The ACI 318 Building Code requires cement to conform to ASTM C150, Standard Specification for Portland Cement; or ASTM C595, Standard Specification for Blended Hydraulic Cements; or ASTM C845, Standard Specification for Expansive Hydraulic Cement. Portland cements meeting the requirements of ASTM C150 are available in Types I to V and air-entraining Types IA to IIIA for use under different service conditions. The ACI 318 Building Code prohibits the use of slag cement, Types A and SA (ASTM C595), because these types are not intended as principal cementing constituents of structural concrete.
Although all the preceding cements can be used for concrete, they are not interchangeable.
Note that both tensile and compressive strengths vary considerably, at early ages in particular, even for the five types of basic portland cement. Consequently, although project specifications for concrete strength are usually based Æ’c on a standard 28-day age for the concrete, the proportions of ingredients required differ for each type. For concrete strengths up to 19,000 psi for columns in highrise buildings, specified compressive strengths are usually required at 56 days after initial set of the concrete. For the usual building project, where the load-strength relationship is likely to be critical at a point in strength gain equivalent to 7-day standard curing (Fig. 9.1), substitution of a different type (sometimes brand) of cement without reproportioning the mix may be dangerous.
The accepted specifications (ASTM) for cements do not regulate cement temperature nor color. Nevertheless, in hot-weather concreting, the temperature of the fresh concrete and therefore of its constituents must be controlled. Cement temperatures above 170F are not recommended (Hot Weathering Concreting, ACI 305R).
For exposed architectural concrete, not intended to be painted, control of color is desirable. For uniform color, the water-cement ratio and cement content must be kept constant, because they have significant effects on concrete color. Bear in mind that because of variations in the proportions of natural materials used, cements from different sources differ markedly in color. A change in brand of cement therefore can cause a change in color. Color differences also provoke a convenient check for substitution of types (or brands) of cement different from those used in trial batches made to establish proportions to be employed for a building.
