Search

New insights into the quality assurance of PP‐fibre reinforced concrete as exemplified by the Kriegsstraße road tunnel The 1.5 km long Kriegsstraße road tunnel in Karlsruhe is being constructed using the cut and cover method, with tunnel walls and ceilings made of PP‐fibre reinforced concrete. Differing from the German ZTV‐ING, Part 5, 1.5 kg of PP‐fibres per m3 of concrete, instead of 2.0 kg/m3 are being added. The lower PP‐fibre dosage along with an extensive quality assurance concept incurred in a higher concrete construction quality, proven through initial, structural element and quality assurance testing. With PP‐fibre dosage reduction a more robust, less temperature sensitive concrete mixture is obtained. Due to the influence of PP‐fibre dosage on fresh concrete properties, PP‐fibre dosage should be considered as a key quality assurance parameter. The dosage precision also clearly depends on the choice between manual or automatic PP‐fibre dosage. If sufficient experience with PP‐fibre reinforced concrete can be proven, the verification process for a PP‐fibre content reduction could be simplified. [ABSTRACT FROM AUTHOR]

Abstract: The workability, the strength and the toughness are the significant factors for self-compacting-high performance concrete (SCHPC). The workability is a significant precondition for application of the Fibre Reinforced SCHPC. This paper presents research results on the workability of Monofibre and Fibre Cocktail (hybrid steel-polypropylene fibre) Reinforced SCHPC. Lots of mixtures made with steel fibres, PP-fibres and fibre cocktail of various dosages have been investigated. The mixtures were tested using various new methods for evaluating the flowability, filling ability and segregation risk of the fresh mortar/concrete. Based on the results of the workability, the suitable fibre types (steel fibres, PP-fibres and fibre cocktail) and the upper level of the fibre dosages for Fibre Reinforced SCHPC have been selected for study of the mechanical behaviour and the failure patterns in the next phase. [Copyright &y& Elsevier]

A mathematical model of hygro-thermo-mechanical phenomena in heated concrete, treated as multiphase porous material is briefly presented. Some modifications necessary to analyse high–temperature performance of a concrete containing the PP-fibres have been introduced, experimentally validated and applied for analysis of performance of a concrete tunnel lining during a 10-MW fire and the ISO standard fire. Three methods for protecting concrete structures against excessive degradation in fire conditions have been numerically analysed by means of the computer model. The analysed protection methods are based either upon application on a structure surface of a reflective layer, or covering it with a protective layer made of a very porous concrete or an addition of the PP fibres to the concrete mix. Efficiency of these methods has been numerically analysed in thermal conditions corresponding to the ISO-834 standard fire. The results obtained show that even relatively simple methods, like application a protective layer or increasing the surface reflectance, can retard to some extent concrete degradation during a fire. [ABSTRACT FROM AUTHOR]