FLEXURAL STRENGTH OF TWO-WAY RC SLABS RETROFITTED USING BASALT FIBER REINFORCED POLYMER (BFRP) WITH MECHANICAL ANCHORAGE. Shubhalakshmi.B.S

Shubhalakshmi.B.S 1 , H N Jagannatha Reddy 2 and K Arjun 1 .  1. Assistant Professor’s, Department of Civil Engineering, Dayananda Sagar College of Engineering, Bengaluru, India-560078. 2. Professor, Department of Civil Engineering, Bangalore Institute of Technology, Bengaluru, India-560004 ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Strengthening of existing reinforced concrete structural elements has been one of the most important activities in civil engineering. The upgrading of existing structures is an integral part of structural engineering practice. A slab is a flat two dimensional planar structural element having small thickness, compared to its other two dimensions. Reinforced concrete slabs are one of the most commonly used structural elements. Composites are used because overall properties of the composites are superior to those of the individual components. Basalt fibers are made from basalt rocks which are the most common rock type in the earth´s crust. An anchor bolt is used to attach objects or structures to concrete. There are many types of anchor bolts, consisting of designs that are mostly proprietary to the manufacturing companies. All consist of a threaded end, to which a nut and washer can be attached for the external load. The experimental work was conducted on slabs to study the effect of BFRP on flexural behavior of the slabs under the static loads, using cross wrapping technique with mechanical anchoring. The BFRP was to be introduced to slabs in the form of cross wrapping at flexural zone by wet lay-up technique then it was anchored with bolts and plates as per the guidelines of the manufacturers. Control slabs were casted and tested after 28 days under uniformly distributed loading case. Strengthened slabs were tested after 6 days of strengthening and once after it were anchored. From the experimental results it was revealed that the initial crack strength and ultimate load strength of retrofitted slabs with mechanical anchoring are found to be increasing by at least 39.585% comparatively and stiffness of wrapped slabs were found to be increased.

ISSN: 2320-5407
Int. J. Adv. Res. 5(4), 1198-1204 1199 has been noted. Structural repair and rehabilitation of reinforced concrete structures has become an increasing important option for all deteriorated/damaged structures to restore, enhance the load carrying capacity and increase the life span of the structure. A slab is a flat two dimensional planar structural element having thickness, small compared to its other two dimensions. Reinforced concrete slabs are among the most commonly used structural elements. The use of FRP to strengthen civil engineering structures started in 1980's. FRP system that is nonmetallic material is considered to be a beneficial technique. Composites are used because overall properties of the composites are superior to those of the individual components. These new materials are applicable to both construction of new structures and maintenance and rehabilitation of existing structures. Fiber-reinforced composites are used in some of the most advanced constructions, and therefore most expensive. Basalt fibers are made from basalt rocks which are the most common rock type in the earth´s crust. The fibers are manufactured from melted rock which is then extruded through small nozzles to produce continuous basalt fiber.

Materials:-
Basalt fibers are made from basalt rocks which are the most common rock type in the earth´s crust. The fibers are manufactured from melted rock which is then extruded through small nozzles to produce continuous basalt fiber. Basalt FRP (BFRP) is the latest FRP composite that has developed within the last ten years and has been proven to have advantages in achieving the goal of enhancing safety and reliability of structural systems compared with the conventional carbon, glass and aramid FRP composites. BFRP shows advantageous characteristics in mechanical, chemical and high ratio of performance to cost in comparison to CFRP, GFRP, AFRP, steel bars. BFRP has a higher strength and modulus, a similar cost, and more chemical stability compared with E-glass FRP; a wider range of working temperatures and much lower cost than carbon FRP (CFRP); over five times of strength and around one third of density than commonly used low-carbon steel bars. Due to above advantages, BFRP has already become an attractive alternative for replacing conventional construction materials and is expected to enhance structural safety and sustainability. An anchor bolt is used to attach objects or structures to concrete. There are many types of anchor bolts, consisting of designs that are mostly proprietary to the manufacturing companies. All consist of a threaded end, to which a nut and washer can be attached for the external load. Mechanical anchors are the type of anchors bolts which works in the mechanical means to hold the base material such as brickwork, blockwork, stone, standard and reinforced concrete. Generally mechanical type anchor bolts are simple, effective and reliable use in hard base materials, common type of mechanical anchors bolts are expansion or wedge type anchors and screw anchors. Mechanical type anchors are commonly used because their ease of installation and economical, compared to chemical anchors. Wedge or expansion anchors are used in this research work. An anchor plate is a MS plate which is used as a fixture with a specified diameter of hole, through which certain diameter of anchor bolt runs into the base material such as brickwork, blockwork, stones and reinforced hardened concrete. The main purpose of the plate used is to hold the FRP sheets against the load and prevent de-bonding.

Method:-
The experimental study was conducted to test the reinforced concrete slabs. This includes testing a control slab and retrofitted slabs. The main objective of the investigation was to study the flexural and ductility behavior of concrete slabs retrofitted with BFRP sheets with mechanical anchorage bonded onto the flexural zone of the slab. Bolts used in this research work are HILTI's wedge anchors or expansion anchors of 8mm diameter 3inch length HST wedge anchor bolts. And 3mm thickness of 65×200mm dimension MS plate as a fixture or anchor plates used in this work. Totally 24 anchors bolts and 4 MS plates were used per anchored slabs. The FRP application included the resin system made of two parts namely the resin, the hardener and the fiber sheets. The concrete surface was cleaned and completely dried before the resin is applied. A first coat of thin layer of resin was applied and the FRP fabric precut to the desired dimension was then wrapped directly onto the surface. After the application of the FRP sheet wrap, a second layer of resin was applied to the surface to allow impregnation. The second layer of FRP sheet was then impregnated on top of the first layer. Adequate pressure was applied until the resin was squeezed out. The wrapped specimens were left at room temperature to allow air curing for seven days to allow bonding of the laminates. Installation of wedge or expansion anchor bolts performed in four steps as fallows; 1. Drill a hole with the prescribed diameter mond core bit. Diameter of drill bit used should equal to diameter of anchor bolt. 2. Cleaning of hole. 3. Using a hammer, tap the pre-assembled anchor through the object being anchored and into the hole. The anchor should be seated firmly against the base plate. 4. Tighten bolt or nut to the specified torque, using a torque wrench or with handy mechanical tools.  Test specimens were subjected to flexural test. The same testing program was applied to both controlled as well as on retrofitted slabs with mechanical anchoring. The specimen was also painted with lime wash in order to easily note the crack pattern of the specimen. The setup was carried out with a 25 ton loading frame, a loading jack was fixed on top of the specimen to apply load. To give the udl effect to the slab, loading channels were used such that the loads that were centrally applied were uniformly distributed on the slab as shown in figure 7. The deflection at the bottom of the slab was measured using dial gauge. Totally five dial gauge's were used for this experiment. The placement of these dial gauges are as one at the centre of the slab and other four at different points as shown in the figure 7.
The load was applied using a hand held lever with uniform increment up to the failure load. The dial gauge readings were noted down to calculate the deflection of the slab. The load was incremented manually and the readings of the 1202 dial gauge were taken at an interval of 2kN. The results and the graphs are discussed separately. The deflection was tabulated at each increment of loading. Also the complete crack patterns and the failure load were recorded in each test.

Result and Discussion:
For the control and retrofitted with mechanical anchoring slab, the deflection was measured at the mid span and other four points. The load-deflection curve has been plotted for the same as shown below.