CHAPTER 3 EXPERIMENTAL INVESTIGATION

Transcription

1 37 CHAPTER 3 EXPERIMENTAL INVESTIGATION 3.1 PROPERTIES OF MATERIALS USED For designing the concrete mix, preliminary tests as per Bureau of Indian standards (BIS) were conducted to find out the basic properties of cement, fine aggregate and coarse aggregate used in this research. ph value of potable tap water used was 7.54 (greater than 6) conforming to IS: The test results are shown in Table 3.1. Table 3.1 Test results of Concrete Ingredients Material Cement Fine Aggregate Coarse aggregate Property Fineness test (% residue on 90µ sieve) Average Test results 1.26 Conducted test as per Indian Standards BIS IS:4031(part-1) 1996 Normal consistency 36% IS:4031(part-4) Initial & Final setting time 125 & 230 Min IS:4031(part-5) Specific gravity 3.10 IS:4031(part-11) Fineness Modulus 2.42 IS: Zone confirm to II Specific gravity 2.65 IS: 2386 (Part III) Moisture content 2.51% Fineness Modulus 7.46 IS: Specific gravity 2.60 IS: 2386 (Part III) Water absorption 1.11% -1963

2 DESIGN OF REFERENCE CONCRETE MIX Based on preliminary test results as presented in Table 3.1, Reference concrete mix was designed as per Indian standard method by IS: The relevant tables are presented in APPENDIX Design Stipulations a) Grade of concrete = M 20 b) Characteristic compressive strength Required at 28 days = 20 MPa c) Maximum size of aggregate =20mm (Angular) d) Degree of workability (Compaction factor) = 0.9 e) Degree of quality control = good f) Type of exposure = mild g) Specific gravity of cement ( s c ) = 3.10 h) Specific gravity of coarse aggregate ( S ca ) = 2.60 i) Specific gravity of fine aggregate ( S fa ) = 2.65 j) Water absorption = 1.11% k) Free surface of moisture of fine aggregate = 2.51% l) Fine aggregate confirming zone = II m) Entrapped air content (E air ) = 2% (Table A.1.6 )

3 Design of Mix Target Mean Strength Target mean strength (f t ) = fck * S (S- Standard Deviation=4, Table A.1.1) = 20 + (1.65x4) = N/mm 2 Water Cement Ratio a. From graph w/c = 0.50 (Figure A.1.1 ) b. From type of exposure w/c = 0.55 (Table A 1.2) c. Take least value of w/c = 0.50 Selection of Water and Sand Content Table 3.2 shows the calculation of Adjustment of values in water content and sand percentage by referring A 1.5. For 20mm size coarse aggregate and sand confirming to zone II, Water content per cubic metre of concrete was 186 kg and sand content as percentage of total aggregate by absolute volume was 35% as per Table A1.3 and 1.4. Table 3.2 Adjustment of values in water content and sand percentage Change in condition Water content Adjustment required in Sand content Sand zone II 0 For increasing compaction factor ( ) = For decrease in water content ratio by ( ) = % -2%

4 40 Required water content = % w = kg Required sand content = 35-2 P = 33% Required cement content for w/c = 0.5, = /0.5 C = kg Weight of Fine Aggregate (FA) F.A = (1000 (1-E air ) w C/s c ) P x S fa F.A = (1000 (1-2/100) (383.16/3.1)) x 33/100 x 2.65 = kg/m 3 Weight of Coarse Aggregate (CA) C.A = (1000 (1-E air ) w C/s c ) (1 P) x S ca C.A = (1000 (1-2/100) (383.16/3.1)) x (1 33/100) x 2.60 = kg/m 3 Table 3.3 Water Adjustment for Actual Quantities of Different Constituents Quantity of water to be changed Water absorption of C.A =1.1% Free surface moisture FA =2.51% Water Cement Fine aggregate Coarse aggregate

5 41 The quantities of materials per cubic metre of concrete as presented in Table 3.3 are summarised as below. a) Cement = kg b) Fine aggregate = kg c) Coarse aggregate = kg d) Water = litres Table 3.4 Calculation of Reference Concrete Mix Ratio Cement Fine aggregate Coarse aggregate Water From Table 3.4, Reference Mix Ratio, RMX = 1: 1.55: 2.98: PRELIMINARY INVESTIGATIONS Optimum Dosage of Superplasticiser Concrete consumption is 10 billion ton per year, which is equivalent to 1 ton per every living person and hence judicious use of cement has distinct economic and environmental effect reported by Nataraja et al (2005). Another report by ACI 212.4R (1993) stated that superplasticisers are added to economise the cement by simultaneous reduction of cement and water content of the reference mix. Hence it is aimed to optimize the dosage of superplasticiser by reducing cement and water content simultaneously, keeping water-cement ratio constant, by the addition of superplasticiser to the reference mix (RMX) at plastic and hardened states. Cement and water content of the reference mix was reduced at a time simultaneously by 5%, 10%, 15% & 20% at each stage, superplasticiser was added at 0.4%, 0.8%,

6 42 and 1.2% by weight of cement. At each level of reduction of cement & water with addition of superplasticiser, workability & strength values were determined and compared. There were 2 water reducers, 4 levels of cement reduction & 3 dosages of water reducers. Thus (2 x 4 x3 =) 24 mixes were made. The following tests were conducted on the reference mix. Table 3.5 and Table 3.6 show mix details and quantities of materials used. a) Slump test and Compaction factor test b) 7 & 28-days compressive strength test The quantity of materials required for conducting slump test, compaction factor test and 7, 28-days compressive strength test were calculated. The materials (cement, fine aggregate, coarse aggregate and water) were weighed and taken separately. Cement and sand were first mixed, and then coarse aggregate was added and thoroughly mixed to form a dry mixture. Water was then added and mixed until a thorough homogenous mixture was obtained. Slump test and compaction factor test were done simultaneously and at the same time, three numbers of 150 mm size concrete cubes were cast as per IS: The concrete cubes were removed from the moulds after 24 hours and placed in water for curing. At the end of 7 th & 28 th days from the date of casting, the cubes were taken out and tested for their 7-days & 28- days compressive strength in a 200 tonne capacity hydraulic compression testing machine.

7 43 Table 3.5 Mix Details Type MIX MIX DETAILS ORD1 RMX 5 % W & C+0.4 % OSP ORD2 RMX 5 % W & C+0.8 % OSP ORD3 RMX 5 % W & C+1.2 % OSP REFERENCE MIX WITH Organic superplasticiser ORE1 ORE2 ORE3 ORF1 ORF2 ORF3 RMX 10 % W & C+0.4 % OSP RMX 10 % W & C+0.8 % OSP R MX 10 % W & C+1.2 % OSP RMX 15 % W & C+0.4 % OSP RMX 15 % W & C+0.8 %OSP RMX 15 % W & C+1.2 % OSP ORG1 RMX 20 % W & C+0.4 % OSP ORG2 RMX 20 % W & C+0.8 %OSP ORG3 RMX 20 % W & C+1.2 % OSP NRD1 RMX 5 % W & C+0.4 % NSP NRD2 RMX 5 % W & C+0.8 %NSP REFERENCE MIX WITH Naphthalene superplasticiser NRD3 NRE1 NRE2 NRE3 NRF1 NRF2 NRF3 NRG1 RMX 5 % W & C+1.2 % NSP RMX 10 % W & C+0.4 % NSP RMX 10 % W & C+0.8 %NSP R MX 10 % W & C+1.2 % NSP RMX 15 % W & C+0.4 % NSP RMX 15 % W & C+0.8 % NSP RMX 15 % W & C+1.2 % NSP RMX 20 % W & C+0.4 % NSP NRG2 RMX 20 % W & C+0.8 % NSP NRG3 RMX 20 % W & C+1.2 % NSP

8 44 Table 3.6 Quantity of Materials used per cubic metre of Concrete without fibres MIX Grade of cement Wt cement per cubic metre of concrete Fa/c Ca/c W/c % Dosage of SP RMX ORD ORD ORD ORE ORE ORE ORF ORF ORF ORG ORG ORG NRD NRD NRD NRE NRE NRE NRF NRF NRF NRG NRG NRG Test Results and Discussion Tests were conducted on each mix to evaluate both workability and strength values.

9 Workability Tests Slump and compaction factor values at various levels of reduction are furnished in Table 3.7. It is found from slump test results that at 5% reduction level of cement and water content, organic based superplasticiser showed high slump values at the dosage level of 0.8 %. While increasing the reduction level of cement and water content to 10% and 15%, sulphonated naphthalene based superplasticiser showed higher slump values at the dosage levels of 0.4 % and 0.8 %. But at 20% reduction level, very low slump values were obtained at the dosage level of 0.4% and collapse slump was obtained at higher dosages of 0.8% and 1.2% of both type of superplasticiser. Compaction factor test showed that the concrete with naphthalene based superplasticiser has medium and higher workability at the dosage level of 0.4% and 0.8%. At 20 % reduction level of cement and water content low workability was obtained at the dosage level of 0.4 %. By overall observation, it was found that at 15% reduction of cement and water content, concrete had the highest slump values of 125 mm and 145 mm and compaction factor values as 0.97 and 0.98 at the dosage level of 0.8% of organic and naphthalene based superplasticiser respectively Compressive Strength Test As the concrete had segregated and collapse slump occurred at 20% reduction of cement and water content, it was decided to conduct only strength test on concrete with both types of superplasticisers from 5% to15% reduction of cement and water content. From the test results shown in Table 3.8, the compressive strength of concrete of reference concrete was found as N/mm 2 and N/mm 2 at 7 and 28 days curing respectively. It is evident from this table that all the concrete mixes had the higher compressive strength than the reference mix. Hence it is discriminated to choose the

10 46 concrete mix with low cement content which has higher strength than the reference mix. Based on the results obtained from workability test and compressive strength test, optimum dosage of superplasticiser was chosen from the mix containing minimum dosage of superplasticiser at the level of maximum reduction of cement and water content. It was found from Tables 3.7 and 3.8 that concrete mix, at the maximum reduction of cement and water content by 15% with 0.8% dosage of superplasticiser, has higher workability and compressive strength than reference concrete mix. Hence it was decided to choose this mix to find optimum dosage of superplasticiser. Based on this reduction level, the reference mix was revised as 1: 1.83: 3.51: 0.49 with 0.8% superplasticiser and is presented in Table 3.9. The dosage of superplasticiser at this revised ratio is defind as the optimized dosage of superplasticiser. Thus dosage of superplasticsier was optimized as 0.8%. Consequent to the revised mix ratio it was found that about 58 kg of cement was saved per cubic metre of concrete and hence economical. Table 3.7 Workability Test Results Phase Mix Slump value in mm Organic based- SP Naph thalene based-sp Compaction factor Organic based- SP 1 REFERRENCE R 5 % W & C+0.4 % SP R 5 % W & C+0.8 % SP R 5 % W & C+1.2 % SP (Collapsed) (Collapsed) R 10 % W & C+0.4 % SP R 10 % W & C+0.8 % SP R 10 % W & C+1.2 % SP (Collapsed) (Collapsed) R 15 % W & C+0.4 % SP R 15 % W & C+0.8 % SP R 15 % W & C+1.2 % SP (Collapsed) (Collapsed) R 20 % W & C+0.4 % SP R 20 % W & C+0.8 % SP (Collapsed) (Collapsed) R 20 % W & C+1.2 % SP (Collapsed) (Collapsed) Naph thalene based- SP

11 47 Table 3.8 Compressive strength after 7 and 28 days curing 7 days strength MPa 28 days strength MPa Organic Naphthalene Organic Naphthalene MIX based- SP based- SP based- SP based-sp Average %imp Average %imp Average %imp Average %imp REFERRENCE R 5 % W & C % SP 6.2 R 5 % W & C % SP 44.3 R 5 % W & C % SP R 10 % W &C % SP R 10 % W &C % SP 3.91 R 10 % W &C % SP R 15 % W &C % SP 15.2 R 15 % W &C % SP 6.67 R 15 % W &C % SP Table 3.9 Revised Mix ratio at 15 % simultaneous reduction of cement and water Cement Fine aggregate Coarse aggregate Water Reference Mix ratio RMX = 1: 1.55: 2.98: 0.49 Case A: Revised Mix Ratio OSP = 1: 1.83: 3.51: % SP Case B: Revised Mix Ratio NSP = 1: 1.83: 3.51: % SP

12 EXPERIMENTAL PROGRAMME The programme was divided into two cases such as Case A and Case B and Figure 3.1 shows flow chart for experimental programme. Table 3.10 shows the materials used for entire experimental programme. Table 3.10 Materials Used Sl No DETAILS QUANTITY 1 Types of Superplasticiser 2 2 Dosage of Superplasticiser 0.8% ( optimized ) 3 Types of Fibres 3 4 Volume of Fibre 0%, 0.2%, 0.4%, 0.6%, 0.8% & 1.0% 5 No. of Mixes Proposed 1 x 2 x 1 x 3x 6 = 36 Mixes CASE A The performance of organic based superplasticiser was evaluated with fibres for mix ratio OSP based on the following phase of tests. PHASE I WORKABILITY TESTS a) Slump Test b) Compaction Factor Test PHASE II STRENGTH TESTS (Before and After Thermoshock) a) 7 & 28 Days Compressive Strength Test b) 7 & 28 Days Split Tension Test c) 28 Days Flexural Strength Test (Third point loading) d) 28 Days Pull-out Test e) 28 Days Impact Test

13 49 PHASE III DURABILITY TESTS (Before and After Thermoshock) a) 28 Days Water Permeability Test b) 28 Days Chloride Penetration Test CASE B The performance of Naphthalene based superplasticiser was evaluated with Fibres for mix ratio NSP based on the following phases of tests. PHASE I WORKABILITY TESTS a) Slump Test b) Compaction Factor Test PHASE II STRENGTH TESTS (Before and After Thermoshock) a) 7 & 28 Days Compressive Strength Test b) 7 & 28 Days Split Tension Test c) 28 Days Flexural Strength Test (Third point loading) d) 28 Days Pull-out Test e) 28 Days Impact Test PHASE III DURABILITY TEST (Before and After Thermoshock) a) 28 Days Water Permeability Test b) 28 Days Chloride Penetration Test

14 50 FLOW CHART FOR EXPERIMENTAL PROGRAMME RMX-M 20 Grade Case A Case B OSP=RMX- (15% Water & Cement) + SP Organic Based NSP=RMX- (15% Water & Cement) + SP Naphthalene Based Fibre s Fibre s Steel AR Glass Polyester Steel AR Glass Polyester 0.2 to 1% (OS1-OS5) 0.2 to 1% (OG1-OG5) 0.2 to 1% (OP1- OP5) 0.2 to 1% (NS1- NS5) 0.2 to 1% (NG1-NG5) 0.2 to 1% (NP1-NP5) TEST Workability Test Strength Test- Before & After Thermoshock Durability Test Before & After Thermoshock [1] Slump Test [2] Compaction Factor Test [1]7 & 28 Days Compressive Strength Test on Cube and Cylinder specimen [2]7 & 28 Days Split Tension Test [3] 28 Days Flexural Strength Test [4] 28 Days Pull-Out Test [5] 28 Days Impact Test 1] 28 Day Water Permeability Test [2] Chloride Permeability Test. Figure 3.1 Flow Chart for Experimental Programme

15 Mix and Specimen Preparation All the ingredients were first mixed in dry condition in the concrete mixer machine for one minute. Then, 75 percent of calculated amount of water was added to the dry mix and mixed thoroughly for one minute. At this stage, remaining 25 percentage of water mixed with superplasticiser was poured into the mixer and mixed for one minute. Later, required quantities of fibres were sprinkled over the concrete mix and mixer machine was allowed to rotate for four minutes to get a uniform mix. The total mixing time was 7 minutes. Thus concrete mix was prepared. To prepare specimen for various mixes, the quantity of materials required and specimen details are presented in Tables 3.11, 3.12 and 3.13 for various experimental works. The prepared concrete mix was poured in moulds (after applying oil inside the mould) in three layers and each layer was tamped 25 times by 16 mm diameter and 600mm long tamping rods and then it was vibrated using table vibrater for 1minitue. The same procedure was adopted for specimen preparation throughout this research work.

16 Details of Mix Proportioning CASE Type MIX PROPORTIONS Case A Case B Reference Mix RMX 1:1.55:2.89:0.49 Organic superplasticiser RMX+0.8%Organic Based OSP SP OS1 OSP+0.2%SF OS2 OSP+0.4%SF OS3 OSP+0.6%SF OS4 OSP+0.8%SF OS5 OSP+1%SF OG1 OSP+0.2% ARGF OG2 OSP+0.4%ARGF OG3 OSP+0.6% ARGF OG4 OSP+0.8% ARGF OG5 OSP+1%ARGF OP1 OSP+0.2% PF OP2 OSP+0.4% PF OP3 OSP+0.6% PF OP4 OSP+0.8% PF OP5 OSP+1% PF Naphthalene RMX+0.8% Naphthalene superplasticiser NSP Based SP NS1 NSP+0.2%SF NS2 NSP+0.4%SF NS3 NSP+0.6%SF NS4 NSP+0.8%SF NS5 NSP+1%SF NG1 NSP+0.2% ARGF NG2 NSP+0.4% ARGF NG3 NSP+0.6% ARGF NG4 NSP+0.8%ARGF NG5 NSP+1% ARGF NP1 NSP+0.2% PF NP2 NSP+0.4% PF NP3 NSP+0.6 %PF NP4 NSP+0.8 % PF NP5 NSP+1% PF Organic based Superplasticiser Naphthalene based Superplasticiser with Steel fibre AR Glass Fibre Polyester Fibre Steel fibre AR Glass Fibre Polyester Fibre

17 53 Table 3.12 Quantity of Materials used per cubic metre of Concrete MIX Grade of cement Wt of cement per cubic metre of concrete Fa/c Ca/c W/c % Dosage of SP % Vol of Fibre Aspect Ratio- Fibre Density of Fibre t/m 3 * RMX OSP OS OS OS OS OS OG OG OG OG OG OP OP OP OP OP NSP NS NS NS NS NS NG NG NG NG NG NP NP NP NP NP * 1 t/m 3 = 9.81 kn/m 3

18 54 Table 3.13 Specimen Details Test Compressive Strength Test after 7&28 days curing Split Tension Test after 7&28 days curing Flexural Strength Test after 28 days curing Pull-Out Test after 28 days curing Impact Test after 28 days curing Water Permeability Test after 28 days curing Rapid Chloride Permeability Test after 28 days curing Thermo Shock period Type of specimen Dimension of specimen mm No of specimen 1 &2 hrs Cube 150x x 4 x 3=396 2 hrs Cylinder 150x x 3 x 3=297 2 hrs Cylinder 150x x 3 x 3=297 2 hrs Beams 500x 100x x 2 x 3=198 - Cube 150x x 1 x 3=99 2 hrs Disc 150 Dia with 62.5 thick 33 x 2 x 3=198 2 hrs Cube 150x x 2 x 3=198 2 hrs Disc 95 Dia with 50mm thick 33 x 2 x 3=198 Total EXPERIMENTAL WORK The experimental works conducted includes workability test, strength test and durability test as described in section Workability Tests Workability tests are conducted for concrete at fresh state. At this stage, concrete should have good workability. At construction place, good workable concrete will have no segregation while handling, no loss of homogeneity while placing, easiness for compacting and finishing. Workability of concrete is obtained by conducting slump and compaction factor tests.

19 Slump Test The test procedure was used as given in IS: Slump test was conducted using a standard slump cone of bottom diameter 200 mm top diameter 100 mm and of height 300 mm. Concrete mix was prepared and filled in slump cone as described in section After filling the concrete, slump cone was then gently and vertically raised. The concrete settles under its own weight and vertical distance from its original level to new level after subsidence was measured. This difference in height is known as slump. From this test, slump value was measured for all the mixes Compaction Factor Test The test procedures were used as given in IS: The value of compaction factor was found by using a standard compaction factor apparatus, which consists of an upper hopper, lower hopper & bottom cylinder. Concrete mix was prepared and filled in upper hopper. Then trap door at the bottom of the upper hopper was opened to allow the concrete to fall into lower hopper. After the concrete comes to rest, trap door of lower hopper was opened to allow concrete to fall into the cylinder. The weight of the concrete in cylinder was determined and this is known as Weight of partially compacted concrete. The cylinder is refilled with concrete from the same sample in layers and tamped for full compaction. Then the weight of the refilled concrete in cylinder was determined and this is known as Weight of fully compacted concrete. From this test, compaction factor was measured for all the mixes from equation 3.1. Weight of partially compacted concrete Compacting Factor = (3.1) Weight of fully compacted concrete

20 Strength Tests Tests were conducted on hardened concrete to find out Compressive strength, Split tensile strength, Flexural strength, Pull-out test and Impact strength as per the procedure given below and the results are presented in chapter Compressive Strength Test The test procedures were used as given in IS: Steel moulds of size 150 x 150x 150 mm were used for casting the specimens. Concrete mix was prepared and specimens were prepared as per section Specimens were allowed for curing in a curing tank for a period of 7days & 28 days. After the curing period the specimens were removed from the curing tank and the surfaces were wiped. The dimensions of the specimens and the weight of the specimens were noted down with accuracy. Area of the specimen (A) was calculated from its dimensions. Weight of all the specimens were in between 8.4 to 8.8 kg. A 200 tonne hydraulic compression testing machine was used. Then specimen was placed in such a manner that the load is applied to opposite side of cubes as caste. The load was applied at the rate of 140 kg/cm 2 /minute till the cube breaks. Maximum load (W) is recorded at the time of concrete failure. Same procedure was adopted for all the mixes and compressive stress was calculated from equation 3.2. Compressive Stress = W A (3.2) Split Tension Test The split tension test is a method of determining the tensile strength of concrete. In its most common form, a cylinder is compressed along two

21 57 opposite generators until it splits across the diametrical plane connecting the loading strips. The test procedures were used as given in IS: Steel moulds of diameter 150mm and of height 300 mm were used for casting the specimens. Concrete mix and specimens were prepared as per section Specimens were allowed for curing in a curing tank for a period of 7days & 28 days. The dimensions of the specimens and the weight of the specimens were noted down with accuracy. Weight of all the specimens were in between 13.2 to 13.6 kg. Then specimen was placed horizontally between the loading surface of the 200 tonne hydraulic compression testing machine and the load was applied till the specimen splitted into two halves. The ultimate load at the time of failure was noted. Same procedure was adopted for all the mixes and split tensile stress was calculated from equation 3.3. Figure 3.2 shows set up for split tensile test. P Concrete Cylinder Poisson s Effect Figure 3.2 Split Tensile Test Set Up Split Tensile Strength = 2P DL (3.3) Where, P is the load on the cylinder L is the length of the cylinder D is the diameter of the cylinder

22 Flexural Strength Test The test procedures were used as given in IS: Steel moulds of size 500 x100 x 100 mm were used for casting the specimens. Concrete mix and specimens were prepared as per section Specimens were allowed to cure in a curing tank for a period of 28 days. The dimensions of the specimens and the weight of the specimens were noted down with accuracy. Weight of all the specimens were in between 12.5 to 12.8 kg The testing machine was provided with two rollers of 38mm diameter on which the specimens were placed and the rollers were spaced such that the distance between two rollers was 400 mm as shown in Figure 3.3. The load was applied through two similar rollers mounted at the third points of the supporting span, at a distance of mm centre to centre. The load was divided equally between the two loading rollers and the rollers were mounted in such a manner that the transverse load was applied along the longitudinal axis and without subjecting specimen to any torsion stresses. The load was applied with out shock and increasing continuously at a rate such the extreme fibre stress increase at approximately 0.7kg/sqcm/ min that is at a rate of loading 180 kg/min. The load was applied until the specimen failed and maximum failure load applied was recorded. Same procedure was adopted for all the mixes. w Figure 3.3 Flexural Strength Test Set Up Dimensions are in mm

23 59 After the failure of this specimen, the position of fracture was noted. If a is the distance between line of fracture and the nearer support and if it is greater than 133mm (that is, middle third of the span), the Flexural Stress (FS) or modulus of rupture of the specimen was calculated from equation 3.4 WL Flexural Stress = 2 BD (3.4) Where, W is the load applied L is the length of the beam B is the breadth of the beam and D is the depth of the beam Pull-Out Test The test procedures were used as per in IS: Steel moulds of size 150 x 150x 150 mm were used for casting the specimens. Concrete mix and specimens were prepared as per section A single reinforcing bar was embedded vertically along a central axis in each prepared specimen as shown in Figure 3.4. The diameter of the bar used was 16mm. The bar should be free from grease, paint or other coatings which would affect the bond between reinforcing bar and concrete. The bar was projected down such that the clear distance between the rod and the bottom face of the cube was about 10 mm and was projected upward from the top face with a convenient distance necessary to provide sufficient length of bar to extend through the bearing blocks and the support of the testing machine and to provide an adequate length to be gripped for application of load. Then, the specimen was mounted on a universal testing machine in such a manner that the bar is pulled axially from the cube. The load was applied to the reinforcing bar at a rate not greater than 2250 kg/mm. The loading was continued until the enclosing concrete fails and the corresponding load was

24 60 noted. Same procedure was adopted for all the mixes and bond stress was calculated from equation 3.5. Bond stress = P dl (3.5) Where P is the load applied L is the length of the steel bar embedded in the cube d is the diameter of the steel bar F ib r e C o n c r e te C u b e P Figure 3.4 Pull-Out Test Set Up Impact Strength Test The test procedures were used as per ACI committee report 544.2R-89. Concrete structures are subjected to short duration (dynamic) loads. Such loads originate from sources such as impact from missiles and projectiles wind gusts, earthquakes and machine vibrations reported by Gopalarathinam (1986). The dynamic response to impact is complex and is dependent on many factors such as velocity of striker, contact area, size of the target structure, material behaviour of the striker on the structure etc. It is necessary to estimate the maximum dynamic energy absorption capacity which a structure would sustain if it were involved in a collision with another body or subjected to explosive loads. The review of literature indicates that

25 61 there were four different methods available to test the impact resistance of cementitious and hybrid reinforced cementitious materials namely, explosive test, projectile impact test, drop weight impact test and Charpy impact test. Drop weight impact test method also known as repeated impact test was the simplest among all the four methods and was devised by Schrader. Dimensions are in mm Figure 3.5 Section Through Test Equipment for Impact Strength In drop weight method the number of blows necessary to cause prescribed level of distress in the specimen is counted and this gives the quantitative estimate of energy absorbed by the specimen at the distressed level. Concrete test specimen is a cylindrical disc having 150mm diameter and 62.5 mm thickness as shown in Figure 3.5. The specimen was coated on the bottom with a thin layer of grease and placed at the base plate. Elastomer pads were placed between specimen to restrict movement of the specimen during testing. A drop hammer was used to apply the impact load. The weight of the hammer was 45N. The number of blows required by the dropping hammer through a height of 457mm to cause the first visible crack and to cause ultimate failure were recorded. Each blow represents 20.2 Nm of energy absorbed by the specimen. The first crack was based on visual observation. Painting the surface of the test specimen facilitated the

26 62 identification of this crack. Ultimate failure is defined in terms of number of blows required to open the crack in the specimen into three or more fractured pieces and butting against the legs of base plate. Same procedure was adopted for all the mixes and Energy absorption capacity was calculated from equation 3.6. Energy absorption capacity= Load x distance x No. of blows required for cracking/failure (3.6) Where Load = 45 N Distance = 457 mm Reserve Strength It is defind as strength or energy stored or absorbed beyond first crack strength upto ultimate failure of concrete. It is assumed that concrete undergoes elastic deformation upto first crack and concrete undergoes inelastic response beyond first crack. The measure of reserve capacity gives ability of concrete to resist inelastic deformation. This is the post cracking strength of concrete. Percentage of reserve strength is calculated from equation 3.7. EAUlt EA Icrack Percentage of reserve strength = x100 EA Icrack (3.7) Where EA Ult - Energy absorption at ultimate failure EA I crack - Energy absorption at first crack Durability Tests Nowadays durability of concrete is a subject of major concern in many countries. It is a wrong notion that strong concrete is always a durable concrete. Strong concrete may be structurally strong enough to withstand the external load. But such structure may fail by environmental effects. For

27 63 example, while it is structurally possible to build a jetty pier in marine conditions with 20 MPa concrete, environmental condition or exposure may lead this structure to a disastrous consequences. Durable concrete will retain its original form, quality and serviceability when exposed to its environment. Hence it is necessary to conduct durability tests on concrete. Under this study, water permeability and chloride penetration test was conducted on concrete. Recent revision of IS: gives more emphasis on durability of concrete apart from strength Permeability Testing of Concrete Water permeability test procedures were carried out as per the standard IS: Though much research has been performed to identify, investigate, and understand the mechanical traits of fibre reinforced concrete, relatively little research has concentrated on the transport properties of this material. Material transport properties, especially permeability, affect the durability and integrity of a structure. Permeability of concrete is due to internal movement of water or other fluids, transporting aggressive agents through the pore structure of the concrete. High permeability, due to porosity or cracking, provides an ingress for water, chlorides and other corrosive agents. If such agents reach reinforcing bars within the structure, the bars get corroded. Hence the study of water permeability of concrete is very important. To conduct the permeability test cubes of side size 150mm were cast and water cured for 28 days. After 28 days of curing, specimens were placed properly in the six cell permeability apparatus. Figure 3.5 shows section of permeability cell. A Rubber sheet of 8mm thick and 150 x 150mm size with a central hole of 100 x 100mm was taken. This rubber sheet was then placed on the top & bottom surface of the cube in the permeability cell. Cover plate was then tightened properly. The rubber sheet acts as a washer and prevents the leakage of water through the annular space between

28 64 specimen and cell. Suitable arrangements were made for supplying compressed air at 10 kg/cm 2 to the cell by a compressor with an adequate supply of cleaned de-aired water for constant supply of pressurized water. Collecting jar was placed under the concrete specimen to collect the discharged water from the concrete. The test was conducted continuously for 100hrs. After 100hrs cubes were then taken out from the cell for finding the coefficient of permeability. There are two common methods for the evaluation of co-efficient of permeability of concrete and they are steady flow method and depth of penetration method. During the test if there is permeability of water, the coefficient of permeability can be calculated using the steady flow method and if there is no permeability of water, the coefficient of permeability can be calculated using depth of penetration method. In this method cubes are splitted and depth of penetration is measured in the specimen. Figure 3.6 Enlarged Section of Permeability Cell While conducting the test, it was monitored for the permeability of water through the specimen. It was found that there was no permeability of

29 65 water through the concrete. Hence co-efficient of permeability (K) was found by depth of Penetration method from equation 3.8. In this method, cubes were splitted and depth of penetration was measured in the specimen at different locations and average depth of penetration was obtained. The method was developed by Valenta referred in Neville (1981), equivalent to that used in Darcy s Law. K = D 2 P (3.8) 2 TH Where K = Co-efficient of permeability in m/s D = Depth of penetration in cm P = Porosity of concrete measured as a fraction T = Time in sec H = Pressure head=100m Porosity Calculation The mix ratio of reference concrete is 1:1.55:2.98:0.49. Neville and Brooks (2008) have dealt in detail the derivation of the formula to find the porosity of concrete. Porosity of concrete (p) was calculated using the formula 3.9. w a 0.17h p c c (3.9) 1 Af 1 Aco w a S c S c c c fa ca Where w/c- Water- Cement ratio h- Degree of hydration a- Volume of entrapped air S- Specific gravity of cement 3.10 S fa - Specific gravity of fine aggregate 2.65 S ca - Specific gravity of coarse aggregate 2.60

30 66 A c, A f, A co - Proportions of cement, fine aggregate and coarse aggregate in the reference mix ratio RMX. Air content of the concrete is calculated from equation The percentage of air content to total volume is 2% (from section 3.2) a v a 0.02 A A A w (3.10) c f co a S S S c fa ca Here, denominator represents the total volume of concrete For w/c=0.49, Degree of hydration h=68% a a The volume of air a was given by a = Porosity (p) of the concrete was therefore from equation 3.9 w a 0.17h p c c 1 Af 1 Aco S c S c fa ca w c a c p X (0.68 ) Thus Porosity of concrete p = Rapid Chloride Penetration Test Corrosion of reinforcement in reinforced concrete structures is one of the most hazardous durability problems. One of the principal sources of this problem is the ingress of chloride ions into porous concrete. Movement of ions in a porous medium under a concentration gradient is called diffusion. It

31 67 is often necessary to ascertain the impermeability of concrete to chloride ions as a quality control measure and also for assessment of improvements effected in properties of new concrete. Measurements of chloride diffusion co-efficient requires a long time for establishment of steady state conditions. Therefore a direct current (DC) potential is usually applied to accelerate migration of ions. Rapid chloride penetration test (RCPT) was performed as per ASTM C 1202 to determine the electrical conductance of the Fibrous concrete at the age of 28 days curing. The test method consists of monitoring the amount of electrical current passed through 50mm thick slices of 95 mm diameter of cylindrical specimens for duration of six hours. The RCPT apparatus consists of two reservoirs as shown in Figure 3.7. The specimen was fixed between two reservoirs using an epoxy bonding agent to make the test setup leak proof. One reservoir was filled with 0.3N Sodium Hydroxide solution and the other reservoir with 3 % Sodium Chloride solution. A DC of 60V was applied across the specimen using two copper des and the current across the specimen was recorded at 30 minutes intervals for duration of six hours. The total charge passed in coulombs during this period was calculated from equation 3.11 given in ASTM C Figure 3.7 Chloride Penetration Test Set Up

32 68 Q = 900 ( I I I I I 360 ) (3.11) Where, Q = Charge passed (coulombs) I 0 = Current immediately after voltage was applied I t = Current at t minutes after voltage was applied The higher amount of electric charge passed in the test represents the higher penetrability of the concrete to chloride ions. The concrete quality (degree of chloride ion penetrability) can be assessed based on the limits as given in ASTM C 1202 and it is presented in Table Table 3.14 Chloride ion penetrability based on charge passed Charge Passed (Coulombs) Chloride ion penetrability >4000 High Moderate Low Very Low <100 Negligible Testing of Concrete After Thermoshock Generally concrete is incombustible and has good fire resistance properties. When concrete is subjected to continuous exposure to elevated temperature under fire and sudden cooling by water, it leads to thermoshock. Thermo shock which may significantly influence the dehydration of the hydrated calcium silicate, the release of chemically bound water, thermal incompatibility between the aggregates & cement paste and these are the main detrimental factors under heating. During exposure to heat, aggregate expands and cement matrix shrinks due to loss of moisture and drying shrinkage type

33 69 stresses will be created. If it exceeds drying shrinkage capacity of concrete, micro cracks are developed at interfacial transition zone and propagate. Such micro cracks lead to decrease its strength and durability of concrete. Hence experimental study of concrete before and after thermoshock is made under strength as well as durability aspects. The residual strength is the strength of heated and subsequently cooled concrete specimen. That is strength of concrete after thermoshock is referred as residual strength (TRS). The residual strength of concrete after subjected to elevated temperature is generally less than its RMX strength. The percentage variation in residual strength is calculated from equation 3.12 TRS RMX Percentage variation Residual strength with RMX = x100 RMX (3.12) Testing Procedure The specimens were placed inside the hot air oven and were heated to a temperature of 200 o C and the temperature was sustained for two hours. After two hours, the specimens were taken out and were immediately quenched in water to simulate the thermo shock effect. The cooling was done for about half an hour. The specimens were then tested for its residual strength. Percentage change in strength was calculated by comparing the strength of specimens without thermo shock. Cube and cylinder specimens were used to test for compressive strength. Thermoshock test was conducted after 1 hr and 2 hr exposure to heat. Similarly test was conducted after 2hrs exposure to heat in case of cylinder specimens. Thermoshock test was performed for specimen under split tension test, flexure test, impact test, water permeability test and chloride penetration test after 2 hrs exposure to heat.