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Today, lime-pozzolan mortars are being used in the repair of historic buildings, replacing the lime-cement mortars that were previously used in this practice, but were incompatible with historic mortars. It has been observed in laboratory research and also in practice that some lime-pozzolan mortars can lose strength over time. The cause of this behaviour is not fully understood, but the main reason seems to be the instability and breakdown of the aluminate phases. In this paper, the role of amorphous Al2O3 content in pozzolans on the long-term mechanical properties of lime-pozzolan mortars is studied. Lime-pozzolan mortars with 40% replacement of lime with pozzolans with different contents of amorphous Al2O3 (metakaolin, pumice, pozzolanic earth, trass, zeolite) were prepared and the changes in strength, porosity and mineralogical composition of the mortars (determined by XRD and TG/DTA) over time were monitored. Mortars containing pozzolans with a high content of amorphous Al2O3 (over 30% by weight) showed a dramatic decrease in strength, changes in porosity and a decrease in the content of monocarboaluminate (C4AcH11) with a simultaneous increase in the content of vaterite and aragonite. The negative effects of carbonation of the aluminate phases are particularly evident in pozzolans with a high content of amorphous Al2O3.

In this article, the physico-mechanical properties and hydration processes of cement pastes containing three additives are introduced. Cement was replaced with pumice, trass, waste chalcedonite powder at 30% by mass and a combination of pumice or trass and waste chalcedonite powder in the amounts of 15% each. The main aim of this research was to assess the properties of two- or three-component binders to save cement in these binders. Rheological properties such as consistency, yield stress, viscosity and thixotropy were determined, in addition to porosity, 7-day and 28-day flexural and compressive strength and bulk density. Additionally, the heat evolution and degree of hydration of the tested pastes were compared. The use of all additives resulted in a reduction in the consistency of the tested pastes. The highest compressive strength measured after 28 days was observed for the cement paste with a 30% content of waste chalcedonite powder, which is related to it having the best pozzolanic activity of the materials used. The results of this research have confirmed that pumice, trass and waste chalcedonite powder can be used as components of blended Portland cements. [ABSTRACT FROM AUTHOR]

The article presents the influence of pumice, trass and chalcedonite powder on rheological properties of cement pastes. Cement was being replaced both of additions 10% or 20% by mass and combination of pumice or trass and chalcedonite powder in the amount 5% or 10% of each of them. The main purpose of the publication was to assess the effects of chalcedonite powder with selected mineral additions in terms of rheological properties and compare them with the results obtained for pastes modified with only one of the additions. In each case, the additive or combination of additives introduced into the paste reduced the flow, compared to the result of paste without additive(s). Rheological properties varied depending on type and amount of additive(s). [ABSTRACT FROM AUTHOR]

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.

Porous pozzolan-active aggregate can be used to prepare lightweight lime mortars with high ability to salt accumulation from masonry, enhanced strengths and improved their acoustic and thermal insulation properties, or fire resistance. In this study, the effect of 3 types of natural lightweight aggregate on acoustic insulation properties of air lime mortars, NHL mortars, and cement-lime mortars has been investigated. Measurements of the signal attenuation in the frequency range of 16 Hz to 16 kHz showed the appreciable effect of binder and aggregate used in the mortars. Pumiceous aggregate caused the highest attenuation of the acoustic signal. The natural zeolite seems to be suitable aggregate to NHL and blended lime-cement plasters because it lightens the mortar and positively affects the acoustic attenuation.

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. [ABSTRACT FROM AUTHOR]

Viscosity enhancing admixtures, widely used to improve characteristics of concrete and ready-mix mortars, are mainly different derivatives of cellulose. Due to the nature of cellulose processing, the environmental-friendlier alternatives should be studied in order to reduce the impact of the building industry on the environment. The rheological study of natural hydraulic lime (NHL) grouts modified by four different biopolymers is carried out to investigate their behaviour in the NHLbased mortars. The biopolymers studied are of seaweed (sodium salt of alginic acid (ALGNA) and carrageenan (CG)) and microbial (diutan gum (DG) and xanthan gum (XG)) origin. The effect of addition of these admixtures in the doses of 0.1%, 0.5%, and 1% was studied using hybrid rheometer with DIN concentric cylinders geometry. The flow properties as well as viscoelastic properties were studied. The addition of any of the admixtures led to the increase in yield stress, with DG being the most effective admixture. Desirable increase in consistency coefficient was observed within the pastes with CG and DG addition having growing dosage dependency, the ALGNA addition also increased the coefficient noticeably, but it was furtherly decreased with growing dose of admixture. The fluidity index lower than 1 expressed shear-thinning behaviour of studied pastes, except the pastes with highest dose of admixtures, and all of the XG pastes. The addition of CG and DG supported the stability of the grout expressed as the increase in critical strain, thus prolongation of linear viscoelastic region. The flow strain was increased by all of the studied admixtures promoting the gel-like behaviour of the pastes. Complex modulus and viscosity measured at 1Hz frequency were unaffected by the DG addition while they were increased notably by addition of other admixtures with ALGNA and XG supporting the resistance to deformation of the grouts studied. Correspondingly to complex modulus increase, the loss tangent is diminished, reporting more elastic behaviour of the material. All of the admixtures studied increased the yield stress, and the influence of most of them had similar trends within other properties. Noticeable differences in efficiency and dosage-dependency were observed. The xanthan gum was overall the worst performing admixture. This was mainly due to higher sensitivity of xanthan to the concentration of bivalent ions in the solution. [ABSTRACT FROM AUTHOR]

Highlights: [•] Properties of blended cement pastes exposed to temperature up to 1200°C and after their rehydration were studied. [•] The addition of slag or fly ash improved the compressive strength of cement paste after heating. [•] The strengths of rehydrated cement pastes were lower than of dehydrated pastes. [•] The direct conjunction between the strength of rehydrated cement pastes and their brownmillerite (C4AF) content was observed. [ABSTRACT FROM AUTHOR]

The subject matter of the work presented here is the development and evaluation of novel lightweight mortars that meet the functional and technical criteria imposed on repair mortars. In a broad experimental campaign, lime, natural hydraulic lime, and lime–cement mortars were designed and tested. Lightweight aggregate, expanded perlite, granules from expanded glass and zeolite were used as full replacements for quartz sand. The hardened mortars were tested at the ages of 28 days and 90 days. The conducted tests and analyses were focused on the assessment of structural, mechanical, hygric and thermal parameters. The salt crystallization resistance and effect of salt presence on the hygroscopicity of the investigated mortars were also investigated. The use of lightweight aggregates in the composition of mortars resulted in their high porosity, low density, satisfactory mechanical parameters, improved water vapor transmission capability and water absorption. The mortars with expanded perlite and glass granulate were ranked among thermal insulation mortars of classes T1 and T2, respectively. The use of lightweight aggregates enabled the development of mortars with great durability in terms of salt action, which was almost independent of binder type. The ability to accommodate water vapor was increased by the effect, i.e., the use of lightweight aggregates and the presence of salt in mortars increased porous space. Taking into account the compatibility, functional, and technical criteria, lime- and natural hydraulic lime-based lightweight mortarswere classified as repair mortars, providing improved thermal performance. The lime–cement lightweight plasters can be recommended only for repair of building structures where cement and lime–cement materials were original applied. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Geopolymers are conventionally prepared from metakaolin, fly ash, or blast furnace slag. In this paper, geopolymer synthesis using two different red-clay ceramic powders and a varying amount of Na 2 O/SiO 2 activator is presented. Experimental results show that despite of the high content of crystalline minerals and lower concentration of amorphous matter, both tested precursors enable to prepare geopolymers with satisfactory mechanical properties. The discussion of measured values of compressive strength with respect to SiO 2 /Al 2 O 3 and Al 2 O 3 /(Na 2 O + K 2 O) ratios in the prepared geopolymer mixes reveals that the consideration of only amorphous portion of ceramics is appropriate. A higher content of CaO in the precursor is found to cause a broader pore size distribution and higher porosity of resulting geopolymers, which is due to the formation of calcium silicate hydrates. [ABSTRACT FROM AUTHOR]

In this article, the physico-mechanical properties and hydration processes of cement pastes containing three additives are introduced. Cement was replaced with pumice, trass, waste chalcedonite powder at 30% by mass and a combination of pumice or trass and waste chalcedonite powder in the amounts of 15% each. The main aim of this research was to assess the properties of two- or three-component binders to save cement in these binders. Rheological properties such as consistency, yield stress, viscosity and thixotropy were determined, in addition to porosity, 7-day and 28-day flexural and compressive strength and bulk density. Additionally, the heat evolution and degree of hydration of the tested pastes were compared. The use of all additives resulted in a reduction in the consistency of the tested pastes. The highest compressive strength measured after 28 days was observed for the cement paste with a 30% content of waste chalcedonite powder, which is related to it having the best pozzolanic activity of the materials used. The results of this research have confirmed that pumice, trass and waste chalcedonite powder can be used as components of blended Portland cements.