Received date: 18 January, 2014; Accepted date: 15 February, 2014
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This paper presents an investigation on the flexural behaviour of High Performance concrete beams produced from metakaolin and quarry dust. The quarry dust be an economic alternative to the river sand. In this investigations Metakaolin as partial cement replacement and Quarry dust as partial fine aggregate replacement. A total of 8 specimens were considered and there reinforcement ratios are uniform (0.75%) were fabricated and tested under both static and cyclic loading. It was observed that the deflection characteristics, crack Patten, ductility indices, compressive strain, tensile strain, ultimate load carrying, moment wise curvature of the beam the results were compared with Conventional Concrete beams.
High performance, Quarry dust, Metakaolin, Moment wise curvature, Flexural behaviour, Compressive strain, Tensile strain
Concrete is basically a mixture of cement, fine and coarse aggregates. High-performance concrete (HPC) conforms to a set of standards above those of the most common applications, but not limited to strength. Some of the standards are ease of placement, compaction without segregation, early age strength, permeability etc. River sand (Fine aggregate), which is one of the constituents used in the production of concrete, has become expensive and scarce. So there is large demand for alternative materials. In India Quarries and aggregate crushers are basic requisites for construction industry and quarry dust is a by product of rubble crusher units. Geotechnical and mineralogical characterization of quarry dust and its interaction behavior with soils can lead to viable solutions for its largescale utilization and disposal of quarry dust as shown in Fig 1. Metakaolin is a cement substitute often used in concrete countertop mixes to boost the physical properties of the concrete. It is a manufactured pozzolanic mineral admixture made by calcining (thermally activating) purified kaolin clay. chemically altered by heat, it reacts very aggressively with calcium hydroxide, a normal cement hydration byproduct, to form additional Cementitious compounds. as shown in Fig. 2. Therefore this paper presents the results of an experimental investigation on the flexural behaviour of High Performance Concrete (HPC) beams. The beams were loaded incrementally until failure and their strength, cracking deformation and ductility behaviour were examined. and the results were compared with Conventional Concrete beams.
Experimental Programme Materials Used
The materials used include Ordinary Portland Cement (43 Grade), metakaolin, super plasticizers, quarrydust, river sand, coarse aggregate and water. The tested for their physical characteristics as per the relevant standards. The results are presented in Table 1.
The compressive strength of concrete was determined at 7, 14, 28, 56,90 and 120 days of curing. Tests were carried out on 150mm x 150mm x 150mm size cubes. A 2000 Kn capacity standard compression testing machine was used to conduct the test. The results are presented in Table 2.
Split Tensile Strength
Split tensile strength was determined for 28, and 56 days. The test was carried out on cylindrical specimens of 150mm diameter and length 300 mm using 2000kN capacity compression testing machine The results are presented in Table 3
Details of Test Specimen
A total of 8 reinforced concrete (RC) beams were cast for flexural test. All the beams were rectangular in cross section and designed as under-reinforced beams. Four beams were Conventional Concrete (denoted with “CC”) and the remaining four were High Performance Concrete which archived in cube test result (10% of cement with Metakaolin and 30% of sand with Quarry Dust) (denote with “MQ”) the beam dimensions were also sufficiently large to simulate a real structural element. The beam details are shown in Table 4 and Fig. 3. The yield strength Fy for tension steel bars were 417.5 N/mm N/mm2 for 8 mm,10mm &12mm bar respectively. sufficient shear lateral ties were also provided along the beams expect at the pure bending region of 600mm.
Description of the form Work
To cast the specimen, one steel moulds were fabricated. The size of the beam was 150 mm×200 mm×1500 mm shown in the Figure 4. The moulds were weld in order to keep the alignment accurately.
Casting and Curing
All the beams concrete was placed in the form work in layers, vibrated thoroughly and finished at top neatly to have uniform top surface. The reinforcement cages were placed in the moulds and cover between cage and form provided was 15 mm. Cement mortar block pieces were used as cover blocks. The concrete contents such as cement, sand, aggregate, Metakaolin, quarry dust, super plasticizer and water were weighed accurately and mixed. The mixing was done till uniform mix was obtained. The concrete was placed into the mould immediately after mixing and well compacted..The test specimens were demoulded at the end of 24 hours of casting. They were marked identifications and specimen was cured with wet gunny bags for 28 , and 56 days. As shown in Fig. 5.
Experimental and Testing
The beam was loaded under two point loading in order to keep the BM constant and predominating at the middle one third regions. Two steel columns were erected over a girder placed on rigid footing. The column head placed with an arrangement on one side is roller and another side as hinge with two plates and a pin at the centre. The beam was placed on those supports with exactly 1200mm distance from the centre of roller to centre of pin. At 1/3 points two round bars of dia 30mm were placed over them. Exactly at the centre between two round rods on the girder a hydraulic jack was placed. The top of the hydraulic jack was fixed with a proving ring with dial gauge of capacity of 50t. the load was applied manually through hydraulic jack. The increment of loading was kept as 2 divisions of dial gauge (2KN) in the proving ring. To record the load precisely a proving ring was used. The load is applied measured for every 2 Kn. The deflection of the beam at the point of loading during test was measured such as 2Kn, 4Kn, and 6Kn respectively. The test setup as shown in Figure 6 and test set up of all the specimen is show in Figure 6.
Loading History for Static Cyclic loading
The beam specimen was subjected to cyclic loading. The displacement sequence consists of 2 mm, 4 mm, 6 mm, and 16 mm. Each displacement level is indicated in dial gauge and corresponding loads are noted from proving ring. In the first cycle, beam was loaded gradually up to 2 mm deflection and then unloaded. beam was loaded gradually up to 10 mm and then unloaded and then unloaded similarly each cycle of load is applied.
All the beams showed typical flexure behavior. No horizontal cracking were observed at level of reinforcement. since all beams were under-reinforced yielding of the tensile reinforcements occurred before crushing of the concrete cover in the pure bending zone.
All the beams exhibit a reasonably ductile performance as shown in Figure7 and 8. Its failure results from the yielding of HPC followed by the crushing of concrete. At about 33% of the ultimate load, well flexural cracks appeared at the bottom of the specimen. With further increase in the load, regularly spaced vertical cracks were observed and they extended from the bottom of the specimen towards the top fiber. The failure occurs in the tensile zone following the appearance of one macro crack in pure bending region. The load was increased up to ultimate stage. After the attainment of ultimate load, the load was maintained till failure due to the confinement effect provided by HPC
Conventional concrete beam specimen and High Performance Concrete (10% metakaolin + 30% quarry dust) which was tested for their flexural behaviors and the average result are plot in to the graph are shown in Figure 9 and 14 .
Moment Curvature Curves
The set of Moment curvature curves does not show significant differences during the loading. The applied load upon the structure increases until failure. The first stage corresponds to the elastic behaviour without any cracks. In the second stage the cracking decreases the moment of inertia and therefore the bending stiffness of the beam. The last stage of the curves corresponds to the yielding of HPC. Typical moment – curvature curves HPC beams are shown in Figure 17 and 18.
Load – Strain Response
The load - strain curves as indicated in Figure 19 and 20 , illustrate the behaviour per unit length until the failure of concrete and steel. For all the Beams the stress - strain response shows a strain hardening behaviour. This allows an increase in the moment supported by the beam.
Energy Absorption Capacity
Ductility can be quantitatively measured in terms of the energy absorption capacity. Energy absorption capacity of the members can be approximated as the area enclosed by the load deflection curve. The ability of a structural member to absorb energy is an important factor in the overall performance of structural elements. At cracking, yielding of tension steel and at ultimate stage, HPC beams exhibited a substantial increase in the energy absorption capabilities thereby indicating improved ductile characteristics.
The tests on beams carried out in this study describe the possibility of using High performance concrete using (10% of cement with Metakaolin and 30% of sand with Quarry Dust) . From the results of the experimental study reported herein, the following conclusions can be drawn
1. Partial replacement of cement by Metakaolin and Quarry Dust by sand in concrete mixes would, not only lead to considerable savings in consumption of cement and natural sand
2. The ultimateload carrying capacity of High performance concrete beam using (10% Metakaolin and 30% Quarry Dust) is found to be 26kN, and 38 kN, at the age of 28,and 56 days of curing . This shows that there is increase in load carrying capacity by 8.33 %,and 26.67 %,of Conventional concrete Beam.
3. HPC beams show good ductility due to the confinement of the compression zone. The displacement ductility factor varies from 1.23 to 1.31. The results reveal that more ductile performance.
4. The Conventional concrete Beam. show the normal behaviour and the energy absorption is normal
5. The advantages of introducing HPC (10% of cement with Metakaolin and 30% of sand with Quarry Dust) included of the slowing down of appearance of first crack and the presence of smaller deflection, compared with Conventional concrete Beam
6. As the age of concrete increases, the compressive strength as well as tensile strength also increases