Effect of Corrosive Solutions on C-S-H Microstructure in Portland Cement Paste with Fly Ash

By means of;Si and;Al magic angle spinning nuclear magnetic resonance（MAS NMR） combined with deconvolution technique, X-ray diffraction（XRD）, scanning electron microscopy（SEM） as well as energy dispersive X-ray system（EDX）, the effect of 5 wt% corrosive solutions( viz. 5 wt% Na;SO;, MgSO;, Na;SO;sup>4+Na Cl and Na;SO;sup>4+Na Cl+Na;CO;) on C-S-H microstructure in portland cement containing 30 wt% fly ash was investigated.The results show that, in MgSO;solution, Mg2+ promotes the decalcification of C-S-H by SO;,increasing silicate tetrahedra polymerization and mean chain length（MCL） of C-S-H. However, the substituting degree of Al;for Si;（Al[4]/Si） in the paste does not change evidently. Effect of Na;SO;solution on C-S-H is not significantly influenced by Na Cl solution, while the MCL and Al[4]/Si of C-S-H in fly ashcement paste slightly change. However, the decalcification of C-S-H by SO;and CO;attack, as well as the activation of fly ash by SO;attack will increase the MCL and Al[4]/Si, which are both higher than that under Na;SO;corrosion, MgSO;or Na;SO;+Na Cl coordination corrosion.