EFFECT OF CAST-IN-PLACE CONCRETE STRENGTH EVOLUTION ON PRESSURE TUNNEL LININGS FOR THE HYDROPOWER PLANT

Abstract

This study aims to explore how cast-in-place concrete strength evolution influences pressure tunnel linings for the hydropower plants. Although conventional concrete has been so far implemented broadly for constructing many engineering structures in general and pressure tunnels in particular, its quality and performance can still be improved using diffirent chemical admixtures. Advanced concrete with the usage of water-reducing admixture has been studied in this paper. Indeed, the mix that involved the admixture with 0.6 and 0.9% of cement content has outperformed one without the admixture usage. Regarding the fresh state, in comparison with the conventional concrete, the advanced concrete did not present the slump loss even though the time retardation was 90 minutes. Besides, the one with 0.9% admixture was still pumpable with a time retardation of two and a half hours. At the hardened state, the advanced concrete excelled in the designed strength class by almost 20%, particularly it had a high early-age strength that provides construction accelerating. The advanced concrete with 0.9% admixture usage has been used successfully for the pressure tunnel linings of the Song Bac hydropower plant, thank to a high early-age strength, it was acceptable for an early removal of slide formwork after 3 days. Because of that, the time to complete one kilometer tunnel of this project was merely half of the counterpartner Tan Giang hydropower plant that involved conventional concrete. Despite the 10% increment of expenditure for the admixture usage in the advanced concrete, the total investment cost has been reduced by 16%. Keywords: Water-Reducing Admixture, Accelerator, High Early-Age Strength, Slide Formwork, Concrete Linings DOI： https://doi.org/10.35741/issn.0258-2724.58.1.53