Durability—general aspects

If it is properly designed and produced for the environment in which it has to serve, concrete is an extremely durable material. If the design or production is inadequate, it may deteriorate. Some environments exist in which no concrete is durable. 

Deterioration may occur through a variety of chemical or physical processes. The rest of this chapter deals with these, with emphasis on chemical processes in which the cement paste is involved. For convenience, the various forms of attack are considered separately, but examination of deteriorated concretes often shows that more than one form of attack has been operative. This is often because one form of attack renders the concrete more susceptible to damage by another. Portland and composite cement concretes are considered calcium aluminate cements were discussed in Section 10.1.11. 

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The second part of this study [92] considered this peculiar point that has considerable consequences in terms of fundamental aspects of both the photooxidation of nanocomposites and the durability of these materials. A special attention was given to the interactions between the antioxidant, the clay (montmorillonite), and the compatibilizing agent (maleic anhydride), in terms of influence of each component on the rate of oxidation of the polymeric matrix. Two kinds of stabilizers were tested a phenolic antioxidant (Scheme 15.14) generally used to process polypropylene and a redox antioxidant of the hindered amine light stabilizer (HALS) class (Scheme 15.15) that is used as long-term stabilizer for polypropylene. 

Anode system. The anode system, which consists of the anode material plus its overlay, must supply the required current for the anticipated service life and distribute it to the reinforcement that needs to be protected. Anode materials and current density aspects have been dealt with in a previous section. The general requirements of an anode system are it has to adhere to the concrete surface it should be suitable for appHcation to the surface needing protection (top, bottom, horizontal, vertical, flat, curved), it should be durable and have low installation cost it should produce acceptable weight addition and change of the appearance and dimensions of the structure. If an overlay is used, it should have durable bond to the substrate concrete, sufficient mechanical strength and electrical characteristics equal to those of base concrete (ionic conductivity). 

The previous chapters have mostly surveyed broad aspects of reinforced plastics durability and have highlighted general principles. This chapter is rather different, being focussed more narrowly on recent research into a specific topic. It seeks to demonstrate that durability (or more precisely, fatigue life) can be affected, not just by the choice of resin or fibers, but by the nature of the boundary region between the two. 

Aspects of this subject are also dealt with in other articles, notably Acrylic adhesives. Durability - fundamentals. Joint design general. Joint design cylindrical joints. Joint design strength and fracture perspectives. In the article on Toughened acrylic adhesives, some properties are compared with those of Epoxide adhesives and anaerobic adhesives. 

Together with often complex aspects of DMFC system design (applicable to both passive and active DMFC system concepts), durable operation of the fuel cell stack and the ability to deliver the required power for several thousand hours are generally considered crucial to the ultimate large-scale commercial success of DMFCs. Other key requirements include cell (stack) operation at a highest achievable voltage and cathode operation at ambient pressure, low airflow, and natural air humidification. 

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