Olafur H. Wallevik

The effect of measuring procedure on the apparent rheological properties of self-compacting concrete

Abstract Torque versus time during testing of the rheological properties of fresh concrete has been investigated. The testing was performed in a BML viscometer and on a self-compacting concrete (w/c=0.45, 70% rapid hardening Portland cement, 3% silica fume, 27% fly ash, third generation superplasticizer). The relaxation period needed to obtain steady-state flow may affect the rheological properties estimated and should be taken into account in the selection of measuring procedures. Nonsteady state is likely to cause an overestimation of the plastic viscosity and an underestimation of the yield value. Furthermore, lack of steady state may explain the apparent shear-thickening behaviour of self-compacting concrete reported elsewhere.

Fracture mechanical properties of high-performance concrete—Influence of silica fume

High-performance concrete and high-quality ordinary concrete, with or without silica fume, were tested for mechanical and fracture mechanical properties. Testing was performed at 28 days and 2 years. Ten percent silica fume resulted in a 20 to 25% increase in the direct tensile strength and a 10 to 20% increase in flexural and compressive strength, but had little effect on the dynamic modulus of elasticity. The brittleness appeared to increase with the presence of silica fume.RésuméLes propriétés mécaniques de la rupture ont été testées sur des bétons de hautes performances et sur des bétons ordinaires de haute qualité, avec ou sans fumée de silice. Les essais ont été effectués à 28 jours et à 2 ans. L’ajout de dix pour cent de fumée de silice a pour effet l’augmentation de la résistance en traction directe de 20 à 25% ainsi que l’augmentation des résistances en flexion et en compression de l’ordre de 10 à 20%, mais a peu d’effet sur le module d’élasticité dynamique. Par ailleurs, la fragilité du béton est accrue en présence de fumée de silice.