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Forschungsbericht 2016
(2016)
Forschungsbericht 2017
(2017)
Forschungsbericht 2015
(2015)
Shotcrete is a material frequently used in underground constructions such as tunnels, where Ca leaching and sulfate attack are important durability issues. In this study, two test methods were employed to investigate the sulfate resistance and leaching behaviour of dry- and wet-mix shotcretes in sulfate solutions on a time-resolved basis. Tests on powdered samples showed the dissolution of AFm, portlandite and C-A-S-H, subsequently followed by the precipitation of calcite and ettringite. The extent of sulfate expansion of drill cores corresponded to the chemical response of the powder materials, particularly on the reactivity of Ca- and Al-containing hydrated cement phases. The use of high-purity metakaolin (7-10 wt%) in the shotcrete binder significantly decreased the sulfate durability, while high amounts of other SCMs such as blast-furnace slag and silica fume (> 20 wt%) had a positive effect on the durability of shotcrete.
Shotcrete is often used for the construction and stabilization of tunnels and other underground structures, where it is susceptible to different forms of physical and chemical attacks affecting its durability. An advanced understanding of the factors that limit the durability of shotcrete is crucial to develop tailored strategies for enhancing its service life. The main focus of this contribution is to shed light on the durability of shotcrete by revising the literature, highlighting what is missing and needs to be addressed, assessing how the knowledge about concrete durability can be transferred to shotcrete, and providing recommendations for durable shotcrete structures. (C) 2018 Elsevier Ltd. All rights reserved.
Filler Effect in Shotcrete
(2019)
The effects of fine limestone powder on the early hydration of cementitious systems accelerated by means of alkali-free aluminum sulfate based products, commonly used for shotcrete applications, were investigated in the course of laboratory and real scale tests. In binary (CEM I + limestone) and ternary (CEM I + limestone + slag) systems the addition of fine limestone led to an enhancement of the hydration degree and strength development at early times (<24 h). The formation of ettringite, aluminate hydrates, and C-S-H is affected by the joint action of the setting accelerator and the fine limestone. Accelerator and limestone, in combination with the cement, can be optimized to enhance ettringite and silicate reaction, in some cases coupled with aluminate reaction inhibition, to produce mixes suitable for sprayed concrete applications. Such optimization can help to reduce the cement content in the mixes without compromising the early strength development of the shotcrete.
The reduction of clinker use is mandatory to lower the negative environmental impact of concrete. In shotcrete mixes, similarly to the case of conventional concrete, the use of supplementary cementitious materials (SCMs) and proper mix design allow for the substitution of clinker without compromising the mechanical properties. However, the impact of the substitution on the durability of shotcrete needs to be further assessed and understood. The results from the present study, obtained from real-scale sprayed concrete applications, show a reduction of the Ca2+ leaching and sintering potential of clinker-reduced shotcrete mixes due to the presence of SCMs. This positive effect, crucial for low maintenance costs of tunnels, is mainly related to a reduced portlandite content, which on the other hand negatively affects the carbonation resistance of shotcrete. Additionally, the hydration of SCMs positively influences the chloride penetration resistance presumably due to a combination of microstructural changes and changes in the chloride binding capacity. Differences found in the pore size distribution of the various mixes have low impact on the determined durability parameters, in particular compared to the effect of inhomogeneities produced during shotcrete application.
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.
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.
