15 - CIVE 2700 Civil Engineering Materials, Winter 2007...

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CIVE 2700 – Civil Engineering Materials, Winter 2007 1 Aggregates Professor George Hadjisophocleous, Ph.D., P.Eng. Carleton University Department of Civil and Environmental Engineering Ottawa, Ontario CIVE 2700 – Civil Engineering materials, Winter 2007, 15.2 Outline • Types of aggregates • Geometric properties • Characteristics of aggregates • Physical properties
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CIVE 2700 – Civil Engineering Materials, Winter 2007 2 CIVE 2700 – Civil Engineering materials, Winter 2007, 15.3 Introduction Mined aggregates constitute about 70 – 80% by volume of Portland cement concretes and 90% of asphalt concretes. They strongly influence the concrete’s freshly mixed and hardened properties, mixture proportions, and cost. Fine aggregates generally consist of natural sand or crushed stone with most particles smaller than 5 mm . Coarse aggregates consist of one or a combination of gravels or crushed aggregate with particles predominantly larger than 5 mm, and generally between 10 mm and 40 mm. Natural gravel and sand are usually dug or dredged from a pit, river, lake, or seabed. Crushed aggregate is produced by crushing quarry rock, boulders, cobbles, or large-size gravel. CIVE 2700 – Civil Engineering materials, Winter 2007, 15.4 Introduction
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CIVE 2700 – Civil Engineering Materials, Winter 2007 3 CIVE 2700 – Civil Engineering materials, Winter 2007, 15.5 Introduction The most commonly used aggregates such as sand, gravel, crushed stone, and air-cooled blast-furnace slag produce wet or freshly mixed normal density concrete of 2200 to 2400 kg/m 3 . Aggregates of expanded shale, clay, slate, and slag are used to produce structural low density concrete with a freshly mixed density ranging from about 1350 to 1850 kg/m 3. For adequate consolidation of concrete, the desirable amount of air, water, cement, and fine aggregate (i.e., the mortar fraction) is about 50% to 65% by absolute volume (45% to 60% by mass). Rounded aggregate, such as gravel, requires slightly lower values while crushed aggregate requires slightly higher values. Fine aggregate content is usually 35% to 45% by mass or volume of the total aggregate content. CIVE 2700 – Civil Engineering materials, Winter 2007, 15.6 Geometric Properties Grading – Grading is the particle-size distribution of an aggregate as determined by a sieve analysis as outlined in CSA Test Method A23.2-2A (ASTM C 136) . – The aggregate particle size is determined by using wire-mesh sieves with square openings. The seven standard CSA A23.1 ( ASTM C 33) sieves for fine aggregate have openings ranging from 160 ! m to 10 mm. – The 11 standard sieves for coarse aggregate have openings ranging from 1.25 mm to 112 mm.
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CIVE 2700 – Civil Engineering Materials, Winter 2007 4 CIVE 2700 – Civil Engineering materials, Winter 2007, 15.7 Geometric Properties • The grading and grading limits are usually expressed as the percentage of material passing each sieve. • The grading and maximum size of aggregate affect
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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15 - CIVE 2700 Civil Engineering Materials, Winter 2007...

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