CONCRETE TECHNOLOGY

Dr. Ali I. Tayeh

SyllabusSyllabus

Lectures Outline:

������DateDateTopicTopic

1st WeekIntroduction.Concrete as a material

2nd WeekCements

3rd WeekMineral Admixtures and Blended Cements4th WeekWater.

5th WeekAggregates.6th WeekFresh Concrete7th WeekReview and Midterm Exam.

8th WeekProportioning Concrete Mixes9th WeekHandling and placing.

10th WeekCuring and strength.

11th WeekTesting of Hardened Concrete12th WeekDurability13th WeekReview

14 th WeekFinal Exam

Chapter 1Chapter 1

ConcreteConcrete

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 MaterialConcrete 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 "concretusconcretus," which means to grow together.

Concrete as a MaterialConcrete as a Material

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 ConcreteThe 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 ConcreteThe 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 PortlandPortland throughout the

text and use a qualifying descriptor only when dealing

with other kinds of cement and concrete.

The Nature Of ConcreteThe Nature Of Concrete

The Nature Of ConcreteThe 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 PortlandPortland through out the

text and use a qualifying descriptor only when dealing

with other kinds of cement and concrete.

The Nature Of ConcreteThe Nature Of Concrete

Advantages Of ConcreteAdvantages 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.TypeTable 1.3.Type

• all properties of concrete are given in Table 1.4.Table 1.4.

Advantages Of ConcreteAdvantages 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 ConcreteAdvantages 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 ConcreteAdvantages 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 ConcreteAdvantages 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 ConcreteAdvantages Of Concrete

The 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 ConcreteAdvantages 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 ConcreteLimitation 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 ConcreteLimitation 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 ConcreteLimitation 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 ConcreteLimitation 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.

End