Structural and operational shortcomings of concrete tanks

Concrete tanks are still used in many countries for drinking water storage. This caused by relatively low cost of erection of such reservoirs.

But it's important to know that having lower initial cost, these tanks require great expences for checkups, repairing, leaks elimination and so on, so sometimes such additional expenses are comparable with tank's cost or sometimes many times exceed this cost.

Imperfection of the regulatory framework, drawbacks of designing, defects received during manufacturing cause to early damage of concrete constructions.

Constructional drawbacks of concret tanks

The most common drawbacks of project sollutions which cause to leaks are:

  • Main constructional drawback of all concrete tanks is bunding, which hinders estimating walls condition and joints between wall panels, also repairing cost if defects appear;

  • Construction of junction of wall panels with monolithic bottom, difficulty of installation of wall panels in groove in bottom with careful adjustment and sealing for receiving required tightness;

  • Using of average cement for joints instead of expanding one;

  • Method of sealing of vertical joints of concrete panels with ring armature using winding machine, very often required tension is not reached;

  • Infringement of technology, not abiding sequence of works.

Influence of water at concrete tanks

Concrete constructions at their general operational period are exposed to water impact, and also to chlorine, sodium hypochlorite and other agents impact during profilactic treatment. In area above water level constructions are constantly exposed to carbon dioxide impact from the air.

Water exposes the following impact to concrete tanks:

  • leaching of calcium hydroxide from the composition of cement stone, causing the softening of concrete in surface layers;

  • interaction of dissolved carbon dioxide from water with calcium hydroxide from cement stone, causing to formation of soluble calcium bicarbonate;

  • interaction of chlorine with alkaline components from the cement (hydroxide, hydrosilicates and calcium hydroaluminate) with formation of calcium chloride as an end product, causing to the dissolution of cement stone in surface layer of concrete, and when chlorides content is more than 0.5% of cement weight, causing to steel reinforcement corrosion;

  • carbonation of concrete by carbon dioxide from the air causes to formation of calcium carbonate. In certain conditions, formed carbonate can fill cracks and pores of the concrete, tearing them from the inside. As it was known from checkups of septic tanks, the depth of carbonation of concrete is high. After 20-30 years of operation, it not only reaches the surface of the reinforcement, but also extends over the entire thickness of the concrete.

In most cases internal surfaces of tank, that was built over 20 years ago, should have a protective layer made of shotcrete. Checkups show that during the period of operation shotcrete is being destroyed thoroughly. Behind the destroyed layer of shotcrete appears the softened layer of concrete. Having normal thickness of protective layer (15-20 mm) steel reinforcement must be free of corrosion, and corrode, if thickness of the protective layer reduced by 5 mm against the project. In this case, it is required to remove the remaining traces of the shotcrete and provide hydro insulation of load-bearing part of the construction.

The greatest destructive effect on concrete structures of sumps and tanks for potable water is caused by water leaks through cracks in bottom, walls and coating. Thermal deformation of separate concrete elements and deformation of the entire structure caused by the uneven soil subsidence are the main reasons of cracking. Access of dissolved oxygen, neutralization of the cracks walls in the concrete (reducing pH) create conditions for the formation of a galvanic couple on the surface of the reinforcement with anode in the crack. In these circumstances, steel in the crack dissolves, while in the concrete near to the crack steel remains passive. Intensive corrosion causes breakage of the reinforcement in the cracks.

Roofing of concrete tank doesn't provide required waterproofing of the slabs and doesn't prevent the ingress of atmospheric moisture on the slabs and inside of tanks.

Repair works in sumps and drinking water reservoirs include repair operations of steel reinforcement, sealing of cracks with the use of modern waterproofing materials, restoration of protective layer of concrete using special compound for protection of concrete structures from exposure to water leaching.

Thus, reinforced concrete tank have lower initial cost, but the final cost of its maintanance far exceeds the cost of installation and operation of ground modular stainless steel tanks.

And few words about modular tanks made of stainless steel:

  • Free of welding technology allows implement erection at explosion-fire-risk places almost without excessive precautions.

  • Assembling indoors with limited access.

  • Aesthetic look of the tank actually doesn't changes after tens of years without additional expensive painting and maintanance.

  • Environmentally friendly material (stainless steel) has proved itself over a century.

  • Our steel tanks have been working already for more than 12 years without any additional investments.

  • Hidden defects are absent.

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