Novel ecosustainable peat and oil shale ash-based 3D-printable composite material Jüri Liiv a, ⁎, Tõnis Teppand b , Ergo Rikmann a , Toomas Tenno a a Tartu University, Estonia b Estonian University of Life Sciences, Estonia abstract article info Article history: Received 20 April 2018 Received in revised form 26 June 2018 Accepted 27 June 2018 Available online xxxx In this study, a novel peat composite construction material suitable for three-dimensional printing of entire house boxes (walls, floors, ceilings, etc.) was developed. Peat was used as filler to achieve excellent thermal prop- erties. Using peat for this purpose has not been mentioned in the earlier literature because it retarding properties to the cementation process. As a binder, combustion fly ash was used. The retarding properties of peat humic sub- stances on hardening of pozzolanic mixtures were successfully overcome by using silica fume as an additive. The same additive also greatly improved the long setting time of oil shale ash. The mechanism of hardening of the composite material was hypothesized as the following: first, upon contact with water, the pH of pore water exceeded 13 due to the high content of oxides of alkali metals in the ash, which promoted the oxidation of hu- mates into oxalate. Then, alkali metal, aluminum and silicate ions (the latter mostly originating from silica fume) with alumina formed insoluble feldspars leading to a decrease in pH. At pH values lower than 12.4, Ca (OH) 2 became soluble and Ca 2+ ions migrated to the liquid phase, allowing pozzolanic reactions to occur and cal- cium oxalate to precipitate. Finally, the residual Ca(OH) 2 reacted with atmospheric CO 2 to form CaCO 3 . Test sam- ples were 3D-printed using experimental apparatus, the printing head involved a nozzle delivering wet peat-ash mixture using compressed air. The material was characterized by measuring its thermal resistance (b0.08 W/(m K)), compressive and bending strengths (1.2 MPa and 0.36 N/mm 2 , respectively). Using peat com- posites in the construction industry allows reducing CO 2 emissions from partially mined peatlands (currently the one of the largest contributors to the total CO 2 emission from Estonia) and increasing the reuse of oil shale ash while providing a cheap and affordable raw material. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Three-dimensional (3D) printing is an advanced manufacturing pro- cess that produces a target object automatically from a 3D computer- aided design model without any tooling, dies and fixtures. The target object, which can have complex shaped geometry, is manufactured in a layer-by-layer manner by depositing material exactly where it is de- fined in the digital model [1]. Although the concept of 3D printing has been hovering around for some time now, only recently has the actual use of 3D printing and its adaption into the construction industry started to become a reality. 3D printing is expected to revolutionize the construction industry by enabling the tackling of the main chal- lenges the construction sector is currently facing, including stagnant ef- ficiency (manufacturing industry vs construction industry from 1995 to 2011 (16 years): 1.7 times less added value) [2] and constantly increas- ing costs. In addition to faster and more accurate construction process, the advantages of using 3D printing in the construction industry include reduced labor costs, waste generation, health and safety risks, and im- proved environmental friendliness, providing opportunities for more sustainable and affordable housing. Using 3D printing, no construction formwork is required [3]. The main objective of this study was to develop an environmentally friendly peat and fly ash based printable construction material. Peat has excellent antibacterial and thermal properties [4] (the thermal conduc- tivity of pure peat is between 0.037 and 0.08 W/(m × K)) [5] and is widely available in many regions in the world [6]. The material can be used to form large blocks or entire construction elements (walls, ceilings, etc.). These elements require minimal after processing, the entire house box can be printed in hours or days includ- ing walls, floors, ceilings, roof, etc. The other key element of the technol- ogy is a mobile 3D printer allowing printing houses using the described material in situ on the building site [3]. Currently, all the 3D-printing technologies are based on concrete/ fiber or clay/fiber compositions. Peat (despite the excellent properties) was not used because of retarding properties avoiding its use in Sustainable Materials and Technologies xxx (2018) e00067 ⁎ Corresponding author. E-mail address: juri.liiv@ut.ee (J. Liiv). SUSMAT-00067; No of Pages 7 https://doi.org/10.1016/j.susmat.2018.e00067 2214-9937/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Sustainable Materials and Technologies journal homepage: www.elsevier.com/locate/susmat Please cite this article as: J. Liiv, et al., Novel ecosustainable peat and oil shale ash-based 3D-printable composite material, (2018), https://doi.org/ 10.1016/j.susmat.2018.e00067