Rheology of lime pastes with biopolymer-based additives

The use of industrial limes implies obtaining mortar pastes with worse plasticity and workability compared to lime putties. To overcome this inconvenience, a great number of additives can be used, the majority of them being plasticisers and water-retaining agents. In this work three natural polysaccharides with hydrogel properties (agar-agar, alginate and hyaluronate derivatives) were added to dry-hydrated and natural hydraulic limes to investigate their influence on the rheology of the lime suspensions, as a function of the mixing and dissolving procedures, the additive type and concentration, and the type of lime. Rheological measurements have shown that the yield stress and viscosity of the lime pastes are increased if the additives are pre-mixed with water before adding the lime powder. All additives significantly increase the rheological parameters of the natural hydraulic lime pastes (with a maximum additive concentration of 0.2g in 1L of water) but only sodium hyaluronate is effective when mixed with dry hydrated lime. Notwithstanding this, sodium hyaluronate-lime pastes have shown a time-dependent behaviour that must be taken into account during mortar formulation and use. This study lays the foundations for the development of new sustainable lime mortars made with additives derived from natural sources.