MAS NMR Studies of Partially Carbonated Portland Cement and Tricalcium Silicate Pastes

Abstract

29 Si, 27 Al, and 1 H MAS NMR studies of partially carbonated mature ordinary Portland cement (OPC) and tricalcium silicate (C 3 S) pastes have been carried out. The water‐to‐solid ratios ( W/S ) have been varied between 0 and 1 at hydration temperatures of 23 o and 90 o C. Various Q n i units with n =0, 1,2,3, and 4, and a Q 3 (1Al) group have been identified using 29 Si NMR. Cross‐polarization experiments, in addition, have made it possible to assign the OH groups. Two types of fourfold‐ and one type sixfold‐coordinated aluminum have been distinguished using 27 Al NMR. In C 3 S pastes for w/s >0.7, progressive carbonation leads to a nearly perfect three‐dimensional network consisting of Q 3 and Q 4 only. In contrast, in OPC pasted only about 40% of the highly polymerized silicate units are formed, partially copolymerized with AlO 4 tetrahedra.