USE OF SCC FOR A TUNNEL OF THE CITYTUNNEL MALMÖ PROJECT WITH 120 YEARS OF LIFE CYCLE

Transcription

1 USE OF SCC FOR A TUNNEL OF THE CITYTUNNEL MALMÖ PROJECT WITH 120 YEARS OF LIFE CYCLE Dr. Frank Abel (1) and Michael Willmes (2) (1) MCG, Malmö City Tunnel Group HB, Sweden (2) Bilfinger Berger AG, Germany Abstract The Citytunneln project is the connection between the Öresund Bridge and the Central Station of Malmö. The concrete had to be designed for a life time of 120 years. Based on this a huge test program for all concretes in this project was necessary and a lot of requirements had to be fulfilled. This paper gives an overview of most of the tests that had to be done for the SCC. For the pillars and beams of the Station Triangeln in the centre of Malmö, SCC was used. The number of requirements has made the mix design development difficult and led to a complex recipe. Special attention had to be drawn on the fire resistance, PP-fibres were used to fulfil the requirements. For the design of the formwork a formwork pressure test was carried out with the intended recipe during a test casting of a Pillar with a height of 7 m. The maximum pressure was app. 65% of the hydrostatic pressure. At the end m³ of self compacting concrete have been cast successfully. 1. INTRODUCTION The Citytunnel project, which consists of 17 kilometres of railway connecting Malmö Central Station and the Öresund Bridge, brings together the railway systems in Southern Sweden and increases the capacity for railway traffic in the future. The underground section of the Citytunnel will run from the Malmö railway yard to Holma, which is a distance of 6 kilometres. The bored part of the tunnel is 4,5 kilometres long and consists of two parallel, tubular-shaped tunnels. The station at Triangeln will be right in the centre of Malmö in the shopping, housing and cultural area known as Triangeln. The station is being built as an subterranean rock cavity station, about 25 metres below ground level and with two tracks and a 250-metre long interjected platform. As the first step of the cavern a pillar tunnel with a height of app. 10 m and a width of app. 8 m had been driven. In this pillar tunnel 29 pillars and a nearly 200 m long head beam had to be cast. Because of the complicated situation at the head beam (formwork at the bottom and the side walls and shotcrete on the top three layers of reinforcement in the top of the beam) self compacting concrete was chosen for the pillars and the beam. 1019

2 2. REQUIREMENTS FOR THE CONCRETE The requirements for the concrete were precisely described in the contract document with 80 pages[1]. This document covers the requirements for the submaterial, concrete, distance pieces, test procedures and so on. In the specification three different concrete types C1, C2 and C3 were defined, on the basis of the impact of water, salt and frost. Most of the concrete for the tunnel had to be classified as a C1, respectively C1F concrete (means under groundwater level, one side water pressure, salty water and partly also frost). Depending on the concrete type, different requirements for the mix design were given. Table 1: Requirements for concrete mix design [1] Property Concrete type C1 C2 C3 Min. durability class C40/50 C35/45 C30/37 Technical life cycle - years 120 Max. WCR 0,40 0,45 0,50 Min. Cement content kg/m³ k-value for silicate substance 2,0 Max. Silica powder content 6,0 % Max. Chloride content 0,10 % Max. Alkali content kg/m³ 3,0 Air additive required in C1F C2F C3F For the self-compacting concrete furthermore special attention had to be drawn to the chemical durability concerning thaumasite-reaction. For the use of limestone filler in the selfcompacting concrete the sulphate content was limited to less than 100 mg/l in the surrounding water and less than 1000 mg/l in the surrounding soil. The use of fly ash was not allowed. To receive the required fire resistance, polypropylene fibres were added to the concrete. Fire tests were carried out, to prove the necessary fire resistance. 3. TEST PROGRAM For each concrete to be used for permanent structures of the tunnel a huge test program had to be carried out. The different steps were as follows. First the preliminary study to fix the recipe of the concrete and to define the target properties, than the pre-testing to get the properties for the simulations / stress calculations and the necessary tests to prove the durability (chloride migration, freeze-thaw-tests) and the full-scale test. Furthermore tests with different mixing times and a petrografic evaluation of the hardened concrete had to be done afterwards 3.1 Preliminary study In a preliminary study different materials were used to create the self compacting concrete. The cement and the aggregates had already been fixed during the pre-testing of the other concretes for this project. The SCC was developed as a powder type based on the Okamuraprinciple [2]. 1020

3 Table 2: Mix design Material Content in kg/m³ Cement 425 Limestone filler 160 Mikrosilica slurry 25,5 PP-fibres 1,2 Water 150 Superplasticiser 3,8 Air entraining agent 2,0 Sand 680 Coarse aggregates The target was to get a good workability and flowability of the SCC over 1.5 hours, to cover production-, test-, transport- and the waiting time until the concrete was pumped into the formwork. This target was reached with the recipe shown in table 2. Figure 1: Fresh concrete properties, left the so called Workability window, right vdz-cone For the determination of the flow time a special cone, which was developed by the German cement association (VDZ) was used. The advantage of this cone is, that both properties flowability and viscosity could be tested very fast an precisely in only one trial by one person. Furthermore the test results are more comparable because the slump flow is not being influenced by different lifting heights ore the lifting speed of the cone and compared to the flow time t 500 the flow time of the VDZ cone could be determined more precisely. To examine the stability of the SCC a lot of J-Ring- and L-Box tests were carried out - with good results. 3.2 Pre-testing For each concrete mix and each type of construction a temperature simulation and a crack risk calculation had to be done. For the C1 concrete the max. tolerable crack width was 0,1 mm. The following material properties were tested: compressive strength, tensile strength, E- Modulus (each at an concrete age of 0,5 / 1 / 2 / 3 / 7 / 14 and 28 days). To calculate the 1021

4 early age strains of the concrete the shrinkage (early age- and drying), creeping, heat development and the thermal expansion coefficient were determined. These parameters and simulations were also used for the design of the internal cooling system (cooling pipes). For the determination of the chloride penetration, petrografic analysis and frost resistance (not necessary for SCC) 1 m³-cubes had to be cast with the intended procedure (pump or chute) and cores had to be drilled from this blocks. Each concrete for the pre-testing had to be produced by the batching plants on site. Mixing time- and truck mixer trials had been carried out to find out the minimum mixing time which guarantees a homogenous concrete with well dispersed materials. Three different mixing durations were used and petrografic analysis were done. It could be recognised, that long mixing times lead to a higher content of coarse air bubbles. During the truck mixer tests two different batches of concrete had to be homogenized in a truck mixer. For the spacers a separate test program had to be carried out. The compressive strength of the spacer concrete should be at least as high as the strength of the surrounding concrete. It has to be proven, that the chloride diffusion in the spacer concrete is on the same level or lower than in the surrounding concrete. The joint between the spacer and the concrete should have the same or a higher resistance against chloride penetration. For this, cores with cast-in spacers were taken from concrete specimen after chloride penetration had occurred and impregnated thin section analysis were carried out at the joint of the spacer and the concrete. 3.3 Full scale test The purpose of full-scale test castings is to demonstrate the applicability of the concrete mixture in relation to the selected implementation methods and at the same time fulfilling all requirements [1]. The structure of the full scale test should have min. half of the dimensions of the real structure. For the SCC a Π-shaped structure consisting of two pillars with a height of 3,3 m and a cross section of 1,4 m to 0,7 m and on top a beam with a length of 7 m and a cross section of 0,9 m to 1,5 m was cast with the pre-tested mix. The SCC was pumped over app. 130 m directly into the formwork. On the formwork pump connections were fixed in 3 different levels. It could be shown, that the batching plant was able to produce the SCC without any problems and that the concrete fulfilled all requirements for the fresh concrete properties. The concrete could be pumped over the long distance without any problems. After stripping the form one could see that the formwork was filled completely and the surface looked well. To prove that all requirements of the hardened concrete were fulfilled a lot of cores had to be drilled(compressive strength, density, chloride diffusion, petrografic analysis, air void analysis and chloride penetration in the joint between spacer and SCC). 3.4 Fire test The fire tests were done at the MFPA Leipzig on specimen with the dimensions 2,20 / 1,20 / 0,40 m. The specimen were cast on site, stored in water for 2 month and then 1 month at a climate of 20 C and 65 % humidity. The temperature curve was according to the contract - rising rapidly up to 1000 C after 20 min, a max. temperature of 1300 C after 3 hours and then 2 hours cooling down. During the fire test the specimen was forced with a stress of 8,6 N/mm². After lifting the specimen, the spalling was determined to 37 and 11 mm in average 1022

5 5th International RILEM Symposium on Self-Compacting Concrete and 65 and 45 in maximum. The contractual limits of 40 mm in average- and 100 mm in maximum spalling were kept.[3] 4. PRODUCTION 4.1 Pillar Reinforcement & Shutters Following completion of the base slab Column and head-beam formwork was partially assembled in the shaft and moved into the tunnel. This formwork could be driven in two halves on supported rails in the Tunnel. Once the main shutters are in place the Reinforcement carrier was also assembled in the shaft and driven into the tunnel. Prior to the reinforcement being installed a bond breaker (PE foil) was fixed to the roof of the tunnel. The reinforcement for the head beam arrived to site prefabricated. This was then delivered via the crane into the shaft. The reinforcement carrier was used to transport the reinforcement to the relevant block. The prefabricated head beam reinforcement was lifted into position using the carrier and locked into position with the bottom of the head beam shutter secured using props. The column & head beam shutter was then also moved forward to reinforced block i.e. block 8. The columns forms were then closed once all reinforcement work was finalised and cooling equipment was installed. Once all shutters have been closed and secured a final survey check was done prior to casting. Inspection or control pipes were also installed approximately every 3m, these acted as an indicator during casting of when the SCC had reached its maximum level the form was full. Figure 2: Reinforcement Carrier (side view) 1023

6 4.2 Casting of the Pillar Structure Once all reinforcement was installed, formwork secured and inspected the casting occurred. The Concrete pump was positioned at the portal of the tunnel with concrete pipes run along the tunnel to the form. Using a series of valves and connections the Pump hoses was connected to the pumping ports on the shutter as shown on the figure3. All connections were made before pumping concrete as far as practical to ensure minimal disruption during casting. Valves were used to close and reconnect the main pump line to the distribution points, thus directing the concrete from one level to the next. Once pumping started from connection 7 and 8 it continued to the final side panels of the head beam shutter. The final side shutter connections were secured manually before pumping resumes for the final portion of the cast. The SCC was then pumped to the crown of the tunnel. In order to ensure a minimal void was left while also taking care not to overfill the form pumping continued until the SCC overflowed from the control pipes which have previously been installed to the high points of the tunnel. On completion of the casting the formwork was partially stripped after approximately 12 hours curing time. Initially the column forms were opened as well as the head beam side panels. The shutter directly underneath the head beam shutter along with the vertical props were left in place to provide support to the head beam structure. This underside shutter were removed after sufficient curing time. The entire column / head beam shutter was moved along the previously installed rail sections to the next block where the above mentioned sequences were repeated Figure 3: Pumping connection points 1024

7 5. CONCLUSIONS The designed life time of the structures of the Citytunnel Project is 120 years. To achieve that life time a lot of requirements are given for the concrete used in that project. Following these requirements a SCC was developed and the properties of the fresh and hardened SCC were tested during the preliminary study and the pre testing program including the fire tests. By fulfilling the test requirements it was shown that the SCC could be used for the achieved life time. For the practical use and the work preparation some full scale tests and formwork pressure tests were done, which showed that the designed SCC could be produced and used in the foreseen way and still fulfils the requirements. With all this testing and preparation in advance the implementation of the real structure was done without difficulties and the casting of the pillar- and head beam structure of Triangeln Station became a success. REFERENCES [1] Citytunneln: contract E201 tunnels and rock chambers; Requirements for concrete Materials, execution and control. Document 8.1, Appendix 6 [2] Okamura, H.; Ozawa, K.: Mix design for self compacting concrete; concrete library of JSCE (1995) Nr. 25, p [3] Dehn, F.; Nause, P.; Hauswaldt, S.; Abel, F.; Willmes, M.: Brand- und Abplatzverhalten von selbstverdichtendem Beton (SVB) für den Tunnelbau. Der Citytunnel Malmö als Beispiel, Beton- und Stahlbetonbau, Heft 1/