In this paper, crushed lava granulate was used as full silica sand replacement in composition of repair mortars based on hydrated lime, natural hydraulic lime, or cement-lime binder. Lava granules were analyzed by X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Particle size distribution of both silica and lava aggregates was assessed using standard sieve analysis. Hygrothermal function of the developed lightweight materials was characterized by the measurement of complete set of hygric, thermal, and structural parameters of the hardened mortar samples that were tested for both 28 days and 90 days cured specimens. As the repair mortars must also meet requirements on mechanical performance, their compressive strength, flexural strength, and dynamic Young’s modulus were tested. The newly developed mortars composed of lava aggregate and hydrated lime or natural hydraulic lime met technical, functional, compatibility, and performance criteria on masonry and rendering materials, and were found well applicable for repair of historically valuable buildings.

In this paper, the behaviour of fresh lime mortars modified by etherified derivatives of guar (hydroxypropyl guar (HPG), carboxymethyl hydroxypropyl guar (CMHPG) and native guar gum (GG)) 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 guar. Non-ionic derivative (HPG) exhibited the biggest impact on the yield stress and elastic properties of the mortars. The ionic CMHPG showed the thickening effect. GG had low impact on water retention, while HPG and CMHPG displayed high water retention capability.

Cellulose ethers (CEs) are widely used as viscosity enhancing, water retaining additives in cement based mortars. Nevertheless, studies about the effect of cellulose ethers on the properties of aerial lime-based mortars are very lack. The use of water retaining additives in lime mortars can influence not only their fresh state properties but also the pore structure and strength of hardened mortars. In this work, four different commercial cellulose ethers were added to lime mortars in order to test their influence on properties of mortars in the fresh state. Mortar rheological parameters (relative yield stress, consistency coefficient and fluidity index) were correlated with flow table tests, relative density measurements, water retention and air content in the mortars. It was found that CEs reduce the spread of lime mortars and increase air content in the mortars. The CEs are not so effective in water retention compared with other types of water retention agents. Most dosages of CEs change the behaviour of mortars from pseudoplastic to dilatant. In contrast to the effect of CEs in cement-based materials, their viscosity enhancing behavior in lime mortars is denied, due to the presence of large amounts of calcium hydroxide. From this point of view, the CEs are not so suitable to use as viscosity enhancing admixtures in lime mortars like derivatives of chitosan or guar gum.

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.

This article studies the influence of biopolymeric viscosity-modifying admixtures with water-retentive function on the physico-mechanical properties of natural hydraulic lime-based mortars and their adherence to the traditional fired-clay brick substrate. The use of admixtures increases the water/binder ratio, which in turn leads to a decrease in the strength of the mortars. The viscosity-modifying function improves the adhesive strength between mortar and pre-wetter brick by increasing the binder paste viscosity, while the water-retentive function along with increased water content may lead to a decrease in adhesive strength. On the contrary, water retention and increased water content are beneficial on a dry surface, while paste viscosity plays only a minor role. When subjected to temperature-varying cycles, the mortars are more prone to in-mortar failure during the pull-off test. The air-entraining function of some admixtures improves the frost resistance of the mortars; however, it would negatively affect the adhesive strength by incorporating pores into the contact zone between the mortar and brick substrate. This study showed that the use of some of the studied admixtures may improve the adhesion of mortar to the brick substrate.