2005 - Putzmeister

Tunnel ConstructionPractical Tip43Clogged delivery pipescan become expensive46On most construction sites which use stationaryconcrete pumps to pump overdistances or to heights, trained machineoperators are responsible for flawless operation,for maintenance works and forcleaning the pumps and delivery lines.And in general, they do a good job.Occasionally, however, Putzmeister customerservice centres are amazed by thelevel of ignorance and by the indifferenceof some machine operators and constructionmanagers. Here is a recent example.47The accommodation camp for the Sedrun tunnel builders with smashing plant for processing the tunnel waste, which is brought up from a depth of 800 m undergroundThe six shotcrete units carry are responsiblefor initially securing the stretches of tunnelwhich have just been driven using steelfibre shotcrete. Approximately 27 kg ofthese roughly 5 cm long steel fibres aremixed into every cubic metre of concrete.The shotcrete is applied in several layers,for a final thickness of 15 to 20 cm.Drainage material and sealing foils will beadded to the shotcrete shell at a later stage.The internal formwork will then be produced.This formwork generally has a wallthickness of 30 cm, but can reach a thicknessof 1.2 m due to the enormous pressuregenerated inside the mountain in theSedrun section.Each of the tunnels is watched over by a patron saint –Saint Barbara44Reliable service, rapid componentacquisition and special concrete additivesThe TRANSCO-Sedrun consortium hascommissioned a specialised, externalservicing workshop to carry out the regularmaintenance works on the shotcrete units.There is also a SIKA employee employedpermanently on the construction site, toliaise with the TRANSO-Sedrun consortium.In addition to the different shotcrete units,SIKA also supplies highly efficient concreteand shotcrete additives for the Sedrun sectionand also for further project sections ofthe Gotthard Base Tunnel. These are mostlyadditives which help to satisfy the sometimesvery specialised and demanding con-crete and shotcrete requirements for thissophisticated tunnel project. Example:additives supplied by Sika include silicafume additives, which increase the watertightnessand the durability of the shotcrete,retarders which enable the required processingtime to be adjusted, a solvent tosecure the stipulated water/cement valuesand a non-alkaline setting acceleratorwhich enables the short concrete settinglead times which are stipulated to be met.The exact mixture breakdowns for the concreteand shotcrete that is used have beentested by the client since 1996 under adetailed and stipulated pre-qualifyingprocess These breakdowns form the basisof the mixtures now used on all Gotthardtunnel construction sites.45A branch of Putzmeister AG rents out astationary BSA concrete pump, approximately140 m of ZX-delivery line, a gatevalve and a stationary MX concrete placingboom for a high-rise project within theirsales region. The machines are ideally setup for the conditions of the constructionsite by the Putzmeister service team andthe delivery line (30 m horizontal and thefirst 20 m vertical) is installed. So far, sogood. The delivery line is extended as thework progresses by the construction sitepersonnel.During the ensuing months of concreting,more and more phone calls are made by theexasperated construction management:there are constant problems when startingpumping, the concrete pump needs toomuch time to deliver the required deliveryrate, the hydraulic pressure of the machineis too high, more and more blockages areoccurring, etc.For these shabby pipes, a ”build-up of lubricating film“ for the concrete delivery is now virtually out of the question...A Putzmeister service technician comes tothe site several times and ”oversees“ ormonitors cleaning after several hours ofpumping. On the following day, no difficultieswere experienced when pumping started.For the next few days, when noPutzmeister personnel are on site when thepump is being cleaned, the relevant constructionmanager/foreman phones upagain to complain about the ”wretched concretepump“.The last few metres have finally been pumpedand the MX boom including deliveryline can be dismantled. When the pump isre-delivered to the Putzmeister branch, theresult of inspecting the pipes can be seen inthe picture above: instead of a smooth48inner wall with a build-up of lubricatingfilm, almost all the 3 metre long pipesreveal a layer of concrete residue on theinside – for a total of approximately 100metres of pipeline. By heating the pipescarefully and then treating them with a2500 bar DYNAJET high-pressure cleanerwith rotating nozzle, it was possible toremove the concrete encrustation (approximately5 mm thick) from the inside of thepipes after much time-consuming, minutework. The damage that was caused byuntrained personnel is estimated at25,000 to 30,000.4920PM 3652 GBA Sika employee is on site constantly to provide liaisonThe encrusted concrete residue can be loosenedfrom the pipe walls with the DYNAJET high-pressurecleaners21PM 3652 GB