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For unstable grout, particles will come out of the grout suspension leading to incomplete grouting and clogging of pipes. The stability of grout can be improved by adding additives such as bentonite. However, bentonite should not be used with very fine cements because its grain size is bigger than that of fine cements. Tests conducted previously confirm that a grout with bentonite is less stable under pressure.
It is commonly accepted that a fissure may be penetrated by grout with the grain size about 3-5 times smaller than the aperture of fissure. Hence, OPC cement may penetrate fissures of aperture greater than 0.4mm while microfine cement and ultrafine cement may penetrate fissures of aperture greater than 0.1mm and 0.03mm respectively.
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