GEL/SPACE RATIO

       As propounded by Duff Abrams many research workers commented on the validity of water/cement ratio law. They have focused on a few of the limitations of the water/ cement ratio law and argued that Abrams water/cement ratio law can only be called a rule and not a law because Abrams’ statement does not include many qualifications necessary for its validity to call it a law. Some of the limitations are that the strength at any water/cement ratio depends on the following things…

   1.Degree of hydration 
   2.Chemical and Physical properties
   3.The temperature at which the hydration takes place
   4.Air content (in case of air entrained concrete)
   5.the change in the effective water/cement ratio and the formation of fissures and cracks due to bleeding or shrinkage

Instead of relating the strength to water/cement ratio, the strength can be more correctly related to the solid products of hydration of cement to the space available for formation of this product. Powers and Brownyard have established the relationship between the  strength and gel/space ratio. This ratio is  defined as the ratio of the volume of the hydrated cement paste to the sum of  volumes of the hydrated cement and of the capillary pores.
Power’s experiment showed that the strength of concrete bears a specific  relationship with the gel/space ratio. He  found the relationship to be 240 x3, where  x is the gel/space ratio and 240 represents the intrinsic strength of the gel in MPa for the type of cement and specimen used.
The strength calculated by Power’s expression holds good for an ideal case.
The fig. below shows the relationship between strength and gel/space ratio. It is pointed out that the relationship between the strength and water/cement ratio will hold.

Gel-Space Ratio

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