Bleeding is a form of segregation in which a layer of water migrates to the surface of the grout during the initial stage of cement hydration process. Later on, some of the floating water is re-absorbed into the grout due to further hydration reactions. Even without the problem of bleeding, there is a total reduction of volume of grout after hydration action when compared with the total initial individual volume of cement and reacted water. Bleeding tests should be carried out for grout because of the following reasons:
(i) During bleeding, the upflow of water from grout mixture leads to the formation of channel paths inside the grout mix. These channels act as potential paths for aggressive materials to pass through as these
channels would not be closed during further hydration of the grout.
(ii) The loss in volume by bleeding generates voids inside the grout mix which affects the properties and performance of the grout. Moreover, it increases the chance of corrosion of steel elements protected by the grout. (e.g. tendons)
(iii) In bleeding test, there is a usual requirement of total re-absorption of water after 24 hours of grout mixing because for some cold countries, this layer of water may cause severe freezing problem leading to frost damage.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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Great information!
Is bled testing the best way to test for how much a backfill grout might shrink, leaving an aperture between it and a structure.