Processing of Cementitious Materials for 3D Concrete Printing (2019-06)¶

Industry 4.0 is considered a new industrial stage in which vertical and horizontal manufacturing processes integration with information and communication technologies can help industries to achieve higher performance. Among these industries, the construction industry is regarded as the horizontal industry as it serves other industries through building infrastructure or other ‘constructed assets’ [1]. Butitisvery unfortunate to learn that the construction industry is more monopolistic in nature and always gives resistance to change for any technological innovations leading to lower productivity and higher cost [2]. Though there has been some improvement in the enterprise or company level strategies to smoothen the supply and demand side requirement, it is always lagging other sectors as there is no scientific change in the conventional construction practices [3]. In addition, the construction industry is not sustainable from economic, social, or environmental perspectives [4]. Consequently, the construction industry is shaken up by multiple global megatrends such as the affordable housing crisis (which is increasing by 2,00,000 people per day) and high greenhouse gas emissions (30% of the total) [1]. Considering all these facts, the building and construction industry is seen to be under a moral obligation to transform and adopt digitalization to its maximum extent. Out of all digital construction methods, the use of 3D printing in construction comes out to be a disruptive technology that starts with the digital design file (CAD) and follows a complete automated cycle to print the entire building with very little human intervention. Concrete 3D printing (3DCP) is a novel construction method that uses the principle of additive manufacturing to build the complete structure in a layered fashion, following the 3D model. Unlike conventional construction methods, mold erection is not required in 3DCP. The application of 3DCP mainly focused on the construction sector for creating modular houses, bridges, offices, public schools, bus stops, low-cost toilet units, etc. [5]. In most of the applications, design freedom and sustainable structures are found to be the two key factors for successful implementation. Concrete printing can be divided into different groups of technologies according to the materials used and their deposition technique. In the case of cement-based material, mainly two techniques have been used so far which are (1) powder-based and (2) extrusion-based printing [6]. This method is the most frequently used one in the construction industry, which was famously known as Contour Crafting (CC) in the initial days [7]. Though this technique follows a similar deposition style used in the Fused Deposition Modeling (FDM) process, the main difference lies in the solidification mechanism of concrete material, which does not set instantaneously, rather stays in an intermediate state, leading to a challenging problem for balancing extrudability and buildability criteria [8]. However, with R&D contribution by industries and academicians, many emerging problems (material design [9], processing technology [10], Reinforcement placement [11], Mechanical and durability properties [12]) have been addressed, and by the end of 2020, a total of 29 houses have been built around the globe using 3D printing technology [13, 14]. Based on current state of the art, Fig. 1 marks the countries involved in 3DCP research and demonstration [5].