Paper studies fresh state and rheological properties of lightweight mortars prepared with constant workability using natural lightweight aggregates, and hydrated or natural hydraulic lime as binder. Fresh state properties are studied by standardised tests and rheological characteristics are obtained utilizing hybrid rheometer. Density of fresh mortar decreased accordingly to the loose bulk densities of aggregates used, while the water retention value remained very high with minor variations. The air content in fresh mortar with pumice as an aggregate was surprisingly high, which may be caused by the open porosity of the aggregate in combination with the test design. The influence of the aggregate weight on the rheological properties was most apparent in the case of hysteresis loop size and mortar stability, where lightweight aggregate with exception of zeolite showed higher loss tangent and lower critical strain, thus shorter linear viscoelastic region.
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