Major Improvements in Long-Term Strength and Toughness of Glass Fiber Reinforced Concrete


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Title: Major Improvements in Long-Term Strength and Toughness of Glass Fiber Reinforced Concrete

Author(s): P. Soukatchoff

Publication: Special Publication

Volume: 190


Appears on pages(s): 165-182

Keywords: alkali resistance; flexural strength; glass fiber cement composites; portland cement; silica fume

Date: 4/1/2000

It is well known that glass fiber cement composites may suffer a loss of strength and toughness when exposed to natural environments. Even though buildings in Europe clad with GFRC panels have performed well for nearly 30 years now, this has restricted its use in certain circumstances because of a lack of confidence on behalf of the designer and specifiers. The loss of long term properties of GFRC is explained by two main phenomena: 0 The chemical attack of the glass fibers. 0 The morphological modification of the interfaces due to the growth of hydrates (Ca(OH)2 + CSH) which leads to em brittlement of the fibers in the matrix. The most widely used solution against the first type of attack is to use Alkali Resistance, AR, glass fibers with Cem-FIL being the original and Cem-FIL 2 giving the best long-term results. However, the way to obtain both constant flexural strength and ultimate strain (toughness) is to use both AR fibers and to modify the cementitious matrix in order to optimize the nature of the hydrate in the interface between the fiber and the matrix. Until recently, no totally satis-factory solution has been found even with the use of low alkali cements such as calcium sulpho-aluminate cement or portland cement with silica fume or flv ash. The CEM-FIL Star mix, developed by the Saint-Gobain group some 1 0 years ago, now has worldwide experience. It is based on using AR fiber with a specific type of the manmade, and therefore controllable, pozzolanic mate-rial, metakaolin, with a portland cement matrix. This reacts in a controllable way with the liberated lime, (calcium hydroxide), thus eliminating the main reason for the embrittlement of GFRC with time. By reacting with and re-moving this lime, long-term properties are improved.