Experimental Study on Bending Mechanical Properties of Sandwich Thermal Insulation Formwork

Sandwich thermal insulation formwork, also known as detachable thermal insulation formwork, is a new type of building material where, after the completion of concrete pouring, the outer formwork of the external wall is not demolished, and as a building formwork, there is no need to support another formwork during construction. At the same time, it can also be used as a building insulation structure, which can reduce building energy consumption. Despite its numerous advantages, including ease of construction and extended service life, this formwork must simultaneously fulfill roles as both a thermal insulator and a structural support. Additionally, during the concrete pouring process, the sandwich insulation formwork must possess sufficient stiffness to withstand construction loads. In order to study the mechanical properties of formwork in the process of concrete pouring, bending tests of eight sandwich thermal insulation formworks under concentrated load were carried out, their failure characteristics were observed, and the bending performance of sandwich thermal insulation formwork was studied. Analysis of the experimental results revealed that the surface layer of the sandwich insulation formwork is relatively thin; consequently, the bonding interface’s requirement to transmit tensile and shear forces throughout the bending process is minimal. The inclusion of grooving measures significantly enhanced the overall performance of the insulation formwork, facilitating the formation of a robust stress bond at the bonding interface. There is no debonding phenomenon in the bending process of thin sandwich thermal insulation formwork. Finally, on the basis of the existing theory, the formulas of bending stiffness, cracking moment, and failure moment of sandwich thermal insulation formwork before and after cracking are deduced. Compared with the eigenvalues of bending tests, the formulas can accurately reflect the bending performance of sandwich thermal insulation formwork and provide a reference for engineering practice.