Effects of Ultrafine Powders on the Properties of the Lubrication Layer and Highly Flowable Concrete

The friction at the steel pipe-flowing concrete interface plays an important role in concrete pumpability. To reduce the friction or improve pumpability, in this paper, various ultrafine powders (nanoclay, nano-CaCO3, and microsized marble powder) are incorporated into a highly flowable concrete mixture with a low water-binder ratio (w/b=0.35) at a dosage of 1% (by weight) as a cement replacement. The effects of these ultrafine powders on rheology of the concrete and the properties of the lubrication layer, near the steel pipe-concrete interface, are studied by a portable rheometer and tribometer. The thickness of the lubrication layer of each concrete mixture is determined using a microindentation test method. The results show that 1% nanoclay and nano-CaCO3 replacement increases the rheological parameter values (e.g., yield stress, viscosity) of both bulk concrete and the lubrication layer. However, 1% marble powder replacement largely reduces the viscosity of the lubrication layer as well as the pumping pressure. The thickness of the lubrication layer of the concrete mixtures studied is about 1-2 mm.