MICROSTRUCTURE OF CEMENT AND ALITE PASTES PROCESSED WITH CONCENTRATED SOLUTIONS OF SODIUM CHLORIDE

摘要

In this paper the microscopic observations and analyses relating to the processes in wellrncementing are reported. The cementitious materials for this purpose are mixed with highlyrnconcentrated brine and used in underground works as the so-called salt cements.rnThe microstructure of pastes produced by mixing of diluted and concentrated sodiumrnchloride solutions with commercial cement as well as with the synthetic alite was observedrnunder SEM and the hydration products were analysed by EDS. Apart from the samplesrnproduced at w/c=0,5, the solid residue separated from suspensions (w/c=10) was alsornexamined.rnNaCl affects the silicate phase hydration both in cement and in alite paste hydratedrnwithin a few days, giving the C-S-H phase extremely compact and dense, with no individualrnparticles. One can observe the cracks surrounding the densified C-S-H gel. The NaCl crystalsrnare present at high NaCl concentration in cement paste and seem to strengthen the structurernThe Friedel’s salt crystals are not observed at early age but after 28 days maturing or more. Inrnalite pastes there are very characteristic snail-like, compact forms of C-S-H, similar to thosernobserved in calcium silicate hydrates produced from alite and silica and put in the salt brine.rnThese forms are relatively poor in Ca and rich in Cl. The products formed at excess of waterrnshow quite different microstructure. The needle-like forms of C-S-H are visible. At high NaClrnconcentration the highly saturated with NaCl , flexible, long fibres are seen.