Failure of the structure due to poor buildability is a major concern in 3D printing of cementitious materials. Evaluation of buildability based on fresh material properties and print parameters is of significance. In this paper, the buildability of printable engineered cementitious composites was investigated and quantified at the material and the structural scale. Fresh ECC material showed excellent load capacity and deformation resistance at the material scale, therefore preventing material failure of the bottom layers, as confirmed by constant shear rate tests and incremental loading tests. To predict vertical deformation of a 3DP structure, a time-dependent strain-stress model of printable ECC was proposed and validated based on the green strength evolution of the material and the buildup rate of the designed structure. At the structural scale, the approach of predicting critical height at self-buckling failure based on stiffness evolution was validated by printing a straight wall and a cylinder structure.@en

As an economical and eco-friendly construction material, coral aggregate concrete (CAC) plays an increasingly important role in emerging marine engineering applications. CAC fully utilizes local raw materials on remote islands. Due to the porous structure and low-strength characteristics of coral aggregates, CAC exhibits unique characteristics compared to ordinary concrete. This paper presents a state-of-the-art review of the properties of CAC, including (1) the physical properties of coral aggregates; (2) the mechanical properties of CAC under uniaxial and multiaxial compression; and (3) the durability of CAC especially its chloride ion resistance and performance under drying-wetting cycles. To overcome the challenges of steel corrosion in marine environments, fiber-reinforced polymer (FRP) has been indicated to be a promising material for applications in CAC construction. The latest studies on the combination of FRP and CAC are reviewed, including the use of FRP tubes and bars.@en

The utilization of coral aggregate concrete (CAC) in marine construction has drawn the attention of engineers and researchers in recent years. Due to the high content of chloride in CAC induced by coral aggregates and sea water, reinforcing CAC with traditional material, i.e., steel, can cause serious corrosion-related durability problems. Replacing steel with corrosion-resistant fiber-reinforced polymer (FRP) has been considered a promising solution. This paper provides insight into the bond behavior between CAC and FRP bars. In total 30 pull-out tests were conducted. The investigated variables included the concrete matrix, FRP bar type, bar diameter, and thickness of concrete cover. Based on the test results, discussions on the bond failure modes, influencing factors of bond strength and bond stress-slip relationship were presented. For splitting failure mode and pullout failure mode, empirical bond stress-slip models were proposed respectively. Adopting the failure criterion of CAC proposed in a previous study, a mechanical model for bond strength under pullout failure mode was developed. Comparisons with test results validated that the proposed models provide reasonable predictions for the bond properties between GFRP bars and CAC.@en

Coral aggregates can replace natural aggregates in marine construction, substantially reducing construction costs and shortening construction period. This paper investigates the compression behavior of coral aggregate concrete (CAC) under uniaxial and triaxial loading, wherein lightweight aggregate concrete (LAC) and normal aggregate concrete (NAC) are used for comparison. The investigated variables include concrete type, concrete strength, lateral pressure and principal stress ratios. The results indicated that the compression behaviors of CAC were different from those of NAC but similar to those of LAC because coral aggregates are more porous and have lower strength than normal aggregates. Based on the test results from this paper and literature studies, constitutive models were suggested for CAC under uniaxial and conventional triaxial compression. Moreover, a failure criterion for LAC proposed in the literature was deemed applicable to CAC under active or passive confinement. The suggested models correlated well with the test results.@en

3D printing of engineered cementitious composites (3DP-ECC) serves as an effective means to enable digital and automated construction while removing the dependence of steel reinforcement typical in normal concrete construction. As generally recognized, process control in 3DP is as crucial as material constituents to the performance of the printed structure. Printing parameters pose direct influence on the micro-structure of material, which further impacts the macro-scale properties of printed ECC. In this paper, the effects of different nozzle standoff distances and nozzle travelling speeds are investigated. It is found that lowering the nozzle standoff distance within a certain range increases the in-plane tensile strength and strain capacity of 3DP-ECC by 39% and 30%, respectively. The tensile performance is also enhanced by a moderate printing speed. In addition, a 141% increase in interfacial fiber bridging force is found with elevated nozzle standoff distance. Furthermore, the micro-structure observed via μ-CT correlates well with the printing parameters, micro-structure and macro-scale properties of 3DP-ECC.@en

Widely reported anisotropy in 3D printed cementitious structures has been a primary concern to structural integrity, especially for fiber-reinforced cementitious material, e.g., engineered cementitious composites (ECC). To alleviate the anisotropy present in 3D printed ECC (3DP-ECC), two innovative printing patterns, “knitting” and “tilting” filaments, were proposed, mimicking the natural crossed-lamellar structure of conch shells. 3D spatial paths were designed to allocate tensile/flexural resistance to multiple directions and to create an interwoven interface system to strengthen the structure. Four-point bending tests loading from three different directions were conducted. It was found that knitted and tilted filaments revealed superior or comparable bending performance to cast ECC in two favorable orientations. Furthermore, flexural performance in the weakest orientation was notably improved by knitting and tilting, with up-to-179% increases in flexural strength compared with that of parallel filaments. This novel approach holds great promise in alleviating anisotropy of 3DP-ECC without introducing additional reinforcement.@en