Abstract: Carbon nanotubes (CNTs) are combined with cement, aggregate and plasticizers to form composites with increased strength. CNT reinforced concretes comprising cement, plasticizer, aggregate, and nanotubes, hydrated with water are disclosed. A mixture of CNTs, cement, and plasticizer can be prepared for later admixture with aggregates and water to form composites having improved strength characteristics. A method for increasing the strength of concrete comprising the steps of admixing CNTs and plasticizer's with cement, aggregate, and water for hydration is also disclosed.