Engineering B45 Concrete Lab Report
Introduction: Concrete is a mixture of sand and rock or similar inert material (aggregates) held together by a cementing material. Usually the cementing material is Portland cement, but sometimes binders such as asphalt or gypsum are used, in which case the concrete may be called asphaltic concrete or gypsum concrete. Properties of concrete are governed not only by the properties of its ingredients (cement, water, sand, and coarse aggregate) but also, to a great extent, by the relative proportions of these ingredients. The proportions must be so selected as to produce a concrete mixture of desired workability, strength, durability, and economy. The most common aggregates are gravel and crushed stone, although cinders, blast-furnace slag, burned shale, crushed brick, or other materials may be used because of availability, or to alter such characteristics of the concrete such as workability, density, appearance, or conductivity of heat or sound. Usually aggregate which passes a sieve with 0.187-inch openings (No. 4 sieve) is called fine aggregate, but that retained by a No. 4 sieve is coarse aggregate, although the division is purely arbitrary. If all the particles of aggregate are of the same size, or if too many fine particles are present, an excessive amount of cement paste will be required to produce a workable mixture; a range of sizes aids in the production of an economical mixture. The best concrete for a given use is usually the one which will provide the necessary strength and the desired workability at the lowest cost. Unless otherwise indicated, strength, as applied to concrete, refers to the ultimate compressive strength of the moist-cured concrete at the age of 28 days. Most concretes are batched to provide an ultimate compressive strength of 2500 to 4000 psi after 28 days. The figure below shows a typical strength curve of concrete with the passage of time. The modulus of elasticity of concrete is about 1000 times...
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