STUDY PROPERTIES OF CONCRETE WITH METAKAOLIN AS PARTIAL REPLACEMENT OF CEMENT

Hemalatha.C and G. Murali #1Second year student, Department of Civil Engineering, Vel Tech High Tech

Dr.Rangarajan Dr.Sakunthala Engineering College, Avadi, Chennai-62#2Assistant Professor, Vel Tech High Tech Dr.Rangarajan Dr.Sakunthala Engineering

Colleges, Chennai 600062, 9944224485, murali_22984@yahoo.com

ABSTRACT

Metakaolin is a cementitious material used as an admixture to produce high strength concrete and is used for maintaining the consistency of concrete. In the case where insufficient or poor curing concrete structures like the seashore, underground structures which undergo severe loss of compressive strength and permeability interconnected durability, use of metakaolin proves to be very useful to modify the properties of concrete. This paper deals with the properties of concrete with varying percentage replacement of metakaolin. The mix M1, M2, M3 and M4 were obtained by replacing 0, 5, 7.5 and 10 percent Mass of Cement by Metakolin. Finally, required specimens were tested to investigate the behaviour such as compressive strength, flexural strength and split tensile strength. The test results indicated that the admixture metakaolin when used at optimum quantity tend to increase the strength of the concrete mix when compared with conventional concrete

1. INTRODUCTIONConcrete is one of the most widely used man-made construction material in the

world. Metakaolin is a cementitious material used as an admixture to produce high strength concrete. Optimal quantity of Metakaolin for M20 and M35 grade concrete has been worked out, which can replace the cement in order to get better strength and durability. And also identification of the dry shrinkage and permeability characteristics of blended cement has been done. Jiping Bai [1] studied that when metakaolin is used as a partial replacement for Portland cement, tends to improve both the mechanical properties and the durability of concrete. Friars and Cabrera [2] investigated the relationship between the pore size distribution and degree of hydration of metakaolin based cement pastes. They reported that metakaolin showed the best improvement on the mechanical properties of concrete. Palomo [3] investigated the chemical stability of metakaolin based cement composites.

2. EXPERIMENTAL PROGRAM2.1 Materials Cement: In this experimental investigation ordinary Portland cement of 53 grade was used. Fine aggregate: Locally available river sand free from impurities was used. The size of it is less than 4.75mm. The specific gravity and fineness modulus of the fine aggregate were found to be 2.67 and 2.56 respectively. The percentage of passing is within the limits as per IS383-1970 [4].Coarse aggregate: The coarse aggregate used is 12.5mm in size, crushed, angular in shape and free from dust. The specific gravity and fineness modulus were found to be

2.82 and 7.03 respectively. The percentage of passing is within the limits as per IS383-1970 [4].Water: Potable water free from injurious salt was used for mixing and curing.Admixture : The properties of metakolin as shown in table 1and 2.

Table 1 physical propertiesSpecific Gravity: 2.60 D10 <2.0umPhysical Form: Powder D50 <4.5um

Color: Off-White D90 <25umBrightness: 80-82 Hunter L Bulk Density (lbs/ft3): 20-25

BET: 15M2/gram Bulk Density (g/cm3): 0.4

Table 2 Chemical propertiesChemical Composition, Wt.: SiO2 51-53% CaO <0.20%

Al2O3 42-44% MgO <0.10%Fe2 O3 <2.20% Na2O <0.05%TiO2 <3.0% K2O <0.40%SO4 <0.5% L.O.I. <0.50%

MIX PROPORTIONS2.1 Grade of concreteThe mix proportion of this investigation was 1:2.4:4.9 as per [5 6] and M20 grade of concrete was adopted

2.2 Preparation of specimensThe strength characteristics of concrete with varying percentage of metakaolin

were studied by casting cubes, cylinders and prisms. The constituents of the concrete viz, cement, fine aggregate and coarse aggregate were mixed to appropriate proportion by adding water. Metakaolin is added to the different mixes in varying proportions as a partial replacement for cement. Moulds for cubes of size (100X100X100mm), cylinders with dimensions of (100mm diameter X 200mm height) and prisms of size (500X100X100mm) were prepared and concrete was poured in to the mould layer by layer and vibrated thoroughly. The specimens were removed from the moulds after 24 hours and then the specimens were cured with water for 28days.

3. Testing Concrete specimens were taken out of curing chamber after 28days. Cubes were tested for compressive strength using a compression testing machine, cylinders were tested for their split tensile strength using a compression testing machine and prisms were tested for their flexural strength using flexural testing machine as shown in figure 4.

4. Results and discussionsIt was found from the experimental results that the compressive strength, split tensile strength and flexural strength has increased for the specimens with varying percentage of metakaolin as replacement for cement when compared with the conventional concrete. The test results obtained are presented in table.3, 4 and 5.

Table 3. Compressive strength

Mix% of

Metakaolin7 days (Mpa)

14 days (Mpa)

28 days (Mpa)

M1 0 18.1 20.6 26M2 5 19.2 21 28.4M3 7.5 19.8 21.5 29.7M4 10 18.5 20.9 28.3

Table 4. Split Tensile strengthMix % of Metakaolin 28 days (Mpa)M1 0 2.76M2 5 2.86M3 7.5 2.98M4 10 2.81

Table 4. Flexural StrengthMix % of Metakaolin 28 days (Mpa)M1 0 3.56M2 5 3.75M3 7.5 3.89M4 10 3.6

It is obvious from the test results that 7.5% replacement of cement with metakaolin increased the compressive strength of concrete by 14.2%, split tensile strength by 7.9% and flexural strength by 9.3%. The other percentage of metakaolin such as 5 and 10 percentages also showed considerable increase in strength characteristics of the concrete when compared with the conventional concrete. The comparison of compressive strength, split tensile strength and flexural strength for different mixes with varying metakaolin proportion are shown in figure 1, 2 and 3 respectively.

Figure 1. Variation of compressive strength

Figure 2. Variation of split tensile strength

Figure 3. Variation of flexural strength

Figure 4. Testing of specimens

CONCLUSIONThe admixture metakaolin when used at optimum quantity tend to increase the strength of the concrete mix when compared with conventional concrete.

7.5% of metakaolin increased the compressive strength, split tensile strength and flexural strength of concrete by 14.2%, 7.9% and 9.3% respectively.

5% of metakaolin increased the compressive strength, split tensile strength and flexural strength of concrete by 9.2%, 3.6% and 5.3% respectively.

10% of metakaolin also showed considerable increase in compressive strength, split tensile strength and flexural strength of concrete by 8.8%, 1.8% and 1.1% respectively.

REFERENCES

[1] Jiping Bai, Albinas Gailius, “Consistancy of Fly-ash and Metakaolin Concrete”, Journal of Civil Engineering and Management, pp. 131-135, (2009).[2] Frias, Moises and Cabrera, JoshepPore Size Distribution and Degree of Hydration of Metakaolin-Cement Pastes. Cement and Concrete Research, 30 (4), pp. 561-569, (2000).[3] Palomo, A., Blanco-Varela, M. T., Granizo, M. L., Vazquez, T. and Grutzeck, M. W. “Chemical Stability of Cementitious Materials based on Metakaolin”. Cement and Concrete Research, 20 (7), pp. 997-1004. (1999):[4]. IS 383-1970 Specification for fine and coarse aggregate from natural sources for concrete (Second revision)[5] IS 456-2000, “Plain and Rein forced concrete” code of practice, Bureau Indian standards, New Delhi, India. [6]. IS 10262-2009 Recommended guidelines for concrete mix design, BIS, New Delhi, India, 2009.