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Introduction and Background
(2021)
The absence of a standardised methodology to evaluate creep in the cracked state of fibre-reinforced concrete (FRC) hindered general comparisons and conclusions that could lead to significant advances in this topic. A coordinated effort was required to improve the knowledge on long-term behaviour of cracked FRC sections and assess the different testing methodologies available. The RILEM Technical Committee 261-CCF launched in 2015 the round-robin test (RRT) on creep behaviour in cracked sections of FRC program. This chapter includes the introduction and background to understand the realisation of this RRT. The main objectives as well as the limitations of the scope of the RRT are explained. The structure of the book is presented to provide a first overview of the book content. Finally, information about institutions involved as well as geographic distribution of RRT participants and number of specimens tested in the RRT is provided.
Statements and Conclusions
(2021)
A round-robin test (RRT) on creep behaviour in cracked section of fibre-reinforced concrete (FRC) was realised with the participation of 19 international laboratories from 22 institutions. The same concrete matrix was used to design two different FRC mixes with steel (SFRC) and macro-synthetic (SyFRC) fibres and to produce 451 FRC specimens. The use of 124 specimens for creep tests for one year following four main methodologies provided a huge database with more than 15,000 data. The main statements and conclusions derived from the RRT database analysis are summarised in this section. Note that the conclusions derived from this RRT are limited to the ranges of parameters, procedures and variables considered here and should not be extrapolated to other cases.
The research project „Advanced and Sustainable Shotcrete - ASSpC“ aims at the improvement of sprayed concrete mix design regarding durability and sustainability. One possible improvement is to replace part of the clinker content in the binder with different supplementary cementitious materials. It is crucial that new mix designs fulfil the basic technical requirements on site concerning workability and early age development, too. One central issue of the project is to
investigate which parameters influence the pumpability of sprayed concrete. Several test methods are used to determine the stability, tendency to segregation, bleeding and of course the consistency
of concrete. An essential test method is a concrete sliding pipe rheometer (Sliper). This rheometer determines the pumping characteristics of concrete in the laboratory and on construction site. In comparison to other rheometers, the Sliper evaluates the rheological characteristics of the thin
layer of paste which is lubricating the wall of the convey ing pipe. The paper presents the tests procedures in detail as well as first results from lab-tests and from site-tests with different
advanced shotcrete mix-designs .
This chapter collects the description of the main creep testing procedures in fibre-reinforced concrete (FRC) as well as the equipment used by each participant laboratory in the round-robin test (RRT). The description of each procedure was directly provided by the participants and follows the same structure for each participant where institution identification and contact information was included. Each participant summarised the most significant data such as specimen’s size, load configuration, parameters or environmental conditions in a quite useful table. Moreover, the participants included description and close-up pictures of the creep frames construction, the support boundary conditions, and the measurement devices used. Finally, the participants provided a complete description of the specific complete creep test procedure followed.
This paper discusses a new fresh concrete control system with the following structure: a rheometer measures the fresh concrete directly after the mixing process, during a short break. The viscosity and the dynamic yield point are determined by a ball rheometer. The rheological parameters viscosity and dynamic yield point describe the consistency and thus the pouring ability and consequently the quality of Self Compacting Concrete (SCC). Data collected from the measurement are the basis for an expert system which will help to readjust mixes with deviating rheology.
Firstly, investigations were carried out during the development of different SCC mixtures in the COST TU 1404 Action. Secondly, investigations were done in two precast plants. A ball rheometer was installed in the respective mixers. The SCC for premium precast products was tested then during ongoing production. In addition, several test series were carried out in the laboratory of the OTH with the respective constitutive materials.
During the test series, the mix designs of the well working SCC’s were modified by using a deviating water content. Subsequently, using the rheological data, water, superplasticizer or stabilizing agents were added to the mix, trying to reach proper workability again. The graphs for the changing rheological properties as a function of the respective amount of start water content and additional water dosage or admixture dosage were generated and analyzed for the mixes of the two precast plants. With this information and experience, an expert system for the mix readjustment is currently under development.
Analysis of the RRT Results
(2021)
The analysis of the results of the round-robin test (RRT) comprised many steps. The variation of the main variables such as the number of samples tested, environmental conditions, pre-crack level or creep index and mechanical performance were analysed among all the RRT participants. In addition, the main methodologies were independently analysed to search significances between the participant procedures. Analysis of the described procedures, test setups and equipment provided relevant information about such existent differences between participants in terms such as load configuration, boundary conditions or frames construction. The creep coefficient and crack opening rate (COR) parameters were defined and analysed. The complementary data number of fibres in the cross section was analysed to assess the influence in the long-term residual performance. Finally, the correlation between different fibre-reinforced concrete (FRC) specimens as well as the influence of ageing of concrete matrix were analysed.
Shotcrete or sprayed concrete in tunneling in connection with the "New Austrian Tunneling Method” has been developed over the last decades to reach a high quality standard. However, at present the development of new shotcrete mixes is required to fulfill durability and stainability requirements, i.e. for superior performance in aggressive environments and reduction of maintenance costs. In the course of the project ASSpC ("Advanced and sustainable sprayed concrete") the research team focuses on producing and testing new and innovative shotcrete mixes using local and environmentally friendly raw materials. Sustainable and durable shotcrete with optimized mechanical and physical properties and improved chemical resistance is developed.
This paper outlines the motivation for the project, gives an overview of the project structure and introduces key reaction mechanisms and environmental controls causing damage of shotcrete in tunnels.