Senthil Kumar Kaliyavaradhan

This research explores the potential of using copper slag as a substitute for river sand in 3D printable concrete (3DPC), aiming to enhance sustainability in construction. The research evaluates three different concrete mixes: a reference mix with river sand (RS-BM) and two mixes with full replacement of copper slag by volume (CS-VR) and by weight (CS-WR). The key aspects analyzed include fresh properties such as rheology, flowability, extrudability, open time, and buildability. The results show that CS-VR mixes maintain desirable flow and slump characteristics, with consistent printability and stability similar to those of RS-BM. The CS-VR exhibited the longest open time and superior buildability, with minimal shape deformation. The rheological analyses reveal that the Modified Bingham model best represents the dynamic yield stress (DYS) for the mixes. The CS-WR consistently shows the highest DYS values, indicating robust printability and structural integrity. The viscosity analysis across shear rates illustrates shear-thinning behavior in all mixes, with RS-BM exhibiting higher initial viscosity compared to CS-VR and CS-WR. This study concludes that copper slag-based mixes (CS-VR and CS-WR) offer potential benefits over 3D printable river sand mixes in terms of material performance and environmental impact.

There are several significant advantages to 3D concrete printing (3DCP) over conventional concreting techniques. Structures are built by printing them one layer at a time. This study aimed to improve the usability and accessibility of this technology to solve on‐site issues, such as those caused by chemical admixture. In order to construct concrete that can be printed in three dimensions, researchers added many chemical admixtures in controlled quantities. This experiment's main goals were to prepare 3D printable concrete (3DPC) without chemical admixture and to evaluate fresh and hardened properties. Slump, flow, extrudability, buildability, open time, and penetrometer tests were carried out for fresh properties. Compressive, flexural, splitting tensile strength, and modulus of elasticity were evaluated for hardened properties. The printed specimens in the longitudinal direction exhibited higher compressive strength than in the downward and lateral directions. Similarly, higher flexural and splitting tensile strength in the longitudinal direction of printed specimens than in the downward and lateral direction. The results of developing 3DPC without chemical admixtures demonstrated good performance in fresh and hardened properties.

This paper investigates the use of non-metallic portion (NMP) reclaimed from e-waste (i.e., waste printed circuit board—PCB) as replacement of natural sand in the blended cement concrete by using Metakaolin (MK) as supplementary cementitious material for its effect on the mechanical, durability, microstructural, and mineralogical properties of concrete. It was found that the blended mixes containing NMP and MK outperformed the control mix. With the addition of 10% NMP and 10% MK, the maximum compressive strength was obtained, with the splitting tensile and flexural strength following the same trend. The performance of the mixes was lowered above 10% replacement levels, although it was still better than the control mixture. When compared to other mixes, 10% NMP and 10% MK concrete had the lowest sorptivity and water absorption values, as well as the highest resistance to chloride-ion penetration. FESEM was used to confirm the results, and then XRD was used to determine the elemental classification. This study lays the groundwork for a long-term strategy for utilising NMP and MK as extremely effective concrete additives.

In recent decades, the use of controlled low-strength material (CLSM) in densely populated cities has increased. CLSM is designed for future excavation with great fluidity, appropriate early strength, and low final strength. CLSM mixtures exhibit variable strength properties and performance due to the distinctive features of wastes (i.e., combustion residues, industry slags, and construction and other solid wastes) produced from various sources. CLSM should increase early strength quickly enough to allow traffic to resume within a few hours while maintaining a low strength for future re-excavation. It is suggested that the initial mixture design for each waste reported in the literature be changed until the combination meets the application standards defined in ACI 229R-13. The effects of adjusting other ingredients (i.e., cement, water, and admixtures) in the wastes incorporated into CLSM mixtures on the strength and re-excavatability properties are also detailed and discussed in this review. From practical and economic perspectives, the supply of materials in the waste streams, transport distance, and material properties and cost are important aspects to consider before their introduction to the construction industry.