The effect of using recycled PET aggregates on mechanical and durability properties of 3D printed mortar

Abstract

3D concrete printing technology of cementitious materials is challenging in many aspects. Despite the workability and mechanical properties of a mix and hardened concrete or mortar, the researchers need to face problems with environmental impact and durability of printed elements. Furthermore, today thousands of tons of waste are produced and natural aggregates which are most used resources by volume in the construction sector are on the verge of exhaustion. To date, limited knowledge about utilized of artificial aggregate (including Polyethylene terephthalate (PET) in 3D printed mortar is available. The main objective of this study is to develop 3D printed mortar with PET granules as the replacement of natural aggregate (10 vol-% to 50 vol-%). The paper contributes to knowledge of properties of 3D printed composites with plastic aggregate. Four printable mixes were made: one reference mix and three mixes in which natural aggregate was replaced by PET granulate in quantities amounting to 10%, 30% and 50% (by volume), respectively. The replacement ratios were chosen on the base of literature review for ordinary cementitious mortars. Several strength tests were carried out for standard and printed specimens. In addition, a freeze–thaw resistance test and high temperature performance test were conducted to evaluate to validate the properties of artificial aggregate. The results show that PET granulate is useful in 3D printing owing to their buildability and extrudability properties. Furthermore, printed mixes with high amount of PET (30% and 50%) granulate shows high decreases in strength (up to 75%). Unfortunately, after the freeze–thaw resistance test specimens with a high amount of PET granulate (30% and 50%) indicated high strength reduction (up to 80%). Exposure to a temperature exceeding the melting point of PET results in significant reduction of compressive strength for printed specimens (up to 68.8 % for 50 % PET addition). In addition, mixes with up to 10% PET can be used for most structural elements even under varying thermal conditions (even under extreme cold temperature).