CONCRETE PIPE Principle Aggressive Factors This section covers specific chemical and physical factors which can be aggressive to concrete pipe and which collectively account for practically all of the durability problems that can be encountered in traditional applications of the product. These factors are: • • • • • Acids Sulfates Chlorides Freeze-thaw and weathering Velocity and abrasion Linings or Coatings Under severe exposure to acids or chlorides, linings or coatings may provide an engineering alternative. But since these exposure conditions are rare, determination that there will be economic benefits necessitates a thorough analysis of service conditions and a realistic definition of aggressive factors encountered. Mitigating effects of short term or intermittent exposure characteristics are also relevant. Potential alleviation of exposure conditions by modification of design details should also be explored, such as the application of the principles of sulfide control to sanitary sewer design. Direct durability enhancement of the concrete pipe can also be considered; for example, increasing total alkalinity for greater acid resistance. Use of pipe linings or coatings as protective measures should be limited to those cases where it will provide the most cost-effective solution for the desired level of durability. Different types of linings and coatings are commercially available and have been used in concrete pipe with varying degrees of success. Thin linings and coatings are generally applied by brush, spray or roller. Single or multiple applications may be used, depending upon the characteristics of the material and the desired total thickness. Thin linings and coatings generally range from 10 mils to 50 mils in thickness. Dependable and uniform adherence to the concrete surface is an essential requirement for long-term performance. Careful preparation of the concrete surface is necessary prior to application. PAGE 46 LAFARGE PIPE eMANUAL