Presence Of Gypsum Research Articles

Use of the neutron method in assessing the changes in soil strength of undisturbed and ameliorated transitional red-brown earths during soil drying cycles

The relationships between penetrometer resistance (qp) and volumetric moisture content (�v) measured using the neutron method in an undisturbed transitional red-brown earth and after an~elioration by application of surface gypsum and slotted gypsum were examined. A very highly significant (P < 0.001) negative correlation was obtained between qp and �v in all treatments. The low r2 values of the regressions were attributed to heterogeneity in strength characteristics of the soil matrix, due to presence of cracks and macropores and the associated wetting patterns. The qp at any given e, was significantly reduced in the slots with lower bulk density compared to the undisturbed soil. The differences in qp- �v relationship of the undisturbed part of the soil under different ameliorative practices were attributed to changes in the swelling characteristic, and hence in the bulk density at any given �v of the undisturbed soil, caused by the presence of gypsum and the slots. Regression equations between qp and neutron count rate (n) for the undisturbed soil and for the slots were developed by combining the qp on �v relationships with the neutron meter calibration for �v measurements. The use of these regression equations and measured n values to predict changes in soil strength profiles during a wheat crop drying cycle in an undisturbed and ameliorated transitional red-brown earth was evaluated on another experimental site. There were no significant differences between the predicted and measured qp values in the non-ameliorated soil and the gypsum-slotted soil. Significant differences were observed between the predicted and measured qp values in the surface gypsum applied soil. The study shows the potential for using the neutron method as a convenient in-situ field technique to predict qp profile changes, preferably using qp on n relationships developed at the experimental site.

Kinetics of hydration of tricalcium aluminate in the presence of gypsum

Based on a conceptual model for the stages of hydration of tricalcium aluminate in the presence of gypsum, a mathematical model was developed for the kinetics of hydration. The model was solved, illustrated and compared to experimental heat release data. Analytical equations were presented for the first two stages, while the last stages of hydration reduced to a previously developed model for the hydration of tricalcium aluminate in the absence of gypsum. Results suggested that pore diffusion through a thickening ettringite barrier layer controlled the first stage of hydration, while pore diffusion through a thinning ettringite barrier layer controlled the second stage. After the ettringite layer disappeared, the reaction of the remaining tricalcium aluminate proceeded more rapidly, but by a similar mechanism, than in the absence of sulfate containing species.

Surface and bulk properties of Ancient Egyptian Mortars. Part III: X-ray diffraction studies (b)

A series of Ancient Egyptian Mortars were extracted from the Khafra Valley Temple, and from the Sphinx face. X-ray diffraction studies revealed, at room temperature in most of the sample, the presence of gypsum, calcite and silica in variable proportions. None of the calcium silicates reported to be found in the case of the Sphinx body core and North side chest were observed in the present study. Heat-treatment of the mortar samples for various periods of time at t 110°C indicated the prevalence of the gypsum phase up to a duration of heating of one hour. In some of the mortars the γ-CaSO 4 modification was observed to exist up to a temperature of 350°C.

Thermal monitoring of flash setting in portland cement clinkers

Flash setting behavior of a Type I Portland cement clinker with and without the presence of gypsum (calcium sulphate dihydrate) used as a set regulator has been studied by using thermogravimetry and differential thermal analyzing techniques. The effect of sulphate addition in controlling the flash set is monitored over the critical initial period of hydration and its consequences on the ultimate setting properties of clinker are discussed. A correlation between degree of hydration and flash setting, caused mainly by a rapid reaction between water and the phase tricalcium aluminate present in the clinker, is also established by estimating the amount of chemically bound water and free calcium hydroxide incorporated in the hydration products formed from clinker-water and clinker-calcium sulphate-water systems. It is shown that the addition of sulphate ions effectively controls the early clinker hydration possibly by reacting with tricalcium aluminate to form ettringite that shields it from further rapid hydration.

Movement of zinc sulphate in a calcium-saturated soil: cation exchange and precipitation of gypsum.

A one-dimensional model for the movement of zinc sulphate through calcium-saturated soil is presented. Processes considered include mass flow, ion exchange, precipitation and dissolution. Precipitation occurs when the solubility product of gypsum is exceeded. In the presence of gypsum, ion exchange takes place at two separate interfaces, which move with different velocities through the soil. At the first interface precipitation of gypsum takes place in conjunction with ion exchange, and at the second interface the gypsum dissolves again and ion exchange proceeds until equilibrium is reached with the leaching solution. The composition of the transition zone between the two interfaces is calculated from the conditions of mass conservation and electroneutrality, the solubility product of gypsum and assuming a linear ion exchange equation. It is shown that the concentration of sulphate in the transition zone is higher than in the leaching solution, due to dissolution of gypsum at the second interface. In the presence of gypsum, zinc penetrates deeper into the soil than in its absence, but the fraction of the adsorption complex saturated with zinc is smaller. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Retention of Cobalt, Cesium, and Strontium in the Hydrates of C3S, C3A, and Gypsum

The retention of cobalt, cesium, and strontium as trace elements in the hydrates of simple ordinary portland cement components has been investigated. The combined characterization of the solid by SEM, electron microprobe, XRD, and SIMS, as well as the chemical analysis of the solutions, allowed us to identify the likely localization of these trace elements in the solid. In particular, cobalt is dramatically incorporated into the solid during the hydration of C3S; we show that this is due to the formation of a cobalt oxychloride, a compound which is unstable at temperatures ≥60°C. Cesium is retained in small amounts in the C‐S‐H and CH mixture. The formation of hydrated aluminates notably increases its retention. Finally, small quantities of strontium are also retained in silicates and, in the presence of gypsum, its retention is markedly higher. This is likely due to the formation of sulfoaluminates.

Relationships between the internal and external evolution of the Monte Cucco Karst Complex, Umbria, Central Italy

The relationships between the internal and external evolution of the Mt. Cucco karst complex are studied. A classic set of equations, involving the oxidation of hydrogen sulphide, originated at depth in an evaporitic formation, is used to explain the presence of massive gypsum deposits in the Mt. Cucco and the Faggeto Tondo caves. The distribution and the morphology of more than 30 caves in the system, the presence of gypsum, always located along faults, and the presence of broken stalactites and columns, suggest that the evolution of the karst system has been controlled by tectonic movements. Relationships between the development of the caves and the geomorphic evolution of the area are proposed.

高性能減水剤存在下のケイ酸カルシウム及びアルミン酸カルシウム水和物の解析

In order to know the reaction between cement and naphthalenesulfonate type superplasticizer (NSNa) quantitatively, Ca(OH)2 and ethyl silicate or aluminum isopropoxide were reacted in the presence of NSH (sulfonic acid form of NSNa). The hydrates obtained were investigated by chemical analysis, XRD and SEM. The effect of the addition of hydrates containing NS on the drying shrinkage of cement mortar was also measured. The results obtained were as follows.(1) NS reacted with silicate and Ca(OH)2. The mole ratio of NS:Ca:Si in the hydrates depended on the mole ratio of Ca/Si in the initial composition.(2) NS also reacted with aluminate and Ca(OH)2. Calcium aluminate hydrates containing NS formed at the mole ratio of approximately NS:Ca:Al=2:2:1 in the absence of gypsum. Ettringite mainly formed in the presence of gypsum.(3) Hydrates containing NS consisted of fine particles (approximately 0.2μm). The addition of hydrates containing NS to cement mortar, in which NS content was kept in a normal dosage, did not influence much on the drying shrinkage of mortar.The hydration of calcium silicate or calcium aluminate under the presence of NS was explained on the basis of the reaction between polyelectrolyte and polybasic acids under the presence of Ca(OH)2.

Marble weathering and air pollution in Philadelphia

Maps of damage to marble tombstones in the urban region of Philadelphia demonstrate a close spatial correspondence with airborne pollutant concentrations. Mean recession rates on upper tombstone faces are an order of magnitude greater (3.5 mm (100a) −1) in the center of the city than they are 20 km away in the suburbs and countryside (< 0.5 mm (100a) −1). Not only are more pollutants emitted in the city, but they are also concentrated in the city center by centripetal air movement into the urban heat island. Gaseous SO 2 appears to be the most damaging pollutant, as is shown by the presence of gypsum in urban stones. Although rainfall is important in removing sulfate reaction products, anthropogenically-induced acid rain has only a minor role in marble deterioration. High urban SO 2 concentrations cause sufficient gypsum accumulation within the stones to exfoliate the durable surface layer. Old photos of tombstones in central Philadelphia cemeteries show that exfoliation greatly accelerated between 1930 and 1960, concurrent with increases in SO 2 levels. Recent improvements in air quality are likely to have slowed stone deterioration.

Lanthanide Solid Phase Speciation

AbstractThe solid phase speciation of La, Ce, and Nd in the Ln2O3‐CaO‐SO4‐PO4‐F‐O2‐CO2‐H2O (where Ln = La, Ce, and Nd) equilibrium system were evaluated using three‐dimensional activity diagrams. Diagrams were constructed from thermodynamic data and interpreted with a knowledge of the ligands associated with La, Ce, and Nd in sewage sludge and sludge‐amended soil particles as characterized by scanning electron microscopy. Throughout a wide range of equilibrium conditions at 298.15 K and 0.101 MPa, the activities of dissolved lanthanides were controlled by a small number of solid phases. These solids were cerianite [CeO2], lanthanite [La2(CO3)3·8H2O] and Nd‐lanthanite [Nd2(CO3)3·8H2O], and La and Nd sulfates [(La,Nd)2(SO4)3·8H2O] in the presence of gypsum. In general, the stable lanthanide solid phases predicted from the thermochemical evaluation were consistent with those directly observed in chemically well‐defined sewage sludge and sludge‐amended soil; thus, illustrating the applicability of such an evaluation when applied to well characterized environments.

Influence of Gluconate, Lignosulfonate, and Glucose Admixtures on the Hydration of Tetracalcium Aluminoferrite in the Presence of Gypsum with or without Calcium Hydroxide

The influence of 0.3 wt% gluconute, lignosulfonate, or glucose on the hydration of 4CaO·A12O3‐Fe2O3 in the presence of gypsum with or without Ca(OH)2, was examined. In the absence of Ca(OH)2 all the admixtures retard both ettringite production and subsequent conversion of ettringite into the monosulfate in the decreasing order glucose &gt;lignosulfonate &gt;gluconate. In the presence ofCa(OH)2 all the admixtures accelerate early ettringite production but do not affect subsequent conversion of ettringite into the monosulfate, at least up to 28 d.

Corrigenda - The effects of gypsum on macroporosity and crusting of two red duplex soils

The effects of gypsum on the physical properties of two red duplex soils in northern Victoria were investigated by assessing the relative abundance of macropores (diameters greater than 75 �m) in the 0-30 mm zone of their cultivated layers. Samples were collected in October 1983 from both fallow cropped and stubble cropped plots. Changes in soil porosity between untreated and gypsum-treated plots were measured on photographic images of thin-sections using a Quantimet 720 image analyser. The soils differed in their clay mineralogy, one being dominated by illite, the other by randomly interstratified material. The results indicate only a minor improvement due to gypsum application in the area of macropores in the soils dominant in illite and kaolinite, whereas in the soil with the higher proportion of randomly interstratified clay minerals the area of macropores approximately doubled on the stubble cropped site and also considerably increased on the fallow cropped site. Micromorphological observations indicated that, in the presence of gypsum, crust formation was reduced because less clay was mobilized and redistributed in the surface soil layers.

The effects of gypsum on macroporosity and crusting of two red duplex soils

The effects of gypsum on the physical properties of two red duplex soils in northern Victoria were investigated by assessing the relative abundance of macropores (diameters greater than 75 �m) in the 0-30 mm zone of their cultivated layers. Samples were collected in October 1983 from both fallow cropped and stubble cropped plots. Changes in soil porosity between untreated and gypsum-treated plots were measured on photographic images of thin-sections using a Quantimet 720 image analyser. The soils differed in their clay mineralogy, one being dominated by illite, the other by randomly interstratified material. The results indicate only a minor improvement due to gypsum application in the area of macropores in the soils dominant in illite and kaolinite, whereas in the soil with the higher proportion of randomly interstratified clay minerals the area of macropores approximately doubled on the stubble cropped site and also considerably increased on the fallow cropped site. Micromorphological observations indicated that, in the presence of gypsum, crust formation was reduced because less clay was mobilized and redistributed in the surface soil layers.

The hydration of doped tricalcium aluminate

The limit of solid solution of iron in tricalcium aluminate prepared in an oxygen atmosphere increases with increasing temperature to give a solid solution of composition Ca3Al1.85Fe0.15O6 at 1325° C. The lattice parameter of the cubic unit cell increases from 1.5263 to 1.5289 nm. Iron-doping causes a significant retardation in the reactivity of the Ca3Ass hydrated in the presence of gypsum. Not only does the rate of disappearance of the C3Ass decrease as the iron content increases, but also the setting time of the paste, the time taken for the gypsum to be totally consumed, and the time when rapid conversion of the AFt phase into the AFm phase takes place all increase. These observations apply even more to samples with iron contents greater than the solid solution limit, due to the presence of CaO and C4AFss in addition to C3Ass.

Influence of gluconate, lignosulfonate or glucose on the C 3A hydration in the presence of gypsum with or without lime

The influence of gluconate, lignosulfonate or glucose at 0.1–0.3% dosages on the C 3A hydration in the presence of gypsum with or without lime has been examined. In the presence of lime all the admixtures at 0.3% dosage stabilize ettringite and retard its conversion to monosulfate; only 0.3% glucose retards gypsum consumption and ettringite production. In the absence of lime stabilization of ettringite by admixtures at 0.3% addition appears to be much less effective; no admixture is able to retard the ettringite production or gypsum disappearance. At 0.1% addition, the influence of admixtures seems to be negligible except when glucose is used in the presence of lime: in this case, the conversion of ettringite into monosulfate is retarded.

Mechanism of the hydration of tricalcium aluminate and gypsum of 1:3 mole ratio at low water/solid ratio and in suspension

The hydration kinetics of tricalcium aluminate, C 3A, with gypsum or anhydrite at 1:3 mole ratio were studied using hydration periods of 5 min up to 7 days. These studies were assessed with the aid of differential thermal analysis, thermogravimetric analysis and X-ray diffractometry as well as chemical analysis. The results revealed that hydration periods of up to 7 days of tricalcium aluminate with gypsum in paste form and in suspension, forms ettringite with unhydrated components of C 3A and gypsum. On the other hand, the only hydration product of the slurry of C 3A with anhydrite is ettringite after 7 days of hydration. The kinetics of hydration were studied by the quantitative determination of ettringite from the TG analysis. The results also illustrate that the rate of ettringite formation is slower in the presence of gypsum than in the presence of anhydrite and also that hydration of the slurry gives more ettringite than the hydration of the paste.

The microstructure and chemistry of tricalcium aluminate hydration

Electron optical techniques have been used to study the hydration of tricalcium aluminate in the presence of gypsum at various pH levels. Calcium aluminosulphate hydrates are precipitated, which have compositional variations and structures that range from highly disordered to highly ordered. Results derived from solubility measurements are able to account for the metastability of ettringite with respect to calcium aluminate monosulphate hydrate at pH more than about 12.8. It is shown that the increased surface area of the precipitates formed at high pH is not sufficient to account for the observed increase in solubility. Consideration of the crystal structure of ettringite and the monosulphate hydrate suggests a further proposal for the type of defect occurring in the ettringite structure at high pH.

CARBONATE MINERALOGY OF LAKE SEDIMENTS AND SURROUNDING SOILS 1. BLACKSTRAP LAKE

The carbonate mineralogy of the Blackstrap Lake sediments in central Saskatchewan indicates that the lake deposits are composed of carbonatic minerals similar to those found in surrounding soils and glacial deposits. Textural differences reflect the transport of finer materials (silts and clay) from the adjacent eroding landscapes. In particular the persistence of dolomite in the silt fractions of the lake sediment is a good indication that part of the calcite together with the dolomite are derived from surrounding soils. The sediment sand fraction contains appreciable Mg-bearing calcite and mollusk shells of pure calcite. Changes in the ionic concentrations of the lake water indicate that dissolution-precipitation processes have affected sediment composition. The increased calcium carbonate equivalent percentages and the presence of secondary magnesium-bearing calcites in the lake sediments suggest that this is so, particularly since erosional processes could not account entirely for the differences observed between the sediments and surrounding soils. The presence of gypsum and the nature of the secondary calcites in the Blackstrap Reservoir sediment tie in well with the known historical background of the Reservoir. The increased ionic concentration of the lake water over the last 15 yr or so since the original inception of the Reservoir is attributed to the influx of drainage waters, evaporation and possibly the effects of groundwater entry from below. Key words: Mg-bearing calcite, dolomite, IAP, erosion

The microstructure of the hydration products of tri-calcium aluminate in the presence of gypsum

The hydration of tri-calcium aluminate in the presence of gypsum has been examined by electron optical methods as a function of pH and hydration time. The location of the alumino-sulphate phase has been related to the solubility of aluminate ions from the precursive platelet phase. At pH ∼ 11.5 the alumino-sulphate precipitate is crystalline and precipitates from solution. When first formed it is deficient in calcium and sulphate with respect to ettringite. If the deficiency is too great, transformation to calcium aluminate monosulphate hydrate may occur as an intermediate step before the equilibrium phases are obtained. At a higher pH (∼ 12.5) the fibres of alumino-sulphate are smaller and more rounded. Long tubular fibres similar to those seen in portland cement were not observed. This has been explained as a consequence of using pure tricalcium aluminate, rather than alkali-containing material. The information obtained has been used to predict the effect of some inorganic additives on the phases produced during the setting of portland cement.

Methods For Correcting Porosity Data in a Gypsum-Bearing Carbonate Reservoir

Summary The McElroy field in west Texas is an example of a carbonate reservoir that contains significant quantities of gypsum. Large amounts of reservoir data have been obtained in this field by conventional core analyses and by sidewall neutron porosity (SNP) logs. These data do not account for the effect of gypsum in porosity determination. In an effort to characterize this heterogeneous reservoir more thoroughly, we used special low-temperature core analysis and developed a new method of log analysis to correct old core and log porosity data for gypsum content. These data then were used for a more accurate determination of OOIP. Introduction The McElroy field is one of the major reservoirs of west Texas. It is located in Crane and Upton Counties (Fig. 1). The reservoir encompasses about 30,000 acres (121.5×106 m2) and contains about 2,000 wells. Production is from the Grayburg-San Andres dolomite formation of the Permian period at an average depth of about 3,000 ft (900 m). The field was discovered in 1926 and has been in various stages of development since that time.1 Most of the porosity data acquired have been in the form of conventional core analyses and SNP logs. These data are known to be affected significantly by the presence of gypsum. Since this reservoir rock has been found to contain significant amounts of gypsum, direct use of these data would lead to significant errors in porosity estimation. In early 1959, a method of core analysis was developed that prevented the dehydration of gypsum.2 As new infill wells were drilled, selected wells were cored, and the cores were analyzed by this technique. To utilize as much data as possible in this very large reservoir. Many of the more recently drilled wells were logged with SNP logs.3 To utilize these data, a method of correcting these logs was developed. The corrections were based on information obtained from special log analysis techniques in nearby infill wells. Porosity data from logs and cores in the new wells and corrected porosity data from logs and cores in the old wells were used in conjunction with capillary pressure measurements to determine OOIP by the volumetric method. Theory and Definitions Core Analysis Gypsum (CaS04·2H20) is an evaporite mineral found in many carbonate and some sandstone reservoirs. In laboratory measurements, gypsum has been observed to convert to anhydrite and water at temperatures above about 140°F (60°C). Assuming that the conversion from gypsum to anhydrite takes place at approximately this same temperature in the reservoir and that a typical geothermal gradient exists, gypsum general1y is not expected to exist below a depth of about 6,000 ft (1800 m). Standard core analysis can cause serious errors in the measurement of porosity if gypsum is present in the cores. Vacuum distillation or retort procedures yield porosity values that are too high by as much as 48 % of the bulk volume of gypsum present. Heating the core samples for cleaning or measurement of fluid content is a necessary step in most forms of standard core analysis. The heat applied is high enough for the gypsum to lose its crystallization water and to form anhydrite. It is the loss of this crystallization water that causes the error in the measurement of porosity. This process was described in detail by Hurd and Fitch2 in 1959. Core Analysis Gypsum (CaS04·2H20) is an evaporite mineral found in many carbonate and some sandstone reservoirs. In laboratory measurements, gypsum has been observed to convert to anhydrite and water at temperatures above about 140°F (60°C). Assuming that the conversion from gypsum to anhydrite takes place at approximately this same temperature in the reservoir and that a typical geothermal gradient exists, gypsum general1y is not expected to exist below a depth of about 6,000 ft (1800 m). Standard core analysis can cause serious errors in the measurement of porosity if gypsum is present in the cores. Vacuum distillation or retort procedures yield porosity values that are too high by as much as 48 % of the bulk volume of gypsum present. Heating the core samples for cleaning or measurement of fluid content is a necessary step in most forms of standard core analysis. The heat applied is high enough for the gypsum to lose its crystallization water and to form anhydrite. It is the loss of this crystallization water that causes the error in the measurement of porosity. This process was described in detail by Hurd and Fitch2 in 1959.