HOW TO IDENTIFY SUB-STANDARD CONCRETE ELECTRIC POLES
Concrete poles are among the major apparatus used in the distribution of electric power by the power stations and their distribution companies in many African countries. the concrete pole records of effectiveness in electric power management has encouraged its use for many countries across Africa.
These concrete poles are basically made with the mixture of sand, cement, granites or limestones, and steel rods to give it its strength. The use of these poles has encouraged external or surface wiring method as against the modern underground cables used by many developed countries. Meanwhile, due to some short comings in the manufacturing of the concrete poles, many of the poles had been seen falling down at any little accidental force on it such as car hitting it, falling trees nearby, heavy rainfall with high breeze, and collapsed building, etc. even though that these poles were being tensioned on the ground to support its strength. Some of the fallen poles are actually of high quality the reason for their fall may just be that the impact force they received that moment was so high that it exceeded their calculated tensile strength. While others fall at a little impact force due to their sub-standard contents.
The demand for the concrete poles is increasing every day following the development that is penetrating into many places and those places needs electricity supply, and the concrete poles is one of the major way to channel the distribution lines to those areas. Hence; the power distributions companies due purchase them as well as individuals who needs to direct the distribution lines to their houses.
The need to identify the original concrete poles from the sub-standard types has become very necessary due to the reason mentioned above, and from a little research concerning these concrete poles below are the things you need to consider, check and do on any concrete poles before buying it;
CHECK FOR VISIBLE INJURIES
As a Non-Destructive Test Inspector I believe that visual inspection results is among the most reliable report in the NDT work, therefore taking a very close look at the concrete poles to check if there is any form of injury like cracks, porosity, and inhomogeneous mixture of the concrete, if there is any of these faults on the body of the electric poles, it is probably indicating poor standard and hence, should not be accepted under contract condition, because any damage to any of the poles will start at those injuries. Therefore visual inspection is the first step.
TEST THE FLEXIBILTY
The flexibility of the concrete pole will reveal the size and strength of the steel rods inside it though it will be cover by the concrete, this practice is mostly employed by the experts who deals on concrete poles business and the supplying agents to power distribution companies. The best way to check this is by allowing the loading of the poles on the truck that will convey it, bringing about 20feet out from to truck such that it suspends itself on the air without any support, if the pole is flexible it will start fluctuating up and down on the part that is on the air, also you will observe a tilt of that edge toward the ground the bigger the tilt the more flexible the pole possesses. Another way to know the flexibility is by fixing the two edges at a rigid position may be concrete walls and using a hydraulic jack to push it at the center, at that instant the measure of the tilting of the center of that pole is its flexibility, though flexibility cannot be avoided in a concrete pole but when the ratio exceed a reasonable amount it shows the potential for easy damage in the future.
The flexibility also reveals the concrete ratio and the concrete overall strength.
The concrete ratio simply means the content of sand, granites or limestone, and cement in the concrete used in molding the pole. A good concrete must have cement at a higher ratio than sand and granite, in my own opinion I believe one or two bags of cement to one wheel barrow of sand, and two wheel barrow of granite is a good mixture for a standard concrete poles, this is because it would serve the same function a building pillar would serve, by carrying the whole weight of the three cables that pass through it to the next pole, and should be able to resist impact forces especially when small private vehicles accidentally hit on them or if a nearby tree should fall on them.
LIME STONES OR GRANITE
The major difference between limestone and granite is the strength that each of them offers in the concrete after solidification. The granite is costlier in the market than the limestone but it offers greater strength to the concrete than limestone, the approximate price for each of them when measured using a trip of 911 truck majorly used in suppling sands, limestones and granites from their dealers should be within N35, 000 for granite and N25, 000 for limestones though individual location and the distance from the dealers may increase or decrease these prices.
The next major thing to consider is the overall diameters of each section of the electric concrete pole. A standard electric concrete pole will have a larger diameter at the bottom area and a smaller diameter at the vertical edge area, the decrease in the diameters will be carried out in such a way that it is in a uniform manner such that starting from the bottom the diameter of the pole starts decreasing uniformly toward the vertical edge. A standard concrete pole would have its bottom diameter between 25centimeter and 30 centimeter while at its vertical edge where cables are connected should be having a diameter between 18centimeter to 20centimeter in a situation where these diameters are lesser then curiosity must be taken on the integrity of the poles in terms of other factors such as the size of steel rods inside it and the concrete mixing ratio of the pole.
THE SIZE OF STEEL ROD
The next thing which should be considered is the size and type of steel rods which were used in the skeleton support of the pole and how they were banded together with quarter rods. The total integrity of the pole lies on the strength of the steel rods because once they bend as a result of any impact road then the concretes will break in pieces and fall off. If you can have access to any visibility of the steel rods in the pole confirm its size and ask for the design diagram from the manufacturer, from the diagram you may know how the rods were positioned and banded together.
A standard concrete pole has steels rods whose thickness is not less than 12mm, higher ranges can be used such as 16mm steel rods just that it will increase the cost of the pole after production. The skeleton support strength of the pole is directly proportional to the thickness of the steel rods and the number of the rods lined up in the skeleton support.
NOTE: in the situation where the concrete mixed ratio is in doubt you may break out a small pieces of concrete from the concrete pole and react it with a diluted tetraoxosulphate (vi) acid (sulphuric acid), if the reaction is dissolving the concrete very fast then the cement and granite may be lesser than supposed while the sand is much. A good concrete in that condition will dissolve slowly with a sulphuric acid.