Durability modelling of glass fibre reinforcement in cementitious environment

Abstract

A main topic of consideration for glass-fibre reinforced cementitious composites is their durability. Recent developments of new cementitious matrices and advances in chemical composition and sizing of glass fibres lead to increased durability of cementitious composites with glass fibre reinforcement. Still, the relative importance of the main degradation mechanisms is not fully understood. A joint experimental program at RWTH-Aachen (Germany) and VUB-Brussels (Belgium) shows that the pH of the matrix has a considerable influence on the durability of the studied composite. Recent investigations on single filaments in high alkalinity solutions and on rovings in concrete show that filaments lose strength mainly due to chemical attack in local weak points of the glass structure. Once this chemical attack becomes diffusion controlled, further corrosion slows down to a considerably lower rate. The aim of these investigations is to finally build a model, allowing prediction of the long-term behaviour of textiles -made of glass filaments -in concrete, which is based on the physico-chemical background of degradation.1359-5997 9 2004 RILEM. All rights reserved. RI~SUME M~me ~ ce jour, la durabilit~ reste une consideration importante clans l'usage des composites h matrice cimentaire renforc~s par des fibres de verre. Les d~veloppements rOcents en matiOre de matrices cimentaires et les progrks r~alisOs dans le domaine de l 'ensimage des fibres de verre ont d~j~ abouti ~ une amelioration de la durabilitO des composites eimentaires renforc~es par des fibres de verre, mais l'importance relative des m~canismes de dOgradation n 'est pas encore ~tablie. R WTH-Aachen (Allemagne) et ULB-Brw

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

“…The following degradation processes are generally reported in the literature: -Corrosion of the fibre material itself due to attack of OH À ions in the pore solution [8][9][10][11][12]. -Static fatigue (delayed failure) of the glass fibre under sustained load in the highly alkaline environment [13][14][15][16][29][30][31][32][33]. -Densification of the matrix adjacent to the filaments and enhancement of the fibre-matrix bond with continued hydration and precipitation of hydration products in the interface between filaments and matrix as well as in empty spaces between the filaments of multi-filament yarn (bundle filling) [4,[17][18][19][20][21][22][23]36].…”

“…The delayed failure of glass fibres is supposed to dominate the other mechanisms according to [29][30][31][32][33]. Purnell [29,30] proposed a static fatigue model to explain the losses in strength of artificially aged GRC, which had been described empirically by Litherland's model [28] before.…”

“…Orlowsky et al [31][32][33] enhanced the static fatigue model by introducing two reaction rate coefficients. These coefficients describe on the one hand the kinetic part of the defect growth (which is due to reactions between stressed glass and water or OH À ) and on the other hand the diffusion-controlled part of damaging process (transport of water or OH À to the defect tip, increasingly hindered by the deposit of recondensed silanol groups) [31].…”

“…These coefficients describe on the one hand the kinetic part of the defect growth (which is due to reactions between stressed glass and water or OH À ) and on the other hand the diffusion-controlled part of damaging process (transport of water or OH À to the defect tip, increasingly hindered by the deposit of recondensed silanol groups) [31]. The model parameters were ascertained by fitting to test results obtained for filaments, yarns as well as composite materials subjected to different aging regimes.…”

“…Already at small displacements of the filaments the Portlandite crystals as well as the brittle shells around the filaments tend to shatter, wedge themselves unfavourably, and exert notching at the filaments and lateral punctual pressure. Furthermore, chemomechanical notching at the fibre surface [11] as well as growth of surface defects (invisible in ESEM) may occur [29][30][31][32][33]. All these effects can lead, separately or in combination with one another, to failure of the filaments even at relatively low loads.…”