3D Construction Printing Standing for Sustainability and Circularity: Material-Level Opportunities

Abstract

Three-dimensional Cementitious materials Printing (3DCP) is a cutting-edge technology for the construction industry. Three-dimensional printed buildings have shown that a well-developed automated technology can foster valuable benefits, such as a freeform architectural design without formworks and reduced human intervention. However, scalability, commercialization and sustainability of the 3DPC technology remain critical issues. The current work presents the ecological fragility, challenges and opportunities inherent in decreasing the 3DCP environmental footprint at a material level (cementitious materials and aggregates). The very demanding performance of printable mixtures, namely in a fresh state, requires high dosages of cement and supplementary cementitious materials (SCM). Besides the heavy carbon footprint of cement production, the standard SCM availability might be an issue, especially in the longer term. One exciting option to decrease the embodied CO₂ of 3DCP is, for example, to incorporate alternative and locally available SCM as partial cement replacements. Those alternative SCM can be wastes or by-products from industries or agriculture, with no added value. Moreover, the partial replacement of natural aggregate can also bring advantages for natural resource preservation. This work has highlighted the enormous potential of 3DCP to contribute to reducing the dependence on Portland cement and to manage the current colossal wastes and by-products with no added value, shifting to a Circular Economy. Though LCA analysis, mixture design revealed a critical parameter in the environmental impact of 3DCP elements or buildings. Even though cement significantly affects the LCA of 3DCP, it is crucial to achieving adequate fresh properties and rheology. From the literature survey, mixtures formulated with alternative SCM (wastes or by-products) are still restricted to rice husk ash, Municipal Solid Waste ashes and recycled powder from construction and demolition wastes. Natural aggregate replacement research has been focused on recycled fine sand, mine tailing, copper tailing, iron tailing, ornamental stone waste, recycled glass, crumb rubber, rubber powder and granules, recycled PET bottles and steel slag. However, flowability loss and mechanical strength decrease are still critical. Research efforts are needed to find low-carbon cement replacements and mix-design optimization, leading to a more sustainable and circular 3DCP while ensuring the final product performance.

Keywords: 3D printing; cement-based materials; circular economy; sustainability; waste valorization.

Figure 11

Worldwide availability of standard and unconventional SCM (Mt/y) that can be incorporated in cement-based materials (data source [110]).

Figure 1

World population (data source [10]) and cement production worldwide (data source [11,12]).

Figure 2

Number of documents published in English related to “3D concrete printing” or “3D printable concrete” or “3D printable cement-based composites” and literature on this topic related to “Circular Economy” or “Sustainability” (Data collected from Scopus in 26 December 2022).

Figure 3

Environmental impact (%) by category of three 3DCP scenarios compared with the reference value of construction of the conventional wall (data source [35]).

Figure 4

Whiskers box of cement-to-binder weight ratio for 157 mixtures design based on literature survey (data source: [30,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,89,90,91,92]).

Figure 5

Whiskers box of aggregate-to-binder weight ratio for 157 mixtures design based on literature survey (data source: [30,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,89,90,91,92]).

Figure 6

Whiskers box of water-to-binder weight ratio for 157 mixtures design based on literature survey (data source: [30,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,89,90,91,92]).

Figure 7

(a) 3DPCC constituent materials sources overview; (b) 3DPCC standard materials used as binder constituents.

Figure 8

Cement-to-binder weight ratio and aggregate-to-binder weight ratio in 22 3DPCCmixtures incorporating unconventional SCM as cement replacement (data source: [60,61,62,63,64]).

Figure 9

Aggregate-to-binder weight ratio and waste-to-total aggregate weight obtained from 3DPCC mixtures using unconventional aggregates (data source: [65,66,68,70,71,72,74,75,76,77,78,79,80,81,82,83,84,85].

Figure 10

Type, type of cement, grade of cement, and class of cement for 157 3DCP mixtures design (%) (data source: [30,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,89,90,91,92]).