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.     

Gypsum plasters II. Constitution and properties of the prepared β-hemihydrates

The constitution of the two types of plasters, previously prepared, was followed using thin-section microscopy and X-ray diffractometry. Moreover, their hydraulic properties were determined to assess their suitability for use in various applications. Results showed that the plasters consist mainly of the β-hemihydrate phase. The X-rays and thin section microscopy in addition to the differential thermal analysis have omitted the presence of gypsum in the investigated plasters. The plaster prepared by rehydration of γ-anhydrite shows better crystallinity than that prepared by direct calcination of gypsum at 90 °C. Both types require small amounts of water giving higher ultimate strength. The rehydrated γ-anhydrite shows normal setting in accordance with the international specifications requirements. The other type exhibits a quick setting property which was related to the presence of minute amounts of gypsum, in the plaster, below the limits of identification of both the X-rays and differential thermal analysis. The prepared plasters could be used for various purposes needing higher strength, lower normal consistency and quick or moderate setting properties.     

SHOP NOTES—PLASTER SHOP

This paper deals with the small problems which arise in the plaster shop, and are a source of annoyance and cost if handled incorrectly. The grade of plasters used, manner of handling, method of payment, extent of reinforcement of molds, care of benches, correct procedure in making the various parts and types of molds, are all touched on.     

GYPSUM PLASTER IN THE CERAMIC INDUSTRIES1

This paper deals with manufacture, properties, and uses of gypsum plaster in the various branches of the pottery industry, i.e., in white ware, stoneware, electric insulators, sanitary ware, etc., in the terra cotta industries, in plate glass, and for sundry minor ceramic uses. The methods of producing calcined gypsum are briefly described and then follows a discussion of the physical and chemical properties of the three principal forms of calcium sulphate as used commercially, (1) crude gypsum, (2) calcined gypsum (gypsum plaster), and (3) gypsum casts of set-up gypsum plaster. The proper methods of mixing, blending, and casting plaster are described, with graphs showing effects of varying such factors as consistency, mixing time, etc. Methods of testing plasters are briefly discussed. Considerable attention is given to difficulties commonly encountered in the use of plaster, with causes and methods of coffeetion. This includes the use and abuse of plaster molds, such as “rotting” of molds, “burning” of molds, efflorescence, etc. The properties of gypsum plaster can be varied within wide limits to meet special requirements. It is shown how the plasters used for pottery and terra cotta molds are quite different from those used in bedding plate glass. The purpose of the paper is to give a more complete picture of how gypsum plaster may and should be used in theceramic industries.     

Grundierungen für organische Dispersionsanstriche auf siliciumorganischer Grundlage und Emulsionsanstriche für Fassaden mit Siliconharzen als Bindemittel

Primers for Organic Dispersion Paints based on Organo-Silicons and Emulsion Paints with Silicon Resin Binders for Buildings It is possible to prepare water resistent, porous cement paints with silicon resin dispersions. Emulsion paints based on silicon resins are completely porous and they can be applied on absolutely fresh plasters even under the most difficult weather conditions. The water content of plaster and the building material was followed by continuous measurements. Alkalisiliconates and certain silicon resin solutions are porous primers for organic binder paints.     

The effects of sterilisation on the properties of calcium sulphate hemihydrate

Plaster of Paris has been recommended as a suitable bone substitute material. In this project both calcined and autoclaved plasters have been prepared and the effects of sterilisation on their properties determined. Samples of plaster suitable for use in animal experimentation have been prepared.     

Performance of clay masonry prisms with light weight plaster exposed to standard fire exposure

Clay bricks are one of the most widely used materials in building construction due to their advantages, including local availability, ease of fabrication and cost-effectiveness. Fire is one of the dangerous hazards that can cause damage the life and property. Lightweight plasters play a vital role in insulating the masonry construction during fire accident. There is only limited data and information available on the fire performance of Clay Brick Masonry (CBM) insulated with lightweight plaster. An extensive investigation was undertaken to evaluate the residual strength properties and physical characteristics of CBM prisms exposed to elevated temperatures. CBM prisms plastered with M-sand mortar, vermiculite mortar, and perlite mortar were used for the investigation. Protected prisms were exposed to elevated temperatures following the ISO 834 standard fire curve for durations of 30 min (821°C), 60 min (925°C), 90 min (986°C), and 120 min (1029°C). Mechanical properties such as axial load carrying capacity, stress–strain behaviour, elastic modulus, and crack pattern were examined. The mechanical properties of CBM prisms were found to be highly influenced by the type of plastering, intensity, and the duration of heating. The microstructure and image analysis confirmed the effects of temperature exposure on protective plasters. Equations are proposed to determine the residual axial compressive strength and the elastic modulus of CBM. It was found that the specimens plastered with perlite mortar had better fire resistance.     

Black plaster composite fiber prepared by upward electrospinning

Black plaster is a traditional Herbal medicine with a long history; it is usually used in paste form. In this study, a black plaster/poly(ethylene glycol) (PEG) composite fiber was prepared by a novel upward melt electrospinning method. Scanning electron microscopy results show that the black plaster composite fiber has good morphology and uniform diameter. Thermogravimetric analysis results indicate that the heating temperature in the electrospinning process does not damage the composition of the black plaster, and drug components are effectively retained in the black plaster. Drug dissolution results show that the dissolution of poorly water-soluble Draconis Sanguis in both pure black plaster fibers and composite fibers are significantly higher than that in traditional bulk black plasters. When the PEG content in the composite fiber is 85 wt %, the drug dissolution amount of Draconis Sanguis in the black plaster composite fiber is the highest. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47662.     

凹凸棒土与纳米二氧化硅对高强石膏浆体3D可打印性的影响

本文研究了凹凸棒土(ATP)和纳米二氧化硅(NS)对3D打印用α半水石膏浆体泵送性、流变性、支撑性等可打印性及固化体力学强度的影响。结果表明,掺入ATP后,泵送力维持在(0.57±0.02) kN,浆体剪切应力与剪切应变曲线不随掺量增加而发生明显变化,0 h、4 h打印体坍塌角分别从空白组的24°、32°降至掺量为2.8%(质量分数,下同)时的8°、11°。与ATP相比,打印浆体掺加NS后泵送力明显增加,掺加2.8%NS浆体的泵送力是同掺量ATP浆体的近2倍,浆体剪切初始应力随NS掺量增加而增大。虽然掺加NS使浆体泵送阻力增大,NS较ATP对打印体的支撑性却明显提升,掺加2.8%NS打印体0 h、4 h均无明显坍塌。ATP和NS在1%~2%掺量时浆体均可打印,且固化打印体抗压强度均有所增加,但层间粘结强度均削弱约2/3。     

聚羧酸大分子的合成及其对石膏强度的影响

以丙烯酸、丙烯酸甲酯、甲基丙烯磺酸钠及烯丙基聚氧乙烯醚为原料,过硫酸铵为引发剂,进行水相自由基共聚反应合成醚型聚羧酸大分子。合成产物对石膏具有明显的缓凝作用。加入质量分数0.2%(以石膏质量计)的合成产物改性的石膏块,养护时间为24 h时,其抗折及抗压强度比纯石膏分别提高31.1%和32.6%,吸水率比纯石膏降低了9.1%。     

Creep behaviour of steel bonded joints under hygrothermal conditions

The aim of this research is to study the influence of moisture absorption at low moisture contents on the creep behaviour of an epoxy adhesive in steel bonded joints. Single lap joints were manufactured using high strength steel adherends and a two-component epoxy adhesive. The single lap joints were tested at load levels corresponding to average lap shear stresses of ± 5%, 15%, 30% and 45% of the dry lap shear strength in both 40 °C air and 40 °C distilled water. Specimens were not pre-aged to be able to analyse the coupled effect of moisture and loading. The test results show that an increase in the load level resulted in an increase in the instantaneous strain and in the creep strain rate. The creep strain of single lap joints loaded in water was generally larger than for the ones loaded in air. For joints loaded in water the creep behaviour was found to be dependent on the moisture concentration in the adhesive. At low moisture percentages creep was suppressed, resulting in a lower instantaneous strain. At higher moisture percentages creep was promoted, resulting in a larger strain rate. The suppression of creep at low moisture percentages is attributed to water molecules bonding to the epoxy macromolecules, resulting in a reduction in molecular mobility and a smaller creep strain. At higher moisture percentages the plasticizing effect of the water dominates, resulting in a larger creep strain. The Maxwell three-element solid model and Kelvin-Voigt three-element solid model were used to simulate the creep behaviour of the single lap joints loaded in air and water. The models gave good representations of the creep response across the different load levels in both water and air, they were however unable to give a correct representation of the instantaneous strain of the single lap joints loaded in water. This is attributed to the models being unable to account for the present short-term relaxation process that is dependent on the moisture concentration.     

Reactivity of lime and related oxides. XVIII. Production of plasters

Conditions for production of plasters are surveyed in relation to variations in phase composition, surface area and crystallite size. The commercially known α- and β-hemihydrate plasters prepared by autoclaving and dry calcination are not two distinct phases—they differ in crystal habit, surface area, crystallite size and lattice perfection. The terminal β-hemihydrate and γ-CaSO₄ produced in vacuo have greater surface areas than samples produced in air. The most active γ-CaSO₄ (Class C plaster) samples are finely porous and rapidly rehydrate in atmospheric water vapour with considerable loss of surface area and porosity. ‘Wet’ rehydration (liquid water) or γ-CaSO₄ causes more rapid development of the 6.01 Å (10.10) spacing, in accord with the c-direction elongation of the ‘α’-hemihydrate crystals prepared by autoclaving or precipitation from 50% HNO₃. The porosity of the γ-CaSO₄ diminishes considerably between 200° and 300°, but remains to a smaller extent up to 500° when the γ-CaSO₄ has changed to β-CaSO₄, anhydrite (Class D plaster). Anhydrite sintered extensively between 500° and 900° before decomposing to lime at temperatures up to 1400° (Estrich Gips plaster). Removal of the SO₂ and O₂ is facilitated by streams of nitrogen or carbon dioxide, which increases the decomposition rate. Calcination at temperatures below 1200° gives anhydrite and lime crystals of more comparable sizes, and avoids complete ‘dead-burning’ of the lime.     

Excessive tool wear and moisture content in ceramic plaster machining

Abstract

In the ceramics industry the creation of moulds for new product design, through the use of rapid machining has become an alternative to traditional techniques. During an investigation into the potential of mould creation through this technique it was noted that the rate of tool wear while machining the plaster material was greater when a ceramic plaster, Molda 3, was completely dry, than when moisture was present. The present paper reports on the causes of excessive tool wear which occurs in the machining of plaster and how the moisture content of the plaster can have a considerable effect on the rate of wear. A series of experiments has been conducted to determine the optimum level of moisture retained in the plaster to achieve the best machining results. In addition, the method of machining was also investigated, to determine if this had any relationship with tool wear.     

Experimental study on the burning behaviour of Pinus halepensis needles using small‐scale fire calorimetry of live,aged and dead samples

Limited research has been conducted on the burning characteristics of live fuels, which are commonly assumed to behave like moist dead fuels. We use small‐scale laboratory calorimetric experiments to investigate the differences in fire dynamics between live and dead Pinus halepensis needles. The study includes laboratory‐aged samples and different moisture conditions (fresh or oven dry). A series of ten fire behaviour parameters are extracted from the measurements to identify and quantify differences. The main parameters are the following: time to ignition; flaming time; mass loss pre‐ignition, during flaming, and during smouldering; peak power; effective heat of combustion; mean and peak CO/CO₂; and radiative fraction. Using these parameters, we show that the most flammable samples are fresh dead and aged needles, followed by dry dead and dry live needles. The least flammable is fresh live needles. Live needles ignite about four times slower, and burn with ~60% lower power and ~50% lower heat of combustion than dead needles. Aged needles resemble most closely the behaviour of dead needles, but many fire behaviour parameters were significantly different. The results confirm the importance of moisture content in the burning behaviour of pine needles, but the differences between live and dead samples cannot be explained solely in terms of moisture but require consideration of plant chemistry and sample drying. © 2015 The Authors. Fire and Materials published by John Wiley & Sons Ltd.     

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.     

Small-scale assessment method for the fire resistance of historic plaster system and timber structures

The primary protection against the charring of timber is ensured by protection materials. Today, there are only a limited number of materials given in design codes as fire protection materials for timber. Historic surface finish materials such as plasters have rarely been studied with respect to fire; no design values exist in the current fire part of Eurocode 5. Full-scale fire testing is costly to assess the fire performance of material combinations, thus this study presents a useful tool that is specifically tailored to evaluate the fire protection ability of materials in small-scale. A review of conducted tests demonstrate that the cone heater of a cone calorimeter is a dependable device to estimate the charring performance of protected timber specimens as the test results approximate the ones obtained from furnace tests. This work contributes to the assessment of fire resistance performance of various combinations and types of plaster systems found in existing timber buildings that often require an individual approach for an adequate fire risk analysis and design decisions to meet current fire safety regulations with respect to the load-bearing capacity and compartmentation of building structures. Increased knowledge on the fire protection performance of traditional plasters is believed to facilitate their wider use in timber buildings, primarily to preserve their significance as part of the cultural built heritage.     

Some observations on the setting of calcium sulphate hemihydrate plaster in the presence of phosphoric acid and hydrated lime

The effects of additions of phosphoric acid and hydrated lime on the setting of calcium sulphate hemihydrate plasters have been examined. At two levels of P₂O₅ concentration (0.75 and 1.5 wt-% P₂O₅) it has been found that extreme retardation of the plaster setting process occurs with lime additions in the range, Ca(OH)₂/P₂O₅ (weight ratio) 0.5 to 1.5. The chemical nature of this effect has not been identified. Formation of either CaHPO₄. 2H₂O or hydroxyapatite in the paste is considered as deleterious to plaster hydration.     

Interaction between α-calcium sulfate hemihydrate and superplasticizer from the point of adsorption characteristics, hydration and hardening process

Superplasticizers (SPs), namely sulfonated melamine formaldehyde (SMF) and polycarboxylate (PC), were independently admixed with α-calcium sulfate hemihydrate based plaster to improve the material's performance. SMF and PC gave, respectively, 38% and 25% increases in the 2 h bending strength at the optimum dosages of 0.5 wt.% and 0.3 wt.%, which are determined essentially by the maximum water-reducing efficiency. The peak shift of binding energy of Ca2p_3/2 detected by X-ray photoelectron spectroscopy (XPS) suggests that SPs are chemically adsorbed on gypsum surface. A careful examination of the strength development of set plaster allowed the hydration and hardening process to be divided roughly into five stages. SMF accelerates early hydration, while PC decelerates it. Both SPs allowed similar maximum water reductions, giving a more compact structure and a decrease in total pore volume and average pore diameter, and thus leading to higher strengths in the hardened plasters with SPs.     

Observations of moisture mass transfer rates in proteinate powders

Water vapour sorption and desorption are crucially important in the preservation of foods, in the manipulation of their textures and more widely in drying. Isotherms and rates of water vapour exchange in a series of protein substrates were measured under isothermal conditions. These substrates consistently displayed type II isotherms and revealed unusual vapour exchange rates for both sorption and desorption. This novel behaviour was observed consistently in dairy and soy proteins and in native proteins and thermally denatured proteins. The addition of a carbohydrate, such as sucrose, to the matrix resulted in type III isotherms and regular exchange rate behaviour. For the proteinates, moisture exchange rate coefficients and apparent diffusivities reached a maximum at a moisture concentration that was associated with the inflection point on the isotherm. This behaviour suggested multiple collisions of the water molecules with the partially hydrated surface in which the stickiness of the water molecules to the surface reached a minimum at the inflection point on the isotherm.     

复合外加剂改性盐石膏的研究

盐石膏的主要成分为无水硫酸钙,其活性差、凝结硬化慢、强度低,需要添加活性剂来激发盐石膏的活性。通过复合外加剂对盐石膏加以改性,并通过XRD和SEM对其作用机理做了分析。结果表明,单掺脱硫石膏和建筑石膏均能缩短盐石膏的凝结时间,建筑石膏的效果较好,但掺量不宜过高。复掺建筑石膏和缓凝剂时,两者比例要控制得当,适宜的建筑石膏和缓凝剂掺量分别为50%和0.10%~0.12%（质量分数）。分析可知,大掺量建筑石膏会增加盐石膏硬化体中二水相和针棒状晶体的含量;缓凝剂掺量的增加,会降低盐石膏硬化体中二水相的含量,棱形晶体增多,从而降低了盐石膏的强度。