| dc.description.abstract | The main goal of this article is to investigate the characteristics of
alkali-aggregate reaction of andesites from coastal range and search for a
solution. In order to inhibit this kind of phenomena, two methods
provided here include the adjustment of alkali contents and andesites’
contents in mortar bar test （ASTM C227）as well as concrete prism
test （ASTM C1293） in order to study the expansion of this reaction.
Furthermore, the cement used in ASTM C227 and ASTM C1293
were replaced with different amounts of fly ash and slag to prevent an
alkali-aggregate reaction. In addition, samples of the drilling core of
precast concrete blocks were obtained from Hualien-Taitung seaside and
analyzed using by uranyl acetate fluorscence method.
Based on our results, we have observed an obvious change in the
alkali-aggregate reaction of andesite from coastal range. Also we have
found that the pessimum content of andesite is around 50% when the
amount of andesite in mortar bar and concrete prism was changed.
Moreover, a small amount of andesite from costal range will create the
expansion dramatically and cause damage.
Thus the addition of fly ash and slag （pozzolan materials） will inhibit
the alkali-aggregate reaction of andesite from the coastal range. It is
also obvious that the better inhibition will be obtained when a higher
content of fly ash and slag is in the concrete. The occurrence of the
inhibition effect is based on the ratio of the contents of pozzolan materials
in concrete, the kinds of pozzolan materials , reactive aggregate and
alkali contents of samples.
We have characterized the alkali-aggregate reactions of precoast
concrete blocks from Hualien-Taitung seaside as the following. An
irregular map crack, the depth of aggregate crack, the appearance of
reactive gel and dark or pale reaction rims surrounding aggregates.
Moreover, when the drilling core samples were tested using the uranyl
acetate fluorescence method, the appearance of pale yellow-greenish
fluorescence surrounding the cracks is evidence of the existance of
reactive gel in the alkali-aggregate reaction. In summary, the
deterioration of precast concrete blocks from Hualien-Taitung seaside is
related to the alkali-aggregate reaction. | en_US |