Tensile creep study of repair material at early age

Restrained shrinkage may initiate crack and deteriorate the long-term durability of repaired system. Tensile creep can relax the stress dramatically especially at early age. Although it is often assumed as compressive creep, their mechanism is different because propagation of micro-crack is not the same during creep. Theoretical model of tensile creep is proposed and a tensile creep apparatus is introduced in this paper. Three kinds of typical structural repair material such as unsaturated polyester resin mortar (UPRM) made from polyester resin 191, which is a kind of industry product in China market, SBR modified cementitious mortar (SBRCM) and common cement mortar (CCM) have been tested at early age in different conditions. Tensile stress is applied as 27% of the tensile strength at loading time. Model parameters of the repair materials are gained by the experiments. Stress reduction caused by tensile creep is calculated with relaxation modulus of repair material. Practical expressions of tensile creep under constant stress and relaxation modulus under constant strain at early age are both suggested. According to the suggested model, relaxation modulus of repair material is time dependent. Initial relaxation modulus of UPRM, SBRCM and CCM are 7778 MPa, 12040 MPa and 14000 MPa respectively. Study shows that theoretical prediction agrees well with test data.