Abstract
Cellulose-based viscosity-modifying admixtures are used on daily basis in a wide range of building materials, dominantly in pre-mixed mortar systems. Lately, alternative admixtures such as different “gums” have emerged. In building materials, the gums have similar viscosity-enhancingeffects as cellulose ethers with different efficiency. Various ways of production, as well as diverse working mechanisms of the biopolymers are to be considered while choosing the most suitable admixture for the intended use. Influence of alternative admixtures in several doses on the microstructure of lime mortars was studied in this paper. Mortars were prepared with the same workability and the air content in fresh mortar was determined, for it can have notable impact on microstructure of hardened mortar. Hydroxypropyl derivative of chitosan showed air entraining ability, while the carboxymethyl derivative reported slight decrease in amount of air entrained into the mixture. In the case of diutan gum, the most water-demanding admixture, the percentage of entrained air dropped with growing dose. Admixture addition increased the volume of pores in diameter lower than 0.1 μm, and in region of pores around 10 μm. Only the diutan gum affected the distribution of capillary pores, which are typical for lime mortars. Hygric properties were in correlation with air content values.
Highlights
The aerial-lime as a binder has been used thorough the centuries for the whole complex building system from the filling concrete in the hollow masonry up to the fine decorative plastering
The total porosity and the main pore diameter increase in the lime paste with growing water content [7] the physico-mechanical properties of aerial lime are reported to be unaffected by the higher porosity, being non-compliant with the Power equation generally accepted in the world of hydraulic binders
The shape of the cumulative curves is typical for the lime-based materials [6, 14] with the main volume of pores situated in the range between 0.1 and 1 μm [1, 3, 6-8, 12, 14 –15]. In this interval the shape of the curve remains similar for the chitosan ethers as well as two lower doses of sodium alginate, seemingly so biopolymer addition compensates the influence of the higher water content [7], while in the case of diutan gum, the growing dosage leads to the flatter curve, wider interval of the typical pore sizes
Summary
The aerial-lime as a binder has been used thorough the centuries for the whole complex building system from the filling concrete in the hollow masonry up to the fine decorative plastering. The total porosity and the main pore diameter increase in the lime paste with growing water content [7] the physico-mechanical properties of aerial lime are reported to be unaffected by the higher porosity, being non-compliant with the Power equation generally accepted in the world of hydraulic binders. The amount of kneading water is still the factor affecting the strength [8] of the lime mortar, but with lower sensibility in the range of usual values in comparison with hydraulic binders [9]
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