This research presents a study of using an additive for the objective of increasing the setting time of a material used in several aspects in the constructional field, this material is "Local-Gypsum" ...which is locally called "Joss", and the additive used in this study is "Trees Glue Powder" denoted by "TGP". Nine mixtures of Local-gypsum (joss) had been experimented in the current study to find their setting time, these mixes were divided into three groups according to their water-joss ratios (W/J) (0.3, 0.4 and 0.5), and each group was sub-divided into three sub-groups according to their TGP contents (0.0%, 0.3% and 0.6%). It was found that, when TGP is added with the two contents (0.3% and 0.6%), the setting time of local gypsum (joss) is increased, and the percentage of this increase at (TGP content = 0.6%) is doubly multiplied as compared to the percentage at (TGP content = 0.3%). Moreover, when TGP content is increased from (0.0% to 0.6%), the percentage of increase in the setting times of joss is reduced with the increase of (W/J) ratio from (0.3 to 0.5). It was also found that, when (W/J) ratio is increased, the setting time of joss is increased, and this behavior is applicable for all TGP contents (0.0%, 0.3% and 0.6%). While, when (W/J) is increased from (0.3 to 0.5), the percentage of increase in the setting times of joss is reduced with the increase in TGP contents from (0.0% to 0.6%).
This study aimed to reveal the effects of the hydration products AHsub.3 and AFt phases on the hydration and hardening properties of calcium sulfoaluminate (CSA) cement. In addition, the effects of ...anhydrite (CS¯) and gypsum (CS¯Hsub.2) on the properties of CSA cement were compared. Calcium sulfoaluminate (Csub.4Asub.3S¯) was synthesized with analytical reagents, and the Csub.4Asub.3S¯-CS¯-Hsub.2O system with different molar ratios of CS¯ and Csub.4Asub.3S¯ was established. The phase compositions and contents of AFt and AHsub.3 were determined by X-ray diffraction (XRD), Rietveld quantitative phase analysis, and thermogravimetric analysis (TG). The effects of pore structure and hydration product morphology on mechanical properties were analyzed by mercury intrusion porosity (MIP) and scanning electron microscopy (SEM). The results showed that the compressive strength exhibited a correlation with the AHsub.3 content. In the case of relatively sufficient anhydrite or gypsum, Csub.4Asub.3S¯ has a high degree of hydration, and the AHsub.3 content can be considered to contribute more to the strength of the hardened cement paste. When anhydrite was selected, the combined and interlocked AFt crystals were covered or wrapped by a large amount of AHsub.3. The mechanical properties of the hardened cement paste mixed with anhydrite were better than those of that mixed with gypsum.
Early investigations on stable isotopes (δ18O and δD) of structurally-bound gypsum (CaSO4·2H2O) hydration water (GHW) suggested that soon after gypsum precipitation, its primary isotopic composition ...could be altered via gypsum re-crystallization or by isotope exchange by diffusion of water into the intact crystals. If this occurs, the use of stable isotopes of GHW as a paleoclimate proxy is compromised. Here we investigated the long-term (up to 6 years) stability of GHW in contact with aqueous solution by conducting isotopic exchange experiments at different temperatures and using varying gypsum grain size. We placed gypsum with known hydration water isotopic composition in 18O/D-enriched and 18O/D-depleted aqueous solutions and monitored any change in the stable isotopes of GHW with time. At low temperature (25 °C) and when the solution is in chemical equilibrium with the mineral, GHW preserves its primary isotopic composition after 2 years. In contrast, when the gypsum-solution system is out of chemical equilibrium, the δ18OGHW and δDGHW values are altered, first via gypsum re-crystallization from the solution and later by isotope exchange via diffusion. Importantly, δ18OGHW and δDGHW stabilized after 2 years to values that represent only an 8 % change relative to the original GHW and remain constant during the subsequent 4 years. Our results suggest that at low temperature the effect of isotope exchange on GHW is limited. At higher temperature (65 °C), chemical equilibrium is not attained after 2 years for fine-grained synthetic gypsum (<250 μm) and its isotopic values continues to change. In contrast, the δ18OGHW and δDGHW in experiments using fine-grained natural gypsum at 45 °C stabilized after 1 year and values changed less than 3 % with respect to initial conditions. Experiments with coarser-grained natural gypsum (1–2 mm) at 45 °C did not show measurable isotopic changes of the GHW, indicating the lack of gypsum dissolution/re-crystallization or diffusion isotopic exchange. We conclude that microcrystalline gypsum crystals (<250 μm) are more readily affected by diagenesis resulting from changes in the gypsum saturation state of the solution, whereas larger gypsum crystals are more likely to preserve their original isotopic compositions. Our results indicate that under certain conditions, GHW can preserve the isotopic composition of its parent fluid and provide valuable information about paleoclimate and paleo-hydrologic conditions.
•Hydration and dehydration of building gypsum are studied using Raman spectroscopy.•Raman band intensity ratios are used to study the phase transformation of gypsum.•Chemometrics and ANOVA are ...conducted to analyze the datasets acquired.•The results suggest the viability of the Raman spectroscopy coupled chemometrics.
The application of conventional and standoff Raman spectroscopy has been a widely explored technique for materials characterization. This study uses Raman spectroscopy coupled with chemometrics analysis to monitor gypsum's hydration and dehydration process. The Raman spectra of the specimens are captured periodically, and the intensity ratios of the selected characteristic Raman bands and the intensity ratios of the characteristics bands are used for chemometric analysis. To determine the statistical significance of the variations of the Raman band intensities with the setting time, a statistical analysis of the intensity ratios was conducted using analysis of variances (ANOVA) followed by Games-Howell post-hoc statistics and pairwise comparison of the groups. As the dehydration progresses and the sample dries, the Raman bands of the water molecule gradually diminish, indicating the loss of water molecules from the specimens. The results demonstrate the capability of the Raman spectroscopy, the chemometric techniques used, and the analysis of variances for distinguishing and monitoring gypsum's hydration and dehydration process. The gradual variation in Raman band intensity ratios and the diminishing bands of water molecules corresponds to dehydration, the loss of water, and the phase transformation from a fluid-like gypsum paste to solid phases.
•Soil pH and exchangeable sodium percentage decreased rapidly in the first year.•Soil electrical conductivity decreased markedly in the second year.•Flue gas desulfurization gypsum addition altered ...the soluble ion composition of salts.•Crop yields reached more than 90% of the local production four years later.•Metals content in soils and crops was lower than the established standards.
Flue gas desulfurization (FGD) gypsum has been used as an amendment to reduce soil salinization and alkalinization worldwide. However, the effective and safe use of FGD gypsum in agricultural land is still debatable in some countries, although many studies have reported its beneficial effects on soil management. Therefore, a study was conducted on wasteland (600 ha) close to the Yellow River in Inner Mongolia, China. The main aim of this research was to evaluate the long-term effects of FGD gypsum application on soil salinity and sodicity, crop production and heavy metals in soils and crops. The results showed that soil pH and exchangeable sodium percentage (ESP) in topsoil (0–20 cm) decreased dramatically during the first year, while a substantial reduction of electrical conductivity (EC) occurred during the second year after FGD gypsum application. Four years later, the EC, pH and ESP levels in reclaimed soils were 58.3%, 92.2% and 95.2% lower, respectively, than those in the initial soils. In addition, the FGD gypsum application altered the major water-soluble ion composition of dissolved salts, showing high Ca2+ and SO42− concentrations and low concentrations of HCO3−, CO32− and other water-soluble ions. After reclamation, the crop yields gradually increased over time, and the sunflower and corn yields reached more than 90% of the levels of local production of these crops. Moreover, the heavy metal (Cd, As, Pb, Hg and Cr) contents of the FGD gypsum-reclaimed soils and crops was far lower than the established standards and below detectable limits. This study provides convincing evidence of the benefits of the large-scale use of FGD gypsum to reclaim saline-alkali soils.
Phosphogypsum is an industrial by-product from the wet preparation of phosphoric acid. Phosphorus building gypsum (PBG) can be obtained from phosphogypsum after high-thermal dehydration. Improving ...the mechanical properties of PBG is of great significance to extending its application range. In this paper, PBG was modified by adding nano-CaCOsub.3. Specifically, this study, conducted on 0.25–2% nano-CaCOsub.3-doped PBG, tested effects on the fluidity, setting time, absolute dry flexural strength, absolute dry compressive strength, water absorption and softening coefficient of PBG, followed by its microscopic analysis with SEM and XRD. The experimental results showed that, with an increase in nano-CaCOsub.3 content, the fluidity and setting time of PBG-based mixes were decreased. When the content was 2%, the fluidity was 120 mm, which was 33% lower than that of the blank group; the initial setting time was 485 s, which was 38% lower than that in the blank group; the final setting time was 1321 s, which was reduced by 29%. Nano-CaCOsub.3 evidently improved the absolute dry flexural strength, absolute dry compressive strength, water absorption and softening coefficient of PBG to a certain extent. When the content was 1%, the strengthening effect reached the optimum, with the absolute dry flexural strength and absolute dry compressive strength being increased to 8.1 MPa and 20.5 MPa, respectively, which were 50% and 24% higher than those of the blank group; when the content was 1.5%, the water absorption was 0.22, which was 33% lower than that of the blank group; when the content approached 0.75%, the softening coefficient reached the peak of 0.63, which was 66% higher than that of the blank group. Doping with nano-CaCOsub.3 could significantly improve the performance of PBG, which provides a new scheme for its modification.
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•High-quality gypsum based on wastes of sulfuric acid and limestone was obtained.•Building gypsum based on synthetic has a brand of strength G5–G7.•High-strength gypsum binder based ...on synthetic gypsum has the brand G10–G22.•Anhydrite was obtained with a purity of at least 98% and strength of >28 MPa.•Materials from wastes better in properties to such from natural raw materials.
Synthetic calcium sulfate dihydrate, obtained from sulfuric acid waste of chemical plants and waste of the fine fraction of limestone, is a potential source of gypsum-containing raw materials. We investigated the processing of synthetic calcium sulfate dihydrate from sulfuric acid waste to gypsum, high-strength gypsum binder, and anhydrite. The effects of technological parameters on the strength indicators of binders were studied. It was found that the obtained samples of binders (based on synthetic gypsum) meet all standards and even exceed the performance of binders obtained from natural gypsum stone. Our studies show that synthetic gypsum is a promising gypsum-containing raw material for the production of gypsum binders and can be a promising alternative to natural gypsum stone.
We analyzed the stable isotopes (δ17O, δ18O and δD) of gypsum hydration water (GHW) in a variety of speleothems, as well as condensation and infiltration waters in five caves of the semiarid gypsum ...karst of Sorbas basin (Almeria, SE Spain). Microclimate parameters (air temperature, relative humidity and effective condensation rate) were also monitored over an annual cycle. We found that the mother solution from which the majority of gypsum speleothems grow is composed of a mixture of condensation (~60%) and infiltration water (~40%) that undergoes evaporation. Although evaporation of infiltration water alone was thought to be responsible for secondary gypsum precipitation in vadose caves, our results suggest that condensation can be a major source of water for the formation of gypsum speleothems. The modelled d-excess and Δ17O trajectories of water during the evaporative process confirm that the majority of speleothems precipitate from a mixture of condensation and infiltration water under relative humidity of 75–85%, similar to that measured in the cave atmosphere during winter. These findings have important implications for future studies of gypsum speleothems as paleoenvironmental archives.
Gypsum-based composites (GCs) have been widely used in interior linings such as walls and ceilings due to their unique advantages including low cost, good habitability, and good fire resistance. The ...existence of many gypsum resources such as natural gypsum (NG) and industrial gypsum by-products ensure that GCs are very popular. The main weaknesses of GCs, especially those originating from industrial gypsum by-products, are brittleness, inferior mechanical properties, and low water resistance, which limit their further applications. Extensive studies have used fibres to enhance the performance of GCs. Fibre-reinforced gypsum-based composites (FRGCs) show excellent comprehensive performance and have wider marketability as building materials, which is beneficial for accelerating the utilization of gypsum by-products and creates many economic and environmental benefits. This paper reviews previous studies of GCs reinforced with fibres and summarizes, reviews, and discusses the sources and properties of gypsum and fibres, the pretreatments of fibres to improve their adhesion with the matrix, the effect of fibres on some properties of FRGCs, the application of FRGCs in three-dimensional (3D) printing and the challenges for further research. This review provides a foundation and guide for future studies and uses of FRGCs.
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![Effects of AH[sub.3] and AF...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1996-1944/small "Effects of AH[sub.3] and AFt on the Hydration–Hardening Properties of the C[sub.4]A[sub.3]S¯-CS¯-H[sub.2]O System")
