Most U.S. structures built before 1980 contained lead-based paints (LBP), which are now known to be a human health hazard. Deconstruction of these LBP-contaminated buildings, many of which reside on military installations, has progressed at a slow rate due to the high disposal costs and environmental impacts. LBP removal techniques present an alternative approach to hazardous waste disposal of deconstruction materials but are at present limited because these methods are time-consuming and not economical for recycling masonry materials from deconstruction and because LBP removal residues are highly concentrated and must be treated before disposal. More cost-effective, environmentally friendly techniques for remedying and reusing deconstructed masonry materials contaminated with LBP are needed.
The objectives of this SERDP Exploratory Development (SEED) project were to (1) provide an effective method for deconstruction of masonry buildings and other permanent structures with minimal environmental impact, cost, and time; (2) sequester and/or physically encapsulate the lead in painted masonry materials by recycling them as concrete aggregate and mixing them with high alkaline portland cement or phosphate cement materials; and (3) develop a mix design for proportioning concrete mixes containing aggregates recycled from field-deconstructed masonry materials.
Typical masonry materials were selected and painted to equal or exceed the lead content found in existing LBP-contaminated masonry structures on military installations. These simulated LBP-contaminated masonry materials were then crushed into sizes that could be processed economically at a deconstruction site and fit general concrete structural design requirements. Features of the recycled aggregates such as density, absorption, gradation, dust content, and lead content were characterized. Different types and amounts of cement then were selected to sequester LBP in the recycled aggregate. A concrete mix design matrix was developed in consideration of aggregate gradation, water-to-cement ratio, and aggregate-to-cement ratio. Screening tests were performed for the designed concrete mixes to ensure the proper selection of mix proportions that abated the lead hazard in the recycled aggregates and met workability and strength requirements for new field construction. Based on screen test results, a concrete mix design nomogram, which showed relationships between the mix proportion parameters and concrete performance, was developed for designing various concrete mixes containing aggregates recycled from field-deconstructed masonry materials.
This research provides Department of Defense (DoD) engineers and facility managers valuable information and practical tools for characterizing and designing recycled-aggregate concrete. These products enable LBP-contaminated masonry materials to be converted into new construction materials, which reduces the amount of hazardous waste disposal currently required of such materials. Implementation can lead to significant reductions in the cost and environmental impact of DoD construction and deconstruction projects. (SEED Project Completed - 2008)