Thermodynamics of geopolymer reaction • N-C-A-S phase equilibria • Identification and characterization of geopolymer gel and C-A-S-H • Our work, results and conclusions SC1, NTU, July 2014, ljs 1 N-C-A-S Phase Equilibria SiO2 (N,C)-A-S-H [Ca] C-A-S-H CH+AFm+ C1.94A0.96SHx CaO C0.72A0.1SHxC0.95A0.06SHx(SS)+ C2ASH8 C-A-S-H (Q1,Q2) (N,C)-A-S-H (Q4) pH C2ASH8 C0.95A0.06SHx+ C2ASH8+AFm Al2O3 SC1, NTU, July 2014, ljs Both figures redrawn from Garcia-Lodeiro et al. 2 Effect of calcium • Addition of calcium increases strength • Addition of calcium shortens set time SC1, NTU, July 2014, ljs 3 Reaction Kinetics Provis and van Deventer CEE502, ljs, 2011 Our Work • Produced geopolymers using metakaolin, calcium hydroxide, sodium hydroxide, sodium silicate • Characterized using MAS-NMR, SEM • pH not controlled, but all syntheses at same high pH SC1, NTU, July 2014, ljs 5 IV V MK Q4 GP Si/Al 1.5 GP Ca/Si 0.15 QP Q3 VI 27Al NMR Results • MK has IV-, V-, and VIcoordinated Al • GP has peak attributed to gel (Q4) • GP with Ca has peak attributed to gel (Q4) and peaks attributed to C-A-S-H (Q2B and Q3) Q2B Kim SC1, NTU, July 2014, ljs 6 Q4(0Al) Q4(2Al) 29Si MK Q4(2Al) GP Si/Al 1.5 Q4(1Al) Q4(3Al) Q4(0Al) Q4(4Al) GP Ca/Si 0.15 Q2(1Al) NMR Results • MK has two peaks • GP has peaks attributed to MK and gel— 10% MK and 90% gel with Si/Al 1.55 • GP with Ca has peaks attributed to MK, gel, and CA-S-H—10% MK, 49% gel with Si/Al 1.45, and 41% C-A-S-H with Si/Al 3.54 Q1(0Al) Kim Q2(0Al) Q3(0Al) Q3(1Al) SC1, NTU, July 2014, ljs 7 Quantitative 29Si Results Kim SC1, NTU, July 2014, ljs 8 Conclusions from Our Work • It is possible to identify and characterize phases in geopolymers • C-A-S-H and geopolymer gel both produced when geopolymer reaction includes calcium • Addition of Ca reduces Si/Al in geopolymer gel • No evidence that N-A-S-H forms only at low pH • Not clear whether Ca incorporated in geopolymer gel SC1, NTU, July 2014, ljs 9