Gypsum Mortars Research Articles

Raman Microspectroscopic Imaging of Binder Remnants in Historical Mortars Reveals Processing Conditions

Binder remnants in historical mortars represent a record of the connection between the raw materials that enter the kiln, the process parameters, and the end product of the calcination. Raman microspectroscopy combines high structural sensitivity with micrometre to sub-micrometre spatial resolution and compatibility with conventional thin-sectional samples in an almost unique fashion, making it an interesting complementary extension of the existing methodological arsenal for mortar analysis. Raman spectra are vibrational fingerprints of crystalline and amorphous compounds, and contain marker bands that are specific for minerals and their polymorphic forms. Relative intensities of bands that are related to the same crystalline species change according to crystal orientations, and band shifts can be caused by the incorporation of foreign ions into crystal lattices, as well as stoichiometric changes within solid solution series. Finally, variations in crystallinity affect band widths. These effects are demonstrated based on the analysis of three historical mortar samples: micrometric distribution maps of phases and polymorphs, crystal orientations, and compositional variations of solid solution series of unreacted clinker grains in the Portland cement mortars of two 19th century castings, and the crystallinities of thermal anhydrite clusters in a high-fired medieval gypsum mortar as a measure for the applied burning temperature were successfully acquired.

Raman band widths of anhydrite II reveal the burning history of high‐fired medieval gypsum mortars

AbstractWhen used as a mineral binder, gypsum is thermally dehydrated and mixed with water, resulting in a paste hardening in the backreaction to calcium sulphate dihydrate (CaSO4 · 2 H2O). Although nowadays mainly hemihydrate‐based (CaSO4 · ½ H2O) binders are employed, higher firing temperatures in medieval kilns yielded anhydrite II (CaSO4). Except for the discrimination of the metastable phases anhydrite III and I due to different crystal structures, variations within the production temperature range of anhydrite II (approximately 300 to 1180°C) were not analytically accessible until recently. This study describes the development of an analytical technique, which is based on steady changes of band widths in room‐temperature Raman spectra of anhydrite II as a function of burning temperature. Raman microspectroscopic mapping experiments enable to pinpoint individual unreacted grains of thermal anhydrite in mortars and to discriminate them from natural anhydrites originating from the raw gypsum. The determination of band full widths at half maximum of down to 3 cm−1 and differences between them of a few tenths of wavenumbers is not a trivial task. Thus, a focus of this work is on peak fitting and strategies for correction of instrument‐dependent band broadening, which is often neglected also beyond the field of mortar analysis. Including other potential influences on band widths, burning temperatures of 400 to 900°C can be retraced in high‐fired medieval gypsum mortars with an uncertainty of approximately ± 50 K, as demonstrated with sample material of a stucco sculpture dated around 1400.

Multi-Analysis Characterisation of a Vernacular House in Doha (Qatar): Petrography and Petrophysics of its Construction Materials

This study characterises the original construction materials (building stones and mortars) of a collapsed two-storey colonnaded structure in the Ismail Mandani house, located in the old city centre of Doha (Qatar). Results were drawn based on interpretation and integration of historical, in situ observations and analytical data. The mortars and stones were characterised following a multidisciplinary approach, combining macroscopic observation with petrographic microscopy, mineralogical analysis (X-ray diffraction) and elemental analysis (handheld X-ray fluorescence) of samples. Moreover, hydric properties, ultrasonic pulse velocity and colour of representative samples of the house were studied. The results revealed the use of two types of stones and three different types of gypsum mortars. The original construction materials came from nearby coastal stones. Gypsum of the most used mortar had a calcination temperature between 120 and 160 °C and its colour was produced by lumps with higher Fe content. The materials’ effective porosity and water absorption were high, and their ultrasonic pulse velocity was low. These petrophysical results indicated they had low quality for construction purposes. The composition and colour of the original construction materials were quantified, which will allow the reproduction of their aesthetic characteristics and improvement of their quality in future reconstruction works.

The effect of doum palm fibers on the mechanical and thermal properties of gypsum mortar

The main objective of this paper is the evaluation of the possibility of using a gypsum mortar reinforced with doum palm fibers as thermal insulators in building material. Several composite configurations with three sizes and five-weight ratios (from 0.5% to 2.5%) of doum palm fiber were prepared for mechanical and thermo-physical characterization. Generally, natural fibers are affected by the alkali environment of gypsum mortar. To overcome this problem, doum palm fibers were treated with a NaOH solution of 1% concentration to enhance their resistance against chemical degradation. Chemical treatment of fiber removes some hemicellulose and lignin and tends to make the fiber more homogenous, which enhances fiber–matrix interfacial properties. In addition, the mechanical properties of the specimens were tested after 7 days, 28 days and 1 year of curing in normal conditions. The obtained results show an improvement in the mechanical performance of composites reinforced with treated fibers. In fact, better results were obtained for gypsum mortar reinforced with treated reinforcement seive2 for the value of 1% of fibers. It was also noticed that NaOH treatment has an influence on the thermal conductivities. In fact, the use of treated doum palm fibers as reinforcement in gypsum mortar seems to be an alternative natural material to be used as a thermal insulator material.

RESISTANCE OF MORTARS WITH GYPSUM, LIME AND COMPOSITE BINDERS AGAINST MOLDS

Resistance of three mortars (the lime mortar, the gypsum mortar and the mortar with the composite binder) against molds was evaluated. Mortars were also compared according to their pH, bulk density, strength and porosity. Experiments showed that the lime mortar has the best resistance against molds and the lowest bending and compressive strength. The mortar with the composite binder has better mold resistance and higher bending and compressive strength than the gypsum mortar.

Phase composition and burning history of high-fired medieval gypsum mortars studied by Raman microspectroscopy

The use of high-fired gypsum as binder for masonry and joint mortars or stuccowork in Central Europe in the Early and High Middle Ages was a regional specific as it depended on local gypsum deposits. The calcination technology possible at the time resulted in an assemblage of calcium sulphate phases dehydrated to different degrees and partly thermally damaged accessory minerals of the raw gypsum. Not hydrated clusters of firing products preserved in the binder matrix are a typical feature of such mortars. A novel Raman microspectroscopic approach, providing access to the burning history of individual anhydrite grains, was applied to samples from medieval South Tyrolean stucco decorations and sculptures. Beyond that, Raman microspectroscopy was employed for tracing and visualising pyrometamorphic reactions in natural impurities of the kiln run. In the discussed examples mineral thermometry indicates process temperatures above 800°C: the breakdown of magnesium-rich chlorite led to the formation of forsterite Mg2SiO4, while the thermal decomposition of dolomite CaMg(CO3)2 to periclase MgO and lime CaO yielded – after hydration and carbonation – magnesite MgCO3, CaCO3 polymorphs and magnesian calcite. Hydration of periclase in the mixed gypsum paste containing sulphate ions also resulted in magnesium sulphate hydrates, here identified in the form of hexahydrite MgSO4·6H2O. Lower burning temperatures left the accessory minerals in their pristine form, but can be traced by measuring the spectra of individual anhydrite crystals in grains of firing products and evaluating Raman band widths. Throughout the present study, calcination temperatures ranging from approx. 600°C to 900°C were determined.

Elementary characterization of samples of Portland cement, natural gypsum and phosphogypsum mortars from Brazil

Portland cement, the basic ingredient of concrete and is manufactured by crushing, milling and proportioning limestone, sand, clay, iron ore and secondary materials such as shells, chalk or marl combined with shale slate or blast furnace slag, fly ash, gypsum, phosphogypsum, and some others. Evaluating the physical and mineralogical characteristics of the cement and its chemical composition is essential to establish the quality of the product. Therefore, the objective of this work was to characterize and quantify the most common chemical elements in the samples of Brazilian Portland cement, natural gypsum, and phosphogypsum mortars by means of X-ray dispersive energy spectroscopy (EDXRF), as well as to evaluate the strength of these mortars. For analysis of the compressive strength, initially prepared samples were submitted to a destructive mechanical test. Subsequently samples were milled and compacted to form thin tablets, which were submitted to the EDXRF analysis. The qualitative and quantitative analyzes showed that for phosphogypsum mortar the largest mass fractions were found of 49.8±2.5% (Si), 24.66±0.96% (S) and 22.10±0.42% (Ca). For gypsum mortar those values were found of 43.41±0.45% (Ca), 33.8 ± 0.8% (S) and 18.9±1.2% (Si), respectively; and for Portland cement mortar, the predominant elements in those samples have the mass fractions of 64.20±0.52% (Ca) and 27.3±1.5% (Si). The results showed that obtained values of mass fraction of the elements Si, S, K, Ca, Ti, Fe are in rather good agreement with quantities indicated for manufacture. Besides, gypsum and phosphogypsum presented almost the same composition and compressive strength.

Gypsum in Ticinese stucco artworks of the 16–17th century: Use, characterization, provenance and induced decay phenomena

This paper focuses on the use of gypsum as a binder in stucco artworks made between the 16th and 17th centuries in canton Ticino (Switzerland). As far as the artistic technique is concerned, a stucco statue is made of composite materials: metal, brick or wood for the supporting structure, lime and/or gypsum mortar with aggregate for the ground and finishing layers. The gypsum addition to the lime binder, found mainly in the ground layer, helps accelerate the setting of the three-dimensional stucco elements and prevents cracks from shrinkage, but a real understanding of the technology of its preparation, as well as the proportion of the mix for the stucco production, has yet to be established. The samples of stucco (167) taken from artworks in the region were analysed in stratigraphy, identifying their chemical and mineralogical composition. The results from these investigations were compared with the information provided by the historical sources and archival documents recording the artistic technique. Results showed that the quantity of gypsum varies greatly depending on the requirements of the stucco masters and that it was a fundamental addition to attain the effects desired by the different artists.

Stucco and clay in the decoration of the monumental buildings of Old Nisa

Unlike the terracotta decoration and the clay sculpture, the stucco production in Old Nisa has been only marginally studied. This is mainly due to the scarcity of figured materials available. Anyhow, recent excavations1 have unearthed some fragments of sculptures in stucco and clay, along with double-moulds in gypsum mortar that shed new light on techniques for the manufacturing of sculptures. The manufacturing process of a sculpture is similar for both materials, since the modelling of the figure occurs through the gradual application of layers of clay or stucco (or both) more and more fine and purified. Moreover, for the two materials, is attested both the simple hand modelling and the use of moulds.

Permeability Characteristic and Failure Behavior of Filled Cracked Rock in the Triaxial Seepage Experiment

Filling is commonly found in natural cracked rock mass. As the weakest part of the rock, the filling properties directly affect the rock deformation and strength, permeability, and so on and affect the safety and stability of the rock mass engineering. In this study, a single slit has been preset in sandstones and filled with different physical properties materials. Based on the laboratory triaxial seepage test, the permeability and strength characteristics of filled cracked sandstones are analyzed, and the failure modes are obtained. The main findings of this study are as follows: (1) The permeability coefficient peak value of the filled cracked rock appears before the stress peak. (2) At the same confining pressure growth rate, the peak stress growth rate of the filled cracked rock is generally higher than that of the intact rock and the strength growth rate of the cracked rock increases with the length of the fracture. The strength characteristics of the filling in the uniaxial compression tests and triaxial seepage tests are significantly affected by the hydraulic properties. (3) The strength and permeability coefficients of cracked rock filled with cement mortar are more sensitive to the change of confining pressure, while under the same condition, the ones of cracked rock filled with gypsum mortar are stable. (4) According to the failure mechanism, under the seepage stress, the secondary cracks can be divided into 3 types and the failure modes can be divided into 2 types.

Non-Destructive Assessment of Masonry Pillars using Ultrasonic Tomography.

In this paper, a condition assessment of masonry pillars is presented. Non-destructive tests were performed on an intact pillar as well as three pillars with internal inclusions in the form of a hole, a steel bar grouted by gypsum mortar, and a steel bar grouted by cement mortar. The inspection utilized ultrasonic stress waves and the reconstruction of the velocity distribution was performed by means of computed tomography. The results showed the possibilities of tomographic imaging in characterizing the internal structure of pillars. Particular attention was paid to the assessment of the adhesive connection between a steel reinforcing bar, embedded inside pillars, and the surrounding pillar body.

NEURAL CONTROLLER FOR THE SELECTION OF RECYCLED COMPONENTS IN POLYMER-GYPSY MORTARS

This study presents research on the development of an intelligent controller that allows optimal selection of rubber granules, as an admixture recycling component for polymer-gypsy mortars. Based on the results of actual measurements, neural networks capable of predicting the setting time of gypsum mortar, as well as determining the bending and compressive strength coefficients were trained. A number of simulation experiments were carried out, thanks to which the characteristics of setting times and strength of mortars containing different compositions of recycling additives were determined. Thanks to the obtained results, it was possible to select the rubber admixtures optimally both in terms of the percentage share as well as in relation to the diameter of the granules.

The influence of different aggregates on the behavior and properties of gypsum mortars

The structure, behavior and properties of gypsum mortars with different types of fine aggregates were studied. Investigation by scanning electron microscopy shows that the presence of aggregate particles significantly influences the shape and size of gypsum crystals in the interfacial transition zone. The porosity of the gypsum matrix in mortars is greater than the porosity of pure gypsum paste and the pore size distribution shifts towards smaller pores. The shape and size of crystals in the transition zone depends on the surface roughness of the aggregate particles. The grain surface roughness was measured by confocal laser scanning microscopy. The properties of mortars also depend on the grain surface roughness. The workability, setting times and thermal conductivity decrease with increasing grain surface roughness, while the strength and water vapor resistance increase.

Influence of fine aggregate on some properties of gypsum mortars

The importance of gypsum as a building material increases nowadays because of its environmental friendliness, excellent fire properties and good workability. Since the gypsum is mostly used in the form of the paste, the influence of aggregates on properties of gypsum mortars is not investigated very often. The article deals with some basic and mechanical properties of gypsum mortars with different aggregates and compares them with the properties of gypsum paste. Type of the aggregates influences the properties of gypsum mortars significantly. The presence of aggregate does not worsen the adhesive strength of the gypsum material in comparison with gypsum paste and the adhesive strength was even improved for some type of aggregates.

Evaluation of Fine Aggregate Surface and Fracture Surface by Confocal Microscope

The gypsum mortars with different types of aggregate were studied. The surface roughness of fine aggregates and the fracture surface roughness were evaluated by a confocal laser scanning microscopy. Four gypsum mortars and one gypsum paste were tested. The results from the confocal laser scanning microscopy (CLSM) are compared with the pictures of grain surface taken by a scanning electron microscopy (SEM) and both methods seem to be appropriate for surface evaluation. The influence of the surface aggregate roughness on some gypsum mortar properties is demonstrated.

Measuring the Burning Temperatures of Anhydrite Micrograins in a High-Fired Medieval Gypsum Mortar

Typical feature of high-fired medieval gypsum mortars is a compact microstructure of squat gypsum crystals containing firing products as remains of the calcination process. So far, the burning history of the binder is estimated based on morphological characteristics of the latter. A novel Raman microspectroscopy approach provides access to the calcination temperatures of individual anhydrite grains based on quantifiable spectroscopic changes appearing due to gradual variations of crystallinity, as independently confirmed by X-ray diffraction analysis of anhydrites synthesised at temperatures between 500°C and 900°C. The approach was successfully applied to the high-fired gypsum mortar of a South Tyrolean stucco sculpture of a pieta dated around 1420. Microparticles of burned anhydrite II with firing temperatures scattered around 650°C and clusters of thermally damaged natural anhydrite II crystals from the raw material were identified and imaged.

Computer simulations of heat transfer in a building integrated heat storage unit made of PCM composite

The paper presents the results of parametric study of thermal performance characteristics of thermal energy storage unit integrated in building structure being also a part of building’s ventilation system. A storage unit is in the form of a ceiling panel with internal channels through which air taken from the environment flows before it is delivered into the rooms. Thermal storage potential of the panel is thanks to phase change material (PCM) which is mixed with gypsum mortar, creating in this way a composite of high thermal capacity in the temperature range corresponding to the temperature required for thermal comfort. In order to perform the analysis of the storage unit a computer program was developed which was based on the mathematical model of complex heat transfer occurring inside the panel, inside a composite material, as well as on the boundary between the panel and air flowing through internal channels. A procedure describing variations of convective heat transfer intensity along the channel can be regarded as a unique achievement in this research. This function was validated based on measurements conducted on the experimental set-up specially prepared for this study. Using the program many computer simulations were performed. Based on the results of this analysis a detailed information on the performance of the panel for different operational parameters, e.g. air mass flow rates, were obtained. Contrary to the study reported in an earlier publication, these simulations were conducted for real environmental conditions, i.e. real ambient temperatures during summer in Central Poland. Also, important conclusions regarding selection of PCM, mainly its melting temperature range, were formulated.

Investigation of structure formation processes at the hydration of modified gypsum binders and mortars

The results of investigations of structure formation processes of a mortar while hardening have been presented in the article. The results obtained indicate that during the period of structure formation and the heat release of solidifying composite gypsum binders and solutions, the heat release in hardening of composite gypsum binders (CGB) and modified gypsum mortars (MGM) proceeds at different rates, and is characterized, in some cases, by the rapid release of hydration heat. As studies have shown, modified gypsum binders and mortars, in order to avoid the appearance of structure defects, should contain setting-time additives, promoting to a decrease in the intensity of heat release and, as consequence, reducing risks of destructive processes. With a large amount of a setting-time retarder, hydration process may be disturbed, and that can be accompanied by following abnormalities (abundant bleeding, slow gain in strength, etc.). Significant heat release during hardening allows using the developed mortars even at negative temperatures, as also evidenced by the results of other researchers.

Gypsum Mortars with Different Types of Aggregates: Design and Properties

The influence of different types of fine aggregates on behavior and properties of gypsum mortars was investigated. The design procedure and results of some basic physical tests are described. The composition of mixtures was designed in order to minimalize all other impacts than type of aggregate. Four types of fine aggregates of different origin, with different shape and surface of particles were used. The presence of fine aggregate in gypsum increases the bulk density and reduces setting time. Crushed stone with angular rough particles worsen workability and reduce setting time more significantly than aggregates with round and smooth particles.

Experimental and Numerical Study on Seismic Behavior of An Infilled Masonry Wall Compared to An Arched Masonry Wall

Sassanid era arches are among the oldest arches in Persian architecture. In this study, an infilled masonry wall and a similar Sassanid era arched masonry wall, both with clay bricks (square bricks of 195mm long) and clay and gypsum mortar, are compared and their seismic behaviors are tested under cyclic loading (as per protocol). The dimensions of both the walls are of L 1720mm, W 1500mm and H 195mm. The diameter of the vault is 900mm. For loading, first, pre-pressure of 58kN is applied on the specimens; then, upon this constant pre-pressure, the lateral cyclic loading is applied on the specimens. The results indicate that the arched wall can well withstand seismic forces. The maximum lateral force of 26.4kN resulted in a 18.12mm lateral displacement tolerated by the arched wall, while the infilled wall tolerated a maximum force of 56.53kN at displacement of 9.12mm. In the hysteresis curve of the arched specimen the pinching effect is observed, while in the hysteresis curve of the infilled specimen this effect is not visible. The infilled specimen in relation to the arched specimen has more energy dissipation. In specimen with arched opening, three plastic hinges occur. The first plastic hinge occurs at the arch crown and two hinges appear on the bottom of the side piers. The fracture mechanism in the arched wall is of crushing at the pressure toes of the wall and the same in the infilled wall is of crushing at the same points in addition to emergence of diagonal cracks in the wall and their expansion under increased load range. In order to validate the experimental results, the walls are modeled in ABAQUS software and concrete is used as masonry material in simulation. Concrete damaged plasticity model and macro modeling approach are adopted in this simulation. The hysteresis curves found for numerical modeling in both specimens are in good agreement with laboratory findings.