Micro-silica, Nano-silica, mortar, concrete, compressive strength.
|PUBLISHED DATE||December 2013|
|PUBLISHER||The Author(s) 2013. This article is published with open access at www.chitkara.edu.in/publications|
This paper reviews the recent developments and present state of the application of silica fume (micro-silica) and nano-silica for sustainable development of concrete industry. This would save not only the natural resources and energy but also protect the environment with the reduction of waste material. Limited work is done on use of nano-silica and microsilica in paste, mortar and concrete and whatever work is available is highly contradictory about their influence on mechanical strength development and durability properties. Various literatures have been reviewed to understand the influence of micro and nano-silica on fresh, hardened and microstructural properties of paste, cement mortar and concrete. Taking advantage of nanostructure and microstructure characterization tools and materials, the simultaneous and also separate optimal use of micro-silica and nano-silica will create a new concrete mixture that will result in long lasting concrete structures in the future.
In the most customary sense, cement is a binder that sets and hardens independently as well as binds other materials together. Cement mortar is a building compound created by mixing fine aggregate and a selection of cementing material with a specified amount of water. Mortar has been used for centuries as a means of adhering bricks or concrete blocks to one another. Cement mortar continues to be used in many different types of construction such as the binder between bricks in walls, fences, and walkways, to make quick repairs in patio slabs and reset loosened stones or bricks in a walkway or retaining wall. Unfortunately, construction industry is not only one of the largest consumers of natural resources and energy, but is also responsible for large emissions of green house gases (GHGs) such as carbon dioxide responsible for global warming. It is estimated that one ton of Portland cement clinker production yields one ton of GHGs. In addition, due to the accumulation of natural aggregate extraction from quarries; it poses an immediate concern for sustainable construction development.
1.1 Concrete and Sustainability
Concrete is probably unique in construction, it is the only material exclusive to the business and therefore is the beneficiary of a fair proportion of the research and development money from industry. Concrete is a composite construction material composed primarily of aggregate, cement, and water, which is a nanostructured, complex, multi-phase material that ages over time. Sustainability is defined by the World Commission on Environment and Development as the development that meets the needs of the present, without compromising the ability of the future generations to meet their own needs. It is basically an idea for concern for the well being of planet Earth with continued growth and human development. The current construction practices are based on the consumption of enormous quantities of building materials and drinking water, resulting in the scarcity of these resources after a long turn. The sustainable development of the cement mortar would save not only the natural resources and energy but also protect the environment with the reduction of waste material. The mortar properties in fresh state such as workability are governed by the particle size distribution and the properties in hardened state, such as strength and durability, are affected by the mix grading and resulting particle packing. Rheological properties of a fresh cement paste play an important role in determining the workability of concrete. The water requirement for flow, hydration behavior, and properties of the hardened state largely depends upon the degree of dispersion of cement in water. Factors such as water content, early hydration, water reducing admixtures and mineral admixtures like silica fume determine the degree of flocculation in a cement paste (Sanchez and Sobolev, 2010).
1.2 Nanotechnology in Concrete
Nanotechnology is rapidly becoming the Industrial Revolution of 21st century (Siegel et al., 1999). It will affect almost every aspect of one’s life (IWGN, 1999). In comparison to other technologies, nanotechnology is much less welldefined and well-structured. It is known that ‘Nano’ is a Greek word and means ‘dwarf’. It does not mean dealing with dwarfs but it became a common word for everything which is smaller than 1 Micron or 1 million of a millimeter. 1 Micron is 1000 Nanometer. The nanoscience and nano-engineering (nanomodification) of concrete are terms that have come into common usage and describe two main approaches of applications of nanotechnology in concrete (Scrivener and Kirkpatrick, 2008; Scrivener, 2009). Until today, concrete has primarily been seen as a structural material. Nanotechnology is helping to make it a multipurpose ‘‘smart’’ functional material. Concrete can be nano-engineered by the incorporation of nano-sized building blocks or objects e.g., nanoparticles, nano admixtures and nanotubes) to control material behavior and add trailblazing properties, or by the grafting of molecules onto the cement particles, cement phases, aggregates, and additives (including nano-sized additives) to provide the surface functionality adjusted to promote the specific interfacial interactions of the molecules. Recently, nanotechnology is being used in many applications and it has received increasing attention also in building materials, with potential advantages and drawbacks being underlined (Campillo et al., 2003; Pacheco-Torgal and Jalali, 2011).
1.3 Silica fume Silica
is the common name for materials composed of silicon dioxide (SiO2) and occurs in crystalline and amorphous forms. Silica fume or micro-silica (SF) is a byproduct of the smelting process in the silicon and ferrosilicon industry. The American concrete institute defines silica fume as ‘Very fine noncrystalline silica produced in electric arc furnaces as a by-product of production of elemental silicon or alloys containing silicon’ (ACI Committee 226., 1987b). It is a grey colored powder, similar to Portland cement or fly ashes. 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 size (diameter) of 150 nm. The main field of application is as pozzolanic material for high performance concrete (Prasad et al., 2003).
1.4 Nano-silica Nanosilica
is typically a highly effective pozzolanic material. It normally consists of very fine vitreous particles approximately 1000 times smaller than the average cement particles. It has proven to be an excellent admixture for cement to improve strength and durability and decrease permeability (Loland, 1981; Aitcin et al., 1981). NS reduces the setting time and increases the strength (compressive, tensile) of resulting cement in relation with other silica components that were tested (Roddy et al., 2008). Nano-silica is obtained by direct synthesis of silica sol or by crystallization of nano-sized crystals of quartz.
|ISSN||Print : 2321-3906, Online : 2321-7146|
Nanotechnology has the potential to be the key to a brand new world in the field of construction and building materials. The role and application of the nano and micro silica particles with cementitious materials have been reviewed and discussed in details. It is evident from the literatures reviewed that none of the researchers have carried out extensive or comprehensive study of the properties of paste and mortar, with nano silica, micro silica and their simultaneous use. There is a limited knowledge about the mechanisms by which nano silica & micro silica affects the flow properties of cementitious mixes. In India, the research work on use of nano silica is still in elementary stage. Thus, a need arises to study extensively the various properties of paste, mortar, and concrete containing various percentages of nano silica, micro silica alone as partial replacement of cement and then studying their combined percentage effects. As the properties of nano-silica and micro-silica reported in literatures relate with those manufactured or exported from abroad, there is urgent need to study the effect of these materials (manufactured in India) on various properties of cement paste, mortar and concrete. Major parties in the construction materials industry should divert more funds to research work on incorporating nanotechnology in construction materials.
Thus, the main motive is to provide practical information, regarding the strength, sustainability & durability properties of nano silica, micro-silica and their simultaneous use in paste, mortar and concrete. Also, the aim is to carry out the extensive studies to conceive the general purpose of testing new sustainable building processes and modern production systems, aimed at saving natural raw materials and reducing energy consumption. Taking advantage of nanostructure and microstructure characterization tools and materials, the simultaneous and also separate optimal use of micro-silica and nano-silica will create a new concrete mixture that will result in long lasting concrete structures in the future. Thus, there is a gap or room available for further research towards the fruitful application of especially nano-silica for construction with different nano structure characterization tools, which will be enable to understand many mysteries of concrete.