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CONTACT US NOW TO KNOW MORE info@ssbuildchem.com | www.ssbuildchem.com CONCRETE WHY SS - CONPROOF CR? ๏Easy To Handle, Mix And Disperse ๏ Crystalline Action To Densify And Waterproof Concrete ๏ Improves Workability And Compaction ๏ Does Not Affect Setting Time, Or Compressive Strength ๏ Only Enhances Watertightness Of Concrete ๏Chloride Free, No Corrosion Promoting Action ๏Tested Upto 16 Bar Pressure WHY USE A CRYSTALLINE ADMIXTURE? ๏Secondary Protection for Underground Structures ๏Helps Densify Concrete and Seal Microcracks ๏Permanent Part of Concrete / Waterproofing ๏Protects Concrete from Aggressive Influences 0358 INTL. CONCRETE CONSTRUCTION TECHNOLOGIES | JULY - AUGUST 2024 Concrete 3D Printing Potential & Problems A. V. Rahul, Assistant Professor & Divya S. Kurup, Research Scholar, Department of Civil and Environmental Engineering, IIT Tirupati , discuss the progress being made in 3D Concrete Printing, applications worldwide, and the ongoing research to mitigate problems such as formation of cracks due to early-age shrinkage. C oncrete 3D printing (C3DP) is a new construction technology in which building components are "3D printed" with specially designed concrete based on a predefined virtual model. The technology has gained significant attention both in the construction industry and academia as it has the potential to automate building processes, create complex geometries without using formwork, and reduce labor cost and waste. However, the high plastic shrinkage cracking tendency is a critical concern with concrete 3D printed elements. This article discusses the research at IIT Tirupati on studying early-age shrinkage susceptibility of 3D printed concrete using non-contact- based digital image correlation techniques. The advantages of the developed test method and how it can be used to formulate shrinkage mitigation strategies are also discussed. Advantages of Concrete 3D printing Concrete 3D printing has drawn much interest in the construction industry in recent years. It is a technique by which a building component is fabricated in an automated manner by layerwise deposition of specially designed concrete using a concrete 3D printer. Automation has shown to be advantageous in many industrial sectors. For instance, industries like automotive, aerospace, and consumer goods production sectors use automation to reduce the cost and duration of their manufacturing processes [1]. Another main attraction of C3DP is that it allows the fabrication of complicated geometries that are difficult to create using traditional construction methods [2]. The C3DP technique lowers the cost of labor and eliminates formwork while improving production efficiency, accuracy, and worker safety. C3DP also reduces waste generation in the building sector. In summary, a compaction and form-free technique is made possible by 3D printing, giving designers previously unheard-of freedom to adapt irregular geometries [3]. However, the rheological properties of the materials used in 3D concrete printing and quick-setting characteristics are critical INTL. CONCRETE CONSTRUCTION TECHNOLOGIES | JULY - AUGUST 2024 9 for ensuring continuous pumping during extrusion and retaining shape integrity after extrusion [4]. Real-world uses of C3DP have been increasing for more than a decade. Some of the recent landmarks in C3DP construction are shown in Figure 1. The Nijmegen Bridge, also known as De Oversteek, spans the Waal River in Nijmegen, Netherlands, and combines modern architectural style with historical relevance (Figure 1a). Figure 1b shows a shape-optimized highway water culvert at Cornwall, United Kingdom, designed using the C3DP technology. Another notable construction project in the Netherlands is the Milestone House project, which highlights the architectural freedom possible through 3D printing and how it can be used to create innovative residential buildings (Figure 1c). Figure 1d is a 3D-printed footbridge named Striatus in Venice, Italy. It is an unreinforced structure made by assembling concrete blocks without using any mortar. The project combines the latest technology of C3DP with the principles of historic unreinforced masonry [15]. Early Research on C3DP Most of the early research on C3DP focused on understanding the rheological requirements and the development of printable concrete mix compositions [5]. Test methods were developed to assess early-age material requirements like extrudability, buildability, pumpability, and open time [6]. Following this, there were studies on the mechanical properties of 3D printable concrete and how it differs from conventional mould cast concrete. Researchers focused on assessing the factors affecting the interlayer bond strength [7] and developing test methods to evaluate the mechanical properties [8]. The current research needs are in developing structural design and reinforcement strategies in C3DP, developing advanced 3D printer systems that involve an accelerator addition, inline mixing at the nozzle for rapid stiffing of the concrete mix after extrusion [9], and the durability of C3DP elements [10]. Concerns in C3DP Another aspect that requires significant attention is shrinkage. Shrinkage has become a major concern in C3DP. For instance, Figure 2 shows severe cracks developed in C3DP elements due to early-age shrinkage. Factors such as the absence of formwork, high binder content, and the addition of fine materials like silica fume substantially increase the early-age shrinkage in the 3D printable mixes. Shrinkage has also been found to adversely affect the bond strength between layers of C3DP elements [11,12]. Research at IIT Tirupati One of the main emphases of the research group at IIT Tirupati has been to examine the early-age shrinkage susceptibility of various C3DP mixes. The main challenge is the lack of a suitable test method for assessing early-age shrinkage. Conventional shrinkage measurement techniques, such as ASTM C157 [16] for free shrinkage or ASTM C1581 [17] for restrained shrinkage, require physical contact with the specimen or need specialized moulds in which the specimen has to be cast. These methods are impractical for a formwork-free construction like C3DP. Figure 1: Landmark 3D-printed constructions around the world. (a) Nimegen Bridge -29 m, Netherlands (taken from [13]) (b) 3D printed highway water culvert, United Kingdom (taken from [14]) (c) Milestone house, Netherlands (taken from [15]), (d) 3D printed footbridge, Italy (taken from [15]) (a)(b) (c) Figure 2: Cracks due to early-age shrinkage in concrete 3D printed elements (taken from [11] (d)Next >