-/ WATER CEMENT RATIO AND COMPRESSIVE STRENGTH/-
=>A cement of average composition requires about 25 percent of water by mass for chemical reaction.In addition,an amount of water is needed to fill the gel pores.The total amount of of water thus needed for chemical reaction and to fill the gel pores is about 42 percent.The general belief that a water-cement ratio of less than 0.40 or so should not be used in concretes------because for the process of hydration,the gel pores should be saturated---is not valid.This is because,even in the presence of excess water,the complete hydration of cement never takes place due to the decreasing porosity of the hydration products.As a matter of fact,a water ----cement ratio of less than 0.4 is quite common in high-strength structural concretes.
In concrete,as explained earlier,the hardened cement paste is a porous ensemble.Also,the concentration of the solid products of hydration in the total space or volume available(the original water and hydrate cement)is an index of porosity.Like any other porous solid,the compressive strength of cement paste(or concrete) is related to the parameter gel-space ratio or hydrate-space ratio.The water-cement ratio which governs the compressive strength ,is really an expression of the concentration of hydration products in the total volume at a particular age for the resultant degree of hydration.
=>A cement of average composition requires about 25 percent of water by mass for chemical reaction.In addition,an amount of water is needed to fill the gel pores.The total amount of of water thus needed for chemical reaction and to fill the gel pores is about 42 percent.The general belief that a water-cement ratio of less than 0.40 or so should not be used in concretes------because for the process of hydration,the gel pores should be saturated---is not valid.This is because,even in the presence of excess water,the complete hydration of cement never takes place due to the decreasing porosity of the hydration products.As a matter of fact,a water ----cement ratio of less than 0.4 is quite common in high-strength structural concretes.
In concrete,as explained earlier,the hardened cement paste is a porous ensemble.Also,the concentration of the solid products of hydration in the total space or volume available(the original water and hydrate cement)is an index of porosity.Like any other porous solid,the compressive strength of cement paste(or concrete) is related to the parameter gel-space ratio or hydrate-space ratio.The water-cement ratio which governs the compressive strength ,is really an expression of the concentration of hydration products in the total volume at a particular age for the resultant degree of hydration.
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