Experimental investigation on high performance RC column with manufactured sand and silica fume

In recent years, the use High Performance Concrete (HPC) has increased in construction industry. The ingredients of HPC depend on the availability and characteristics of suitable alternative materials. Those alternative materials are silica fume and manufactured sand, a by products from ferro silicon and quarry industries respectively. HPC made with silica fume as partial replacement of cement and manufactured sand as replacement of natural sand is considered as sustainable high performance concrete. In this present study the concrete was designed to get target strength of 60 MPa as per guide lines given by ACI 211- 4R (2008). The laboratory study was carried out experimentally to analyse the axial behavior of reinforced cement HPC column of size 100×100×1000mm and square in cross section. 10% of silica fume was preferred over ordinary portland cement. The natural sand was replaced by 0, 20, 40, 60, 80 and 100% with Manufactured Sand (M-Sand). In this investigation, totally 6 column specimens were cast for mixes M1 to M6 and were tested in 1000kN loading frame at 28 days. From this, Load-Mid height deflection curves were drawn and compared. Maximum ultimate load carrying capacity and the least deflection is obtained for the mix prepared by partial replacement of cement with 10% silica fume & natural sand by 100% M-Sand. The fine, amorphous and pozzalonic nature of silica fume and fine mineral particles in M- Sand increased the stiffness of HPC column. The test results revealed that HPC can be produced by using M-Sand with silica fume.


Introduction
Globally many countries are growing rapidly in the construction industry which uses natural resources for the development of the infrastructure such as highways, hydraulic and industrial projects, hydroelectric power projects etc. The improved performance of concrete plays the role to meet the requirements of industrialization the need for high performance concrete is vital. The mechanical and durability properties of HPC is mainly affected by the use of these mineral admixtures mainly due to their filler effect and Pozzolonic reaction [1 ,2]. A by -product obtained from the production of silicon and ferrosilicon alloys is silica fume which has high SiO 2 content. Silica fume has an amorphous state and extreme fineness as compared to other supplementary cementitious materials which improves mechanical and durability properties [3,4]. Researchers found that 5-15% replacement of cement by silica fume with a smaller dosage of super plasticizer makes the concrete workable and also improves strength of concrete [5,6]. The natural sand has extracted continuously from river beds leads to many environmental problems such as disruption to aquatic life, lowering of the underground water table which affects agriculture, sliding of river bank etc. In order to balance this situation many alternative materials have been identified as a substitute for river sand [7,8]. M-Sand is a crushed aggregate produced from hard stone which is rough, angular shape, washed and properly graded is used as a substitute for river sand. The mechanical and durability properties of concrete are improved due to its filler and interlocking effect between the particles of M-Sand. [9][10][11].Taking into consideration of the above mentioned points, this research work poses to use the manufactured sand as a replacement of natural sand in varying percentages (0%, 20%, 40%, 60%, 80% and 100%) which would be efficient in conserving the natural resources if adopted in the construction sector throughout the country and world. The 10% of silica fume was partially replaced with cement. Glenium B233 super plasticizer was added to 1.5% by weight of binder (cement & silica fume).

Cement
Portland cement 53 grade of specific gravity 3.15 were used. Table 1 illustrated the physical and chemical properties of cement.

Silica fume
Commercially available silica fume was named Elkem -Micro silica 920 D in dry densified form conforming the requirements of ASTM C1240[12] was used. Table 1 illustrated the properties of cement and silica fume.

Natural Sand
Locally available river sand was used and the specific gravity is 2.65. The bulk density is and Fineness modulus of river sand is 1726 kg/m 3 and 2.69 respectively.

Manufactured Sand
Manufactured Sand was collected from I Blue Minerals Pvt. Ltd. Karur, India and the bulk density is 1748 kg/m 3 . It has specific gravity and fineness modulus of 2.65 and 2.86 respectively. The test results from sieve analysis are presented in Table.2.

Coarse Aggregate
Coarse aggregate confirming to Indian standard 383 (1970) was used and it satisfied its requirement. Aggregate passing through 12.5 mm sieve, 10 mm sieve and 4.75 mm sieve was 90-100%, 40-80% and 0-10% respectively. The specific gravity of coarse aggregate is 2.71.

Super plasticizer
Glenium B233 was used as chemical admixture, poly-carboxylic ether based to improve the workability of concrete. The specific gravity of the superplasticizer is 1.09 .

Water
Fresh portable water, was used for mixing the concrete as it is free from acid and organic substance. Columns were cast using wooden moulds as per Figure 1. The concrete specimens cube and beams were cast using standard steel moulds. Cube of 100mm size of three numbers for compressive strength and beam of 100mm x 100mm x 500mm size three numbers for flexural strength were cast for each mix. The quantities of cement, fine aggregate, coarse aggregate, silica fume, M-Sand was measured and homogeneous mixing of the above is achieved by means of pan mixer. The W/B (Cement & Silica fume) was kept constant as 0.32 . The dosage of super plasticizer was used at 1.5% by weight of binder to get the workability of concrete. The concrete was compacted by needle vibrator. The specimens were de moulded after 24 hours from the moulds and were being cured with water for 28 days. . The columns ends were supported with rubber pads to get the hinged end condition. The column specimens were brought into the centre line of the axial load and was ensured that the load was applied axially with permissible eccentricity throughout the test . All the columns were tested for compression in a loading frame of capacity of 1000 kN. To measure the lateral deflection of the column LVDT were placed at mid-section of the column. Table.3. gives the variation of compressive strength and flexural strength at the age of 28 days.

Structural behavior of column
Comparison of load verses mid span deflection curves was presented in Figure 2.  From Table 4, it can be noted that the deflection is increasing linearly with the load. It is noticed that for control concrete mix M1, the first crack appears at a load of 170 kN and it does not appear for the optimum concrete mix M6 until 216kN. For the mix M1, the ultimate load carrying capacity of was 208 kN and for mixes with 10% silica fume, the ultimate load capacities were found to be  210kN, 222kN, 252kN , 255kN and 265 respectively for 20, 40, 60 and 100% of M-Sand. The capacities of mixes M2, M3, M4 and M5 increased about 1, 6, 21,23 and 27% respectively when compared to the M1 HPC mix. From the above observations, it is seen that the combination of 100% M-Sand and 10% silica fume replaced by fine aggregate and cement respectively. The load carrying capacity is found to be very high compared to M1 (about 20%) and the corresponding deflections are found to be lesser.

Conclusion
Based on the investigations, following conclusions can be made  By gradually increasing the percentage of M-Sand from 0 to 100% with 10% of silica fume the compressive strength and flexural strength of concrete increases.  The optimum percentage of 100% M-Sand replaces natural sand in presence of cement by 10% of silica fume for achieving maximum compressive and flexural strength.  The RC columns with M-Sand sustained more load under axial loading, and developed smaller deflections than the column with river sand.  The load carrying capacity is found to be 27% higher for the concrete made with 100% M-Sand and 10% silica fume is replaced with cement by comparing to column with natural sand.  Based on the test results, High Performance Concrete with silica fume and complete replacement of natural sand by M-Sand can be used in the construction industry to minimize the environmental pollution.