Characterization of Lubrication Layer of Fresh Concrete Acquired Using the Modified Pipe Flow Apparatus

Abstract

A thin layer of micromortar called a lubrication layer (LL) forms around the inner periphery of the pipe during the pumping of fresh concrete. This LL aids in the movement of concrete under pressure. The composition of the LL is of prime importance in understanding the flow behavior of concrete under the action of shear and the prediction of pressure for pumping applications. In the present study, an attempt was made to determine the LL composition of the concrete mixtures using fly ash, ground granulated blast-furnace slag, and limestone calcined clay as supplementary cementitious materials with a water to binder (w/b) ratio ranging from 0.3 to 0.5 supplemented with a superplasticizer. In this regard, the LL was extracted by modifying the existing pipe flow apparatus. The collected LL was characterized for its composition, which includes w/b, binder to sand ratio (b/s), and particle-size distribution. The results indicated that the nominal maximum particle size of LL was around 600 μm. The average binder to sand ratio of LL obtained was 3.0. The w/b of LL was found to be higher than that of the bulk concrete. The characterization of LL carried out in the current work generated a database regarding the potential composition of LL, which would aid in the rheological studies for fundamental understanding and the pressure prediction of concrete.