ACI 201.2R-16 Guide to Durable Concrete

ACI 201.2R-16 Guide to Durable Concrete. 3.1—Introduction Concrete is a multiphase porous medium consisting of a multiscale porous cement paste matrix with aggregate inclu- sions. Liquid and gas may be present in any pores and micro- cracks. As such, it is susceptible to the ingress and move- ment of substances (fuids or ions) from its environment within and through its pore system. This chapter discusses the transport of gases, liquids, and ions in solution through concrete (Lichtner et al. 1996; Baer 1988; Hearn et al. 2006; Hall and Hoff 2012). Methods for improving the durability of concrete and some of the common test methods used to measure the transport properties, along with their advantages and limitations with regard to assessing concrete durability, are also discussed. It is recognized that the rate of ingress of fuids and ions will increase by the presence of cracks. However, the specifc infuences of different types of cracks and crack widths are not discussed herein. The ingress of gases, liquids, or ions in solution through concrete may initiate chemical processes, physical processes, or both, that affect the durability of the concrete under a given set of service conditions. Water itself may be harmful because of its ability to leach calcium hydroxide (CH) from the hard- ened cement paste and because of osmotic pressures gener- ated as water fows to sites of higher alkalinity (Powers et al. 1954; Powers 1975; Helmuth 1960b,c). In addition, water may also be acidic or carry harmful dissolved chemicals, such as chlorides or sulfates, into the concrete. The ingress of gases such as oxygen and carbon dioxide through the concrete pores can contribute to the corrosion of steel reinforcement. Johannesson (2003) developed a theoretical model for diffusion of different types of ions in concrete pore solution. The model incorporates diffusion caused by concentration gradients of ions (for example, due to drying), internal elec- trical potential, convection, effects of changes in moisture content, and mass exchange of ions between solution and solid hydration phases. Chung and Consolazio (2005) developed a fnite difference model to simulate heat and mass transport in rapid heating conditions, such as fres in reinforced concrete structures. The model accounts for the interference between liquid and gas phases, slip-fow effects in steam fow, and the interference of steel reinforcement in moisture movement in concrete.ACI 201.2R pdf download.