycled aggregates. Studies  shows that recycled aggregates with higher contents of ceramic tend to release higher quantities of chromium and sulfate. The main cause for pollutant release is contact with rainwater, which provokes leaching  . Although the mechanical performance of concrete containing waste has been studied , few studies have evaluated its environmental impact. In this sense, the purpose of this study was to analyze the quality of water leached from pervious concrete made with recycled aggregates containing ceramic material. Multiple incubation times were employed to yield as complete a picture as possible. MATERIAL AND METHODS Recycled aggregates Funding: This research received no external funding. Acknowledgments: The authors thank C-LABMU/UEPG for their support and for performing atomic absorption spectrometry. Conflicts of Interest: The authors declare no conflict of interest.