The Development of Soil-Based 3D-Printable Mixtures: A Mix-Design Methodology and a Case Study

Abstract

Concrete 3D printing is one of the newest technologies in the field of construction. However, despite the various opportunities that this technique offers today, it still has a high environmental impact, as most 3D-printable materials contain high amounts of cement. On the other hand, due to the large volumes of soil excavated each year across the world, there is a pressing need for proper management to dispose of it or reuse it efficiently. This study aims to develop sustainable and resistant 3D-printable materials with low environmental impact using excavated soil. Firstly, a series of tests were carried out to find the most appropriate superplasticizer and the amount required to develop the printable mixtures. Next, the extrudability and buildability were evaluated and verified to validate the printability of the developed mixtures. A 3D laboratory printer was also used to validate the printability of the mixtures on a larger scale. Then, the fresh and hardened properties of the printable mixtures were investigated. Three printable mixtures were developed, with the most environmentally friendly mixture having a soil content of 1602 kg/m3 and a cement content of 282 kg/m3. The mixtures demonstrated satisfactory characteristics and properties in both fresh and hardened states. On the one hand, the mixtures were extrudable and buildable at two laboratory scales. On the other hand, the mixtures presented sufficient compressive strengths, ranging from 16 MPa to 34 MPa, despite their high soil content and low cement content. In addition, their compressive strengths were found to be higher than the minimum strength required for structural concrete. Consequently, this study highlights the possibility of developing ecological, sustainable and resistant mixtures that can be used in 3D-printing construction applications using excavated soil.

First Impressions on Three-Dimensional Printing with Earth-Based Mortar at the Faculty of Engineering of the University of Porto

“…The use of superplasticisers in earth mortar can minimise or even eliminate the occurrence of finishes with less smooth textures or material discontinuity [11].…”

Additive Manufacturing of Earth-Based Materials: A Literature Review on Mortar Composition, Extrusion, and Processing Earth

“…Due to the limited capacity to construct layers, some authors created samples over multiple-day sessions [ 64 ], which can result in weak points between the layers [ 83 , 84 ]. Other authors preferred to build a solid multilayer block [ 26 , 44 , 59 ], aiming to avoid the collapse of the structure and subsequently cutting smaller samples. In this case, higher weight pressure or voids between layers can be created.…”

“…During layer-wise construction, the previously printed layer needs to develop enough strength to support the additional load of subsequent layers. In the literature, various methods of stabilization to enhance the early strength development of earth-based mortars can be found [ 26 , 62 , 85 ]. However, as previously mentioned, to create a sustainable mortar, the materials should obey the principles of sustainability; so, low quantities of calcinated materials and chemicals must be used.…”

“…Many other factors can be added to the characterization of the material pumpability, including the lubrification layer [ 94 , 101 ] and segregation [ 26 , 101 ], which influence the quality of the extruded material. Additionally, the fabric material, diameter, and length of the hose impact the pump pressure due to friction forces and mortar viscosity.…”

“…However, it is important to recognize that earth possesses a high degree of versatility and can be utilized more effectively and intensively in buildings. Apart from the low energy associated with transport, crushing, and milling, there is no energy used for calcination [ 6 , 26 ]. The labor costs depend on the country’s social and cultural aspects, as well as on building technology.…”