CHAPTER-III EXPERIMENTAL PROGRAM. Reactive powder concrete (RPC) has initiated an interest and

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1 37 CHAPTER-III EXPERIMENTAL PROGRAM 3.0 INTRODUCTION Reactive powder concrete (RPC) has initiated an interest and possibility of expecting ultra high performances from commercially available materials. They possess ultra high strength and high ductility with advanced mechanical properties and consist of a specific microstructure, which was optimized by precise gradation of all particles in the mix to yield maximum density. It uses extensively the pozzolanic properties of highly refined silica fume and optimization of the Portland cement chemistry to produce the high strength hydrates. The properties of hardened Ultra High Performance Concrete (UHPC) were determined by the very dense structure of this material. The microstructure of UHPC differs significantly from normal- and highstrength concrete. With respect to the mechanical behavior, UHPC with fibres shows, depending on the type and quantity of fibres contained in the mix, ductile behavior under compression as well as in tension. In contrast to this, UHPC without fibres behaves brittle, if no additional measure such as confinement is chosen. Since the pre-peak behavior does not show significant differences, the elastic properties of UHPC with and without fibres can be described, in common whereas the influence of fibres has to be described separately. By introducing fine steel fibres, they can exhibit remarkable strengths and energy absorptions. However, lot of research works were carried out for the

2 38 production of RPC, which is an UHPC, very few studies, precisely compares in detail their mechanical properties with UHPC. In addition, the role of fibre addition on the compressive and flexural strengths of RPC is required to understand and set optimum limits on the fibre content. This chapter presents the details of development of Reactive Powder Concrete and the various test programs conducted. The study is aimed at identifying and optimizing the salient parameters that influenced the mixture proportions of the Reactive Powder Concrete and its curing methods. Also, study of various mechanical properties of RPC is carried out to find the feasibility of using RPC as structural components such as angle sections. The various test programs are as follows. 3.1 EXPERIMENTAL SCHEDULE Production of RPC with a target compressive strength of approximately 200 MPa using conventionally available materials (viz., cement, fine aggregate, silica fume, quartz powder, and micro fibre) and following appropriate heat curing cycles. 1. Study of mechanical properties of RPC 2. The effect of fibre addition on the compressive and flexural strengths was also studied to establish optimum limits on fibre content. 3. Investigation on use of RPC for specific application. 4. Design of RPC mixes for target compressive strength of MPa 5. Material characterization by conducting studies on following Mechanical properties

3 39 i. Study of compressive strength of RPC ii. Stress-strain characteristic of RPC under compression iii. Study of Tensile Properties of RPC by conducting a)direct tension test using Dog-bone shaped specimen b) Evaluating the cracking behavior of RPC under tension using the micro-mechanical modeling technique. iv. Three point bending test v. Shear strength 6. Investigation on use of RPC for specific Applications i. Performance Evaluation of RPC angle section with various heights under compression. ii. Performance Evaluation of RPC angle sections under flexure. iii. Performance Evaluation of RPC infilled tubes under Compression. 7. Investigation on Connection Details. i. Study of Bolted RPC plates under direct tension. 3.2 MATERIALS USED AND THEIR PROPERTIES Ordinary Portland cement confirming to IS: was used for the study. The silica fume used in this study had a Blain s fineness of 20m 2 /g. The silica fume contained 94% silicon dioxide while the quartz powder contained mostly silicon dioxide. The chemical composition and the particle size distribution of the cementitious powders are shown in Table 3.1 and 3.2. Standard sand confirming to IS: 650 were used for producing Reactive powder concrete (RPC). The maximum and nominal

4 40 size of aggregates used for RPC is 2.36mm respectively. Based on size of aggregates, two lengths of micro steel fibres were used 6mm, and 13mm micro-steel fibres (for RPC). Eventually the workability was controlled using adequate quantities of third generation poly-carboxylic based superplasticizers. The properties of these fibres are shown in Table 3.4. The mix proportions used for the production of RPC are tabulated in Table FORMULATION AND PROPERTIES OF RPC A Reactive Powder Concrete formulation developed at the Structural Engineering Research Center, Chennai, based on extensive investigations [Harish et. al., , Dattatreya.J.K., et. al., ] was used for production of RPC and the behavior of cylinders with various combinations of fibre content are investigated. The various experimental activities involved in this study were presented in the following paragraphs. Table 3.1 gives the properties of the materials used in this investigation The materials used in the present investigation are listed below: 1. Ordinary Portland cement of Grade 53 conforming to IS: : Silica Fume 3. Quartz powder 4. Standard Ennore Sand conforming to IS: 383 : 1970

5 41 5. Quartz sand 6. Poly-acrylic ester type Super plasticizer 7. Steel fibre of diameter 0.16mm and length 13mm & 6mm having tensile strength of 2000MPa. 3.4 PREPARATION OF RPC MIX The standard mix proportion and quantity of materials per m 3 of reactive powder concrete mix formulation developed at CSIR-SERC, Chennai is shown in Table A Hobart Planetary mixer (Fig.3.1) machine (10 kg capacity) was used to mix the RPC 2. Well-mixed dry binder powder was then slowly poured in to the bowl while the mixer was rotating at a slow speed. 3. The water and admixture were slowly added to the mixing bowl and mixing was continued at slow speed 4. The speed of the mixer was increased and the mixing process was continued for two to three minutes. 5. Additional mixing was performed at this speed until a uniform mixture was achieved and the mixture was transformed to a flowable self-compacting consistency by dosing with additional SP, if necessary. The total mixing time for the various mixtures ranged from 5 to 10 minutes. 6. In case of RPC mixtures with fibres, after all the powder

6 42 ingredients were mixed thoroughly with water and Super plasticizer (SP) and when flowable consistency was achieved, the fibres were added to the mixing bowl slowly with the mixer operating in low gear. Care was taken to ensure random distribution of fibres. The speed was increased and further mixing was carried out by incorporating additional SP, if necessary, to account for the possible stiffening of mixture due to fibre addition. Fig. 3.1 Hobart Planetary Type Mixer Machine These mixing sequences did not result from an optimization process; rather, they were selected to allow for RPC samples to be taken with different lengths fibres, to observe the influence of fibres on the rheology of RPCs. While in usual fibre reinforced concretes, the addition of steel fibres results in a drastic decrease of the workability of the mix the opposite occurs in RPCs. This behaviour can easily be explained by the

7 43 differences in the relative size of steel fibres with respect to the maximum size of the coarse aggregate. In usual fibre reinforced concrete, steel fibre length is of the same order at the maximum size of coarse aggregate, creating a strong interference with the aggregates. That is why it was always recommended to slightly decrease the maximum size of the coarse aggregate in steel fibre reinforced concrete and to increase the sand content. On the contrary, there is no such interference in RPC because the steel fibres are 20 times longer (13mm) than the coarser aggregate (600µm). As a comparison, keeping the same aspect ratio, adding steel fibres to RPC like adding 400mm long rebar to a normal concrete made with a 20mm coarse aggregate. The physical properties such as density, water absorption and air voids were determined as per ASTM C 642 already tested and confirmed at CSIR-SERC while formulating the mix proportion. In addition, the ultrasonic pulse velocity (UPV) measurements were taken using the PUNDIT apparatus as per ASTM C 597 procedure. The fresh and physical properties of the RPC mixtures were tabulated in Table 3.6.

8 44 Table 3.1 Chemical composition of powders Oxides Portland cement Silica fume Sio Al2O Fe2O _ CaO _ MgO 1.13 _ Na2O K2O 0.47 _ TiO _ Mn2O _ SO Free Lime 0.45 _ Chlorides LOI Table 3.2 Physical Properties of the Materials Sl.No Materials Used Sym Properties 1. Cement C 2. Silica Fume SF 3. Quartz Powder Q OPC: 53 Grade; SG = 3.15; SC = 28%; IST = 110 min; FST = 260 min; CS = 58 MPa at 28 days SG = 2.25; % Passing through 45μm sieve in WSA=92 %. SG = 2.59; % Passing through 45μm sieve in WSA=75 % 4. Ennore Sand SG = Super Plasticizer SP Poly-Acrylic Ester Based 6 Micro-steel fibres STF L=6, and 13 mm & D=0.16mm Note: OPC Ordinary Portland cement, SG Specific Gravity, CS Cube Strength, PSR Particle size range, SC Standard Consistency, WSA Wet sieve analysis of aggregates, L Length, D Diameter.

9 45 Table 3.3 Particle Size Distribution of Powders Powders Specific gravity Particle size(µm) D 10 D 30 D 50 D 60 Cement Quartz Silica * 3* 7* 9* fume * Higher average particle size of silica fume is due to use of fused silica fume Table3.4 Properties of steel fibres Type of fibres Beakaert carbon straight micro-steel fibres Dimension of fibre Strength L(mm) D(mm) MPa Table 3.5 Standard Mix Proportions for Reactive Powder Concrete Mix Proport ions SF C Q FA w/c SP STF (2% by vol.) Quantity of Materials / m 3 of concrete SF C Q Sand w/c SP STF kg kg Kg kg l L kg SF Silica Fume, C Cement Q Quartz, FA Fine Aggregate, W Water, SP Super Plasticizers

10 46 Table 3.6 Fresh and Physical Properties of the Mixtures Types of Concrete Flow Density(kg/m 3 ) Porosity(%) RPC RPC-1% 6mm RPC-2% 6mm RPC-3% 6mm RPC-1% 13mm RPC-2 % 13mm CURING REGIME The curing protocol adopted is indicated in Fig. 3.2 and is the outcome of a study of different combinations of normal water curing, hot water curing and high temperature curing. [Harish et al., 2008] 36 Fig. 3.3 shows the equipments used for the different curing regimes. After 7 days of different regimes of curing, the specimens were cured in water until the testing.

11 Temper ature (C ) ROH: 1 hr HAC ROC: 1 hr ROH: 4.8 hrs HWC 50 ATC NWC NWC till DOT Curing Period (days) Fig. 3.2 Curing Regime for RPC ATC-Ambient temperature, NWC-Normal water curing, ROH- Rate of heating, HWC-Hot Water Curing, HAC-Hot Air Curing, ROC-Rate of curing, DOT-Date of Testing i) Normal water curing ii) Hot water 90 0 C iii) Hot air 0 C Fig.3.3 Equipments Used For Different Curing Regimes 3.6 TESTS FOR MECHANICAL PROPERTIES The tests conducted for studying mechanical properties of RPC include compression, direct tension, and flexure. Table 3.7 illustrates the test program of this investigation. The standard procedure followed and the dimensions of specimen used for the mechanical tests are

12 48 shown in Table 3.8. The static modulus of elasticity was determined from compression test as per ASTM C 469 procedure using 100 x 200 mm cylinders for RPC. All the tests were conducted after 28 days of respective curing cycles. The toughness characteristics of these concretes were calculated by first plotting the flexural strength - deflection plot and then calculating the area under the plot. The toughness index was calculated at different deformation levels namely I5, I10 and I20 as per ASTM C The energy absorption characteristic was conducted for RPC concretes by first plotting the stress-strain curve in compression and then determining the area under the stressstrain plot. Table 3.9 gives the mixture proportions of RPC mixtures with different fibre contents and Table 3.6. Fibre Table 3.7 Experimental program Compressio n Fle xur e Toughne ss Energy absorption Mix ID Length (mm) % RPC - 0 C C - C _ RPC - 1% 6 1 C C C C C RPC - 2% 6 2 C C C C C RPC - 3% 6 3 C C C C C RPC - 1% 13 1 C C C C C RPC - 2% 13 2 C C C C C RPC - 3% 13 3 C C C RPC - 1%+1% RPC - 1%+2% C Tests Conducted C C _ C C C C _ C C Direct tension

13 49 Table 3.8 Tests conducted to study the Mechanical Properties of RPC Tests Compression Tension Properties studied Stress-strain plot & Energy absorption Type of concrete RPC with all % fibres Standards ASTM C 469 Direct tension RPC _ Flexure and toughness RPC ASTM C 348 Specimen size 100 x200 mm cylinder Briquette s shape(dogbone shape) 70x70x350 mm prism Table 3.9 Mixture proportions Mix ID Fibre Length Mix proportions of RPC concrete with respect to cement C S Q FA W SP SF % % RPC _ _ RPC -1% 6mm RPC -2% 6mm RPC - 3% 6mm RPC - 1% 13mm RPC -2% 13mm RPC - 3% 13mm RPC- 1%+1% RPC- 1%+2% 6mm+13mm mm+13mm C.A.&F.A.,coarse and Fine aggregate, W Water, SP Superplasticizers (quantity of SP is represented in percentage by weight of cementiitous material), SF Steel fibres (quantity of SF is represented in percentage by volume of the total mixture

14 PREPARATION OF TEST SPECIMENS Preparation of Compression Specimens The RPC cylinders of 100mm diameter and 200mm height were cast with various fibre content and combinations as follows. i. 1% of 6mm fibres ii. iii. iv. 2% of 6mm fibres 3% of 6mm fibres 1% of 13mm fibres v. 2% of 13mm fibre vi. vii. 1% of 6mm fibres + 1% 13mm fibres 1% of 6mm fibres + 2% 13mm fibres The specimen for compression tests consisted of 100mm diameter by 200mm long cylinders. All the specimens were subjected to the curing regimes as specified in Fig. 3.2 and prepared for the test. Both the end of the specimen were carefully leveled and coated with sulphur to get plain and parallel surfaces Preparation of Tension Specimen The most commonly used specimen geometrics for testing of UHPC (Ultra High Performance Concrete) behavior under tension were socalled dumb-bell prisms. The shape of such prisms avoids failure in the area of bond introduction in the specimen, which otherwise occurs due to an unavoidable multiaxial stress state and/or an abrupt change in stiffness in the transitory region from loading plates to specimen. A smooth transition from or wider part of the specimen to the narrow,

15 51 middle portion as used in the experiments appears to be, at least theoretically, the most appropriate geometric shape needed to avoid local stress concentration. To overcome the problems associated with specimen grips, end tapered specimen were tested in tension. The geometry of typical specimen was shown in Fig.3.4. The cross section in the constant width portion is 200mm. The overall height of the specimen was 350mm and both end edge is 150mm. Special steel moulds were designed and fabricated for the preparation of direct tension test specimens. The tension tests were carried out on Dog-bone shaped tensile specimens with notches 10mm deep 2mm wide cut at middle length. The cross-sectional area of a typical specimen, at the doublenotched points, is 1886mm 2.The geometric details of the specimen are shown in the Fig Typical test specimen with end grips is shown in Fig.3.5. Overall, about 32 specimens were prepared and tested (Fig.3.6).

16 52 Fig. 3.4 Typical Tension Specimen with dimension (All dimensions are in mm) Fig. 3.5 Photographic View of Tension Specimen with End Grips Fig. 3.6 Over All View of Tension Specimen with various fibre dosages

17 Preparation of Flexure and shear Specimen RPC beams of size 70 x 70 x 350 mm with different lengths of fibres [l/d (mm), 6/0.16, 13/0.16] single or in combination and different volume fractions were prepared and tested. Note: All Dimensions are in mm Fig.3.7 Fig. 3.8 Fig. 3.7 Beam Specimen Schematic Diagram Fig. 3.8 Photographic views of Beam Specimens Table 3.10 Details of Notched RPC Beam Specimens Serial no. ID Fibre content (%) 6mm 13mm 1 R RS RD RD RS2L RS3L Specimen Geometry Specimens prepared were beams of rectangular cross section with a notch at the mid-length to a depth of 1/6 times the beam depth. The depth (D) and width (B) of the cross section of the specimen were both 70 mm. The loading span (S) was 300 mm (0.3D). The total length of the specimen (L) was 350 mm (3.5D). The notch depth width (ao) was

18 54 5mm. The notch was formed by embedding an acrylic plate of the 5mm thickness during casting. Adequate measures were taken to prevent bonding between the plate and concrete. The specimens shall be subjected to testing in a condition immediately after completion of the specified curing procedure Preparation of test specimen for Bolted Plates A Reactive Powder Concrete formulation developed at the Structural Engineering Research Centre, Chennai based on extensive investigations is used for production of RPC plate elements and the behaviour of bolted plates was investigated under direct tensile loading which is the most critical condition for a bolted connection. The various experimental activities involved in this study are presented in the following paragraphs Casting RPC panels were cast in wooden moulds of clear dimensions of 350 x 350 mm and thickness 15mm. The RPC mix was poured into the mould and compacted in two layers using a Table vibrator. After 24 hours specimens were demoulded and subjected to the specified curing regimes optimized by CSIR-SERC (Fig.3.2). Cured specimens were cut to the required dimensions using concrete cutting machine. Holes were drilled using concrete drilling machine at 1.5d, 2.5d and 3.5d from the edge of plates (d- diameter of the bolt hole).

19 Preparation of Angle Specimens RPC-Angle casting device For casting the RPC angles, a special device was designed and fabricated as shown in the Fig Using the special mould angle sections of 80mm x 80mm x 10mm angle sections were cast for 1m length. Then the angle sections were cut to different heights or lengths to conduct the flexure and compression tests. The mould consists of two V-shaped plates, one fixed and the other one movable, which is fitted with a handle. The concrete is placed on the fixed angle and pressed against, by the movable angle plate. A plate with bolt holes is fixed at the bottom angle mould to fix the thickness of angle sections. The thickness of the angle sections can be adjusted, by fixing the moving angle mould to the corresponding bolt holes fixed at the bottom angle mould. With this mould one can cast angle sections of thickness 5mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm and 20mm. The following describes the specimens used in this study for determining the mechanical properties of various RPC angles. Specimens of 80mm x 80mm x 10mm angles sections with the following volumes of fibres contents were caste for testing. 1. 1% of 6mm fibres 2. 2% of 6mm fibres 3. 3% of 6mm fibres 4. 1% of 13mm fibres 5. 2% of 13mm fibres 6. 1% of 6mm fibres + 1% 13mm fibres 7. 1% of 6mm fibres + 2% 13mm fibres

20 56

21 57 Fig. 3.11(a) Fig. 3.11(b) Fig.3.11 a &b Angle casting mould for RPC Description of the mould A rigid four-legged self-straining frame with top sides connected by angle section is the main frame of the mould. At 17 cm from the bottom of the mould, a channel section was fixed as crossbeam as shown in Fig Over the cross beam a 20 x 12 cm angle section of 100 cm length was connected longitudinally. Another channel section was placed in inverted position to get flat surface on top and welded over the movable angle section as shown in Figs.3.11a&b. Over the flat top surface of 100 cm length 10 cm size angle was placed with both free edges faced top and free edges in same horizontal line and the angle joint portion on middle line of the base channel and rigidly welded. End plates on both sides of the bottom angle were fixed by bolt and nut to avoid the RPC mix leakage at sides. This angle acts as base of the mould. A rotatable vertical shaft was fixed at the centre of the movable angle. The vertical shaft was fully threaded and passed through the threaded hole which was fixed at the top of the frame. By rotating, the

22 58 pressure is transferred through the movable angle to the materials in the base fixed angle mould. Fig.3.10, Figs.3.11 (a) &3.11(b) shows the details and photographic view of the device. The entire loading device was placed on the table vibrator. The well mixed RPC mixture was poured in the female angle mould to uniform thickness. The male angle was lowered up to touch the RPC material placed in the female angle by rotating the vertical shaft. Vibration was applied on the entire device. Simultaneously vertical pressure was applied through the male angle to the material in the female mould. The thickness guides were fixed on both sides of the female mould. Pressure was applied until the male angle reaches the thickness guide. The excess material if any was squeezed out through the gap between the guide and the male angle. The thickness of the RPC angle product was possible from 5mm to 20mm. After 24 hours, the pressure on the material was released by raising the male angle. The specimen was removed from the female mould and cured by the standardised curing regime (Fig. 3.2) Preparation of Reactive Powder Concrete Infilled Tubes The mix proportion for the infill and the quantity of material used per m 3 of reactive powder concrete mix formulation are as per the Table 3.2 and 3.3.

23 Details of Reactive Powder Concrete infilled tubes(rfit) Specimens Used To investigate the performance of RPC infilled steel tubes, compressive test were carried out. The test specimen details are shown in Table3.11. Table: 3.11 Details of infilled RPC Specimen Specimen Compressive Test Specimen Hollow tubes 3 In filled Steel tubes Fabrication of Steel Tubes Locally available hollow steel tubes of the following dimensions are used for the fabrication. Steel tube specification:- Steel tube diameter = 60 mm Steel tube length = 600 mm Steel tube thickness = 2 mm Steel plate diameter (Bottom) = 75 mm Steel plate diameter (Top) = 60 mm Steel plate thickness = 6 mm The fabricated steel tube specimens are shown in Fig Fig 3.12 Steel Tube Specimens Casting of Infilled Steel Tube And Controlled Specimens The prepared mix was poured into the hollow steel tube by a small trowel and the tube was filled with the prepared mix and it was

24 60 properly compacted by a table vibrator. A 10 mm aluminium tube was provided at the centre of the steel tube, for inserting the 7 mm prestressing wire. The inside portion of the steel tube is shown in Fig Fig Fig Fig 3.13 Inside Portion of the Steel Tube Fig 3.14 Steel Plate After the casting, the steel tube is closed with a plate with a central hole (Fig. 3.14). A central hole was made in the plate for the insertion of the pre-stressing wire. The pre-stressing of steel tube was carried out after the curing of the specimen. Inside of the steel tube contains 8 mm rod which act as a shear connector. It also helps to increase the bonding between steel tube and the concrete Casting of Infill The selected RPC mix details are shown in Table 3.2. The casting was done in an EIRICH Intensive Mixer, which consist of a rotating pan of speed 30 rpm placed at an angle of 30 0 to the horizontal. The inclined rotor consists of three numbers of steel blades, which can rotate at a speed varying from 0 to 300 rpm. The mixing was carried out in EIRICH mixer, until a highly fluid consistency was achieved First dry mixing of

25 61 ingredients consisting of combination of cement, sand, silica fume was done for 5 minutes. Subsequently 75% of water and 75% of superplasticizer (Structuro-100) with the dry mix was added and again mixed for 3 minutes. Further the rest of water along with the super-plasticizer was added and mixed for 5 minutes. Finally steel fibre were slowly added and mixed for few minutes, till the desired mix consistency was obtained. The fibre was uniformly distributed throughout the mix volume. The mixing was continued till the required flow was achieved. Fig 3.15 shows steel tube specimen just after the casting. Fig 3.15 Steel Tube Specimens Just After the Casting