Copyright Goodheart-Willcox Co., Inc. 110 Section 3 Specifications and Materials mixes can vary from job to job and area to area depending on engineering and structural requirements. Any material added to the concrete mix—other than cement, sand, aggregate, and water—is known as an admixture. Admixtures are used to make the mix more workable, retard or speed up hardening, increase freeze resistance, or increase chemical resistance. Common admixtures to concrete include air entrainment, used to t improve durability in freeze/thaw environments retarders, used to slow down the initial set of fresh concrete, especially in hot weather accelerators, used to speed up the initial set of fresh concrete in cold weather water reducers, used to reduce the amount of water required for a desired workability and water-to-cement ratio for strength and coloring agents, used for altering the color of the concrete mixture. Concrete is typically transported to the job site in a ready-mix truck. See Figure 7-4. The five basic types of cement include: • Type I, Normal Cement (most common) • Type II, Moderate Sulfate Resistance (slow-reacting) • Type III, High Early Strength (fast-setting) • Type IV, Low Heat of Hydration (low heat generation) • Type V, High Sulfate Resistance These cements, along with aggregates and admix- tures, are available to produce special types of concrete. For example, Type IV cement is for low heat generation for large construction building foundation projects, such as dams. Other cements have high early strength to produce concrete that gains strength faster than normal, Type I or II cements, permitting earlier form removal and thus speeding cold weather construction. Still others are more resistant to deterioration caused by sulfates and alkalis in the soil. Concrete Mixes A concrete mix should be designed to produce the desired result. Characteristics and properties of concrete depend on the materials, and their proportions, that make up the mixture. This will determine the work- ability, strength, durability, economy, volume stability, and appearance of the finished hardened concrete. Enough water is added to make the mixture plastic, so that it will flow into the forms. Too much water, however, will reduce the strength and durability of the concrete, so the contractor needs to be careful. A typical mix would consist of 10% cement, 15% water, 25% fine aggregates, 45% coarse aggregates, and 1% to 5% entrained or entrapped air. See Figure 7-3. Concrete Water 15% Air entrainment 1%–5% Coarse aggregates 45% Fine aggregates (sand) 25% Cement 10% 1 cubic yard Goodheart-Willcox Publisher Figure 7-3. Common proportions of materials making up concrete. Proportions can vary depending on local materials, design mix and strength requirements, and air entrainment. Fly Ash Fly y ash s is produced o when coal is burned ne to pro od uce electricity. ec This by-product can c be u us ed in concrete c n a as a replacement for part o of the Portlan nd cement. m m Environmental benefits f s of re eu sin ng fly ash h to replace ep Portland cement includec con ns e er vation on of resources and energy, y , reduc ct ion o of gree g en house us gas emissions, and redu d uc ed cost c ts . In addition, a d fly ash improves the worka k ab ility o of the fresh s c co ncret e te requires less water, wh hi c ch reduce d es cra ac king and n d makes the final product more dur ra ble because ca permeability is reduced.u GREEN BUILDING