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CONCRETE TECHNOLOGY. Dr. Ali I. Tayeh. Syllabus. Chapter 1. Concrete. Concrete as a Material. Concrete. Concrete as a Material. The Nature Of Concrete. Advantages Of Concrete. Limitation Of Concrete.
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CONCRETE TECHNOLOGY Dr. Ali I. Tayeh
Chapter 1 Concrete Concrete as a Material
Concrete Concrete as a Material • The Nature Of Concrete • Advantages Of Concrete • Limitation Of Concrete
Concrete is a material that literally forms the basis of our modern society. Scarcely any aspect of our daily lives does not depend directly or indirectly on concrete. We may live, work, study, or play in concrete structures to which we drive over concrete roads and bridges. Our goods may be transported by trucks traveling on concrete super high ways. by trains that run on rails supported on concrete crossties., by ships that moor at concrete piers in -harbors protected by concrete breakwaters, or by airplanes landing and taking off on concrete runways. Water drinking and for raising crops is stored behind massive concrete dams and is distributed by systems of concrete waterways., conduits., and pipes.. Concrete as a Material
Concrete plays a key role in oil production, being used to construct massive off shore platforms for drilling . We take concrete for granted in our everyday activities and tend to be impressed by the more dramatic impacts of technology. it can be truly said that many of the achievements of our modern civilization have depended on concrete, just as many of the enduring achievements of the earlier civilization of Rome were ;made possible by the use of the forerunner of modern concrete. The word concrete comes from the Latin verb "concretus," which means to grow together. Concrete as a Material
The Nature Of Concrete Concrete is a composite material composed of coarse granular material (the aggregate or filler) embedded in a hard matrix of material (the cement or binder) that fills the space between the aggregate particles and glues them together. Aggregates can be obtained from many different kinds of materials, although we mostly make use of the materials of nature common rocks.
The Nature Of Concrete They are essentially inert, filler materials that, for convenience. are separated into fine and coarse factions. Similarly, the cement can be formulated from many diverse chemicals. "Cement"' is a generic term that can apply to all binders. Therefore, descriptors must he used to qualify this term when referring to specific materials. A civi1 engineer may have cause to use
The Nature Of Concrete Portland cement concrete, calcium aluminates cement concrete, or polymer concrete ,where the binders are Portland cement, calcium aluminate cement, or a polymer resin, respectively. In concrete construction, the engineer will use Portland cement concrete 95% of the time. Thus, for convenience, we will often drop the name Portlandthroughout the text and use a qualifying descriptor only when dealing with other kinds of cement and concrete.
The Nature Of Concrete Portland cement concrete, calcium aluminates cement concrete, or polymer concrete ,where the binders are Portland cement, calcium aluminate cement, or a polymer resin, respectively. In concrete construction, the engineer will use Portland cement concrete 95% of the time. Thus, for convenience, we will often drop the name Portlandthrough out the text and use a qualifying descriptor only when dealing with other kinds of cement and concrete.
Advantages Of Concrete Concrete is the predominant material used in construction . It competes directly with all other major construction materials-timber, steel, asphalt, stone, etc.- The major advantages and disadvantages of concrete are summarized in Table 1.3.Type all properties of concrete are given in Table 1.4.
Advantages Of Concrete concrete properties can vary significantly from the figures given, depending on the choice of materials and proportions of a particular application. For example, subsequent chapters will show how concrete can be designed to have compressive strengths <10 MPa (1500 Ib/in.2) or > 100 MPa (15,000lb/in.2) with concomitant changes in modulus of elasticity. The ability of concrete to be cast to any desired shape and configuration is an important characteristic that can offset other shortcomings.
Advantages Of Concrete Concrete can be cast into soaring arches and columns, complex hyperbolic shells, or into massive, monolithic section; used in dams, piers, and abutments. On-site. construction means that local materials can be used to a large extent, thereby keeping costs down. Cement costs only about 7-10 cents/kg (3--4 cents/lb) (2001) and aggregates less than 2 cents/kg (<1 cents/b). Furthermore. fabricating concrete on site, its properties may be tailored for the specific application.
Advantages Of Concrete On the other hand, on-site production is a mixed blessing because the quality of concrete must be carefully controlled. Environmental conditions fluctuate, so that it is difficult to assure uniform process41g of concrete throughout a job Constituent materials are less carefully characterized than they might be and can have undesirably high variations in properties. The use of an unskilled or semiskilled work force means that in the absence of proper supervision on the job site, undesirable practices they be adopted and tolerated. Casting of concrete can also be adapted to factory-controlled production. precast building elements for standardized low. cost building systems arc more common in European countries, but have also been developed in the United States.
Advantages Of Concrete precast concrete block has become a very popular building element, and precast concrete pipe is widely used in drainage, sewage, and water-supply projects. precast, prestressed concrete beams, girders. and panels in various configurations are used increasingly in many structures. precast concrete can be produced more uniformly with closer tolerances compared to concrete cast on site, but requires a more skilled work force and generally more sophisticated equipment. Good Quality concrete is a very durable material and should remain maintenance free for many years when has been properly designed for the service conditions and properly placed.
Advantages Of Concrete The Advantages Of Concrete: • It has a relatively high compressive strength. • It has better resistance to fire than steel. • It has a long service life with low maintenance cost. • In some types of structures it is the most economical structure material as dam and footing. • It is easy to form. • It yields rigid members with minimum apparent deflection.
Advantages Of Concrete Disadvantages Of Concrete: • It has a low tensile strength of about one tenth of its compressive strength. • It needs mixing and curing all of which affect the finial strength of concrete. • The cost of form which will be used in casting is high • It has low compressive strength with respect to steel which lead to large section in columns of multistory buildings. • Cracks develop in concrete due to shrinkage and application of live loads
Limitation Of Concrete However, concrete does have weaknesses that may limit its use in certain applications and must be allowed for when designing structures. Concrete is a brittle material with very low tensile strength. Concrete should generally not be loaded in tension (except for low bending stresses that may be permitted in unreinforced slabs on grade), and reinforcing steel must be used to carry tensile loads; inadvertent tensile loading causes cracking. The low ductility of concrete also means that concrete lacks impact strength and toughness compared to metals.
Limitation Of Concrete Even in compression, concrete has a relatively low strength-to-weight ratio, and a high load capacity requires comparatively large masses of concrete, although, since concrete is low in cost, this is economically possible. The volume instability of concrete must also be allowed for in design and construction. It shows volume stability that is more characteristic of timber and quite unlike that of steel, which is a volume-stable material under normal conditions of service.
Limitation Of Concrete Concrete undergoes considerable irreversible shrinkage due to moisture loss at ambient temperatures and also creeps significantly under an applied load even under conditions of normal service. Awareness of these problems with concrete enables us to compensate for them, by using suitable designs and by controlling them, in part, through a suitable choice of materials and construction practices.
Limitation Of Concrete A great deal of research effort has been devoted to ameliorating these problems and now ready-mixed concrete with compressive strengths of 100 MPa (15,000 Ib/in.2) can be routinely produced in some areas. Over the last 30 years, new types of concrete have been developed, such as fiber. Reinforced concrete, shrinkage-compensated concrete, Cement based materials with flexural strengths exceeding 150 MPa (22,000 Ib/in.2) or with tensile strains greater than 1% have been produced.
