They are available with different silicon dioxide concentrations depending on the purity of the silicon metal being produced. It would be convenient if silica fumes are integrated to the cement mixtures. Studies have shown that silica fumes strengthen concrete structures. This experiment aimed to determine establish the effect of replacing percentages of cement with silica fume.
The main objective of this experiment is to determine the effect of the utilization of silica fume in the production of Portland cement.
This experiment specifically aims to:
1. produce three concrete mixes. Mix 1, Mix 2A and Mix 2B containing 0, 5, and 10% silica fume respectively.
2. and test the fabricated mixes in terms of slump test, maximum load, flexural strength, stress test, and compressive strength under European standards.
Review of Related Literature
Silica fumes are by-product of the manufacture of silicon metals or ferrosilicon alloys (Dunster 2009). It is called various names such as silica dust and microsilica (Kuennen 1996). This is because it consists of very fine spherical glassy particles. Its silicon dioxide content ranges from 61 to 98 percent depending on the silicon purity of the metal from which production the silica fumes are collected (ACI Committee 2000). Silica fume was first characterized in the 1950s. It was discovered to be harmful to the environment in the 1970s (Dunster 2009). Because of this, it has been a concern to use it instead of releasing it as an air-pollution. Silica fumes are lighter that cement, having density of about 2200 kg/m3 while that of the latter is 3100 kg/m3. Its surface area ranges from 13,000 to 30,000 m2/ kg while that of cement is 300 to 400 m2/ kg (ACI Committee 2000). Because of these properties, silica fume particles pack in between larger cement particle which enhances mechanical performance and chemical resistance of concrete. For example, silica fume decreases chloride penetration of concrete (Kuennen 1996). This property makes it suitable construction material for bridges, decks and other specialized structures since it reduces harmful effects of chloride in salt water, other chemicals and abrasions. In general, hardened silica fume concrete has lower permeability, improved durability, greater resistance to abrasion and impact, higher flexural strength, compressive strength and modulus of elasticity. Silica fume can also be added to concretes containing micro-fibers for explosive applications such as those involving exposure to fire (Dunster 2009). Studies show that the higher the silicon dioxide content of silica fumes, the more reactive it is with concrete (ACI Committee 2000). Materials and Equipment Raw Materials The raw materials used for this experiment were CEM 1 Portland cement, coarse aggregate, silica fume and water. Slump Test (British Standard Institution 2009) Most important equipment for the slump test was the mould. It was made of metal so it would not be readily attacked by cement paste. Its wall was at least 1.5mm thick. It was also smooth and free from projections and dents as required by the standard procedure. Its shape was a hollow frustum of a cone with base diameter of 200 mm, top diameter of 100 mm and height of 300 mm. The base and top were both right angles to the axis such that both were perfectly horizontal and parallel to each other. It had a base that it can be securely clamped to and two handles near the top. A compacting rod was also used in the experiment. It was straight and made of steel with a diameter of 16 mm and length of 600 mm. It was a straight rod with rounded ends. A square-mouthed shovel and a container were used for the remixing of sample before filling of mould. As required, the container was a flat tray made of a non-absorbent rigid material. A