Relevance of rice husk ash for the sustainability of construction industry

Rice husk ash (RHA), used as a pozzolanic admixture in cement and concrete, is obtained from the combustion of rice husk (RH) under certain conditions of the surrounding environment, temperature and residence time in a combustor, and subsequent size reduction. It contains low unburned carbon, and silica is mostly in amorphous form. RHA manufactured in the modern fluidized or cyclonic bed reactors has high surface area of the order of 20–40 m²/g, comparable with that of silica fume (SF).

It is a material with proven pozzolanic characteristics and is added to cement and concrete as a partial replacement of Portland cement. However, its application has not been widely commercialized as yet, mainly on account of the non-availability of RHA of the desired pozzolanic characteristics on a large scale on the one hand and the lack of awareness about the potential for RHA as a mineral admixture on the other.

The RH produced in farms and rice mills is conventionally employed as a fuel or dumped as waste. Many researchers found that the use of properly manufactured and treated RHA improves the performance and the durability of concrete.

RHA possesses the potential to replace SF in high-strength and high-performance concrete. RHA manufactured through controlled burning of RH shows performance comparable with that of SF, when added to concrete in binary (Portland cement [PC] + RHA) or tertiary (PC + RHA + FA) blends, in terms of strength and reduced permeability toward the external deteriorating agents.

The major characteristics of RHA are its high water demand and coarseness in comparison to SF. In order to improve these characteristics, RHA needs to be ground finer into particle size range of 4–8 μm (1 μm = 10^-6 m) and a superplasticizer is added to reduce water requirement.

RH is presently considered as an agricultural waste and used as fuel, as mentioned earlier, where its pozzolanic value lies unutilized. Thus, the incorporation of RHA in concrete as a mineral admixture adds value, both from the economical and ecological point of view.

Rice, produced from paddy, is a cereal grain and the most important staple food for a large part of the world’s human population, especially in tropical Latin America, the West Indies, and east, south, and southeast Asia.

According to one estimate, the world paddy production is expected to touch 847–915 × 10⁶  ton by the year 2030, from the current (2008) level of 683 × 10⁶  ton; out of which around 600–774 × 10⁶  ton paddy and from that around 120–155 × 10⁶  ton RH shall be produced in the Asian countries. The abundant availability of RH in the rice producing countries  provides us a huge scope to recover its heat value to generate power and to use the RHA produced in cement and concrete on a large scale.

The production of RHA with cogeneration of power as well as its application in cement and concrete, both contribute toward the reduction of green house gas (GHG) emissions. It is found that the generation of power through the combustion of RH reduces carbon emissions, in comparison to coal, oil, and natural gas.

RHA is added to cement and concrete as a partial replacement of cement to the extent of 30%. Thus, it reduces the consumption of PC and to that extent contributes toward the reduction of CO2 emission, which is a GHG, in the manufacture of PC.

The reduction of GHG through such practices has been provided with incentives under the United Nations (UN) framework. The Kyoto Protocol is part of the United Nations Framework Convention on Climate Change (UNFCCC) and has set an agenda for reducing global GHG emissions. If CO2 emissions can be shown and verified to be reduced due to different practices, then Certified Emission Reductions (CERs) are issued under the Clean Development Mechanism (CDM) of UNFCCC. These CERs are tradable in the primary and secondary market and generate revenue for the CERs holding party. The readers are advised to go through the UNFCCC documents to obtain more information on the subject.  When RHA is used in cement and concrete manufacture as a cement substitute, there is potential to earn CERs.

There are other environmental benefits of substituting Portland cement with RHA. The need for quarrying and mining primary raw materials and fuel is reduced, namely, limestone, clay, and coal, and thus overall reduction in emissions of dust, CO2, and acid gases is attained. As the cement and concrete industry uses RHA with amorphous silica, the health issues, mainly associated with the fine crystalline silica, are minimal.

The large-scale application of RHA in the construction industry requires industrial and economic policy planning and efforts in the following areas:

a) Creation of general awareness about the benefits of using RH in power generation and RHA in cement and concrete. In India, the government took lead promoting the utilization of pulverized fuel ash (PFA) in cement and concrete, through the Fly Ash Mission. It is time that similar missions are taken up to create awareness about

the less known mineral admixtures, such as RHA.

b) RH is produced by the farmers in their paddy fields. The RHA producing unit will require continuous supply and adequate storage of RH. Thus, a viable method of collection and transportation of RH from the paddy fields to the RHA producing unit will have to be put in practice.

c) Identification of a techno-economically feasible method to produce and process RHA along with the cogeneration of power to suit the local conditions.

d) Formulation of national Standards on the quality assessment and the use of RHA in cement and concrete.

In summary, the application of RHA in the construction industry shows tremendous potential for the rice-producing countries, both from the point of view of promoting the sustainable development of construction industry and as a valuable input for the economic growth of these countries.

Ref: “Mineral Admixtures in Cement and Concrete”, CRC Press (http://www.crcpress.com/product/isbn/9781439817926). Author: Dr J D Bapat (http://www.drjdbapat.com)

Written for engineers, book focuses on making more workable and durable concrete using mineral admixtures. For each mineral admixture, book looks at manufacturing and processing, physical characteristics, chemical and mineralogical composition, quality control, and reported experiences. It also examines the provisions of national standards.It encourages engineers to more effectively use these and other wastes in cement and concrete to support more sustainable growth of industry. Buy this book online to obtain 20 % discount and free shipping. Download details: http://bit.ly/online_purchase

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Recycled plastic bridge: sustainable! truly!!

An innovative new construction project has seen Wales achieve a European first in the construction sector.

A 90-foot thermoplastic bridge - made entirely from recycled materials - has been used to span the River Tweed at Easter Dawyck in Peeblesshire.

The bridge, which is made 100 per cent from re-used plastic weighs 50 tonnes and is capable of supporting traffic.

Vertech, which was responsible for the technology that underpins the project and managing subcontractors, said that the unique approach makes for maintenance-free, sustainable construction.

Recycled plastic bridge

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Green Bridge

The Tennant Avenue Bridge is a typical overpass that one may see throughout the United States. Its construction wasn’t unique; that is, no changes were made to its construction schedule to compensate for the reduced carbon footprint. The carbon footprint was reduced 25% compared to traditional mixes and may well have been further reduced. The specifications by which the concrete mixes were allowed to be used represent a dramatic change that provides a glimpse into the future sustainable design and construction of the infrastructure

The Tennant Avenue Bridge

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Energy efficiency in buildings and cities

Sustainable energy consumption, the use of renewable energies, energy efficiency and the reduction of CO₂ emissions are the current challenges that cities and communities must overcome if they want to achieve the ambitious energy and climate targets if they want to achieve the set out by the EU in their EU 2020 strategy. By the year 2020, the European Commission wants to cut CO₂ emissions by 20 per cent, increase the share of renewable energies to 20 per cent and improve energy efficiency by 20 per cent.

Under the CONCERTO project, a total of 1,830000 square metres of building space has been newly constructed or renovated to date, delivering a saving of 530,000 tons of CO₂. All projects share a common goal: to reduce CO₂ emissions in the most cost-effective manner while at the same time improving quality of life in the urban environment.

The monitoring of technological data, the evaluation of demonstration projects, the transfer of knowledge and the information campaign will be conducted over the next two years by Steinbeis-Europa-Zentrum (SEZ) and the Karlsruhe Institute of Technology (KIT). The analysis of the projects and the experience gained from them form the basis for future urban development projects, particularly for future projects of the EU's Smart Cities and Communities Initiative.

Ref: Karlsruhe Institute of Technology (2011, September 28). Energy efficiency in building and cities. ScienceDaily. Retrieved September 29, 2011

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Characteristics of sustainable construction

"Sustainable development" meets the needs of the present without compromising the ability of future generations to meet their own needs. Such development requires the selection and judicious application of materials that minimize the social, environmental, and economic impact of development. "Sustainable construction materials" could thus be defined as materials that support sustainable development and are characterized as being environmentally friendly. Some characteristics of sustainable construction materials include:

• Durability
• Local or regional extraction and production to minimize transportation needs
• Contains recycled materials
• Manufactured with little or no pollution or does not itself pollute
• Minimum amount of energy required to produce
• Reusable on projects
• Rapidly renewable
• Capable of being used in an innovative way to lessen social, environmental and economic impacts.

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Green Buildings Economy:

Prima facie, green buildings cost more. However between three to five years, unlike a normal construction, a green building actually starts giving you returns. Since a green building conserves energy and also makes the most of sunlight the energy costs are slashed by 40 to 50 per cent. A US study, for example, found that certified green buildings cost 1.8% more to design and construct, but yield 20% cost savings over the life of the building. However the obstacles to achieving these benefits in the fragmented property sector are also well documented. The sustainable building design, green materials and green technology are often more expensive than normal building blocks and are often not easily available but the upside monetary advantages more than compensate for that. These buildings are also eligible for carbon credits, since they save the environment from carbon-dioxide emissions. That opens up another revenue stream for the developer. It is therefore no surprise that the projected growth potential for green buildings in India is Rs 2,000 crores.

The financial barriers, including high initial cost barriers and an inadequacy of traditional financing instruments, are a key element preventing private actors from engaging further towards making the residential building sector more energy efficient, according to a study from the International Energy Agency (IEA). Despite the proven cost-effectiveness of energy-efficient technologies, their potential remains untapped in the building sector "due to numerous market barriers", states the IEA, based on the results of case studies of the residential sector in France, Germany, the UK, Japan and the US.

The green buildings are important for India. In spite of India's per capita consumption of energy being far lower than western economies, it's building sector has climbed to an usage of nearly 30 percent energy, up from a low 14 percent in the 1970s. India's energy conservation laws for buildings are voluntary but this is one area in which the country is already greener than in many parts of the developed world. According to the Indian Green Building Council (IGBC) set up in 2000, the country's modest 25,000 square feet of green buildings in 2003 have grown to a phenomenal 25 million sq.ft in just 4 years, projected to grow to one billion sq. ft per year by 2010. One of the reasons for this rapid growth is India's high economic growth and emerging status as the global business giant, resulting in imminent demand for commercial, infrastructural and residential construction. The country seconds China in its growth and demand of infrastructural development. The IGBC's standard of green buildings is based on the U.S.' Leadership in Energy and Environmental Design (LEED). The savings in cost of energy and water alone are attracting more commercial builders into the IGBC

Condition air with tinted windows:

A new product may soon emerge from the race to create better materials for green building. Sage Electrochromics, based in Faribault, Minnesota, recently raised $20 million from investors to continue its development of tinted windows, which automatically shift from light to dark as environmental conditions change.

The electrochromic windows and skylights sense the change in surrounding temperature and respond accordingly to save energy. If it is warm, the windows darken to keep the building cool. When it is cool, the windows appear clear again. The technology aims to reduce the need for air conditioning, which is notoriously energy-inefficient and increasingly costly.

The windows are undeniably cool. But, as this article notes, the high-tech electrochromic windows may find it difficult to compete with other lower-tech, less expensive solutions already on the market:

Other companies, such as Denmark's PhotoSolar, make windows that block solar heat with a simple passive film inserted between two sheets of glass. The windows have a permanent, gray tint to them, but you can still see out of them. More importantly, they don not require any electronics or controls.