1、土木工程概论Introduction to Civil Engineering第二章土木工程材料第二章土木工程材料Chapter 2 Materials for Civil Engineering Materials for Civil Engineering What is Materials of Civil Engineering?It covers the development,processing,evaluation,applications,and performance of construction materials in civil engineering.Wide v
2、arieties of materials are used for making engineering structures and buildings.It is necessary for an engineer to have a basic knowledge of these materials which are available either from natural resource or manufactured.Stones:Stones are used in Civil Engineering constructions in different forms.St
3、one blocks irregular in size called rubbles are used for building walls.Smaller irregular stones are used for constructing the base of floors and roads.Stones broken into smaller pieces are called aggregates.Stones required in these ways are obtained from rocks.Materials for Civil EngineeringCements
4、:Even in 100 BC,Roman builders used a special volcanic ash for cementing stones.When this ash was mixed with limestone,burnt and combined with water,it became a very strong cement.The builders found this cement would harden with water.Hence,it was called Hydraulic cement.Materials for Civil Engineer
5、ingUses of cements:To make cement mortar and cement concrete Wide varieties of purposes staring from ordinary foundation to roofs of multistory skyscrapers Sulphate resisiting cement is used to protect the foundations and other components in contact with the earth against the chemical action of sulp
6、hate in the soil Rapid hardening cement and early strength cement have been used in works which need early strength gain like chimneys and underwater concreting White and colored cements are used for making ornamental plastering and floor finishMaterials for Civil EngineeringConcrete:When stone or g
7、ravel,sand,cement and water are mixed together,they form an easily workable plastic mixture which can be moulded and cast into desired shapes or structures.This cement and water in the plastic mixture undergo a chemical combination in a few hours after the mixing results in a solidification and grad
8、ual hardening.This mixture is called concrete.Materials for Civil EngineeringConcrete:Concrete is a structural material which consists of Portland cement,aggregate(sand and rock),and water(to make the chemical reaction called hydration occur).Concrete can sometimes contain other substances,such as f
9、ly ash from industrial smoke stacks,which can change its properties.Materials for Civil EngineeringConcrete:Concrete is a very strong material when it is placed in compression.It is,however,extremely weak in tension.It is for this reason that we use reinforcement in concrete structures.The reinforce
10、ment,which is usually steel,takes up the slack for the weakness of the concrete in tension.Materials for Civil EngineeringConcrete:There are many ways to test the strength of a batch of concrete.The tests used can be categorized as destructive and nondestructive tests.We will perform both types of t
11、ests in this class.Materials for Civil EngineeringConcrete:Usually when a batch of concrete is ordered on a job site it is specified to be of a specific compressive strength-4000 psi,for instance.When the concrete comes to the job site in a ready-mix truck,the contractor places some of the batch in
12、cylinders which are 6 inches in diameter and 12 inches in height.Materials for Civil EngineeringConcrete:These cylinders are cured for 28 days and tested by compression until they are crushed.This will give the contractor or the engineer the compressive strength for that batch of concrete.He or she
13、can then compare that value to the design value used to make sure that the structure was constructed properly.Materials for Civil EngineeringConcrete:Once the concrete has been placed for a particular structure,there is a nondestructive test which can be performed to estimate the strength of the con
14、crete.This method uses a Schmidt hammer(also called a Swiss hammer).This method of testing is based on the inertia of a ball inside the Schmidt hammer testing apparatus that is bounced off of the concrete.Materials for Civil EngineeringConcrete tests:Each group will perform two tests on a concrete c
15、ylinder.The first test will be the Schmidt hammer test.Each person in the group will take a turn using the Schmidt hammer and the results of the group members will be averaged.Each group will then take their cylinder into the structures lab where it will be tested to crushing in a compression testin
16、g machine.Materials for Civil EngineeringConcrete strength:Concrete and steel are the most widely used materials in engineering design.Concrete is very important material for the civil engineer designing because steel is not readily available and can be very expensive to bring to the site.Materials
17、for Civil EngineeringConcrete strength:Some advantages of using concrete in design are as follows:high fire and weather resistance,relatively low cost(most of the materials can be obtained locally),can be poured to fit odd shapes(good for unusual architectural designs).As you drive down I-75,I-4,or
18、on the turnpike you will notice that almost all the bridges are constructed of concrete.Materials for Civil EngineeringConcrete strength:As you walk around Weil Hall(the building you are in now)you will notice that the beams and columns are made of concrete.The new South End zone for the University
19、of Floridas Football Stadium and the new addition to the commuter parking garage were constructed using concrete.These are just a few examples.Materials for Civil EngineeringConcrete strength:Concrete is composed of four ingredients:cement,sand,aggregate(stones,gravel,etc.),and water.The strength an
20、d other properties of concrete are dependent on how these four ingredients are proportioned and mixed.The most common type of cement is Portland.Materials for Civil EngineeringConcrete strength:Unlike steel,concrete is adequate in strength in only one direction.Concrete is very good in compression b
21、ut useless in tension.Engineering design is based on concretes compressive strength.Compressive strength,fc,refers to what concrete is capable of resisting from loads when they are pushing on the concrete(compression).Materials for Civil EngineeringConcrete strength:Compressive strengths for concret
22、e are usually in the range of 3 000 to 5 000 psi(pounds per square inch).To correct for the lack of tension strength in concrete,high tensile strength steel is placed in the tension side of concrete.The steel used for reinforcement usually consists of round steel bars often called rebars.When this c
23、ombination occurs it is called reinforced concrete.Materials for Civil EngineeringConcrete strength:When Civil Engineers design,they obviously need to know the strength of the material that they are using.By knowing the strength of the material that is being used and the loads(forces i.e.people,cars
24、,furniture)that will be acting on the particular member(beam,column,arch,etc.)the engineer can pick the correct dimensions for the design.Materials for Civil EngineeringConcrete strength:In todays lab,two tests will be introduced to check the structural quality of concrete(find its strength).The fir
25、st test involves loading the concrete cylinder shown in the drawing until failure.This test is useful for checking the strength of the concrete that is presently being used for a construction site.Materials for Civil EngineeringConcrete strength:The American Concrete Institutes Code specifies that a
26、 pair of cylinders shall be tested for each 150 yd3 of concrete or for each 5 000 ft2 of surface area actually placed.This is a quality control measure.Materials for Civil EngineeringConcrete strength:The other test that we will conduct in the lab today is called the Schmidt(or Swiss)Hammer Test.Thi
27、s test gives an estimate of the concretes compressive strength.This test is performed in situations where the concrete has already been poured and a cylinder test is not possible.Materials for Civil EngineeringConcrete strength:If a structural engineer wanted to check a beam for its concrete strengt
28、h 6 months after the building had been constructed the engineer might use this test.What are possible sources of error between the two tests and within the tests themselves?Materials for Civil EngineeringSteel:Steel is a structural material which consists mostly of iron and carbon.It can,however,con
29、tain other additives which might change the steels properties.Steel can be hot rolled or cold formed into structural shapes,such as the familiar I beam known today as a wide flange.Steel has the same strength in tension as it has in compression,unlike concrete.Materials for Civil EngineeringSteel:We
30、 will perform two tests which can be related to steel.These tests will be a tension test,which can be used to measure the material properties of a steel(or really any material,for that matter),and a beam bending test,which can be used to measure the material properties of a specimen and the effectiv
31、eness of the orientation of the beam.Materials for Civil EngineeringSteel:We will be using small aluminum beam specimens to simulate steel beams.The mechanics are the same only aluminum is more flexible than steel,so it is easier to see deflections with aluminum.Materials for Civil EngineeringSteel
32、tests:We will perform the tensile test first.A cylindrical coupon made of steel will be placed in the tensile testing apparatus.The coupon will then be pulled until it breaks.A displacement indicator will be attached to the coupon to take strain readings.From the information gathered from this test,
33、we can calculate the modulus of elasticity,the stress experienced by the coupon,and the strength of the steel which made up the coupon.Materials for Civil EngineeringReinforced Concrete:Concrete has a great compressive strength.However,its tensile strength is very low.In reinforced concrete,steel an
34、d concrete are combined to take advantage of high compressive strength of concrete and high tensile strength of steel.The location of steel within the concrete is important.The tensile area needs steel reinforcement.Materials for Civil EngineeringReinforced Concrete:The location of steel within the
35、concrete is important.The tensile area needs steel reinforcement.Materials for Civil EngineeringBasci Civil and Mechanical EngineeringReinforcment concrete beamTimber:Woods are generally classified for construction as hard wood,medium hard wood,and softwood classes.Wood is graded according to natura
36、l defects present in the timber,like knots and sloping grains.Materials for Civil Engineering What are the forms in which stones are used in Civil Engineering?What are the qualities of good building stones?What are the dimensions of ordinary bricks?What are the general uses of bricks?What is the con
37、stituent of concrete?Explain in brief the manufacture of cements.What are the uses of cements?Explain the influence of water-cement ratio on the properties of concrete.What is the need for providing reinforcements to a concrete beam?What are the advantages of steel as a construction material?Review QuestionsMaterials for Civil Engineering
