Hydraulic lime mortars for the restoration of historic masonry in Crete

This study presents the results of the physico-chemical characterization of original mortars and plasters and the evaluation of the repair ones prepared with natural hydraulic lime (NHL) as binding material and siliceous sand and crushed brick as aggregates. The repair mortars were applied in restoration works of a historic masonry in Crete, Greece. The proportions of binder, aggregates and water were selected in order to achieve optimum workability. Original mortars, containing magnesian lime, had to be replaced since previous interventions with cement-based mortars have provoked damage acceleration. Water absorption by capillarity, compressive strength, modulus of elasticity, porosity and pore size distribution were determined at early stages and after 1 year of curing time; these properties prove the suitability of the proposed mortars for such an application. After 3 years of intervention with NHL-based mortars and plasters, macroscopic survey and analyses of the applied materials reveal that no cracks or release of soluble salts occur.     

Physico-chemical study of Cretan ancient mortars

Mortars from monuments of various periods in Crete, from Minoan up to now, have been studied (concerning mineralogical and chemical composition, grain size distribution, raw materials, tensile strength) in order to assess their durability in a marine and humid environment. The lime technology and raw materials, irrespective of the various historic periods, diversify the final composites into mortars, such as: (a) lime, (b) hydraulic lime, (c) lime with crushed brick, and (d) lime with pozzolanic material. These present binders in quantities ranging from 22% (pozzolanic mortars) to 29% (lime mortars). Hydraulic compounds, such as calcium silicate/aluminate hydrates, and tensile strength are higher in the pozzolanic mortars followed by crushed brick lime, hydraulic lime, and lime mortars. High quantities of water-soluble salts identified in the lime mortars indicate their risk of disintegration. A calculation procedure is presented herein, based on the combination of mineralogical and chemical analyses that allows the determination of the binder/aggregate proportion.     

Compatibility between ecocement produced from incinerator ash and reactive aggregates in ASR expansion of mortars

Recently, in Japan, two new-type hydraulic cements, high early strength type ecocement (HEC) and normal type ecocement (NEC), have been developed using incinerator ashes up to 50% of the raw materials. In this study, the compatibility of these ecocements with various types of reactive aggregates with respect to alkali-silica reaction (ASR) was studied. Ordinary Portland cement (OPC) and blast furnace slag cement (BFSC) were also used for a comparative study. Two types of the accelerated mortar bar expansion test, the JIS A1146 and the Danish methods, were used to clarify the expansion behavior of mortars made with the above cements. The influence of a combination of the chemical and mineralogical compositions of cement and the reactive components of aggregate on both the amount of ASR gel and the expansion rate of the mortar was also investigated. From the results, it was found that the expansion behaviors of mortars due to ASR varied significantly depending on a combination of both the mineralogical composition of cement and the reactive component of aggregate.     

Durability Improvement of Ancient Bricks by Cementation of Porous Media

The physicomechanical properties of historic bricks in Toledo (Spain) that have undergone a time-dependent self-healing by natural weathering processes have been improved by porous infill with gypsum, ettringite, and, mainly, calcite. Both these bricks and their experimental replica bricks, made from the original calcareous clays fired at the appropriate historical temperatures (700°–900°C), have been analyzed by X-ray diffraction, optical and scanning electron microscopy, mercury intrusion porosimetry, and ultrasound velocities to compare pore structure and strength evolution by mineral cementation. The resultant microstructure and mineral fillings depend on the brick calcareous composition and firing temperature, the brick location environment, burial, indoor or outdoor walls, the lime-based joint mortars and coat plasters, and infiltration waters.     

The Adhesion Properties of Mortars in Relation with Microstructure

The interaction between masonry units and mortar is a crucial factor for the quality of a wall. The most important factor is the adhesion between bricks and mortar in order to construct a masonry wall with adequate strength, good impermeability, and durability. In this work mortars were produced with various cement/lime/aggregates ratio. The adhesion properties of the mortars with clay bricks were tested with a simplified tensile/tear testing measurement. In order to investigate the adhesion properties in relation with microstructure the mortars were characterized with X-ray diffraction and were further investigated with scanning electron microscopy and stereoscopy. It was found that adhesion is favored by the formation of a Si–Al matrix with a low Ca content in the brick/mortar interface and the formation of fine Ca–Al–Si phases which can penetrate into the brick.     

Ettringite formation in historic bath brick-lime plasters

Two types of historic hydraulic brick-lime plasters from a selected Ottoman bath are examined to characterize their technology and the appropriateness of their use in bath. The first type of plaster is original and structurally sound, while the historic repair plaster is the second type and is found to have deteriorated despite being exposed to the same environment. This difference is investigated by comparing their raw material compositions and the pozzolanic activities of the brick powders used in the plasters. Although these results showed no significant differences, ettringite crystals are detected in the historic repair ones by XRD, FTIR, and SEM-EDS analysis. The repair plaster may have lost its integrity owing to the expansion generated by the growth of ettringite crystals in the plaster. In this study, the ettringite formation is discussed in relation to hydration reaction products of lime-brick plasters, possible sources of gypsum, and the climatic conditions of historic bath building.     

Investigation of Shale Brick Interface with Cement-Lime and Polymer-Modified Mortars

Bonds between cement-lime mortar and shale brick, and between polymer-modified mortar and shale brick, were studied using a scanning electron microscope (SEM). The results showed that the bond is greatly influenced by the microstructure and chemical composition of the mortar at the interface contact area and by the microstructure of the brick surfaces. For relatively porous bricks, cement-lime mortars give a better bond, apparently due to better interpenetration of the fresh mortar into the open pores of the brick, creating a greater bond area. The presence of calcium contributes to good bonds, while large amounts of silicon were found in poorly bonded areas. Latex-modified mortars are not able to penetrate brick surfaces and are able to create strong bonds only on limited locations and allow water to enter brick masonary.     

Microscopy of historic mortars—a review

Mortars with mud, gypsum and lime as binder have, since ancient times, been used for very different applications. The characterisation of these historic mortars was until 1970-1980 mostly based on traditional wet chemical analyses but the interpretation of these results is difficult and often impossible without a good knowledge of the nature of the different mortar components. More recently developed mortar characterisation schemes have optical microscopy as a first step in identifying the aggregates, of the various mineral additions (latent hydraulic), binder type, binder-related particles and in describing the pore structure. Optical microscopy is also a valuable aid for damage diagnosis of degraded historic mortars and for the study of the interfacial zone, the bonding and possible reaction rims between aggregates, bricks or stone and the mortar. Automated image analysis techniques or manual point-count/linear traverse methods can be used to determine mix proportions, binder/aggregate ratio, aggregate size distribution and air void system.     

Occurrence of thaumasite in gypsum lime mortars for restoration

For restoration purposes, it is essential to have compatible mortars for historic masonry built originally with gypsum mortars. For that reason, gypsum lime mortars with high weathering resistance were developed. Due to the added hydraulic components and carbonate components of the used limes of these mortars, the occurrence of thaumasite can take place. Different mortar mixtures with variable binder contents, using lime with differing amounts of hydraulic components, were prepared and stored under two contrasting curing conditions. Over 90 days of curing, these mortars were investigated using physical-mechanical and chemical-mineralogical techniques. The results have shown that the potential for the growth of thaumasite depends on the composition of the raw materials, especially of the lime. In gypsum lime mortars which were used for restoration purposes, small amounts of thaumasite were also detected, but these small amounts of thaumasite do not reduce mechanical properties. This assumption was confirmed by investigations of gypsum lime mortars, which were exposed outdoors for 13 years.     

Opal-A rich additives used in ancient lime mortars

Ancient stone and brick masonry mortars from three monuments in Konya, Central Anatolia dated to the Anatolian Selçuk Period (12th and 13th centuries AD) were examined for their raw material composition and durability characteristics to understand some characteristics of medieval mortar technology.Optical microscopy, XRD, SEM, EDX, FTIR and TGA analyses revealed that the mortars contained high percentage of lime binder totally carbonated into micritic calcite. Coarse and medium aggregates were mainly composed of sandstone and metamorphic rock fragments, quartz, feldspar and mica minerals. Opal-A was found in considerable amounts in the fine aggregates, likely not derived from the coarser ones but added separately. Pozzolanic activity of the fine aggregates was determined by conductometric measurements. Their ability to form C-S-H was observed by treating them with saturated Ca(OH)₂ solution.Bulk density and total porosity measurements showed that the mortars were highly porous due to the use of high amount of lime. On the other hand, they possessed sufficient mechanical strength. Mechanical properties were determined by point load tests and ultrasonic pulse velocity measurements. They were expressed as uniaxial compressive strength (UCS) and modulus of elasticity (E_mod) in MPa.The results were also discussed in terms of durability characteristics of the mortars. They were expressed with the use of uniaxial compressive strengths in dry and wet states, and total porosity values. The mortars were considered to have high durability to wetting and drying cycles but had poor durability to the crystallization of water-soluble salts.     

Use of granite sawing wastes in the production of ceramic bricks and tiles

Granite process industry generates a large amount of wastes, which pollute and damage the environment. This work aims to characterize and evaluate the possibilities of using the granite sawing wastes, generated by the process industries from Paraı́ba State, Brazil, as alternative ceramic raw materials in the production of ceramic bricks and tiles. Samples of granite sawing wastes were collected from companies located in Paraı́ba State. Their characterization were carried out with the determination of density, particle size distribution, surface area (BET), chemical composition, and by DTA, TGA, XRD, and SEM. In a second part of the work, tests in ceramic compositions were conducted in order to evaluate the suitability of addition of wastes in ceramic compositions used in the production of ceramic bricks and tiles. The results showed that the granite wastes have physical and mineralogical characteristics that were similar to those of conventional ceramic raw materials. The ceramic bodies produced from reformulated ceramic compositions had technological characteristics in agreement with the Brazilian standardizations for ceramic bricks and tiles.     

Mechanical and adhesion properties of polymer-modified cement mortars in relation with their microstructure

In this study, cement mortars were modified with a commercial polymer admixture. The aim of this study is to investigate the influence of the polymer content on the mechanical and adhesion properties of the mortars and to relate these properties with mortars’ microstructure. A series of mortars were produced with various polymer/cement/water/aggregate ratios. The adhesion properties of the mortars to clay bricks were tested with a simplified tensile testing measurement. The microstructure of mortars, as well as interfaces, were evaluated by Scanning Electron Microscopy (SEM). It was found that with high polymer content, large size hardened particles are formed, reducing the compressive strength of the mortars. Polymer addition enhances the adhesion between the mortar and brick. The mortar microstructure at the interface affects the adhesion properties and the mode of failure.     

锰渣与再生砖骨料制备免烧砖的性能及应用

锰渣与再生砖骨料均属于大宗固废,提升大宗固废利用率具有重要的环境效益和经济效益。本文利用锰渣、再生砖骨料等制备了免烧砖,探究了锰渣掺量对免烧砖各项性能的影响,且对其微观结构及有害物质浸出行为进行了分析。结果表明:制备的免烧砖外观质量优良,色泽均一,尺寸标准;结合强度要求和抗冻性要求,锰渣掺量不超过10%(质量分数)时,可制备出强度、耐水性和耐久性优异的MU20免烧砖,锰渣掺量不超过15%时,可制备出性能优异的MU15免烧砖;掺适量锰渣的免烧砖中形成了较多的钙矾石相,有利于强度发展。锰渣和再生砖骨料制备的免烧砖可以应用于人行道等市政工程,应用效果良好。研究结果可为锰渣低碳资源化利用以及生态砖制品的生产和应用提供技术支持。     

Post-mortem analysis of MgO–Al2O3–C bricks containing bauxite used in steel ladle walls

A serious problem with integrated masonry linings ladle was that the ladle wall bricks were difficult to be partially replaced. Thus, the service life of the ladle was determined by the properties of ladle wall bricks. In this study, the new generation of MgO–Al₂O₃–C bricks with bauxite aggregates was tested in a ladle lining of an integrated steel ladle for 103 cycles, and the corroded microstructure of the used brick was investigated. A multilayered structure of bauxite aggregates could be observed in the used brick, which inhibited the slag penetration along the boundary of the magnesia aggregates and reduced the degree of the aggregates fall off from the used bricks. Besides, during the process of slag penetration, bauxite aggregates could melt into the slag, which increased the viscosity of the slag and weakened the penetration ability of the slag. The MgO–Al₂O₃–C bricks with bauxite addition could improve the service life of the ladle to a certain extent.     

Lime-pozzolana mortars in Roman catacombs: composition, structures and restoration

Analyses of microsamples collected from Roman catacombs and samples of lime-pozzolana mortars hardened in the laboratory display higher contents in carbonated binder than other subaerial Roman monuments. The measured environmental data inside the Saint Callistus and Domitilla catacombs show a constant temperature of 15-17 °C, a high CO₂ content (1700 to 3500 ppm) and a relative humidity close to 100%. These conditions and particularly the high CO₂ concentration speed-up the lime calcitization roughly by 500% and reduce the cationic diffusion to form hydrous calcium aluminosilicates. The structure of Roman catacomb mortars shows (i) coarser aggregates and thicker beds on the inside, (ii) thin, smoothed, light and fine-grained external surfaces with low content of aggregates and (iii) paintings and frescoes on the outside. The observed high porosity of the mortars can be attributed to cracking after drying linked with the high binder content. Hardened lime lumps inside the binder denote low water/mortar ratios for slaking. The aggregate tephra pyroclasts rich in aluminosilicate phases with accessorial amounts of Ba, Sr, Rb, Cu and Pb were analysed through X-ray diffraction (XRD), electron microprobe analysis (EMPA) and also by environmental scanning electron microscopy (ESEM) to identify the size and distribution of porosity. Results support procedures using local materials, special mortars and classic techniques for restoration purposes in hypogeal backgrounds.     

Masonry repair lime-based mortars: factors affecting the mechanical behavior

The increasing use of lime-based mortars for the restoration of historic buildings and structures justifies the research on these materials. The focus of this paper is the effect of technological variables on pore structure and mechanical properties of lime-based mortars. The influence of curing time, binder-aggregate (B/Ag) ratio, aggregate attributes and porosity is discussed. Mortars prepared with aerial lime, varying aggregate types and B/Ag ratios ranging from 1:1 to 1:5 by volume were tested. Compressive and flexural strength measurements, as well as X-ray diffraction (XRD) and thermal studies, were performed after 3, 7, 28, 91, 182 and 365 days. A strong increase in strength of mortar mixtures after 365 curing days (as compared to 28 curing days) is found. In spite of the fact that larger amounts of binder increase the total porosity, the strength of these mixtures is also increased. A good interlocked structure is obtained as binder contents increase. Also, higher porosities allow better portlandite carbonation. A relationship between mechanical properties and pore structure was established. However, in case of binder excess, the increase in voids leads to a strength reduction. The use of calcareous aggregates improves strength more as compared to the use of siliceous aggregates. Factors as grain size distribution and grain shape of the aggregates have also been considered.     

Hercynite and magnesium aluminate spinels acting as a ceramic bonding in an electrofused MgO–CaZrO3 refractory brick for the cement industry

Innovative chrome-free basic refractory bricks have been design based on electrofused magnesia–calcium zirconate (MgO-CaZrO₃) technology using as ceramic bonding magnesium aluminate spinel (MgAl₂O₄) and hercynite spinel (FeAl₂O₄) in order to improve their properties. Industrial refractory bricks have been manufactured by solid state sintering of magnesium and calcium zirconate aggregates with MgAl₂O₄ and FeAl₂O₄ spinels at 1650 °C in a tunnel kiln. Physical and microstructural characteristics of new refractory bricks have been characterised in terms of density, porosity, crystalline phases, phase distribution and morphology. X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM) with microanalysis (using energy dispersive spectroscopy analysis -EDS) have been used. The mechanical behaviour has been evaluated in terms of cold crushing strength (CCS) at room temperature and three point bending modulus of rupture (MOR) at 25 and 1260 °C. Static and dynamic resistance test by chemical attack of clinker raw meal constituents have been carried out at 1450 °C. Results have shown that thermo-mechanical properties of new refractory bricks significantly improved with increasing both type of spinel in content. Microstructural analysis revealed that spinel phases aided to develop a strong bond between the magnesia and calcium zirconate refractory aggregates. Finally, these refractory matrixes exhibit a good thermal stability and an excellent chemical resistance against clinker raw meal.     

Composition of Periclase and Calcium-Silicate Phases in Magnesia Refractories Derived from Natural Microcrystalline Magnesite

Mineralogical and microstructural properties of sintered and fused magnesia grains and refractory bricks derived from natural magnesite were examined. Although their CaO/SiO₂ ratios can be used to approximate their mineralogical compositions, detailed X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies revealed significant deviations from the expected phase assemblages. Their microstructures vary widely in terms of proportions of direct periclase bonding, amounts and phase constitution of the siliceous bonding, and the size and composition of the periclase crystals. An exceptionally high solid solubility of CaO in periclase crystals was detected. Most of the phases of the siliceous bond exhibit nearly stoichiometric compositions and show intriguing substitutions.     

The use of recycled paper processing residues in making porous brick with reduced thermal conductivity

Production of porous and light-weight bricks with reduced thermal conductivity and acceptable compressive strength is accomplished. Paper processing residues were used as an additive to an earthenware brick to produce the pores. SEM-EDS, XRD, XRF and TG-DTA analysis of the paper waste and brick raw material were performed. Mixtures containing brick raw materials and the paper waste were prepared at different proportions (up to 30 wt%). The granulated powder mixtures were compressed in a hydraulic press, and the green bodies were dried before firing at 1100 °C. Dilatometric behaviours, drying and firing shrinkages were investigated as well as the loss on ignition, bulk density, apparent porosity, water absorption and thermal conductivity values of the fired samples. Their mechanical and microstructural properties were also investigated. The results obtained showed that the use of paper processing residues decreased the fired density of the bricks down to 1.28 g/cm³. Compressive strengths of the brick samples produced in this study were higher than that required by the standards. Thermal conductivity of the porous brick produced in this study (<0.4 W/m K) showed more than 50% reduction compared to local brick of the same composition (0.8 W/m K). Conversion of this product to a perforated brick may reduce its thermal conductivity to very low values. Successful preliminary tests were conducted on an industrial scale.     

Results of a competition for the most resistant ladle brick

Conclusions The wear of the Chasov-Yar ladle brick was less than that of bricks made by the other factories; its average resistance for the five ladles was 13.3 melts.The average wear of the ladle brick made by the Zaporozh Plant exceeded the wear of the Chasov-Yar brick. The average resistance of this brick for the five ladles was 13.2 melts.The wear of the ladle brick made at the Belokamen Firebrick Plant is uniform, with only slight washing-out of the joints. The surface of the ladle after service was smooth and glazed.Examining all the materials tested during the competition the award panel awarded: first place in the compeitition to the Chasov-Yar Combine; second place to the Zaporozh Plant; third place to the Belokamen Plant.On the basis of material on the technology for the manufacture of ladle bricks used in the plants taking part in the competition, and also the service factors of the products during competitive testing, and on the basis of proposals from the All-Union, Ukraine and Vostok Institutes of Refractories for improving the quality of ladle brick, the award panel of the competition made the following recommendations for further improving the quality of ladle bricks:scientific-research institutes for refractories in collaboration with factory producers should carry out tests of fired ladle bricks made from chamotte and semiacid bodies, kaolinized and high-alumina raw materials and unfired products, and also should test linings made from rammed bodies in ladles of different capacities in different conditions of service;concerns should specialize in the manufacture of ladle bricks and install modern grinding, blending and pressing equipment;the assortment of bricks should be reexamined and the sizes of ladle bricks should be increased with the aim of reducing the number of joints in the structure;output of adequate supplies of high-grade special packaged mortars should be ensured.