APPARENT STRENGTH RETROGRESSION OF SILICA-FUME CONCRETE

In recent years, use of silica-fume concrete has become more prevalent. Recently, a few researchers expressed concerns about the long-term strength retrogression they found when studying the compressive and flexural strengths of air-cured silica-fume concrete, while other researchers did not find any strength retrogression in apparently similar experimental conditions. These contradictory results are not supported by the few field results obtained on cores where compressive strength stability, at least, has always been observed. The objective of this paper is to develop fundamental information on the long-term behavior of some silica-fume concretes after a long dry air curing. Scope of the work includes a review of available literature on long-term compressive strength of concrete specimens submitted to air curing. This literature review is followed by the presentation of the drying behavior of two silica-fume concretes and one that does not contain silica fume. Experimental results show that these three concretes dry in different ways. After a certain period of time, one can exhibit a strong moisture gradient, while others do not. An explanation of the apparent strength loss of the silica-fume concrete is proposed. If this explanation is accepted, it is shown that the apparent strength loss can never be more than two times the tensile strength of concrete. This theoretical maximum strength retrogression agrees well with the published data.