223 / 2022-06-11 10:37:58

Development of 3D printable ECC and its bio-mimetic flexural members

3D concrete pinting, Bio-memitic, Engineered cementitious composites, Four-point bending test

3D concrete printing (3DCP) is gaining more and more attentions due its easy operation, quick construction, and low labour cost. However, there still remains challenges to embed longitudinal reinforcement into printed concrete during the printing process. This study aims to develop a self-reinforced concrete (i.e., engineered cementitious composites, ECC) with appropriate printability and superior tensile strain capacity for 3DCP.



To obtain the mix proportion of printable ECC, the printability and mechanical properties of ECC were tailored by changing the dosage of water reducer and replacing silica sand with different volume fractions of crumb rubber, respectively. Based on the developed proportion, the workability of the ECC was quantitatively evaluated by jumping table tests and consistency tests at different open times. As shown in Fig.1, the optimal open time interval was determined as 5~35 min, the corresponding spreading diameter and penetration depth were 49~162 mm and 53~80 mm, respectively.



A series of tensile tests and compressive tests under different loading directions were carried out to explore the hardened propertyies of printed ECC. The tensile and compressive stress-strain curves are plotted in Fig. 2 and Fig.3, respectively. It was found that the printing process showed negative effect on the fiber orientations of printed ECC, resulting in decreased tensile properties. The average tensile strength and strain capacity of printed ECC were 5.75 MPa and 7.54%, respectively. The printed ECC exhibited enhanced compressive strength than the mold-cast ECC. The compressive strength of printable ECC ranged from 36.7 MPa to 44.6 MPa.



Based on the developed printable ECC, a series of bio-mimetic flexural members with no reinforcement were designed for four-point bending tests, including nacre-inspired beams, hollow-assembling beams, and hollow-assembling slabs. The results indicated that all the printed members exhibit multiple cracking, flexural hardening, and ductile failure mode despite the absence of longitudinal reinforcement, as shown in Figs. 4~6. The deflection-span ratio of all printed beams and slabs exceeded 1/50 at the ultimate state. This article preliminarily confirmed the feasibility of using ECC to achieve 3D printed structure without longitudinal reinforcement.