An Experimental Study of the Effects of Low-Calcium Fly Ash on Type II Concrete

In this study, the compressive strength and the permeation properties of fly ash-based Geopolymer were experimentally investigated. Type 2 Portland cement (T2PC) was partially or entirely replaced with 0, 10, 20, 30, 50, 70, and 100% of fly ash (FA). The laboratory tests were conducted for compressive strength at 7, 28, and 90 days, and permeation properties such as water absorption at 7 and 28 days. The main goal was to produce eco-friendly concrete with high strength and low permeability through blending cementitious materials including low Calcium (Ca) (T2PC and FA) for protecting concrete against sulphate attacks and other chemically destructive compounds in the environment. This study focused on the effectiveness of the curing period, combinations of chemical activators by varying the molarity of alkaline solutions between 4.16 and 12.96 M and keeping the sodium silicate (SS) to sodium hydroxide (SH) by the weight ratio of 2.5. Lab observations from this study demonstrated that the compressive strength was enhanced with the increment in fly ash content at all ages, with optimum being at 20% as the replacement of T2PC.

CO2/N2 Gas Separation Using Pebax/ZIF-7—PSf Composite Membranes

In this study, we mixed the zeolitic imidazolate framework-7 (ZIF-7) with poly(ether-b-amide)® 2533 (Pebax-2533) and used it as a selective layer for a composite membrane. We prepared the composite membrane’s substrate using polysulfone (PSf), adjusted its pore size using polyethylene glycol (PEG), and applied polydimethylsiloxane (PDMS) to the gutter layer and the coating layer. Then, we investigated the membrane’s properties of gases by penetrating a single gas (N2, CO2) into the membrane. We identified the peaks and geometry of ZIF-7 to determine if it had been successfully synthesized. We confirmed that ZIF-7 had a BET surface area of 303 m2/g, a significantly high Langmuir surface area of 511 m2/g, and a high CO2/N2 adsorption selectivity of approximately 50. Considering the gas permeation, with ZIF-7 mixed into Pebax-2533, N2 permeation decreased from 2.68 GPU in a pure membrane to 0.43 GPU in the membrane with ZIF-7 25 wt%. CO2 permeation increased from 18.43 GPU in the pure membrane to 26.22 GPU in the ZIF-7 35 wt%. The CO2/N2 ideal selectivity increased from 6.88 in the pure membrane to 50.43 in the ZIF-7 25 wt%. Among the membranes, Pebax-2533/ZIF-7 25 wt% showed the highest permeation properties and the characteristics of CO2-friendly ZIF-7.

Effect of Aggregate Roughness on Strength and Permeation Characteristics of Lightweight Aggregate Concrete

This paper aims to examine the effect of surface roughness of lightweight aggregate particles (LWA) on the strength and permeation characteristics of lightweight aggregate concrete (LWAC). Changing the smooth surface texture of LWA particles was achieved by applying surface polishing to make rough texture of the aggregate particle surface. LWAC mixes with different LWA surface roughness (smooth and rough) were produced, and their strength and permeation properties were investigated. Cut section method was adopted to measure the surface roughness of LWA particles. The surface profile was measured by using ImageJ software on images captured using the optical microscope (OM) and scanning electron microscope (SEM) with different magnifications. The ability of making the surface of LWA particles rough by polishing them was proved by means of 2D roughness measurements. From the results, it was found that using treated LWA with rough surface helped in enhancing the strength (compressive) and the permeation properties (water absorption and sorptivity) of lightweight aggregate concrete (LWAC). Making the LWA rough helped in improving the compressive strength by about 13.5% owing to enhancing the ITZ between the LWA particles and the cement paste as well as improving the chemical bonding and mechanical interlocking forces between them. In addition, using rough lightweight aggregate led to reduce the water absorption and cumulative volume of water absorbed by about 9% and 12%, respectively, compared to values of mix with original (smooth) LWA.

Determination of permeation properties of hydrogen gas in sealing rubbers using thermal desorption analysis gas chromatography

Permeation properties of hydrogen gas (H2) into nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM) which are the strong candidates for sealing material in H2 energy infrastructures, was quantified using a thermal desorption analysis gas chromatography (TDA GC) and a self-developed diffusion-analysis program. The samples were charged with H2 in a high-pressure chamber for 24 h then decompressed into atmosphere, and the mass of H2 released from the sample was measured as a function of elapsed time after decompression. The developed program calculated the total charging amount C0 and diffusivity D, which were then used to calculate the H2 solubility S and permeability P for variation of pressure. The samples were polymerized with and without carbon black (CB) filler in cylindrical shapes with different diameters. There was no appreciable pressure up to 12 MPa or diameter dependence investigated in this study on D, S and P. NBR and EPDM showed dual hydrogen diffusion with fast and slow diffusion behaviors caused by CB, whereas FKM showed a single diffusion behavior. The determined D are Dfast, NBR = (1.55 ± 0.28) × 10–10 m2/s, Dslow, NBR = (3.1 ± 0.5) × 10–11 m2/s, Dfast, EPDM = (3.65 ± 0.66) × 10–10 m2/s, Dslow, EPDM = (3.3 ± 0.5) × 10–11 m2/s, DFKM = (7.7 ± 0.8) × 10–11 m2/s. It appeared that the filler contributes to increase S and decrease D. The uncertainty analysis against the evaluated data was carried out, too, in order that the method could be applicable as a standard test for the permeation properties of various polymer membranes.

Effect of thickness and build orientation on the water vapor and oxygen permeation properties of laser-sintered polyamide 12 sheets

Purpose This study aims to investigate the effect of the material thickness and build orientation on the mass transfer of low molecular weight substances through polyamide 12 (PA12) structures produced by laser sintering (LS). Design/methodology/approach Disc-shaped PA12 sheets having a nominal thickness ranging from 700 to 2,000 µm were built in horizontal, vertical and diagonal orientations and their permeation properties to oxygen and water vapor were measured. The structural properties of the sheets were examined by X-ray micro-computed tomography, differential scanning calorimetry and polarized light microscopy. Findings All the LS sheets that were investigated had water vapor and oxygen permeation coefficients that are in the range of those of PA12 produced by traditional manufacturing technologies. Despite significant differences in the porosity characteristics, the permeation properties of sheets built in different orientations were similar. The pores seem to have no measurable effect on the mass transfer rates in the sheets, and the transport processes seem to predominantly follow the rules of a regular solution-diffusion mechanism. The results showed a non-significant trend toward thickness-dependent permeation coefficients, which agrees with the observed differences in the crystal structures of the sheets. Practical implications The results are an important basis for the qualification of LS technology for direct manufacturing in applications requiring special barrier performance. Originality/value This study provides new information on mechanisms of mass transport through LS PA12 and the effect of the material thickness and build orientation. Furthermore, the results enhance understanding of the structural properties of thin polymeric sheets produced by LS.