Air entrainment was found by accident in the mid-1930s.[2] At that time, cement manufacturers have been using a grinding help to reinforce the whole process of grinding cement. This grinding aid was a mixture of various chemicals, together with salts of wood resin, which were additional on the cement during https://3d-filament37036.angelinsblog.com/34478430/helping-the-others-realize-the-advantages-of-concrete-foaming-machine