The effect of barium hydroxide on the physicochemical properties of lime-based conservation mortars

The research undertaken concerns the analysis of original Byzantine mortars and the study of new compatible lime-based mixtures, for conservation purposes, which present enhanced resistance to sulphates. The thesis focuses on the effect of barium hydroxide, as an additive, to both the physicochemical properties and the durability of conservation mortars. Both binary pastes and mortar mixtures, containing varying amounts of barium hydroxide, were prepared and their physicochemical properties and durability determined. Comparisons were made with a reference mixture containing no barium hydroxide. The laboratory mixtures were synthesised according to the analysis of original mortars, collected from six different Byzantine mosaic pavements. The durability of the mortar mixtures against sulphate action was studied through the use of accelerated aging tests: crystallisation of soluble salts; electrochemical degradation; sulphate fixation; and resistance to leaching of cementing material. The results of these tests were considered together with the physical properties of the mortars, since these also influence their durability. From the interpretation of the results it was shown that the setting of lime-based barium mixtures can be described by two mechanisms; the carbonation process of calcium hydroxide and barium hydroxide; and the precipitation of a barium calcium carbonate [BaCa(CO3)2] solid solution. It has been shown that the presence of barium hydroxide in lime-based mortars has a physical effect on the pore space characteristics of the mortar. It has also been shown that its presence improves the durability of the mortar, playing a protective role against sulphate attack

Lime-natural pozzolan conservation mortars: parameters that affect reactivity and strength

The natural pozzolans studied are commercial products and come from the volcanic islands of Milos and Kimolos, as well as North Greece mainland. The materials were characterised mineralogically and chemically by XRD and SEM/EDX respectively, while their reactivity with calcium hydroxide was studied through a pozzolanic activity test. In addition, five different lime-pozzolan mixtures were prepared and studied for their compressive strength at four preset curing periods (one, three, six and twelve months). The results indicated that when chemical and mineralogical composition was similar, the main parameter affecting the reactivity of the pozzolans and the strength of the produced mixtures was the grain-size distribution of the pozzolans within the range of 0-63μm

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study.

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications.EPSR

The effect of barium hydroxide on the physicochemical properties of lime-based conservation mortars

The research undertaken concerns the analysis of original Byzantine mortars and the study of new compatible lime-based mixtures, for conservation purposes, which present enhanced resistance to sulphates. The thesis focuses on the effect of barium hydroxide, as an additive, to both the physicochemical properties and the durability of conservation mortars. Both binary pastes and mortar mixtures, containing varying amounts of barium hydroxide, were prepared and their physicochemical properties and durability determined. Comparisons were made with a reference mixture containing no barium hydroxide. The laboratory mixtures were synthesised according to the analysis of original mortars, collected from six different Byzantine mosaic pavements. The durability of the mortar mixtures against sulphate action was studied through the use of accelerated aging tests: crystallisation of soluble salts; electrochemical degradation; sulphate fixation; and resistance to leaching of cementing material. The results of these tests were considered together with the physical properties of the mortars, since these also influence their durability. From the interpretation of the results it was shown that the setting of lime-based barium mixtures can be described by two mechanisms; the carbonation process of calcium hydroxide and barium hydroxide; and the precipitation of a barium calcium carbonate [BaCa(CO3)2] solid solution. It has been shown that the presence of barium hydroxide in lime-based mortars has a physical effect on the pore space characteristics of the mortar. It has also been shown that its presence improves the durability of the mortar, playing a protective role against sulphate attack

Design and optimization parameters of cement-based spherical macrocapsules for self-healing cement applications

Encapsulated healing agents is a promising solution for extending the service life of critical infrastructure, providing long-term healing efficiency. This research focuses on the shell properties of cement-based spherical macro-capsules, aiming to achieve increased survivability during mixing of mortar mixtures and efficient triggering upon crack propagation. In this framework, the pan coating technique was examined for the production of capsules with a cementitious shell, developed for the protection of powder healing agents. The main properties that were studied included the crushing load as a function of capsules size and the shell hydration facilitated by different setting accelerators, and their consequent effect on the survivability and the triggering efficiency of the capsules. The results show that the use of setting accelerators allows the rapid densification of the shell microstructure and improves the crushing load of capsules, resulting in high survivability during mixing process. The enhanced compatibility of capsules with the matrix allowed the efficient triggering of capsules during crack propagation, initiating the autonomous healing process

19th century ornamented metal trays from Greece and Turkey: metallurgy and provenance

Twelve ‘Japanned’ metal trays from Greece and Turkey, dated in the 19th century, were subjected to macroscopic and microscopic examination (stereoscopy, metallography, scanning electron microscopy) as well as to XRF and SEM-EDX analysis. The trays represent two stylistic types made of wrought iron either tin-plated or protected with a primer. Two were manufactured by forging while the rest were made by rolling prior to die forming with drop hammers or machine presses. Wrought iron was produced indirectly from cast iron with fossil fuels. Only in one case charcοal fuel was implied. Most pure iron was recognized for four trays dated at the end of the 19th century. Three of them also revealed the deliberate incorporation of metallic manganese while one of them was found to be alloyed. The other metals used such as copper, brass, silver and tin as also the methods applied, seem to follow the industrial evolution of the iron substrate but more analysis is required. As regards origin, the metallurgical results, even limited, combined with historical information, indicated that the metals/techniques used, were probably originally produced in west Europe although the supply of materials could have depended on different sources

Setting process of lime-based conservation mortars with barium hydroxide

This paper presents the effect of barium hydroxide on the setting mechanism of lime-based conservation mortars, when used as an additive material. The study focuses on the monitoring of the setting process and the identification of the mineral phases formed, which are essential for furthering the study of the durability of barium mixtures against chemical degradation. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and thermal analysis (DTA–TG) were used to monitor the setting processes of these mixtures and identify new phases formed. The results suggest that barium hydroxide is evenly distributed within the lime and produces a homogeneous binding material, consisting of calcite (CaCO3), witherite (BaCO3) and barium–calcium carbonate [BaCa(CO3)2]. Finally, it was found that barium carbonate can be directly bonded to calcitic aggregates and therefore increases its chemical compatibility with the binding materia

A new approach to conservation mortars designed for the urban environment

Sulphate attack of mortars continues to play the most important role in their deterioration, while causing implications for both the amenity and performance characteristics of monuments. The degradation that results also has economic consequences for architectural heritage, as the total damage cost is the sum of the renovation cost and amenity loss. In addressing the problem of dissolution of binding material caused by sulphate attack, this research focuses on the effect of barium hydroxide, as an additive, on the physical and chemical properties and durability of conservation mortar

Sulphate resistance of lime-based barium mortars

This work studies the effect of barium hydroxide on the sulphate-resistance of lime-based mortars when used as an additive material to the lime binder. The overall aim of the work was to study the potential of barium hydroxide to produce a mixed binder with lime, which is able to fix the sulphate ions, block the diffusion of sulphate solutions and, therefore, reduce the degradation rate of mixtures. The durability of different mixtures was studied through sulphate salt crystallisation and acid rain simulation tests, along with the characterisation of their pore-space properties. X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX) and inductively coupled plasma spectroscopy (ICP) were used for materials characterisation. Experimental results proved that barium hydroxide increases the durability of hardened mixtures against sulphate attack without affecting the microstructure characteristics

The effect of natural pozzolans in conservation mortars

Archaeological evidence in Greece proves that natural pozzolans have been used for mortar syntheses since antiquity. Mixing pozzolans with lime produces mortars with combined properties; on the one hand increasing their mechanical strength, and on the other improving their resistance to moisture. The syntheses produced this way are ideal for constructions that require resistance to water (water-tanks, aqueducts, renders) (Papayanni and Stefanidou, 2006). In the present study, research is dealing with the efficiency and reactivity of three natural pozzolans supplied from volcanic areas of the Aegean Sea, and furthermore with the effect of these materials to the physical and mechanical properties of the lime-pozzolan conservation mortars used for the restoration of archaeological monuments. The pozzolans studied are marketed volcanic products from Milos, Kimolos and Western Macedonia, and are supplied in various grain sizing (silt+clay <0.063mm, and coarser, up to 0.5mm or even up to 2mm). The practical aspect of the present study is indicated not only from the extensive usage of pozzolans on many significant restoration projects in Greece (Acropolis, Dafni Monastery, Nicopolis, Rhodes, Athos, Chania, Rhethymno), but also from the need of decoding the mechanism of reaction of such volcanic materials to conservation mortars. Sufficient amounts of the above mentioned materials were analyzed for their chemical and mineralogical composition using electron microscopy (SEM-EDX) and X-ray diffraction (XRD), respectively (Fragoulis et. al., 1997). The reactivity of the pozzolans was studied in the laboratory through their ability to react with calcium ions when dissolved in saturated solution (McCarter and Tran, 1996) and the remaining products were analysed with X-ray Diffraction (XRD). Further study investigated the effect of those pozzolans when used in lime-based mortars, relative to the ratio of the pozzolan participation within the binder, the sizing of the material and the curing period of the mixtures. The dry mortars were tested for their physical characteristics and microstructure using optical and electron microscopy (SEM), as well as for their compressive strength. In addition, the binding products of the mixtures were analyzed with X-ray Diffraction (XRD) and Thermal Analysis (DTA/TG). The outcome of the research proved that the ability of a pozzolan to react with lime depends on its sizing, as well as on its mineralogical composition. It was thus indicated that the reactivity of a pozzolan increases when the material is ground to smaller sizing, but when comparing different kinds of pozzolans, a coarser material may be of equal reactivity, or even greater, to a finer one. The latter proves that the mineralogy is the main factor that affects reactivity. The factors that contributed to the increase in strength properties were the mineralogical characteristics, the sizing, the ratio participation of the pozzolan within the mixture and the duration of curing of the mortars. The greatest strength-increase was observed in the mixture with 50% participation of pozzolan, ground below 63μm and after twelve months of curing. Compared to pure mortars, the pozzolanic syntheses achieved up to eight times higher values of compressive strength. Conclusively, when synthesising a mortar for a restoration project, the criteria that should be considered are firstly the composition of the materials, and secondly the grain sizing and their ratio participation in the binder, so that ultimately the mixture has the properties required