Concrete Water Storage Tanks, Structures & Reservoirs
case studies - Covac Completion Reports
For detailed documentation of some of the concrete water storage tank repair and refurbishment we have completed, please see the case study links below.
We are all now under an obligation to ensure that concrete potable water storage tanks and reservoirs comply with the practical guidance of ACOP L8 and subsequently, the stringent WRAS and/or DWI Regulations. Water quality should be confirmed by regular water testing analysis and "maintenance of the cleanliness of the system and the water in it".
Unfortunately, once concrete starts the process of erosion, blow holes (more commonly known as "bug holes") and exposed aggregate can become more prominent, providing a potential harbouring ground for bacteria such as micro-aquatic organisms within the concrete water storage tank.
Concrete is a mixture of Portland cement, water, fine and course mineral aggregates and various admixtures. On mixing all these ingredients in the correct proportion, a complex chemical reaction is set in motion. Concrete feels like it is a very strong and hard substance, but unprotected and bare concrete is also subject to deterioration. It is an inherent quality of concrete to have micro-pores, and if these are interconnected, causing a build up of moisture and pollutants. If the reaction of cement with water generates heat, then it creates the possibility of developing micro-cracks due to shrinkage. Constant water and chemical permeation and abrasion can also wear down the paste and the aggregate. Water can penetrate concrete, freeze and expand when the temperature drops and weaken the concrete from inside. In addition, the reinforcement steel bar can fall apart with oxygen, moisture, and chloride ions infiltrating the concrete water storage tank.
Concrete can be very variable and it is often difficult if not impossible to identify the aggregate and ad-mixture source of older tanks or indeed the composition of jointing compounds used at construction stage, noticeably the problems with PCBs (Poly Chlorinated Biphenyls) from jointing compounds historically used. PCBs can damage the immune, reproductive, nervous and endocrine systems. They can also impair children's physical and intellectual development and according to the Agency for Research on Cancer, PCBs are strongly linked to both animal and human cancer.
Over time, all concrete absorbs water and early stages of problems can be seen by rust staining from the reinforcing bars, which is clearly going to have an adverse effect on water quality quite apart from the integrity of the structure. Also, as concrete is a porous substrate, it can harbour waterborne organisms such as bacteria and subsequently; the substrate will require a relatively high demand for disinfection chemicals.
Concrete Water Retaining Structures
In summary, concrete is an extremely variable construction material and usually exhibits low surface tensile strength.
Blowholes, micro-pores and air pockets provide an easy access route for water and chloride migration to the steel reinforcing.
Under load concrete will crack providing further access points for these corrosive forces. When used for transportation and storage of water, even the mildest of chemical solutions, can have a rapid deterioration effect on concrete.
A protective coating system for concrete should therefore meet the following requirements:
Acothane DW meets with the above requirements and has successfully been applied to a variety of concrete water storage tanks and structures for both dry and total immersion service.