Effect of the Ambient Temperature on the Structural Build-Up of 3D Printed Concrete (2024-09)¶

One of the main advantages of extrusion-based 3D printing technology is that no formwork is required. This gives new degrees of freedom for architectural design, and saves costs and resources in parallel. On the other hand, extrusionbased 3D printing techniques create new questions and challenges for material design. In the classical approach, the formwork is needed to carry the load of the fresh concrete until it hardens. In the absence of the formwork, concrete needs to build-up a more rigid structure right after placement. The structural build-up properties are adjusted through the mix design and the printing parameters. However, since extrusionbased 3D printing technology is used for full-scale application on construction sites, influences of the environmental conditions must be considered. In this extended abstract, the effect of the ambient temperature on the structural build-up of 3D printed concrete is studied. An experimental, and a numerical model are developed to capture the ambient temperature influence.The structural build-up of cementitious materials is affected by thixotropy and hydration of cement at rest over the course of time. The process of structuration depends on various influencing factors like mixture composition and ambient parameters. In previous works, the authors investigated the influence of ambient temperature on the structural build-up of cement paste using small amplitude oscillatory shear (SAOS) tests and measured the static yield stress of printable mortar under different temperature levels [1, 2]. In both cases, a strong influence of the ambient temperature on the evolution of the storage shear modulus (G’) and the static yield stress was observed. A bi-linear relation [3] was extended allowing the prediction of the temperature influence. Yet, the full characterization of structural build-up of 3D printed concrete requires the determination of the Young's modulus (E) and its development over the course of time measured under different ambient temperatures. When the Young's modulus and the storage modulus are identified, using the following equation the fundamental material parameter, i.e. Poisson's ratio can be estimated using equation (1): E = 2G (1+ν) (1) To measure the Young's modulus development in our study a squeeze flow test was utilized. This test includes placing a sample of fresh concrete between parallel plates and applying the oscillation force following the measurement of (E’ and E’’) (Fig. 1). Simultaneously, the sample is subjected to small amplitude oscillatory shear load to determine G’ and G’’ evolution. Measurements were made in a thermal chamber allowing to vary or keep the ambient temperature within 14 and 35 ºC. To avoid overdrying, samples were protected with silicone oil. From the obtained results, a linear viscoelastic model extended by age and temperature influences is proposed for predicting the structural behavior of the printed layer under different ambient conditions. The material parameters can be modeled by temperature and time-dependent functions using the equivalent age form as in the maturity method [3]. The increased stiffness with increasing temperature as well as increasing age is detected. The model parameters are fitted with experimental data using Bayesian inference including the uncertainties.