Flexural Behavior of Geopolymer Beam and Slab Elements Reinforced with Different Types of Wiremesh

Transcription

1 IJIRST International Journal for Innovative Research in Science & Technology Volume 3 Issue 03 August 2016 ISSN (online): Flexural Behavior of Geopolymer Beam and Slab Elements Reinforced with Different Types of Wiremesh Vinu P Dr. Ramesh Manoli M. Tech Student Professor Department of Civil Engineering Department of Civil Engineering GAT, Bengaluru GAT, Bengaluru Dr. M T Prathap Kumar Professor Department of Civil Engineering GAT, Bengaluru Shiva Kumar KS Assistant Professor Department of Civil Engineering GAT, Bengaluru Abstract The aim of this experimental investigation carried out is to know the flexural strength of hardened Geopolymer concrete elements reinforced with different types of wire meshes in which the Geopolymer concrete is made using GGBS and Fly ash in equal proportions as the Cementacious materials and sodium hydroxide and sodium silicate as the alkaline activators. The elements such as slabs and beams are cast using the Geopolymer concrete and different wire meshes keeping the size of the slab as 700mm x 150mm x 30mm. The beams are made of size 700mm x 150mm x 150mm. Three types of meshes were used such as square woven metal mesh, square welded metal mesh and hexagonal expanded metal mesh. These meshes were placed inside the beam, slab elements in one two and three layers each, cured under the sun for 7 days and 14 days, and tested the beams for flexure and the slabs for deflection. The obtained results were then plotted in a graph and the feasibility of using the type and layer of meshes were identified. Keywords: ferrocement, Geopolymer concrete, metal mesh, Sodium hydroxide and sodium silicate as alakaline activators General: I. INTRODUCTION The aim of this experimental investigation carried out is to know the flexural strength of hardened Geopolymer concrete elements reinforced with different types of wire meshes in which the Geopolymer concrete is made using GGBS and Fly ash in equal proportions as the Cementacious materials and the alkaline activators used are sodium silicate and sodium hydroxide. The elements such as slabs and beams are cast using the Geopolymer concrete and different wire meshes keeping the size of the slab as 700mm x 150mm x 30mm. The beams are made of size 700mm x 150mm x 150mm. Three types of meshes were used such as square woven metal mesh, square welded metal mesh and hexagonal expanded metal mesh. These meshes were placed inside the beam and slab elements in one two and three layers each and cured under the sun for 7 days and 14 days and tested the beams for flexure and the slabs for deflection. The obtained results were then plotted in a graph and the feasibility of using the type and layer of meshes were identified Ferrocement is used widely in many places. High tensile properties and high tensile strength, resilience, ductility, resistance to cracking, ability to undergo large deflection before collapse, impact resistance and toughness, strength to weight ratio all these properties being very higher makes ferrocement a very versatile material. Even though the slabs made of ferrocement and other products are used in India for either structural or non-structural purposes the standard test and procedure for design are not carried out. Hence, here is an attempt to study the behaviour of Geopolymer ferrocement slab and beam elements in flexure. Geopolymer concrete is a concrete consisting of materials like Fly ash or GGBS or combination of both instead of cement, coarse and fine Aggregates and Alkaline activators instead of water. Reaction of aluminates and silicate bearing materials with an activator gives the Geopolymer concrete. generally, waste materials such as fly ash obtained from the nuclear reactors or ground granulated blast furnace slag from iron and metal production are used as the binders, which facilitates easy disposal of such wastes. Fly ash based Geopolymer concrete is a new material in which Portland cement need not be present as a binder. Though Geopolymer can be manufactured from various materials which are rich in alumina and silicate like fly ash, ground granulated blast furnace slag (GGBS) and meta- kaolin etc., fly ash and GGBS based Geopolymers are very popular. The objective of this experimental investigation was mainly to develop a viable housing component that could be used as a multipurpose structural element. Experimental studies were carried out on Geopolymer ferrocement slab and beam elements. In this context, multipurpose structural elements are meant as Geopolymer ferrocement elements, which can be used as both floor All rights reserved by 93

2 and wall elements. Ferrocement slab which were stiffened by square and rectangular sections were found to be suitable shapes for such elements. In this experiment, Geopolymer ferrocement elements having the shape of rectangle were chosen. Stages in Polymerization Process: A fast chemical reaction under the influence of high alkaline condition on Silica or Aluminium minerals will results in a polymeric chain of three-dimensions and the ring structure involving Silica-Oxygen-Aluminium-Oxygen bond which causes the geopolymerisation is as expressed below. Mn[-(SiO2)z AlO2]n.wH2O Where: M is the cation or alkaline element such as sodium, potassium, and calcium, n is the degree of polymerization, z is in the order 1, 2, 3, or higher, upto 32. The model made by Glukhovsky divides the process of geopolymerisation into the following three stages: 1) destruction-coagulation; 2) coagulation-condensation; 3) condensation-crystallization. In recent studies, different authors have elaborated and extended the theories of Glukhovsky and used the knowledge gained about the process of synthesising zeolitic in order to explain the process of Geopolymerisation as a whole Fig1 represents a simplified reaction for the Geopolymerisation mechanism. This reaction mechanism outlines the key processes occurring in the transformation of a solid aluminosilicate source into a synthetic alkali aluminosilicate Fig.1: Geopolymerisation Process Applications: Nuclear Radioactive and toxic waste containers. Manufacture of Bricks, block sand ceramics. Foundry gear s-warmth resistant composites. Industry Sealants. Chemically resistant wall panels. Sewer pipeline products. Sleepers for Railways. Fiber strengthened laminates. Strengthening of concrete structures. The materials used in the present study are as follows Class F Fly ash II. MATERIALS AND METHODOLOGY All rights reserved by 94

3 GGBS Coarse aggregates of 12mm down size Sodium hydroxide and sodium silicate as alakaline activators Water Mesh reinforcements (3 types) Effect of Curing on Compressive Strength of Geopolymer Concrete Cubes: Flexural Behavior of Geopolymer Beam and Slab Elements Reinforced with Different Types of Wiremesh The sizes of the specimens for the compressive strength test are fixed as Cubes of 150mm x 150mm x 150 mm. The moulds are prepared for the above required sizes of the specimen. The moulds are cleaned and oiled for required size. The Cubes were cast without any reinforcements just to know the time required by the Geopolymer concrete mix to attain the target strength.the cubes of dimension 150 mm x 150 mm x150 mm which were cast without any reinforcement are kept for sun drying and they are tested for compressive strength in the compressive strength testing machine after 7 days, 14 days and 28 days to know the time required for the concrete to attain the target strength for which the Geopolymer concrete mix is designed for. Flexural Strength of Geopolymer Concrete Beams: The Beams were cast with wire mesh reinforcements in 3 successive layers. Each mesh with 1, 2 and 3 layers of reinforcement were casted which makes 3 beam specimens for each type of mesh. This is then tested for flexural strength. The casting of elements includes preparation of mould, placing of mesh reinforcement, and placing of mixed concrete. The moulds are cleaned and oiled for required sizes. The meshes were cut to the size of moulds area and arranged to meet the requirements. The concrete is mixed and placed up to clear cover in the mould and reinforcement meshes were placed. First specimen with one layer of mesh. Next specimen with 2 layers one at the top and another at bottom, another layer in the centre is introduced as 3 rd layer in case of beam specimens. The beams of size700 mm x 150mm x 150mm are casted with 1, 2 and 3 layers of reinforcement for all the 3 types of meshes which are sun dried and tested for flexural strength after 7 days and 14 days in the flexural strength testing machine and the results were compared with that of the beam without any reinforcement. The figures below show the placing and testing of beam specimens in the flexural strength testing machine. The beams reinforced with wire meshes showed prolonged failure with a hint of the failure as shown in the above figure with the failure patterns whereas the unreinforced beams were brittle and showed a sudden failure. Strength of Unreinforced and Reinforced Geopolymer Concrete Precast Slabs: The Slabs were cast with wire mesh reinforcement in 2 successive layers as placing 3 layers in 30mm depth was very difficult. Each meshes with 1 and 2 layers of reinforcement were cast which makes 2 slab specimens for each type of mesh. The casting of elements include preparation of mould, placing of mesh reinforcement, and placing of mixed concrete. The moulds are cleaned and oiled for required sizes. The mesh was cut to the size of moulds area and arranged to meet the requirements. The concrete is mixed and placed up to clear cover in the mould and reinforcement meshes were placed. First specimen with one layer of mesh. Next specimen with 2 layers one at the top and another at bottom was introduced. The slabs of size 700mm x 150mm x 30mm are casted with 1 and 2 layers of mesh reinforcement and also without any reinforcement. And the specimens are sun dried and tested for deflection after 7 days and 14 days and the results were compared. The Geopolymer concrete slab of 30 mm thickness which is casted and cured in sun drying for 14 days is tested for deflection as shown in the above figure The slab is placed over the cylinder and cubes as simple supports which were available in the laboratory and the dial gauge is fitted below the slab as shown to measure the deflection of the slabs after loading. The dialguage of least count 0.01 mm was used to measure the deflection of the slabs Loading is made on the test specimen using the concrete cylinders of known weight. for each cylinder placed the corresponding deflection in the slab if found is recorded III. RESULTS AND DISCUSSIONS In the present study, Geopolymer concrete cubes were cured under sunlight for 7, 14 and 28 days to determine the compressive strength. The effect of curing under sunlight was analyzed to determine the number of days required to achieve the target strength. Three different types of meshes were used as reinforcements to determine the flexural strength as well as suitability of these reinforcements for precast slabs with Geopolymer concrete. Effect of Curing on Compressive Strength of GPC Cubes: The Geopolymer concrete cubes were cast as per mix design explained in chapter 4. 3 specimens were casted and cured under sunlight for 7, 14 and 28 days. Table 1 shows average compressive strength obtained at 7, 14 and 28 days. The mix design for GPC was done for target compressive strength of 40 N/mm 2. It was found that with 7 days of sunlight curing the compressive strength exceeded the target compressive strength. Figure 1.1 shows the graphical variation of compressive strength with curing period. It was found that the compressive strength increases significantly when curing period increases from 7 to 14 days. Whereas only a marginal increase occurs when curing is varied from 14 to 28 days. Hence for testing beams and precast slabs with GPC, 14 days curing period was adopted. All rights reserved by 95

4 Table 1 compressive strength of Geopolymer concrete cubes No. of trials Days of curing Load (kn) Compressive strength (N/mm 2 ) Average compressive strength (N/mm 2 ) Flexural Strength of Geopolymer Concrete Beams: Fig. 1.1: Variation of compressive strength of cubes with curing period. The Flexural strength of Geopolymer concrete beams cast and cured for 7 and 14 days, with and without reinforcements was determined at 7 and 14 days curing under sunlight. The strength of reinforced beams was determined by varying number of layers from 1, 2 and 3 under 7 and 14 days. Flexural Strength of Beams without Reinforcement All the beams were tested using flexural testing machine with two points loading. The test configurations have been explained in the chapter 4. Table 2 shows Flexural strength obtained at 7 and 14 days for unreinforced Beams. Figure 2 shows the variation of flexural strength for unreinforced beams at 7 and for 14 days. It can be observed that the flexural strength at 14 days curing was greater than that obtained at 7 days curing. The results of this were used to compare with the Flexural strength of reinforced beams using Square woven metal mesh, Square welded metal mesh and expanded hexagonal metal mesh. Table 2 Flexural Strength of Unreinforced Beams All rights reserved by 96

5 Fig. 2: Variation of flexural strength of unreinforced beams with number of trials Flexural Strength of Beams Reinforced with Square Woven Metal Mesh: The square woven metal mesh having 6 holes per inch were used by varying number of layers from 1, 2 and 3. Wherein, the reinforcements were placed at the bottom, top and center. Table 3 and figure 3 shows variation of flexural strength at 7 and 14 days of curing. It can be observed that the increase in the number of layers of reinforcement increases the flexural strength and is maximum for beams reinforced with 3 layers of meshes. Table 3 Flexural strength of beams reinforced with square woven metal mesh Fig. 3: Variation of flexural strength of beams with number of layers of reinforcements for square woven metal mesh Flexural Strength of Beams Reinforced with Square Welded Metal Mesh: Similar tests were done for beams reinforced with square welded metal mesh. Table 4 and figure 4 shows variation of flexural strength with increase in the number of layers of reinforcements. It was observed that there was no significant variation in flexural strength for beams reinforced with 2 and 3 layers of reinforcements at 14 days of curing. However marginal increase in flexural strength occurs when number of layers from 2 to 3 at 7 days of curing. Table 4 flexural strength of beams reinforced with square welded metal mesh All rights reserved by 97

6 Fig. 4: Variation of flexural strength of beams with number of layers of reinforcements for square welded metal mesh Flexural Strength of Beams Reinforced with Expanded Hexagonal Metal Mesh: Similar tests were done for beams reinforced with expanded hexagonal metal mesh. Table 5 and figure 5 shows variation of flexural strength with number of layers of reinforcements. It was observed that the flexural strength increased with increase in number of layers for both 7 and 14 days of curing. However, for beams reinforced with 3 layers of reinforcements, there was no change in flexural strength both at 7 and 14 days. Results of present study indicates that the flexural strength increases with the increase in number of layers for both square woven metal mesh and expanded hexagonal metal mesh, increased flexural strength marginally when compared with beams reinforced with square welded metal mesh. Table 5 flexural strength of beams reinforced with expanded hexagonal metal mesh Fig. 5: Variation of flexural strength of beams with number of layers of reinforcements for expanded hexagonal metal mesh Strength of Unreinforced and Reinforced Geopolymer Concrete Precast Slabs: The effect of reinforcement on precast Geopolymer concrete slabs were studied using the square woven metal mesh, square welded metal mesh and expanded hexagonal metal mesh. The numbers of layers were varied from 1 and 2 layers of reinforcement. The testing methodology has been explained. The load and deflection were measured to study the effect of deflection reduction as well as to assess the load at failure. All rights reserved by 98

7 Slabs Reinforced with Square Woven Metal Mesh: Table 6 shows load and the corresponding deflection obtained for precast slabs without reinforcement and with 1 layer and 2 layers of reinforcements. Figure 6 shows the variation of load versus the deflection for all the cases tested. It can be seen that the load at failure for unreinforced precast slabs is significantly lower when compared to reinforced Geopolymer concrete slabs. Further with increase in the number of layers of reinforcement, the load at failure increases. To assess the effect of reinforcement, on deflection the Deflection Reduction Factor was estimated in percentage. Table 7 shows the Deflection Reduction Factor obtained between Geopolymer concrete precast slabs reinforced with 1 layer of mesh and without reinforcement, Geopolymer concrete precast slabs reinforced with 2 layers of mesh and without reinforcement and Geopolymer concrete precast slabs reinforced with 1 layer of mesh and 2 layers of mesh. It can be seen that significant reduction in Deflection Reduction Factor for all reinforced Geopolymer concrete precast slabs. Maximum Deflection Reduction Factor was obtained for Geopolymer concrete precast slabs reinforced with 2 layers of mesh. For Geopolymer concrete precast slabs reinforced with 2 layers and 1 layer, the reduction is significant at lower value of load and the deflection reduction factor reduces with increase in the load. Thus introducing of reinforcements in the Geopolymer precast slabs increases the load at failure as well as increases the DRF and hence beneficiary. Table 6 Deflection of slabs reinforced with square woven metal mesh Fig. 6: variation of load versus the deflection of slabs reinforced with square woven metal mesh and slabs without reinforcement. Table 7 Deflection reduction factor for slabs reinforced with square woven metal mesh All rights reserved by 99

8 Slabs Reinforced with Square Welded Metal Mesh: Table 8 shows load and the corresponding deflection obtained for precast slabs without reinforcement and with 1 layer and 2 layers of reinforcements. Figure 7 shows the variation of load versus the deflection for all the cases tested. It can be seen that the load at failure for unreinforced precast slabs is significantly lower when compared to reinforced Geopolymer concrete slabs. Further with increase in the number of layers of reinforcement, the load at failure increases. To assess the effect of reinforcement, on deflection the Deflection Reduction Factor was estimated in percentage. Table 9 shows the Deflection Reduction Factor obtain between Geopolymer concrete precast slabs reinforced with 1 layer of mesh and without reinforcement, Geopolymer concrete precast slabs reinforced with 2 layers of mesh and without reinforcement and Geopolymer concrete precast slabs reinforced with 1 layer of mesh and 2 layers of mesh. It can be seen that significant reduction in Deflection Reduction Factor for all reinforced Geopolymer concrete precast slabs. Maximum Deflection Reduction Factor was obtained for Geopolymer concrete precast slabs reinforced with 2 layers of mesh. For Geopolymer concrete precast slabs reinforced with 2 layers and 1 layer, the reduction is significant at lower value of load and the deflection reduction factor reduces with increase in the load. Thus introducing of reinforcements in the Geopolymer precast slabs increases the load at failure as well as increases the DRF and hence beneficiary. Table 8 Deflection of slabs reinforced with square welded metal mesh Fig. 7: variation of load versus the deflection of slabs reinforced with square welded metal mesh and slabs without reinforcement. Table 9 Deflection reduction factor for slabs reinforced with square welded metal mesh. All rights reserved by 100

9 Slabs Reinforced With Expanded Hexagonal Metal Mesh: Table 10 shows load and the corresponding deflection obtained for precast slabs without reinforcement and with 1 layer and 2 layers of reinforcements. Figure 8 shows the variation of load versus the deflection for all the cases tested. It can be seen that the load at failure for unreinforced precast slabs is significantly lower when compared to reinforced Geopolymer concrete slabs. Further with increase in the number of layers of reinforcement, the load at failure increases. To assess the effect of reinforcement, on deflection the Deflection Reduction Factor was estimated in percentage. Table 11 shows the Deflection Reduction Factor obtain between Geopolymer concrete precast slabs reinforced with 1 layer of mesh and without reinforcement, Geopolymer concrete precast slabs reinforced with 2 layers of mesh and without reinforcement and Geopolymer concrete precast slabs reinforced with 1 layer of mesh and 2 layers of mesh. It can be seen that significant reduction in Deflection Reduction Factor for all reinforced Geopolymer concrete precast slabs. Maximum Deflection Reduction Factor was obtained for Geopolymer concrete precast slabs reinforced with 2 layers of mesh. For Geopolymer concrete precast slabs reinforced with 2 layers and 1 layer, the reduction is significant at lower value of load and the deflection reduction factor reduces with increase in the load. Thus introducing of reinforcements in the Geopolymer precast slabs increases the load at failure as well as increases the DRF and hence beneficiary. Table 10 Deflection of slabs reinforced with Expanded Hexagonal metal mesh Fig. 8: variation of load versus the deflection of slabs reinforced with Expanded Hexagonal metal mesh and slabs without reinforcement. Table 11 Deflection reduction factor for slabs reinforced with Expanded Hexagonal metal mesh. All rights reserved by 101

10 Load at Breakage for Slabs: Table 12 shows summarized values of load T breakage for Precast Geopolymer concrete slabs. It can be seen that the load at breakage reinforced precast Geopolymer concrete slabs were significantly higher when compared to that of unreinforced slabs. Marginal increase in failure load occurs with the increase in number of layers of reinforcement. Square woven metal mesh and square welded metal mesh showed better load carrying capacity. Table 12 Load at breakage for slabs Load at Breakage for slabs (kn) Metal Mesh unreinforced Square Woven Square Welded Expanded Hexagonal 1 layer 2 layers 1 layer 2 layers 1 layer 2 layers Table 13 shows summarized values of Deflection Reduction Factor obtained for all the 3 types of mesh reinforcements. DRF for both 1layer and 2 layers reinforced Geopolymer precast concrete slabs were significantly larger than that obtained for unreinforced Geopolymer precast concrete slabs. Square welded metal mesh showed significant Deflection Reduction Factor compared with other 2 types of meshes. Introduction of 2 nd layer of reinforcement causes a marginal increase in the Deflection Reduction Factor at all levels of loading. Table 13 Deflection reduction factor for slabs unreinforced and reinforced with different types of meshes Deflection reduction factor for slabs unreinforced and reinforced with different types of meshes Square woven metal mesh Square welded metal mesh Expanded Hexagonal metal mesh Load (kn) DRF between 1 layer and unreinforced DRF between 1 layer and unreinforced DRF between 1 layer and unreinforced DRF between 2 layer and unreinforced DRF between 2 layer and unreinforced DRF between 1 layer and 2 layer DRF between 1 layer and 2 layer reinforced reinforced DRF between 2 layer and unreinforced DRF between 1 layer and 2 layer reinforced IV. CONCLUSIONS On the basis of present experimental study, the following conclusions are drawn: 1) At 7 days of sun light curing the compressive strength exceeds the target compressive strength. The compressive strength increases significantly when curing period increases from 7 to 14 days. Hence a curing period of 7 to 14 days is sufficient to achieve the target strength. 2) The flexural strength at 14 days sun light curing was greater than that obtained at 7 days curing. Increase in the number of layers of reinforcement increases the flexural strength and is maximum for beams reinforced with 3 layers of meshes. 3) The effect of sunlight curing indicated that there is no significant variation in flexural strength for beams reinforced with 2 and 3 layers of reinforcements at 14 days of curing. However marginal increase in flexural strength occurs when number of layers from 2 to 3 at 7 days of curing. 4) The flexural strength increases with the increase in number of layers for both square woven metal mesh and expanded hexagonal metal mesh. 5) The load at failure for unreinforced precast slabs is significantly lower when compared to reinforced Geopolymerprecast concrete slabs. Increase in the number of layers of reinforcement increase the load at failure. 6) Maximum Deflection Reduction Factor is observed for Geopolymer concrete precast slabs reinforced with 2 layers of mesh. For Geopolymer concrete precast slabs reinforced with 2 layers and 1 layer, the reduction is significant at lower value of load and the deflection reduction factor reduces with increase in the load. 7) Marginal increase in failure load occurs with the increase in number of layers of reinforcement. Square woven metal mesh and square welded metal mesh showed better load carrying capacity. 8) Use of square welded metal mesh indicates a significant Deflection Reduction Factor compared with other 2 types of meshes. Introduction of second layer of reinforcement causes a marginal increase in the Deflection Reduction Factor at all levels of loading. All rights reserved by 102

11 9) The trend in results thus indicates that introduction of reinforcements in the Geopolymer precast slabs increases the load at failure as well as increases the DRF and hence beneficiary. 10) Geopolymer Precast concrete slabs exhibits better load carrying capacity at shorter interval of curing under day light. Hence it is a viable alternative to ordinary cement base precast concrete slabs in construction industry. REFERENCES [1] AphaSathonsaowaphaka, PrinyaChindaprasirt, KedsarinPimraksa. Workability and strength of lignite bottom ash geopolymer mortar, Journal of Hazardous Materials, 168(2009) [2] Suresh Thokchom, Partha Ghosh, Somnath Ghosh. Acid resistance of fly ash based geopolymer mortars, International Journal of Recent Trends in Engineering, No. 6, 1(2009) [3] Djwantoro Hardjito, Chua Chung Cheak, Carrie Ho Lee Ing. Strength and setting times of low calcium fly ash-based geopolymer mortar, Modern Applied Science, 2(2008) [4] Djwantoro Hardjit o, M.Z Tsen. Strength and thermal stability of fly ash-based geopolymer mortar, The 3rd International Conference-ACF/VCA, [5] FrantišekŠkvára, TomášJílek, LubomírKopecký. Geopolymer materials based on fly ash, Journal Ceramics-Silikáty, 49(2005) [6] Gurdev Singh. Rational assessment of flexural fatigue characteristics of ferrocement for reliable design, Cement and Concrete Composites, 17(1995) [7] Jamal Shannag M. Bending behavior of ferrocement plates in sodium and magnesium sulfates solutions, Cement and Concrete Composites, 30(2008) [8] Kondraivendhan B, Bulu Pradhan. Effect of ferrocement confinement on behavior of concrete, Construction and Building Materials, 23(2009) [9] M.A. Al-Kubaisy, MohdZaminJumaat. Flexural behaviour of reinforced concrete slabs with Ferro cement tension zone cover, Construction and Building Materials, 14(2000) [10] Mohammed Arif, Pankaj, Surendra K. Kaushik. Mechanical behaviour of ferro cement composites: an experimental investigation, Cement and Concrete Composites, 21(1999) [11] Noor Ahmed Memon, SalihuddinRadinSumadi, MahyuddinRamli. Performance of high workability slag-cement mortar for ferro cement, Building and Environment, 42(2007) [12] Songpiriyakij S. Effect of temperature on compressive strength of fly ash-based geopolymer mortar, Silica Fly, No.4, 48(2000) [13] Waleed A. Thanoon, YavuzYardim, M.S. Jaafar, J. Noorzaei. Structural behaviour of ferro cement brick composite floor slab panel, Construction and Building Materials, 24(2010) All rights reserved by 103