Title: Long Term Mechanical Properties of Low Water to Cement Ratio Ultra High Strength Concretes

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Publication: CIA

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Date: 2/13/2011

Abstract:
Ultrahigh strength concretes (UHSC) are characterized by a very low water to binder ratio as well as very high amounts of cement, secondary binders and fillers. Usually no coarse aggregates are used. The hardened UHSC have a very dense microstructure, small amount of portlandite and no interfacial transition zones (ITZ). UHSC are reported to have a good durability. Shrinkage and creep values are higher in comparison with high strength concretes. This paper presents the results of the research on the incorporation of coarse aggregates into the UHSC matrix and its influence on the long term mechanical properties and durability. The studied concretes had water to binder ratio between 0.16 and 0.20, 25 % of amorphous undensified silica fume, fine quartz fillers and coarse aggregates. Short steel fibers were added to some of the mixes. The curing included water storage at 20oC followed in some cases by 48 hours of heat treatment at 90oC. The test results revealed that UHSC with coarse aggregates have reached a 28-day compressive strength of up to 200 MPa and flow-like workability. The one year old test concretes showed higher increase of the compressive strength in the case of the no heat treated concretes; however, the ultimate strength was lower in comparison with the corresponding heat treated specimens. The presence of coarse aggregates lowered the creep and shrinkage values.