Folke Björk

Degradation of components in flooring systems in humid and alkaline environments

Constituents from products that are used in the flooring on a concrete slab such as carpets of plasticised PVC and water-based adhesives sometimes degrade in an alkaline and humid environment. The concrete itself could be such an environment. In order to examine the effect of different levels of alkalinity and humidity on the mentioned products a specialised procedure was developed. By this procedure it was possible to imitate the effect of an environment of alkalinity and humidity corresponding to a recently produced concrete slab on different substances and also collect volatile degradation products produced. Degradation of some of the constituents was dependent on the levels of alkalinity and humidity, although there were significant differences in the possibility to resist the environmental factors. For some of the components, an increase in alkalinity resulted in a much higher production of degradation products even when the relative humidity was kept on a comparatively low level. The results give basis for a recommendation not to adhere plastic floorings directly to a recently produced slab of high-quality concrete because the alkaline material in the concrete could cause degradation.

Sustainable refurbishment in building technology

Purpose – The aim of this review article is to identify a number of key research efforts related to decision making tools in building refurbishment projects and selected energy efficiency efforts i ...

Measurement of alkalinity in concrete by a simple procedure, to investigate transport of alkaline material from the concrete slab to a self-levelling screed

A test procedure for measurement of alkalinity for cementitious materials that is, reliable, simple. and only needs a small amount of sample, was developed and applied to check whether transport of ...

Stress relaxation of a nitrile rubber surrounded by an oil that increases the network density

Abstract When a rubber item is subjected to a periodically varying deformation, the restoring force can exhibit a much more rapid decay than when the deformation is held constant. This is studied by dynamic mechanical stress relaxation. Based on well known relations from statistical rubber elasticity theory, a theory for the dynamic mechanical stress relaxation is proposed. In this paper it is shown that the special dynamic stress-relaxation behaviour has network degradation as its origin at elevated temperatures, and that data from measurements of continuous stress relaxation and intermittent stress relaxation can be related to results from measurements of dynamic stress relaxation. Results are reported from stress-relaxation measurements on nitrile rubber surrounded by a naphthenic oil with a gear-lubricant additive, which is found to be the origin of a reaction that increases the network density in the nitrile rubber.

Dynamic mechanical properties of single-ply roof coverings for low-slope roofs and the influence of water

Abstract The results of five different commercial single-ply roof-covering products for low-slope roofs, i.e. atactic polypropylene (APP)-modified bitumen, styrene-butadiene-styrene copolymer (SBS)-modified bitumen, ethylene-copolymerized bitumen (ECB), plasticized PVC and ethylene-propylene-diene-methylene (EPDM)-rubber, studied by dynamic mechanical thermal analysis are summarized in this paper. Two samples of each product were tested, one which had only been conditioned at 20 °C, 50% relative humidity, and another which had been immersed in distilled water at 50 °C for 4000 h. The difference in the dynamic properties at the glass transition region of the two samples is discussed. The influence of water immersion on material properties such as T g and T onset was observed for the products of APP-modified bitumen, SBS-modified bitumen and plasticized PVC. The changes in these material properties may have significance for the durability of the products. Dynamic mechanical thermal analysis can be a useful tool for characterizing products used for single-ply roof coverings of low-slope roofs. It may be useful in understanding how different types of products behave in application with different types of dynamic stresses.

Long-term studies of rubber materials by dynamic mechanical stress relaxation

Abstract The measurement of dynamic stress relaxation can reveal otherwise hidden weaknesses in rubber materials. The stress relaxation of the minimum of the restoring foce has the undesirable characteristic of being greater than the continuous stress relaxation. An increase in the amplitude of the deformation increases the decay in the minimum values of the varying retractive stress, and an increase in the prestrain makes it smaller. The normalized curve for continuous stress relaxation is found to lie somewhere between the normalized curves for the maximum and minimum of the retractive stress. The measurement of network density on specimens aged under continuous and dynamic stress relaxation indicate that the mechanism behind the degradation of the rubber network is the same in both cases. The relations between intermittent, continuous, and dynamic stress relaxation give a reasonable estimate of the dynamic stress relaxation from the other two when proper values of the coefficients are used. This relati...

Influence of the formation of an oxidized layer on the dynamic-mechanical properties of natural rubber

Abstract Natural rubber cylinders vulcanized with two different systems, TMTD and S/CBS, were aged for more than 2000 h in an air oven at 100 °C. During the ageing an oxidized layer formed on the surfaces of the specimens. To study the differences between the interior of the materials and their surfaces, and to find out how the interior of the materials was affected by the ageing, measurements were performed both on whole specimens and on specimens from which the surface layer had been removed. Dynamic mechanical (complex) modulus and loss-angle were recorded intermittently. The surface layer was hard and brittle because of thermo-oxidative crosslinking and probably had a low permeability to oxygen. The modulus of the interior material decreased slightly during the ageing. After ageing, the specimens cracked easily during deformation. The difference between surface and interior was greater, and the formation of the surface layer started earlier, when the material was vulcanized with S/CBS.

Joints between roofing felt and sheet metal flashings —short- and long-term tests

The adhesion between roofing felt and sheet metal flashings has been measured and analysed and test methods for this have been developed. Both bituminous and polymeric roofing felts have been used. The steel has been PVC-coated galvanised steel sheets and the bituminous roofing felts have been of both SBS and APP modified type. All the joints have been made with heat welding. The tests show that it is possible to obtain joints with sufficient strength using the contractors ordinary welding procedures.

Wind load resistance of heat-welded seams in polymer-modified bituminous roofing membranes

Abstract The aim of the study was to evaluate the wind load resistance of heat-welded seams in polymermodified bitumen for roofing membranes and to investigate the fracture behaviour of seams subjected to wind load. Wind load resistance tests of two commercial polymer-modified bituminous roofing products, namely cne styrene-butadiene-styrene copolymer (SBS)-modified bituminous product and one atactic polypropylene (APP)-modified bituminous product, were carried out in accordance with the Nordtest Method NT BUILD 307. The results showed that for the SBS product heat-welded seams of only 30 mm width could resist a wind load of over 4900 N m 2 . However, the welding of seams more than 100 mm wide, which is recommended by material manufacturers, is necessary to avoid peeling stress in the seam caused by wind uplift, since the peel strengths of polymer-modified bituminous roofing membranes are lower than their shear strengths. It was also concluded that for APP products the welding work must be carried out more carefully by allowing for pressure roller weight and welding speed.

Air gaps in building construction avoiding dampness and mould

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. The patented Air Gap Method, which is a slight modification of the common infill wa ...