Natural Recycling of Aggregate

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 ongoing 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

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 the equipments that used during recycling process. According to Aggregate and Quarry (n.d.), all the machinery used have to fit with the effective mufflers to reduce the noise from the processing activity.

Sources of Recycled Aggregate

Traditionally, Portland concrete aggregate from the demolition construction are used for landfill. But nowadays, Portland concrete aggregate can be used as a new material for construction usage. According to Recycling of Portland Cement Concrete (n.d), recycled aggregate are mainly produced from the crushing of Portland concrete pavement and structures building. It stated that the isolated areas of 1 inch of asphalt concrete can be used to produce the recycled aggregate. The main reason that choosing the structural building as the source for recycled aggregate is because there is a huge amount of crushed demolition Portland cement concrete can be produced.

Equipments used during Recycling Process

The equipments that used during recycling process are various from the site conditions and also country to country. There are few different types of equipment had been used effectively to break up the Portland cement pavement and structural building.

Portland Cement Pavement

Recycling of Portland Cement Concrete (n.d) mentioned that there are few different types of equipment had been used for crushing the Portland cement pavement. The equipments are as below:

Diesel pile – driving hammer. It is mounting on a motor grader that sticks in the Portland cement pavement on around 30cm grid pattern.

Figure 2.1: Diesel Pile – Driving Hammer

(Source: Recycling of Portland Cement Concrete, (n.d))

Rhino – horn – tooth – ripper – equipped hydraulic excavator. It is used to remove all the steel reinforcement that remaining in the Portland cement pavement.

Figure 2.2: Rhino – horn – tooth – ripper – equipped Hydraulic Excavator

(Source: Recycling of Portland Cement Concrete, (n.d))

Structural Building

Hong Kong Building Department (n.d) mentioned that the following methods had been used to crush the structural building.

1-Mechanical by hydraulic crusher with long boom arm . The concrete and steel reinforcements are broken by the crusher through the long boom arm system. This method is suitable for the dangerous buildings.

Figure 2.3: Hydraulic Crusher with Long Boom Arm

(Source: Hydraulic Circuit Technology, 2000)

2-Wrecking ball. The building is demolished by the impact energy of the wrecking ball which suspended from the crawler crane.

Figure 2.4: Wrecking Ball

(Source: The Trading Tribe, 2003)

3-Implosion. A design included pre – weakening of the structure, the placement of the explosives and the building collapse in a safe manner have to develop.

Figure 2.5: Kingdome Implosion

(Source: Davinel, 2000)

Transportation

After the structural buildings and Portland cement pavements are demolished, the concrete debris has to send to the recycling plants for processing. Construction and Demolition Waste Recycling Information (n.d.) mentioned that it is good to use the roll – off containers or large dump body trailers to transport the mixed load of construction and demolition debris. This is the most effective and cost effective means of the transportation. It also mentioned that the construction and demolition debris can be transport by the closed box trailers and covered containers.

Crushing Plant

Crushing is the initial process of producing the construction and demolition debris into recycled aggregate. The concrete debris is crushed into pieces in this process. Aggregate and Quarry (2001) stated that generally the equipments used for crushing process are either jaw or impacted mill crushers. It also stated that all the recycling crushers have a special protection for conveyor belts to prevent damage by the reinforcement steel that in the concrete debris.

They are fitted with the magnetic conveyors to remove all the scrap metal. According to Recycling of Portland Cement Concrete (n.d.), the equipments used to crush and size the existing concrete have to include the jaw and cone crushers. The concrete debris will break down to around 3 inches by the primary jaw crusher. It also mentioned that the secondary cone crushers will breaks the materials to the maximum size required which vary between ¾ and 2 inches. During the crushing process, all the reinforcing steels have to remove away. Professor S

L Bakoss and Dr R Sri Ravindarajah (1999) stated that there are three methods of sorting and cleaning the recycled aggregate, which are electromagnetic separation, dry separation and wet separation. Electromagnetic separation process is removal of reinforcing steel by the magnet that fitted across the conveyor belt in the primary and secondary crushers.

Dry separation process is removing the lighter particles from the heavier stony materials by bowing air. This method always causes lot of dust. Wet separation process is the aquamator, which the low density contaminants are removed by the water jets and float – sink tank, and this will produces very clean aggregate.

According to COST 337 Unbound Granular Materials for Road Pavements (n.d.), the wood pieces that contained in the concrete debris can be removed by hand – picking from a special platform over the discharge conveyor. After finish the crushing process, the materials are then sent to the screening plant.

Screening Plant and Washing Plant

Screening is the process that separates the various sizes of recycled aggregate. The screening plant is made of a series of large sieves separates the materials into the size required. Recycling of Portland Cement Concrete (n.d.) stated that the size of screen that used to separate the coarse recycled concrete aggregate and fine recycled aggregate is 3/8 inch. The size of screen used to separate the coarse recycled aggregate can be under or over ¾ inches.

It also stated that one more screen should be used to separate those particles that more than the specified size. After the screening process, the recycled are then sent to the washing plant. COST 337 Unbound Granular Materials for Road Pavements (n.d.) stated that the recycled aggregate that produced have to be very clean when using in the high quality product situation.

Stockpile

After all the recycling process, recycled aggregate are stored in the stockpile and ready to use. All the recycled aggregate are stored according to the different size of aggregate. According to Recycling of Portland Cement Concrete (n.d.), the stockpile has to prevent from the contamination of foreign materials. It also mentioned that the vehicles used for stockpiling have to be kept clean of foreign materials.

Comparison of Recycled Aggregate and Natural Aggregate

Recycled aggregate has the rough – textured, angular and elongated particles where natural aggregate is smooth and rounded compact aggregate.

According to Portland Cement Association (n.d.), the properties of the freshly mixed concrete will be affected by the particle shape and surface texture of the aggregate. The rough – texture, angular and elongated particles require much water than the smooth and rounded compact aggregate when producing the workable concrete. The void content will increase with the angular aggregate where the larger sizes of well and improved grading aggregate will decrease the void content.

Natural Aggregate

Recycled Aggregate

Figure 2.16: Comparison between Natural Aggregate and Recycled Aggregate

Quality

The quality is different between recycled aggregate and recycled aggregate. According to Sagoe and Brown (1998), the quality of natural aggregate is based on the physical and chemical properties of sources sites, where recycled aggregate is depended on contamination of debris sources. It also stated that natural resources are suitable for multiple product and higher product have larger marketing area, but recycled aggregate have limited product mixes and the lower product mixes may restrain the market.

Density

The density of the recycled concrete aggregate is lower than natural aggregate. Sagoe and Brown (1998) stated that when compare with natural aggregate, recycled concrete aggregate have lower density because of the porous and less dense residual mortar lumps that is adhering to the surfaces. When the particle size is increased, the volume percentage of residual mortar will increase too.

Strength

The strength of recycled aggregate is lower than natural aggregate. Sagoe and Brown (1998) stated that this is due to the weight of recycled aggregate is lighter than natural aggregate. This is the general effect that will reduce the strength of reinforcement concrete. Further discussion on the strength of recycled aggregate will be mentioned in chapter 5.

Location

Natural aggregate are derived from a variety of rock sources. The processing plant for natural aggregate depends on the resource. It usually occurs at the mining site and outside the city.

Recycled aggregate are derived from debris of building constructions and roads. The locations of recycling plants are depended on where the structures are demolished. The recycling process is often located in the urban area.

Properties and Testing of Aggregate

Recycling of concrete is a relatively simple process similar to crushing natural aggregate. It involves breaking, removing and crushing existing concrete into a material with a specified size and quality. For a good quality product it is essential to separate out different types of material before it enters the crusher. A high level of cleanliness of the material is essential to creating a quality end product that can be reused.

Water Absorption of Course and Aggregate

Water absorption is the amount of moisture absorbed in the aggregate. The water absorption capacity is based on saturated surface dry condition and oven dried condition. Australian Standard HB64 (2002) mentioned that the amount of water in a concrete mix has direct effect on the setting time and compressive strength of concrete. It also stated that moisture content of the aggregate had to determine first before preparing a mix design for a particular aggregate.

If the moisture content of the concrete is not met the target, then more water have to add to avoid a loss of workability. If the moisture content exceeds the target, then less water should be added. The determination of water absorption of aggregate was according to AS1141.5 and AS 1141.6.1.

In this project, determination of water absorption of aggregate were based on natural aggregate with grain size of 10mm, recycled aggregate with gain size of 10mm. All the testing was carried out in the engineering laboratory of University of Wolverhampton.

Apparatus and Test Procedure of Course Aggregate

The following apparatus and equipments used were complied with AS1141.2.

Water Bath

Balance:

Oven

Container

Dishes

The test procedure was according to AS1141.6.1 – 2000. The procedures were as below:

1. Immersed the aggregate in the water at room temperature with the 20mm height of water above the top of aggregate. The aggregate was stirred occasionally to dislodge the air bubbles. The aggregate was immersed for one day (24hours).

2. All the aggregate was transferred to a dish to weight and record.

3. The aggregate was dried in the oven at the temperature of 105ºC to 110ºC to get the constant mass.

Result and Analysis

Table 3.1: Weight of course aggregate in the test.

	Natural aggregate	Recycled aggregate
A, Mass of oven dried aggregate (g)	2732	3023
B, Mass of immersed aggregate (g)	2899	3317

Absorption ratio =*100

• Natural Aggregate

Absorption ratio = * 100 = 6.11 %

• Recycled Aggregate

Absorption ratio = * 100 = 9.73 %

Mix Design

Before having any concrete mixing, the selection of mix materials and their required materials proportion must done through a process called mix design. There are lots of methods for determine concrete mix design. According to Sullivan (2003), the method called British Method was widely used. In this project, altogether five batches of mixtures were determined in this project.

The initial mix batch will be 100% natural coarse aggregate mix batch (control mix). Second mix batch was 75% natural coarse aggregate and 25% recycled coarse aggregate. There was increased of every 25% of recycled coarse aggregate added into every series of mix batch. To fully compare the different types of full recycled aggregate concrete.

The design of a concrete mix, refer to Table 5.1, is usually based on a compressive strength which is sufficient to achieve both of two principal requirements of the hardened concrete for obtaining good quality concrete.

• The water/cement ratio should be low enough to give the required strength for structural and durability purposes.

• The mix should be workable and cohesive enough to ensure a thoroughly compacted and homogenous material

Percentage of aggregate used in all 5 batches of mixes.

	Batch 1	Batch 2	Batch 3	Batch 4	Batch 5
Natural aggregate (%)	100	75	50	25	0
Recycled aggregate (%)	0	25	50	75	100

Initial data for mix design.

Target strength (MPa)	25
Water/cement ratio	0.55
Aggregate / cement ratio	3

Proportion and weight of each mix materials.

Replacement % of recycled	Cement kg	Water kg	Sand kg	New coarse Agg kg	Recycled Coarse Agg kg
0	12.16	6.70	18.24	36.48	0
25	12.16	6.70	18.24	27.36	9.12
50	12.16	6.70	18.24	18.24	18.24
75	12.16	6.70	18.24	9.12	27.36
100	12.16	6.70	18.24	0	36.48

Mixing Concrete

The performance of the recycled aggregate concrete was influenced by the mixing. This means that a proper and good practice of mixing can lead a better performance and quality of the recycled aggregate concrete. The quality of the concrete also can influence by the homogeneity of the mix material during the mixing and after the placement of fresh concrete. A proper mix of concrete is encouraged to the strength of concrete and better bonding of cement with the aggregate.

Once the concrete mix design was calculated, the mixing of the concrete can be carried out. The mixing of recycled aggregate concrete was carried out with a manually pan mixer, which was conducted in the concrete laboratory of University of Wolverhampton. Before the concrete mixing begins, all of the mix materials were weighted and prepared according to the mix design.

The apparatus and equipments used for mixing were as below:

1. Mixer: A pan mixer with capacity of 25 litres mixing. In this project the mixing was manually.

2. Buckets: Suitable size of buckets for containing the materials before mixing.

3. Wheel Barrier: A suitable size of wheel barrier to contain the fresh concrete for workability tests and also place the fresh concrete into the moulds.

The test procedure for the process of mixing was as below:

1. All of the material was weighted and prepared according to the mix design.

2. Before the mixing begins, the surface of the mixer was damped with a wet cloth.

3. All of the aggregate were added into the mixer till the aggregate uniformly distributed throughout the mixer.

4. The cement was poured into the mixer after the aggregate were added.

5. The water was added into the mixer slowly while the mixing of the aggregate and cement was going on.

6. The concrete was mixed approximately 8 minutes after the water was added.

7. The concrete fill into the wheel barrier for make slump test than casting of concrete.

Placing, Compaction and Casting of Concrete Specimens

Before the placing of concrete, the concrete mould must be oiled for the ease of concrete specimens stripping. The oil used is a mixture of diesel and kerosene. Special care was taken during the oiling of the moulds, so that there no concrete stains and left on the moulds.

Once the workability test of recycled aggregate concrete was done, the fresh concrete must placed into the concrete moulds for hardened properties tests. Every batch of recycled aggregate concrete required 8 cubes 100*100*100mm size, and two reinforcement beams with dimensions 100*150*700mm (height*width*length) with still reinforcement 2 in the top and the bottom.

During the placing of fresh concrete into the moulds, vibrations were done using an immersion vibration. The vibration of concrete allows full compaction of the fresh concrete to release any entrained air voids contained in the fresh concrete. If the concrete specimens were not compact in a proper manner, the maximum strength of the concrete cannot be achieved.

The vibration was done every sufficient one third layer of the fresh concrete was poured into the moulds. It is found that the placing and compacting of concrete is getting difficult when the percentage of recycled aggregate increased. This shows that the workability of recycled aggregate used in the concrete is very poor.

The levelling of concrete was done on the surface of the concrete. Levelling is the initial operation carried out after the concrete has been placed and compacted. After the levelling of the fresh concrete specimen was done, the concrete in the mould was left overnight to allow the fresh concrete to set.

Stripping and Curing of Concrete Specimens

After leaving the fresh concrete in the moulds to set overnight, the concrete specimens in the moulds were stripping. The identification of concrete specimens was done and the moulds were cleaned and oiled for the next batch of concrete mix. All concrete specimens were placed into water tank for curing with a controlled temperature of 27ºc in further for 7 and 17days for the hardened properties test of recycled aggregate concrete.

Summary

It shows that the mix design depends on the variables of aggregate/cement ratio, water absorption and proportioning of the aggregates. It seems that volume of aggregate for each mix batches were different.

Once the fresh concrete was mixed, the workability test of the fresh concrete will be conduct. Moreover, after required days of the concrete specimens were cured, the compression test was conducted on day 7 and14.All the test procedures and methods on workability and hardened properties were discussed in chapter 4.

Experimental Methodology

This chapter discussed on the testing procedure for the workability test and hardened concrete specimens test. Workability test included slump test.

Hardened concrete specimens tests included compression test, Absorption test, ultrasonic test, and flexure strength test.

Workability Tests of Fresh Concrete

Sabaa and Ravindrarajah (1999) had mentioned that workability is a very important property of concrete which will affect the rate of placement and the degree of compaction of concrete.

Cement Association of Canada (2003) stated that the workability is the ease of placing, combining and finishing freshly concrete mixed and the degree to which it resists segregation.

According to Cement Manufacturer’s Association India (n.d), a good concrete must has workability in the fresh state and also develop sufficient strength. It also mentioned that there are four factors that can affect the workability. They are as below:

1. Consistency: The degree of consistency is depended on the nature of works and type of compaction.

2. Water/cement Ratio or Water Control of a concrete: Water/cement ratio is the ratio of water in a mix to the weight of cement. The quality of water that required for a mix is depended on the mix proportions, types and grading of aggregate.

3. Grading of Aggregate: The smooth and rounded aggregate will produce a more workable concrete than the sharp angular aggregate.

4. Cement Content: The greater workability can be obtained with the higher cement content.

Slump Test

Slump test is used to determine the workability of fresh concrete. The test is simple and cheap. It is suitable to use in the laboratory and also at site. Although the test is simple, but the testing has to be done carefully due to a huge slump may obtain if there is any disturbance in the process.

Logic Sphere (n.d.) mentioned that the slump test will give a reasonable indication of how easily a mix can be places although it does not directly measure the work needed to compact the concrete. It also mentioned that a slump less than 25mm will indicate a very stiff concrete and a slump that more than 125mm will indicates a very runny concrete.

Australia Standard (2002) stated that slump test will not indicate well for the concrete with very high workability and also very low workability. This is because a very high workability concrete will lose the shape by flowing and collapse, where a very low workability concrete will not collapse.

Apparatus and Test Procedure of Slump Test

1. Mould: A hollow frustum of a cone that made from galvanized steed sheet. The thickness is between 1.5mm to 2mm. The mould has a foot piece, and handles on outer surface, and smooth internal surface. The bottom diameter of the mould is 200mm, the top diameter of the mould is 100mm and the vertical diameter of the mould is 300mm.

2. Rod: A metal rod of 16mm diameter, 600mm long and having a 25mm height of spherical shape at one end with a radius of 5mm.

3. Base plate: A 3mm thickness of a smooth, rigid and non absorbent material base metal plate.

4. Scoop: A suitable size to carry the aggregate of concrete.

5. Ruler: A suitable steel ruler to measure the height of slump.

Figure 4.1: The Apparatus for Slump Test

The test procedure

1. Before the test, the internal surface of the mould was cleaned and moistened with a damp cloth.

2. The mould was placed on a smooth and horizontal surface that free from vibration or shock. While the mould was being filled, it was hold firmly by standing on the foot pieces.

3. The mould was filled in three layers. Each layer was around one – third of the height of the mould. Each layer was being rod with 25 strokes of rounded end of the rod. Each stroke has rod in a uniform manner that over the cross section of the mould.

4. The surface concrete was rolled off after the top layer has been rod. Then, remove the mould immediately by raising it slowly and carefully in the vertical direction.

5. Measured the height of slump immediately. It was determined between the height of the mould and the average height of the top surface of the concrete.

Testing on Hardened Concrete Specimens

Concrete is a combination of Portland cement, water and aggregate that consists of rocks and sand. Normally, concrete is strong in compression but weak in tension.

The testing for the strength if concrete is very important in the civil works. University of Florida (n.d.) mentioned that the engineers can compare the value of the testing to the designed value used for the building structure. This is to make sure that the structure was built well.

This chapter consists of four of hardened concrete testing. They are compression test, flexure strength test, ultrasonic test, and Absorption test.

Compression Test

According to Cement Association of Canada (2003), compressive strength of concrete can be defined as the measured maximum resistance of a concrete to axial loading. Compression test is the most common test used to test the hardened concrete specimens because the testing is easy to make. The strength of the concrete specimens with different percentage of recycled aggregate replacement can be indicating through the compression test.

The specimens used in the compression test were 100*100*100mm. There are two specimens were used in the compression testing in every batches. Differences of the strength among the different percentage of recycled aggregate used in the age of 7and14days also indicated through the compression test. The compression test was carried out in the engineering laboratory of University of Wolverhampton.

Apparatus and Test Procedure of Compression Test

• Testing Machine: ‘Avery’ testing machine.

• Ruler: 400mm long ruler to measure specimen dimensions.

The test procedure

1. The testing for the specimens should be carried out as soon as possible after took out from the curing tank. The specimens need to get the measurements before the testing.

2. The dimensions of the specimens were measured and recorded. The

weight of each specimen was measured and recorded too.

3. The platens of the testing machine were cleaned with a clean rag.

4. Cleaned the uncapped surface of the specimen and place the specimen in the testing machine.

5. Carefully placed the rubber cap on the specimen.

6. The platen was lowered to the rubber cap until the uniform bearing was obtained.

7. The force was applied and increased continuously at a rate equivalent to 20MPa compressive stress per minute until the specimen failed.

8. Recorded the maximum force from the testing machine.

Water absorption test

Apparatus:

• Balance of capacity with a limit of performance not exceeding ±0.5g.

• Rack with wire hangers for suspending the specimen in water.

• Water tank could provide cover of at least 50mm above the top of the

• Drying oven with controlled temperature of 100°C to 110°C.

Test Procedure:

Flexural Strength

The flexural strength of the concrete specimens was determined according to

ASTM C78-84, Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) [5]. For each beam specimen, the flexural strength was determined by loading the beam at third points over a 305 mm (12 inch) clear span. To minimize the torsion effect that is possible due to the specimens not having perfectly square bottoms, one support was manufactured so as to be free to rotate in the direction transverse to the beam’s longitudinal axis. The 100 x 150 x 700 mm, beams were tested at the ages of 14 days. Beam specimens were loaded to failure at a rate of 3.6 KN per minute. The test setup for the flexural test is shown in Figure 2.7.

Ultrasonic test

Ultrasonic pulse velocity measurements are used extensively as a non-destructive test method to establish the in-situ strength of hardened concrete. This method used in combination with drilled cores and rebound test gives reliable information regarding the quality of the concrete used. Ultrasonic pulse velocity is also used to locate crack and non homogeneous areas in concrete.

The velocity of ultrasonic pulses traveling in a solid material depends on the density and elastic properties of that material. The quality of some materials is sometimes related to their elastic stiffness so that measurement of ultrasonic pulse velocity in such materials can often be used to indicate their quality as well as to determine their elastic properties. Materials which can be assessed in this way include, in particular, concrete and timber but exclude metals.

When ultrasonic testing is applied to metals its object is to detect internal flaws which send echoes back in the direction of the incident beam and these are picked up by a receiving transducer. The measurement of the time taken for the pulse to travel from a surface to a flaw and back again enables the position of the flaw to be located. Such a technique cannot be applied to heterogeneous materials like concrete or timber since echoes are generated at the numerous boundaries of the different phases within these materials resulting in a general scattering of pulse energy in all directions.

Method of testing

For assessing the quality of materials from ultrasonic pulse velocity measurement, it is necessary for this measurement to be of a high order of accuracy. This is done using an apparatus that generates suitable pulses and accurately measures the time of their transmission (i.e. transit time) through the material tested. The distance which the pulses travel in the material (i.e. the path length) must also be measured to enable the velocity to be determined from:-

Pulse velocity = Path length / Transit time

Path lengths and transit times should each be measured to an accuracy of about ±1%. The instrument indicates the time taken for the earliest part of the pulse to reach the receiving transducer measured from the time it leaves the transmitting transducer when these transducers are placed at suitable points on the surface of the material. The direct transmission arrangement is the most satisfactory one since the longitudinal pulses leaving the transmitter are propagated mainly in the direction normal to the transducer face.

The indirect arrangement is possible because the ultrasonic beam of energy is scattered by discontinuities within the material tested but the strength of the pulse detected in this case is only about 1 or 2% of that detected for the same path length when the direct transmission arrangement is used. Pulses are not transmitted through large air voids in a material and, if such a void lies directly in the pulse path, the instrument will indicate the time taken by the pulse that circumvents the void by the quickest route. It is thus possible to detect large voids when a grid of pulse velocity measurements is made over a region in which these voids are located.