Assessing the recycling potential of glass fibre reinforced plastic waste in concrete and cement composites

Glass has many excellent properties, e.g. good chemical resistance. This is particularly evident in natural glasses but also in glasses made by human hand. The first period in this field of research is characterized by obtaining a great deal of empirical experience and the collection of data. The main dependences are to be found in the second period, while in the third period the physico-mathematical treatment begins, especially the interpretation of the chemical durability as a diffusion process. The present or fourth period is characterized by the use of new methods for analysing the leached glasses. This new knowledge and the critical judgement of the hitherto known results show that it is necessary to correct some existing conceptions. This is true especially with regard to the leached layers where the glass structure and H2O molecules seem to play an important role for the chemical durability. During leaching the structure of the glass is changed and the moving particles are altered, which means that some fundamentals for applying the usual diffusion equations are not valid. Therefore the fifth period of the chemical durability claims new ideas.

Chemical durability of glasses

Glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems containing up to 33 wt% ZrO2 were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO2 content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm−2 for the fibres containing 17 to 26 wt% ZrO2, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO2 showed higher resistance.

Preparation of glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems from metal alkoxides and their resistance to alkaline solution

Improvement of the mechanical properties of glass fibre reinforced plastic waste powder filled concrete

Changes in the strength and toughness of textile-reinforced concrete with increasing age are determined essentially by the durability of the armouring fibres, the matrix itself, and the bond between the matrix and the fibres. Based on new experimental results, important mechanisms influencing the durability of the fibre–matrix bond are treated in this article and discussed as to their significance. The investigations were conducted on multi-filament yarns of AR-glass which were imbedded in matrices of varying alkalinity and hydration kinetics. The loading capacity of the fibre–matrix bonds was determined in direct tension tests on under-reinforced specimens after they had undergone accelerated aging. Further, the condition of the microstructure between fibre and matrix was ascertained with both image analysis and analytical procedures. It was concluded that measured reductions in the toughness of the composite material could be attributed to the diminishing protective effect of organic polymer sizing on the surface of the filaments as well as to the disadvantageous new formation of solid hydration phases (mainly Portlandite) in the fibre–matrix interface.

Experimental investigations on the durability of fibre–matrix interfaces in textile-reinforced concrete

The rate of removal of ions from a zircono-silicate glass fibre by aqueous extracts of Portland cement has been experimentally determined. To accelerate the reaction, digestions have been carried out at elevated temperatures. The reaction rate for the glass composition investigated favours a log-time dependence. The reacted fibres show a relative enrichment of Zr on the surface, although no definite zirconia-containing phase has been identified. Soda-lime and borosilicate glass fibres which have been similarly examined for comparison purposes, required considerably shorter periods of digestion to produce suitable concentrations of glass breakdown products. The reaction rate for soda-lime glass appears to be largely controlled by Na+ diffusion. With borosilicate glass, no simple interpretation can be applied to the breakdown mechanism because of the complex nature of the reaction products. The significance of these results in the interpretation of the durability of zircono-silicate glass fibre cement composites is discussed.

K. Speakman

Papers

Chemical interactions between glass fibres and cement