POZZOLANIC REACTIONS OF 6 PRINCIPAL CLAY-MINERALS - ACTIVATION, REACTIVITY ASSESSMENTS AND TECHNOLOGICAL EFFECTS

Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH)(2) [CH] in the presence of simulated cement pore solution, and with ordinary Portland cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland cement - clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay - CH mixtures are C-S-H-2 and C(4)AH(x), while C(2)ASH(8) and C(3)AH(6) were also detected with clays rich in Al.