The invention discloses a modified
metakaolin-based
permeation-resistant and crack-resistant agent for concrete. The modified
metakaolin-based
permeation-resistant and crack-resistant agent for concrete comprises: by
mass, 10 to 75% of modified
metakaolin, 5 to 40% of fine limestone
powder, 4 to 40% of superfine
coal ash, 1 to 20% of calcined
hydrotalcite, 2 to 40% of fine
quartz sand and 0.2 to 20% of
solid silane powder. A preparation method of the modified metakaolin comprises the following steps of putting dry and washed kaolin into a bowl mill, carrying out
grinding to obtain kaolin
powder, carrying out
calcination of the kaolin powder at a temperature of 500 to 1000 DEG C for 0.5 to 6.0 hours to obtain metakaolin, putting the metakaolin into a dispersion
machine, adding an organic modifier of sulfamate or
triethanolamine into the metakaolin, wherein a
mass ratio of the metakaolin and the organic modifier is in a range of (5000: 1) to (100: 1), and carrying out dispersion to obtain the modified metakaolin having a
contact angle of 50 to 100 degrees and a specific surface area of 8000 to 15000m<2> / kg. The modified metakaolin-based
permeation-resistant and crack-resistant agentfor concrete can be utilized as a concrete additive, improves strength of concrete at different ages, does not produce obvious influences on concrete
work performances, obviously improves anti-
chloride ion penetration capability of concrete, reduces total shrinkage of concrete and improves
crack resistance of concrete.