Tomáš Žižlavský

Lime mortars with partial replacement of lime by fine natural zeolite were first characterized in detail and then subjected to freeze-thaw cycles as well as to three different salt. Use of natural zeolite as pozzolanic admixture has led to a improvement in the frost resistance of lime mortars. Despite the decreasing porosity of the samples with increasing zeolite content, zeolitic mortars showed better ability to salt accumulation. The concentration of the monitored anions in the lime-zeolite mortars after treatment with saline solutions increased more than 100 times. The use of natural zeolite-modified lime mortars for desalination of chloride-contaminated masonry seems to be particularly suitable. From a comprehensive point of view, 40% replacement of lime with zeolite appears to be the most effective. It is possible to deliberate the use of these mortars for the repair of historical mortars in desalination of masonry as sacrificial renders, especially.

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.

This paper presents an innovative study on the partial replacement of lime binder with foam glass dust to explore a new application of this waste dust as a lime mortar additive. Standard air lime mortars and natural hydraulic lime (NHL) mortars were made by incorporating from 0% to 40% of foam glass dust in replacement to lime, and their mechanical performances, microstructure, and durability were determined. The waste foam glass dust showed an unusually high pozzolanic activity, predicting an improvement in the mechanical properties and durability of lime mortars. As the replacement level in air lime mortars increased, the performance properties of the mortars improved. The pozzolanic reaction of foam glass dust did not compensate for the loss of hydraulic binder in NHL mortars; therefore, these mortars have gradually lost their strength. The progress in mortars carbonation, as well as the pozzolanic reaction of foam glass dust, led to the formation of denser and more frost-resistant structure in air lime mortars, whereas the partial binder replacement in NHL mortars with foam glass dust had no significant effect on their frost resistance. The highly effective use of foam glass dust as a supplementary material was assessed to air lime mortars.

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.

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.