Air Entrainment was discovered accidentally during the mid-1930s.[two] At that time, cement manufacturers had been utilizing a grinding assist to improve the process of grinding cement. This grinding aid was a mix of varied chemicals, including salts of wood resin, which were additional on the cement throughout the grinding approach. https://johnathankvelt.tdlwiki.com/1506640/5_simple_techniques_for_naphthalene_sulfonate_in_concrete