Yusei Ohshiro

Three-dimensional printing (3DP) has gained increasing attention in construction as a means of addressing labor shortages and improving efficiency. Various studies have investigated fiber-reinforced mortars for 3DP. However, only a few studies have examined mixture design strategies aimed at controlling early structural build-up, and the relationships between early structural build-up, printability, and interlayer stability remain largely unexplored. This study aimed to establish a practical method for evaluating the static yield stress and early buildability of 3DP mortars under construction-site conditions. Vane shear and 15-stroke flow tests were conducted to assess the static and dynamic behavior of mortars incorporating polyvinyl alcohol (PVA) fibers, and their compressive and flexural strengths were also evaluated. According to the results, the vane shear test sensitively captured the rheological changes associated with variations in fiber content and superplasticizer dosage. The addition of PVA fibers increased the maximum shear stress of the mortar, resulting in atypical static yield stress development compared to fiber-free mortars. While the 15-stroke flow test further elucidated flowability, the vane shear test revealed a stronger correlation between mechanical properties and overall buildability. Thus, vane shear testing can be reliably used to assess early-age structural build-up and interlayer stability in 3DP mortars for optimizing print performance.

Three-dimensional printing (3DP) has attracted growing attention in the construction industry due to labor shortages and the need for greater efficiency. However, there have been only a few previous studies focused on mixture design strategies that address the thixotropy of fiber-reinforced mortars for 3DP. In addition, the relationships among thixotropy, printability, and interlayer stability have not been sufficiently verified. This study aims to establish a quantitative method for evaluating the thixotropic properties of mortars used in construction 3DP, specifically on their practical applicability at construction sites. Vane shear and 15-stroke flow tests are conducted on mortars incorporating polyvinyl alcohol (PVA) fibers to assess their thixotropic behavior under static and dynamic conditions. Fiber-reinforced mortar mixtures are prepared, and their compressive and flexural strength developments over time are examined. The results indicate that the vane shear test is a sensitive and effective method for detecting changes in mortar rheology, particularly in response to variations in fiber content and admixture dosage. The inclusion of PVA fibers increased the maximum shear stress owing to fiber aggregation, resulting in atypical thixotropic behavior compared to that of fiber-free mortars. While the 15-stroke flow test provided supplementary information on flowability, the vane shear test exhibited a stronger correlation with mechanical properties and printed build quality. These findings suggest that vane shear testing offers a practical and reliable means of evaluating and managing the thixotropic properties of mortars for 3DP, thereby enhancing quality control in additive construction.