Construction Materials CENG 2092 Past Paper PDF 2024

Construction Materials CENG 2092 November 2024 Chapter One Nature & Properties of Materials  Contents 1 Classification of Materials 2 General Properties of Materials 3 Nature and Properties of Materials Under Load  1.1 Classification of...

Construction Materials CENG 2092 November 2024 Chapter One Nature & Properties of Materials  Contents 1 Classification of Materials 2 General Properties of Materials 3 Nature and Properties of Materials Under Load  1.1 Classification of Construction Materials Introduction Material: a substance or thing from which some thing else can be made. Examples: Cement , brick, aluminum, soil, water…  Material Engineering refers to the understanding and review of properties and uses of materials commonly used in engineering. Classification: Materials that are used for construction purpose can be broadly classified based on their:  Metallic Property  Physical Nature  Mode of Production  Company Logo Classification Based on Metallic Property 1.Metallic : in general metals can be classified in to :Ferrous and Non-ferrous. a. Ferrous: is the metal in which the principal element is iron. Examples : steel, wrought iron & cast iron b. Non-ferrous : is the metal in which the principal element is not iron. Examples: copper, aluminum , lead, zinc, etc 2. Non metallic: Examples ; concrete, timber, stone, lime etc. Classification Based on Physical Nature Solids Liquids Gas  Classification Based on Mode of Production a) Naturally Occurring Materials  stone  timber b) Industrially produced materials  Cement  glass C) Materials produced at construction site  Concrete  mortar  1.2 General Properties of Materials Properties Which relate to materials are: 1. Physical properties  Density & specific gravity  Thermal property  Acoustic /sound permeability  Fire resistance  Porosity 2. Chemical properties  Corrosion Resistance  Combustibility  Toxicity  Decay Resistance  Cont’….. 3.Mechanical Properties The resistance of material to:  The action of external static forces (compressive, tensile, bending, shear, torsional strength).  The action of dynamic external forces (impact and vibratory loads).  Company Logo 1.3 Nature and performance of materials under load When force is applied on a solid body under equilibrium, two results are produced.  Internal resisting forces are developed to balance the external force &  The body is deformed to a varying degree. The internal forces & deformations are called stresses & strains respectively.  Depending up on the arrangement & direction of the external forces, the stresses produced in a body may be A/ Tensile stress B/ Compressive stress C / Shearing stress D/ Bending stress E/ Torsional stress F/ various combinations of the above.  Testing of Materials for Mechanical Properties Mechanical tests are classified : A. With reference to the arrangement & direction of the external forces; I. Tension Test  Specimen under tension test is subjected to an axial tensile force.  Tensile stress is developed on cross-sectional area perpendicular to the line of action of the force.  The specimen increase in length.  Cont…… II. Compression Test Specimen is subjected to an axial compressive force. Compressive stress is produced. The specimen decrease in length..  Cont…… III. Shear test  In this test, shearing stress is determined on the x-sectional area parallel to the line of action of the external forces.  Cont…… IV. Bending Test  Specimen is subjected to forces that give rise to bending moments  The resulting stresses are compressive on one side of the neutral axis & tensile on the other side.  Shear stress exist throughout the beam.  Cont…… V. Torsion Test This test is conducted to determine the torsional strength of a material. The specimens for torsion test are generally cylindrical in shape.  Cont…… B. With reference to the rate & duration of the load application Static Tests  Made with gradually increasing load. eg. ordinary tests in tension & compression etc. Dynamic Tests  Made with suddenly applied loads. Wear Tests  Made to determine the resistance to abrasion & impact. Long time Tests  These are made with the loads applied to the object for long period of time. Fatigue Tests  These tests are made with fluctuating stresses repeated a large number of times  Cont…… C. With Reference to the effect on the specimen. Destructive Test  The specimens are either crushed or ruptured and made useless at the end of the tests.  Tests conducted on the following materials are best examples  Ultimate strength of steel  Compressive strength of concrete Non-destructive Tests  Are used to test the strength of members of existing structures without affecting their performance. Example: hammer test  2.4 Stress-Strain Properties in Simple Tension Test  In standard conventional tension test, specimen is subjected to a gradually increasing axial tensile force ‘P’ by means of testing machine.  At various increments of load ,the change in length ∆L of the specimen is measured. ∆L=L-Lo where L= new length Lo=original length  It is assumed that the stress is uniformly distributed for all points on each x-section. This stress is computed as follow; σt =p/Ao where σt =tensile stress Ao=X-sectional area P= applied load  Cont……  The uniform stress will produce a uniform elongation ∆L. The elongation per unit length is strain & expressed as: ε= ∆L / Lo Where ε= strain ∆ L= elongation Lo=original length of the specimen  With the values of strain & stress known for various tensile loads ,a diagram showing the relation between stress & strain ,called stress-strain diagram can be plotted.  Cont…… Properties in the elastic range: 1.Proportional Limit: is the greatest stress which a material is capable of withstanding without deviation from the law of proportionality of stress to strain( Hook’s Law= σ ∞ ε). (point A of fig 1) 2.Elastic Limit: is the greatest stress which a material is capable of withstanding without a permanent deformation remaining up on the release of stress. (point a of fig 1) 3.Yield Point : is the stress at which there occurs a considerable increase in strain without an increase in stress. Only ductile materials have both lower & upper yield points. (point B of fig 1)  Cont…… 4. Modulus of Elasticity(young’s modulus): is the slope of the initial linear part of stress-strain diagram.  The greater the modulus of elasticity, the smaller the elastic strain resulting from the application of a given values. Methods of determining modulus of elasticity, E. i. For ductile materials, with linear stress – strain portion, E= ∆σt ∕ ∆ ε ii. For materials with non-linear stress-strain curves.  The slope of the stress- strain curve varies and the modulus of elasticity cannot be readily determined.  The following three methods are employed to define E:  Cont…… a. Initial-Tangent modulus: The slope of the stress –strain curve at the origin which has a value of E 1 =tanф1 Stress (σt ) ф1 Strain(ε )  Cont…… b. Secant modulus : the slope of the line joining the origin and the selected point on the stress-strain curve with the value of E 2 =tanф2 Stress (σt ) ф2 Strain(ε ) 25  Cont…… c. Tangent modulus: The slope of the tangent to the stress –strain curve at the selected point with the value of E 3 =tanф3 ф3 Stress (σt ) Strain(ε ) 26  Cont…… 5.Stiffness  is the measure of the ability of material to resist deformation.  The higher the modulus of elasticity, the stiffer the material.  A material has a higher stiffness value when its deformation in the elastic range is relatively small.  Comparing steel alloys with E=210Gpa and aluminum alloys with E=70Gpa,the steel alloys are about three times as stiff as the aluminum alloys i.e steel alloys will deform about one-third as much as aluminum alloys for the same stress. 6.Poisson’s Ratio  Is the ratio of the unit deformations or strains in transverse direction to the longitudinal direction within proportional limit. µ= ε’∕ ε where ε’ = transverse strain, ε =longitudinal strain  Poisson’s ratio is a measure of the stiffness of the material in the direction at right angle to applied load.  Cont…… Properties for the plastic range:  The characteristic at the plastic range is that there is a permanent deformation in the stressed body after complete removal of the load. 1.Ultimate Strength: -is the maximum strength a material can possibly resist before failure.  Depending on the stress strain relationship of a particular material, the plastic strength will correspond to the ultimate strength or to the fracture(rupture)strength.  Cont…… Stress (σt ) Stress Fracture Ultimate (σt ) Ultimate or fracture strength strength strength Strain(ε ) Strain(ε ) Ductile material Brittle material 29  Cont…… 2.Ductility  represents its ability to deform in the plastic range.  Ductile materials show relatively higher plastic deformation, i.e they are capable of being drawn-out ,before rupture occurs.  Ductility is measured by the percentage elongation or percentage reduction in area. De= Lf –Lo * 100 Da = Ao- Af *100 Lo Ao 3.Toughness  Is the ability of material to absorb energy in the plastic range.  A material with high toughness can absorb high values of strain energy in the plastic range.