6505-2 - Aggregates for Concrete Aggregate ( 60 - 80 % by...

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1 Aggregates for Concrete Aggregate ( 60 - 80 % by volume ) FUNCTIONS OF AGGREGATE IN CONCRETE Economy (aggregate as space filler) Strength Reduction in shrinkage and expansion DESIRABLE CHARACTERISTICS OF AGGREGATES Hard, strong & durable Free of organic impurities Low alkali reactivity with cement Proper gradation (for good workability and packing of voids)
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2 Cracking of concrete from use of alkali-reactive aggregate The level of liquid in the graduates, representing voids Aggregate of Same size Same size Different sizes combined Classifications of Aggregate By Size Coarse aggregate - particles retained on No.4 sieve (4.75mm or 3/16 in.) Fine aggregate - particles passing No. 4 sieve. By Source Natural mineral aggregate - sand, gravel , crushed stone. Artificial or synthetic aggregate - blast-furnace slag, expanded clay, expanded shale.
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3 Classifications of Aggregate (continued) By Types of Rock Igneous rock - formed on cooling of the magma. Intrusive igneous - formed by slow cooling beneath earth’s surface. Characteristics: completely crystalline minerals, coarser grain. Examples: granite, trap rock. Extrusive igneous - formed by more rapid cooling at or near earth’s surface. Characteristics: finer grain, minerals with smaller crystals or glassy structures. Examples: basalt, perlite. Classifications of Aggregate (continued) Classification of igneous rock based on SiO 2 content Acid - more than 65% SiO 2 Intermediate - 55 to 65% SiO 2 Basic - less than 55% SiO 2 Sedimentary Rock - formed from disintegration of other rocks and deposited as sediments Examples: limestone, sandstone, shale Metamorphic Rock - Igneous or sedimentary rocks that have changed its structure due to heat and pressure. Usually harder and denser. Examples: marble, slate. Prediction of Behavior of Aggregates in Service From past performance record - The best basis for prediction of performance. From mineral composition. For example: the minerals amorphous opal, chalcedony & tridymite are known to cause alkali-silica reaction. From results of tests - This method is most commonly used.
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4 L.A. Abrasion Test Test for hardness or resistance to abrasion Los Angeles Abrasion Machine ASTM C 131 -For aggregates smaller than 37.5 mm (1.5 in.) ASTM C 535 aggregates larger than 19.0 mm (3/4 in.) L.A. Abrasion Machine L.A. Abrasion Machine
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5 L.A. Abrasion Test Procedures 1. Run sieve analysis on test sample to determine weight retained on #12 sieve (1.7 mm or 0.067 in.). Place test sample in L.A. testing machine (rotating drum with metal balls inside) C131 - 5,000 g sample, 6 to 12 metal balls (depending on aggregate size) C535 - 10,000 g sample, 12 metal balls 2. The L.A. machine is rotated at a speed of 30 to 33-rpm for 500 revs. L.A. Abrasion Test Procedures (Continued) 3. Run sieve analysis on test sample after the test.
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This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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6505-2 - Aggregates for Concrete Aggregate ( 60 - 80 % by...

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