Q.: I know that Type III cement is high-early strength cement, but what gives it a higher early strength than type I cement?

A.: The main difference between Type I and III cements is fineness. Type III is ground finer. The greater fineness speeds cement hydration because there's more cement surface area that comes in contact with water. A faster hydration rate speeds strength development during the first 7 days of curing. It also causes more heat to be released during the early curing period.