Guide to the construction of reinforced concrete in the Arabian peninsula

Guide to the construction of reinforced concrete in the Arabian peninsula

• Overview

This book provides those working with reinforced concrete in the Arabian Peninsula with information and guidance on the production of high-quality, durable concrete, able to withstand the region’s extremely harsh environment. Much of the guidance is also applicable to concrete construction in other hot-wet and hot-dry environments around the world. The principles set out in the Guide are applicable for the whole range of construction activity, from small-scale building works to large civil engineering projects.

The Guide is in four parts. The first outlines the principles underlying the successful use of concrete construction in the Arabian Peninsula. The extreme environment and the geological and geomorphological conditions are discussed in detail. The second part provides a comprehensive guide to the materials available. Execution of concrete works is covered in the third part, while the final part presents guidance on mix design. Appendices provide data on local climate and on formwork pressures. A detailed subject is included. The book was prepared by a working party as part of a collaborative project between CIRIA and The Concrete Society, working with authorities and organisations based in Arabia.

• Abstract

Outlines the principles underlying the successful use of concrete construction in the Arabian Peninsula. The extreme environment, and the geological and geomorphological conditions, are discussed in relation to these principles. Provides guidance on the materials available. Covers site operations and guidance on mix design. Also includes data on local climate and formwork pressures.

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Qatar Construction Specifications

Qatar Construction Specifications QCS 2014

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Cement

Concrete Component

Cement

·        What is cement and how it is working

Portland cements are hydraulic cements composed primarily of hydraulic calcium silicates Hydraulic cements set and harden by reacting chemically with water. During this reaction, called

hydration, cement combines with water to form a stone like mass, called paste. When the paste (cement and water) is added to aggregates (sand and gravel, crushed stone, or other granular material) it acts as an adhesive and binds the aggregates together to form concrete, the world’s most versatile and most widely used construction material. Hydration begins as soon as cement comes in contact with water. Each cement particle forms a fibrous growth on its surface that gradually spreads until it links up with the growth from other cement particles or adheres to adjacent substances. This fibrous build up results in progressive stiffening, hardening, and strength development. The stiffening of concrete can be recognized by a loss of workability that usually occurs within three hours of mixing, but is dependent upon the composition and fineness of the cement, any admixtures used, mixture proportions, and temperature conditions. Subsequently, the concrete sets and becomes hard.Hydration continues as long as favorable moisture and temperature conditions exist (curing) and space for hydration products is available. As hydration continues, concrete becomes harder and stronger. Most of the hydration and strength development take place within the first month, but then continues, though more slowly, for a long time with adequate moisture and temperature. Continuous strength increases exceeding 30 years have been recorded

·         MANUFACTURE OF PORTLAND CEMENT

Portland cement is produced by pulverizing clinker which consists primarily of hydraulic calcium silicates. Clinker also contains some calcium aluminates and calcium aluminoferrites and one or more forms of calcium sulfate (gypsum) is interground with the clinker to make the finished product.

Materials used in the manufacture of portland cement must contain appropriate amounts of calcium, silica, alumina, and iron components. During manufacture, chemical analyses of all materials are made frequently to ensure a uniformly high quality cement.

Selected raw materials  are transported from the quarry ,crushed , milled, and proportioned so that the resulting mixture has the desired chemical composition.

The raw materials are generally a mixture of calcareous (calcium carbonate bearing) material, such as limestone, and an argillaceous (silica and alumina) material such as clay, shale, fly ash, or blast-furnace slag. Either a dry or a wet process is used. In the dry process, grinding and blending are done with dry materials. In the wet process, the grinding and blending operations are done with the materials mixed with water in a slurry form.

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Fundamentals of Concrete

What is Concrete and How can we Control quality of Concrete, Why is concrete an excellent building material

·       What is concrete

Concrete is derived from the Latin word “concretus” meaning grown together or compounded.

Concrete is basically a mixture of  two components: aggregates and  paste. The paste, comprised of portland cement and water, binds the aggregates (usually sand and gravel or crushed stone) into a rock like mass as the paste hardens because of the chemical reaction of the cement and water Supplementary cementitious materials and chemical admixtures may also be included in the paste.

Aggregates are generally divided into two groups: fine and coarse. Fine aggregates consist of natural or manufactured sand with particle sizes ranging up to 9.5 mm (3⁄8 in.); coarse aggregates are particles retained on the 1.18 mm (No. 16) sieve and ranging up to 150 mm (6 in.) in size. The maximum size of coarse aggregate is typically 19 mm or 25 mm (3⁄4 in. or 1 in.). An intermediate-sized aggregate, around 9.5 mm (3⁄8 in.), is sometimes added to improve the overall aggregate gradation.

The paste is composed of cementitious materials, water, and entrapped air or purposely entrained air. The paste constitutes about 25% to 40% of the total volume of concrete. Fig. 1-2 shows that the absolute volume of cement is usually between 7% and 15% and the water between 14% and 21%. Air content in air-entrained concrete ranges from about 4% to 8% of the volume. Since aggregates make up about 60% to 75% of the total volume of concrete, their selection is important. Aggregates should consist of particles with adequate strength and resistance to exposure conditions and should not contain materials that will cause deterioration of the concrete. A continuous gradation of aggregate particle sizes is desirable for efficient use of the paste. Throughout this text, it will be assumed that suitable aggregates are being used, except where otherwise noted.

·       Concrete Quality

The quality of the concrete depends upon the quality of the paste and aggregate, and the bond between the two. In properly made concrete, each and every particle of aggregate is completely coated with paste and all of the spaces between aggregate particles are completely filled with paste, For any particular set of materials and conditions of curing, the quality of hardened concrete is strongly influenced by the amount of water used in relation to the amount of cement Unnecessarily high water contents dilute the cement paste (the glue of concrete).

Following are some advantages of reducing water content:

• Increased compressive and flexural strength

• Lower permeability, thus lower absorption and increased water tightness

• Increased resistance to weathering

• Better bond between concrete and reinforcement

• Reduced drying shrinkage and cracking

• Less volume change from wetting and drying

The less water used, the better the quality of the concrete—provided the mixture can be consolidated properly. Smaller amounts of mixing water result in stiffer mixtures; but with vibration, stiffer mixtures can be easily placed. Thus, consolidation by vibration permits improvement in the quality of concrete.

The freshly mixed (plastic) and hardened properties of concrete may be changed by adding chemical admixtures

to the concrete, usually in liquid form, during batching. Chemical admixtures are commonly used to

1.      adjust setting time or hardening,

2.      reduce water demand,

3.      increase workability,

4.      intentionally entrain air,

5.      adjust other fresh or hardened concrete properties.

·       Why is Concrete an excellent building material

After completion of proper proportioning, batching, mixing, placing, consolidating, finishing, and curing, concrete hardens into a strong, noncombustible, durable, abrasion-resistant, and watertight building material that requires little or no maintenance.

 Furthermore, concrete is an excellent building material because it can be formed  into awide variety of shapes, colors, and textures for use in an unlimited number of applications

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