Effects Of Pore Solution On The Drying Shrinkage Of Hardened Cement Pastes And Its Mechanism

The hardened cement paste is the primary deformation phase in concrete. The shrinkage of hardened cement paste is the origin of shrinkage of concrete. The hardened cement paste is a porous material. The pore structure and pore solution have a major impact on the drying shrinkage. The shrinkage may be different with the surface tension and nature of pore solution.The paper studies the effects of pore solution on drying shrinkage of hardened cement pastes, and reveals the nature of drying shrinkage of it in order to solve the problem of shrinkage of concrete in project. It takes the hardened cement pastes which was soaked in saturate Ca(OH )2 solution as benchmark , changes the pore solution by soaking the hardened cement pastes in different saturate solution, and then studies the effects of pore solution on drying shrinkage of hardened cement pastes, and investigate thoroughly the mechanism of drying shrinkage. In order to separate the irreversible drying shrinkage, it uses the test methods of"rewetting"which soak the hardened cement pastes in the former saturate solution.The hardened cement paste was cut into round sheet with thickness of 0.8mm, which accelerates the drying process of hardened cement paste greatly. And using the saturated salt solution control the air humidity of container to stabilize at certain rang. So the hardened cement paste can achieve equilibrium in a relatively short time.By the above study and analysis , the main results of paper as follows:①In replaying, the hardened cement paste has deformation. The deformation can be shrinkage, and also can be expansion. If it is shrinkage,and it deceases with the water cement ratio increases, even changes into expansion. If it is expansion, and it increases with the water cement ratio increases.②In replaying, the deformation of hardened cement paste is related with the age. If it is shrinkage, it has a decreasing trend with age extending. While it is expansion, it has a increasing trend with age extending.③The hardened cement paste that has been soaked with solution has volume deformation and weight loss when it dries in a container with constant humidity. Compared with the initial point drying, the deformation can be shrinkage, and also can be expansion. If it is shrinkage, it has a decreasing trend with drying humidity increasing. While it is expansion, it has a increasing trend with"drying"humidity increasing.④The hardened cement paste that has been soaked with solution has volume deformation when drying, and has a resuming trend to the state of the starting drying point.⑤When the hardened cement paste is soaked in saturation solution of NaCl or Ca (NO3)2, it has volume deformation and weight gain. The hardened cement paste which is soaked in saturation solution of NaCl has little deformation. In drying, the volume and weight almost has no change when RH=84%, 74%, and the volume shrinks when the drying humidity RH <74%.The effect of water cement ratio is not obvious.⑥When the hardened cement paste is soaked in saturation solution of CaCl2, the volume has obvious deformation in replaying the weight increase. In drying, the weight and volume have no obvious change when RH=54%. The volume expands and the weight gains when the"drying"humidity RH>54%. And the volume shrinks and weight losses when drying humidity RH<54%.⑦When the hardened cement paste is soaked in pure solution of ethanol or isopropyl alcohol, the volume shrinks and weight losses in replaying. The volume and weight almost has no change when drying humidity RH=84%, 74%, and the volume shrinks when the drying humidity RH<74%. The drying shrinkage increases with the water cement ratio increase.⑧When the hardened cement paste is soaked in pure solution of ethanol or isopropyl alcohol, the volume shrinks and weight changes, and the value of the weight change is little. The volume shrinks when drying. The drying shrinkage increases with water cement increases, while weight loss deceases with water cement increases.