Influence of Engineered Natural Fiber Reinforcement in 3D Printed Earth-Based Cementitious Composites (2026-01)¶

3D printing using earth has attracted increasing interest from both scientific and industrial communities. Despite the low embodied carbon of earth constructions often suffer several challenges such as moisture sensitivity, dimensional instability, and low strength. These challenges can be addressed through stabilization by using low-carbon binders and integrating natural fiber reinforcement in 3D-printed earth (3DPE). Thus, this research investigates the effect of blended binders and engineered natural coir fibers on extrudability and engineering performance of printable stabilized earth mixes. Coir fiber was selected for its moderate strength, excellent microbial resistance, and abundant availability in tropical regions. However, its inherent hydrophilic nature weakens the fiber-matrix interface due to moisture absorption, thereby affecting the overall performance of 3D-printed stabilized earth. To address this limitation, the coir fibers were engineered by two means: (i) chemical treatment by soaking in a 5 % w/v of calcium hydroxide solution (FLi) for 24 h, and (ii) accelerated carbonation of lime-treated coir fibers (FLc) at 15 % CO2 and 65 % relative humidity(RH) for 5 h, resulting in the formation of calcium carbonate crystals on the fiber surface. Accordingly, three fiber cases comprising untreated coir fibers (F), FLi, and FLc were employed as reinforcement, possessing a 20 mm length and 0.5 wt% of total solids. Binder systems included ordinary Portland cement (OPC) and a blend of 70 % OPC and 30 % ground granulated blast-furnace slag (GGBS), with 50 % of the natural sand replaced by excavated soil. Experimental findings revealed that the flow retention of FLc-based mixes improved by 10–20 % compared to the F-based mixes, attributed to 8–14 % reduction in water absorption by the FLc fibers. This results in a moderated yield stress, contributing to enhanced shape retention in printed FLc-based mixes. Improved adhesion bonding (10–15 %) in FLc-based mixes resulted in an 8–15 % enhancement in 28-day compressive strength and flexural toughness. Notably, the drying shrinkage of FLc-based mixes was mitigated by 15–20 % compared to FLi- and F-based mixes, thereby improving dimensional stability. Additionally, capillary water absorption was reduced by ≈ 15 %, enhancing resistance to moisture ingress. Overall, the findings offer an effective pathway for improving the resiliency of natural fiber-reinforced 3DPE constructions through engineered coir fiber reinforcement.