Self stressing cement

If, however, the expansive stresses generated initially are higher than needed just to outbalance the tensile stresses caused by drying, then the hydrated material remains imder expansive stresses even after it has dried completely. Such stresses may attain a magnitude of up to 8 MPa. To preverrt excessive expansion and crack formation tmder these conditions the concrete body must be restrained or reirrforced by a srritable reinforcement. Binders of this kind are called self-stressing cements. They may be... 

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

Mikhailov, V.V. (1960) Stressing cement and the mechanism self-stressing concrete regulation, in Proceedings 4th ICCC, Washington, Vol. 2, pp. 927-955. 

Xue, J. et al. (1986) Study on high self-stress aluminate cement, inProceedings 8th ICCC, Rio de Janeiro, Vol. 4, pp. 306-311. 

Mikhailov, V. V., Stressing Cement and the Mechanism of Self-stressing Concrete Regulation, Proc. 4 Int. Symp. on Chem. Cement, 2 927-955 (1960)... 

Flow and self-leveling characteristics of these products are governed by the rheological behavior of the slurrylike materials. At the low water-cement ratios required to ensure proper suspension of the solids, most selfleveling compositions are characterized by a yield stress and thixotropic behavior [75]. To obtain self-leveling properties, the yield stress has to be reduced and this is achieved by the selection and combination of suitable mix ingredients at... 

The pivotal role that superplasticizers play in the formulation of self-leveling mortars is due to the dramatic effects they produce on flow behavior. Such effects are believed to be derived by the adsorption of the admixture on the surfaces of cement grains, thereby providing surfaces of a similar or zero charge which are mutually repulsive. They thus fully disperse cement particles, freeing more water for lubrication and reducing interparticle attraction. Both yield stress and plastic viscosity are decreased and the decrease is greater for yield stress it may be completely eliminated if sufficient admixture is added so that Newtonian behavior is observed (Fig. 7.25) [75, 76]. 

The two groups of expansive cements can be distinguish, based on the tensile stress produced to 2 MPa and to 4, or even 6 MPa. They are used in the self-pre-stressed concrete manufacturing. There is an opinion that the tensile stress should... 

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