Assessment of plasterboards containing chemically modified gypsum waste

The standard recycling process for construction, refurbishment and demolition plasterboard waste involves several mechanical steps that include manual segregation, grinding, sieving, and ferrous and non-ferrous magnetic separation. However, one of the main challenges to obtain suitable recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste comes from the difficulty of achieving consistently high purity levels via current mechanical recycling technologies. In addition, post-consumer plasterboard waste contains water-soluble impurities that affect paper-gypsum bonding during plasterboard production. As a result, most post-consumer plasterboard waste is not recycled and ends up in landfills, decomposing and releasing toxic hydrogen sulphide, or used in low-grade applications such as agriculture or additive in cement production. A modified mechanical process and a novel acid leaching purification process were developed and combined to obtain a recycled gypsum product from post-consumer plasterboard waste with consistent purity values above 96 wt%, fulfilling all quality requirements from plasterboard manufacturers. After acid leaching, the purified gypsum was recovered via two methodologies: i) filtration and gypsum cake washing, and ii) acid neutralisation and filtration. Then, plasterboards with dimensions 200 mm × 200 mm × 12.5 mm were prepared at laboratory scale containing either 35 wt% of purified gypsum (washed or neutralised) or 10 wt% of business-as-usual recycled gypsum. These plasterboards were characterised to determine their thermal, physical and mechanical properties. The results showed no significant differences in the thermal, physical and mechanical properties of the plasterboards containing 35 wt% purified gypsum and the plasterboard with 10 wt% recycled gypsum. These findings validate the introduction of high shares of purified gypsum (35 wt%) during standard plasterboard manufacturing.