Abstract
The interaction between concrete and steel occurs during concrete mixing and finishing processes, during filling of concrete moulds, formwork, composite columns and during pumping of concrete mixtures. More experimental investigation is required to predict variations in interface friction, as a result of the composition of the lubrication layer which depends on the composition of concrete. This study provides experimental results to allow for a better understanding of friction at concrete-steel interface, with changes in the coarse aggregate (CA) content in the aggregate mixture (AM). Friction tests on fresh concrete have been carried out using the BTRHEOM tribometer (Nantes, France) and the interface parameters were calculated on the basis of the interface friction between the concrete and the steel wall, through the ADRHEO software. The roughness parameters were measured along the length of the rotary steel cylinder of the tribometer. In addition, the roughness of new and modified metal form-lining in steel composite columns was also measured. Variations in the CA content in the AM in the 42 to 52% range had minimal effects on the yield stress of the interface. The viscous constant of the interface as measured with a tribometer decreased, when the roughness parameter Rt values of the rotary cylinder wall, which refer to the absolute vertical distance between the maximum profile peak height and the maximum profile valley depth along the sampling length, were in the 17.10 to 28.73 μm range. The roughness profile peaks’ asperity recorded, was higher for the worn metal form-lining and for the steel composite columns with the inner surface covered in rust, when compared to the rotary cylinder roughness profile. The hypothesis is based on the principle that a sufficient lubrication layer, with the required thickness of fine mortar is created at the interface between the concrete and the metal form-lining or steel composite column wall, when the CA content in the AM varies in the range from 42 to 52% and the wall roughness parameters (Rt) of these elements varies in the 15.00 to 30.00 μm range.
Highlights
Friction at the fresh concrete/steel interface plays an important role during various stages of construction processes
The comparison of surface roughness between steel rotary cylinder, metal form-lining and different types of steel composite columns showed that the maximum profile peak height and the maximum profile valley depth along the sampling length (Rt) values varied in approximately the same range–15.00 to 30.00 μm, except for the worn metal form-lining and the steel tubes with inner surface which were in part covered in rust, where the determined roughness parameters (Rt) values are higher
The hypothesis is based on the principle that a sufficient lubrication layer can be created with the required thickness of fine mortar at the interface between the concrete and the metal form-lining or steel composite column walls, when the coarse aggregate (CA) content in the aggregate mixture (AM) varies in the range from 42 to 52% and the wall roughness parameters (Rt) of these elements varies in the range from 15.00 to 30.00 μm
Summary
Friction at the fresh concrete/steel interface plays an important role during various stages of construction processes. These include concrete mixing and finishing, filling concrete moulds, formwork, and composite columns, and pumping of concrete mixtures, where concrete moves relatively to the surface of the wall. It is important to investigate the relationship between the concrete mix design and the steel wall parameters, in order to reduce variations in friction at the concrete-steel interface. In the case of pumped concrete, fresh concrete moves through the pipe, by sliding over a lubrication layer, consisting of a fine mortar, close to the pipe wall [1,2,3,4]. The concrete mix design can impact the properties of the lubricant layer produced between concrete and the pipe
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