DOI: 10.24355/dbbs.084-202510290959-0
title: Fabrication of Dry Connection through Stamping and Milling of Green-State Concrete

description: This study explores efficient fabrication strategies for producing geometrically diverse dry connections in concrete, addressing challenges related to cost, production time, and geometric precision. The research focuses on developing rebar-free dry joints using two complementary processes: stamping and green-state CNC milling. Each method is systematically evaluated in terms of dimensional accuracy, tool wear, and energy consumption. In the stamping investigation, a design-of-experiments (DOE) framework was applied to assess the effects of water content, concrete age, stamping load, and operational variables (vibration and formwork type) across four geometries: cone, truncated cone, truncated pyramid, and pyramid. Results indicate an optimal working window between 90 and 120 minutes after mixing, with the most favorable performance typically around 90–105 minutes. Specific deviations—such as ~68 minutes for the truncated cone and ~130 minutes for the pyramid—were attributed to geometry–age interactions rather than outliers. Among the parameters tested, water content most strongly affected lateral dimensional deviation (diameter/width), while age primarily governed vertical accuracy. For green-state milling, both extrusion-printed and shotcrete-printed specimens were machined at 90 minutes, 1 day, and 1 week. Results show that tool abrasion and energy consumption increase with curing time, and that extrusion-printed stock required slightly higher energy than shotcrete at equivalent ages. Two engagement modes—side (flank) milling and end-face (head) milling—were analyzed independently. The end-face mode caused markedly higher tool wear, accounting for tolerance drift in the final joint geometries. In addition, a soil-based forming approach was demonstrated, in which a stamp was pressed into oil-treated fine sand to create a reversible mold. This method achieved high-fidelity replicas with smooth release surfaces, offering a practical alternative when friction or demolding limitations restrict direct stamping. This study explores efficient fabrication strategies for producing geometrically diverse dry connections in concrete, addressing challenges related to cost, production time, and geometric precision. The research focuses on developing rebar-free dry joints using two complementary processes: stamping and green-state CNC milling. Each method is systematically evaluated in terms of dimensional accuracy, tool wear, and energy consumption. In the stamping investigation, a design-of-experiments (DOE) framework was applied to assess the effects of water content, concrete age, stamping load, and operational variables (vibration and formwork type) across four geometries: cone, truncated cone, truncated pyramid, and pyramid. Results indicate an optimal working window between 90 and 120 minutes after mixing, with the most favorable performance typically around 90–105 minutes. Specific deviations—such as ~68 minutes for the truncated cone and ~130 minutes for the pyramid—were attributed to geometry–age interactions rather than outliers. Among the parameters tested, water content most strongly affected lateral dimensional deviation (diameter/width), while age primarily governed vertical accuracy. For green-state milling, both extrusion-printed and shotcrete-printed specimens were machined at 90 minutes, 1 day, and 1 week. Results show that tool abrasion and energy consumption increase with curing time, and that extrusion-printed stock required slightly higher energy than shotcrete at equivalent ages. Two engagement modes—side (flank) milling and end-face (head) milling—were analyzed independently. The end-face mode caused markedly higher tool wear, accounting for tolerance drift in the final joint geometries. In addition, a soil-based forming approach was demonstrated, in which a stamp was pressed into oil-treated fine sand to create a reversible mold. This method achieved high-fidelity replicas with smooth release surfaces, offering a practical alternative when friction or demolding limitations restrict direct stamping.