Air entrainment was discovered by accident from the mid-1930s.[two] At that time, cement manufacturers were using a grinding help to reinforce the whole process of grinding cement. This grinding support was a mixture of various chemicals, like salts of wood resin, which were being included to the cement in the https://spherical-tungsten-powder37148.oneworldwiki.com/6808891/what_does_fibre_reinforcement_mean