Combined Effect of Silica Fume and Saw Dust as a Partial Replacement of Cement in Concrete

Concrete is widely used as construction material for various types of structures the cost of construction materials like cement and reinforcement bars, has led to increased cost of construction. This, coupled with the pollution associated with cement production, has necessitated a search for an alternative binder which can be used sorely or in partial replacement of cement in concrete production. More so, disposal of waste materials such as rice husk, groundnut husk, corn cob and Saw Dust have constituted an environmental challenge, hence the need to convert them into useful materials to minimize their negative effect on the environment. Research indicates that most materials that are rich in amorphous silica can be used in partial replacement of cement. It has also been established that amorphous silica found in some pozzolanic materials reacts with lime more readily than those of crystalline form. Use of such pozzolanas can lead to increased compressive and flexural strengths.

Agricultural wastes Rice husk ash is a major agricultural product obtained from paddy. For every 40 kN of rice 10kN of husk is produced. The husk is disposed off either by dumping it in an open heap near the mill site or on the road side to be burnt later. Burning the rice husk generated about 15-20% of its weighing as ash.

The Bagasse Ash is the fibrous waste produced after the extraction of the sugar juice from cane. This material usually poses a disposal problem in sugar factories particularly in tropical countries. In many tropical countries there are substantial quantities of Bagasse (the fibrous residue from the crushing the sugar cane) and husks from rice both are rich in amorphous silica, which react with lime.

Groundnut shell is an agricultural waste obtained from milling of groundnut. The ash from groundnut shell has been categorized under pozzolana, with about 8.66% Calcium Oxide (CaO), 1.93% Iron Oxide (Fe2O3), 6.12% Magnesium Oxide (MgO), 15.92% Silicon Oxide (SiO2), and 6.73% Aluminum Oxide (Al2O3). The utilization of this pozzolana as a replacement for traditional stabilizers will go a long way in actualizing the dreams of most developing countries of scouting for cheap and readily available construction materials. Groundnut shell ash has been used in concrete as a partial replacement material for cement.

Sawdust Ash (SDA) generated from saw mills is usually delivered to landfills for disposal. Using of sawdust ash in concrete is an interesting possibility for economy on waste disposal sites and conservation of natural resources .This paper examines the possibility of using sawdust ash as replacement in cement for a new concrete. Cement was partially replaced (1%, 2% and 3%) with SDA.

Silica fume, also known as microsilica, (CAS number 69012-64-2, and EINECS number 273-761-1) 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. The main field of application is as pozzolanic material for high performance concrete.

In the present study we are partially replacing the cement by Saw Dust Ash (SDA) and silica fume for M20 Grade concrete in different percentages 0%, 1%, 2%, 3% of Saw Dust Ash and 5%, 10%, 15% of silica fume casted 30 no of cubes of 150mm x 150mm x 150mm and done comparative study on normal concrete and Saw Dust Ash + Silica Fume concrete.

The basic materials for mixing concrete are required such as 6. Cement 7. Fine aggregate 8. Coarse aggregate 10. Silica fume 11. Water Cement The cement used was OPC 53 grade cement. The different tests were conducted as per Indian Standards to determine the properties of this cement. For initial & final setting time IS: 8112-1989 is used and for standard consistency of cement IS: 4031(part-4) 1988. For specific gravity of cement (IS: 2720- part 3) is used. The Table 2.1 shows the results

Fine aggregate The sand is used as fine aggregate is used in the concrete. Various tests were conducted to determine the properties of fine aggregate which are shown in the Table 2.2. Grading is the particle- size distribution of an aggregate as determined by a sieve analysis. The tests were done according to IS: 2386 (Part-1) – 1963.

Aggregate is commonly considered inert filler, which accounts for 60 to 80 percent of the volume and 70 to 85 percent of the weight of concrete. Maximum size of aggregate affects the workability and strength of concrete. In this study the natural coarse aggregates are used, which was bought from the nearby quarry. Aggregates of 20 mm passed and 12.5 mm retained size were chosen for the experiment which is clean and free from deleterious materials. The following Table 2.3 shows the tests conducted in order to determine the properties of this aggregate.

Sawdust is a by-product from timber, it is a waste product obtained during sawing of timber into standard sizes. The sawdust was obtained from timber milling market (ogbosisi) Owerri. This material was first dried to remove the natural moisture. The waste was burnt in an enclosure (i.e. open drum) at temperature of about 400-500°C to obtain sawdust ash. The ash was allowed to cool; thereafter the ash was sieved with 150μm sieve aperture to obtain the finest particle of material which approximates to the fineness of that of cement used.

In the present study we are partially replacing the cement by saw dust ash and silica fume for M20 Grade concrete in different percentages 0%, 1%,2%, 3%, SDA and 5%,10%,15% casted 30 no of cubes of 150mm x 150mm x150mm.To achieve the objectives of the investigation the experimental program was planned to cast around 30 No of cubes. The compression testing machine and the tensile strength of specimens are determined.

Compressive strength test on cubes were carried out using the Universal Testing Machine (UTM). Compressive test were carried out on cubes of dimensions 150 × 150 × 150 mm after 7 days 14 and 28 days. For each test and for each mix three specimens were tested. The compressive strength was computed using the expression Fc= P/A for cubes, Where, Fc is the compressive stress in MPa. P is the maximum load applied in Newton and A is the cross sectional area in mm2. Standard cast iron moulds of size 150x150x150mm for cubes are used in the preparation of specimens. The experimental setup is shown in below figures.

Tensile strength is an important property of concrete because concrete structure are highly vulnerable to tensile cracking due to various kinds of effect and applied load itself, however tensile strength of concrete is very low compared to compressive strength of concrete.

From the tests conducted on SDA and silica fume replaced in cement for concrete as presented in various sections, the following conclusions are made.

• It is observed that for a given mix, the water requirement increases as the SDA content increases.

• The compressive strength of cubes of the concrete for all mix increases with age of curing SDA and silica fume is available in significant quantities as a waste and can be utilized for making concrete. This will go a long way to reduce the quantity of waste in our environment.

• The optimum replacement level in cement with SDA is 2% and Silica fume 10%. It gives maximum Strength of 14.02 N/mm2,19.86 N/mm2,24.33 N/mm2, for 7, 14, 28 days Respectively

• The tensile strength with replacement of cement with SDA is 2% and Silica fume 10%

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PG Student Structural Engineering, Sindhura College of Engineering & Tech, Ramagundam, Kaimnagar