Table of Contents
Silica fume is known to improve the mechanical characteristics of concrete. It is observed that the optimum dose of silica fume is 5% (by weight), when used as part replacement of OPC. The silica fume inclusion increases the workability and strength of concrete considerably.
Does silica decrease workability?
The results show that partial cement replacement up to 10% silica fume does not reduce the concrete workability. Silica fume at replacement contents up to 20% produce higher compressive strengths than control concretes; nevertheless, the strength gain is less than 15%.
How does silica fume affect workability?
Concrete. Workability: With the addition of silica fume, the slump loss with time is directly proportional to increase in the silica fume content due to the introduction of large surface area in the concrete mix by its addition. Although the slump decreases, the mix remains highly cohesive.
Does silica increase strength?
Silica fume has been successfully used to produce very high-strength, low-permeability, and chemically resistant concrete. Addition of silica fume by itself, with other factors being constant, increases the concrete strength.
Why does silica fume increase strength?
30% of cement replaced with silica fume has a higher strength than cement- silica fume paste with the same water- cementitious ratio. They concluded that the addition of silica fume to mortar resulted in an improved bond between the hydrated cement matrix and sand in the mix, hence increasing strength.
What are the disadvantages of high silica cement?
disadvantages of silica fume in concrete Silica fume concrete is too viscous and difficult to apply.it is not easy to wipe the surface. Silica fume requires a high amount of water and needs to be used with a superplasticizer. The price of silica fume is relatively high compared to cement and fly ash.
Is silica fume toxic?
Repeated exposure can damage the eyes. * High exposure to Silica, Amorphous (Fume) can cause a flu-like illness with headache, fever, chills, aches, chest tightness and cough. * Repeated exposure to Silica, Amorphous (Fume) can cause lung damage (fibrosis).
Is silica fume expensive?
Condensed silica fume costs from $400-$1,000/ton, which is significantly higher than portland cement ($90/ton).
Why do we add silica fume in concrete?
Condensed silica fume is a very fine, amorphous, and reactive mineral admixture. It reacts readily with the calcium hydroxide, which is produced during Portland cement hydration. Silica addition refines pore structure and produces concrete of improved mechanical strength.
Is silica fume A admixture?
Silica fume is a mineral admixture, composed of submicron particles (100 to 150 times smaller than a grain of cement) of amorphous silicon dioxide.
What is micro silica used for?
Several materials have recently been used for the improvement of concrete properties. Microsilica or silica fume is an excellent admixture for concrete as it leads to better engineering properties. It reduces thermal cracking, improves durability, and increases strength.
What does silica fume do?
Silica fume, a by-product of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. It may be added directly to concrete as an individual ingredient or in a blend of portland cement and silica fume.
Which is not pozzolanic material?
Which of the following is not a pozzolanic material? Explanation: Pozzolans are silicate based materials that form cementitious materials. Fly ash, silica fumes and slag are composed of oxide of silicon. Cinder is a coal residue.
What is the difference between fly ash and silica fume?
Silica Fume is typically much more reactive, particularly at early ages , because of its higher silicon dioxide content and because of its very small particle size. Disadvantages of Fly Ash: – High-carbon fly ash materials tend to use more water and darken the concrete as well.
Is silica present in concrete?
Crystalline silica is found in materials such as concrete, masonry and rock. Concrete and masonry products contain silica sand. Since concrete and masonry are primary building materials, there are numerous ways for construction workers to be exposed.
What is silica fume and how is it produced?
Silica fume is a by-product from the production of elemental silicon or alloys containing silicon in electric arc furnaces. At a temperature of approximately 2000°C the reduction of high-purity quartz to silicon produces silicon dioxide vapor, which oxidizes and condenses at low temperatures to produce silica fume.
What are the advantages of using fly ash in concrete?
Fly Ash has very small particles which makes the concrete highly dense and reduces the permeability of concrete. It can add greater strength to the building. The concrete mixture generates a very low heat of hydration which prevents thermal cracking. Fly Ash concrete is resistant to acid and sulphate attacks.
Which of the following grades is not ordinary concrete?
Hence, M40 grade of concrete is not used as ordinary concrete.
Is silica a carcinogen?
Silica, Crystalline (Respirable Size). NTP classification: Known to be a human carcinogen. International Agency for Research on Cancer (IARC) Monographs on the Evaluation of Carcinogenic Risks for Humans.
Is silica safe to eat?
According to the United States Department of Labor, about 2.3 million people in the U.S. are exposed to silica at work. As long as you aren’t inhaling silica in its crystalline form, it appears to be safe to consume at the levels set out by the FDA.
How much silica does it take to get silicosis?
Because silicosis is caused by cumulative or repeated exposure to respirable crystalline silica, it makes sense that we would want to limit exposure as much as possible! OSHA has set the Personal Exposure Limit (PEL) at 50 micrograms per cubic meter of air, averaged over an 8 hour shift.
What is the difference between silica fume and microsilica?
Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide(SiO2). Concrete containing silica fume can have very high strength and can be very durable. Micro Silica Fume or Microsilica is finer particle than Cement. It is produced by some chemical processing of the ash.
What is the price of silica?
Questions & Answers on Silica Sand Product Description Price 5kg bag Rs 23 10kg bag Rs 45 25kg bag Rs 106 50kg bag Rs 200.
Is silica a silicon dioxide?
Silicon dioxide (SiO2), also known as silica, is a natural compound made of two of the earth’s most abundant materials: silicon (Si) and oxygen (O2). Silicon dioxide is most often recognized in the form of quartz. It makes up more than 95 percent of known rocks on the planet.
