Fresh and harden properties of concrete

This module covers the fresh and harden properties of concrete

1. CE6002 CONCRETE TECHNOLOGY Module 4 FRESH AND HARDEN PROPERTIES OF CONCRETE

2. FRESH AND HARDEN PROPERTIES OF CONCRETE 2/26/2018 Dr.V.Kannan 2 1. Fresh Properties 2. Harden Properties 1. Workability 2. Segregation 3. Bleeding 1. Compressive strength 2. Flexural Strength 3. Young’s Modulus Tests for workability: Slump cone test Compaction factor test Vee -Bee consistometer test Flow table test Tests for harden property Compression test Flexural strength test Stress-Strain relationship

3. WORKABILITY Workability   is one of the physical parameters of concrete which affects the strength and durability as well as the cost of labor and appearance of the finished concrete.  Concrete is said to be workable when it is easily placed and compacted homogeneously i.e without bleeding or Segregation Factor affecting the workability (Refer unit-3 and 1): Water content Mix proportion Size of aggregate Shape of aggregate Surface texture of aggregate Grading of admixture Use of admixtures (Chemical / mineral admixtures) 2/26/2018 Dr.V.Kannan 3

4. Segregation and Bleeding Bleeding: Bleeding is generally occurred due to higher water cement ratio it is defined as some of the water is come out to the surface of the concrete is called bleeding. Segregation: Aggregates and cement paste are separated due to higher water cement ratio or poor mix proportions are called segregation. It is also seriously affecting the quality of the concrete. 2/26/2018 Dr.V.Kannan 4

5. Segregation and Bleeding (cont.) Effects of bleeding / Segregation in concrete: Due to bleeding / segregation, concrete loses its homogeneity. Bleeding or segregation is responsible for causing permeability in concrete. The strength of concrete will be reduced Reduces the bond between the reinforcement and concrete. In pavement construction bleeding water delays surface finishing and application of curing compound. 2/26/2018 Dr.V.Kannan 5

6. TESTS FOR WORKABILITY OF CONCRETE The following tests are commonly used to check the WORKABILITY properties of concrete; Slump cone test (being in syllabus) Compaction factor test (being in syllabus) Vee -bee consistometer test Flow table test 2/26/2018 Dr.V.Kannan 6

7. 1. SLUMP CONE TEST Test apparatus: Slump cone Tamping rod 2/26/2018 Dr.V.Kannan 7 200 mm 300 mm 100 mm Handle

8. 1. SLUMP CONE TEST (cont.) Test Procedure: The cone is placed in smooth surfaced base plate and the cone is filled with concrete in three layers. Each layer of concrete is properly tamped 25 times with steel rod of 16 mm diameter. When the cone is completely filled with concrete, the top surface is leveled by using trowel. The mould should be firmly held its base during the entire test After proper filling of concrete in cone, the cone is slowly lifted to vertical direction and then the concrete settles down is called slump, the slump value is measure from the top. The settlement of concrete is categorized in to three types 2/26/2018 Dr.V.Kannan 8

9. 1. SLUMP CONE TEST (Cont.) a. True slump: In this type of slump, the concrete is settled less from the top, and there is no any segregation on its shapes and indicate low workability b. Shear slump: In a shear slump, the top portion of the concrete shears off and slips sideways This kind of shear slip of concrete is clearly indicating the lack of cohesion of the concrete mix. c. Collapse slump: In this type of slump, the concrete is completely collapsed due to higher water cement ratio of the mix. This collapse indicates that the higher fluidity of the mix and instability of the mix, which cannot be used in any kind of important structures. 2/26/2018 Dr.V.Kannan 9

10. 1. SLUMP CONE TEST (Cont.) True slump, (b) Shear slump and (c) Collapse slump Recommended Values of Concrete Slump Tests for Various Purposes: 2/26/2018 Dr.V.Kannan 10 Slump Slump Slump (a) (b) (c) No. Types of concrete Slump 1 Concrete for road construction 20 to 40 mm 2 Concrete for tops of curbs, parapets, piers, slabs and wall 40 to 50 mm 3 Concrete for canal lining 70 to 80 mm 4 Normal RCC work 80 to 150 mm

11. 2. COMPACTION FACTOR TEST 2/26/2018 Dr.V.Kannan 11 Container 150 mm dia. and 300 mm height 125 mm 250 mm Upper Hopper Lower Hopper Steel post

12. 2. COMPACTION FACTOR TEST Procedure: Compaction factor is also called the degree of compaction; First the concrete is placed gently at the upper hopper without any compaction. The bottom door of the upper hopper is then released and the concrete falls into the lower hopper. The bottom door of the lower hopper is also released and the concrete falls into the cylinder (container). Excess concrete is then removed from the cylinder.  Now this partially compacted concrete weight is measured.  Then, the fresh concrete is compacted by three layer in cylinder and it is weighted is called fully compacted concrete Usually, the compaction factors various from 0.7 to 1. 2/26/2018 Dr.V.Kannan 12

13. 2. COMPACTION FACTOR TEST (Cont.) More compaction factor is indicating more workability of the concrete mix. It may be calculated by the ratio of weight of partially compacted concrete to the weight of fully compacted concrete 2/26/2018 Dr.V.Kannan 13 Degree of workability Compaction factor Very low 0.78 Low 0.85 Medium 0.92 High 0.95 Very high Above 0.95

14. TEST FOR HARDEN PROPERTIES OF CONCRETE Many destructive and non destructive tests are conducted on hardened concrete to measure their properties such as strength, permeability and durability; 2/26/2018 Dr.V.Kannan 14 Destructive testing (Specimen is broken down) Non-Destructive testing (Specimen is not broken down) Compressive strength test Flexural Strength test Splitting tensile test Modulus of elasticity Pull out test etc. Ultrasonic pulse velocity test Rebound hammer test Electrical resistivity test Other corrosion studies

15. TEST FOR HARDEN PROPERTIES OF CONCRETE Before starting these tests some of the points should be considered, Concrete mix should be uniform and well compacted Curing should be proper At least three specimens are needed for a single test and average value of these three specimens is taken. Each specimen test result should not exceed 5% of the result of other specimens, if exceeded it indicates the poor mix of concrete. 2/26/2018 Dr.V.Kannan 15

16. 1. Compressive strength of concrete 2/26/2018 Dr.V.Kannan 16 P Bottom plate of Universal Testing machine Cylindrical Specimen Top plate of Universal Testing machine

17. 1. Compressive strength of concrete Testing procedure These cured specimens are taken from the curing tank and excess water is removed from the surface. The cleaned specimens are tested by compression testing machine after 7 days curing or 28 days curing as required. Load should be applied gradually till the Specimens fails. Load at the failure is noted and the compressive strength of concrete can be calculated by the ratio of failure load to surface area of the specimen i.e f= P/A 2/26/2018 Dr.V.Kannan 17

18. 1. Compressive strength of concrete As per Indian standard code, the compressive strength improvement percentages is presented in the table 2/26/2018 Dr.V.Kannan 18 Curing period in days Strength improvement in percentage 1 16 3 40 7 65 14 90 28 99

19. 2. Flexural strength test 2/26/2018 Dr.V.Kannan 19 L/3 L/3 L/3 L/2 L/2 L L (a) (b) P P P

20. 2. Flexural strength test Test procedure: Prepare the test specimen by filling the concrete into the mould in 3 layers of approximately equal thickness. Tamp each layer 25 times using the tamping bar. The specimen is placed to the machine as shown in above figure. Hence the load is applied gradually to the specimen and failure of the specimen is carefully noted. After getting of failure loading, the flexural strength can be calculated by using following expression, fb = PL/bd 2 Where, P-load, L-Length of the specimen, B and d- breadth and depth of specimen 2/26/2018 Dr.V.Kannan 20

21. Stress-Strain relationship 2/26/2018 Dr.V.Kannan 21 Stress (σ) Strain (e) f ck 0.67 f ck 0.67f ck / γ m 0.002 0.003 =Characteristic Curve of cube =Characteristic Curve of Structure = Design Curve

22. Stress-Strain relationship (cont) The Figure showing the stress – strain curve for concrete. Usually, the curve may be assumed to be rectangular, trapezoidal, parabola or any other shape. The curve will be linear in lower grade of concrete and nonlinear in higher grade of concrete. For design purposes, the compressive strength of concrete in the structure shall be assumed to be 0.67 times the characteristic strength. The partial safety factor γ m , = 1.5 shall be applied in addition to this. While studying the stress-strain relationship, tensile strength of the concrete is ignored. 2/26/2018 Dr.V.Kannan 22

23. Determination of Modulus of elasticity 2/26/2018 Dr.V.Kannan 23 Top layer of UTM machine Bottom layer of UTM machine Compressometer Dial gauge Specimen (150 mm dia. with 300 mm height)

24. Determination of Modulus of elasticity (cont) Testing procedure Assemble the top and bottom frame by adjusting the screws. Keep the pivot rod on the screws and lock them in position. Keep the compressometer centrally on the specimen so that the tightening screw of the bottom and top frame are at equal distance from the two ends. Place the specimen with compressometer in the compression testing machine and center it. Apply load continuously without shock at a rate of 140 kg /cm²/minute Maintain the load at this stress for at least one minute and reduce gradually to an average stress of 1.5 kg/ cm²(a load of 0.3 Ton) Note the compressometer reading at this load. Reduce the load gradually and take readings at an interval of 1Ton Plot the graph using stress (y-axis) and strain (x-axis) Then the Young’s modulus (Initial / Secant / Tangent) may be calculated by corresponding stress to strain. 2/26/2018 Dr.V.Kannan 24

25. Determination of Modulus of elasticity (cont) 2/26/2018 Dr.V.Kannan 25 Strain

26. THANK YOU 2/26/2018 Dr.V.Kannan 26