Reviewing The Different Combinations Of Concrete Construction Essay

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1.1. GENERAL ASPECTS

Present concrete is typically a combination of sand, gravel, water and cement. Even in the ancient period when red lime was used as cementing component, sand, gravel and water were the main components in making concrete. In the civil structural applications, concrete is not only a crucial essence but also a central essence in many other applications enclosing the construction business making it one of the significant and most seek product in the engineering business itself. This is because concrete is the main design component in conclusive upon the strength and other physical elements that supervise the stability of a given building. Now a day, concrete has the honor of being the largest man-made material in the world. And as a construction material concrete is very significant in our daily lives, because we spend 90% of our time in buildings and using infrastructures like roads, highways, bridges and so on. World-wide concrete consumption in the year 2010 was estimated to be 16 billion tons[1] which expressed as roughly more than two tons of concrete placed per capita per year gives perspective of the large scale concrete usage. This quantity is expanding consequentially every year.

There are several reasons for increasing the volume of construction and demolition waste (C&DW) all around. Some of them are as follows [12]:-

All around the world many old buildings, concrete pavements, bridges and other structures have reached their end of age. Some of them are beyond repairs condition and need to be demolished.

The structures are not serving the needs in present scenario, so it needs to be demolished for meeting present demand.

Economic growth in many countries needs new construction for better for better performance.

Natural disasters like earthquake, tsunami, cyclone, tornado and floods cause structures turned into debris.

Manmade disaster (war) creating waste from building and infrastructure.

The disposal of material coming from above fields cause exertion on the existing landfills which are quickly taking up their full volume. Besides this, concrete industry is depicting huge volume of NA and througing large quantities of construction and demolition wastes (C&DW) in landfills. Both these are damaging the environment and are no longer considered sustainable.

Application of natural aggregate (NA) in construction work has started approximately 3000 years B.C. whereas application of RCA has started almost 70 years ago just after the Second World War, when many structures were demolished by bombing. In the rebuild, the demolished concrete was used as aggregate in especially base or sub-base coarse in new road construction. Now a day RCA is used very successfully in many countries (like USA, UK, China, Japan, Holland, etc) in many fields like road construction, bank erosion, parking areas, as well as structural concrete. A number of structures in Germany, Norway, UK, Finland, and Holland have been made where RCA was used as partially or fully replacement of NA.

There are first world countries where 90% of construction and demolished waste (C&DW) are recycled. However, in South Africa the use of RCA is recent and limited. The consequential application of RCA internationally has conducted to a large puddle of characterization data on mechanical and durability performance of concrete containing RCA. In many countries, while RCA has been found suitable for large scale non-structural applications such as base and sub-base layers of new road pavements, a general approach for use in structural concrete is to blend RCA and NA, and limit the proportion of RCA. The limit varies internationally from 10% to 30% and up to 45% for specific applications.

Research results on the use of RCA in concrete mix design, as well as aspects of the physical and the mechanical properties have been extensively reviewed and discussed [2, 3, 4]. The general finding has been that the strength, stiffness and even durability performance of concrete containing RCA are reduced compared to concrete containing NA, but they are still sufficient for some practical applications in civil engineering. A study by the American National Ready Mix Concrete Association (NRMCA) has concluded that up to 10% recycled aggregate is suitable as a substitute for virgin aggregate for most concrete applications, including structural concrete [5]. UK research recommends that up to 20% recycled aggregate can be used for most applications including structural [6]. Australian guidelines state that up to 30% recycled aggregate can be used for structural concrete without any noticeable difference in workability and strength compared with natural aggregate [7]. The Dutch standard VBT 1995 allows up to 20% replacement of natural aggregate with RCA or recycled mixed aggregates (RMA) without a need for additional testing for all concrete up to a characteristic strength of 65MPa and all relevant environmental classes (equivalent to specific maximum levels of W/C) [11].

However in South Africa wide availability of natural stone with relatively lower cost in comparison with others countries, natural aggregate as coarse aggregate in concrete is very popular. As a result the use of RAC in structural concrete is not a major concern yet. But it does not mean RCA is not used in South Africa. Information from a local land fill site indicates that the use of RCA in South Africa has already started and has become very popular especially in road construction and some foundation work.

RCA is the result of processing suitable construction and demolition waste. This study is an merging of the existing information of RCA on the use of structural concrete. Tests results show that concrete containing RCA in South Africa fulfil strength class requirements for structural concrete as same as concrete made from natural aggregate.

1.2. DESCRIPTION OF NA AND RCA

Natural Aggregate (NA): Naturally occurring concrete aggregates are a mixture of rocks and minerals. A mineral is a naturally occurring solid substance with an orderly internal structure and a chemical composition that ranges within narrow limits. Rocks, which are classified as igneous, sedimentary, or metamorphic, depending on origin, are generally composed of several minerals. For example, granite contains quartz, feldspar, mica, and a few other minerals; most lime stones consist of calcite, dolomite, and minor amounts of quartz, feldspar, and clay. Weathering and erosion of rocks produce particles of stone, gravel, sand, silt, and clay [13].

Recycled Concrete Aggregate (RCA): Recycled concrete aggregate, or crushed waste concrete, is a feasible source of aggregates and an economic reality, especially where good aggregates are scarce. RCAs are aggregates derived from the processing of materials previously used in a product and/or in construction. Examples include recycled concrete from construction and demolition waste material (C&DW), reclaimed aggregate from asphalt pavement. According to Cement Concrete & Aggregates Australia (2008) [10] coarse recycled concrete aggregate is produced by crushing sound, clean demolition waste of at least 95% by weight of concrete, and having a total contaminant level typically lower than 1% of the bulk mass. Other materials that may be present in RCA are gravel, crushed stone, hydraulic-cement concrete or a combination thereof deemed suitable for premix concrete production. Conventional stone crushing equipment can be used, and new equipment has been developed to reduce noise and dust during processing of RCA.

1.3. WHY RECYCLED CONCRETE AGGREGATE

When any concrete structures are demolished or repaired, a common method of utilizing the C&DW is concrete recycling and it is increasingly every day. There was a routine work of C&DW dumped to the landfills site for disposal, but benefits from recycling has made a alternative charming option in the present day where there are of greater environmental awareness, more environmental laws, and the desire to keep construction costs down. Recycling can be the best ways for us to have a positive impact on the world in which we live. Recycling is important to both the natural environment and us. We must act fast as the amount of waste we are creating all the time. Recycling helps in preserving the resources available for our future generations. If the current generation utilizes the resources more efficiently by reusing them and converting them into a new product, it means they are saving the consumptions of the natural resources which will be available for their next generations. It is possible to make an eco-friendly and greener environment with proper recycling. Also it is a very healthy solution to reduce pollution and promote healthy living. Some reasons for recycled aggregates [8]-

It is accepted by ASTM and AASHTO and some other codes as a source of aggregate into new concrete.

RCA has high quality which meets or sometimes exceeds the requirement in specifications.

RCA are lighter weight per unit of volume in compare with virgin aggregate, as a result less weight per cubic yard, resulting in reduced material costs, haul costs, and overall project costs.

In many countries RCA are currently being used in concrete and asphalt products with better performance in compare with conventional aggregates.

RCA minimize the environmental impacts in an Urban Quarry setting.

RCA offers a way to reduce landfill waste streams.

Weights of RCA are ten to fifteen percent (10%-15%) less than comparable virgin quarry products (concrete).

RCA provides for superior compaction and constructability in pavement work in compare with virgin aggregate.

F:\Stellenbosch University\Picture of Concrete\NA & RA\NA 1.JPG

Figure 1.: NA used in this study

1.4. ADVANTAGES OF RECYCLING

Recycling is the most quickly and successfully developing procedures of environmental preservation. In fact, these days it is the most talked issue among all and the large number of people is participating in recycling waste in varied ways.

People are trying their ever best possible to save the environment because they have realized the importance of environment and thus they move to use the items that are waste for them now in alternative ways. The products that are recyclable like demolished concrete, glass, paper, metal and plastics are thus collected and then transported to the concerned facilities for converting them in finished products of alternative use. It is possible to prevent emission of the greenhouse gases like carbon dioxide into the atmosphere through proper recycling which is another great advantage of recycling and saves our world. The industrial processes which involves in the manufacturing of different products often release these toxic greenhouses gases that can also be well reduced by recycling.

Here are some of positive results and advantages of Recycling:

1.4.1. RECYCLING SAVES ENERGY

It is possible to save lot of energy using recycled products as raw materials of new products. Manufacturing of new products consumed much energy when virgin materials are used. Besides, the transportation of natural raw materials from their origins cost energy consumption which also can be saved by recycling used product. Also the energy which is required to clean and protect the environment from the pollutant of waste products, especially those which are non-biodegradable (plastic) and fill up the landfill areas can be minimized by recycling.

F:\Stellenbosch University\Picture of Concrete\NA & RA\RA 2.JPG

Figure 1.: RCA used in this study

1.4.2. RECYCLING CREATES EXTRA JOB OPPORTUNITIES

When people will start recycling business, there will be opportunity for many people in this new technology, such as specialized and skilled persons, general workers, drivers and etc. which will reduce unemployment problems. This will create a positive impact for our society.

1.4.3. RECYCLING SAVES NATURAL RESOURCES

Recycling is the processing and usage of the core essences of an old product for the production of new products. It helps in rescuing our original wealth to a large range. For example, if we recycle old newspaper we can save lot of tree for producing new paper products and this way we can save our environment from several damages. This way, proper recycling can help us preserve our natural resources for our future generations and maintain the balance of the existing nature.

1.4.4. EOCONIMIC BENEFITS

It is possible to save a lot of energy, natural resources, expense and demanded for the production of new products from 'virgin' materials. These expenses include the entire production cycle starting from acquiring the raw materials, transferring them from their origin to production places, processing and manufacturing costs. According to American Concrete Pavement Association [9], recycling concrete from demolition project can result in considerable savings since it saves the costs of transporting concrete to the landfill (as much as $ .25 per ton/mile), and eliminates the cost of disposal (as high as $100 per ton). In 1986 the Danish government introduced a tax on waste disposed off at landfill sites. Today the tax is DKK 375 (approx. EURO 50) per ton of waste disposed off at landfill sites. Recycling process creates employment opportunities for a lot of people, involved in the various stages of the process. This in turn contributes to the economic development of the state or country.

1.4.5. RECYCLING SAVES SPACE FOR WASTE DISPOSAL

When waste products are disposed it occupies lot of spaces, but it is possible to recover the space through effective recycling. Normally in landfill site different types of waste dumped together and there are some wastes materials belong to non-biodegradable category which takes a long time to decompose. It is possible to enable proper usage of these waste products and saves space for landfills by proper recycling. So, we may have to face shortage of the landfills unless we start following recycling at our own home and spread the word to others.

1.4.6. SUSTAINABILITY

The amount of waste materials used for landfill can be reduced through usage of recycled aggregate and this will also reduce the amount of digging for virgin aggregate. Therefore this will extend the lives of natural resources and also extend the lives of sites that using for landfill.

1.4.7. GOOD WIDEMARKET

The markets for recycled aggregate in many fields are wide in world-wide including South Africa. According to Environmental Council of Concrete Organization, recycled aggregate can be used for sidewalk, curbs, bridge substructures and superstructures, concrete shoulders, residential driveways, general and structural fills. It also mentioned that recycled aggregate concrete can be used in structural concrete. Industry studies have shown that in Europe recycled concrete aggregate can sell for 3 to 12 € per ton with a production cost of 2.5 to 10 € per ton [9]. The higher selling price is obtained on sites where all C&DW is reclaimed and maximum sorting is achieved, there is strong consumer demand, lack of natural alternatives and supportive regulatory regimes.

1.5. DISADVANTAGES OF RECYCLING

Although there are many successful application and advantages by using RCA in different sector but there are still some disadvantages in recycled aggregate.

1.5.1. LACK OF CODES, SPECIFICATIONS, STANDARD AND GUIDELINES

Still in many countries there is no specification or any guideline when using recycled concrete aggregate in the constructions. In many cases, the strength characteristic for certain field will not meet the requirement when using recycled aggregate concrete. Therefore, more testing should be considered when using recycled aggregate. There must be proper guidelines for using RCA in different sectors.

1.5.2. AIR POLLUTION

Demolished concrete contain lot of extra mortar in body which create dust during recycling process and cause air pollution surrounding the demolition area. This air is harmful for human health and cause many diseases.

1.5.3. WATER POLLUTION

The wash water from RCA contains high pH value which is a serious environmental issue. According to Building Green (1993), the alkalinity level of wash water from the recycling plants is pH12. This water is toxic to the fish and other aquatic life.

1.5.4. POOR IMAGE

There is a tendency in people mind that by-products materials are not main stream and are not of high quality in nature. Of course, if the by-product had higher quality, it would already be in the market, so there must be some disadvantages. However, in reality people always try to use over-specified materials in applications even though by-products satisfy the same requirements, so the right materials must be used in the right places.

1.5.5. LACK OF EXPERIENCE

In any fields, when there is a new material or new construction methods come, experience is required in order to ensure safety of that new product. This may be a contradicting requirement, and may sometimes constitute a barrier to introducing new technology.

1.5.6. LOW QUALITY

Generally, recycled materials are of lower quality than virgin materials. However, there are many techniques for concrete materials that help to apply such materials to structures without humiliating the quality of structures. Performance-based design methods are favorable for using recycled materials. We must recognize that trials to raise the quality of recycled materials lead to improvements in technologies. For example, machines for processing recycled aggregate from demolished concrete have been replaced by a crushing machine for new aggregate, but the requirement to obtain more recycled aggregate with low water absorption led to improvements in the machine. In many countries, there are new types of processing machines have been developed which enable to produce higher quality RCA with lower energy consumption.

1.5.7. VARIATIONS IN QUALITY

The quality of recycled concrete varies from one site to another. The recycling plants with small and have lack large stock yards, improper facilities for recycling causes wide variations in the quality of recycled materials from the plants, and is also the case for other by-products. Wide variations of RCA may require special quality control testing and concern about the quality of structures made using such aggregate in concrete.

1.6. APPLICATIONS OF RECYCLED CONCRETE AGGREGATE

Thronging in landfill is the traditional application of RCA. Since people are more concern about environment and also the land is scared in many countries, nowadays, the applications of recycled aggregate in construction areas are wide. But the applications of RCA are different from country to country.

In general, applications of RCA -

1.6.1. GRANULAR BASE COURSE MATERIALS

In many countries, as granular base course in the road construction RCA are very popular. According to Market Development Study for Recycled Aggregate Products (2001) in Australia, recycled aggregate had proved that better than natural aggregate when used as granular base course in roads construction. They also found that when the road is built on the wet sub grade areas, recycled aggregate will stabilize the base and provide an improved working surface for pavement structure construction.

1.6.2. EMBANKMENT FILL MATERIALS

RCA can be used in embankment fill successfully. The reason for being able to success to use in embankment fill is same as it is used in granular base coarse construction. The embankment site is on the wet sub grade areas. RCA can stabilize the base and provide an improved working surface for the remaining works.

1.6.3. PAVING BLOCKS

RCA are using as paving blocks in many countries world-wide especially in USA and UK. According to Hong Kong Housing Department, recycled aggregate are used as typical paving blocks. A trial project had been started to test the long - term performance of paving blocks made with recycled aggregate in 2002.

1.6.4. ROAD CONSTRUCTION

Several roads project in USA, UK, Japan and China where RCA has been used successfully and running over last few decades. The C&DW from old road or building are recycled, and usually used as base coarse under normal concrete road or runway slab. This is an obvious case for RCA but it is not likely to be applicable in South Africa where concrete roads are comparatively new.

1.6.5. BANK PROTECTION

RCA can be used in bank protection without any noticeable change of property. After removal of contaminants through selective demolition, screening, and /or air separation and size reduction in a crusher to aggregate sizes, crushed concrete can be used as:

new concrete for pavements, shoulders, median barriers, sidewalks, curbs and gutters, and bridge foundations

structural grade concrete

soil-cement pavement bases

lean-concrete and

bituminous concrete

1.7. PROBLEM STATEMENT

In recycled concrete, the reclaimed concrete used to make coarse aggregate for new concrete may come from different sources. It can be obtained through the demolition of concrete elements of roads, bridges, buildings and other structures, or it can come from the residue of fresh and hardened rejected units in precast concrete plants. The quality of the recycled concrete aggregate will normally vary depending on the properties of the recovered concrete. Variations between concrete types result from differences in aggregate quality, aggregate size and texture, concrete compressive strength, and uniformity. Therefore, there is a need to investigate the effect of the origin of the recycled concrete aggregate on the strength properties of the new concrete. Specifically, it is desired to quantify the consequences of using recycled concrete coarse aggregate with lower, equal, or higher strength than the target strength of the new concrete.

1.8. PROPERTIES OF CONCRETE MADE WITH RECYCLED AGGREGATE

Concrete mixes using RCA can be designed in much the same way as those using NA, provided the extra absorption in the former is appropriately accounted for when determining the unit water content. The salient features of the recommendations of the RILEM committee (RILEM, 1994) for proportioning of RAC are given below:

• When designing a concrete mix using recycled aggregate of variable quality, a higher standard deviation should be employed in order to determine a target mean strength based on a required characteristic strength.

• When coarse recycled aggregate is used with natural sand, it may be assumed at the design stage, that the free w/c ratio required for a certain compressive strength will be the same for RAC as for conventional concrete.

• For a recycled aggregate mix to achieve the same slump, the free water content will be approximately 5% more than for conventional concrete.

• The sand-to-aggregate ratio for RAC is the same as when using NA.

• Trial mixes are mandatory and appropriate adjustments depending upon the source and properties of the RA should be made to obtain the required workability, suitable w/c ratio, and required strength, of RAC.

1.9. THE NEED FOR C&D WASTE MINIMIZATION

In all communities it has always been common practice to retrieve valuable materials from the arising waste, e.g. metals and building materials. After some decades in this century with an extensive "use-and throw-away" philosophy it has been recognized that we cannot continue this uninhibited use of natural resources and pollution of the world with waste. It is necessary to change our habits and to revise former common practices within the building & construction industry, as well as within other industries, households, etc.

In many countries, industrial as well as developing, C&D waste is considered as harmless, inert waste, which does not give rise to problems. However, C&D waste consists of huge amounts of materials that are often deposited without any consideration, causing many problems and encouraging the illegal dumping of other kinds of waste. Whether C&D waste originates from clearing operations after natural disasters or from human-controlled activities, the utilization of such waste by recycling can provide opportunities for saving energy, time, resources and money. Furthermore, recycling and the controlled management of C&D waste will mean that less land is used and better opportunities will be created for the handling of other kinds of waste.

1.10. AIM OF RESEARCH

Motivations for adopting recycled concrete as an aggregate source include the preservation of natural resources, effective utilization of growing waste stream and financial and energy savings. Although current practices of using RCA in South Africa is infrequent and the use of recycled concrete as an aggregate source in structural concrete application is rare. To make RAC feasible, its properties must be related to the properties of new concrete that utilizes the recycled aggregates. In response to this need, this dissertation was undertaken to investigate the feasibility of using RCA as a viable alternative to NA in the production of concrete manufactured in a conventional ready mix concrete plant. Aggregate properties and hardened and fresh concrete properties of RCA concrete were studied and compared with the associated properties derived from NAC. Results indicated that RCA is a viable alternative to NA in the production of concrete. Furthermore, it was confirmed that the properties of RAC dictate the hardened properties of the reconstituted concrete and that RCA from certain strength placements limited the resulting possible strengths of concrete produced from it.

Many studies dealing with physical and mechanical properties of recycled aggregate and their durability performance have been carried out in world. However, there are little studies that attempt to forecast future trends of RCA used in structural concrete. This study aims at filling this gap.

1.11. CHAPTER OVERVIEW

CHAPTER 1: INTRODUCTION

This chapter will give the reader a brief introduction on the topic, description of RCA, advantages and disadvantages of RCA, problem statement and research aim. The chapter sets the stage for the overall research presented in the report.

CHAPTER 2: LITERATURE REVIEW AND BACKGROUND OF RECYCLED CONCRETE AGGREGATE

In this chapter a historic overview on the concrete and the use of Recycled Concrete Aggregate (RCA) is presented to the reader. This is then followed by the research problem and background, waste production in world, RCA application in the civil structural applications from a historic perspective and method of recycling. The chapter is concluded with an overview on the economic factors and benefits realized through the use of the Light Aggregate Concrete (LAC) in the civil structure applications with examples. The economic overview also throws light on the key aspects of RCA that benefit the overall concrete composition in structural applications as well as provide a detailed review of the various RCA compositions used in the past during the initial stages of RCA's use in the construction industry.

CHAPTER 3:  RECYCLING BUSINES

This chapter presents a detailed overview of recycling business, equipments required for recycling, South African construction waste pattern, steps required to introduce recycling in South Africa.

CHAPTER 4: EXPERIMENTAL PROGRAM

This chapter presents a detailed overview of materials used in this study, physical properties of materials, preparation of specimens and test setup and method for specimens.

CHAPTER 5: CONCRETE TEST RESULTS AND DISCUSSION

This chapter presents a critical analysis on the properties of RCA and the various combination of recycled aggregate that is used in different categories of the construction. The research throws light on the various compositions of recycled aggregate and their distinct features that help achieve the desired benefits in a structural application. The chapter then presents a critical overview on the regulations pertaining to the RCA followed by the composition analysis based on the materials that are available locally to a given geographical location.

CHAPTER 6: DURABILITY PERFORMANCE OF NAC & RAC

This chapter of dissertation covers durability performance of 30% replacement of RCA in NA which has been compared with 100% NAC. Three tests oxygen permeability test, Water sorptivity test and Chloride conductivity test has performed and finally results has presented graphically.

CHAPTER 7: CONCLUTION AND RECOMMENDATION

This chapter reviews the objectives of the research followed by providing the conclusion to the report which indicate the overall economics of recycling and performance of recycled concrete aggregate compared with conventional concrete and recommendations on further work.

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