- volume ▁applications . ▁This ▁is ▁also ▁the ▁case ▁for ▁E MC ▁made ▁from ▁natural ▁po zz ol ans ▁( e . g ., ▁vol can ic ▁ash ). ▁ ▁Vol can ic ▁ash ▁depos its ▁from ▁Southern ▁California ▁were ▁independently ▁tested ; ▁at ▁ 5 0 % ▁Port land ▁c ement ▁replacement , ▁the ▁resulting ▁con cre tes ▁exceed ed ▁requirements . ▁At ▁ 2 8 ▁days , ▁the ▁compress ive ▁strength ▁was ▁ 4 , 1 8 0 ▁p si ▁/ ▁ 2 8 . 8 ▁M Pa ▁( N / mm ²). ▁The ▁ 5 6 - day ▁strength ▁exceed ed ▁the ▁requirements ▁for ▁ 4 , 5 0 0 ▁p si ▁( 3 1 . 1 ▁M Pa ) ▁concrete , ▁even ▁taking ▁into ▁account ▁the ▁safety ▁margin ▁as ▁recommended ▁by ▁the ▁American ▁Con crete ▁Institute . ▁The ▁concrete ▁made ▁in ▁this ▁way ▁was ▁work able ▁and ▁sufficiently ▁strong , ▁exceed ing ▁the ▁ 7 5 % ▁standard ▁of ▁po zz olan ic ▁activity ▁at ▁both ▁ 7 ▁days ▁and ▁ 2 8 ▁days . ▁ ▁The ▁surface ▁smooth ness ▁of ▁po zz ol ans ▁in ▁the ▁concrete ▁was ▁also ▁increased . ▁ ▁Dur ability ▁of ▁con cre tes ▁produced ▁and ▁high - per formance ▁con cre tes ▁( HP C s ) ▁Tre ating ▁Port land ▁c ement ▁with ▁E MC ▁activation ▁will ▁yield ▁high - per formance ▁con cre tes . ▁These ▁H PC s ▁will ▁be ▁high ▁strength , ▁highly ▁dur able , ▁and ▁exhib iting