| dc.description.abstract | 3D printing concrete technology is an automated construction method that offers greater geometric freedom and lower material consumption compared to traditional casting methods. This study employs various types of sustainable materials to replace conventional materials at high ratios and incorporates fibers to enhance performance, creating sustainable 3D printed fiber-reinforced concrete. The fresh properties, hardened properties, and drying shrinkage of the concrete are tested to evaluate the compatibility and engineering properties of sustainable materials and fibers in 3D printing concrete.
This research is divided into three phases: ＂Effects of Sustainable Cementitious Materials on the Engineering Properties of Cement Paste,＂ ＂Effects of Sustainable Materials on the Engineering Properties of 3D Printing Concrete,＂ and ＂Effects of Fibers on the Engineering Properties of 3D Printing Concrete.＂ The first phase investigates the impact of different sustainable cementitious materials (densified silica fume(SFD), undensified silica fume(SFU), fly ash(FA), ground granulated blast furnace slag(BF), limestone(LS), metakaolin(MK), paper sludge fly ash(PSFA), ultra-fine fly ash(RUFA), oyster shell powder(OSP), and calcium sulfate whisker(CSW)) on the fresh and engineering properties of cement paste at various resting times (0 min, 10 min, and 30 min). The second phase explores the effects of promising sustainable cementitious materials at different replacement ratios (30 %, 40 %, 50 %, and 60 %) for cement(PC), and the use of sustainable aggregates (manufactured sand(MS), and artificial sand(AS)) in 3D printing concrete, evaluating their impact on fresh properties, printability, hardened properties, and drying shrinkage, proposing mixtures that meet engineering properties and sustainability benefits. The third phase examines the impact of adding fibers (polyoxymethylene fiber (POMF), polypropylene fiber (PPF), carbon fiber (CF), and CSW) on the engineering properties of 3D printing concrete, designing composite fiber mixes based on different fibers characteristics, and evaluating the effectiveness and compatibility of composite fibers in improving 3D printing concrete.
The results of the first phase show that replacing 30 % of PC with SFD, SFU, FA, BF, MK, and RUFA does not affect printability and provides sufficient hydration capacity to maintain concrete strength. The second phase results indicate that using promising sustainable cementitious materials (SFD, FA, and BF) and sustainable aggregates in 3D printing concrete meets printability standards after adding appropriate admixtures, though flow values vary by material, with shape retention rates above 85 %. Considering the sustainability and strength of the mix, the optimal replacement ratio of sustainable cementitious materials for PC is 50 %; higher ratios decrease strength, while lower ratios lack sustainability. For drying shrinkage, suitable replacement ratios of different sustainable cementitious materials reduce specimen shrinkage, with FA performing best, followed by BF, while excessive SFD (> 60 %) increases shrinkage. Among the sustainable aggregates, AS has good shape retention but low strength and serious volume stability issues, MS performs well in both shape retention and strength, making it suitable for 3D printing concrete. The third phase results show that different fibers affect mechanical properties in various ways: POMF and PPF enhance concrete toughness but reduce strength, while CF and CSW increase strength but do not improve toughness. For drying shrinkage, adding up to 1.5 % POMF and 1.0 % CF reduces shrinkage rate, while PPF and CSW increase shrinkage with higher content. The 3D printing process results in lower concrete strength compared to traditional casting methods and introduces anisotropy. For compressive strength, the anisotropy without fiber addition is observed as X > Z > Y, and with fiber addition as X > Z ≒ Y. In terms of flexural strength, the anisotropy consistently shows Y > X. However, the overall coefficient of variation remains close to 0, indicating minimal strength differences across different directions. Based on the test results, the final proposed mix is a 1:1 volume ratio replacement of PC with SFD and FA, totaling 50 %, with the addition of 0.5 % PPF and 1.0 % CSW by volume. This mix achieves a 50 % replacement ratio of PC, with 28-day compressive and flexural strengths reaching 88.9 MPa and 13.6 MPa respectively, and improved toughness. Compared to other studies, the replacement ratio of sustainable materials increased by 3 % ~ 38 %, compressive strength improved by 14 % ~ 154 %, and flexural strength increased by 65 % ~ 185 %, further reducing CO2 emissions from concrete while enhancing mechanical properties. This mix achieves structural strength requirements with less material, offering excellent sustainability and mechanical properties. | en_US |