A Study on Durability of Concrete by using Air-Cooled Blast Furnace Slag Aggregate

Abstract

Concrete is the most widely used material in construction industry due to its relatively high strength and high durability. However, various environment deteriorate concrete performance. In order to improve its properties, researches were held to develop high performance, high durable concrete by using industrial by-products. By-products were not only used to develop concrete properties but also application as an aggregate in concrete were researched. In particular, by-products in steel industry, Blast Furnace Slag aggregate were proposed for years. However, in case of Republic of Korea, it is relatively limited in its usage and also durability evaluation were barely performed. Therefore, Experiments of not only physical properties but also durabilities of fully substituted Air-cooled Blast Furnace Slag (ACBFS) aggregate were conducted by basic mix design to mock-test in the field. As a basic progress, binary (20%) and ternary mix (10%) were prepared to select mix type of binders by immersing specimens in 3% of sulfuric acid solution during 60days. Compare to the Natural aggregate series, GGBFS and MK with ACBFS presented high resistance in terms of mass reduction rate. After mix were selected it was applied to concrete binder type and its compressive strength were over 40MPa even if it was slightly lower than same type of mix with Natural aggregate series. Alike previous test, 3% sulfuric acid for 91 days of immersion, mass reduction of concrete with Natural aggregate ranged from 4-13% while that of ACBFS were less than 2%. Also, from the compressive strength reduction result, ACBFS series were observed to maintain its strength compare to the normal aggregate series. Particles collected from the immersed concrete in order to perform SEM & EDAX analysis to verify its product, however, no big difference were found in the view point of component. However, as a result of observing surface of concrete surface, shape of surface were considered to be maintained, which is both verified in NA, ACBFS as a gypsum, its shape to block sulfuric acid penetration. On the other hand, due to its porous structure of ACBFS, chloride penetration and carbonation depth were relatively high then that of NA series. After stability of concrete were verified from mini mock-up test, mock-up test in field were performed. However, in order to ensure its workability in precast factory, additional water reduce agent were inevitable. Therefore, further research will be required to verify change of concrete properties in terms of compressive strength and durability.