This paper presents the results from an experimental study on the optimum amount of polypropylene fibres to be used in lightweight high-strength concrete to prevent spalling when exposed to hydrocarbon fire, taking into consideration the characteristics of the lightweight aggregate, the water-to-cement ratio (W/C) of the mixtures, and the length and thickness of the fibres.Twelve different concrete mixtures were made. One block, 610x425x770 mm in size, was cast from each mixture and tested for fire resistance under hydrocarbon fire exposure. The temperature in the blocks during the test was recorded. After the test, the condition of the blocks was evaluated, and cores were taken for determining the residual compressive strength of the concrete.Results from the study show that close to 3.5 kg of the 20-mm polypropylene fibres per cubic meter of concrete is required to prevent the spalling of a low W/C lightweight concrete made with a silica fume-blended cement when subjected to hydrocarbon fire but that only 1.5 kg of the finer 12.5-mm fibres per cubic meter is sufficient.The amount of 20-mm fibres required to prevent spalling for a higher W/C of 0.42 is significantly less: of the order of 1.5 kg per cubic meter of concrete.The susceptibility of the concrete to spalling increases with the degree of absorption of the lightweight aggregate used in concrete.

The inclusion of air voids in the determination of total porosity for neat cellular concretes permits the determination of a single strengthporosity relation for a given cement. •This relation can be expressed in terms of water-cement ratio-and_ densil_y,_ thus providing_ a simp_le tool for the design of these concretes. L'inclusion des pores d'air clans la d~termination de la porosit~ totale pour les betons cellulaires purs nous permet de determiner une seule relation resistance/porosite pour un ciment donne. Cettc relation peut etre exprimee en fonction du rapport ~ et de la densite; ainsi elle nous donne un instrument simple pour le calcul de ces betons.

A rotating arm apparatus capable of circumferential speeds up to 475 m/s (Mach 1.4) has been used to make quantitative measurements of the velocity and angle dependence of ram erosion for a wide range of materials. It has been possible to relate the mechanical properties of some materials with their rain erosion resistance. The behaviour of the drops during impact has been studied by high speed photography.

The destruction free determination of the ageing status of a polymeric cable insulation is a significant issue in the assessment of the cable residual life. Ageing of apolymer changes the electrical, physical, mechanical and morphological properties of the insulation. Using the computer aided lsothermal-Relaxation-Current-Analysis (IRCAnalysis) the depolarization after dc poling of the insulation is measurable and the separation of different time dependant relaxation mechanisms is feasible. The machine intelligent diagnostic tools for the ageing classification and the residual strength prognosis of installed mediumvoltagecable is described. Withthecalibrationperformed inthe field at one of the major German cable manufacturers using destructive methods (voltage and water tree tests) and the development of the machine intelligent diagnostic software, a non-destructive test procedure for already installed XLPE cable systems is created. The diagnosis reliability ofthe IRC-Analysis based on several on-site tests is also discussed.