Behavior and mix design development of concrete made with recycled aggregate from deconstructed lead-contaminated masonry materials

The present study is to develop an effective method for using deconstructed, lead-contaminated masonry materials in new concrete so as to minimize the environmental impact, cost, and time of the deconstruction. The approach to this method is to use crushed masonry materials to replace natural aggregate in conventional concrete. Two different types of masonry materials (concrete blocks and clay bricks) were collected, painted with lead-based paint (LBP), and then crushed to simulate recycled LBP-contaminated masonry materials. Three types of cement (type I Portland cement, Calcium Sulfoaluminate (CSA) cement, and Portland cement with 5% phosphate addition) were selected for sequestering lead in the recycled aggregate. A concrete mix design matrix was developed with different water-to-cement ratios (w/c), aggregate-to-cement ratios (a/c), types of cements, and types of masonry materials. Based on the test results, mix design nomographs were developed for concrete made with the recycled, LBP-contaminated masonry materials. The results indicate that the lead can be sequestered, or rendered non-leachable, due to the high alkalinity of cement. The concrete therefore no longer has the toxicity characteristic for lead and is suitable for various types of new construction, such as foundation and pavement, reinforced beams, columns, and walls.