ACI 304R-00 Guide for Measuring, Mixing, Transporting, and Placing Concrete. 2.2.3 Storage—Stockpiling of coarse aggregate should be kept to a minimum because fines tend to settle and accu- mulate. When stockpiling is necessary, however, use of correct methods minimizes problems with fines, segrega- tion, aggregate breakage, excessive variation in gradation, and contamination. Stockpiles should be built up in hori- zontal or gently sloping layers, not by end-dumping. Trucks, loaders, and dozers, or other equipment should not be operated on the stockpiles because, in addition to breaking the aggregate, they frequently track dirt onto the piles (Fig. 2.1). Provide a hard base with good drainage to prevent contami- nation from underlying material. Prevent overlap of the different sizes by suitable walls or ample spacing between piles. Protect dry, fine aggregate from being separated by the wind by using tarps or windbreaks. Do not contaminate stockpiles by swinging aggregate-filled buckets or clam- shovels over the other piles of aggregate sizes. In addition, fine aggregate that is transported over wet, unimproved haul roads can become contaminated with clay lumps. The source of this contamination is usually accumulation of mud between the tires and on mud flaps that is dislodged during dumping of the transporting unit. Bottom-dump trailers are particularly susceptible to causing contamination when they drive through discharged piles. Clay lumps or clay balls can usually be removed from the fine aggregate by placing a scalping screen over the batch plant bin. 3.1—General requirements 3.1.1 Objectives—An important objective in producing concrete is to achieve uniformity and homogeneity, as indi- cated by physical properties such as unit weight, slump, air content, strength, and air-free unit weight of mortar in indi- vidual batches and successive batches of the same mixture proportions (U.S. Department of Reclamation 1981, U.S. Department of Commerce 1966, Bozarth 1967, ASTM C 94, Corps of Engineers 1994b). During measurement operations, aggregates should be handled so that the desired grading is maintained, and all materials should be measured within the tolerances acceptable for desired reproducibility of the selected concrete mixture. Another important objective of successful batching is the proper sequencing and blending of the ingredients (U.S. Department of Commerce 1966; Bozarth 1967). Visual observation of each material being batched is helpful in achieving this objective.ACI 304R pdf download.
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