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

Abstract

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.