**1. Introduction**

High-strength concrete is increasingly used in the construction market in the United States and on a global scale. High-strength concrete is characterized by high early strength, high final strength, increased durability, and improved long-term performance. The use of high-strength concrete is advantageous in heavy construction projects, especially in precast/prestressed bridge construction. The mechanical advantage of high-strength concrete is attributed to the incorporation of supplementary cementitious materials (SCMs) in partial replacement of Portland cement. SCMs with different sizes and fineness are incorporated in the stepwise replacement of cement to create a binary mix (using one SCM) or ternary mix (using two SCMs). Incorporated SCMs increase the amount of the binder in the mix, which increases the mix strength. In addition, the improved packing order of the cementitious matrix reduces the mix void ratio and, hence, improve its durability and long-term performance. High-strength concrete was primarily used in the design and construction of high-rise buildings in major European cities and large/crowded American States as New York, Illinois, and California. In addition, the high compressive strength enabled bridge design engineers to precast long-span bridge girders with very high span-to-depth ratios (span/depth ratio greater than 30).

Recently, concrete mixes with higher strength and improved long-term performance were developed using SCMs, steel fibers, and a very low water-to-powder ratio. These mixes, commercially available in the United States construction market under the term *ultra-high-performance concrete*, are standardized by different agencies including the Federal Highway Administration (FHWA) in the United States, Association Francaise de Genie Civil (AFGC) in France, and the Japanese Society of Civil Engineers (JSCE). In their definition of the UHPC, the aforementioned organizations define UHPC as a cement matrix with minimum compressive strength of 150 MPa due to the high proportion of SCMs and very low water-to-powder ratio, and significant tensile strength due to the incorporation of random high-strength steel fiber. Different UHPC proprietary mixes are available in the international markets with standard characteristics. Examples of the proprietary mixes are BSI "Beton Special Industrial" (special industry concrete) developed by Eiffage, Cemtec developed by LCPC, and different kinds of ductal concrete mixes jointly developed by Bouygues, Lafarge, and Rhodia. Ductal concrete marketed by Lafarge and Bouygues is the only proprietary UHPC mix commercially available in the United States local construction market.

This chapter introduces different types and classifications of concrete mix designs, based on mix strength, workability, and long-term performance, different types of SCMs currently used in developing special concrete mixes, their impact on mix properties, and the main impediments to the widespread of SCMs application in precast/prestressed concrete industry.
