A methodology for designing 3D printable mortar based on recycled sand

This paper proposes a methodology for the mixture proportioning of 3D printable mortar containing recycled sand (RS), having similar fresh and hardened properties to a reference 3D printable mortar made with natural sand (NS). The methodology is based firstly on a fast and accurate characterization of the water absorption coefficient of the RS and secondly on the volume substitution of the NS by RS. This allows hardly changing the composition of the cement paste, slightly modifying the admixture dosage with a constant W eff /C ratio. The proposed methodology is applied to two different recycled sands. Results at the fresh state show that the structuration rates of recycled mortars are slightly lower than those of the reference mortar due to the slight increase in superplastizer content, but the close obtained values suggest that the W eff /C ratios are very similar in the three mortars. This result is confirmed by the porosity measurement on hardened mortars, which shows that the porosities of the cement pastes of the three mortars are almost identical. The compressive strength of recycled mortars is slightly lower than that of the reference mortar, which can be attributed to the lower intrinsic properties of RS compared to NS. This methodology enables the use of recycled sand as a sustainable alternative to natural sand in 3D printing applications.