Portland-pozzolan cement, or pozzolanic materials added to the concrete at the mixer, have been used on several mass concrete jobs in recent years. These cases are reviewed and discussed in connection with the characteristics of concrete made with such cementing materials and the advantages which they offer for mass construction. Material savings have been achieved by replacing a portion of the cement usually used with pozzolan, with resultant lower temperature rise and reduced cracking tendency without sacrificing ultimate strength in the concrete. It has also been shown that some pozzolans will aid in securing sound concrete with reactive aggregates. Comparison is made with two old dams, built with so-called “sand-cement,” wherein the present-day objectives in coping with cracking were achieved with concretes of low cement content supplemented with fine siliceous material.