A NEW ALKALIFREE WATER-SOLUABLE RAPID SETTING ADMIXTURE FOR HIGH PERFORMANCE SHOTCRETE

摘要

This paper presents an investigation on a new high performance shotcrete that can be formed by adding an alkalifree powder admixture IVA to the conventional shotcrete mix formula. The new admixture possesses excellent properties including water-soluble, non-causticity, and suitable for both dry and wet mix process systems. Results of the reheology tests on the fresh pastes modified with IVA or other admixtures demonstrated the good contribution to the reduction of rebounds losses during spraying process. Photographs observed by scanning electron microscope displayed a distinct membranaceous colloidal materials coating on the cement paste during the initial hydration stage. This observation provided a rational explanation on the rebound control mechanism for shotcrete. Experiment results also presented for the compressive strength among different types of cement pastes and concrete with or without IVA. It showed that the IVA could increase significantly the early period strength, and it did not reduce the shotcrete ultimate strength. Meanwhile, the test results on durability of harden pastes with IVA showed that the IVA reduced the crystal defects and improved the resistance to sulphate attack on the shotcrete evidently. Finally, the paper presents a case study of application of the new shotcrete to underground excavation.