PUBLICATION NO. 44 2/2011 NORDIC CONCRETE RESEARCH EDITED BY THE NORDIC CONCRETE FEDERATION CONCRETE ASSOCIATIONS OF: DENMARK FINLAND ICELAND NORWAY SWEDEN PUBLISHER: NORSK BETONGFORENING POSTBOKS 2312, SOLLI N - 0201 OSLO NORWAY VODSKOV, DECEMBER 2011 Preface Nordic Concrete Research is since 1982 the leading scientific journal concerning concrete research in the five Nordic countries, e.g., Denmark, Finland, Iceland, Norway and Sweden. The content of Nordic Concrete Research reflects the major trends in the concrete research. Nordic Concrete Research is published by the Nordic Concrete Federation that beside the publication activity also organizes the Nordic Concrete Research Symposia that have constituted a continuous series since 1953 in Stockholm. The Symposium circulates between the five countries and takes place every third year. The XXI Symposium on Nordic Concrete Research and Development was held in Hämeenlinna, Finland from 30 May to 1 June 2011. The next symposium, no. XXII, will be held Reykjavik, Iceland 17 – 19 June 2013 only two years ahead, just before an already planned conference, ECO-CRETE 19 – 21 June 2013. During the latest years, growing interests in participating in the Nordic Concrete Research symposia, as well as for publishing in NCR have been observed. Since 1982, 378 papers have been published in the journal. Since 1994 the abstracts and from 1998 both the abstracts and the full papers can be found on the Nordic Concrete Federation’s homepage: www.nordicconcrete.org Vodskov, December 2011 Dirch H. Bager Editor, Nordic Concrete Research PUBLICATION NO. 44 2/2011 CONTENTS 1. Eigil V. Sørensen Fatigue life of high performance grout in wet or dry environment for wind turbine grouted connections ....................................................................................1 2. Andrea Folli Photocatalytic cementitious materials containing highly active nanosized TiO2: Mechanisms of air pollution remediation and the effect of the alkaline environment ............................................................................................11 3. Torsten Lunabba & Hemming Paroll Moisture Monitoring in Concrete Bridges 1990-2011 ..........................................25 4. Taisto Haavasoja Optical Moisture Measurement in Concrete Aggregates .....................................45 5. Jan Arve Øverli, Paola Mayorca, Alexander Furnes & Ole-Martin Hauge Static and Fatigue Capacity of Partially Loaded Areas in Concrete Structures . 55 6. Richard Mc Carthy & Johan Silfwerbrand The Swedish User´s View of Self-Compacting Concrete ......................................75 7. Håkan Hansson & Richard Malm Non-linear Finite Element Analysis of Deep Penetration in Unreinforced and Reinforced Concrete .......................................................................................87 8. Robert Hällmark, Peter Collin & Martin Nilsson Concrete shear keys in prefabricated bridges with dry deck joints ................... 109 9. Merit Enckel New Årsta Railway Bridge – A case study on the long-term Structural Health Monitoring with Fibre Optic Sensors .................................................................. 123 10. Peter Simonsson & Mats Emborg Robust self compacting concrete for bridge construction .................................. 143 11. Martin Nilsson, Ulf Ohlsson & Lennart Elfgren Effects of Surface Reinforcement on Bearing Capacity of Concrete with Anchor Bolts ......................................................................................................... 161 12. Jukka Lahdensivu, Hanna Tietäväinen & Pentti Pirinen Durability Properties and Deterioration of Concrete Facades Made of Insufficient Frost Resistant Concrete................................................................... 175 13. Gabriel Sas, Thomas Blanksvärd, Ola Enochsson, Björn Täljsten, Arto Puurula & Lennart Elfgren Flexural-Shear Failure of a Full Scale Tested RC bridge Strengthened with NSM CFRP. Shear capacity analysis........................................................... 189 1 Fatigue life of high performance grout in dry and wet environment for wind turbine grouted connections Eigil V. Sørensen Ph.D., Associate Professor Department of Civil Engineering, Aalborg University, Denmark E-mail: [email protected] ABSTRACT The cementitious material in grouted connections of offshore monopile wind turbine structures is subjected to very high oscillating service stresses. The fatigue capacity of the grout therefore becomes essential to the performance and service life of the grouted connection. In the present work the fatigue life of a high performance cement based grout was tested by dynamic compressive loading of cylindrical specimens at varying levels of cyclic frequency and load. The fatigue tests were performed in two series, one with the specimens tested in air and one with the specimens submerged in water during the test. The fatigue life of the grout, in terms of the number of cycles to failure, was found to be significantly shorter when tested in water than when tested in air, particularly at low frequency. Key words: High performance grout, dynamic loading, fatigue resistance, test environment, offshore wind turbine. 1. INTRODUCTION The foundation of an offshore wind turbine often consists of a steel monopile driven into the sea bed (Fig. 1). At the upper end of the pile a transition piece, i.e. a steel tube with a larger diameter than the pile, is connected to the pile by casting a cementitious grout in the annulus between the pile and the transition piece. The thickness of the grout layer is normally in the range 50 – 125 mm. The transition piece has a flange at its top to which the first section of the tower is bolted. 2 Figure 1 - Illustration of grouted connection Recently it was found that cylindrically shaped grouted connections tend to have their load carrying capacity reduced with time when subjected to alternating dynamic bending moments [1]. The grouted connection is subjected to both axial (vertical) load from the dead weight of the structure above the connection, and moment due to the wind action on the blades and the tower, and due to wave action on the structure. Reaction pressure develops in the grout to resist the bending moment which induces high stresses in the grout locally at the grout section ends. This may lead to local fracture and crushing of the grout [1]. The stresses will typically appear periodically as oscillations caused by the wind and wave action. Hence, the resistance against fatigue failure of the grout material under dynamic compressive loading becomes essential to the performance and service life of the grouted connection. Furthermore, it has been found that the fatigue capacity of concrete subjected to stress ranges in compression is reduced when the concrete is surrounded by water rather than by air [1]. Due to the lack of fatigue test data for grout in water the DNV has recommended that further tests be performed [1]. The objective of the study presented in this paper was to investigate the fatigue capacity of a high performance grout material designed for grouted connections, in air as well as in water. 3 2. EXPERIMENTAL 2.1 Materials The grouts used for grouted connections are usually high performance cementitious materials. The grout investigated in the present study was a commercially available product based on a high performance cementitious binder material, containing microsilica and other mineral additions, and being prepared at ultra-low water to cementitious material ratio facilitated by a high dosage of superplasticizing admixture. The aggregate consisted of natural sand with a maximum grain size of 4 mm. Due to its composition the grout develops an extremely dense microstructure and attains a very high compressive strength and an excellent durability to resist the harsh marine service environment. Mechanical properties of the grout were measured after 28 days curing in water at 20°C [2]. The details of the testing and the results are presented in Table 1. Table 1. Mechanical properties of the grout after 28 days curing in water at 20°C Property Specimen type Test Result standard Compressive strength Cubes, 75x75x75 mm EN 12390-3 141 MPa Flexural strength Mortar bars 40x40x160 mm EN 196-1 18.4 MPa Splitting tensile strength Cylinders ø100x200 mm EN 12390-6 8.6 MPa Modulus of elasticity Cylinders ø100x200 mm EN 13412 50.9 GPa Poisson’s ratio Cylinders ø100x200 mm - 0.199 Traditional cement based grouts prepared at water to cement ratios by weight of about 0.40 and below exhibit significant shrinkage, even when sealed against loss of moisture to the surroundings. This so-called autogenous shrinkage increases with decreasing water to cement ratio [3]. The autogenous shrinkage of the present grout was measured over a period of 315 days and was found to be negligible due to shrinkage compensating measures included in the material formulation [2]. The lack of autogenous shrinkage enhances the friction between the grout and the steel surface of the grouted connection. 2.2 Fatigue test The behaviour of the grout under cyclic loading was studied using cylindrical specimens, 60 mm in diameter and 120 mm high. The cylinders were stored in mould at 20°C for one day, then demoulded and stored in water at 20° until testing. The cylinder ends were ground plane immediately prior to using them for the test. The tests were performed using a 500 kN servo-hydraulic test machine from MTS. At each stress range level the static compressive strength was first determined using