CONSTRUCTION MATERIALS. Role of Material Science in CE Combining several sciences Chemistry ...

CONSTRUCTION MATERIALS

Role of Material Science in CECombining several sciences

Chemistry Physics Mechanics

Behavioral understanding of materials is based on knowledge of these sciences.

Predicting BehaviorCivil Engineers design complex

systems using relationships between Stress vs. Strength Strain vs. Deflection Exposure vs. Durability Risk vs. Consequence Cost vs. Aesthetics & Life Cycle Others

Materials Science Atomic nature of materials Microstructure Relationship between material structure

and engineering properties Altered structures to customize

properties

Construction Materials Concrete Steel Timber

Concrete (Beton) The word concrete comes from the Latin word "concretus"

(meaning compact or condensed), the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow)

Concrete is a composite material composed mainly of water, aggregate, and cement.

In concrete, there is approximately: 10% cement 20% water and air 30% sand 40% gravel

by volume In Turkish the Word ‘beton’ comes from French.

Concrete Concrete is an easily shaped construction material. Before setting, fresh concrete is as soft and viscous

as a clay paste. Over time, the cement forms a hard matrix which

binds the rest of the ingredients together into a durable stone-like material with many uses.

When cement, water and aggregates are mixed together, they form a fluid mass that is easily molded into shapes makes concrete a very practical and useful construction material compared to timber and stone.

It can be both produced in a factory or at the site.

Concrete

The decrease in volume of the concrete after pouring the concrete is called shrinkage (rötre in Turkish).

The main reason for shrinkage is loss of water. While the fresh concrete is still plastic, the excess water comes to the

surface and evaporates. Some of the water is also used in chemical bonds. Therefore, too much water is lost at a very short time.

Properties of concreteCompressive strength 35 MPa

Bending strength 6 MPaTensile strength 3 MPaElasticity Modulus 28000 MpaPoisson’s Ratio 0.2Shrinkage 0.005 – 0.1 %Density  

High density concrete >2800 kg/m3

Normal concrete 2350 kg/m3

Lightweight concrete 1800 kg/m3

ConcreteConcrete must both have high mechanical strength. Durability (to the chemical external effects)

Concrete is classified according to their compressive strength. Concrete Class 28-day compressive

strength(cylinder)(N/mm2)

28-day compressive strength(cube)

(N/mm2)

C-14 14 16C-16 16 20C-18 18 22C-20 20 25C-25 25 30C-30 30 37C-35 35 45C-40 40 50C-45 45 55C-50 50 60C-55 55 67C-60 60 75C-70 70 85C-80 80 95C-90 90 105

C-100 100 115

Concrete The interesting point about concrete is that the tensile

strength of concrete is very small compared to the compressive strength.

For this reason, the reinforcement bars (steel) is used.

Compression stress

Tension stress

Unit deformation(strain)

(Elongation)

(Shortening)

Steel has a high tensile strength and may elongate under high tensile forces.

Behaviour of Reinforced Concrete Materials

Reinforced concrete Concrete and steel is coherent to each other. So reinforced concrete (betonarme) structures can be built. After setting, the concrete and the steel work together as if they are only one

material. They react the temperature changes similarly (their thermal expansion

coefficients are close to each other.) Otherwise, the use of reinforced concrete structures will be very limited.

Brittle Behavior A material is brittle if, when subjected

to stress, it breaks without significant deformation (strain).

Brittle materials absorb relatively little energy prior to fracture, even those of high strength.

Breaking is often accompanied by a snapping sound.

Brittle materials include most ceramics and glasses (which do not deform plastically) and some polymers.

Ductile Behavior In materials science, ductility is a solid

material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. 

OR The response to stress of certain

materials which undergo permanent deformation without fracturing

Schematic appearance of round metal bars after tensile testing.a) Brittle fractureb) Ductile fracturec) Completely ductile fracture

Brittle and Ductile Behavior

Brittle and Ductile Behavior We want the reinforced concrete structural

elements to behave ductile. Because under earthquake loads, when the load bearing capacity of the elements are exceeded, the ductile elements can make large deformations without failure and absorb the earthquake energy.

A structural elements behaves elastically up to a certain limit, then it begins to crack (a permanent deformation). After cracking begins, the amount of deformation at the element is a sign of its ductility or brittleness.

Brittle and Ductile Behavior

Material Behavior

Steel All purpose Durable Ductile

Steel is built with changing the amount of carbon in iron.

There is a high amount of carbon in iron. We have to reduce this amount. Every production has its own recipe. (the beam of a

skyscraper, a submarine or a knife different steel types.)

Material of the modern life

Steel Raw iron has 5% Carbon Steel has 0.16 – 0.20 % Carbon Increasing carbon amount, increases the

strength and rigidity of steel. Iron and steel is being used for 5000 years. But

they are used for the construction industry first in 18th century in England.

First structures built using iron are bridges. Steel used in the structures today has a crystal

formation, it is isotropic and homogeneous.

Mechanical properties of steel is determined by steel tensile tests.

Tensile tests are conducted in tensile test machines, providing controlled uniformly increasing tension force, applied to the specimen. As the force increases, the length of the sample increases and the cross-sectional area decreases. The force is increases until the bar cracks. The elongation and stress values during the test are determined and a stress-strain curve is drawn.

Steel for Reinforced Concrete Structures

As the tensile strength of concrete is too low, steel is used where there are tensile stresses.

Additionally it is used as stirrups. First reinforcement is done in 1850. Reinforcement bars have circular cross

sections. The surface can be either plain or deformed.

Deformed bar has higher strength and locks into the concrete better than the plain ones.

Plain bars have a limited use in Turkey after 2007 Earthquake Code.

Deformed bars are welded as a mesh and they are used in large surface areas such as floors, tunnels and concrete roads.