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Micro-sillies effect on fiber cement products
One of the most important reasons of using micro sillies on fiber cement products is the ability to complete the pozzolanic reaction
The word pozzolan comes from the name of ancient Italian city pozzuli in which soft volcano ashes were found that are usually mixed with calcium oxide to produce cement. As it is illustrated in figure 1 pozzolan with lime or calcium hydroxide Ca(OH)2 and water forms the paste of calcium silicate hydrate or CSH. This reaction is similar to the binding part of cement hydration. The hydration of type 1 Portland cement produces about 20% lime. Lime or calcium hydroxide is a week and dissolving material that does not contribute to resistance. The reaction between micro-sillies and the lime produced in hydration process produces paste and causes more resistance.
Figure1- micro-sillies with lime or calcium hydroxide and water produces paste phase of calcium silicate hydrate.
One of the other reasons to use micro-sillies is to fill the microtomic holes in the product:
The infinitely small size of micro-sillies fills the relatively big holes between the cement pieces and causes an increase in the resistance and durability. (Fig2 and 3)
Fig2: filler effect of micro-sillies on microtomic holes in fiber cement boards.
Fig3: the effect of different volumes of micro-sillies use in the bulk and diameter of holes in air cured fiber cement boards.
One of the other reasons to use micro-sillies on fiber cement products is to enhance the bending strength and the density and to reduce water absorbent:
In figures 4, 5 and 6 the effect of micro-sillies on the bending strength, density and water absorbent of fiber cement products are shown. Every 1% increase in micro-sillies use in fiber cement products causes an increase in bending strength by 0.5 Mpa or 5kg/cm2. Micro-sillies also causes an increase in plasticity in green sheets and prevent cracks happening while bending the corrugated sheets.
Fig6: the effect of different percentage use of micro-sillies on water absorbent of fiber cement boards.
Fig5: the effect of different percentage use of micro-sillies on the weight of fiber cement boards.
Fig4: the effect of different percentage use of micro-sillies on the bending strength of fiber cement boards.
The last main reason to use micro-sillies is to increase the freeze-thaw cycles of the product:
Freeze-thaw cycles causes expansion in the product which leads to the gradual separation of the layers in fiber cement products. Micro-sillies causes an increase in the cohesion between the layers and increases the freeze-thaw cycles. By increasing the use of micro-sillies by 5% swelling of the product after 700 freeze-thaw cycles in free air decreases by a factor of 1.3. For products which are made by auto claw by increasing the use of micro-sillies by 5% swelling of the thickness of the product after 1000 freeze-thaw cycles decreases by one third of the original amount.
Fig7: the effect of different percentage use of micro-sillies on the swelling of the thickness of fiber cement boards.
Fig8: the effect of different percentage use of micro-sillies on the swelling of the thickness of fiber cement boards produced by auto claw method.
