Chapter5 Cement concrete

1. Chapter5 Cement concrete

2. Main topics Technical Performances of Concrete Concrete Mixture Design Concrete Admixture 5.2 5.3 5.1 Concrete for Road 5.4

3. Technical Performances of Concrete 5.1

4. Technical Performances of Concrete ——Introduction 5.1 • Cement concrete is a man-made stone material, which is compound that consists of cement, aggregates and water in proper proportion. • Cement concrete is widely used in civil engineering, its characteristics are: ——richness in resources and simple for construction; ——concrete and reinforcement have same linear expansion coefficient and fine bond strength between them, which is much beneficial to make reinforcement concrete and prestressed concrete; ——through changing the composition proportion, different feature concretes can be obtained to meet different requirements； ——good mechanical behaviors and better durability.

5. Technical Performances of Concrete ——Construction workability 5.1 • Definition: ——workability is a property which means fresh cement concrete mixture is easy to construction operation (including mixing, transportation, concreting, vibrating and surface treatment) , uniformity on quality and dense in structure. • Workability including: ——flowability (流动性): is easy to fill formwork in uniformity and compactness； ——tamping feasibility (捣实性): is likely to remove all air in concrete mixture to be dense.

6. Technical Performances of Concrete ——Construction workability 5.1 ——cohesiveness (黏聚性): without separation and disintegration to fresh concrete depending on some cohesion; ——water-retaining (保水性): to have good water retention abilities without bleeding problem.

7. Technical Performances of Concrete ——Construction workability 5.1 • Workability test method: ——slump test(坍落度试验) ——Vebe consistometer test(维勃稠度试验)

8. Technical Performances of Concrete ——Construction workability 5.1 • Influencing factors on workability (1)internal cause: component materials: ——water and cement ratio (W/C); ——quantity of water per unit； ——sand percentage； ——raw materials: cement and cement fineness, aggregates; ——admixture; (2) external causes ——environmental factor: temperature, humidity, wind speed; ——time.

9. Technical Performances of Concrete ——Strength Characteristics 150mm 150mm 300mm 150mm 150mm 150mm 150mm 150mm 150mm Test diagram of flexural strength 150mm 150mm 5.1 Test diagram of axis compressive strength 150mm Test diagram of compressive strength 150mm Test diagram of splitting strength 150mm • Concrete strength ——cubic compressive strength; ——axis compressive strength; ——flexural strength; ——splitting strength.

10. Technical Performances of Concrete ——Strength Characteristics 5.1 • Cubic compressive strength( ) ——definition: the compressive strength of a cubic with 150mm length on each side; ——method of calculation: ——the standard values on the cubic compressive strength ( ): the strength satisfied the requirement of assurance rateunder standard condition:

11. Technical Performances of Concrete ——Strength Characteristics 5.1 • Grades of concrete strength ——there are 12 concrete strength grades in our country nowadays. Each of them can be expressed as “C” plus “standard value of strength” : ——C7.5, C10, C15, C20, C25, C30, C35, C40, C45, C50, C55, C60.

12. Technical Performances of Concrete ——Strength Characteristics 150mm 150mm 150mm 150mm 150mm Test diagram of flexural strength 5.1 • Flexural strength

13. Technical Performances of Concrete ——Strength Characteristics 5.1 • Influencing factors on concrete strength (1) concrete composition: ——cement strength: the higher cement strength, the higher concrete strength; ——water cement ratio (W/C): concrete strength has close relationship to W/C according to a lot experience, which is the lower W/C, the higher concrete strength is.

14. Technical Performances of Concrete ——Strength Characteristics 5.1 ——Characteristics of aggregate: ① rough surface and plentiful edges preferred; ② closely to cubic or round shape, rather than elongated or flat; ③ larger of maximum size is beneficial to compressive strength but unbeneficial to flexural strength, and when size of coarse aggregate is too larger, it is unfavorable to workability. Normally, nominal maximum size of coarse aggregate for concrete is no more than 31.5mm; ④ concrete mixture in continuous gradation has better workability and more dense; Comparatively speaking, gap gradation has less cement consumption compare with continuous concrete, but it is poor in workability; ⑤ Generally, sand with less specific surface area and less void ratio is preferred which has the ideal gradation.

15. Technical Performances of Concrete ——Strength Characteristics 5.1 (2) curing condition ——curing temperature; ——curing humidity; ——aging.

16. Technical Performances of Concrete ——Strength Characteristics 5.1 • Evaluation on the quality of concrete strength • Statistical method—Unknown standard deviation method： • Nonstatistcal method:

17. Technical Performances of Concrete ——Deformation Characteristics stress σ 5.1 α ε strain Diagrams of secant modulus • Elastic deformation ——it can be expressed by the secant modulus (割线模量); • Creep deformation ——it is the deformation under sustained loading condition; • Temperature deformation • Dry shrinkage deformation

18. Technical Performances of Concrete ——Durability Characteristics 5.1 • Impermeability of concrete ——it is a capability that concrete resists permeability of gas or water; ——according to the behavior of concrete standard specimen without water seepage (渗水) underspecified water pressure, 6 grades on impermeability are set; • Frost resistance ——it is a capability that concrete resists freeze/thaw cycling (冻融循环) ； ——there are 9 grades to evaluate concrete freezing-thawing durability; • Resistance to chemical attack • Abrasive resistance.

19. Asphalt Pavement Abrasive Experiment

20. Concrete Mixture Ratio Design 5.2

21. Concrete Mixture RatioDesign ——Technical requirements for raw materials 5.2 • Cement ——types of cement: according to cement adaptability which is affected by the project features and environmental condition, proper type of cement is selected; ——grades of cement: concrete grade and cement grade should be matched; • Coarse aggregate ——quality: satisfied the specified quality requirements, such as strength, soundness etc.;

22. Concrete Mixture Ratio Design ——Technical requirements for raw materials 5.2 ——detrimental (有害的) impurity: including clay, sludge(泥土), sulfate and organic materials etc., they are affect mostly on cohesive property between cement and aggregate; • Fine aggregate: Besides requirements on the quality and detrimental impurity same as coarse aggregate, particular requirements are ——grading: based on the cumulative on the sieve size 0.6mm, the grading of fine aggregate can be classified as I, II, III types, among them type II is better on the characteristics, because it has higher density and lower specific surface area, which gives concrete good water-retaining and less cement consumption;

23. Concrete Mixture Ratio Design ——Technical requirements for raw materials 5.2 ——fineness modulus: normally medium sand shows better performance; • Water ——any domestic water can be used in concrete mixture; • Admixture ——it is a special material which uses a little quantity but influence very much on the concrete properties.

24. Concrete Mixture Ratio Design ——Basic concept about mixture design 5.2 • Representation of concrete proportions ——unit volume method: mass of each material per one cubic meter, for example: cement : water : sand : coarse aggregate. 300 : 150 : 600 : 1200 (kg/m3) ——relative quantity method: which means that mass of cement considered as one unit while other materials convert into a relative units related to cement, for example: cement : sand : c.agg., water/cement ratio = 1 : 2.00 : 4.00 , W/C= 0.50

25. Concrete Mixture Ratio Design ——Basic concept about mixture design 5.2 • Design requirements ——meet strength requirement: put forward a preparation strength(配制强度 ) which is higher than the design strength(设计强度 ); ——meet workability requirement: select appropriate workability based on dimension or shape of the structure, reinforced layout situation and construction method.

26. Concrete Mixture Ratio Design ——Basic concept about mixture design 5.2 ——meet durability requirement: control concrete “maximum W/C ratio” and “minimum cement requirement” according to environmental conditions; ——meet economic requirement: use local materials or waste materials based on qualified requirement of workability and mechanics.

27. Concrete Mixture RatioDesign ——Basic concept about mixture design 5.2 • Design parameters ——W/C: it is a key parameter which affects concrete performances: such as strength, workability and durability; ——water requirement: it decides quantity of cement paste under same W/C ratio; ——sand-ratio: it is closely related to concrete cohesiveness and water-retaining.

28. Concrete Mixture RatioDesign ——Basic concept about mixture design 5.2 • Design processes (1)stage of initial design: according to requirement of the design document, initial mix proportion is found by experience way based on the characteristics of raw materials; (2)stage of testing, adjusting and confirming: final mix proportion is determined in lab by the way of slump test and strength test; (3)stage of work site design: the process is to find the mix proportion to construction based on moisture content of aggregate in the site.

29. Concrete Mixture Ratio Design ——(1)Stage of initial design 5.2 • Determining the preparation strength: • Calculation of W/C:

30. Concrete Mixture Ratio Design ——(1)Stage of initial design 5.2 • Determining of water requirement ( ): ——can be get through checking the table when W/C comes within the range of 0.4~0.8; • Determining of sand ratio ( ): ——also get through checking the table by interpolation (插入法); • Calculation of cement requirement: W/C=0.40 砂率： 27~32% =0.45 ？ =0.50 30~35% 31%

31. ——Volume method ——Density method Concrete Mixture Ratio Design ——(1)Stage of initial design 5.2 • Calculation of sand and coarse aggregate requirements, respectively ( ): • So the initial mix proportion of this stage is:

32. Concrete Mixture Ratio Design ——(2)Stage of adjustment 5.2 • Basic mix proportion ——It is the process that adjusts initial concrete design based on slump test; ——one of the possibilities for the test is shown in the following table; ——this stage result can be expressed as:

33. Possibilities of Slump Test

34. Concrete Mixture Ratio Design ——(2)Stage of adjusting design 5.2 • Design mix proportion ——finding the relationship between strength and W/C ratio, so to determine final W/C ratio to ensure the strength which meets the requirement: W/C

35. Concrete Mixture Ratio Design ——(2)Stage of adjusting design 5.2 ——based on the final W/C and basic water requirement considered as , to calculate the final cement requirement again ( ); ——then calculating the sand and coarse aggregate requirements under new cement and water requirements , , so this stage result can be expressed as:

36. Concrete Mixture Ratio Design ——(2)Stage of adjusting design 5.2 ——according to correction factor of density ( ) to calculate final mix proportion: ——final mix proportion in lab can be expressed as:

37. Concrete Mixture Ratio Design ——(3)Stage of construction design 5.2 • Because sand and coarse aggregate materials in construction site are kept moist, so mix proportion for construction site should be adjusted according to moisture content of sand and coarse aggregate( ):

38. Concrete for Road 5.3

39. 5.3 Ordinary concrete for road——Special requirements • Composition ——there are some special characteristics in cement composition, which are higher C4FA and lower content of C3A; • Workability • depends very much on the method of Concrete paving, normally paving method are: ——Concrete synovial paving method(滑膜摊铺法): slump 25~30mm; ——Concrete track paving method(轨道摊铺法): slump 40~60mm; ——Concrete paving method with three roll shaft(三辊轴摊铺法) : slump 30~50mm； ——Small machine paving method(小型机具法) :slump 10~40mm.

40. 5.3 Ordinary concrete for road——Special requirements • Durability ——Besides controlling the maximum W/C ratio and the minimum requirement, durability of concrete for road has the requirement on air content; ——amount of air entraining content should consider normally environment condition, and nominal maximum size of coarse aggregate.

41. Road Concrete Design ——Determining preparation strength 5.3 Concrete for road Common concrete

42. Road Concrete Design ——Calculation W/C 5.3 Common concrete Concrete for road

43. Road Concrete Design ——Find sand ratio 5.3 By table lookup method. related factors: ——slump value; ——type of coarse aggregate; ——nominal maximum size of aggregate. By table lookup method. Related factors: ——fineness modulus; ——type of coarse aggregate; Concrete for road Common concrete

44. Road Concrete Design ——Find water requirement 5.3 Through the calculation method to find water requirement； Through the look-up table method to find water requirement； Related factors: ——W/C ratio; ——type of coarse aggregate; ——nominal maximum size of aggregate. Common concrete Concrete for road

45. Road Concrete Design ——Calculation requirements of cement, and aggregates 5.3 • There is no differences on the calculation method of mix design for cement, fine and coarse aggregates requirements between common concrete and road concrete; • It should emphasize that filling volume of coarse aggregate is calculated, which is not less than 70%. (mass over tap density of coarse aggregate).

46. Concrete Admixture 5.4

47. Concrete Admixture ——introduction 5.3 • Concrete admixture is a special compound which mixed into concrete during mixing process. • Quantity of admixture added is not much (generally no more than 5% by weight of the cement) , but it brings about significant impact on concrete performances, such as workability, strength etc.; • The main function of admixture is reducing construction cost, obtaining desirable workability and meeting some special requirements.

48. Concrete Admixture ——introduction 5.4 Water reducer, Air entraining agent, Pumping aid, Water-retaining agent. Improving rheological behavior Retarder, Early strength agent, Accelerating agent. Adjusting speed of setting and hardening Classification Air entraining agent, Foam agent, Defoamer. Adjusting air content Air entraining agent, Antifreeze agent, Anti-permeability agent, Corrosion inhibitor. Improving durability

49. Concrete Admixture ——Ordinary admixtures 5.4 • Reducing water agent ——it is an agent that can reduce water requirement without affecting workability of concrete, especially flowability; ——the main functions of this admixture are: (1) because of reducing water requirement and lowering W/C ratio, so concrete strength corresponding is improved; (2) remarkably improving workability under the condition of no any change on concrete component and strength; (3) without change on workability and strength, it can reduce cement consumption so to cut coast.

50. Concrete Admixture ——Ordinary admixtures 5.4 ——Mechanism of action： (1) oriented absorption and dispersion (定向吸附和分散作用); (2) lubrication (润滑作用)； (3) promotion hydration(促进水化作用) ； ——types of reducing water agent: (1) common type: reducing water requirement about 5~15%; (2) superplasticizer: reducing water requirement about over about 20%; (3) compound type: besides reducing water requirement, also having other characteristics.