Calcitic-based stones protection by a low-fluorine modified methacrylic coating

Atmospheric pollutants, such as NOx, SO2, and particulate matter, together with water percolation inside the stone pores, represent the main causes of cultural heritage decay. In order to avoid these undesired phenomena, the application of protective coatings represents a reliable solution. In this context, the present study focused on the synthesis of low-fluorine content methacrylic-based (MMA) polymeric resins characterized by seven F atoms (namely F7 monomer) in the lateral chains. Four different percentages (1.0, 2.5, 5.0, and 10.0%) of the present monomer were adopted to obtain a final polymeric structure showing the desired hydrophobicity, processability, and structural and thermal stability (even after accelerated UV aging tests). MMA_F7(1.0) seemed to be the optimal one; therefore, it was further applied onto Candoglia marble. Specifically, the treated substrates showed good surface hydrophobicity, water repellency, and water vapor transpirability. No color variation was observed even after a 1.5-year exposure in a real polluted environment (Monza Cathedral). Interestingly, the application of this coating hindered the atmospheric nitrates penetration inside the stones and, at the same time, it limited the sulfates (gypsum) formation, thus revealing a very promising marbles protection resin.

Not Mining Sterilization of Explored Mineral Resources. The Example of Native Sulfur Deposits in Poland Case History

The sterilization of mineral resources makes considerable amounts inaccessible for future use and may be a barrier to the free supply of commodities. During the exploitation of mineral deposits, some parts of their resources become sterilized as inaccessible because of natural hazards or unfavorable economic conditions. Not mining land use and the social opposition against mining is the purpose of sterilization of considerable demonstrated mineral resources of deposits not yet engaged in exploitation. The native sulfur deposits in Poland are a good example of such “not mining” sterilization, which makes a considerable part of known resources inaccessible. On the northern border of the Carpathian Foredeep within the Miocene gypsum formation, the systematic exploration had demonstrated about 1 billion tons of sulfur resources located in the deposits of varied dimensions. The sulfur opencast mining and underground melting (the modified Frasch method) flourished from 1958 up to 1993. The increasing sulfur supply, recoverable from hydrocarbons, caused the closing down of sulfur mines, leaving a place with considerable untouched resources. About 67% of sulfur resources left by closed mines and of other explored but not exploited deposits are sterilized by the advancement of settlements, industrial plants, road construction, and by social opposition against mining.

Microbial sulfur cycling during the formation of Primary Lower Gypsum in Mediterranean marginals basins

<p>During the first phase of the Messinian Salinity Crisis, massive amounts of sulfate (SO<sub>4</sub><sup>2-</sup>) have been sequestred in the form of up to 200m thick gypsum deposits (Primary Lower Gypsum) in Mediterranean marginal basins. The sulfur isotopic composition of the sulfate ion of this unit (δ<sup>34</sup>S<sub>SO4</sub>) (on average 22.3 ‰) strongly suggests that gypsum was formed by concentration of marine sulfate. Interestingly, the preservation of sulfide globules within the gypsum and marls interbeds suggests that the basin sulfate was not only involved in gypsum formation but a fraction was also reduced through microbial sulfate reduction. Moreover, filamentous fossils interpreted to be the remnants of sulfide oxidizing bacterias are entrapped in this gypsum and indicate, together with the occurrence of sulfide globules and dolomite, that an active biogeochemical sulfur cycling was active at the time of Primary Lower Gypsum deposition. To investigate the role of this active sulfur cycling in Mediterranean marginal basins, we analyzed the multiple sulfur isotopic composition of sulfate and sulfide minerals (δ<sup>34</sup>S andΔ<sup>33</sup>S)<sub></sub>from Primary Lower Gypsum of the Vena del Gesso basin (Italy). Whereas the isotopic composition of gypsum (δ<sup>34</sup>S<sub>SO4 </sub>from 21 to 24‰ and Δ<sup>33</sup>S<sub>SO4 </sub>from -0.001 to 0.049‰) display very homogenous values that are close to those of the Messinian ocean (δ<sup>34</sup>S<sub>MSC </sub>~22±0.2‰ and Δ<sup>33</sup>S<sub>MSC</sub>~0.039±0.015), the analyzed reduced sulfur compounds display a wide range of variability  with -36 to +9‰ in δ<sup>34</sup>S and -0.017 to 0.125‰ in Δ<sup>33</sup>S. This suggests huge hydrologically-driven redox variations during Primary Lower Gypsum deposition in the Vena del Gesso basin, possibly involving intermittent stratification of the water column and an active microbial cycling of sulfur.</p>

Properties of Anti-spalling Self-compacting Mortars - An Approach Towards Multifunctional Building Composite

This study investigates the micro structural studies of self-compacting mortars by the addition of PP, Nylon and Jute fibers and the amount of Gypsum formed. The amount of all fibers in the proposed mix was limited to 0.5% by weight of the mortar. Four types of mortars one of which was reference mortar and other three mortars contained PP, Nylon and Jute fibers of amount 0.5% by weight, respectively. The workability of the self-compacting mortars was monitored by Mini Slump Flow diameter test. From the results it was found that more compacted microstructure and less amount of Gypsum formation occurred for mortar samples containing PP fibers as compared to control mortar and mortar samples containing Nylon and Jute fibers respectively.

Multi-episodic recrystallization and isotopic resetting of early-diagenetic dolomites in near-surface settings

ABSTRACT The lower Eocene Rus Formation in Qatar reflects carbonate deposition in a semirestricted to fully restricted marine setting on a shallow ramp. Petrographic, mineralogical, and geochemical evidence from three research cores show early diagenesis has extensively altered nearly every petrological attribute of these rocks despite not having been deeply buried. In southern Qatar, the lower Rus (Traina Mbr.) consists of fabric-retentive dolomite intervals that preserve mudstone, wackestone, and packstone textures that are interbedded with depositional gypsum beds. In northern Qatar, the same member is dominated by fabric-destructive planar-e dolomite, and evaporites are absent. In both northern and southern Qatar, the upper Rus (Al Khor Mbr.) is composed of fabric-retentive dolomite intervals as well as limestone intervals rich with Microcodium textures that display evidence of dedolomitization. Geochemical analysis reveals that the limestones have an average δ18Ocal of –10.73‰ VPDB and δ13Ccal of –7.84‰ VPDB, whereas average dolomite δ18Odol is significantly higher (–1.06‰ VPDB) but δ13Cdol values (–3.04‰ VPDB; range –10 to 0‰) overlap with δ13Ccal values. Additionally, δ13Cdol trends toward normal marine values with depth away from the calcite–dolomite contact in all three cores. Petrographic observations demonstrate that dolomite crystals are commonly included in calcite and partially to completely replaced by calcite in these intervals and suggests that dolomite formed before calcite in the Microcodium-bearing intervals. Furthermore, the dolomites are commonly cemented by gypsum in the Traina Mbr. in southern Qatar, suggesting that dolomitization may have also occurred before, or concurrent with, bedded gypsum formation and indicates that dolomitization occurred early. Early dolomites were subsequently replaced by Microcodium-bearing limestones at and immediately below paleo-exposure surfaces, and at greater depths recrystallized in mixed marine–meteoric fluids, producing a negative δ13Cdol signature that trends toward more positive values away from the limestone–dolomite contact. Lastly, the dolomites underwent another phase of recrystallization in either marine-dominated fluids or possibly a well-mixed aquifer setting, resulting in a near-0‰ δ18Odol signature but retaining the negative δ13C signature. These findings thus have implications for reconstructing the diagenetic history of carbonate rocks, as they suggest that early diagenesis of carbonates can be extremely complex, resulting in multiple stages of mineral replacement and isotopic exchange in meteoric and shallow marine fluids before significant burial. Furthermore, this study shows that dolomitization of a limestone does not necessarily prevent additional early diagenesis and multiple recrystallization events. Lastly, it emphasizes the importance of incorporating petrographic observations with geochemical data when interpreting the diagenetic history of carbonate rocks.

Gypsum Precipitation under Saline Conditions: Thermodynamics, Kinetics, Morphology, and Size Distribution

Gypsum (CaSO4·2H2O) is the most common sulfate mineral on Earth and is also found on Mars. It is an evaporitic mineral that predominantly precipitates from brines. In addition to its precipitation in natural environments, gypsum also forms an undesired scale in many industrial processes that utilize or produce brines. Thus, better insights into gypsum formation can contribute to the understanding of natural processes, as well as improving industrial practices. Subsequently, the thermodynamics, nucleation and crystal growth mechanisms and kinetics, and how these factors shape the morphology of gypsum have been widely studied. Over the last decade, the precipitation of gypsum under saline and hypersaline conditions has been the focus of several studies. However, to date, most of the thermodynamic data are derived from experiments with artificial solutions that have limited background electrolytes and have Ca2+/SO42− ratios that are similar to the 1:1 ratio in the mineral. Moreover, direct observations of the nucleation and growth processes of gypsum are still derived from experimental settings that can be described as having low ionic strength. Thus, the mechanisms of gypsum precipitation under conditions from which the mineral precipitates in many natural environments and industrial processes are still less well known. The present review focuses on the precipitation of gypsum from a range of aspects. Special attention is given to brines. The effects of ionic strength, brine composition, and temperature on the thermodynamic settings are broadly discussed. The mechanisms and rates of gypsum nucleation and growth, and the effect the thermodynamic properties of the brine have on these processes is demonstrated by recent microscopic and macroscopic observations. The morphology and size distribution of gypsum crystals precipitation is examined in the light of the precipitation processes that shape these properties. Finally, the present review highlights discrepancies between microscopic and macroscopic observations, and studies carried out under low and high ionic strengths. The special challenges posed by experiments with brines are also discussed. Thus, while this review covers contemporary literature, it also outlines further research that is required in order to improve our understanding of gypsum precipitation in natural environments and industrial settings.

A numerical study on the regional in situ stress field of the Keshen section and interface dislocation in the composite salt-gypsum layer

Salt rock found in the stratum of the sedimentary basin is considered to be exemplary in terms of quality among the class of cap rocks, and it engulfs a certain proportion of the world’s hydrocarbon resources. In recent years, approximately 40% of newly discovered hydrocarbon resources in China have been detected under deep salt layers. Statistics suggest that nearly 40% of drilling accidents and 50% of casing damage incidents occur near the layer interfaces within a composite salt-gypsum formation. For the in-depth characterization of processes such as deformation and damages occurring at the interfaces, analysis of the regional in situ stress field characteristics and distribution in salt structures is vital. For this purpose, the structure of the Keshen section of the Kelasu structural belt under the Tarim Oilfield was studied. Our study establishes a geomechanical model, which tends to be mainly based on constitutive elastic and rheological models (applicable to different layers, i.e., the upper salt layer, salt layer, and presalt layer). Furthermore, the stability of the composite salt-gypsum layer and prediction of formation stress were evaluated. Investigation of drilling accidents and wellbore integrity problems revealed that the perturbation at the interfaces was not earnestly contemplated. The results show a discontinuous pattern in the regional in situ stress distribution in all of the salt layers. The salt layer is characterized by creep behavior with differential stress of less than 1.0 MPa. The interface between the upper layer and the salt layer tends to bear inconsistent deformation of approximately a few centimeters along the wellbore wall.

The Durability of One-Part Alkali-Activated Slag-Based Mortars in Different Environments

The paper assesses the durability of one-part alkali-activated slag-based mortars (AAS) in different aggressive environments, such as calcium chloride- and magnesium sulphate-rich solutions, in comparison with traditional cementitious mortars at equal water to binder ratio. Moreover, the freezing and thawing resistance was evaluated on mortars manufactured with and without air entraining admixture (AEA). Experimental results indicate that the alkali content is a key parameter for durability of AAS: the higher the alkali content, the higher the resistance in severe conditions. In particular, high-alkali content AAS mortars are characterized by freeze–thaw resistances similar to that of blast furnace cement-based mixtures, but lower than that of Portland cement-mortars while AAS with low activators dosages evidence a very limited resistance in cold environment. The effectiveness of AEA in enhancement of freeze–thaw resistance is confirmed also for AAS mortars. Moreover, AAS mixtures are quasi-immune to expansive calcium oxychloride formation in presence of CaCl2-based deicing salts, but they are very vulnerable to magnesium sulphate attack due to decalcification of C-S-H gel and gypsum formation.