Experimental Investigation on Steel Fibre Reinforced Fly Ash (Class-C) Based Alkali Activated Geo-Polymer Concrete

Geo-polymer concrete (GPC) are representing the most promising green and eco-friendly alternative to Ordinary Portland cement (OPC). This paper presents the results of an experimental program on the mechanical properties of steel fibres reinforced geo-polymer concrete (SFRGPC) such as Compressive strength, Split tensile strength, Flexural strength, Water absorption, Alkali attack, Acid attack and Abrasion resistance. SFRPGPC contains Fly ash (ClassC), alkaline liquids, fine aggregate, coarse aggregate and steel fibres. Alkaline liquid to fly ash ratio was fixed as 0.45 with 100% replacement of OPC. For alkaline liquid combination ratio of sodium silicate to sodium hydroxide solution was fixed as 2.5. Steel fibres was added to the mix in volume fractions of 0%, 0.25%, and 0.5% by volume of geo-polymer concrete. Specimens were subjected to air curing at room temperature. Based on the test results Compressive strength, Split tensile strength and Flexural strength showed maximum values for 0.5% dosage of steel fibre. Hence , it is concluded that the addition of 0.5% steel fibres dosage increase the strength of geo-polymer concrete which is due to the hooked end shape of steel fibres, which provide better adhesion between fibre and concrete and can be used in the marine environment.


Fine aggregate:
Fine aggregate is defined as those materials that passes through 4.75mm sieve and will for the most part, be retained on a 75µ sieve. In this work, India river sand is used as fine aggregate. The sand was washed and screened at site to remove deleterious materials.

Coarse aggregate:
Coarse aggregate consists of river gravel, crushed stone or manufacturing aggregate with particle size equal to or greater than 4.75mm. In this research coarse aggregates of maximum size 10-12 mm were used and the specific gravity is 2.71.

Steel Fibre:
Hooked end steel fibres were added to geo-polymer concrete to increase the crack resistance, flexibility, ductility and toughness of the concrete. It results in high tensile strength, improves load bearing capacity etc., The ending shapes of the fibre ie., hooked end steel fibre are very important to grant adhesion between fibre and concrete. The length and diameter of steel fibres used is 30mm and 0.60mm. The aspect ratio is 50.

Alkaline solution:
Sodium hydroxide solution mixed with Sodium silicate solution was used as an alkaline activator for geo-polymerization. The commercially available sodium hydroxide in the form of flakes was used in this study. Sodium silicate is in liquid form.
2.6 X-ray diffraction: X-Ray Diffraction (XRD) qualitatively identifies the crystalline phases of the fly ash sample.
Electrons hit a solid sample and x-rays are emitted. When the x-rays hit a crystal structure, some x-rays diffract based on this crystal structure but other x-rays penetrate further into the sample until colliding into a crystal. The machine reads all of the angles of diffracted, scattered x-rays and their intensities to create a pattern. These patterns are plotted, creating a diffractogram, relating diffracted intensity to diffraction angle. The X-Ray Diffraction for Fly ash Class-C is represented in the form of graph in( Figure1) Figure 1 X-Ray Diffraction pattern for Class-C X-Ray Diffraction studies were carried out for C-Class fly ash and the pattern confirms the presence of Al2O3 and SiO2 as predominant materials. The XRD pattern for C-Class fly ash illustrates that the main crystalline phases are quartz (JCPDS No. 89 -1668) and mullite (JCPDS No. 88 -0107) and the other crystalline phases present are hematite (Fe2O3) and calcium oxide (CaO). These patterns were matched with (JCPDS No. 89 -7746) and (JCPDS No. 82 -1690) respectively. These patterns were similar to the C-Class fly ash values recorded earlier. Very high intensity of calcium oxide in XRD pattern validates significant presence of calcium in C-Class fly ash. According to ACI (American Concrete Institute), the presence of quartz, hematite and calcium oxide increases strength and improves the durability of concrete.

Mix proportions
The following (Table 2) shows the mix proportions of geo-polymer concrete using fly ash (class-c) for one paver block.

Preparation of alkaline solution:
The weighed quantity (480 g) of Sodium Hydroxide (NaOH) in the form of flakes to suit 8 Molarity (8M) is allowed to dissolve in distilled water and made up to one litre. By trial and error, 300 gms of NaOH solution can be obtained when 120 gms of NaOH flakes are mixed in a makeup jar of 250 ml.

Casting the specimen:
First, the dry materials used for preparing geo-polymer concrete were mixed. Then alkaline solution and the required extra water were mixed. Machine oil was tarnished and the freshly mixed geopolymer concrete was placed into the paver mould. Each mould was then vibrated for 15 seconds using a mechanical vibrator. After the top surface was leveled the moulds were left at room temperature for ambient curing. (Figure 2) shows the casted specimens. (Table 3) shows the number of specimen cast.

Split tensile strength test:
The test was carried out along the longest splitting section of the specimen, parallel and symmetrical to the edges, in such a way that the distance of the splitting section to any side face was at least 0.5 times the thickness of the specimen over at least 75 percent of splitting section area. Since the section of the specimen is hexagonal in plan, the splitting section was chosen in such a way that it was the shortest length passing through the centre of the plan area.

Water absorption test:
The specimen was weighed initially and was completely immersed in water at room temperature for 28 days. Then the specimen was removed from water and dried in room temperature for 24 hours. The dried specimen was weighed and with this noted weights water absorption percentage was calculated. ( Figure  5) shows the water absorption test.

Alkali attack test:
Initially weight of the specimen was noted. Alkaline solution is prepared in a container by dissolving 4% of sodium hydroxide in water. The specimen was completely immersed in alkaline solution and the whole setup was kept in room temperature for 28 days, after which the specimen was removed from the solution and dried in room temperature for 24 hours. The dried specimen was weighed and using this noted weights alkali attack percentage was calculated.

Acid attack test:
Initially the weight of the specimen was noted. Acid solution was prepared in a container by mixing 5% of concentrated sulphuric acid in water. The test specimen was completely immersed in acid solution and the whole setup was kept in room temperature for 28 days. Then the specimen was removed from the solution and dried in room temperature for 24 hours. The dried specimen was weighed and using this noted weights acid attack percentage was calculated. (Figure 6) shows the alkali attack test, acid attack test.

TEST RESULTS
The results obtained by conducting various experiments are presented here.

5.1Compressive strength, Split tensile strength and Flexural strength
The casted paver blocks have been tested for compression, split tension and flexure. The results of compressive strength test, split tensile strength teat and flexural strength test are tabulated in (Table 4) and represented as bar chart in Figures ( 8, 9 & 10) respectively. The Compression Strength test for paver block has been carried out. From the above result it is absorbed that compressive strength is maximum when 0.5% steel fibre is used. This indicates that compressive strength increases with addition of steel fibres. As the maximum compressive strength is 26.20 N/mm 2 , this geo-polymer concrete can be used where M20 grade concrete.

Figure 8 Compressive Strength
The Split Tensile test has been carried out for paver block in shortest length passing through center area. From the above result it is absorbed that the split tensile strength is maximum when 0.5% steel Fibre is used.This indicates that split tensile strength increases with addition of steel Fibres. From the above result, the maximum split tensile strength obtained is 0.90 N/mm 2 .

Figure 9 Split tensile Strength
The Flexural strength test for paver block has been carried out. From the above result it is absorbed that the Flexural strength is maximum when 0.5% steel Fibre is used. This indicates that Flexural strength increases with addition of steel Fibres.From the above result, the maximum Flexural strength obtained is 3.81 N/mm 2 .

Water absorption percentage:
The water absorption test for paver block has been carried out and the results are tabulated in Table 5 and represented graphically in (Figure 11). The overall average of water absorption percentage is= 1.29%. As the overall water absorption percentage is less than 10%. This geo-polymer concrete can be used for construction.

Alkali attack percentage:
The alkali attack test for paver block has been carried out and the results are tabulated in (Table 5) and represented graphically in (Figure 12). The overall average of alkali attack percentage is = 2.57 %.As the overall alkali attack percentage is less than 10 %. This geo-polymer concrete can be used for construction Figure 12 Alkali absorption

Acid attack percentage:
The acid attack test for paver block has been carried out and the results are tabulated in (Table 5)and represented graphically in (Figure 13). The overall average of acid attack percentage is = 4.09 %.
As the overall acid attack percentage is less than 10 % This geo-polymer concrete can be used for construction. Figure 13 Acid absorption

Abrasion loss percentage:
The abrasion test for cube specimen has been carried out and the results are tabulated in (Table 5) and represented graphically in (Figure 14).The overall average of abrasion loss percentage is = 0.413 %.
As the overall abrasion loss percentage is less than 10 %. This geo-polymer concrete can be used for construction.

CONCLUSION
The addition of steel fibre dosage increases the strength of geo-polymer concrete which is due to the hooked end shape of steel fibre, which provides better adhesion between fibre and concrete.The addition of 0.5 % of steel fibre dosage gave maximum compressive strength of 26.2 N/mm 2 . Hence it is concluded that this geo-polymer concrete can be used were M20 grade concrete is used. Also split tensile and flexural strength results showed maximum values for the same dosage of steel fibre.Since the overall water absorption percentage, alkali attack percentage and acid attack percentage values are less than 10% it is concluded that this geo-polymer can be used for construction purpose.
Hence, from the results obtained the author concludes that this geo-polymer concrete with steel fibre reinforcement containing Class-'C' fly ash can be used for normal construction purpose and thereby we can reduce the carbon-di-oxide (CO2) emission during the usage of conventional concrete.