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Shrinkage testing of end-restrained shotcrete on granite slabs
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
2014 (English)In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, 1300348- p.Article in journal (Refereed) Published
Abstract [en]

This study investigated the shrinkage of shotcrete (sprayed concrete), especially the case of shotcrete sprayed on drains – a part of tunnel lining not continuously bonded to the rock. A newly developed method for testing the shrinkage of end-restrained shotcrete slabs is presented and evaluated. The test setup, which is designed to capture in situ behaviour, consists of shotcrete sprayed on an instrumented granite slab partly covered with a plastic sheet. The primary goal was to practically use and evaluate the test method with shotcreted test samples. Results from restrained shrinkage tests are presented along with results for free shrinkage. It is shown that the method realistically captures the behaviour of shotcrete drains on hard rock in situ. In addition, the corresponding compressive strength and flexural crack strength as functions of shotcrete age are also reported. The test method can be used for an evaluation of different solutions for avoiding shrinkage cracks in shotcreted soft drains, or in shotcrete that is fully bonded to a rock surface, with respect to preventing cracking or distributing the shrinkage strain into several fine cracks instead of one wide crack.

Place, publisher, year, edition, pages
2014. 1300348- p.
Keyword [en]
cracking, fibers
National Category
Construction Management
Identifiers
URN: urn:nbn:se:kth:diva-145674DOI: 10.1680/macr.13.00348ISI: 000339879000001Scopus ID: 2-s2.0-84906828128OAI: oai:DiVA.org:kth-145674DiVA: diva2:719540
Funder
Formas
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Time dependent material properties of shotcrete for hard rock tunnelling
Open this publication in new window or tab >>Time dependent material properties of shotcrete for hard rock tunnelling
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing.

The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration.

Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiv, 79 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 124
Keyword
Shotcrete, rock, granite, bond strength, compressive strength, pullout testing, failure modes, interfacial transition zone, micro structure, ettringite, set accelerator, shrinkage, drains, glass fibres, laboratory testing, tunnels & tunnelling
National Category
Construction Management
Identifiers
urn:nbn:se:kth:diva-145678 (URN)
Public defence
2014-06-12, Sal F3, Sing-Sing, Lindstedtsvägen, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2014-05-26Bibliographically approved

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