Influence of alkali on restrained shrinkage behavior of cement-based materials

Experiments have been conducted to study effects of high alkalinity on restrained shrinkage behavior and cracking sensitivity of cement-based materials at early ages. The restrained shrinkage test has been conducted with an ellipse ring setup and the initial cracking time was monitored with a continuous conductive strip. Alkali content and alkali type as well as the shrinkage-hydration relationship have been studied. The experimental results have shown that the cracking sensitivity of a cement-based material is increased with an increase in alkali content. The influence of the excess alkali on the cracking sensitivity is more obvious for cement paste with a low water-to-cement ratio (w/c) than that with a high w/c. The hydration processes and microstructure development of cement paste have been investigated using heat of hydration measurement and electrical resistivity measurement. The superimposed resistivity curve and heat evolution curve provide more comprehensive understanding on factors influencing shrinkage development.