| Abstract | This study is concerned with the effects of mortar composition on carbonation and
corrosion rate. The following condition are selected in this study, 1: 0. 7: 4.5 of cementious:
water: sand mix portion, 0%, 15% and 30% fly ash content as the replacement of OPC and
0%, 0.5% and 2% chloride ion by the addition of calcium chloride, 9 types of specimens are
constituted according to the designed mix composition. The specimens with steel bar cured in
control room are used for the corrosion experiment, and the specimens without steel bar
curing water tank are used for the carbonation experiment. In addition, half numbers of
specimens with steel bar are subjected to pre-carbonation in order to observe the difference
of corrosion between carbonation and non-carbonation. The specimens were exposed at AIT
in Thailand for two months and four months. The measurement of carbonation rate, weight
loss, surface roughness and visual observation are conducted in this experiment.
The results showed that high pressures carbon dioxide dramatically accelerates the
carbonation process. Carbonation depth increases with time, it was bigger for the specimens
with fly ash than without fly ash, and it increased with the increase of the addition of chloride
ion in mortar.
The morphology of corroded steel bar exhibited the black corrosion product Fe304.3H20
below the red-brown corrosion products Fe(OH)3, and the scale of corrosion product was
founded in relative serious case. Weight loss is bigger for the specimens with fly ash than
without fly ash, weight loss increases with the order from 0%, 0.5% to 2%, weight loss
increases with exposure period. At 0% and 0.5% chloride ion level, the carbonated specimens
have slightly bigger weight loss than non-carbonated ones, at the 2% chloride ion level, the
serious corrosion occurs in non-pre-carbonation specimen containing 30% fly ash for two
and four months exposure, 15% fly ash for four months exposure. The serious roughening of
surface on the corroded steel bar takes place in higher chloride ion concentration, and higher
fly ash content. These results show that very severe pitting corrosion occurs under
coexistence of high fly ash content and high Cl- concentration. |