| The problem lies in the fact that concrete produces lime during the hydration process.: |
| OPC(Ordinary Portland cement) +H20 -> CSH + Ca(OH)2 (Lime) |
Lime, calcium hydroxide, is extremely aggressive and severely attacks both the surface and molecular structure of conventional E-glass fibers.The E-glass rapidly loses its ability to sustain loads because the alkali in the concrete corrodes the fiber. |
| Alkali Resistant glass fiber, or AR fiber, is a specially formulated engineered fiber and zirconia (in form of ZrO2) was added into the glass. It was designed specifically for use in concrete and mortars and are stable in this aggressive lime environment (usually PH=12). Since it is special, it is expensive - over two times as much as E-glass.
The AR glass have the following advantages in the concrete: |
> The AR glass is itself alkali resistant, It does not depend on any coating. |
| > Fine individual filaments: a very large number of fibers are released when mixed in the concrete. and the filament do not protrude from the surface and be invisible when the concrete surface weathers |
| > Have a high tensile strength to withstand stresses during shrinkage |
| > Have a high modulus of elasticity to absorb shrinkage stresses before the concrete cracks. |
| > Have a superior bond(mineral/mineral interface) with the concrete |
| > Present no health hazards. |
| > AR glass fibers reinforce both plastic and hardened concrete |
While not all AR glass fiber is equal, the alkali resistance of glass fiber depends principally on the content of Zirconia (ZrO2) in the glass, The higher the zirconia content the better the resistance to alkali attack. So please remember--choose an experienced supplier who could supply AR glass fiber with high zirconia content(16% min.)
The followings please find more details of Alkali Resistant glass fiber:
AR glass fiber spray roving to be used in GRC/ GFRC
AR glass chopped strand for premix use
AR glass HD fiber for concrete anti-crak and asbestos replacement in fiber cement sheet products.
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