The Role of Natural Pozzolans in Sandcrete Performance

Chapter One Of The Role of Natural Pozzolans in Sandcrete Performance

INTRODUCTION

BACKGROUND STUDY

Various research works have been carried out on the binary blends of ordinary Portland cement with different pozzolans in making cement composites.

The need to reduce the high cost of Ordinary Portland Cement in order to provide accommodation for the populace has intensified research into the use of some locally available materials that could be used as partial replacement for Ordinary Portland Cement (OPC). Supplementary cementitous materials have been proven to be effective in meeting most of the requirements of durable concrete and blended cements are now used in many parts of the world (Bakar 2010).

The cost of building materials nowadays is so high in some parts of the world particularly developing countries like Nigeria, that only the government, industries, business cooperation and few individual can afford it. This high and still rising cost can however be reduced to a minimum by use of alternative building materials that are cheap, locally available and bring about a reduction in the overall dead weight of the building. Some industrial and agricultural products that would otherwise litter the environment as waste or at best be put into only limited use could gainfully be employed as building material (Oluremi 1990).

Rice husk which is an agricultural by–product is abundantly available all over the world. Most of the rice husk, which is obtained by milling paddy, is going as waste materials even though some quantity is used as bedding material, fuel in boilers etc. its ash, which not only occupy large areas causing space problems, but also cause environmental pollution. Thus the concrete industry offers an ideal method to integrate and utilize a number of waste materials, which are socially acceptable, easily available, and economically within the buying powers of an ordinary man. Presence of such materials in cement concrete not only reduces the carbon dioxide emission, but also imparts significant improvement in workability and durability. In the present investigation, a feasibility study is made to use Rice Husk Ash as an admixture to already replaced Cement (Portland Pozzolana Cement) in Concrete.

With increasing industrialization, the industrial by-product (waste) are being accumulated to a large extent leading to environmental and economic concerns related to this disposal. The concerns of our global environment and increasing energy insecurity has led to an increasing demand in renewable energy and their sources among the resources, biomass resources (forestry and agricultural wastes) and power fuelled by them as a promising source of renewable energy with economically low operational cost.

Rice Husk Ash (RHA) which is an agricultural by-product has been reported to be a good pozzolan by numerous researchers. Sandcrete blocks comprise of natural sand, water and binder. Cement, as a binder, is the most expensive input in to the production of sandcrete blocks. This has necessitated producers of sandcrete blocks to produce blocks with low OPC content that will be affordable to people and with much gain. The poverty level amongst West African Countries and particularly Nigerian has made these blocks widely acceptable among the populace so as to minimize the cost of construction works. The improper use of these blocks leads to microcracks on the walls after construction. The use of alternative cheaper local materials as stabilizer will greatly enhance the production of sandcrete blocks with the desired properties at low cost. It will also drastically reduce the cost of production and consequently the cost of construction works (Cordeiro 2009).

A survey by raw materials research and development Council of Nigeria on available local building materials reveals that certain building materials deserve serious consideration as substitute for imported ones. Few of these materials includes: cement / lime stabilized bricks /blocks, sundried (Adobe) soil blocks, burnt clay bricks/ blocks, cast in-situ walls, rice husk ash (RHA), mud and straw, lime and sandcrete blocks.

In the urban and rural areas of Nigeria, local milling is being done mostly by women. They mainly use firewood as heat source and as such one hundred percent of the rice husk from the mill is a waste. It occupies 20 –24% of the rough rice produced, although the ratio differs by variety. About 108 tonnes of rice husks are generated annually in the world.

In Niger State in Nigeria, about 96,660 tonnes of rice grains were produced in year 2000. In developing countries like Nigeria, proper utilization of agricultural waste has not been given due attention. The rice husk thereby constitutes an environmental nuisance as they form refuse heaps in the areas where they are disposed. The use of rice husk ash as a partial replacement to cement will provide an economic use of the by – product and consequently produce cheaper blocks for low cost buildings.

Rice is a major food crop in many regions of the world. Global rice production in 2007 was approximately 638 million tonnes and Malaysia’s contribution was 2.2 million tonnes [Food and Agriculture Organisation for the UN, 2008]. Due to global demand, rice production is expected to grow from year to year. Rice husk (RH) is the outer covering of the rice grain and is obtained during the milling process. Rice Husk constitutes 20% of the total rice produced [G. Giaccio 2007].

As a renewable material, the use of Rice Husk can eliminate waste disposal and support environmental protection. Even though Malaysia is not a prominent rice-producing country, large quantities of Rice Husk are produced every year after the harvest season (November to March). Commercially, other applications of Rice Husk are as silicon carbide whiskers to reinforce ceramic cutting tools and as aggregates and fillers for concrete and board production. However, most of this agricultural by-product is simply disposed, thus representing an environmental problem.

Rice hulls (or rice husks) are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material (Wikipedia.com).

The phenomenal pace of population growth and urbanization drives the cement requirement to many folds. The quantum jump in production of cement results in alarming level release of CO₂ to the atmosphere. One way of addressing this issue is to reduce the CO₂ emission from cement manufacturing process by replacing cement with locally available by-products which are pozzolanic in nature.

Pozzolan is a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (Mehta, 1987).

Also, the high cost of cement used as binder in the production of mortar, sandcrete blocks and concrete has led to a search for alternative. In addition to cost, high energy demand and emission of CO₂ this is responsible for global warming. The depletion of limestone deposits are disadvantages associated with cement product.

Research on alternative to cement has so far centred on the partial replacement of cement with different materials.

Rice Hull (or Husk) Ash as a Pozzolan

Rice hulls (or rice husks) are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material, or fuel (Wikipedia.com).

Production

Rice hulls are the coatings of seeds, or grains, of rice. To protect the seed during the growing season, the hull is formed from hard materials. The hull is mostly indigestible to humans.

Winnowing, used to separate the rice from hulls is to put the whole rice into a pan and throw it into the air while the wind blows. The light hulls are blown away while the heavy rice fall back into the pan. Later pestles and a simple machine called a rice pounder were developed to remove hulls. In 1885 the modern rice hulling machine was invented in Brazil. During the milling processes, the hulls are removed from the raw grain to reveal whole brown rice, which may then sometimes be milled further to remove the bran layer, resulting in white rice.

Uses of Rice Hulls

Combustion of rice hulls affords rice husk ash (acronym RHA). This ash is a potential source of amorphous reactive silica, which has a variety of applications in materials science. Most of the ash is used in the production of Portland cement when burnt completely, the ash can have a blaine number of as much as 3,600 compared to the blaine number of cement between 2,800 to 3,000, meaning it is finer than cement. Silica is the basic component of sand, which is used with cement for plastering and concreting. This fine silica will provide a very compact concrete. The ash also is a very good thermal insulation material. The fineness of the ash also makes it a very good candidate for sealing fine cracks in civil structures, where it can penetrate deeper than the conventional cement sand mixture.

A number of possible uses for RHA include absorbents for oils and chemicals, soil ameliorants, a source of silicon, insulation powder in steel mills, as repellents in the form of “vinegar-tar” release agent in the ceramics industry, as an insulation material.

ENVIRONMENTAL IMPACT

The majority of rice husk goes into landfills since the burning in open piles is not acceptable due to environmental constraints.  This makes the research on the potential uses of rice husk and rice husk ash of primary importance in the USA and around the world.  The manufacturing of cement produces carbon dioxide (CO₂), which is a prime contributor to the global warming.  Typically, cement production results in CO₂ emissions of about 0.8 – 1.2 tonnes/tonne of cement product depending on the production process and the fuel used.  Also, using RHA in concrete will help to reduce the amount of cement due to the partial substitution of cement by RHA and by making the concrete last longer (Folliard K.J 2002)

AIM OF THE STUDY

The aim of this research is to enhance the understanding of the role of natural pozzolans in sandcrete performance and to see how pozzloanic material would replace cement in the near future.

OBJECTIVES OF THE STUDY                         

1) To enlighten people on rice husk Ash pozzolan Carryout a cost comparative analysis to ascertain the affordability and sustainability of rice husk ash.

2) To investigate the effectiveness of using naturally occurring pozzolan materials as an additive or substitute for cement in sandcrete mixtures.

3) Carryout an analysis to ascertain the affordability and sustainability of rice husk ash.

SCOPE OF STUDY

This research work examined the use of Rice Husk Ash as partial replacement for Ordinary Portland Cement in concrete. It involved the determination of workability and compressive strength of the sandcrete at different level of replacement.