▁the ▁alk ali - sil ica ▁reaction , ▁a ▁slow ▁de grad ation ▁process ▁causing ▁the ▁sw elling ▁and ▁the ▁crack ing ▁of ▁concrete ▁containing ▁aggreg ates ▁rich ▁in ▁re active ▁am orph ous ▁sil ica . ▁In ▁a ▁very ▁similar ▁way , ▁Na OH ▁greatly ▁facil it ates ▁the ▁dissol ution ▁of ▁the ▁am orph ous ▁sil ica . ▁The ▁produced ▁sod ium ▁sil icate ▁then ▁react s ▁with ▁the ▁calci um ▁hydro x ide ▁( port land ite ) ▁present ▁in ▁the ▁hard ened ▁c ement ▁paste ▁to ▁form ▁calci um ▁sil icate ▁hyd rate ▁( ab bre vi ated ▁as ▁C - S - H ▁in ▁the ▁c ement ▁chem ist ▁notation ). ▁This ▁sil ic ification ▁reaction ▁of ▁Ca ( OH ) 2 ▁on ▁its ▁turn ▁continu ously ▁releases ▁again ▁sod ium ▁hydro x ide ▁in ▁solution , ▁maintain ing ▁a ▁high ▁p H , ▁and ▁the ▁cycle ▁continues ▁up ▁to ▁the ▁total ▁disapp earance ▁of ▁port land ite ▁or ▁re active ▁sil ica ▁in ▁the ▁exposed ▁concrete . ▁Without ▁the ▁catal ysis ▁of ▁this ▁reaction ▁by ▁sod ium ▁or ▁pot ass ium ▁sol ub le ▁hydro x ides ▁the ▁alk ali - sil ica ▁reaction ▁would ▁not ▁proceed ▁or ▁would ▁be ▁limited ▁to ▁a ▁very ▁slow ▁po zz olan ic ▁reaction . ▁The ▁alk ali ▁sil ica ▁reaction ▁can ▁be ▁written ▁like ▁the ▁s oda ▁l ime ▁reaction , ▁by ▁simply ▁subst itut ing ▁CO 2 ▁by ▁Si O 2 ▁in ▁the ▁re actions ▁mentioned ▁here ▁above ▁as