Study on Application of Class C Fly Ash for RCC dam in Nam Ngiep 1 Hydropower Project in Lao PDR

The Nam Ngiep 1 (NNP1) Hydropower Project in Lao PDR has constructed a 167 m-high roller compacted concrete (RCC) dam. Class C fly ash (FA) procured from the Mae Moh coal-fired power plant in Thailand has been selected as a supplemental cementitious material for the NNP1 RCC dam, to control hydration heat generation and improve workability. Though rarely used globally for RCC, it was found that the Class C FA was acceptable for the NNP1 RCC because it did not undergo a large temperature rise in its early age and because of the relatively high compressive strength of the concrete as the age in the medium-term and long-term as compared with general features of the concrete with Class C FA. To clarify the reaction mechanism for Class C FA, factors affecting the above features of Class C FA are analyzed and evaluated by observing FA particles and concrete core specimens of NNP1 RCC through a variety of devices, including Field Emission-Electron Probe Micro Analysis (FE-EPMA). This paper clarifies the reaction mechanism of the concrete with Class C FA and demonstrates its applicability for RCC dam and other structures.