3D Printing of Hybrid Cements Based on High Contents of Powders from Concrete, Ceramic and Brick Waste Chemically Activated with Sodium Sulphate (Na2SO4)

Abstract

This article evaluates the synthesis, characterization and 3D printing of hybrid cements based on high (70%) contents of powders from concrete waste (CoW), ceramic waste (CeW) and red clay brick waste (RCBW) from construction and demolition waste. For the synthesis of the hybrid cements, 30% (by weight) of ordinary Portland cement (OPC) was added. Sodium sulphate (Na2SO4) (4%) was used as a chemical activator. The effect of the liquid/solid ratio on the properties in the fresh state of the mixes was studied by means of minislump, flowability index, and buildability tests. The compressive strength was evaluated at 3, 7, 28 and 90 days of curing at room temperature (≈25 °C), obtaining strengths of up to 30.7 MPa (CoW), 37.0 MPa (CeW) and 33.2 MPa (RCBW) with an L/S ratio of 0.30. The results obtained allowed selecting the CoW 0.30, CeW 0.33 and RCBW 0.38 mixes as optimal for carrying out 3D printing tests on a laboratory scale, successfully printing elements with good print quality, adequate buildability, and compressive strength (CoW 0.30 = 18.2 MPa, CeW 0.33 = 27.7 MPa and RCBW 0.38 = 21.7 MPa) higher than the structural limit (≥17.5 MPa) established for concrete by Colombian Regulations for Earthquake Resistant Construction (NSR-10).