Properties of Building Materials - .pdf

University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Properties of Building Materials 1-Introduction: B...

University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Properties of Building Materials 1-Introduction: Building material can be defined as any material that is used for a construction purpose. Several natural materials, such as clay, sand, wood, and rocks, have been used in construction. Also, many man-made products are in use, have been in use for a long time such as cement, bricks, and concrete blocks. Building materials (or construction materials) may vary in their physical, mechanical, and chemical properties. Also, the ability of these materials for carrying loads may vary as well. Also, the ability of their resistance to the natural condition can be different. Therefore, engineers must study the properties of building materials since it will help them to select the suitable materials at the lowest possible cost. Building materials that are used in a specific project service for different purposes and must meet the requirements for that project. For example, structural materials should have suitable mechanical properties to resist the applied loads, waterproof materials should be impermeable and water-resistant, and wall materials should be able to insulate heat and sound. Also, in general, building materials should be durable against external factors such as wind, rain, and sun. 2-Classification of building materials The following is the most common classification: 1- Chemical classification: Based on the chemical components, building materials can be classified into inorganic and organic materials A. Inorganic materials can be divided into three groups.  Metals such as steel, iron, aluminum, etc.  Metalloid such as natural aggregates, cement, concrete, glass, etc.  Metal-metalloid composition such as reinforced concrete. B. Organic materials such as plastics, wood, rubber, petroleum, etc. 1  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 2-Function classification: Based on this classification, building materials can be classified as follow. A. Structural materials: materials that are mainly used to resist loads such as reinforced concrete and steel that are used in beams, columns, foundation, etc. B. Nonstructural materials: typically, are the materials that are not designed to carry loads such as brick or wood partitions. 3: Physical properties of building materials: 1- Density: can be defined as the mass per unit volume of a material as described below. M ρ = (g/cm3) V Where: M = mass under dry conditions (g) V = volume under absolute compact conditions (cm3). 2- Apparent Density (ρ0): Apparent density is the dry mass per unit volume of a substance under natural conditions. It is defined by: M ρ° = V° (Kg/m3) Where: M = mass under dry conditions (g) V° = volume under absolute compact conditions (cm3). 2  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 3- Bulk Density (ρb): Bulk density is the dry mass per unit volume of a substance under the conditions that powdery or granular materials are packed. It is defined by: M ρb = Vb (Kg/m3) Where: M = mass under dry conditions (Kg) Vb = volume under packing conditions (m3). 4- Unit weight (𝛄): is the weight per unit volume of a material. It is defined by: W 𝛾= , W=M*g V M∗g M 𝛾= , ρ° = V V 𝛾 = 𝜌. 𝑔 5- Specific gravity (Gs): Is the ratio between the density of the solid material and the density of distilled water at a temperature. Because the density of distilled water in this temperature is equal (1 g/cm3) or (1000 kg/m³), 𝜸𝒘 = 𝟗. 𝟖𝟏 𝒌𝑵 /𝒎3. ρs 𝐺𝑠 = ρ𝑤 γs 𝐺𝑠 = γw 6- Porosity (η): is the percentage of the pores volume to the total volume with the volume of a substance. (The ratio between the sizes of the voids in the material to the total size). It is defined by: Vv 𝜂= , V 7- Voids ratio (e): Is the ratio between the volumes of voids to the volume of solid material. Vv 𝑒= Vs 3  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 8- Moisture content (m): Is the percentage ratio between the weights of the water in the voids to the weight of solid material. Mw 𝑚% = ∗ 100% Ms 9- Degree of saturation (s): Is the percentage ratio between the volumes of water in the voids material to the total volume of voids. Vw 𝑆% = Vv 10- Water Absorption: Is the ability of the material to absorb and retain water. It is expressed as percentage in weight or of the volume of dry material: Ms − Md 𝑊𝑤% = ∗ 100 Md Where: Ms= mass of saturated material (g) Md = mass of dry material (g) Example: In the laboratory test a sample of a brick has the following characteristics: The total volume of 2116 cm³, the total mass of 3555g, the mass of the solid =3250 g. The specific gravity of the solid = 1.83, Find: 1- Porosity (η) 2- Voids ratio (e) 3- Moisture content (m). 4- The degree of saturation (s): 4-Mechanical Properties of Materials: The mechanical behavior of materials is the response of the material to external loads. All materials deform in response to loads; however, the specific response of a material depends on its properties, the magnitude and type of load, and the geometry of the element. The important mechanical properties considered for building materials are: strength, compressive, tensile, bending, impact, hardness, plasticity, and elasticity and abrasion resistance. Strength of Materials: is the ability of the material to resist failure under the action of stresses caused by loads, the most common being compression, tension, bending and impact, shear strength and others. 1- Stress (σ): is amount of force applied to a unit of area (N/mm^2). Defined as load, P, divided by the area P 𝜎= A σ is the (stress) strength of a material (MPa); P is the largest load of a specimen when it is destructed (N); A is the force bearing area of a specimen (mm2). 4  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood There are several types of stress depend of the type force acting for example: 1-compression stress 2-Tension stress 3-Shear Stress Torsion stress 5  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 2- Strain (ɛ): is defined as amount of deformation per unit length of an object when a load is applied. The deformation (strain) ε, defined as change in length, ΔL, divided by original length L. ΔL 𝜀= L Clearly the deformation from loading on an element or test specimen will depend on both its size and the properties of the material from which it is made. Strain = change in length/original length and therefore its dimensions are [Length]/ [Length], i.e. it is dimensionless. Elongation (e %): is the largest amount of elongation occurs at failure or the ratio between the amount of the resulting elongation at failure and original length : ΔL 𝑒% = ∗ 100% = L Longitudinal strain: is calculated by dividing the total deformation of the dimension parallel to direction of applied force by the original dimension ΔL 𝜀𝐿 = Lo Where: ΔL= change in length Lo= original length Lateral strain: is calculated by dividing the total deformation of the dimension vertical to direction of applied force by the original dimension. ΔY 𝜀𝑎 = Yo 6  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood In the axial tension test, as the material is elongated, there is a reduction of the cross section in the lateral direction. In the axial compression test, the opposite is true. Poisson’s ratio (V): is the ratio of lateral strain to the longitudinal strain 𝜀𝐿 𝑉= εa Poisson’s ratio has a theoretical range of 0.0 to 0.5, where 0.0 is for a compressible material in which the axial and lateral directions are not affected by each other. The 0.5 value is for a material that does not change its volume when the load is applied. Most solids have Poisson’s ratios between 0.10 and 0.45. Linearity and elasticity should not be confused. A linear material’s stress strain relation follows a straight line. An elastic material returns to its original shape when the load is removed and reacts instantaneously to changes in load. Example: steel bar with a diameter (10 mm) proved to be the distance between two points (50mm), a tensile stress (8 KN) applied on it that increased the distance between two points by (0.025mm) and decreased diameter by (0.0015mm). Calculate: 1- Stress generated in the steel bar 2- Longitudinal strain and Lateral strain 3- Poisson’s ratio (V) Classification of building material according to nature of deformation: 1-Elastic materials: the material that has ability to recover the original shapes after removal of the load applied on it. Such as rubber. 7  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Young observed that different elastic materials have different proportional constants between stress and strain. For a homogeneous, isotropic, and linear elastic material, the proportional constant between normal stress and normal strain of an axially loaded member is the modulus of elasticity or Young’s modulus, E, and is equal to; σ 𝐸= ε Where: σ Is the normal stress and ε is the normal strain. The elastic modulus is a measure of the ability to resist deformation. The bigger E is, the more difficultly the material deforms. Different types of modulus of elasticity 8  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Typical Modulus and Poisson’s Ratio Values (Room Temperature) 2-Plastic materials: the material that cannot recover its original shapes after removal of the load applied on it. Such as Clay. For some materials, as the stress applied on the specimen is increased, the strain will proportionally increase up to a point; after this point the strain will increase with little additional stress. In this case, the material exhibits linear elastic behavior followed by plastic response. When the load is removed from the specimen, some of the deformation will be recovered and some of the deformation will remain. 3-Elasto-plastic materials: the material that has ability to recover part of changes in its shape after the removal of the loading applied on it, such as steel, concrete and wood 9  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Stress–strain behavior of plastic materials: (a) example of loading and unloading, (b) elastic– perfectly plastic, and (c) elasto–plastic with strain hardening. Example: Compression force applied gradually to a sample of concrete, if the stress is generated in the sample and its corresponding strain are listed in the table below, draw stress –strain curve? Stress 0 5 10 15 20 15 (MPA) Strain *10-4 0 2 5 9 15 21 Example2 A rod made of aluminum alloy with the gage length of (100 mm), diameter (10mm) and yield strength (150 MPA) was subjected to a tensile load of (5.85 KN), if the gauge length was changed to (100.1 mm), and the diameter was changed to (9.9967mm), calculate the modulus of elasticity and poison ratio? Typical stress-strain curve. 10  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 1-elastic strain: is the strain that subsides after the removal of the applied stress. 2- Plastic strain: is the strain which not subsides after the removal of the applied stress. 3-elastic range: is the stress range that do not to cause plastic strain. 4- Yield stress: is the stress at which gets increase in strain without any increasing in the stresses. 5-Ultmate stress: is a maximum stress can be applied on the material before they fail. 6-strain hardening: increase in stresses by an increase in strain without collapse in the material Example: An elasto-plastic material with strain hardening has the stress-strain relations, the modulus of elasticity is 25*106Psi, yield strength is 70ksi, and the slope of hardening portion of the stress –strain diagram is 3*106 psi. Calculate: A-the strain that correspond to a stress of 80 ksi. B-if the 80 ksi removed, calculate the permanent strain. Example: PL Prove Δ𝐿 = 𝐴𝐸 Example: find percentage of elongation of the steel rod , when it is subjected to an axil pulling force of 50KN. Whose diameter is 30mm and it is 3 m length ,take E- 200*105MPA Some properties of material: 1- Weathering Resistance is the ability of a material to endure alternate wet and dry conditions for a long period without considerable deformation and loss of mechanical strength. 2- Water Permeability is the capacity of a material to allow water to penetrate under pressure. Materials like glass, steel and bitumen are impervious. 3-Frost Resistance denotes the ability of a water-saturated material to endure repeated freezing and thawing with considerable decrease of mechanical strength. 4- Thermal Conductivity The property of a material that indicates its ability to conduct heat is known as thermal conductivity. It is influenced by the nature of the material, its structure, and porosity. Materials of low thermal conductivity are used as thermal insulation. The reciprocal of the thermal conductivity is the thermal resistance (or insulating value, R) 11  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood 10. Thermal Expansion Practically all materials expand as temperature increases and contract as temperature falls. The amount of expansion per unit length due to one unit of temperature increase is a material constant and is expressed as the coefficient of thermal expansion: 𝛿𝐿 𝛿𝑇 𝛼L= 𝑳 𝛼L: Linear coefficient of thermal expansion 𝛿𝐿: Change in the length of the specimen 𝛿𝑇: Change in temperature L: Original length of the specimen While α for structural materials is different, the materials will strain at different rates with the increase or decrease in temperature. This might lead to fracture. Steel and concrete have closely the same α. Concrete may also cracks, due to thermal expansion and contraction (in summer and winter), therefore joints are used in buildings, bridges and concrete pavements. Example: A steel bar with 3m length, diameter 25mm, modulus of elasticity 207 GPA, and linear coefficient of thermal expansion of 0.000009m/m /Co is fixed at both ends when the amendment temperature is 40 Co, if the amendment temperature decreased to 15 Co, what internal stress will develop due to this temperature changes? Is this stress is tension or compression? Why? 12  University of Halabja Course Name: Building Materials Civil Engineering Department First Stage-Second Semester 2022-2023 Lecture: Hersh F Mahmood Fire Resistance: is the ability of a material to resist the action of high temperature without any appreciable deformation and substantial loss of strength. Chemical resistance: is the ability of a material to withstand the action of acids, alkalis, seawater and gases. Durability: is the ability of a material to resist the combined effects of atmospheric and other factors. Hardness refers to the property of a material to resist pressing-in or scratch of a sharp object. The materials of different kinds of hardness need various testing methods. Abrasive resistance refers to the capacity of a material to resist abrasion. It is expressed by the abrasion ratio, calculated as: 𝑁 = (𝑚1 − 𝑚2)/𝐴 Where: N=abrasion ratio (gm. /cm2) m1= mass before abrasion (gm.) m2 =mass after abrasion (gm.) A=is abrasive area (cm2) 13