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What is autogenous shrinkage?

Q. What is autogenous shrinkage?


A. It is change in volume due to the chemical process of hydration of cement, exclusive of effects of applied load and change in either thermal condition or moisture content. The internal volume reduction associated with the hydration reactions in a cementitious material is typically 1.66 to 1.94 in.3/lb (6 to 7 mL/100 g) of fully hydrated cement. The basic reactions of cement clinker are well understood and generally defined in terms of four ideal clinker phases, namely, C3S, C2S, C3A, and C4AF. Each of these clinker minerals requires water for reaction, and results in a decreased volume of the reaction products. Chemical shrinkage is like a molecular-level volume change, and creates the underlying driving force for the occurrence of autogenous shrinkage that is the macroscopic bulk deformation of a closed, isothermal, cementitious material system not subjected to external forces.


References: ACI 231R-10; ACI 209.2R-08

Topics in Concrete: Shrinkage; Cementitious Material; Concrete Fundamentals

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