Abstract
The fresh state properties of mortars are eminently important since determine the material workability and also have a great influence on its hardened state characteristics. In this paper, the behaviour of fresh lime mortars modified by etherified derivatives of chitosan (hydroxypropylchitosan (HPCH) and carboxymethylchitosan (CMCH)) is assessed with the purpose of exploring a new application of such derivatives as lime mortar admixtures. The rheological parameters (relative yield stress, consistency coefficient and fluidity index) and viscoelastic properties were correlated with flow table tests, relative density measurements, water retention abilities of mortars and air content in mortars. Results were seen to be strongly dependent on substituents of the chitosan. Non-ionic derivative (HPCH) had a plasticizing influence on the mortars; the ionic CMCH showed the thickening effect. The effect of chitosan ethers was found to be dosage-dependent. CMCH had low impact on water retention, while HPCH displayed high water retention capability. It was concluded, that the ionic derivative (CMCH) is very similar by its viscosity enhancing effect to starch ether.
Highlights
Organic thickening admixtures are widely used in the new types of cement-based or lime-based readymix render mortars
The incorporation of HPCH led to an increase in the air content of the mortars
It might have been considered that the higher the amount of HPCH, the larger the entrained air and the higher water retention of lime mortars
Summary
Organic thickening admixtures are widely used in the new types of cement-based or lime-based readymix render mortars. The raw material of chitosan, is a skeletal polysaccharide in many organisms in nature. This polymer and its derivatives have been used as biomaterials because of their biocompatibility, biodegradability, and biological activities [3]. Chitosan is soluble in water and acidic solutions, it is insoluble in alkaline media, which limits its applications in cement and lime mixtures [4,5]. The introduction of ionic carboxylic groups onto the amino groups of chitosan gives rise to water soluble, amphoteric polyelectrolytes, carboxyalkyl chitosan derivatives [7]. Non-ionic chitosan ethers does not significantly affect the fresh state properties of mortars, but the ionic ethers show a marked effect [8,9]. The role of chitosan on the fresh state properties of lime mortars have not been investigated far
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