Waterproof membrane can be applied safely on sprayed concrete reinforced with Dramix steel fibre type 3D 65/35BG

Transcription

1 Dramix Waterproof membrane can be applied safely on sprayed concrete reinforced with Dramix steel fibre type 3D 65/35BG In double shell tunnel construction, a waterproof membrane combined with a geotextile, will serve as a buffer between the sprayed concrete support and the final cast in-situ concrete layer. This buffer will level out the irregularities of the sprayed concrete. There was a serious concern about the danger of steel fibres protruding from the sprayed concrete surface and punching through the waterproof membrane Rock Sprayed concrete Drainage protection fleece Sikaplan 5 Fastener strip 6 Inner concrete lining TECHNICAL INFO SHEET WATERPROOF MEMBRANE 1

2 From rumors and opinions to facts and figures What do we learn from tests performed in independent laboratories? Two detailed examples 1 In 1993, The CETU (French Tunnelling administration) already financed puncture tests (under hydraulic pressure) on the geomembranes placed on fibre-reinforced shotcrete supports. These revealed the importance of the lower protection geotextile. However, they did not reveal puncturing risks when it was placed between the PVC geomembrane and the fibre-reinforced shotcrete (at the time Dramix fibers) TOS The purpose of the tests was to determine the effect of steel fibres in shotcrete on waterproof membranes. Different types of membranes were applied on various concrete panels: TESTING SYSTEM CETU AFTES REPORT complexe 1 10 sprayed concrete panels (on site) with a membrane EI 20/10 + geotextile 600 complexe 2 10 sprayed concrete panels (on site) with a membrane EI 15/10 + geotextile 600T complexe 3 10 sprayed concrete panels (on site) with a membrane EI 15/10 + mixed protection complexe I 1 lab panel with a membrane EI 15/10 but without protection sheet complexe II 1 lab panel with a membrane EI 15/10 + geotextile 600T complexe III 1 lab panel with a membrane EI 15/10 + mixed protection TECHNICAL INFO SHEET WATERPROOF MEMBRANE 2

3 The three lab panels were constructed in order to simulate the worst possible situation with steel fibres. The membrane and protection sheet covered the concrete samples and a hydrostatic pressure of 1,5 bar was applied for about 20 hours. Periodically, the membrane was checked for possible perforations. At the end of the test the membranes were put under pressure in order to find all possible perforations. With the sprayed concrete panels no perforations were registered. Similar results were obtained with the lab panels, except for the one panel covered with the membrane without any protection. 2 Another test series was realized in 1998 at the Osterreichisches Kunststoffinstitut in Vienna (Austria). This laboratory has been approved by DAP Deutsches Akkreditierungssystem Prüfwesen GmbH, according to DIN EN Three sprayed steel fibre reinforced concrete samples (80 cm x 20 cm x 15 cm) were covered with a geotextile (Polyfelt TS 006/A 500 g/m²) and a waterproof membrane (Winklerplan 200 2,0 mm). During 24 hours a uniform load of 900 kg/m² was applied on top of the waterproof membrane. Afterwards the complex of the geotextile sheet and the waterproof membrane were removed and replaced by a new complex of the same materials. This time a uniform load of 8000 kg/m² was applied. Both tested samples of the waterproof membrane were controlled. Not a single perforation was found. Report nr concludes: After being loaded during 24 hours by a uniform load of 900 kg/m² resp kg/m² no punching holes have been detected in the waterproof membranes. It can be concluded that using a protecting geotextile sheet there is no danger for steel fibres protruding from the shotcrete layer to punch or damage the waterproof membrane. TECHNICAL INFO SHEET WATERPROOF MEMBRANE 3

4 What do we learn from job site experience? As with the practical experience on many sites, these test results clearly confirm that there are no problems with the membrane/protection sheets in combination with steel fibre reinforced sprayed concrete. Indeed, the aggregate and the roughness of the support are the main points of concern. However, some additional recommendations are nevertheless time to time specify as: 1. 3 cm unreinforced sprayed concrete (Egis Tunnel - Design office). 2. Or higher grammage > 800 gr/m 2 instead of 600 gr/m 2 (Example technical advice published by the CETU N French Tunnel Study center of Ministry). What about polymer fibre and roughness of the support? All initial shotcrete surfaces are prepared so as to achieve the smoothness and regularity required to preserve the membrane integrity. Additional shotcrete has to be used where required to smooth surface irregularities and meet the criteria below. TECHNICAL INFO SHEET WATERPROOF MEMBRANE 4

5 PM = Mean maximum depth averaged over 40 measurements / 25 m 2, p = sidewall, v = roof TECHNICAL INFO SHEET WATERPROOF MEMBRANE 5

6 Extract from TOS sept 2009 (Tunneling Magazine offficial organ of AFTES, the French Tunneling Association) It should be noted that several experiments have been carried out on the use of polypropylene fibers in shotcrete. However, since the presence of polymer fibers may increase the roughness of the support (irregularities formed by the fiber/concrete mix) and consequently modify its PMp and PMv (table No. 1 of AFTES recommendations concerning the preparation of tunnel supports receiving a geomembrane sealing system TOS No. 150), AFTES recommends specifying a 800 g/m 2 geotextile instead of the 600 g/m 2 one ordinarily used in tunnels. The physicomechanical properties of this geotextile must comply with table No.1 of the AFTES recommendations concerning the tightness and drainage of underground works TOS No Indeed, as in other composite systems, compatibility problems may occur between the fibres and the cement, due to the different chemical natures and the different thermal expansion coefficients. What should you keep in mind? => Tests in independent labs have demonstrated that steel fibre type Dramix RC65/35BN will not create any puncturing risk and could be used very safely. => Measurement of spray concrete surface roughness is one of the key acceptance tests in tunnel waterproofing. => Indeed, aggregates are the most sensitive elements. The surface of the shotcrete should be smooth and even. The shotcrete aggregates shall have a diameter of 4 10 mm. => Polymer fibre may increase the roughness of the support (irregularities formed by the fibre/ concrete mix). TECHNICAL INFO SHEET WATERPROOF MEMBRANE 6