Enhanced durability performance of fly ash concrete for concrete-faced rockfill dam application
Introduction
Considering the important fact that a dam is a “permanent” structure, it is needless to stress the importance of durability of concrete, which is diminished due to varying water levels, freezing and thawing, water penetration, crack, etc.
Table 1 shows the cause of damage in concrete dams in America, Canada and Japan [1]. As given in Table 1, the causes of damage in concrete dams are freezing, water penetration, degradation, and erosion. Therefore, it is important that durability of concrete in dams be enhanced.
Many facts were considered in order to enhance the durability of concrete. Among them is the fact that fly ash concrete enhances both freshly mixed concrete and hardened concrete by pozzolanic reaction [2], [3], [4], [5]. It was found that the durability of concrete was improved when some of the cement was replaced by fly ash [2], [3], [4], [5], [6], [7].
As the amount of fly ash replacement increased, the durability of concrete improved, but during the initial stages, the compressive strength of fly ash concrete was lower than that of ordinary Portland cement (OPC) concrete, because strength development was slow [2], [3], [5]. Therefore, fly ash concrete with strength accelerator admixture was being used in some developed countries.
In this study, to enhance the durability of concrete-faced rockfill dam (CFRD), fly ash was mixed with face slab concrete in order to make the material of surface an impermeable wall. An examination of the durability of fly ash concrete was also carried out. As a result, the optimal fly ash concrete, which satisfied the durability and economic efficiency requirements, was developed and applied. The results obtained in this examination would be useful in establishing mixture proportions for fly ash replacement of dam concrete.
Section snippets
Material properties
Type I OPC, produced in Korea and which satisfied ASTM C 150, was used. Physical and chemical properties of cement are shown in Table 2. River sand and gravel, produced in San-chung, Kyung-nam, were used as fine and coarse aggregates, respectively. Physical properties are shown in Table 3.
Fly ash, produced in Samchonpo and which satisfied ASTM C 618-97, was also used. Physical properties are shown in Table 4. High-range water reducing AE agent was used to obtain the target slump and air content
Compressive strength test
Compressive strengths were measured at the ages of 7, 28 and 91 days, and the results are shown Table 6 and Fig. 1.
At the age of 7 days, the compressive strength of OPC was higher than that of fly ash concrete; however, as the age increased, the compressive strength of fly ash concrete became higher relative to that of OPC. This was primarily because sufficient pozzolanic action of the fly was activated. In Fig. 1, fly ash concrete was more effective than OPC in long-term strength, which was
Conclusions
(1) For the result of chloride penetration test, estimated at the ages of 28 and 91 days, considering the amount of charge past, fly ash replacement of 15% was shown to be most effective for increasing permeability resistance.
(2) For the result of the abrasion resistance test, at the age of 28 days, as replacement of fly ash was increased, the efficiency of abrasion resistance increased. While at the age of 91 days, the efficiency of abrasion resistance increased up to 15% of fly ash
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