Experimental Study on Partial Replacement of Cement by Silica Fume with Glass Fiber in M25 Grade Concrete

Concrete is one of the most versatile building materials. It can be cast to fit any structural shape from a cylindrical water storage tank to be rectangular beam or column in a high-rise building. Conventional concrete is composed of aggregates (sand, gravel), cement, water and admixtures where it is necessary. Concrete with a uniform structure, good plasticity and the ability of deformation by form, sound and thermal insulation and the capability of quality development by admixtures, is getting more and more popular in structural industries every day. Considering all the concrete benefits, we cannot deny its weaknesses. The first fundamental problem of concrete is low tensile strength which is approximately 10%-15% of its compressive strength nevertheless this crucial problem can be solved by the reinforcement. In addition, reinforcement must be calculated to prevent brittle failure in order to have plastic behavior; the maximum standards must be respected to prevent corrosion of reinforcement. The advantages of using concrete include high compressive strength, good fire resistance, high water resistance, low maintenance, and long service life. The major disadvantage is that concrete develops micro cracks during curing. It is the rapid propagation of these micro cracks under applied stress that is responsible for the low tensile strength of the

overcome these disadvantages. The initial interest in the use of silica fume was mainly caused by the strict enforcement of air-pollution control measures in various countries to stop release of the material into the atmosphere. Silica fume is a pozzolanic material which is a by-product of the silicon smelting process. Silica fume is known to produce a high strength concrete and is used in two different ways: as a cement replacement, in order to reduce the cement content and as an additive to improve concrete properties. Therefore, utilization of silica fume together with glass fiber provides an interesting alternative and can be termed as high strength concrete. The use of fiber in concrete increases the mechanical properties such as compressive strength. It also possesses the ability to reduce plastic shrinkage in concrete.

Silica fume, also known as microsilica is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm.

2.3 Fine aggregate

Glass Fiber available in the market was used in this experimentation. The length of the fiber is 6mm and the diameter of 14μ.

2.5 Coarse aggregate The coarse aggregate of 20 mm size was used. Test results listed below conforming IS: 383-1970(Part-3).

In this study, silica fume was used to replace OPC 53 of M25 grade cement at various levels of 5%, 10% and 15% and the glass fiber of 1%, 2% and 3% were used with water cement (W/C) ratio 0.5.

Initially the dry materials cement, aggregate, & sand are mixed. The liquid component of the mixture was then added to the dry materials and mixing continued for further about 3-6 minutes t manufacture the fresh concrete. The fresh concrete was cast into the moulds immediately after mixing, in three layers for cube specimens. For compaction of the specimens each layer was given 60-70 manual strokes using a tapping rod, and then vibrated for 12-15 seconds on a vibrating table. Before the fresh concrete was cast into the observed.

After completion of casting process wait for 24 hours and open the moulds, take the blocks and dry it for 1-2 hours. Then after take Portable water free from impurities and salt used for curing the concrete blocks for 7, 14 and 28 days.

4. TESTING PROCEDURE

An intensive experimental program is performed to study the effect of internal curing on different types of concrete properties 1. Fresh properties(slump, compaction factor) 2. Mechanical properties like compressive strength.

The cubes were tested under 200 tons compression testing machine to study the compressive strength of the cubes.

At the time of testing, each specimen must keep in compressive testing machine. Size of the test specimen is 150mm*150mm*150mm. The maximum load at breakage of concrete block has been observed. From the observed values the compressive strength has been calculated by using formula

Ratio for special concrete and compressive strength of concrete listed in table no.7.

• With the increase of percentage of Silica Fume and Glass Fiber by weight of Cement, the strength of the Concrete increases.

• Cracks could be controlled with addition of glass fiber within the optimum dosage. Excessive addition i.e., greater than 2% of glass fiber leads to crack due to the presence of voids in concrete.

• The percentage increase in compressive strength at 7 days, 14 days and 28 days of 10% silica fume with 2% glass fiber are 22.98 N/mm2, 26.47 N/mm2 and 29.42 N/mm2 over control specimen without silica fume and glass fiber is 20.82%.

• Glass fiber also helps in controlling shrinkage cracks and silica fume helps in achieving early strength gaining property.

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B. Tech, Final Year Students, Department of Civil Engineering, Vivekananda Institute of Technology & Science, Karimnagar