Search results for "Gypsum"

Multianalytical Approach to explain the darkening process of hematite pigment in paintings from ancient Pompeii after accelerated weathering experime…

2013

[EN] In this paper, recently excavated fresco painting fragments from the House of Marcus Lucretius (Pompeii) and not exposed to the atmosphere since the eruption of the Mount Vesuvius were subjected to a controlled SO2 atmosphere and high relative humidity. These experiments were conducted in order to simulate under accelerated conditions the possible deterioration of the hematite pigment and plaster. The mineralogical transformation of the polychromy and plaster was monitored using mainly Raman spectroscopy, a non-destructive technique, but also infrared spectroscopy (FT-IR) and scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS). After different exposure cycles to…

A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol

2006

The aim of this study is to characterize the pedogenic clay minerals by using simple approach: Mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD ana…

Small scale secondary CaCO3 accumulations in selected sections of the European loess belt. Morphological forms and potential for paleoenvironmental r…

1997

Eighteen important Quaternary loess paleosoil sites have been studied across the European loess belt. They included approximately 50 buried soils, the over and/or underlying loess and the present-day surface soils (where possible). From the numerous types of secondary CaCO3 accumulations recognized, only the small scale accumulations are discussed in this paper, including calcified root cells, CaCO3 hypocoatings, needle-fiber calcite, powdery calcite coatings, earthworm biospheroliths, and calcite pseudomorphs on gypsum. Most of the features studied are found in the rhizosphere microecosystem. Each of these features showed a unique relationship with organic matter, micro-organism and plant …

Correlation between surface forces and surface reactivity in the setting of plaster by atomic force microscopy

2000

Abstract The setting of mineral binders (cement, plaster, etc.) arises as a direct consequence of surface reactivity by a process of dissociation and rehydration. This transformation induces a complete change of surface forces, of which the nature remains still unknown. The general process of the setting has been studied by means of plaster (CaSO 4 ·0.5H 2 O) crystals, chosen for an experimental convenience. The surface alteration (growth, dissolution, atomic resolution) of the plaster crystal with respect to the introduction of the calcium sulfate solution has been followed by using atomic force microscopy (AFM. Alternatively, this apparatus has been adapted by gluing a plaster microcrysta…

Effect of superplasticizers on the rheological properties of fly ash suspensions containing activators of the pozzolanic reaction

2000

Rheological studies have been carried out on the effect of a superplasticizer from the sulphonated melamine formaldehyde (SMF) group upon the properties of fly ash suspensions containing a small quantity of mineral admixtures such as cement, lime and gypsum. The superplasticizers' efficiency has appeared to depend greatly on the admixture used. The highest liquefaction degree was found in fly ash suspensions containing both cement and gypsum together and the next it was, when only cement was added. These suspensions exhibit features of a newtonian fluid of low plastic viscosity, when the water to solid ratio (w/s) is 0.3 and a superplasticizer has been used. However, fly ash suspensions wit…

Spontaneous ecological recovery of vegetation in a red gypsum landfill: Betula pendula dominates after 10 years of inactivity

2019

International audience; Red gypsum is the product of the neutralization of titanium dioxide (TiO 2) extraction residue from ilmenite and anatase. The disposal of red gypsum creates heterogeneous plots with layers that may include Fe, Ca, Al, Mg, Mn, S, and other elements and an alkaline pH that makes revegetation complicated and slow. The vertical and horizontal dispersion of the sediment particles are the main concern. Therefore, the establishment of precise vegetation cover is needed to address this issue. One of the aims of this study was (1) to explore the distribution of the spontaneous vegetation found along a red gypsum-formed landfill located at the Ochsenfeld site in eastern France…

Influence of temperature on the hydration products of low pH cements

2012

International audience; The chemical evolution of two hydrated "low pH" binders prepared from binary (60% Portland cement + 40% silica fume) or ternary (37.5% Portland cement +32.5% silica fume + 30% fly-ash) mixtures was characterized over one year at 20 degrees C. 50 degrees C, and 80 degrees C. The main hydrates were Al-substituted C-S-H. Raising the temperature from 20 to 80 degrees C caused a lengthening and cross-linking of their silicate chains. Ettringite that formed in pastes stored at 20 degrees C was destabilized. Only traces of calcium sulfate (gypsum and/or anhydrite) reprecipitated after one year in some materials cured at 50 degrees C and 80 degrees C. The sulfates released w…

Influence of three types of superplasticizers on tricalciumaluminate hydration in presence of gypsum.

2006

International audience; Different types of superplasticizers have been widely used over the past few decades in order to produce a more fluid or very high strength and durable concrete. These chemical admixtures interfere with the various physico-chemical processes occurring in early cement paste. In this paper we present results from a study on the influence of superplasticizers on pure tricalciumaluminate hydration in presence of gypsum. The suspensions hydration has been investigated by conductimetry, isothermal calorimetry and total organic carbon analysis of the liquid phase. The time taken for ettringite formation has been determined without superplasticizer and in presence of three d…

Geomorphological and speleological aspects of the Vallone Ponte-Grotte d'Acqua karst system (Sant'Angelo Muxaro - AG)

2009

Risk assessment of gypsum amendment on agricultural fields: Effects of sulfate on riverine biota

2022

Gypsum (CaSO4 ∙ 2H2 O) amendment is a promising way of decreasing the phosphorus loading of arable lands, and of thus preventing aquatic eutrophication. However, in freshwaters with low sulfate concentrations, gypsum-released sulfate may pose a threat to the biota. To assess such risks, we performed a series of sulfate toxicity tests in the laboratory and conducted field surveys. These field surveys were associated with a large-scale pilot exercise involving spreading gypsum on agricultural fields covering 18% of the Savijoki River catchment area. The gypsum amendment in such fields resulted in about fourfold increase in the mean sulfate concentration for a 2-month period, and a transient, …