UC Davis

The short residence time of certain building materials, such as carpets, results in a notable waste stream that has the potential to be a resource for other material systems. In this work, we explore the utilization of post-consumer carpet calcium carbonate (PC4) consisting primarily of the material from carpet backing, which has thus far found few markets, as a potential mineral admixture in the production of concrete. The effects on mechanical and material properties are examined for concrete mixtures with PC4 used as 5 and 15% mass replacement of Portland cement, and PC4 used as 5 and 15% mass replacement of fine aggregates. The effects of PC4 on the slump, air content, unit weight, and setting times were assessed. Additionally, compressive strength, flexural strength, coefficient of thermal expansion, shrinkage, bulk density, void volume, and absorption were measured. Due to the known presence of antimony in PC4, leachate from cured specimens was examined. Additionally, greenhouse gas emissions to manufacture the mixtures were quantified. The results indicate that PC4 can increase air content in concrete by 3.5–10% and decrease the unit weight by up to 11% in fresh concrete. PC4 also led to a loss in compressive strength by up to 60%. Thus, the findings indicate that it is possible to form a less dense, more porous concrete by using PC4 as a mineral constituent in concrete, but with some loss in performance. Through appropriate selection of applications or through supplementary treatment of PC4, it may find a suitable market in the concrete industry.