ABSTRACT
Abstract A long-term investigation is currently being conducted at the NSF Center for Advanced Cement-Based Materials (ACBM) to examine the long-term durability of concrete. This paper provides an overview of recent results to illustrate the influence of mixture proportioning on permeability, mechanical properties, and early-age shrinkage cracking. The permeability study investigated a large array of concrete mixture proportions with various aggregate volume fractions, gradings, and maximum sizes for several different water-to-cement ratios (w/c). The effects of dilution, tortuosity, interfacial transition zone, and percolation on the permeability of concrete are discussed. In addition, a relationship between crack width and water permeability of concrete was investigated. Restrained shrinkage testing has been performed to understand the influence of mechanical properties on early-age cracking, especially for mixes with chemical and mineral additives. Results are provided to illustrate the influence of the water-to-cement ratio, silica fume replacement, latex, and a shrinkage reducing admixture; on strength, permeability, and restrained shrinkage cracking. These results illustrate that a specification based solely on strength may not ensure a durable concrete. It is proposed that three criteria: strength, permeability, and cracking resistance; are necessary to design a durable concrete.
