Q. Bleeding test for grout – an essential requirement?
Bleeding is a form of segregation in that a layer of water migrates to surface of the grout at the time of the initial stage of cement hydration process. Afterward some of the floating water is re-absorbed into the grout because of further hydration reactions. Even without problem of bleeding, there is a total reduction of volume of grout after hydration action when compared with total initial individual volume of cement and reacted water. Bleeding tests must be carried out for grout due to the below reasons:
(i) At the time of bleeding, up flow of water from grout mixture leads to formation of channel paths inside the grout mix. These channels behave as potential paths for aggressive materials to pass through as these channels will not be closed during further hydration of the grout.
(ii) Loss in volume by bleeding generates voids inside the grout mix that affects the properties and performance of the grout. Furthermore it increases the chance of corrosion of steel elements protected by the grout. (Such as tendons)
(iii)In bleeding test, there is a typical requirement of total re-absorption of water after 24 hours of grout mixing since for some cold countries, this layer of water can cause severe freezing problem leading to frost damage.