More efficient use of mortar at the building site. Pumping and rheological properties of LWA concrete

A comprehensive work on the parameters governing pumping and pumpability of certain mortars and concretes has been done. The aim has been to achieve pumpable mixes based on normal density (ND) aggregates and light weight aggregates (LWA) but also to study the relationship between rheological parameters and pumpability. The conclusions that can be drawn based on a series of 4 ND and 5 LWA mixes are: • Pumpability has been achieved partly by increasing the paste volume and in LWA concrete to use high enough water content to assure excess of water after mixing and pumping as the LWA concrete under pumping matures and the LWA particles absorb water. (Neither effective w/b, paste- nor matrix volumes were comparable between the parallel ND and LWA mixes??) • The LWA concrete proportioned in this way seems to have higher pump flow compared to traditional mortars at constant pump frequency. • The LWA concrete mixes have lower initial yield stress and viscosity compared to the reference mixes (at equal matrix- or paste volumes? effective w/b???). • The particular LWA concretes needed less energy in the pump engine, which can be explained by the mix design. • A simplified analysis of the degree of plug flow indicates that there is a considerable variation within the present mixes from pratically full plug flow to complete flow velocity profile. • The theoretical output calculated with a simple analytical model combining the Hagen Poiselle flow and the Bingham rheology model, is in the same range as the measured, and by adjusting the viscosity slightly there will be a match. The necessary slight adjustment seems to vary randomly in addition or subtraction. • A recommendation for further projects could be to look into details about measuring errors, instrument dependency (using several different measuring techniques) and material behaviour such as thixotropy, in addition to numerical simulations.