| The deformation and crack of concrete and other cement-based materials have become worldwide problems, which attract close attention from science and engineering fields of concrete both at home and abroad. In many influencing factors, shrinkage often is at the origin of crack formation, and it is unavoidable and hard to control. Alkali have an important influence on shrinkage, especially nowadays. Because more kinds of additive and admixture are added to the cement-based materials, which result in alkali content increase greatly. Therefore, it is necessary to know how the alkali effect drying shrinkage and find a new way to study the drying shrinkage.This thesis based on the two kinds of cement-based materials, one is mortar and the other is concrete. Tests of compressive strength, three point bending, dynamic elastic modulus, ion chromatography and drying shrinkage were carried out in mortar. The influences of alkali content on cement-based materials were investigated experimentally. For the concrete part, a kind of new method about water diffusion and drying shrinkage of cement-based materials was introduced. The data of water loss and shrinkage were analysed with the latest software, which was developed by V.Slowik who was in Leipzing University of Applied Sciences in Germany.The results indicate that the flexural strength of mortar increases with NaOH added, when the amount of NaOH less than 1.5% (by mass of cemnet). But the compressive strength reduces with NaOH increased. The concrete and mortar loss more water and have a greater degree of shrinkage with the relative humidity going lower. The degree of shrinkage and the amount of water loss change small when the relative humidity between 100% and 76%, but change larger between 76% and 55%. The water loss of motar can be promoted by alkali (NaOH) and this phenomenon is very notable. The alkali has the different influence on the shrinkage in different relative humidity. More NaOH and shrinkage bigger when RH=36%, more NaOH and shrinkage bigger in a certain range when RH=55%, no obvious influence on shrinkage when RH=76%. The diffusion coefficient of the cement-based materials has been obtained from the inverse analysis. Through the numerical analysis, the curve of water loss and shrinkage have been achieved which are close to the fact. |
