By: Anthony M. Sorcic
There has been quite a movement within our industry toward the use of performance specifications in concrete work. Not only is moving toward performance a good idea, but it also is a necessary one. Many locations simply cannot provide the necessary ASTM C150 cements for the various destructive mechanisms that can affect concrete in the field.
One item in particular that has been gaining notoriety is that of sulfate attack. In many areas of the country where Type II cement was thought to be sufficient, further soil testing has indicated that sulfate levels are higher than expected and now require the use of ASTM C150 Type V cement. The problem is that not all cement-manufacturing plants are capable of producing such cement.
For a plant to produce Type V cement, it will require additional plant cost and natural resources. In addition, because of the burning process and manufacturing associated with Type V cement, a lesser total quantity of cement can be produced at a specific plant, thus lowering the total product available for our industry. With concrete in such high demand and the cement shortage so ever-present, this will further add to the strain on the construction industry.
The movement toward performance-based specifications also is strongly supported by the National Ready Mixed Concrete Association in their Prescription to Performance initiative. Producers see this as a way to use the best available technologies in an effort to produce a product that meets explicit performance requirements.
Over the past few decades, there has been ample research done in the use of supplementary cementitious materials to combat the destructive nature of sulfate attack. The use of materials such as Class F fly ash and slag cement in concrete mix designs has been shown to be an effective means in controlling sulfate attack. These systems, coupled with lower water-cement ratios and chemical admixtures, can truly provide the concrete producer the means to combat these issues in the field.
Ternary mixes, like those of portland, fly ash and slag cement, have been used in practically every concrete application. Ternary mixtures can be designed for high strength, low permeability, sulfate resistance and alkali-silica reactivity resistance just to name a few. Furthermore, the use of these additional cementitious materials helps to reduce emissions, energy and virgin material requirements when compared with 100% portland mixtures. By moving to these types of ternary mixtures, we are not only producing a greener concrete, but also working together to become more environmentally friendly.
It is imperative that state and local agencies, along with specifiers and owners, be made aware of the alternative concrete systems available. In most cases, these alternative concrete mixes are going to be more economical and provide a longer concrete life span than the traditional one-component mixes.
The ultimate goal here is to provide the end user with a safe and long-lasting concrete structure, one that is economical and environmentally sound, without additional waste of our natural resources.
