Laboratory investigation of the properties of cement fly ash gravel for use as a column-supported embankment

摘要

Deep cement mixing (DCM) columns are used to support embankments built on soft clay, but these columns have limitations in terms of their engineering properties such as low column strength and low column permeability. Therefore, the use of cement fly ash gravel (CFG) instead of DCM columns has been introduced. The objective of this paper is to present an experimental investigation of the properties of CFG. Gravels with sizes of 4.76 to 12.70 mm were mixed with ordinary Portland cement (OPC) Type 1 and fly ash (FA) to create CFG materials. OPC was partially replaced by FA at levels of 0 to 25% by weight of OPC. The engineering properties of the CFG materials were studied through the porosity, compressive strength, flexural strength, modulus of elasticity, and permeability coefficient after curing for 28, 50, and 90 days. The microstructures of the OPC-FA pastes were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Finally, preliminary guidelines for selecting a suitable porosity of CFG columns were proposed. Test results show that the porosity of the CFG materials ranged from 25.8 to 31.1% and affected the strength and permeability. The strength of CFG was 6 to 13 times greater than that of a DCM column, and the permeability of CFG was 9 to 17 mm/s, which was much higher than that of a DCM column, indicating that the use of a CFG column-supported embankment built on soft clay was more effective than the use of a DCM column in terms of the column bearing capacity and acceleration of consolidation settlement. The replacement of 15% of the OPC with FA exhibited the highest strength and smallest porosity because it provided the greatest amount of calcium silicate hydrate. Preliminary guidelines show that small-sized gravel with medium porosity is proper for generating column-supported embankments on soft clay to carry medium loads and to accelerate the consolidation process. (C) 2020 Elsevier Ltd. All rights reserved.