Experimental Data Of Normal Strength Concrete Biology Essay

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The experimental investigation was carried out in order to engender experimental data of normal strength concrete, high strength concrete and self-compacting concrete required to generate and validate a method to determine the true uniaxial tensile strength. On the basis of theoretical parametric studies a very simple correction factor has been developed by Raoof and Lin (1999). The correction factor k is given as

Where; ft' = Cylindrical splitting strength calculated using the closed-form formula ft'= 2Q/ld

fc = Concrete compressive strength determined by compressive test of the cylindrical concrete samples

a,b = constants which are dependent on the value of packing strip

For the above proposed correction factor a high set of experimental data was required in order to meet consistency and adequacy. Hence batches of concrete were cast for all three types of concrete i.e. NSC (4 batches), HSC (16 batches) and self-compacting concrete (4 batches). The main reason of casting above three types of concrete was to compare and analyse the correction factor's workability. Each batch consisted of 12 samples. 6 cylindrical samples were casted in order to determine the splitting tensile strength (cylindrical splitting test) and compressive strength (cylindrical compressive/crushing test). Furthermore three samples of beams were also casted in order to determine the modulus of rupture for the comparison with corresponding tensile strength. Each batch also consisted of 3 cube samples which was casted in order to measure the cube compressive strength for quality control and to maintain a record for future use. All the batches that were casted had certain variation and the variations were imposed in order to observe the effect on the concrete strength. Variation was either made on the aggregate type, age of specimen or the quantity of materials. All the NSC was casted for 7 days strength; all HSC was casted for 3 days strength whereas self-compacting concrete was casted for 3,7,14 and 28 days. The mixing proportion was according to the standard mix design. Aggregates of sizes 10mm and 20mm were used for NSC and, and insert about gravel for HSC was used.

PROCEDURE

3.2.1. Materials

Portland cement: Castle multicem was used in order to carry out this research. The cement used complies with the requirements of BS EN 197-1: 2000 CEM II/A-LL Portland-limestone cement strength class 32,5R. it contributes to superior plastic properties in concrete.

Water: water obtained from the normal tap water source was used which was free from any impurities that could have affected the performance and strength of fresh and hardened concrete.

Aggregate: 10mm and 20mm sized river gravel was used for the manufacture of normal and high strength concrete. Something was used for SCC. The different aggregates sizes were used in order to see the effect of size, shape on the strength of the trial mixes. The bigger size particle has known to produce lower strength due to their settlement rate being higher and possibility of air voids formation.

Sand; very fine aggregate was used for manufacturing all the batches of NSC, HSC and SCC. The sand was well graded river sand.

Silica fume: Elkem Microsilica grade 940, in powder form, was used in the batching process. It contained more than 90% of SiO2 with a typical bulk density of 200-300 kg/m3.

Superplastiser: Sika viscoconcrete 25MP was sued as the superplastiser with a relative density of 1.06 and is free from chloride. It complies with EN 934 part 2 table 3.1/3.2- high range water reducing/ superplasticising admixtures. Available in the form of yellow coloured liquid helps in the fast strength development. The 28 day compressive strength of Sika viscoconcrete 25MP is an average of 69 N/mm2 with a w/c ratio of 0.40.

Viscosity modifying admisture: STRUCTURO 480 was used in order to provide a good consistency and stability. The advantage of using this product is that it provides hydraulic binder-based material excellent stability, opposes sweating, segregation and sedimentation in treated concrete. It has a specific gravity of 1.01 at 200C.

3.2.2 Mixing, casting and curing

In order to gather accurate and error free sets of experimental data, accurate and careful execution of processes and steps is vital. Firstly before preparing any mixture, it has made sure all the materials are available and in good state of use (expiry date, safety precautions) such as plasticiser and superplasticiser. Both coarse aggregate and fine aggregate were dried in the heating tray and left to cool for at least 24 hours. This will ensure that any moisture or water content is removed i.e. the moisture condition of aggregates being in dry state. A total of 0.05m3 of mix was prepared however 10% consistency volume was added to the mixture making it a total of 0.05m3 of mixture volume.

Both the fine and coarse aggregate were adequately weighted and put on the mixture. Then the cement and silica fume was added slowly and was adequately buried in the aggregate. This procedure will help stopping the lightweight cement and silica particles from escaping. The mixture was started for a short period of time. at all time of mixing ear defender, eye protector and steel toe capped boots were worn. Next water and superplasticiser was added on the mixture in two steps so that a fine mixture would be prepared. The gradual addition of the water and superplasticiser would improve the workability. The amount of the materials were added according the standard proportion guide provided. After all the materials were put, the mixture was left to run for 2-3 minutes to ensure thorough mixing.

Once the mixture was prepared then the concrete was poured into the steel cylinder, cube and modulus of rupture moulds placed on the vibrating table using scoops. Compaction was carried only in case of NSC and HSC, firstly with the metal rod and later followed by the vibrating machine. In case of Self-compacting concrete no compaction was used and allowed to settle on its own. It was ensured that neither excessive nor less compaction was done. The compaction was carried out in 3 multiple stages of placing concrete on the mould and vibrating them. Compacting occurred nearly for 1-2 minutes until a smooth layer was seen on the surface of moulds. The top surface of each mould was levelled by using trowel to ensure a smooth surface as load is applied directly on to the surface as uneven surface would effect on the uniform distribution of load. The moulds were then covered properly with polythene sheet and placed on the ground surface to cure in the normal lab temperature of 20-22°C for 24 hours. The mould were then de-moulded, weighed and transferred in the water curing tank maintained at 20° C for either 3, 7, 14 or 28 days depending upon the age of testing set previously. The samples were taken out only on the day of test. Firstly the samples were dried with paper roll and allowed to dry further in open air. The samples were then again weighed and then tested.

Details of Specimen

Experimental data carries value only when all the stages are executed according to the required standard. Hence the entire specimens were handled with great care and high level of precision. This means that almost the entire specimen had perfectly flat surface ready to be tested. Each batch consisted of twelve samples i.e. six cylinders, three modulus of rupture sample (beam) and three cube samples. Each batch was given a unique reference number which would help in correct recognition, for example B2HSC3D where "B" represents the batch number, "HSC" represents high strength concrete and "D" represents days. The size of the specimens is given in the table below:

Shape of mould

Length (L)

Mm

Width (b)

mm

Depth(d)

mm

Diameter (d')

mm

Cube

100

100

100

-

Rectangular beam

500

100

100

-

Cylinder

304.8

-

-

152.4

It was always made sure that the entire samples were precise, accurate and perfectly flat.

Testing Procedure:

Cube compression, cylinder splitting and cylinder compression test was carried on the loading machine called Samuel Denison 7230C/90092 whereas the modulus of rupture test was carried out on the other machine located on the right hand side, both the machine were operated using the central control box with the operational guidance provided, using the correct rate of loading for each individual test.

Firstly cube compression test was carried with the perfectly flat surface facing towards the loading plate. While the above process was carried on, a thick paste of ….. powder was prepared by mixing thoroughly with water and applied on top of the cylinder that were to be used for compressive testing. The paste was evenly spread using trowel and then capped with steel plate and left to dry for about 15-20 minutes so that more even/flat surface could be achieved. Once dry, the plate was removed and then loaded to the crushing machine until failure.

For the cylindrical splitting test a steel jig that hold the specimen was placed inside the machine followed by the specimen. Packing strip of 15mm wide and 5mm thick was placed on either side of the specimen and the specimen was secured on the jig with a heavy steel loading bar along which the load was applied.

Finally modulus of rupture test was carried out. For this the mid section of the beam was measured so that the sample could be placed in the machine in the correct scale with the flat surface facing towards the roller support.. The testing was carried out using symmetrical four points loading.

Rates of Loading

The entire specimen was tested on the European standard of loading. The loading rates were set manually from the control box. The following table gives the summary of the loading rates,

Specimen

test

Loading Rate (KN min)

100mm cube

Compression

360

6" cylinder

Compression

657

6" cylinder

Tensile Splitting

219

100m beam

MOR Test

10

Experimental data collection

As stated earlier only three samples were tested for each strength parameter due to limited time and resources. Special attention was given if there were any variation in the range of data generated by the three samples. Attention was not only given on the numerical value of strength but also careful attention was given on the failure mode, any presence of segregation, voids etc. The process of accepting the results was based on the average value of the results compared to the individual values. If the individual results were in the region of 10-15% of the average then it was accepted or else rejected. It is worth to point out that sometime even when there is presence of segregation or voids all the three samples may bear the same strength. In such cases the acceptance of the data would be through group discussion (supervisor and tester) and comparison with the standard targeted strength. As a whole the main objective of the experimental data collection is to keep it real.

Normal Strength Concrete mixes

NSC mix was prepared according to the standard mix design. The normal strength mix prepared was the target strength of C40. Four batches were casted, two with 10mm coarse aggregates and the remaining two with 20 mm coarse aggregates. All the samples were casted, cured and tested according to the above outlined procedure. Even for the same target strength variation was seen between compressive and tensile strength. The strength was higher for the mixes with 20mm coarse aggregate. This is possibly dues to the higher settlement rate of 20mm coarse aggregate as compared to 10mm and carries higher potential of void formation. The compressive strength ranged from 24.55 to 31.24 N/mm2. The mix design of C40 is given below:

Target Strength

Cement (kg)

Coarse Aggregate (kg)

Fine Aggregate(kg)

Free Water (kg)

Extra Water (kg)

C40

19.2

70.7

33.3

8.8

1.5

High Strength Concrete Mixes

High strength concrete often balances the increase in material cost. HSC provides greater extent of advantage such as reduction in the member size resulting in (a) increase in space (b) reduction in the volume of produced concrete with the accompanying saving in the construction time. HSC is greatly influenced by the constituents (type, quality and quantity). The HSC concrete mixes used in this research contained, Portland cement, coarse and fine aggregate, silica fume and multi-functional ready-mix admixture called Sika ViscoCrete 10 (GB). Concrete structural systems constructed from 103-138 MPa concretes are being built today. All the concrete mixes were manufactured two times first with 10mm coarse aggregate and 20mm coarse aggregate respectively. Although in high strength concrete cement and admixture are the dominating factors that contribute towards the strength of concrete, 10mm and 20mm of aggregates were chosen to establish precision and increase value of the experimental data.

Generally HSC are manufactured using fly ash, silica fume, and pulverised fuel ash. The materials are chosen according to their workability and properties. For the above research, silica fume was used as it increases the water demand in the mixture and workability. It also greatly helps to produce high compressive, tensile and flexural strength. The chemical admixture used was Sika ViscoCrete 10 (GB). It has been used as standard water reducing admixture. The use of this chemical helps to give high early strength as its is used as an accelerating high range water reducer. All the HSC samples were produced according to the procedure discussed above. The target strength of the HSC used for the study ranged from C30 to C110 in order to ensure that various HSC mix has been used. Target strength of C20 was not used. The lower ranges of strength were established in comparison with the results obtained from previous researchers and were manufactured in the descending order. Also concrete with higher ranges of strength value are used in construction. The target strength testing time was 3 days for all the HSC mixes. The cylindrical splitting strength ranged from 2.7 N/mm2 to 4.6 N/mm2 whereas the cylinder compressive strength ranged from 27 N/mm2 to 51 N/mm2. A table has been provided detailing the quantities of constituent material used to produce various mixes. All the quantities are in Kg except superplasticiser which is given in litres.

Target Strength

Cement

Coarse Aggregate

Fine Aggregate

Free Water

Extra Water

Silica Fume

Superplasticiser

C30

15.4

53.9

53.8

7.7

0.9

1.7

0.34

C40

17.8

53.9

51.6

7.7

0.9

2.0

0.35

C50

19.0

53.9

50.3

7.7

0.9

2.1

0.39

C60

20.1

53.9

49.0

7.7

0.9

2.2

0.44

C70

21.4

53.9

47.9

7.7

0.8

2.4

0.47

C80

22.8

53.9

46.5

7.7

0.8

2.5

0.51

C90

24.5

53.9

44.8

7.7

0.8

2.7

0.54

C100

26.1

53.9

43.2

7.7

0.8

2.9

0.58

C110

27.7

53.9

41.6

7.7

0.7

3.1

0.62

Self compacting Concrete

The hardened self compacting concrete is dense, homogenous and has the same engineering properties and durability as traditional vibrated concrete. For the research only one trial mix was used. The trial mix consisted of 4 batches of sample with same quantity of constituent material but was manufactured for 3, 7, 14 and 28 days of target strength. Fly ash has been as an addition as it provides increased cohesion and reduced sensitivity to changes to water content. STRUCTURO 480 was used as stabiliser. It provides hydraulic binder -based material excellent stability, opposes sweating, segregation and results in concrete with high level of fluidity that makes the mixture easy to handle and can be poured in the moulds without the need of vibration. The table below summarises the constituents quantities of the materials used to prepare the mix. All the quantities were measured in kg.

Insert TAble

RESULTS AND DISCUSSION

Fresh Concrete Testing

Only SCC mixes were tested for slump flow, viscosity, passing ability and segregation. The results of the test carried out and their analysis is given below:

Slump Flow Test

The slump flow test was carried out in order to access the workability and flow-ability of SCC. In this test two diameter of the flow spread at right angles were measured to give an average value. Again the concrete was checked for segregation. The table blow gives the result obtained, it can be seen that all the test results have similar average diameter. According to the European guideline the average value should fall in between 650-800mm and the result does. This means that the SCC mix produced was workable and indicates it's the filling ability:

Target Strength

3 Days

7 Days

14 Days

28 Days

Diameter (mm)

720.50

720

740

778.5

1.2. V-funnel Test

V-funnel test was used in order to consider the viscosity and filling ability of mix design. In this test the time taken by the mix to empty the V-funnel was measured. The accepted time for the flow out of concrete from V funnel is 2-5 seconds. The results obtained shown in the table number shows the time taken. Here the value of the time taken is slightly above the accepted value. This means that the mix was not viscous as should have been to be used. The results being slightly higher than acceptance value has been found to be because of the dry surface of v-funnel which was not wetted enough as per the standard procedure.

Target Strength

3 Days

7 Days

14 Days

28 Days

Time taken (s)

5.30

6.32

4.0

5.6

1.3. L-box test

The L-box test was carried on in order to evaluate the passing ability of SCC mix design to flow through tight openings without segregation. For this test concrete placed in the L-box was released and when the movement of concrete was stopped the vertical distance, at the end of the horizontal section of the L-box, between the top of the concrete and the top of the horizontal section of the box were measured. The accepted value i.e. the ratio of two heights is ≥0.80 (for three bars). The results in the table number indicate that the ratio obtained are consistent, acceptable and does possess the ability to pass through opening gaps.

Target Strength

3 Days

7 Days

14 Days

28 Days

Ratio

0.9

0.9

0.9

0.9

1.4. J-ring Test

1.5. Sieve Segregation Test

This test was carried out in order to evaluate the opposition of SCC mix design to segregation. In this test the fresh concrete that has been allowed to stand for 15min is checked for bleed water separation. The segregation ratio is calculated as the proportion of the sample passing through the sieve. The accepted value of segregation is <20%. The table number gives the segregation ratio, it can be easily confirmed that the trial mix did segregate.

Target Strength

3 Days

7 Days

14 Days

28 Days

Segregation Ratio (%)

28

40

60

40

2.0. Strength Test

Modulus of Rupture test, Compressive strength test, Splitting test and Cube compression test was carried out for all the samples. The results shows the variation in the strength between NSC, HSC and SCC

2.1. Normal strength concrete (NSC)

As mentioned only four batches of normal strength concrete were casted all with the same target strength of C40 (7 day strength) the variation being only the use of two different sizes of aggregates i.e. 10mm and 20mm coarse aggregate. The table number shows the results from the testing carried out. It can be seen that there was the variation in strength between 10mm and 20mm coarse aggregate. The C40 with 10mm coarse aggregate had higher splitting strength (average of 3.06 MPa), compressive strength (29.94 MPa) and flexural Strength (4.58 MPa). This was probably due bigger size coarse aggregate settling on the bottom of the moulds rather than uniform distribution as a result of longer vibration.

 

Cylinder Splitting Test

Cylinder Compression Test

Modulus of Rupture Test

Cube Compression Test

Batch

P (N)

f't

f'tAve

P (N)

fc

fcAve

P (N)

f't , MOR

f't , MORAve

P (N)

fcu

fcu

C40 (20mm)

203000

2.78

 

 

452500

24.81

 

 

14230

4.27

 

 

276500

27.65

 

 

 

185200

2.54

476200

26.11

14820

4.45

311300

31.13

 

201500

2.76

2.69

475700

26.08

25.66

12630

3.79

4.17

354500

35.45

31.41

C40 (20mm)

201300

2.76

 

 

464700

25.47

 

 

13350

4.01

 

 

310700

31.07

 

 

 

182500

2.50

446300

24.47

12510

3.75

312900

31.29

 

199500

2.73

2.66

432700

23.72

24.55

15630

4.69

4.15

315200

31.52

31.29

C40 (10mm)

219200

3.00

 

 

571200

31.31

 

 

15190

4.56

 

 

344600

34.46

 

 

 

249100

3.41

568800

31.18

15080

4.52

338100

33.81

 

227000

3.11

3.18

569700

31.23

31.24

14710

4.41

4.50

362100

36.21

34.83

C40 (10mm)

196600

2.69

 

 

518500

28.42

 

 

16370

4.91

 

 

314500

31.45

 

 

 

223000

3.06

515400

28.25

14450

4.34

322800

32.28

 

224200

3.07

2.94

533300

29.24

28.64

15750

4.73

4.66

327000

32.70

32.14

2.2. High strength concrete (HSC)

The main focus of the research is the use of correction factor on high strength concrete. The table number shows the results obtained from testing carried out on 16 batches of high strength concrete all tested for 3 days strength.

 

Cylinder Splitting Test

 

 

Cylinder Compression Test

 

 

Modulus of Rupture Test

 

 

Cube Compression Test

 

Batch

P (N)

f't

f'tAve

P (N)

fc

fcAve

P (N)

f't , MOR

f't , MORAve

P (N)

fcu

fcu

C100 (10mm)

322000

4.41

 

910900

49.94

 

21400

6.42

 

576400

57.64

 

 

338300

4.64

 

953700

52.28

 

20700

6.21

 

499900

49.99

 

 

302100

4.14

4.40

925800

50.75

50.99

19400

5.82

6.15

608500

60.85

56.16

C90 (10mm)

269100

3.69

 

803000

44.02

 

20200

6.06

 

403200

40.32

 

 

280700

3.85

 

761900

41.77

 

20500

6.15

 

531300

53.13

 

 

245700

3.37

3.63

775200

42.50

42.76

16960

5.09

5.77

530100

53.01

48.82

C80 (10mm)

273700

3.75

 

775300

42.50

 

20100

6.03

 

490900

49.09

 

 

273900

3.75

 

759300

41.62

 

20200

6.06

 

541700

54.17

 

 

267000

3.66

3.72

766800

42.04

42.05

19940

5.98

6.02

525500

52.55

51.94

C70 (10mm)

200300

2.75

 

580300

31.81

 

15590

4.677

 

331300

33.13

 

 

202800

2.78

 

436600

23.93

 

13880

4.164

 

408500

40.85

 

 

238600

3.27

2.93

596000

32.67

32.24

13940

4.182

4.34

402500

40.25

38.08

C60 (10mm)

230800

3.16

 

591100

32.40

 

13070

3.921

 

387200

38.72

 

 

220500

3.02

 

591200

32.41

 

12900

3.87

 

399300

39.93

 

 

211200

2.89

3.03

562500

30.84

31.88

14580

4.374

4.06

405500

40.55

39.73

C50 (10mm)

198900

2.73

 

482600

26.46

 

13070

3.921

 

349100

34.91

 

 

204700

2.81

 

482400

26.45

 

13690

4.107

 

363200

36.32

 

 

204700

2.81

2.78

478800

26.25

26.38

13740

4.122

4.05

293300

29.33

33.52

C40 (10mm)

197200

2.70

 

466800

25.59

 

16470

4.941

 

359000

35.90

 

 

155000

2.12

 

473700

25.97

 

14660

4.398

 

384400

38.44

 

 

232600

3.19

2.67

472300

25.89

25.82

14470

4.341

4.56

317700

31.77

35.37

C100 (20mm)

271800

3.73

 

760900

41.71

 

16890

5.067

 

584000

58.40

 

 

292300

4.01

 

423400

23.21

 

14650

4.395

 

596400

59.64

 

 

278600

3.82

3.85

566900

31.08

36.40

14120

4.236

4.57

566200

56.62

58.22

C90 (20mm)

261300

3.58

 

807000

44.24

 

14680

4.404

 

607000

60.7

 

 

231900

3.18

 

751500

41.20

 

16970

5.091

 

542700

54.27

 

 

278300

3.81

3.52

764700

41.92

42.45

16310

4.893

4.80

584300

58.43

57.80

C30 (10mm)

201800

2.77

 

420000

23.02

 

13720

4.116

 

274200

27.42

 

 

131100

1.80

 

418800

22.96

 

12980

3.894

 

261200

26.12

 

 

195400

2.68

2.72

427900

23.46

23.15

12460

3.738

3.92

283200

28.32

27.29

C80 (20mm)

231300

3.17

 

515700

28.27

 

13350

4.005

 

497600

49.76

 

 

220500

3.02

 

528400

28.97

 

15190

4.557

 

518800

51.88

 

 

215020

2.95

3.05

635400

34.83

30.69

13730

4.119

4.23

520500

52.05

51.23

C70 (20mm)

200300

2.75

 

575300

31.54

 

12660

3.798

 

386200

38.62

 

 

198600

2.72

 

574000

31.47

 

13770

4.131

 

400700

40.07

 

 

199000

2.73

2.73

547600

30.02

31.01

13670

4.101

4.01

420200

42.02

40.24

C60 (20mm)

190100

2.61

 

495300

27.15

 

13670

4.101

 

354800

35.48

 

 

208400

2.86

 

474400

26.01

 

11890

3.567

 

379100

37.91

 

 

188000

2.58

2.68

507300

27.81

26.99

13140

3.942

3.87

378600

37.86

37.08

C50 (20mm)

203600

2.79

 

441500

24.20

 

12590

3.78

 

370400

37.04

 

 

226300

3.10

 

512000

28.07

 

13280

3.98

 

370200

37.02

 

 

215300

2.95

2.95

477100

26.15

26.14

12250

3.68

3.81

366600

36.66

36.91

C110 (20mm)

331400

4.54

 

899000

45.60

 

20350

6.11

 

716300

71.63

 

 

352000

4.82

 

900000

45.00

 

20430

6.13

 

740200

74.02

 

 

319000

4.37

4.58

899000

46.90

45.83

19830

5.95

6.06

714600

71.46

72.37

C110 (10mm)

318800

4.37

 

947500

47.90

 

18190

5.46

 

756600

75.66

 

 

354100

4.85

 

940600

46.90

 

20500

6.15

 

777100

77.71

 

 

336900

4.62

4.61

907400

46.90

47.23

22600

6.78

6.13

789100

78.91

77.43

From the above table, the variation in the tensile strength (cylindrical splitting) and the compressive strength among the various batches can be easily observed. The splitting tensile strength varied from 2.72 MPa (C30, 10mm) to 4.61 MPa (C110, 10mm) while the compressive strength varied from 23.15 MPa ( C30, 10mm) to 50.99 MPa (C100, 10mm). The strength of HSC concrete mixes increased as the proportion of silica fume and superplasticiser increased i.e. C30 had the 1.7kg of silica fume and 0.34litres of superplasticiser and had an average compressive strength of 23.15 n/mm2 while C110 constituted of 3.1kg of silica fume and 0.62 litres of superplasticiser and possessed average compressive strength of 46.5N/mm2. This shows that higher the proportion of admixtures and superplasticiser increases the workability, viscosity and strength of the concrete. The dispersion effect of the superplasticiser improved the efficiency of hydration making the strength of the concrete less dependent upon the cement content and w/c ratio. The higher the superplasticiser dosage, the higher the compressive strength of the concrete for a given workability as long as the mix remained cohesive.

Self-Compacting Concrete (SCC)

Four batches of SCC were manufactured and tested. These batches were casted in order to compare with the results of HSC. The trial mix of SCC was tested for 3, 7, 14 and 28 days strength. The table number shows the results obtained from testing carried out in the four batches.

 

Cylinder Splitting Test

 

 

Cylinder Compression Test

 

 

Modulus of Rupture Test

 

 

Cube Compression Test

 

Batch

P (N)

f't

f'tAve

P (N)

fc

fcAve

P (N)

f't , MOR

f't , MORAve

P (N)

fcu

fcu

TM8, 28 days

234600

3.22

 

521400

28.58

 

16360

4.91

 

486000

48.60

 

 

 

256900

3.52

 

502100

27.53

 

16300

4.89

 

462900

46.29

 

240600

3.30

3.34

390300

21.40

28.05

15350

4.61

4.80

458300

45.83

46.91

TM8, 14 days

153400

2.10

 

272100

14.92

 

12430

3.73

 

486000

48.60

 

 

 

206400

2.83

 

270700

14.84

 

11780

3.53

 

507900

50.79

 

152000

2.08

2.34

273000

14.97

14.90

11920

3.58

3.61

392900

39.29

46.23

TM8, 3 days

190200

2.61

 

393200

21.56

 

8800

2.64

 

217700

21.77

 

 

 

171500

2.35

 

395700

21.69

 

10380

3.11

 

219300

21.93

 

180400

2.47

2.48

392700

21.53

21.59

9770

2.93

2.90

211600

21.16

21.62

TM8, 7 days

141900

1.94

 

410800

22.52

 

13720

4.12

 

353600

35.36

 

 

 

132900

1.82

 

386800

21.20

 

12000

3.60

 

395100

39.51

 

154300

2.11

1.96

394900

21.65

21.79

15800

4.74

4.15

325900

32.59

35.82

The tensile splitting strength of SCC varied from 1.96 MPa (TM8, 7days) to 3.34 MPa (TM8, 28 days) while the compressive strength of the concrete varied from 14.90 MPa (TM8, 14days) to 28.05 MPa (TM8, 28days). The tensile strength and compressive strength of SCC that was tested on 28th day was observed to be high in comparison to the same mix tested at 3, 7 and 14 days. This shows that the age of testing does matter. However there was a slight problem i.e. the strength of the mix tested on 14 days was lower than that of 7 or 3 days strength. This can possibly due to the error in execution of the procedure for that batch. The possible error is error in manufacturing and testing. However the same mix followed the pattern for cube compressive strength (46.23 N/mm2).

Comparative analysis of Splitting strength and Flexural Strength (MOR)

Previous studies has shown that modulus of rupture is greater than cylindrical splitting strength. From the experimental results the above statement exits to be true and is demonstrated by the graphs in case of all three NSC, HSC and SCC as shown below. Splitting tensile strength and modulus of rupture has been analysed against the cube compressive strength and cylinder compressive strength.

MOR and splitting strength against cylinder compressive strength

When MOR and Splitting strength is plotted against cylinder compressive strength, the following graph is obtained

From the above three graphs it can be noticed that the modulus of rupture for NSC, HSC and SCC was relatively high than the splitting tensile strength. This concludes that no matter what the type of mix is MOR is always greater than STS (splitting tensile strength). Again from the graphs it can be seen that the NSC showed higher difference than HSC and SCC.According to Dewar (1964), at low strengths the indirect tensile strength (cylinder splitting strength) may be as high as 10% of the compressive strength but at higher strengths it may reduce to 5%. The similar pattern can be seen in the above graphs.

MOR and splitting strength against cube compressive strength

When MOR and Splitting strength is plotted against cube compressive strength, the following graph is obtained

Again when the splitting strength and MOR was compared with cube compressive strength similar pattern was found i.e. MOR > uniaxial tensile strength. However the only difference is that the MOR and uniaxial value was found at higher cube compressive strength than cylinder compressive strength for the same. The plot for HSC didn't show apparent difference in behaviour although the data are significantly scattered.

Cube and cylinder compressive strength relationships

From the experimental data collected for NSC, HSC and SCC a plot is produced in order to show the relationship between cylinder/cube compressive strength ratio and cube compressive strength. The relationship for all three mixes has been compared against the relationship proposed by Domone 2006. The three graphs are shown below. For normal strength concrete the ratio for the experimental data increase 0.78 to 0.89. again the when the data was plotted against the pattern proposed by Donome (2006) only one data fell near to the acceptable position. Hence the proposed pattern cannot be verified as the number of experimental data is low and further investigation is required.

For HSC the ratio remained same i.e. around 0.78. This is possibly due to the reason that all the HSC mixes were tested for 3 days strength and hence followed the similar ratio of cylinder/cube strength for the whole range of cube compressive strength. Again very few data fell into the acceptable region.

However a big jump can be seen in SCC i.e. it started at 0.35 and went near to 0.99. The possible reason for the difference in the ratio variation between SCC and HSC/ NSC can be related to the use of aggregates. All the experimental data for SCC did not fall anywhere near to the pattern proposed by Donome as shown in the plot below. Hence once again his proposal can be verified as more data would be required.

Again it must be pointed that cube failure is as a result of biaxial stress rather than the centre section of cylinders Domone (2006). SCC has a ratio as close to 0.99 possibly due to the reason that the shear movement occurs at lower stress level giving similar values of cube and cylinder compressive strength

Calculation of correction factor and determination of the concrete uniaxial tensile strength fta

The correction factors have been calculated according to the method proposed by Raoof and Lin (1999). Here the method uses cylinder splitting and cylinder compressive strength using eqn…… where the values of 'a' and 'b' are 5.9316 and 0.5647 respectively to find the factor 'k'. Here the uniaxial tensile strength is found using the relation ft=kft`. The other factor k1 is found using the eqn…. where the values of a´= 4.8147 and b´= 0.8408. Again a tensile strength is calculated using the correction factor and the modulus of rupture using the equation . Below are the calculated values for NSC, HSC and SCC. Full calculation is provided in appendix:

For normal Strength concrete:

f't / fc

k

ft (N) = ftc (N)

K1

K1 / K

fta = MOR/(K1/K)

fta / ftc

0.104974

1.496535

4.031595921

1.700017

1.135968485

3.669115873

0.910090184

0.108525

1.585019

4.223625752

1.760894

1.11096047

3.734606327

0.884218098

0.10167

1.422651

4.518867946

1.647045

1.15772916

3.88519194

0.859771072

0.102699

1.444873

4.249517885

1.663189

1.15109708

4.045705683

0.952038747

For High Strength concrete:

f't / fc

k

ft (N) = ftc (N)

K1

K1 / K

fta = MOR/(K1/K)

fta / ftc

0.097667

1.342346

6.1923987

1.587119

1.182346653

5.183758914

0.837116466

0.086224

1.155863

5.08184079

1.437618

1.243761147

4.944679303

0.973009488

0.084986

1.13874

4.138316976

1.423108

1.249721689

4.613827264

1.114904269

0.08849

1.188554

4.423055517

1.464938

1.232537992

4.887476117

1.104999948

0.090921

1.225757

3.59331579

1.495436

1.220009809

3.558168113

0.990218595

0.094925

1.292387

3.911447261

1.548534

1.198196975

3.384251576

0.865217233

0.10533

1.504958

4.182164518

1.705929

1.133539604

3.572879136

0.854313387

0.117589

1.866721

5.080879458

1.938023

1.038196268

3.771926484

0.742376692

0.103482

1.462258

3.90652269

1.675691

1.145961333

3.979191855

1.018602007

0.099912

1.386241

6.348024594

1.620186

1.168762655

5.185826202

0.816919677

0.105776

1.515663

5.834914842

1.713408

1.130467571

4.039036694

0.692218619

0.083021

1.112597

3.921325626

1.400685

1.258932902

3.809575548

0.971501964

0.099259

1.373174

4.183050529

1.610422

1.172773663

3.604276027

0.861638176

0.088087

1.182611

3.230201226

1.460009

1.234563158

3.248112479

1.005544934

0.099272

1.373441

3.679907207

1.610622

1.172691504

3.300100654

0.896789095

0.11275

1.704947

5.02532409

1.839249

1.078772272

3.533646626

0.703167908

For self-compacting concrete

f't / fc

k

ft (N) = ftc (N)

K1

K1 / K

fta = MOR/(K1/K)

fta / ftc

0.119215

1.928201

6.448841022

1.973639

1.023565135

4.690468478

0.727335108

0.156888

8.136512

19.02381049

3.437008

0.422417808

8.553143195

0.449601997

0.114696

1.766519

4.374785242

1.87774

1.062960337

2.723525892

0.622550763

0.089958

1.210751

2.373407545

1.483209

1.225032371

3.389298191

1.428030428

From the above calculation firstly it can be seen that the ratio of uniaxial tensile to compressive strength are in the range of 0.08 to 0.11. Focusing on high strength concrete, as the compressive strength increases there is very small change in the ratio of uniaxial tensile strength to compressive strength. Most of the correction factor calculated fell in the range of 1.13 to 1.9. this value seems reasonable when compared against the ratios proposed by Lin and Wood (2003) where the values are in the range of 1.08 to 1.37 for fc = 30 N/mm2. The calculated ratio of the correction factor k1/k showed very good consistency with most of the values falling in the range 1.02 to 1.25. The ratio of the two calculated uniaxial tensile strength fta / ftc for most of the data was in the range of 0.6 to 1.11 while a few of the results being outside the range. As we already mentioned in the literature that ,..........

From the above plot it can be seen that almost all the data were in the acceptable region for the proposed ......... except the one for SCC TM8 7day strength mix where the point was out of the acceptable region. The possible reason for this data not to follow the pattern can be the defect in the manufacturing process or testing process.

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