Abstract: Taking limestone for research objects, the thermal expansion property is studied under high temperature; the porosity, ultrasonic wave velocity and elemental composition are studied in order to find out the reason caused thermal expansion. The results show that: the limestone produces thermal expansion under high temperature; the curves between thermal expansion and test time includes four steps, size of thermal expansion is determined by temperature; and the relation is nonlinear; the porosity increases as temperature increases after high temperature; it can be divided into two stages based on division temperature of 500 ℃, including slow increase step and rapid increase step; the test of ultrasonics shows that the law of wave velocity is complex wavy type after high temperature; the test of elemental composition shows the contents of key elements in limestone samples has a larger change; the change of both porosity and elemental composition is the key reason causing thermal expansion of limestone under high temperature

Key words: limestone, thermal expansion, porosity, ultrasonic wave, elemental composition