Surface studies of hydrated β-C2S

ESCA (electron spectroscopy for chemical analysis) studies of β-C₂S in the early stages of hydration have yielded valuable information on the chemical changes on the hydrating surface. These changes are less pronounced than, but very similar to, those noted for C₃S. The data indicate that, although β-C₂S hydrates more slowly than C₃S, the same hydration mechanism applies to both. The studies also suggest surface hydroxylation as a first step in the hydration process.     

Towards quality requirements via animated formal specifications

Assuring a high quality requirements specification document involves both an early validation process and an increased level of participation. An approach and its supporting environment which combines the benefits of a formal system specification and its subsequent execution via a rapid prototype is reported. The environment assists in the construction, clarification, validation and visualisation of a formal specification. An illustrative case study demonstrates the consequences of assertions about system properties at this early stage of software development. Our approach involves the pragmatic combination of technical benefits of formal systems engineering based techniques with the context‐sensitive notions of increased participation of both developer and user stakeholders to move us closer towards a quality requirements specification document.     

An electro-optic holography system with real-time arithmetic processing

This paper reports the use of a real-time arithmetic image processor in an electro-optic holography system. A speckle interferometer is used to combine an image of an object, lit by laser light, with a mutually coherent reference beam. A CCD TV camera detects the interference pattern, and the phase of the reference beam is advanced by 90° between frames. An image is generated from each set of four sequential TV frames by subtracting alternate frames, squaring, and adding the two results. The result is improved picture quality compared with the use of binary pixels and compared with electronic speckle pattern interferometry. Experimental results are shown.     

The influence of profiled sheeting thickness and shear connector’s position on strength and ductility of headed shear connector

A three-dimensional finite element model is developed, validated and used in the parametric study to investigate the influence of shear stud’s position and profiled sheeting thickness on the strength, ductility and failure modes of the headed shear stud welded to the modern profiled sheeting. A total of 240 push tests were analysed with different sheeting thicknesses, positions of the shear stud in the trough, concrete strengths and transverse spacings. The results showed that the sheeting thickness influenced the shear connector resistance of studs placed in the unfavourable position more than studs placed in favourable and central positions. The strength of the shear connector placed in the unfavourable position increased by as much as 30% when the sheeting thickness was increased. The shear connector resistance of the unfavourable stud was found to be primarily a function of the strength and the thickness of the profiled sheeting rather than the concrete strength. The strength prediction equations for unfavourable and central studs were also proposed. The results suggested that the strength of the shear connector increased as the distance of the shear stud increased from the mid-height of the deck rib in the load bearing direction of the stud. The load-slip behaviour of the studs in the unfavourable position was more ductile than the studs in the favourable position, with slip of 2-4 times higher. It was found that the increase in sheeting thickness and transverse spacing improved the ductility of the stud in unfavourable position, but had no effect on the stud in the favourable position. The failure modes suggested that the favourable and central studs failed by concrete cone failure and unfavourable studs failed by rib punching together with crushing of the narrow strip of the concrete in front of the stud.     

Effects of calcium fluoride mineralization on silicates and melt formation in portland cement clinker

The mineralizing effect of 0.5% F^? as CaF₂ on the high-temperature reactions in the quaternary system CaOAl₂O₃Fe₂O₃SiO₂ was studied in the presence of minor amounts of MgO and K₂SO₄. The partitioning of fluorine between the calcium aluminate and calcium silicate phases was determined in relation to the burning temperature and the presence of MgO.     

Effect of gypsum on C3S hydration

The effect of gypsum on the early stages of C₃S hydration is explored by means of DTA, high-resolution STEM, and liquid phase studies.     

Determination of fluoride in cement and related materials

This paper describes the determination of fluoride in cement and cement-related materials using a fluoride ion selective electrode. Different sample preparation methods and complexing buffers were investigated. It was concluded that the fluoride electrode offers a rapid and accurate method for fluoride determination in cement and cement-related materials when a suitable buffer medium capable of complexing Si, Al, and Fe in the solution is used. Sintering with Na₂CO₃6ZnO is preferable to LiBO₂ fusion for decomposing materials high in SiO₂, Al₂O₃ and Fe₂O₃. However, the latter method is more rapid and gives the same results as the former method for samples with relatively low SiO₂, Al₂O₃ and Fe₂O₃ contents.     

Experimental and Numerical Analysis of Heat Transfer in a Tall Vertical Concentric Annular Thermo-siphon at Constant Heat Flux Condition

The present work deals with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon. Spatio-temporal behavior of fluid flow is also studied for variety of heat fluxes. The annuli in the present study have a radius ratio of 1.184 and aspect ratio (length to annular gap) equal to 352. The objective of the present work is to quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient. Experiments have also been conducted on a similar system with water at constant heat flux of 1 kW/m², 2.5 kW/m², 5 kW/m², 7.5 kW/m², 10 kW/m², 12.5 kW/m² and 15 kW/m². For numerical purpose, a two-dimentional solver has been developed for direct numerical simulation of the essential thermally induced flow dynamics The numerical solution was thus performed for Rayleigh numbers ranging between, 4.4 × 10³ and 6.61 × 10⁴ which correspond to the given heat flux, respectively.