A concrete rheometer and its application to a rheological study of concrete mixes

SummaryThe description of aCouette type rheometer which has been developed for measuring some rheological properties of fluid concrete mixes is given with a discussion of experimental results.The instrument produces a recorded trace which is essentially a stress decay curve attributed to thixotropic breakdown of the material structure. This breakdown curve is predicted better by an expression of the power law type than of the exponential type. Analysis of the empirical flow curves shows that, despite some limitations in its essential geometry, the instrument reflects the flow behaviour of the full concrete mix. Up to rotational speeds of 26 r.p.m., the flow curves are typical ofBingham plastics.The yield values and plastic viscosities of the mixes which are very fluid and typical of piling concrete are of the order of 2.5–12.0 kN/m2 (or 25000–120000 dynes/cm2) and 5–40 kilopoises (5000–40000 poises) respectively. These quantities vary with concrete mix parameters, and increase exponentially with decrease in water/cement ratio.