# Experimental Study on Flexural Properties of Polyurethane-Cement Composites under Temperature Load
###### Abstract  
Polyurethane cement composite is a new organic-inorganic composite material with high strength, corrosion resistance, and fast curing. It is a complement and alternative to traditional cement materials. The flexural properties of polyurethane cement composites are the basic mechanical index of the material. In order to study the flexural properties under different temperature loads, a molecular model was established, the chemical reaction process of polyurethane cement and the temperature response mechanism was analyzed, and the preparation process of polyurethane cement was proposed. Then, bending tests were carried out in strain-controlled mode to obtain the specimens' bending strength and stiffness modulus under different temperature loads. The test results showed that the tensile strength of polyurethane cement decreased first, then increased, and finally decreased with the increase in temperature, while the bending stiffness modulus decreased with the increase in temperature. Combined with the theoretical derivation, the damage mode of the samples under different temperature loads was analyzed, and the \"L-type\" damage strain curve was obtained. The results showed that the proposed theory could effectively explain the mechanism of action and flexural properties of polyurethane cement composites under temperature loading, which is a significant improvement to the application of polyurethane cement composites in practical engineering. damage mode; flexural properties; molecular structure; polyurethane cement; reaction mechanisms; temperature loading +
Footnote †: journal: Applied Sciences  
The variety of products is increasing yearly, and it occupies a very important position in the material industry [6]. In 2012, the worldwide sales value of polyurethane materials reached about 43.2 billion pounds, with an annual growth rate of nearly 7.4%. The sale of polyurethane products can be predicted to rise to about 88.2 billion pounds in 2022 [7]. Many scholars at home and abroad have carried out a series of studies on the excellent properties of polyurethane in civil engineering materials. (1) Mixing polyurethane with other materials can significantly improve the ductility and flexibility of the raw material [8]. Due to the environment, concrete building materials undergo carbonation and need to be repaired or reconstructed [9]; when reinforced concrete surfaces are coated with a thin layer of polyurethane protection, they are protected from corrosive environments and improve structural ductility, flexibility, and energy absorption [10, 11]. (2) Polyurethane has stable chemical properties and good corrosion resistance and can be used as a surface protective coating for metal structures. A study by [PERSON] [12] showed that a 6 mm thick polyurethane lining could provide a service life of 20 years, while a steel pipe without a lining wears out within 12 weeks. This study demonstrates that the polyurethane coating can protect the metal structure well. (3) Polyurethane materials have the potential for self-healing and can repair themselves without external interference [13]. Polyurethane, as a healing agent, can restore the strength and stiffness of cementitious materials, reduce water permeability, and extend the service life of the material [14]. (4) Polyurethane also has good thermal stability and is a good refractory material. Modifying polyurethane and adding composite flame retardants can offer good flame retardant and smoke suppression effects on the outer walls of high-rise buildings and improve the safety performance of building structures [15, 16]. (5) Polyurethane is a polymer material that contains a significant amount of isocyanates, which can react with aromatic compounds in asphalt in an additional reaction to achieve a modified treatment of asphalt materials [17]. Polyurethane-modified asphalt has excellent resistance to permanent deformation; the modified asphalt is less sensitive to temperature and significantly improves the asphalt's high-low temperature rheological properties.