raw materials for making concrete pole

1 Raw Materials

1.1 Steel

The main component of steel is iron, in which there is a little other elements such as carbon, silicon, manganese, phosphorus and sulfur. The amount of carbon has a great effect on the performance of steel. If amount of carbon is higher, the strength of steel will be higher, the rigidity is higher and the toughness is lower. If the carbon content is low, the strength of steel will also be low, the rigidity will be low, but the toughness and plasticity will be better. At present, the steel of concrete cement products business can be divided according to the chemical component into high-carbon steel C>0.6%, low-carbon steel C<0.25%, medium-carbon steel C 0.25%-0.6%. The low carbon steel and high carbon steel mainly be used in the structure of reinforced concrete and prestressed concrete. Recent years the carbon content of parent metal of prestressed concrete steel wire used widely in cement products is high, contains C0.7%～0.8%. After complicated controlling and heating process, the external surface has evolved into the spiral rib shape with good adhesiveness to concrete cement thereby increasing the grip of concrete. What's more, as the high strength and reasonable toughness, it has been greatly used in a variety of prestressed products production. By using it you can not only save a number of steel but also much money.
As the number of annular and longitudinal bar of pole has been stipulated by national standard GB4623, so regarding to the small diameter, low loading pole, when designing consumption of steel and choosing the materials varieties, the economical factor can be only considered. The practical experience has proved that the low carbon cold draw steel wire for low voltage, low loading capacity pole is most safe and economic. conversely, the pole with higher bearing capacity used in middle and high voltage transmission and transformation using high carbon steel wire is very safe and economic.

1.2 Usage of steel bar

In the past, when A3 steel is used widely in the concrete member, because of its good plasticity, toughness, weldability and safe usage, it is used widely and with a great number. As times goes on, people realize that the strength 650Mpa of cold-drawn low-carbon steel wire is far more than the strength 380MPa of its parent metal(A3). After a safe standard is stipulated, its usage especially in cement products has reached a fairly high and widespread level. With the learning of concrete and steel wire grip the cold-drawn spiral and cold rolled ribbed surface-deforming steel wire comes out. The application of new style reinforcing steel has a great effect on the improving of various performance indexes of concrete pole.

1.3 Cement
The production of concrete pole mainly adopts the technology of centrifugal molding. By the curing of saturated steam, the hydration reaction rate will increase and the strength which required by exerting pressure will be reached. So, better to use ordinary portland cement with the characteristics of fast condensation time, high early strength and application to steam curing.

1.4 Aggregate
It's better to use medium-coarse sand according to GB4623 for sand; rubble or pebble with the diameter of 5mm～20mm have been proved applicable to stones, and required to have good granular composition.

2 Concrete
The cement products are commonly made of ordinary cement concrete and composed of cement, sand, stone, water and admixture. In order to meet the production requirement of concrete pole, the concrete must have good workability, which effected by many factors such as cement variety, water, admixture, aggregate, environmental condition and technology condition and what is mostly used is to reduce the water consumption in concrete.

3 Centrifugal concrete
The concrete cross section meeting the requirement should display coarse and fine aggregate arranging evenly, without clearance and air hole; the nest paste of inner and external thickness is within 5 mm generally, and the thickest inner surface can exceed beyond 10mm; there is no sedimentation in centrifugal molding concrete products. The coarse aggregate presses against the external surface compactedly and closely. The paste content should be so full that the products will be smooth and artistic.

4 Centrifugal equipment and centrifugal technology

4.1 centrifugal equipment
The centrifugal equipment has a direct impact on the production quality of concrete pole. Actually, the certified centrifugal equipment is the combination of cengtrifugal spinning machine, spun concrete pole mold and good operation process.

4.2 centrifugal technology
In the centrifugal technological procedure the centrifugal time is generally set within 16min～18min. At present some enterprises making concrete poles has shortened the time to 12min which is the ultimate time of technological procedure. To get eligible products the strict process system must be built, and the high-speed shoule occupy 1/2 of the total centrifugal time. In order to decrease the centrifugal speed the accuracy of installation and adjustment of centrifuge spinning machine should meet the standard, the precision of pole steel mold meeting the standard to meet the requirement of high-speed running, increase the density of concrete and shorten the time of water excess water-extracting.
The centrifugal molding system is proceeding by low speed-medium speed-high speed.
Low speed(slow speed): when the slump of concrete is <6cm,the revolving speed is100rpm～120rpm, the spinning time is 1.5min～2min.
medium speed: In order that the equipement and products avoid the impact and vibration meantime ensuring that the excess water can be slowly drained thus the concrete will get compacted gradually. Spining time 1.5m～2min.
High speed: It's the molding speed during the revolving which ensures the excess water being removed with the full centrifuge and correct apprerance. Revolving speed>360rpm, time 7min～8min.

5 several common quality problems
bending : the bending degree can't exceed L/1000. The casuing reason includes that rigidity of pole mold is not enough, the strength and quality of concrete or the break of steel bar causes bending during manufacturing.
Wall thickness: the prestressed concrete pole with same specification has a best thickness. When the thickness increases, the cross section prestress decreases and the bearing capacity reduces.
Exposed reinforcing bar: inner expose and outer expose. The inner exposing reinforcing bar results from the the slump of concrete causing by the impact and vibration of reinforing bar. The outer exposing bar results from the binding of spiral reinforcing bar during the framework molding.
Thickness of protective layer: the prestressed steel wire can be exposed outside or it will speed the structure damage of concrete pole.
Joint close paste leaking: the paste leaking of seam close and end is a usual quality defect of apperace which can be avoided by improving the seam closing accuracy of mold, cleaing the concrete debris on the mold and filling the cotton rope, paper string in the commissure or oiling, controling the operation process strictly.