Shrinkage compensated

The expansion achieved in concrete containing these admixtures is dependent on the type of aggregates used in the mixture. Thus the desired level of shrinkage compensation should take into account the modulus of the aggregate to be used on the job. The effect of cement and water contents on the extent of expansion should also be considered. Minimum cement content required to achieve desired expansion should be determined through mix trials. Compatibility with other admixtures may also need trials and the manufacturer s recommendation should be followed [80]. 

The commonly used ratios of admixture to cement for the purpose of shrinkage compensation are 9-11 (admixture) to 91-89 (cement). At these ratios the properties of CSA concrete are similar to Portland cement concretes of similar mix proportions. At admixture dosages exceeding 11% however, concrete workability and strength decrease, while expansion and air entrainment increase. When expansion is umestrained and exceeds 0.3%, strength is reduced [74]. 

CSA admixtures are more prone to loss of activity due to C02 and moisture pick up than are shrinkage compensating or Portland cements [74,79, 85], Consequently, exceeding the shelf life may seriously reduce the expansive potential. The materials are therefore packed in water-proof bags which should always be stored in a dry... 

Expanding cement (shrinkage-compensated cement) do not shrink upon hardening. Addition of 10 to 15% of calcium sulfate or aluminate even effects an expansion ( managed gypsum bursting ). 

Fig. 9.7 Volume changes of expansive, shrinkage compensation and classic Portland cement...

The shrinkage-compensated concrete mixture is designed in the same way as in the case of ordinary concrete. Their properties, such as strength, elasticity modulus, drying shrinkage, creep, and freeze-thaw resistance are very similar. 

Figure 21.2 Volume changes and stresses in OPC, shrinkage-compensated and self-stressing cement pastes due to hydration and drying.

Fu, Y. et al. (1995a) Effect of chemical admixtirres on the expansion of shrinkage-compensating cement containing a prehydrated alttmina cemerrt-based expansive additive. Cement and Concrete Research 25,29-38. 

Wang, Y., and Lou, Z. (1992) Retarded expansion for cooling shrinkage compensation in mass concrete, inProceedings 9th ICCC, New Delhi, Vol. 5, pp. 129-135. 

HAC is used where rapid strength gain is required, in refractory applications and, with calcium sulfate, to form ettringite-based products either for shrinkage compensation or for high waterxement ratio grouts (e.g., 5 1). It is important to control carefully the relative proportions of HAC and calcium sulfate in ettringite-based systems to ensure optimum properties. 

Collepardi, M., Borsoi, A., Collepardi, S., Olagot, J. J. O., Troli, R. (2005) Effects of shrinkage reducing admixture in shrinkage compensating concrete under non-wet curing conditions, Cement and Concrete Composites, 27 704—8. 

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