FEM-analys av värme- och tidig hållfasthetsutveckling i 3D-printad betong vid låga omgivningstemperaturer

Sammanfattning

The production and use of concrete and cement in the construction industry have a substantial negative impact on the climate. As a response, 3D-printed concrete has been developed to improve resource efficiency and reduce material waste. The 3D-printing process is based on a layer-by-layer principle, where each layer must develop sufficient strength before the next layer is applied. At low temperatures, curing is delayed, increasing the risk of permanent damage if the concrete doesn’t reach 5 MPa before freezing. This study analyzes the curing process of 3D-printed concrete under three ambient temperatures: 0°C, -5°C and -10°C. Wall thickness is also varied between three standardized printing dimensions: 20x10 mm, 40x10 mm and 50x10 mm, resulting in nine different cases. The cases are modelled in CALFEM using a two-dimensional finite element model with transient heat transfer calculations. The temperature progression is used to calculate the equivalent time required to reach critical strength, based on curing development curves. The temperature development was compared with another calculation for concrete with a cast at -15°C, to validate the model’s reliability. The comparison indicated that the model has reasonable cooling behavior but did not fully validate the model’s reliability. The results show that all wall thicknesses reach critical strength at 0°C. However, at - 5°C and -10°C, none of the cases reach critical strength within the studied time period. At -10°C, the temperature falls below 0°C before 24 hours, indicating a risk of permanent damage. The study shows that wall thickness and ambient temperature are critical factors in the curing process. Protective measures are therefore necessary to enable concrete printing under low temperature conditions and ensure sufficient early strength development.