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Full Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012

Influence of Silica Fume on Strength Characteristics of Fly Ash Alumino Silicate Concrete R.Gopalakrishnan1 and K .Chinnaraju2 1

Asst.Professor, Department of Civil Engineering, Sri Venkateswara College of Engineering, Sriperumbudur- 602 105, India. E-mail: rajagopalan.gopalakrishnan0@gmail.com,1 2 Associate Professor, Division of Structural Engineering, Anna University, Chennai-25, India. geological origin or by product material such as fly ash. In terms of reducing global warming, geo polymer technology could reduce approximately 80% of CO2 emission to the atmosphere caused by cement and aggregate industry [3] compared with ordinary Portland cement concrete, geo polymers show many advantages. Geo polymers show substantially superior resistance to fire [4] and acid attack [5] and much less shrinkage than OPC Concrete. Geo polymer concrete can obtain 70% of the final compressive strength in the first four hours of setting. The compressive strength after 14 days was found in the range of 5-50 MPa. [6] The tensile strength of geo polymer concrete falls within the range observed for OPC based concrete. Also, the flexural strengths are generally higher than the standard model line for OPC based concrete. This favourable behaviour can be attributed to the type of matrix formation in geo polymer concrete.[7] It has been reported that the stress strain relationship of fly ash based geo polymer concrete is almost similar to that of ordinary Portland cement concrete.[8). These advantages make the geo polymer concrete a strong alternative for replacing ordinary Portland cement concrete. Fresh concrete made with silica fume is more cohesive and therefore less prone to segregation than concrete without silica fume. The main benefit from increased cohesion can be seen in shot Crete whether it is for new construction, repair of existing structures or ground support in tunnelling operations. Because of the very high surface area of the silica fume and the usually very low water content of silica fume concrete, there will be very little, if any bleeding. Silica fume gained initial attention in the concrete market place because of its ability to produce concrete with very high compressive strength. Improvements in other mechanical properties such as modulus of elasticity or flexural strength are also seen. This paper presents the results of an experimental investigation on strength characteristics of geo polymer concrete prepared by using fly ash and NaOH and Na2Sio3 as alkaline liquid which was taken as activator and a partial replacement to fly ash by Silica fume(Micro silica) with various percentages were investigated.

Abstract - The consumption of Ordinary Portland cement (OPC) caused pollution to the environment due to the emission of CO 2. As such, alternative material had been introduced to replace OPC in the concrete. Fly ash is a by-product from the coal industry, which is widely available in the world. Moreover, the use of fly ash is environmental friendly and save cost compared to OPC. Fly ash is rich in silicate and alumina, hence it reacts with alkaline solution to produce alumina silicate gel that binds the aggregate to produce a good concrete. The compressive strength increases with the increasing of fly ash fineness and thus the reduction in porosity can be obtained. Fly ash based geo polymer also provided better resistance against aggressive environment and elevated temperature compared to normal concrete. In this present investigation the strength properties of different concentration of molarity of fly ash- geo polymer concrete by partially replacing fly ash by Silica fume was studied. It is concluded that higher concentration of molarity and a partial replacement of silica fume to the fly ash increases the Compressive Strength and Tensile strength of geo polymer concrete. Index terms - Fly ash, silica fume, geo polymer, alkaline solution, Compressive strength, Tensile strength

I. INTRODUCTION Demand for concrete as construction material is on the increase so as the production of cement. The production of cement is increasing about 3% annually. [1] Among the green house gases CO2 contributes about 65%of global warming. The production of one ton of cement liberates about one ton of CO2 to atmosphere. Furthermore, it has been reported that the durability of ordinary Portland cement concrete is under examination, as many concrete structures, especially built in corrosive environments start to deteriorate after 20 to 30 years, even though they have been designed for more than 50 years of service life. Although the use of Portland cement is unavoidable in the foreseeable future, many efforts being made to reduce the use of Portland cement in Concrete. In this respect geo polymer is very promising technique.The term Geo polymer describes a family of mineral binders with chemical composition same as Zeolite. Hardened geo polymer concrete has an amorphous microstructure [2] which is quite similar to that of ancient structures such as Egyptian pyramids and Roman amphitheatres. Geo polymer is produced by a polymeric reaction of alkaline liquid with source material of

II. E XPERIMENTAL PROGRAMME The experiments were carried out using two different concentrations of NaOH solution. In the fly ash-geo polymer concrete, the fly ash was replaced by silica fume at the rate of 20 and 40%. Compressive strength and Tensile strength were

1

Assistant Professor and Cu rrently Research Schola r @ Anna University, Chennai (corresponding author). E-mail: rajagopalan.gopalakrishnan0@gmail.com

Š 2012 ACEE DOI: 02.AETACE.2012.3.505

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