Effect of geopolymer composition and curing conditions on efflorescence in lightweight porous geopolymers

Lightweight geopolymers are more readily produced and give higher fire resistant performance than foam cement concrete. The fly ash-based lightweight geopolymers stones could be used for decoration due to the similarity in appearance and color to natural vesicular basalts. Efflorescence can be even more nettlesome issue in commercialization of lightweight porous geopolimers. Lowering the density of solid geopolymers can be achieved by inducing chemical reactions that entrain gases to foam the geopolymer structure. The apparent density of lightweight porous geopolymers has a range from 0.7 to 1.2 g/m3 with 0.025, 0.05 and 0.10 wt% of Al powder concentration, which corresponds to about 37~60 % of the apparent density, 1.96 g/cm3, of solid geopolymers. The compressive strength of cellular structured geopolymers decreased to 6~18 % of the compressive strength, 45 MPa of solid geopolymers. The microstructure of geopolymers gel was equivalent for both solid and cellular structured geopolymers. The efflorescence can be controlled by reducing targeted Na/Al molar ratio less than 1.0 or water content in geopolymers or curing at high temperature. Please click Additional Files below to see the full abstract

Potential of IGCC slag as an alkali activated material

Integrated gasification combined cycle (IGCC) is a next generation energy production technology that converts coal into syngas with enhanced power generation efficiency and environmental performance. IGCC produces coal gasification slag as the solid by-product. Recycling of IGCC slag is still in the early stages, but the recycling process has been around the cement and concrete industry. We calculated the reactive Si/Al ratio of IGCC slag which is generated from a pilot plant in South Korea, and evaluated the potential of it as an alkali-activated material. Samples which were activated with the combined activator of sodium silicate solution and caustic soda had an average compressive strength of 4.5 MPa, showing swelling on the top free surface. Expansion of the alkali-activated slag was possibly caused by free CaO and MgO in the slag. While the samples that were activated with the combined activator of sodium aluminate and caustic soda had an average compressive strength of 10 MPa. Hydroxy sodalite and C3AH6 were found to be the new crystalline phases. IGCC slag can be used as an alkali-activated material, but the strength performance should be improved with proper mix design approach which can alleviate the expansion issue at the same time. Acknowledgement This study was supported by Korea Western Power Co., Ltd. in South Korea

Benefits of sealed-curing on compressive strength of fly ash-based geopolymers

There is no standardized procedure for producing geopolymers; therefore, many researchers develop their own procedures for mixing and curing to achieve good workability and strength development. The curing scheme adopted is important in achieving maximum performance of resultant geopolymers. In this study, we evaluated the impact of sealed and unsealed curing on mechanical strength of geopolymers. Fly ash-based geopolymers cured in sealed and unsealed moulds clearly revealed that retention of water during curing resulted in superior strength development. The average compressive strength of sealed-cured geopolymers measured after 1 day of curing was a modest 50 MPa, while after 7 day curing the average compressive strength increased to 120~135 MPa. In the unsealed specimens the average compressive strength of geopolymers was lower; ranging from 60 to 90 MPa with a slight increase as the curing period increased. Microcracking caused by dehydration is postulated to cause the strength decrease in the unsealed cured samples. These results show that water is a crucial component for the evolution of high strength three-dimensional cross-linked networks in geopolymers

Beam‐induced redox transformation of arsenic during As K‐edge XAS measurements: availability of reducing or oxidizing agents and As speciation

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143709/1/jsy2rv5078.pd

Impacts of the Quinazoline-Based Alpha1-Antagonist, Terazosin, and of the Sulfonamide Derivative, Tamsulosin, on Serum Prostate-Specific Antigen and Prostate Volume

The aim of this study was to compare the impacts of terazosin and tamsulosin, on prostate activity, i.e., serum prostate-specific antigen, total prostate volume (TPV), and transition zone volume (TZV). A total of 90 patients who presented with lower urinary tract symptoms (LUTS) secondary to benign prostatic hyperplasia (BPH), ranging in age from 52 to 83 yr (median 65 yr), were included in the study. Patients were given 0.2 mg tamsulosin, 2 mg terazosin, or 4 mg terazosin once daily for an average of 14 months (range, 6-56 months). Subjective (International Prostate Symptom Scores, I-PSS) and objective (maximal flow rate and post-void residual) parameters were assessed both at baseline and at treatment cessation. Serum prostate-specific antigen (PSA) levels were found to be unaffected by treatment (1.2 and 1.3 ng/mL). In total patients, multivariate analysis showed that baseline TPV was the only independent predictor of treatment-related TPV reduction. Moreover, baseline TPV ≥30 g was found to be associated with a higher likelihood of TPV reduction (odds ratio [OR], 3.939; 95% confidence interval [CI], 1.506-10.304; p=0.005), and a baseline TZV of ≥10 g was associated with a 7.1-times greater chance of TZV reduction (OR, 7.100; 95% CI, 2.428-20.763; p<0.001). The same model showed that patients on 2 mg terazosin had a 10.8-fold greater likelihood (OR, 10.770; 95% CI, 1.409-82.323; p=0.022) and that those on 4 mg terazosin had a 9.0-fold greater likelihood (OR, 9.001; 95% CI, 1.724-46.995; p=0.009) of a TZV reduction than those on 0.2 mg tamsulosin. In addition, symptoms improved regardless of prostate activity after taking alpha1-blockers. Our findings suggest that terazosin reduces TZV and demonstrate that the relief of symptoms associated with BPH may not be due to a prostate activity reduction induced by apoptosis in the prostate gland

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 &gt; 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

Preparation of Calcined Zirconia-Carbon Composite from Metal Organic Frameworks and Its Application to Adsorption of Crystal Violet and Salicylic Acid

Zirconia-carbon (ZC) composites were prepared via calcination of Zr-based metal organic frameworks, UiO-66 and amino-functionalized UiO-66, under N2 atmosphere. The prepared composites were characterized using a series of instrumental analyses. The surface area of the ZC composites increased with the increase of calcination temperature, with the formation of a graphite oxide phase observed at 900 °C. The composites were used for adsorptive removal of a dye (crystal violet, CV) and a pharmaceutical and personal care product (salicylic acid, SA). The increase of the calcination temperature resulted in enhanced adsorption capability of the composites toward CV. The composite calcined at 900 °C exhibited a maximum uptake of 243 mg·g−1, which was much greater than that by a commercial activated carbon. The composite was also effective in SA adsorption (102 mg·g−1), and N-functionalization of the composite further enhanced its adsorption capability (109 mg·g−1). CV adsorption was weakly influenced by solution pH, but was more dependent on the surface area and pore volume of the ZC composite. Meanwhile, SA adsorption showed strong pH dependence, which implies an active role of electrostatic interactions in the adsorption process. Base-base repulsion and hydrogen bonding are also suggested to influence the adsorption of CV and SA, especially for the N-functionalized composite