CHLORIDE INGRESS IN HIGH-VOLUME FLY ASH CONCRETE
Through contact with de-icing salts or as a result of sea salt spray or direct seawaterwetting, chlorides can enter a concrete structure causing a break-down of the passivation layeraround steel and subsequently corrosion. In high-volume fly ash concrete, fly ash reacts withcalcium hydroxide leading to a lower degree of alkalinity of the pore solution and in turn ahigher capacity to bind chloride ions. The pozzolanic reaction products will refine theconcrete microstructure. However this reaction proceeds at a slower pace than the hydrationof portland cement making high-volume fly ash concrete at young age much more permeablethan traditional concrete with no replacement of cement by fly ash. The resistance againstchloride ingress of concrete mixtures with 0％, 35％, 50％ and 67％ of the cement contentreplaced by low calcium fly ash was measured with a non-steady state migration test (NTBUILD 492). At 28 days, the chloride migration coefficient increased with increasing fly ashcontent. Due to the proceeding pozzolanic reaction, the chloride migration coefficients atthree, six and twelve months were lower for all concrete mixes with fly ash compared totraditional concrete. However, chloride ingress can occur not only by diffusion, but also bycapillary absorption. With equipment for accelerated degradation test, developed in-house, thefour concrete mixtures were subjected to a cyclical submersion test into 3.5％ NaCl solutionfor 14 weeks. This test resulted in a decreased resistance of the mixtures with fly ashcompared to the reference concrete. To model the chloride ingress, different types of transportbehaviour of chloride ions should be taken into account.
G.Baert E.Gruyaert K.Audenaert N.De Belie
Magnel Laboratory for Concrete Research,Ghent University,Ghent,Belgium
国际会议
南京
英文
473-482
2008-10-13（万方平台首次上网日期，不代表论文的发表时间）