Optimizing Paving Mixtures for Durable,Cost-Effective,and Sustainable Concrete

This paper presents 7-, 28-, and either 56- or 90-day compressive strength data from 17 field projects collected by the Federal Highway Administration’s Mobile Concrete Laboratory from 13 states. This paper also presents data on the concrete strength required to open to construction traffic and data on permeability for the same projects. The data indicate that, in most cases, the 28-day strength requirement of the respective agencies was met in only 7 days. On average, the 28-day strength requirement was exceeded by more than 60%, and the 56- or 90-day strength exceeded the 28-day strength requirement by more than 80%. This paper argues that such high strengths, especially high early strengths, are not warranted and can be detrimental in many ways to the long-term performance of concrete pavements. Overall, the strength data from all 17 field projects indicate that there is a huge opportunity to optimize the mixture designs typically produced. From the mixture design information obtained from these projects, it appears that most agencies and contractors are already utilizing optimized gradation wherever possible and also have increased the use of supplementary cementitious materials. Further optimization of the mixture designs is possible, however, by reducing the cement contents. There are many drawbacks to higher cement content. It leads to higher amounts of water, which can in turn lead to higher shrinkage and higher potential for cracking. Higher cement content also increase the cost of production and contributes to higher carbon dioxide emissions.