Physico-chemical and mechanical characterization of hydraulic mortars containing nano-titania for restoration applications

In this work nano-titania of anatase and routile form has been added in mortars containing: (a) binders of either hydrated lime and metakaolin, or natural hydraulic lime and, (b) fine aggregates of carbonate nature. Mortar composition was tailored to ensure adhesion of fragments of porous limestones from the Acropolis monuments. The aim was to study the effect of nano-titania in the hydration and carbonation of the above binders, as well as the mechanical properties and the adhesive capability of the designed mortars, where the nano-titania proportion was 4.5–6% w/w of binder. The physico-chemical and mechanical properties of the nano-titania mortars were studied and compared to the respective ones, without the nano-titania addition. DTA-TG, FTIR, SEM and XRD analyses indicated the evolution of carbonation, hydration and hydraulic compound formation during a 1 year curing. Results indicate enhanced carbonation, hydration and modulus of elasticity of mortar mixtures with nano-titania. A specifically designed experimental procedure for measuring the direct tensile strength of the mortar–stone system proved that nano-titania mortars can be used as adhesive materials for porous limestones.     

Wet deposition studies of hydraulic mortars

Cement mortars and lime-pozzolan mortars have been exposed to wet/drying cycling of ‘acid rain’ solution, using realistic presentation rates, to simulate outdoor conditions. Cement type, water/cement ratio, and curing temperature were also examined. Form the pH of run-off solution, it is evident that reaction between the mortar and the ‘acid rain’ proceeds over the exposure period, with significant weight increases for the cement mortars and little influence of curing temperature for lime-pozzolan mortars. Exposure of the cement mortar gives to significant calcium loss to run-off and is also associated with retained souuble stalts; these results from the presence of free hydrated lime in the mortar. Conversely, lime-pozzolan mortars, associated with a clacium carbonate compounds, reveal comparatively reduced calcium loss,i.e by about one-tenth that of cement mortar.     

古希腊的体育与建筑

体育是关系到国家和民族生死存亡的大事。 希腊戏剧是从学羊叫开始的。早在公元前7世纪晚期,希腊戏剧就诞生了,随之,世界上最早的剧场出现了。     

Quantitative composition of ancient mortars from the Notre Dame Cathedral in Tournai (Belgium)

A combined micro- and macroscopical approach was implemented for the quantification of the main constituents in a set of 41 ancient mortar samples from Tournai (Belgium). The samples range in age from Roman to Romanesque. The microscopical study consisted of point counting on thin sections prepared from these mortars. If sufficiently large samples were available, Image Analysis on plane polished surfaces was used to quantify the larger objects (> 1 mm) as lime lumps or ceramics. In spite of possible uncertainties, general conclusions about these mortars could be drawn. The Roman and Palaeochristian mortars are all comparable in containing a considerable amount of ceramic fragments, whereas their presence was not systematic during later times. The binder/aggregate ratios varied from 0.4 to 2.3. Romanesque mortars seem to have a less variable binder to aggregate content compared to the older mortar samples.     

Characterization of mortars used for the construction of Saithidai Heroon Podium (1st century AD) in ancient Messene, Peloponnesus, Greece

The Saithidai Heroon Podium is a Mausoleum dated to the Roman Period located in ancient Messene, Peloponnesus, Greece. Its outer walls were constructed with porous and massive limestone blocks with no mortar in the joints. The core of the podium was filled by rock chips to angular boulders of sandstone, limestone, sand, gravel and earthy groundmass material. The groundmass is mostly composed of quartz and calcite, with minor amounts of clay minerals. Small, irregular lime lumps also occur, composed of authigenic euhedral calcite crystal assemblages and rare sub-microscopic quartz fragments, or rod-like CaO/SiO₂-rich mineral assemblages developed in pore spaces on fine-grained authigenic calcite crystals. The mortar used for the filling material of the Podium was poorly homogenized semi-hydraulic lime derived from the calcination of pure limestone and siliceous limestone fragments, possibly the waste material from the finishing of the building blocks of the Podium walls.     

Analytical study of ancient pottery from the archaeological site of Aiani,northern Greece

The present study is a multi-analytical approach on the characterization of several potsherd samples, dated from prehistoric to hellenistic times, from Aiani, ancient Upper Macedonia, northern Greece. In particular, X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Environmental Scanning Electron Microscopy, coupled with Energy Dispersive X-ray system (ESEM-EDX) were used for the determination of the morphological, chemical and mineralogical characteristics of the potsherds. The preliminary results indicated a rather local provenance of the analyzed ancient pottery samples and a finer texture and thus better ceramic manufacture as getting to hellenistic era. The use of a silicious or calcerous raw material is probably related to the specific utilization of each ceramic vessel in ancient times. The presence of gehlenite or pyroxene minerals in the ceramic matrix indicated higher firing temperatures, while lower temperatures were deduced when finding phylosilicate minerals. The preliminary results of this study do not necessarily imply that all the pottery of this area, belonging to the same chronological type, have similar physicochemical characteristics.     

A study of the workability of natural hydraulic lime mortars and its influence on strength

Lime mortars are currently used for both repairs to historic buildings and new construction. An important mortar property is workability. Lime mortars are often described as highly workable, however, due to the many variables contributing to workability, this is difficult to quantify. Workability largely depends on water content, and this will greatly affect compressive and flexural strengths, which in turn will determine the overall quality and durability of a mortar. The objective of this paper is to examine the relationship between workability and strength of naturally hydraulic lime (NHL) mortars in order to optimize their properties for a more efficient use in building. To this aim, mortars of several hydraulic strengths were mixed with different water contents in order to vary flow diameters and characterize workability. Compressive and flexural strength were then tested to measure the effect of the initial flow on the strength of the hardened mortar. This paper demonstrates that NHL 3.5 and 5 mortars require a flow value close to that of 185 mm prescribed by the European standards whereas NHL 2 mixes require a significantly lower value. This paper concludes that one universal flow value is inadequate when trying to optimize strength of NHL mortars and that, in order to optimize strength, mortars should be mixed to attain a different flow diameter for each hydraulic strength. However, other properties such as bond strength and water retention need to be considered before unique flow diameters are prescribed to lime mortars of different hydraulic strengths.      

Analysis of the abstraction of water from freshly mixed jointing mortars in masonry construction

Sharp front theory is used to derive an equation describing the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The equation shows that the time taken to dewater a mortar joint is directly proportional to its thickness and inversely proportional to the transfer sorptivity, itself a function of the sorptivity of the substrate and the desorptivity of the wet mix. Experimental data are presented which validate this equation and the results show that the time to dewater a mortar depends on both the hydraulicity and the initial water content of the mix. For the practically important case of jointing mortars applied in 10 mm layers to a typical facing brick we show that dewatering times range from 20 s to 1 min for Portland cement and NHL 2 mortars, respectively, and that 40–60% of the original mix water is lost in the process.     

Material characterization of ancient Indian copper

A chalcolithic (2350-1800 BC) copper chisel from Balathal has been characterized by X-ray diffraction, microstructural and electrochemical methods. The surface patina was composed of sulfates and oxysulfates in the outer layers while the inner layers were rich in copper oxides. The chisel exhibited smaller grain sizes near two of the surfaces while the structure in the interior was equiaxed. The deformed grains and inclusions near the surfaces and variation in the microhardness of the sample from different faces proved that the copper chisel was processed by cold deformation after initial casting of the square cross-section chisel. The electrochemical behaviour of chalcolithic Cu has been compared with that of a modern Cu sample by potentiodynamic polarization studies. The corrosion rate of chalcolithic Cu in aerated 3.5% NaCl solution was only marginally higher than that of modern Cu. The higher rate of corrosion has been attributed to the presence of second phase sulfide inclusions. The excellent condition of preservation of the 3800-year-old copper object, with no indications of stress corrosion cracking, suggests that pure copper or copper-based materials can be seriously considered as candidate canister materials for long-term underground storage of nuclear wastes in underground repositories.     

Composition,uses, provenance and stability of rocks and ancient mortars in a Theban Tomb in Luxor (Egypt)

The rock-cut tomb–chapel of Djehuty (Luxor, Egypt, 1470 bc) was excavated and restored including a mineralogical, chemical, textural and petrophysical study of mortars and host rocks together with micro-environmental parameter recordings to deduce the techniques used by the ancient Egyptian builders. The host rock is made by alternations of massive, nodular and finely bedded micritic limestone and the tomb was excavated in the stratigraphic section with better mechanical properties. Different types of gypsum and lime mortars were found in the funerary complex: mortar for bedding, exterior render, surface repair and decoration, and interior plaster and coating. Mortars show formulae according to their specific applications and locations. The sources of the raw materials for the mortar reveal a local provenance. Micro-environmental conditions play an important role in the evolution of the mortar pastes, and determine the current characteristics and stability of mortars. Results from this research will make it possible to design mortars compatible with conservation in the funerary complex of Djehuty and to define safe micro-environmental conditions for the preservation of such mortars and paintings.     

Kinetics of Ni-Mo electrodeposition from Ni-rich citrate baths

The kinetics of Ni-Mo alloy electrodeposition on steel substrates from an aqueous citrate-ammonia complex baths has been investigated by means of steady-state polarisation measurements in a system with a rotating disc electrode (RDE). Partial current densities for discharge of Ni(II) and Mo(VI) ions and hydrogen evolution as a function of molybdate concentration in the bath, cathode potentials and the rate of mass transport were determined. It has been shown that - under all investigated conditions - Ni-Mo alloy deposition is more favourable than pure nickel and the cathodic process is strongly influenced by the Mo(VI) content in the solution. The Ni(II) electroreduction rate initially increases, as the cathode potential shifts towards more negative values and the concentration of molybdate grows in the solution. However, for the highest examined MoO₄^2 − content, a considerable decrease in the rate of the process is subsequently observed at certain limit potentials, the values of which depend on molybdate concentration and hydrodynamic conditions. This effect, related to the formation of intermediate molybdenum oxides (characterised by very low overvoltage for hydrogen evolution), becomes less pronounced when the RDE rotation speed is increased. Hydrogen evolution is strongly associated with molybdenum deposition. An increase of the molybdate ions concentration in the bath, as well as an increase in the rate of mass transport, leads to an increase in Mo content in deposits and to the reduction of current efficiency. The Ni-Mo coatings electrodeposited from the designed bath (with the current efficiency of about 70%) containing about 30 wt.% Mo, are characterised by a shiny-grey appearance and good adhesion to the steel substrate. They are characterised by column growth and amorphous microstructure with randomly distributed nanocrystallites of the MoNi₄ intermetallic phase.     

Characterization of zinc phosphate coatings obtained from modified baths

Zinc phosphate coatings obtained from phosphating baths modified with long-chain flotation surfactants, were characterized by scanning electron microscopy. X-ray diffraction and X-ray photoelectron spectroscopy techniques. The results of these characterization studies were correlated to the mechanism proposed to explain the influence of these additives on the nature and quality of the phosphate coatings obtained in their presence, as well as to explainthe behaviour of these coatings in aggressive environments. These studies indicate that the surfactant additives not only control the initial nucleation process but also participate during the subsequent stages of coating deposition, and regulate its growth.     

Zinc recovery and waste sludge minimization from chromium passivation baths

This work reports the feasibility of applying emulsion pertraction technology (EPT) aiming at zinc recovery and waste minimization in the zinc electroplating processes that include Cr (III) passivation. The assessment consists of firstly the lifetime extension of the passivation baths by selective removal of the tramp ions zinc and iron, and secondly, the recovery of zinc for further reuse. Spent passivation baths from a local industry were tested, being the major metallic content: Cr³⁺ 9000 mg L⁻¹, Zn²⁺ 12,000 mg L⁻¹, Fe³⁺ 100 mg L⁻¹. Working in a Liqui-Cel hollow fiber membrane contactor and using the extractant bis(2,4,4-trimethylpentyl) phosphinic acid, reduction of zinc and iron concentrations below 60 mg L⁻¹ and 2 mg L⁻¹, respectively were obtained, while trivalent chromium, the active metal that generates the passivation layer, was retained in the baths. Zinc was selectively transferred to an acidic stripping phase that in the experimental time reached a concentration of 157,000 mg L⁻¹. Zinc recovery by electrowinning from the acidic stripping phase without any pretreatment of the electrolyte solution provided a purity of 98.5%, matching the lower commercial zinc grade. As a result of the extension of the life time of the passivation bath, significant environmental advantages are derived such as minimization of the volume of hazardous wastes and savings in the consumption of raw materials.     

α-tricalcium phosphate synthesis from amorphous calcium phosphate: structural characterization and hydraulic reactivity

In the present study, amorphous tricalcium phosphate (TCP) has been synthetized by a wet route to obtain low temperature α-TCP at 650 °C (LT-αTCP) and compare its structural, physical–chemical and thermal properties with those of α-TCP obtained by the conventional solid-state reaction method at 1400 °C (HT-αTCP). Even if no significant differences were observed concerning the values of lattice parameters measured by Rietveld refinement, LT-αTCP presented lower crystallinity and higher crystal strains than HT-αTCP. The reactivity in water of the α-TCP obtained by the two different routes was assessed. Both raw samples appeared relatively inert in solution and did not favour the nucleation of calcium deficient apatite (CDA); the LT-αTCP and HT-αTCP were converted into apatite only after milling. The mechanical process leads to a decrease in crystallinity and the formation of an amorphous phase, which is supported in this work by Raman spectroscopy. The faster rate of conversion of milled LT-αTCP compared to HT-αTCP can be assigned to its higher specific surface area, lower crystallinity and higher residual crystal strain; these favour the dissolution of the α-TCP phase. Finally, the setting properties of α-TCP-based bone cements were compared regarding their synthesis route. Although the synthesis route does not significantly affect the setting times, the kinetic of conversion into CDA was faster for LT-αTCP than for HT-αTCP. Thus, the modulation of the dissolution rate of α-TCP-based cement determined by the preparation route and the grinding process allows control of the overall setting reaction.

Graphical abstract

     

Analysis of continuous solvent extraction of nickel from spent electroless nickel plating baths by a mixer-settler

It is urgent to develop an effective technique to treat the large amount of spent electroless nickel plating bath and recycle the high concentration nickel. In our previous study, high recycling efficiency of nickel from the model spent bath was obtained by continuous solvent extraction with 2-hydroxy-5-nonylacetophenone oxime (LIX84I) as the extractant and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) as the accelerator using a mixer-settler extractor. It was observed that the extraction efficiency was affected by the operation parameters such as the flow rates of the aqueous and organic phases and the total stage number. In the present study, the effects of the operation parameters on the extraction efficiency were quantitatively studied on the basis of the pseudo-first-order interfacial extraction rate equation together with the hydrodynamic properties in the mixer. The organic phase holdup, measured under varying conditions of the flow rates of both phases, was analyzed by the Takahashi-Takeuchi holdup model in order to estimate the specific interfacial area. The overall extraction rate coefficients defined by the product of the interfacial extraction rate constant and the specific interfacial area were evaluated using the experimental data and ranged from 3.5 x 10(-3) to 6.7 x 10(-3)s(-1), which was close to the value of 3.4 x 10(-3)s(-1) obtained by batch extraction. Finally, an engineering simulation method was established for assessing the extraction efficiency of nickel during a multistage operation.     

Chemical composition of mortars from the Ganga canal system

Investigations of the chemical composition of the lime mortars from the Ganga Canal System do not indicate the presence of any calcium hydroxide in the free state. The samples, however, were found to be heavily carbonated, and several compounds have been indicated.     

The petrography and microstructure of medieval lime mortars from the west of Scotland: Implications for the formulation of repair and replacement mortars

Twelfth and thirteenth Century lime mortars from the west of Scotland were examined using optical polarising microscopy and SEM on impregnated, polished thin sections, and of fracture surfaces by secondary electron SEM. The non-hydraulic calcite binder in these mortars is loclly inhomogenouse, exhibiting variations in texture and density. Spongiform binder with porosity of size 10–20μm has sharp transitions with neighbouring zones of dense binder. Sub-isopachus concentrically accreted calcite pore linings delineate extensive areas of secondary porosity created by dissolution of binder. Common lime inclusions (lime lumps) suggest that hot mixing processes were used. Textural characteristics of lime lumps are similar to reaction rims on partially burnt primary source limestone suggesting that provenance for the lime can be deduced from the petrographic features of incompletely burnt relics. The evidence for the dissolution and reprecipitation of carbonate binder materials suggests the need for a careful reconsideration of practical historic mortar analysis. These historic mortars are texturally and compositionally more complex than their modern equivalents. These textures provide evidence for historic lime burning and mortar mixing practices in Scotland during the middle ages, as well as ageing processes, and allows the possibility of a more sophisticated approach to formulating compatible replacement mortars.

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Résumé Les échantillons de mortiers de chaux, utilisés aux douzième et treizième siècles dans l’ouest de l’écosse, ont été examinés par un microscope optique polarisé et un microscope électronique à balayage (MEB) sur des fines sections polies et des surfaces fracturées par des électrons secondaires d’un MEB. La calcite non-hydraulique dans ces mortiers était hétérogène étant donné la variation de sa texture et de sa densité. La porosité spongieuse, ayant des diamètres de 10–20 μm, présente des transitions d’une zone dense du mélange à une autre zone. Dans la porosité secondaire créée par la dissolution du mélange, la calcite a été déposée sur la surface intérieure. Les inclusions dans la chaux suggèrent qu’un mélange à chaud a été utilisé. Les caractéristiques de la texture de ces inclusions sont similaires à celles d’une calcite issue d’une cuisson primaire partielle. Il semblerait donc que la provenance de la chaux peut être déduite à partir de l’analyse pétrographique des restes de mortier ayant subi une cuisson incomplète. La dissolution et la reprécipitation du carbonate dans le mortier conduisent donc à reconsidérer l’analyse pratique des mortiers historiques, car ils ont une texture et une composition beaucoup plus complexes que leurs équivalents modernes. La texture des mortiers historiques de l’écosse prouve que la cuisson et les pratiques de malaxage ainsi que le processus de vieillessement permettent une approche plus sophistiquée pour formuler les mortiers de remplacement compatibles.

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Editorial Note Dr. John J. Hughes is a RILEM Senior Member. He participates in RILEM TC 167-COM: ‘Charaterisation of old mortars with respect to their repair’.