Manufactured Sand and Crushed Stone in Portland Cement Concrete


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Title: Manufactured Sand and Crushed Stone in Portland Cement Concrete

Author(s): Frank P. Nichols, Jr.

Publication: Concrete International

Volume: 4

Issue: 8

Appears on pages(s): 56-63

Keywords: aggregate gradation; aggregates; air-entrained concretes; coarse aggregates; concrete durability; fine aggregates; mix proportioning; sands.

Date: 8/1/1982

Reviews results of an extensive laboratory study of the effects of variations in gradations and particle shape of manufactured fine aggregates, and of variations in coarse aggregate factor and coarse aggregate maximum size on properties of freshly mixed and hardened air-entrained portland cement con cretes. Using a range of fixed cement contents, mix ing water was varied as needed to produce slumps within a narrow range above or below a single specified target value of 3 in. (76.2 mm). The complete study included 171 experimental mix tures made from a single source of cement, a single source of crushed stone coarse aggregate, and six sources of fine aggregate. One fine aggregate was a commercially processed natural sand, the other five were manufactured sands with various gradation and particle shapes from five sources of crushed stone Particle shape ranged from 47 to 55 in terms of NCSA Shape Index, a measure of percentage of voids in 2 loose condition. Gradation variables were particulary concerned with the amount of dust of fracture or microsand included. A more complete and detailed report by L. V. Kalcheff, who directed the study, has been given limited distribution. Copies are on file a: the National Crushed Stone Association (NCSA) Heat. quarters. Results show that satisfactory air-entrainec portland cement concrete can be produced in the normal strength range with fine aggregates containing considerably more microsand passing the No. 100 and 200 sieves than has been commonly allowed in typical specifications. However, ASTM Specification C 33 states that fine aggregate failing to meet the normal sieve analysis and fineness modulus requirements may be accepted provided that.concrete of the class specified, made with the fine ag gregate under consideration, will have relevant properties at least equal to those of concrete made with fully acceptable fine aggregates. Thus, the results of this study confirm the validity of the permissible devia tions from the gradations normally specified, as now included in ASTM C 33.