Will More Cement in Your Mixture Hurt You?

An old rule of thumb states that if you need more strength in a concrete mixture, just throw more cement at it. Sometimes that helped, sometimes not. Today many engineers realize that there are many other variables in a mixture that effect strength as much as, or more than, cement content. They also realize that increased cement content in a concrete mixture can lead to a number of effects that may reduce the life of the pavement. Many properties of concrete are adversely affected by over-cementing the mixture. These are discussed to help the reader understand why optimizing the cement content will help produce an efficient mixture that will meet the project requirements. By first determining the voids in the aggregate portion of the concrete mixture and then increasing that volume by an amount necessary for workability, a volume of paste can be determined that will approximate the optimum cementitious content to both maximize strength and also provide a workable mixture. Also discussed are the effects of increasing the cement content in a concrete mixture, including durability, strength, heat generation, shrinkage, set time, workability, CO2 footprint, as well as cost.