Change in microstructure and compressive strength of alkali-activated slag paste at temperature exposure of 50°C

This paper presents a study on the evolution of strength and alteration microstructure of alkali-activated slag (AAS) pastes exposed to 50°C. Ground granulated blast furnace slag (GGBFS) was used as thestarting material to prepare slags pastes which were then activated with a range of activators. The preliminary results from the study of these pastes are presented. It was found that all the pastes show a significantlystrength loss after exposure to 50°C for 24 hours. This is independent on the activators used. The paste samples were further examined by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electronmicroscopy (SEM) and sorptivity tests. A hypothesis for strength loss is proposed based on the observations in change of microstructure. This hypothesis will be further validated by the study of the AAS pastesprepared by using phosphorus slags.

Free and restrained shrinkage behaviours of OPC and slag concretes with admixed polypropylene fibres

This paper presents the results of an investigation that studied the effects of admixed polypropylene (PP) fibres on the long-term drying shrinkage of hardened concrete. Five concrete mixtures, made with 100% Ordinary Portland Cement (OPC) as the binder and containing different volume fractions of PP fibre (0%, 0.05%, 0.1%, 0.2% and 0.5%) were tested. Also, three concrete mixtures were made with 65 % slag-blended cement binder incorporating 0% and 0.2% volume fraction of PP. The results show higher water loss and higher drying shrinkages in concretes that incorporate PP fibres than concrete without fibre. The results of early age cracking tendency of slag concrete, with and without fibre, under fully restrained and drying conditions, show that that PP fibre concrete had higher cracking tendency than concrete without fibre. Higher cracking tendency of PP fibre concrete was due to higher drying shrinkage and elastic moduli.

Ammonia dissociation in the fluidised bed furnace

Ammonia dissociation is the controlling reaction for several important thermochemical heat treatment processes; nitriding, nitrocarburising (ferritic and austenitic) and carbonitriding. The fluidised bed furnace is a convenient and widely used medium for all of these treatments, yet understanding of the reaction in a fluidised bed context is minimal. This paper deals with the influence of process parameters on nitrogen activity aN; temperature, fluidising flowrate, ammonia inlet level, carbonaceous gas. Two basic behaviours were observed; inlet NH3-dependant and inlet NHr insensitive, with a transition region at intermediate temperatures. The nitrocarburising response of steel specimens was measured by optical microscopy of the layer thicknesses and glow discharge optical emission spectroscopy (GD-OES) determination of nitrogen depth-penetration profiles. aN was found by gas analysis of the exit stream ammonia with the aid of a dissociation burette.

Reduction of fuel consumption in an industrial glass melting furnace

Reduction of fuel consumption in glass melting furnaces can cut the cost of production, and tackle the global warming. This paper presents three independent solutions to reduce the fuel consumption in industrial glass melting furnaces. The solutions include air preheating, raw material preheating, and improving the insulation of combustion space refractory. Energy balance equations are derived and used to identify the effects of each solution. The results indicate that the three solutions reduce the fuel consumption by 9.5%, 17%, and 34%, respectively.