Assessment of concrete cover quality is necessary for proper maintenance of concrete structures. Concrete durability is evaluated primarily based on chloride penetrability, neutralization and other external factors. The present study attempts to analyze concrete quality and its mass transfer resistance performance by measuring the air permeability and its relation with concrete durability indicators like chloride diffusion and neutralization. The applicability of air permeability as a durability indicator is validated using concrete with different materials, parameters and curing conditions. The tests are conducted on laboratory prepared concrete as well as for concrete exposed to actual marine conditions. From the experimental results, it is found that air permeability coefficient, neutralization coefficient and chloride ion diffusion coefficient have high correlation. It is suggested that air permeability could be considered as an alternative to estimate mass transfer resistance of concrete and as a concrete durability indicator.

This manuscript elucidates the mechanisms responsible for aging-induced reduction in lead leaching from scrubber residues. Leaching tests (JLT13) were conducted on 48 types of scrubber residues and lead solubility was found to be significantly reduced independent of incinerator type or type of gas treatment method. Reaction kinetics that result in lead solubility reduction were shown to be proportional to carbon dioxide partial pressure and in many cases were limited by mass transfer to the residue. With forced gas convection through the residue and a CO2 partial pressure of 0.3%, the concentration of lead in leachate was reduced from 84 mg L(-1) to < 0.5 mg L(-1) in two days. Ettringite analogs (Ca6Al2 (SO4) 3(OH)2 . 26H2O) were identified by X-Ray Diffraction in the wetted scrubber residues early in the aging process; these appear to have been converted into gypsum (CaSO4 . 2H2O) and vaterite (CaCO3) in the aged material. All of these solid phases are believed to substitute lead into their crystal structure and evidence for this attenuation mechanism is presented.

Good weld quality requires control of weldpool width and cooling time. The cooling time t 8/5 (from 800 °C to 500 °C) is related to the weld metal hardness. The weld metal is affected by rapid heating and rapid cooling, with various metallographic structures being formed. An important factor is appropriate selection of the cooling time to obtain a good structure and suitable strength after welding. The cooling time is strongly affected by the heat input (arc voltage U, welding current I, welding speed S, and heat input efficiency η).Numerical simulations of TIG pipe welding were initially performed by the finite difference method on the basis of heat conduction theory. The weldpool width and cooling time were then calculated at various welding currents and welding speeds. A weldpool model was constructed by a neural network using the above data as teaching signals. The welding speed and welding current were determined to obtain the required weldpool width and cooling time using the neural network model.

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