Effect of supplementary cementitious materials on properties of 3D printed conventional and alkali-activated concrete: A review

Abstract

3D printing is a novel technology that has been introduced to construction industry and has been found to have numerous potentials including high speed fabrication of customized building elements without formworks and low material waste. Despite such superiority, to ensure the extrudability of materials and their coherent adhesion, most commonly, a higher content of the Portland cement (PC) with other chemical admixtures are used in 3D printed concrete (3DPC) mixes. This common practice, however, can result in augmentation of greenhouse gas emissions and also increase in the costs associated with 3D printing. To avoid this, and provide favorable printability properties, supplementary cementitious materials (SCMs) have gradually become a key ingredient of 3DPC. Utilizing SCMs, previous studies have found the critical effects of SCMs on operational aspects of 3D printers and their controls on a variety of functional parameters. To closely evaluate such parameters, the present study provides a review of the effect of SCMs on 3DPC with and without alkaline activator, focusing on manufacturing techniques, rheological properties, mechanical properties, bond strength between printed layers, effect of curing regime, and shrinkage behavior. The main challenges and future research direction of 3DPC are also presented. Based on the presented review, it is found that coal fly ash, silica fume, blast furnace slag and metakaolin are the main SCMs that are commonly used to enhance pumpability, printability, and buildability of 3DPC, as well as addressing environmental issues associated with the larger use of PC in 3DPC.