below a detailed description is given of the procedure for erecting the concrete towers used in wind turbines , which are the object of this invention , with reference to the accompanying drawings , which represent , merely as an example which is in no way restrictive , of the preferential form of realisation susceptible to all those detailed variations which do not presuppose any fundamental alteration to the essential characteristics of the improvements . according to the example of execution represented , the procedure for erecting concrete towers used in wind turbines illustrated in this preferential form of realisation consists basically of various stages or phases which may be developed at the same time on a parallel basis with the various towers in a wind farm , thus making optimum logistical use of the resources , materials and times necessary for assembly . the aforementioned procedure includes two different cycles of activity , which may be developed alongside each other : the pre - assembly cycle and the erection cycle . in the example of realisation illustrated , both cycles have the same productive capacity : two towers per week . the pre - assembly cycle begins its activities some weeks beforehand , so that there is always a minimum advantage of having various towers in the erection cycle , thus avoiding interference of one over another . each section ( 4 ) of the tower structure may be composed of different number of segments ( 1 ) based on their position in the height of the tower . thus , in this example , an 80 meter high tower , the first section ( 0 - 20 ) corresponding to the first twenty meters of height of the tower is made up of four segments , each limited by vertical sections ( 8 ) of that section of tower . the second section ( 20 - 40 ) between twenty and forty meters of the tower height , is composed of three segments , as well as the third section ( 40 - 60 ) that is , at a height of forty to sixty meters of the tower height which is also composed of three segments . the fourth section ( 60 - 80 ) however , comprises two segments , which come already pre - assembled in the factory in one single part . the aforementioned pre - assembly for each section consists of a procedure divided into the following phases , for each section comprising different segments : one phase for transport and erection of each segment , therefore there are as many phases as there are number of segments , followed by a final filling stage of the vertical joints ( 8 ) of each section . thus , in the present example of realisation the pre - assembly of the first section ( 0 - 20 ) will be carried out in six stages , one comprising the arrival and assembly of each of the four segments , a fifth phase for filling the horizontal joint with the base footing and a sixth phase of filling the vertical joints , whereas the two following sections ( 20 - 40 ) and ( 40 - 60 ) shall be erected in four phases each , three for the arrival and erection of each segment and a fourth for filling the vertical joints . the pre - assembly of the first section can be directly carried out on the base footing or foundation of the wind turbine , while the other intermediate sections shall be erected on mounting bases ( 5 ), which may be placed on the ground in the zone of the platforms provided in the proximity of the base of each wind turbine , or on the base itself in a position next to the tower . therefore , the aforementioned cycle of erection , is initiated following the first pre - assembly cycle in the same wind turbine , and consists of the placing of each section on the previous one ; in this case , the placing of three sections each 20 meters high . in this operation each section is hoisted with the aid of a crane . therefore , the pre - assembly cycle is begun with erection of the segments of the first section of the present structure of each concrete tower for wind turbines , which in this preferential form of realisation comprise the 20 first meters of the tower . the structure of the aforementioned first section comprises four segments ( 1 ) in the form of a section of the trunk of a straight or curved generator cone provided with hoisting bolts ( 10 ) enabling them to be mounted directly onto the definitive foundation . thus the pre - assembly of the first section of each tower comprises the following stages : 1 . verification of the geometry , levelling and implements of the foundations and the prior placing of the levelling plates with the pre - adjusted thickness for obtaining levelling of the part . the initial thickness of the plates is 20 mm . 2 . the segments are transported and arrive at the site and are not stored at the wind farm but are placed directly from the lorry onto the foundation ( or on the pre - assembly bases in the case of the segments in sections 2 and 3 ). 3 . in the lorry the first segment is coupled by the hoisting crown bolts to the erection crane and by the lower bolts ( 13 ) to another retention crane or to a second pulley tackle of the erection crane . 4 . the segment is turned in the air ensuring that the protruding lower bars ( 9 ) ( of the attachment to the base footing ) do not collide or are damaged or bent . having achieved the vertical position , the lower retaining bolts ( 13 ) are released and the segment hangs solely from just the crown bolts ( 10 ). the segment is then placed upright in its final location . 5 . the segment is lowered placing the connection bars in their jacketing . as the segment is lowered the strut 2 is activated in order to adjust the end of the perforated plate of the foundation . 6 . the position of the segment is checked . this is adjusted using the strut or the crane , increasing or reducing thickness of the levelling plates if necessary . 7 . the operation is repeated with the diametrically opposed segment . 8 . erect the third segment , connecting it to the two segments already fitted by means of mechanical clamps ( 3 ) located in the vertical joints . with the segment at the appropriate height , tighten the clamps and check the opening of both vertical joints ( 8 ) along their height . the segment position is checked and the crane is released . 9 . the fourth closing segment is erected by attaching it to the two first segments using the same procedure as with the third segment . 10 . having erected the 4 segments , the overall position is checked once more and any necessary adjustments made 11 . the grills of the vertical joints are introduced from the upper end 12 . the 2 struts ( 2 ) are removed using the crane at the upper part of the section and any other elements required are introduced using the crane . 13 . formwork is laid around the horizontal joint of the base footing using a 5 cm high frame outside and inside the segments , separating their faces at a distance of 5 cm , the non - retractile mortar is then poured . 14 . previously , after or simultaneous to the pouring of the mortar for the lower horizontal joint , the mortar is poured in the vertical joints . 15 . having achieved sufficient resistance in the mortar of the vertical joints , the clamps ( 3 ) of the vertical joints are removed . the procedure continues with the pre - assembly of sections 2 ( 20 - 40 m ) and 3 ( 40 - 60 m ). the procedure is similar to that of erection of the first section except that it is carried out on provisional foundation using ( 5 ) pre - assembly bases and with the following differences : the first segment erected is provided with a cross bracing support ( 2 ) in order to guarantee its provisional stability . for the second segment it is necessary to tighten the clamps ( 3 ) of the vertical joint . the erection of the third closing segment is similar to the closing segments of the first section . the lower horizontal joint will not be concreted . below the procedure for erecting the concrete towers used in wind turbines continues with the erection of the sections ( 4 ) pursuant to the following stages : 1 . placement of levelling plates on the crown of the first section . 2 . placement around the edge of a profile of self - adhesive foam , tangential to the external edge of the surface of the crown of section 1 °, and a profile with an l shaped section which serves as internal formwork . 3 . coupling of the crane to the crown bolts ( 10 ) of the second section , using slings . 4 . access to the platform ( 12 ) of the previous section ( the first ). lifting of the second already pre - assembled section , and placement in its final location . 5 . lowering of the section , introducing the protruding reinforcement ( 9 ) into the jacketing ( 11 ) of the first section until it rests on the levelling plates . 6 . checking of the level of the second section . correction of the position , if necessary acting on the thickness of the steel plates , while suspending the section with the crane . 7 . access to the upper platform ( 12 ) of the second section in order to uncouple the crane . 1 . the fourth section is pre - assembled in the factory , on a lorry . using slings the erection crane is coupled by 2 metal coupling elements ( 14 ), which are screwed to the section crown . another retaining crane or other pulley tackle from the same crane will hook onto a belt ( 6 ) surrounding the section at approximately one meter from the lower end and which passes through a hook ( 7 ) which holds the lower rib of the section and stops the belt from slipping in the turning operation . 2 . the fourth section is raised approximately one meter and the transport vehicle is removed . 3 . the section is then turned by lifting the upper end with the erection crane while the crane , or second pulley tackle retaining it holds the lower end at sufficient height to ensure that the protruding bars ( 9 ) do not hit the ground . 4 . having achieved a vertical position , the crane or second retaining pulley tackle releases the load , transferring the full load to the erection crane . the belt and the coupling from the lower end are removed . 5 . the fourth section is located on top of the third section and a similar procedure is followed for placing the second and third sections in their final position . in order to realise the horizontal joints ( 15 ) where the system for joining the horizontal joints is by fitting passive bars ( 9 ) in jacketing ( 11 ) with connective mortar , the following stages will be followed : 1 . the non - retractile mortar is produced using a special mixer with a dosage specified according to the manufacturer instructions . 2 . firstly , all the jacketing of each joint are filled , checking the volume of the mortar introduced . there are openings in the head of all the jacketing in order to facilitate this operation . 3 . following controlled filling of the jacketing , the mortar is poured , filling the space of the horizontal joint ( 15 ) between sections . finally , the form materials and dimensions and number of parts may vary , and in general anything which is an accessory or secondary may be employed provided that it does not alter , change or essentially modify the improvements described herein .