MICROSTRUCTURE, STRENGTH, AND REACTION-PRODUCTS OF GROUND GRANULATED BLAST-FURNACE SLAG ACTIVATED BY HIGHLY CONCENTRATED NAOH SOLUTION

Ground granulated blast-furnace slag was reacted in 5 M (pH 14.7) and 1.5 M (pH 14.2) NaOH solutions at a water/slag ratio of similar to 0.4 , and characterized by unconfined compressive strength testing, scanni ng electron microscopy, energy dispersive spectroscopy, and x-ray diff raction. The reacted material consisted of a dense layered matrix inte rspersed with unreacted glass particles and regions of reaction produc ts with higher porosity. CSH(I) and (C,M)(4)AH(13) were identified by x-ray diffraction. The C-S-H (calcium silicate hydrate) phase is propo sed to consist mainly of structurally imperfect layers of tobermorite, interleaved with layers of (C,M)(4)AH(13). Other cations, most signif icantly Na+, are incorporated into the structure. Use of the highly co ncentrated solution (5 M) produced a higher degree of reaction and, co nsequently, higher compressive strength (38 MPa after 28 days for 5 M solution vs 21 MPa for 1.5 M).