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Natural Recycling of Aggregate

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Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of UK Essays.

Published: Fri, 09 Feb 2018

Introduction

For many years peoples have been trying to keep the environmental clean and mention the natural balance of life. The scientific studies provide us the information and methods to achieve these objectives and the recycling of waste and by product materials represent the main role in these studies [1-4]. As a result of reconstruction of existing buildings and pavements, wars and natural disasters such as earthquakes the amount of construction and demolition materials are increasing every year.

At the same time approval of additional facilities for waste disposal or treatment are become more difficult to obtain. Furthermore increasing restrictive environmental regulations have made waste disposal more difficult and expensive. Also the available natural aggregate in some countries decreases and may be become insufficient for the construction projects in these countries in the future [5]. So, the reuse of construction and demolition materials in construction has benefits not only in reducing the amount of materials requiring disposal but also can provide construction materials with significant saving of the original materials.

According to the third Building Waste Monitoring Report [6], there is an increase in the recorded amount of building waste in the sectors of the building debris, road scarification and building site waste. It has arisen in Germany by 11.5 million tons, from 77.1 million tons in the period 1997/1998 to 88.6 million tons in the period 1999/2000. According to Rahlwes and Schmidt [7, 8], for concrete only, the annual crushed concrete quantity in west Germany only is about 30 million tones and in the European Union is approximately 130 million ton. Due to intensive building activities in the last decades, these amounts are expected to considerably increase after the year 2000.

The properties of recycled coarse aggregate with a grain size above 4 mm and its reuse in concrete production and pavements construction have been evaluated and described in many.

It has been estimated that approximately 50 million tons of concrete are currently demolished each year in the European Economic Communities [1], Equivalent figures are 60 million tons in the United States ([2], [3]), and in Japan [12] the total quantity of concrete debris available for recycling on some scale is about 10 to 12 million tons. Very little demolished concrete is currently recycled or reused anywhere in the world. The small quantity which is recovered is mainly reused as unstabilized base or subbase in highway construction.

The rest is dumped or disposed of as fill. For Environmental and other reasons the number of readily accessible disposal sites around major cities in the world has decreased in recent years. Both disposals volume and maximum sizes of wastes have been restricted. In Japan disposal charges from USD 3 to 10 per ton are not uncommon. Moreover, distances between demolition sites and disposal areas have become larger and transportation costs higher.

At the same time critical shortages of good natural” aggregate is developing in many urban areas, and distances between deposits of natural material and sites of new construction have grown larger, and transportation costs have become correspondingly higher, It is estimated that between now and year 2,000, three times more demolished concrete will be generated each year than is today. For these reasons it can be foreseen that demolition contractors will come under considerable economic and other pressure to process demolished concrete for reuse as unscreened gravel, base and subbase materials, aggregates for production of new concrete or for other useful purposes.

Large-scale recycling of demolished concrete will contribute not only to the solution of a growing waste disposal problem. It will also help to conserve natural resources of sand and gravel and to secure future supply of reasonably priced aggregates for building and road construction purposes within large urban areas of the world.

Applications of Recycled Aggregate

The recycled concrete aggregate shown in Figure 1.1 can be defined as crushed concrete composed of aggregate fragments coated with cement paste or cement mortar from the demolition of the old structures or pavements that has been processed to produce aggregates suitable for use in new concrete. The processing, as with many natural aggregates, generally involves crushing, grading and washing. This removes contaminant materials such as reinforcing steel, remnants of formwork, gypsum board, and other foreign materials.

The resulting coarse aggregate is then suitable for use in concrete. The fine aggregate, however, generally contains a considerable amount of old cement paste and mortar. This tends to increase the drying shrinkage and creep properties of the new concrete, as well as leading to problems with unworkable mix and strength. Therefore, many transportation departments have found that using 100% coarse recycled aggregate but with only about 10% to 20% recycled fines works well.

Regarding the results of most of the previous research that has been done so far, the application of Recycled Aggregate is mostly currently in low quality/strength concrete, for example, pavement base and slab rather than used in structural concrete. The most common application of Recycled Concrete Aggregate is the use in concrete

sub-base in road construction, bank protection, noise barriers and embankments, many types of general bulk fills and fill materials for drainage structures. After the 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; moulded concrete bricks and blocks; bituminous concrete etc.

However, there is an example of recycled concrete being used for part of the structural slabs in a high-rise building in Japan but there was no too much detail available on this project. According to research that has been conducted in Australia, current use of recycled aggregates is still only around 7% of road construction material in South Australia. Victoria Road also use recycled aggregate for their road base construction projects in Victoria but MainRoads in Queensland does not currently. Traditionally, the application of recycled aggregate is used as landfill. Nowadays, the applications of recycled aggregate in construction areas are wide. The applications are different from country to country.

Concrete Kerb and Gutter Mix

Recycled aggregate have been used as concrete kerb and gutter mix in Australia. According to Building Innovation & Construction Technology (1999), Stone says that the 10mm recycled aggregate and blended recycled sand are used for concrete kerb and gutter mix in the Lent hall Street project in Sydney.

Granular Base Course Materials

According to Market Development Study for Recycled Aggregate Products (2001), recycled aggregate are used as granular base course in the road construction. It also stated that 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.

Embankment Fill Materials

Market Development Study for Recycled Aggregate Products (2001) stated that recycled aggregate can be used in embankment fill. The reason for being able to use in embankment fill is same as it is used in granular base course construction. The embankment site is on the wet sub grade areas. Recycled aggregate can stabilize the base and provide an improved working surface for the remaining works.

Paving Blocks

Recycled aggregate have been used as paving blocks in Hong Kong. According to Hong Kong Housing Department (n.d.), 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.

Backfill Materials

Recycled aggregate can be used as backfill materials. Mehus and Lillestol (n.d) found that Norwegian Building Research Institute (n.d) mentioned that recycled concrete aggregate can be used as backfill materials in the pipe zone along trenches after having testing in laboratory.

Building Blocks

Recycled aggregate used as building blocks. Mehus and Lillestol (n.d) stated that Optiroc AS had used recycled aggregate to produce the masonry sound insulation blocks. The masonry sound insulation blocks that produced had met all the requirements during the laboratory testing.

International Status

Mehus and Lillestol (n.d.) stated that RESIBA had constructed a new high school in Sorumsand, outside the city of Oslo, Norway in 2001. Recycled concrete aggregate had been used in this project. Thirty – five percent of coarse aggregate were replaced by recycled concrete aggregate in the foundations, half of the basement walls and columns. Several tests were conducted based on fresh and hardened concrete properties and the results shown that the concrete with thirty – five percent of recycled concrete aggregate have good freeze – thaw resistance.

The use of recycled concrete aggregate did not shown any noticeable increase in cracking. According to Grubl, Nealen and Schmidt (n.d.), there is a building project, the “Waldspirale” by Friedensreich Hundertwasser, made from concrete with recycled aggregate in Darmstadf from November 1998 to September 1999. Numerous tests were evaluated for freshly missed and also hardened concrete properties. The result shown that the consistency controlled method for concrete with recycled aggregate is applicable. And it leads to concrete of equal quality when compared with concrete made from natural aggregate.

According to Regain (1993/94), recycled aggregate were used as capping and sub-base layers in housing development at North Bracknell, UK in 1993/94. Visual inspections and condition surveys were carried out by using the falling weight deflectometer in 1998. The result shown that the sections with recycled aggregate did not show any difference in appearance compared to the sections that using natural aggregate. The tests gave the larger values of elastic modulus in the recycled aggregate sections.

According to Regain (2001), footway paving slabs are being replaced gradually in London Borough of Bexley. Recycled aggregate are used as coarse aggregate in the concrete mix with a 12:1 aggregate to cement mix

Advantages

There are many advantages through using the recycled aggregate. The advantages that occur through usage of recycled aggregate are listed below.

Environmental Gain

The major advantage is based on the environmental gain. According to CSIRO (n.d.), construction and demolition waste makes up to around 40% of the total waste each year (estimate around 14 million tones) going to land fill. Through recycled these material, it can keep diminishing the resources of urban aggregated. Therefore, natural aggregate can be used in higher –grade applications.

Save Energy

The recycling process can be done on site. According to Kajima Technical Research Institute (2002), Kajima is developing a method of recycling crushed concrete that used in the construction, known as the Within-Site Recycling System. Everything can be done on the construction site through this system, from the process of recycled aggregate, manufacture and use them. This can save energy to transport the recycled materials to the recycling plants.

Cost

Secondly is based on the cost. The cost of recycled aggregate is cheaper than virgin aggregate. According to PATH Technology Inventory (n.d.), the costs of recycled concrete aggregate are sold around $3.50 to $7.00 per cubic yard. It depends on the aggregate size limitation and local availability. This is just around one and half of the cost for natural aggregate that used in the construction works.

The transportation cost for the recycled aggregate is reduced due to the weight of recycled aggregate is lighter than virgin aggregate. Concrete Network (n.d) stated that recycling concrete from the demolition projects can saves the costs of transporting the concrete to the land fill (around $0.25 per ton/ mile), and the cost of disposal (around $100 per ton). Beside that, Aggregate Advisory Service (n.d.) also state that the recycling site may accept the segregates materials at lower cost than landfill without tax levy and recycled aggregate can be used at lower prices than primary aggregate in the construction works.

Job Opportunities

There will be many people involved in this new technology, such as specialized and skilled persons, general workers, drivers and etc. According to Scottish Executive (2004), a Scottish Market Development Program is developed. The purpose of this program is to recycle the materials that arising in Scotland. This program will provide 150 new jobs in the Scottish industry.

Sustainability

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

Market is Wide

The markets for recycled concrete aggregate are wide. According to Environmental Council of Concrete Organization (n.d), recycled concrete aggregate can be used for sidewalk, curbs, bridge substructures and superstructures, concrete shoulders, residential driveways, general and structural fill. It also mentioned that recycled concrete aggregate can be used in sub bases and support layers such as unstabilized base and permeable bases.

Disadvantages

Although there are many advantages by using recycled aggregate. But there are still some disadvantages in recycled aggregate.

Hard to have permit

Jacobsen (1999) stated that it is hard to get the permit for the machinery that needed air permit or permit to operate during the recycling process. These has to depend on the local or state regulations whether this technology is implemented or not.

Lack of Specification and Guidelines

According to Kawano (n.d), there is no specification or any guideline when using recycled concrete aggregate in the constructions. In many cases, the strength characteristic will not meet the requirement when using recycled concrete aggregate. Therefore, more testing should be considered when using recycled concrete aggregate.

Water Pollution

The recycled process will cause water pollution. Morris of National Ready Mix Concrete Association (n.d) had mentioned that the wash out water with the high pH 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.

Project Aim

The aim for this on – going project is to determine the strength characteristic of recycled aggregate for application in high strength structural concrete, which will give a better understanding on the properties of concrete with recycled aggregate, where can be an alternative material to coarse aggregate in structural concrete.

Project Scope

  • Review and research of recycled aggregate.
  • Construct the concrete specimens by using different percentage of recycled aggregate.
  • Investigation and laboratory testing on high strength concrete with recycled aggregate.
  • Analysis the results and recommendation for further research area.

Dissertation Overview

This dissertation is structured in the following format.

  • Chapter 2 provides a review of relevant literature, overview of recycling process, as well as comparison of recycled aggregate and natural aggregate. This chapter also discussed the previous investigation and testing done with recycled aggregate.
  • Chapter 3 includes the preliminary design and information on the recycled aggregate testing and design of the concrete mix.
  • Chapter 4 describes the experimental methodology carried out in order to obtain the required data.
  • Chapter 5 discusses the results and analysis of all experimental results obtained from the testing procedures.
  • Chapter 6 contains the conclusions of the research and recommendations on further work.

Literature review of Recycled Aggregate

Literature review of Recycled Aggregate

Conventional concrete aggregate consists of sand (fine aggregate) and various sizes and shapes of gravel or stones. However, there is a growing interest in substituting alternative aggregate materials, largely as a potential use for recycled materials. While there is significant research on many different materials for aggregate substitutes (such as granulated coal ash, blast furnace slag or various solid wastes including fiberglass waste materials, granulated plastics, paper and wood products / wastes, sintered sludge pellets and others), the only two that have been significantly applied are glass cullet and crushed recycled concrete itself.

Even though aggregate typically accounts for 70% to 80% of the concrete volume, it is commonly thought of as inert filler having little effect on the finished concrete properties. However, research has shown that aggregate in fact plays a substantial role in determining workability, strength, dimensional stability, and durability of the concrete. Also, aggregates can have a significant effect on the cost of the concrete mixture.

Certain aggregate parameters are known to be important for engineered-use concrete: hardness, strength, and durability. The aggregate must be “clean,” without absorbed chemicals, clay coatings, and other fine materials in concentrations that could alter the hydration and bond of the cement paste.

It is important to note the difference between aggregate and cement, because some materials have found use both as a cementitious material and as aggregate (such as certain blast furnace slags). Materials that have been researched or applied only as cement substitutes are addressed in another Technology Inventory article – Cement Substitutes.

Aggregate composed of recycled concrete generally has a lower specific gravity and a higher absorption than conventional gravel aggregate. New concrete made with recycled concrete aggregate typically has good workability, durability and resistance to saturated freeze-thaw action. The compressive strength varies with the compressive strength of the original concrete and the water-cement ratio of the new concrete. It has been found that concrete made with recycled concrete aggregate has at least two-thirds the compressive strength and modulus of elasticity of natural aggregate concrete.

Field-testing has shown that crushed and screened waste glass may be used as a sand substitute in concrete. Nearly all waste glass can be used in concrete applications, including glass that is unsuitable for uses such as glass bottle recycling. Some of the specific glass waste materials that have found use as fine aggregate are “non-recyclable” clear window glass and fluorescent bulbs with very small amounts of contaminants. Possible applications for such waste-glass concrete are bike paths, footpaths, gutters and similar non-structural work.

Lack of widespread reliable data on aggregate substitutes can hinder its use. To design consistent, durable recycled aggregate concrete, more testing is required to account for variations in the aggregate properties. Also, recycled aggregate generally has a higher absorption and a lower specific gravity than conventional aggregate.

Research has revealed that the 7-day and 28-day compressive strengths of recycled aggregate concrete are generally lower than values for conventional concrete. Moreover, recycled aggregates may be contaminated with residual quantities of sulfate from contact with sulfate rich soil and chloride ions from marine exposure.

Glass aggregate in concrete can be problematic due to the alkali silica reaction between the cement paste and the glass aggregate, which over time can lead to weakened concrete and decreased long-term durability. Research has been done on types of glass and other additives to stop or decrease the alkali silica reaction and thereby maintain finished concrete strength. However, further research is still needed before glass cullet can be used in structural concrete applications.

The applications of recycled aggregate in highway construction as a road base material are very board and have been in use for almost 100 years. There has been much research based on the use of recycled aggregate that has been carried out all around the world. The research on recycled aggregate that has been carried out indicated that the successful application of crushed aggregate in concrete can be achieved. This successful research has been achieved in many countries, in particular in Europe; United States; Japan and China. This chapter presents literature reviews on the effects of various factors on the recycled aggregate from research from those countries.

The major objective of most of the experiments or research on recycled aggregate is to find out the results in the strength characteristic area and what is the best method to achieve high strength concrete with recycled aggregate.

Strengths of Recycled Aggregate Concrete Made Using Field-

Demolished Concrete as Aggregate

Tavakoli M. (1996) studied the compressive; splitting tensile and flexural strengths of 100% recycled coarse aggregate concrete and 100% natural sand to compare them with normal concrete made of natural crushed stone. The water-cement ratio was 0.3 and 0.4 in the concrete mix design.

The test result shows the compressive, tensile and flexural strengths of RCA are little higher than the natural aggregate at the same size of 25.4mm at 28-day specimen. This indicates that if the compressive strength of the original concrete that is being recycled is higher than that of the control concrete, then the recycled aggregate concrete can also be made to achieve higher compressive strength than the control concrete.

The results also indicates increase L.A. abrasion loss and water absorption capacity of recycled aggregates, which partly reflect the increased amount of water, adhering to the original stone aggregate, generally lead to reduced compressive strength of recycled aggregate concrete.

Dhir et al. (1998) studied the effect of the cleanliness and percentage of the replacement of RCA. They found out that the degree of cleanliness of aggregate has significantly affected on the results of the properties of both the plastic and hardened concrete. The workability and compressive strengths both were lower than the quarried aggregate from 17% to 78% depending on the percentage of replacement of RCA. The results also indicated recycled aggregate has very high air content.

Limbachiya and Leelawat (2000) found that recycled concrete aggregate had 7 to 9% lower relative density and 2 times higher water absorption than natural aggregate. According to their test results, it shown that there was no effect with the replacement of 30% coarse recycled concrete aggregate used on the ceiling strength of concrete. It also mentioned that recycled concrete aggregate could be used in high strength concrete mixes with the recycled concrete aggregate content in the concrete.

Sagoe, Brown and Taylor (2002) stated that the difference between the characteristic of fresh and hardened recycled aggregate concrete and natural aggregate concrete is relatively narrower than reported for laboratory crush recycled aggregate concrete mixes. There was no difference at the 5% significance level in concrete compressive and tensile strength of recycled concrete and control normal concrete made from natural aggregate.

Limbachiya (2003) found that there is no effect by using up to 30% of coarse recycled concrete aggregate on the standard 100mm concrete cube compressive strength. But when the percentage of recycled concrete aggregate used increased, the compressive strength was reducing.

Behavior of Construction and Demolition Debris in Base and Subbase Application

Pappjr et al (1998) studied using recycled aggregates in Base and Subbase applications. They found that recycled concrete yielded higher resilient modulus than the dense graded aggregate currently used. Furthermore, the results have been shown that recycled concrete have less permanent deformation than dense graded aggregate.

They concluded that recycled concrete could be a valuable alternative to natural materials for base and subbase applications.

Influence of recycled aggregate quality on concrete properties

Sanchez de Juan et al. (2000) studied what is the maximum percentage, from 20% to 100%, replacement of recycled aggregate in concrete. The results showed that the compressive strength of recycled concrete is lower than that of a control concrete with equal water/cement ratio and same cement content.

Recycled concretes with a percentage of recycled coarse aggregate lower than 50% show decreases in the range 5-10%, while for concretes with 100% recycled aggregates, decreases ranged from 10-15%. Experimental results also indicated that properties of conventional concretes and recycled concretes with same compressive strength when less than 20% of recycled coarse aggregate are used. The exception being modulus of elasticity was decreased until 10% can be found in recycled concretes.

When the percentage of recycled aggregate is lower than 50%, tensile strength and drying shrinkage of recycled concrete is similar to conventional concrete with same compressive strength. As a result of the testing, all properties of concrete with a 100% of recycled coarse aggregate are affected.

Some studies on durability of recycled aggregate concrete

Mandal et al. (2002) studied the durability of recycled aggregate concrete and found that recycled aggregate had less durability than natural aggregate. However, when 10 percent replacement of cement by fly ash was used with recycled aggregate, the durability observed was increased. It significantly improved the compressive strength up to 46.5MPa, reduced shrinkage and increased durability to a level comparable to natural aggregate. Therefore, the results of this study provide a strong support for the feasibility of using recycled aggregate instead of natural aggregate for the production of concrete.

Use of recycled aggregates in molded concrete bricks and Blocks

Poon et al. (2002) developed a technique to produce concrete bricks and paving blocks from recycled aggregates. The test result showed that replacing natural aggregate by 25% to 50% had little effect on the compressive strength, but higher levels of replacement reduced the compressive strength. The transverse strength increased as the percentage of recycled aggregate increased. The concrete paving blocks with a 28-day compressive strength of at least 49MPa can be produced without the incorporation of fly ash by using up to 100% recycled aggregate.

According to the study, recycled aggregate has been used in structural engineering.

For example, a viaduct and marine loch in the Netherlands in 1998 and an office building in England in 1999. The project in the Netherlands had shown that 20 percent of the coarse aggregate was replaced by recycled aggregate. The project also indicated even there are some disadvantage of recycled aggregate such as being too weak, more porous and that it has a very higher value of water absorption.

However, the study showed that these weaknesses could be avoided by using mechanized moulded concrete bricks. The workability also could be improved by poring the mix into the mould. Therefore, the performance of the bricks and blocks was also satisfactory in the shrinkage and skid resistance tests.

Concrete with Recycled materials as Coarse Aggregates:

Shrinkage and Creep Behavior

Tawrwe et al. (1999) compared limestone aggregate with concrete rubble. They found the concrete rubble had a very high water absorption compared to the limestone aggregate (0.74% against 6.83% of dry mass). Furthermore the porous aggregate absorbed water slowly in some tests. For example, it was difficult to determine accurately the amount of water that had to be added to obtain suitable workability. The critical shrinkage of the limestone aggregate concrete was higher than the concrete rubble, but after a year the shrinkage was greater for the concrete rubble based aggregate.

Treatments for the improvement of recycled aggregate

Katz (2004) stated two methods to improve the quality of the recycled aggregates. The superplasticizer (1% weight of silica fume) was added to the solution of 10L of water and 1 kg raw silica fume to ensure proper ispersion of silica fume particles. After the silica fume impregnation, the SF treatment seems to improve significantly the compressive strength up to 51MPa at ranged from 23% to 33% at 7 days of the recycled aggregate concrete. Ultrasonic cleaning of the recycled aggregate to remove the loose particles and improve the bond between the new cement paste and the recycled aggregate, which, in turn, increased 7% of strength.

Kantawong and Laksana (1998) mentioned that the fineness modulus and percentage of water absorption used instead with the recycled aggregate is higher than natural aggregate. The results of compressive strength of added reduce water admixture concrete is higher than the one that not added reduce water admixture concrete, ane the compressive strength of concrete produced that using recycled aggregate is higher than concrete using natural coarse aggregate.

Sawamoto and Takehino (2000) found that the strength of the recycled aggregate concrete can be increased by using Pozzolanic material that can absorb the water.

Mandal (2002) stated that adjusted the water/cement ratio when using recycled concrete aggregate during the concrete mixing can improved the strength of the recycled aggregate concrete specimens. From the obtained result, recycled aggregate concrete specimens had the same engineering and durability performance when compared to the concrete specimens made by natural aggregate within 28days design strength.

Chen and Kuan (2003) found that the strength of the concrete specimens was affected by the unwashed recycled aggregate in the concrete. The effect will more strange at the low water cement ratio. These effects can be improved by using the washed recycled aggregate.

Construction and Demolition Waste Recycling Reuse as Aggregate in Concrete Production

Limbachiya (2004) studied the properties of recycled aggregate compared with natural aggregates and found out the density of RCA is typically 4-8% lower and water absorption 2-6 times higher. The results showed that a reduction in slump value with increasing RCA concrete mix. The results also slowed that up to 30% coarse RCA has no effect on the standard concrete cube strength but thereafter a gradual reduction with increasing RCA content occurs. This means that some adjustment is necessary of the water/cement ratio to achieve the equivalent strength with high proportions of RCA.

Review on Recycled Process

This section discusses the recycling process and method.

Recycling Plant Recycling plant normally located in the suburbs of cities due to the noise pollution that make by t


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