Building Materials, Third Edition

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Since Abrahm’s w/c ratio law has many limitations researchers do not agree to call it a law but
they say it to be a rule. Strength at any w/c ratio is a function of following:

1. degree of hydration of cement, its physical and chemical properties.


2. temperature at which hydration takes place.


3. air content in case of air entrained concrete.


4. change in the w/c ratio.


5. formation of cracks due to bleeding and shrinkage.
   Some researchers feel that the strength can be related better and more correctly to the
   hydration products than to the space available for the formation of these products.
   Gel-space ratio is defined as the ratio of volume of hydrated cement paste to the sum of the
   volumes of the hydrated cement and that of the capillary pores. Power and Brownyard
   established a relationship between the strength and gel-space ratio. A typical curve relating
   gel-space ratio to the compressive strength is shown in Fig. 10.16.

S = 240x^3
Where S = strength of concrete
x = gel space ratio
240 = intrinsic strength of gel in N/mm^2 for the type of cement and specimen used

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