Table of Figures

Table 1- Materials Studied 2

Table 2: Waste Materials Types and Remarks 25

Table 3: Traditional Materials and waste material 26

Table 3: Traditional aggregate versus Waste material aggregate 27

Table 4: Highest compression strength, Tensile Strength and Density 28

1.0 Introduction

Concrete is the single most widely used material in the world it contributes 5% of the annual anthropogenic CO2 production (1). Most of the CO2 production comes as a result of producing cement. The U.S. Environmental Protection Agency (EPA) estimates that 250 million tons of waste was produced in 2011 (2). Aggregates comprise about 60% to 75% of the total volume of concrete (3). In 2011 the US Geological Survey estimated 1.16 billion metric tons of crush stone was produced in the United States, 80% of all the aggregate produced most was used in highway construction and road construction and maintenance as well as residential construction and sewers (4).

The US Geological Survey also estimates that 810 million metric tons of gravel and stone was produced in 2011 for construction purposes (5). These factors have resulted in studies being conducted on the use of alternate materials derived from waste in concrete production. This study will analyse the potential applications of solid waste as aggregate in structural concrete by:

Defining structural concrete and solid waste.

Describing the waste materials to be studied (Table 1)

Reviewing research conducted on use the waste material studied as an aggregate in concrete production.

Reviewing the research conducted to determine their limitations of waste materials as concrete

Compare and contrast the limitations and compressive strengths of using the waste materials studied

Table 1- Materials Studied

1.1 Definitions

1.1.1 Solid Waste

Solid waste is any discarded material resulting from community, household, industrial, commercial, mining and agricultural activities. Solid waste can either be a solid, semisolid, or liquid.

1.1.2 Structural Concrete

Concrete is a material produced by mixing a binder, water, and aggregate. The binder undergoes hydration which "glues" the aggregate together to produce concrete. Structural concrete is concrete of a specific quality that is capable of carrying a structural load or forming an integral part of a structure (6). For the purposes of this study, the compressive strength of structural concrete will range from 20 MPa (3000 psi) for residential purposes and 34 MPa (5000 psi) and higher for commercial structures. Other mechanical factors such as soundness, freeze/thaw, durability and porosity weren't considered as a part of this study.

2.0 Waste Materials

2.1 Polystyrene

Millions of tons of waste polystyrene are produced in the world yearly. Polystyrene is an organic polymer derived from oil which can be ridged or foam. Due to its inability to be decomposed, a lot of research has been conducted to investigate methods of reusing polystyrene.

Expanded polystyrene foam (EPS) is a rigid, tough, closed-cell foam usually white in colour and made of pre-expanded polystyrene beads. The average density, thermal conductivity and compressive strength of waste EPS is approximately were 10 kg/m3, 0.0368 W/mK, and 0.12 MPa, respectively (7). As a result modern research conducted in the use of polystyrene has centred on improving the mechanical properties of EPS

This study will review the use of EPS as an aggregate by focusing on research by Abdulkadir Kan Ramazan Demirboğa, 2009; B.A. Herki, J.M. Khatib and E.M. Negim 2013; and S.G. Park and D.H. Chisholm 1999.

2.1.1 S.G. Park and D.H. Chisholm 1999

Description

During the 90's research into the use of waste EPS was focused more on using concrete made from EPS as insulation. The research conducted by S.G. Park and D.H. Chisholm 1999 used a mix of cement, fly ash, sand and polystyrene. The mix proportion which yielded the highest compressive strength was the P1000 mix which consisted of 450 kg/m3 cement, 0 kg/m3 fly ash, fine aggregate 340 kg/m3 EPS 850 kg/m3 (8). Concrete produced by this mix design had a density of 1040 kg/m3 and a 28 day compressive strength of 6.7 MPa

Limitation

The research conducted by S.G. Park and D.H. Chisholm 1999 showed care must be exercised while mixing, pouring and compacting concrete using vibratory techniques to minimize segregation.. Fly ash reduces water demand but causes a significant compressive strength reduction (8).

2.1.2 Abdulkadir Kan Ramazan Demirboğa 2009

Description

Experiments by (Kan & Demirboga, 2009) show that heat treatment increased the mechanical properties while decreasing the volume of the waste EPS. The best results for this heat treatment were discovered when waste EPS was heated in a hot air oven for 15 minutes at 130 ˚C to form modified waste expanded polystyrene (MEPS). The average density, thermal conductivity and compressive strength of MEPS, increased to 217 kg/m3, 0.0555 W/mK and 8.29 MPa, respectively. This resulted in a concrete with a density of between 900-1700 kg/m3 depending on the mix proportion of MEPS to Natural aggregate Fine Aggregate and Course aggregate. The 28 day compressive strengths of MEPS concrete range from 12.58 MPa to 23.34 MPa depending on the mix proportion of MEPS to Natural aggregate Fine Aggregate and Course aggregate. The ratio with the highest density 1700 kg/m3 and highest compressive strength 23.34 MPa was the one which contained 25% fine MEPS aggregate (< 4mm) 25% natural sand 50% coarse natural aggregate (9).

Limitations

The experiment conducted by Abdulkadir Kan Ramazan Demirboğa, 2009 showed that care must be exercised while mixing, pouring and compacting the fresh concrete to minimize the segregation of concrete mixture. The smooth and plane surface of the some coarse MEPS particles can significantly weaken the bond between the cement paste and aggregate particles. Testing shows that short term compressive strength and ultrasonic pulse velocity is very low but increases as curing time increases. Research by Abdulkadir Kan Ramazan Demirboğa 2009 shows that an increase in the amount of the MEPS reduces compressive strength since adherence cannot fully be achieved between the MEPS and cement paste and that the MEPS particles themselves are quite weak (9).

2.1.3 B.A. Herki, J.M. Khatib and E.M. Negim 2013

Description

Using a method derived by another researcher EPS is modified to produce Stabilised Polystyrene aggregate SPS. The research by B.A. Herki, J.M. Khatib and E.M. Negim 2013 showed that using a mix design of 60% SPS, 768 kg/m3 natural aggregate (fine and course), 0 kg/m3 fly ash and 320 kg/m3 Portland cement. The 28 day strength of the concrete produced with this mix design was 11 MPa with a density of 1800 kg/m3.

Limitations

The research by B.A. Herki, J.M. Khatib and E.M. Negim 2013 had similar limitations found in the research of S.G. Park and D.H. Chisholm 1999.

2.2 Clay Brick

11,700,000 metric tons of clay have been produced in the United States in 2011 with 4.490,000 metric tons of clay bricks were produced (10). 85% of all the bricks taken from demolition sites are dumped with 10% being reused and 5% being recycled (11). The compressive strength of

Natural aggregate can range from approximately 20 - 40 times that of crushed poor quality bricks. Research in the use of brick as aggregate is limited. For this study research by Jafar Bolouri Bazaz1 and Mahmood Khayati 2012 and Farid Debieb, Said Kenai 2008 will be reviewed.

2.2.1 Farid Debieb, Said Kenai 2008

Description

Research by Farid Debieb, Said Kenai 2008 investigated the use of recycled bricks as a fine and coarse aggregate replacement for natural aggregate. It was found that using fine and course aggregates derived from crush brick gives a 28 day compression strength of 18 MPa. Using a plasticiser can increase strength to 21MPa due to the reduction of water. Replacing 25% of the coarse natural aggregate with crushed recycled brick and 75% of natural fine aggregate with crushed recycled bricks results in a 28 day compressive strength is 23MPa (12).

Limitations

An increase in crushed brick aggregate to 100% results in some level of segregation of the aggregates. Increasing the amount of crush brick used as aggregate results can result in as high as a 40% reduction in compressive strength over natural aggregates. Increasing water content of 0.03 can result in a loss of 3 MPa. Including brick instead of natural aggregate can reduce the 7 day compressive strength almost half that of using natural aggregates. Shrinkage increased significantly after 28 days, when compared to using only natural aggregates, and increased as the crush brick to natural aggregate ratio increased (12).

2.2.2 Jafar Bolouri Bazaz1 and Mahmood Khayati 2012

Description

Jafar Bolouri Bazaz1 and Mahmood Khayati 2012 researched the use of low quality bricks, i.e. a brick with a compressive strength between 3 -7 MPa, as a coarse and fine aggregate within concrete. It was found that using fine and course aggregates derived from crush brick gives a 28 day compression strength of 18 MPa. Adding silica fume and a plasticizer can increase the 28 day compressive strength of concrete made with low quality bricks to 25MPa from 18MPa. Hard burned bricks like those used by Khaloo 1994 were used by Jafar Bolouri Bazaz1 and Mahmood Khayati 2012. Concrete which was made using this type of brick yielded a 28 day compressive strength of 28 MPa. Concrete produced with hard burned crushed brick as aggregate is durable, has low permeability, is light weight and performs well in the soundness and freezing-and-thawing tests (11).

Limitations

Brick quality and brick type can result in a difference of 10 MPa between high quality bricks and low quality bricks. The process of brick recycling seems to be uneconomical. (11).

2.3 Glass

The US Environmental Protection Agency estimates that waste glass makes up 11.5 million tons of municipal waste yearly. United Nations estimates that worldwide 14 million tons of glass is disposed of yearly (13). Due to glass having an angular shape when broken most research into the use of glass in construction focuses on using glass as an aggregate in asphalt and as a road base. There is some research which focusses on using glass as an aggregate in concrete however glass is silica rich and during hydration the cement forms Ca(OH)2 (which is alkali). This leads to a alkali-silica reaction (ASR) with alkali silica gel being produced which can cause cracks weakening the concrete due to expansion of the ASR gel. For this study research by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 and Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013 will be reviewed.

2.3.1 Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013

Description

Research by Dr. Zubaidah Abdullateef M. A. Al - Bayati aimed to prove that crushed glass could be used as an adequate replacement for fine aggregate. The research conducted by Dr. Zubaidah Abdullateef M. A. Al - Bayati focused on producing concrete with natural sand partially replaced by 10%, 20%, 30%, 40% and 50% glass powder from crushed bottles. 97% of crush glass was less than 4.75mm. A mix ratio of 445 kg/m 3 cement, 1240 kg/m 3 coarse aggregate 478.8 kg/m 3 fine aggregate and 53.2kg/m 3 glass (20% fine aggregate) has a compressive strength of 37.5 MPa (14).

Limitations

Colour of the glass matters in mitigating ASR as seen in research by Blumenstyk (2003) who concluded that using glass from green bottles mitigated ASR due to the existence of chromium oxide which gave the glass its green colour. Particle size of the glass must be small since an increase in particle size can result in a reduction in compressive strength over natural aggregate. ASR can affect long-term durability and strength if enough pozzolonic material isn't used to minimise this reaction (15)

2.3.2 Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006

Description

Research by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 focussed on determining the consistency and compressive strength of concrete produced with 5%,10%, 15% and 20% glass replacing the natural fine aggregate. All the glass used in the experiment was smaller than 9.5 mm with 90% smaller than 4.75mm. The experiment conducted by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 indicated that as the percentage of glass increased so did the compressive strength. They concluded this was a result of the natural aggregates having a lower compressive strength than glass. The results also showed that consistency wasn't affected by an increase in glass. A mix ratio of 446 kg/m 3 cement, 961 kg/m 3 coarse aggregate 468 kg/m 3 fine aggregate and 109.8 kg/m 3 glass (20% fine aggregate) has a compressive strength of 45 MPa (15).

Limitations

Research by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 resulted in limitations similar to those found in the research by Dr. Zubaidah Abdullateef M. A. Al - Bayati 2000 except that adding more glass results in a higher compressive strength than using natural aggregates.

2.4 Plastic

The US Environmental Protection Agency estimates 30 billion PET bottles a year are disposed of in the US and 5 million tons of high density polyethylene is produced yearly in the US for use as appliances, car parts and laundry detergent bottles and milk jugs. For this study research by Malek Batayneh, Iqbal Marie, Ibrahim Asi in 2006, Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod 2005 and Semiha Akcaozoglu , Kubilay Akcaozoglu, Cengiz Duran Atis 2013will be reviewed to see if plastic can be used as a suitable aggregate.

2.4.1 Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006

Description

Research by Malek Batayneh, Iqbal Marie, Ibrahim Asi in 2006 focussed on determining the consistency and compressive strength of the concrete produced with 5%, 10%, 15% and 20% plastic replacing the natural fine aggregate. The experiment performed showed that workability was slightly reduced as the percentage of plastic increased and it was concluded this was due to the plastic particles having sharper edges. The results produced showed that as little as 5% plastic aggregate resulted in 23% reduction in compressive strength when compared to concrete produced using traditional materials. When 20% of the fine aggregate is replaced by plastic the compressive stress reduces by 72% compared to traditional aggregates. A mix ratio of 446 kg/m 3; cement 961 kg/m 3; coarse aggregate 555.7 kg/m 3; fine aggregate and 17.8 kg/m 3 plastic has a compressive strength of 26 MPa (15).

Limitations

Care must be taken when adding plastic to the mixture as a slight increase in the percentage of plastic to fine aggregate can result in a large reduction in compressive strength.

2.4.2 Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, Sun-Kyu Chod 2005

Description

The study by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod 2005 focused on the use of PET bottles and granulated blast-furnace slag GBFS as a replacement for fine aggregate. The coarse aggregate used in the experiment was crush stone with a maximum size of 20mm, the fine aggregate used was clean river sand and lightweight aggregate made from PET bottles and GBFS (WPLA). The lightweight aggregate was manufactured according to the following procedure. The PET bottles cut up and placed in a mixer. The mixer was then heated to 250 °C while being spun for 20 s. The GBFS was then placed in the mixer with the waste PET bottles to solidify the surface of aggregates. Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod 2005 tested the mechanical properties of the concrete produced with 25%, 50% and 75% WPLA used as a replacement for river sand. The experiment by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod used a water content of 45%, 49%, and 53%.in each concrete mixture. The experiment by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod in 2005 had a compressive strength of 33.8 MPa using a replacement WPLA of 25% and a water content of 45% (16).

Limitations

As WPLA increases workability decreases resulting. As the WPLA content increases the compressive strength of the concrete produced decreases.

2.4.3 Semiha Akcaozoglu , Kubilay Akcaozoglu, Cengiz Duran Atis 2013

Description

Research by Semiha Akcaozoglu , Kubilay Akcaozoglu, Cengiz Duran Atis 2013 focused on the use of PET bottle granules as a replacement for uncrushed quartzitic natural sand. To improve workability a superplasticiser was added, with its volume increasing as the volume of PET bottle aggregate increased. Unlike the research by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, Sun-Kyu Chod 2005 the PET bottle granules weren't modified and the mechanical properties of the concrete produced by replacing 30%, 40%, 50%, 60% of the natural fine and coarse aggregate was investigated. Concrete produced with 402 kg/m 3coarse aggregate, 615 kg/m 3 fine aggregate , 218 kg/m 3PET bottle and 500 kg/m 3had the a compressive strength of 25.3 after 28 days which was the highest of the 4 samples of concrete with PET bottle granules as aggregate (17).

Limitations

The limitations of the concrete produced were similar to the research by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, Sun-Kyu Chod 2005. The surface of the PET bottle granules aggregate was smooth and had a weaker bond strength, between the aggregate and the cement paste, than using natural aggregate (17).

2.5 Sawdust

Hundreds of thousands of tons of natural waste are created yearly from bio polymers such as timber, rice husk, bagasse, palm kernel etc. Saw dust can be defined as loose particles or wood chipping created as a result of sawing timber into standard sizes e.g. 2"x4"in a saw mill. The total amount of sawdust originating in U.S. exceeds 15 million tons a year (18) For this study research by Ramachandran, Vangipuram Seshachar 1981 and F.A. Olutoge 2010 will be reviewed.

2.5.1 Ramachandran, Vangipuram Seshachar 1981

Description

Research by Ramachandran, Vangipuram Seshachar in 1981 was focussed more on the thermal resistance and resilience and less on the compressive strength of the concrete produced using only sawdust as an aggregate. A mix design of 1 part cement to 2 parts sawdust results in a compressive strength of 7.5 MPa. Concrete produced with sawdust can be nailed and sawed (19).

Limitations

Decay in the wood sometimes interferes with the curing process of concrete. Saw dust must be soaked to remove soluble matter to allow the concrete to be mixed properly. Concrete containing large amounts of concrete is flammable. Concrete made from materials with good mechanical properties e.g. pine and spruce produces concrete with acceptable mechanical properties. Sawdust concrete can absorb large amounts of water and expand. (19)

2.5.2 F.A. Olutoge 2010

Description

The sawdust used in the experiment conducted by F.A. Olutoge 2010 was sourced from planks and furniture markets in Lagos, Nigeria. The saw dust produced consisted of chippings from various hardwoods which were sundried in waterproof bags. The research by F.A. Olutoge 2010 focussed on replacing sawdust as fine aggregate at the following percentages 25%, 50%, 75%, 100%. The compressive test indicated that as the saw dust content increased compressive strength decreased. The mix proportion which yielded the highest compressive strength after 28 days was 6.170 kg cement, 3.085 kg sawdust, 9.255 kg sand and 24.690 kg granite and had a compressive strength of 15.9 MPa. All samples crushed had 10mm high yield reinforcement cast within them (20).

Limitations

Sawdust with a large amount of bark introduce a high content of organic material that may upset the reactions of hydration (20). Similar to limitations of concrete produced in experiments by Ramachandran, Vangipuram Seshachar 1981

2.3 Recycled Concrete

850 million tones of construction and demolition waste is generated yearly in the EU while in the United States of America it is estimated that each year the construction and demolition waste generated is 123 million tons per year. Usually this material would be placed in landfills but some countries such as the United States of America, China and England have begun enforcing restrictions on waste by the use of taxation and the creation of prohibitions in recent times (21). In Hong Kong the government has even gone as far as to set up a recycling plant to produce aggregate from recycled concrete and has also encouraged the adoption of recycled aggregate within government departments (22). Research into the use of recycled concrete as aggregate has intensified to determine if concrete can be a suitable replacement for structural concrete and to determine if there is a better practice which can be used to produce concrete from recycled concrete. This study will focus on research from P.C. Yong, D.C.L Teo 2009, Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010 and Vivian W.Y. Tam, X.F. Gao, C.M. Tam 2005

2.3.1 P.C. Yong, D.C.L Teo 2009

Description

Research by P.C. Yong, D.C.L Teo 2009 focused on the use of recycled concrete for structural concrete. For the experiment conducted by P.C. Yong, D.C.L Teo 2009 the recycled concrete aggregate used was generated from crushed concrete test cubes. The RCA was used had a max size of 25mm and a min size of 4.75 mm. the recycled concrete had a compressive strength of 30 MPa. The researchers chose to investigate the mechanical properties of concrete produced with 50% of the coarse aggregate Natural and the remainder RCA and 100% of the coarse aggregate as RCA. A test was also conducted using using 100% saturated surface dry (SSD) RCA. Replacing 50% of the natural aggregate with RCA results in concrete with a 28 day compressive strength that is quite similar to the compressive strength of concrete produced with natural aggregates. There was approximately a 10 Mpa difference in the 28day compressive strength when 100% of the natural aggregate was replaced by RCA and when 100% of the natural aggregate was replaced by SSD RCA but after 56 days the compressive strength of SSD RCA is slightly less than RCA . Using 100 % RCA as a coarse aggregate resulted in the highest 28 day compressive strength 57.99 MPa which is higher than using natural aggregates however at 56 day the compressive strength of natural aggregates is higher than using 100% RCA.

Limitation

The strength of the concrete used as an RCA must be known to determine if it can be used to produce structural concrete. RCA concrete has lower flexural strength than traditional concrete. The 56 day compressive strength of RCA concrete is lower than that of concrete produced using natural aggregates.

2.3.2 Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010

Description

Research by Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010 focused on the use of recycled concrete for structural concrete. For the experiment conducted by Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010 the recycled concrete aggregate used was generated from crushed concrete test cubes and one precast column. The RCA was used had a max size of 32 mm and a min size of 4 mm. the recycled concrete had a compressive strength of 37 MPa for the crushed cubes and 50 MPa for the precast column. The researchers chose to investigate the mechanical properties of concrete produced with 50% of the coarse aggregate Natural and the remainder RCA and 100% of the coarse aggregate as RCA.. Replacing 50% of the natural aggregate with RCA results in concrete with a 28 day compressive strength slightly higher than using natural aggregate. There was little difference in the 28day compressive strength when the natural aggregate was replaced by RCA. Using 100 % RCA as a coarse aggregate resulted in the highest 28 day compressive strength 45.66 MPa which is higher than using natural aggregates. The concrete produced with 100% RCA was used to cast a test beam which failed similarly to beams casted using natural aggregates. Increasing RCA to 100% increased the concrete compressive stress up to 25% in test conducted on the test beam

Limitations

Research by Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010 had similar limitations to the research conducted by by P.C. Yong, D.C.L Teo 2009. Concrete produced using RCA can be susceptible to extreme conditions.

2.3.3 Vivian W.Y. Tam, X.F. Gao, C.M. Tam 2005

Description

Research by Vivian W.Y. Tam, X.F. Gao, C.M. Tam 2005 focused on determining if the 2 stage mixing method produced concrete with a higher compressive strength. Using the method described in Figure 1 resulted in a 14% increase in the 28 day compressive strength between using the using the normal mixing approach and using the two stage approach when mixing concrete with 30% of the natural coarse aggregate replaced. Replacing the coarse aggregate with RCA and using the two stage mixing method resulted in a compressive strength of 66.2 MPa which was the highest compressive strength of the 6 test and was 8.13 MPa more than using the normal mixing approach

Figure 1: Mixing Procedures of the Normal Mixing Approach versus the Two Stage Mixing Approach (23)

Limitations

Research by Vivian W.Y. Tam, X.F. Gao, C.M. Tam 2005 had similar limitations to the research conducted by by P.C. Yong, D.C.L Teo 2009 and Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010

3.0 Discussion

3.1 Polystyrene

When it came to the determining the use of polystyrene as an aggregate in structural concrete this study focused on research by S.G. Park and D.H. Chisholm 1999 which focused on producing light weight concrete which was suitable as insulation while Abdulkadir Kan Ramazan Demirboğa 2009 focused on modifying expanded polystyrene (MEPS) foam to produce structural lightweight concrete(MEPS concrete) and B.A. Herki, J.M. Khatib and E.M. Negim 2013 used another method of modification to produce a light weight concrete with a low compressive strength.

Research into the use of polystyrene as an aggregate has revealed that the following considerations:

The weak bonds between the aggregates and the cement paste

Difficulties of mixing, pouring and compacting using vibratory techniques without causing segregation of the aggregate

Although using MEPS aggregate can produce concrete with a compressive strength which is adequate for residential purposes, it is susceptible to the same problems experienced when using polystyrene as an aggregate. Therefore MEPS concrete and polystyrene concrete isn't practical for use in the construction industry at the moment. Using polystyrene as a lightweight aggregate in structural concrete is still in its testing phase and must be perfected and is much better suited as insulation in cavity walls and for non-structural purposes and not as structural concrete.

3.2 Clay Brick

When it came to the determining the use of waste clay bricks as an aggregate in structural concrete this study focused on research by Farid Debieb, Said Kenai 2008 which focused on replacing 25% of the natural fine aggregate with recycled bricks and Jafar Bolouri Bazaz1 while Mahmood Khayati 2012 focused on replacing all the fine and coarse aggregate with hard burnt brick.

Replacing natural aggregate with bricks as aggregate resulted in a reduction of the compressive strength of the concrete produced. The research revived in this study showed a reduction of 25.81% as seen in the research by Farid Debieb, Said Kenai 2008 and 22.65% as seen in the research by Jafar Bolouri Bazaz1 and Mahmood Khayati 2012 over using natural aggregate.

Concrete produced by crushed brick as aggregate has good performance in the soundness and freeze thaw test. Research by Jafar Bolouri Bazaz1 and Mahmood Khayati 2012 showed that using silica fumes along with the use of a super plasticiser to increase workability without increasing water content can produce concrete with a compressive strength which is 31% lower than using natural aggregate but produces a concrete which is adequate for residential purposes. Although hard burnt brick produced the highest compressive strength of the research reviewed as seen in

Table 5, hard burnt brick isn't as readily available as poor quality brick.

Research into the use of brick as an aggregate has revealed that the following considerations:

Concrete Shrinkage increases significantly after 28 days over using natural aggregate

Water content must be monitored carefully as a 0.03 increase in water content can result in a loss of 3 MPa

The change in quality of brick can result in a significant change in concrete produced

Once these limitations are considered and designed for there is no reason why concrete couldn't be used as structural concrete for residential purposes or non-structural concrete.

3.3 Glass

When it came to the determining the use of glass as aggregate in structural concrete this study focused on research by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 and Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013 when trying to determine if glass was an adequate replacement for fine aggregate in structural concrete see

Table 2. The research reviewed in this study came to conflicting results concerning the compressive strength of concrete produced using glass as a fine aggregate. Although both researchers used glass with a maximum size of 4.75 mm in varying volumes Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 found that increasing the percentage of glass in the concrete mixture caused an increase in compressive strength of the concrete produced which is contrary to the research by Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013 see Error! Reference source not found.. Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013 stated that they believed the decrease in compressive strength of between the concrete produced with crush fine glass aggregate and the concrete produced from fine natural aggregate was due the difference in compressive strength between the two materials. It should be noted that when the 28day compressive strength of concrete produced with 10% of the fine aggregregate replaced both researchers produced concrete with a compressive strength of 37.5% (14) and 38% (15). The compressive strength of the concrete produced using glass increased, as the proportion of glass increased in the research by Malek Batayneh, Iqbal Marie, Ibrahim Asi 2006 while research by Dr. Zubaidah Abdullateef M. A. Al - Bayati 2013 showed the opposite result. This may be due to the method by which the glass was crushed and the shape of the crushed glass particles. Research into the use of crush glass as an aggregate has revealed that the following considerations:

ASR can affect long term durability of concrete as ASR gel expands over time

Colour can affect properties of concrete e.g. mitigate ASR

The research used in this study focused on the use of glass as an aggregate for structural concrete and didn't focuss on the long term effects of ASR on the concrete produced. Research by Shayan 2002 suggests that the use of pozzolonic material could minimise the effects of alkali-silica reaction (15) while research by Zdenek 2000 concluded that the effect of alkali-silica reaction will be eventually be eliminated if the particles size is small enough (24). Although concrete produced using glass as a replacement for fine aggregate can produce concrete with a compressive strength that can be used for residential purposes and commercial purposes the long term effects of ASR and mitigation techniques must be investigated further to determine if it is adequate for use in construction.

3.4 Plastic

When it came to determining the use of plastic waste as an aggregate in structural concrete this study focused on analysing the research by Malek Batayneh, Iqbal Marie, Ibrahim Asi in 2006, Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod 2005 and Semiha Akcaozoglu , Kubilay Akcaozoglu, Cengiz Duran Atis 2013. The research by Malek Batayneh, Iqbal Marie, Ibrahim Asi in 2006 and Sun-Kyu Chod 2005 focussed on the use of plastic as a replacement for fine aggregate while Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc focused on replacing fine aggregate with modified PET bottle granules. Sun-Kyu Chod 2005 and Semiha Akcaozoglu , Kubilay Akcaozoglu, Cengiz Duran Atis 2013 used unmodified PET bottle bottles as a replacement for fine and coarse natural aggregate see

Table 2.

Using plastic as a replacement for coarse and/or fine aggregate can result in a in a significant reduction in compressive strength while replacing 25% of the fine aggregate with PET bottlegranules modified using heat and GBFS as seen in the research by Yun-Wang Choia, Dae-Joong Moonb, Jee-Seung Chungc, and Sun-Kyu Chod 2005 resulted in a 10% decrease in strength over using natural aggregates.

Research into the use of plastic as an aggregate has revealed that the following considerations:

The weak bonds between the aggregates and the cement paste

Increasing plastic content decreases workability

Some research shows that a slight increase in the percentage of plastic aggregate can result in a large reduction in compressive strength.

Using any of the methods reviewed can produce concrete which is suitable for residential purposes. Using WPLA modified with GBFS to replace 25% of fine aggregate can produce concrete which is almost suitable for commercial purposes.

3.5 Sawdust

This study focused on research by Ramachandran, Vangipuram Seshachar in 1981 and F.A. Olutoge 2010 when it came to determining the suitability of sawdust as an aggregate in concrete.

Research into the use of sawdust as an aggregate in concrete has revealed that the following considerations:

Too much organic material and decay can affect hydration

Too much sawdust is flammable

The type of tree used can produce concrete with better mechanical properties

Concrete made from concrete and expand due to too much water

These considerations and the low compressive strength of concrete produced using sawdust as a replacement for fine aggregate indicate that timber is a poor substitute for the production of light weight structural concrete.

3.6 Recycled Concrete

This study focused on research by P.C. Yong, D.C.L Teo 2009, Mirjana Malešev, Vlastimir Radonjanin and Snežana Marinković 2010 and Vivian W.Y. Tam, X.F. Gao, C.M. Tam 2005 when it came to determining the suitability of recycled concrete as an aggregate in concrete.

Using recycled concrete as a replacement for coarse natural aggregate produces concrete which has a higher compressive strength. Changing the method of mixing also results in an increase in the compressive strength of the concrete produced using RCA.

Research into the use of sawdust as an aggregate in concrete has revealed that the following considerations:

The mechanical properties of the concrete used must be know

Some research showed that the 56 day compressive strength of RCA concrete was lower than that found in traditional concrete

Concrete is susceptible to extreme conditions

RCA is the most researched waste aggregate used to produce concrete, and has been used primarily for non-structural purposes in the construction industry mostly due to its susceptibility to extreme conditions and the fact that the RCAs mechanical properties are normally unknown. Once those considerations are met there is no reason why RCA concrete couldn't be for producing structural concrete for commercial purposes.

*7day strength value

N.B. Replacement aggregate are given as a % of the total fine and coarse natural aggregate unless stated otherwise

Table 4: Traditional aggregate versus Waste material aggregate

4.0 Conclusion

Most of the waste materials in this study can be used as aggregate for the production of structural concrete for residential purposes except using sawdust. However the discrepancies in the 28 day compressive strength of the concrete produced using certain material show that there is still some way to go before these materials would be accepted in the construction industry. At the moment using these materials require personnel with the experience to produce concrete which can be used as structural concrete. For the most part replacing at least some of the fine and/or course natural aggregate could result in a huge reduction in the waste which goes to the land fill yearly and the energy cost associated with mining virgin material.

The push by some developed countries to tax dumping heavily and the lack of space for landfills have started the movement towards reusing waste materials. Unfortunately many countries especially in the Caribbean haven't adopted this practice and this may need to change this.

There also needs to be a change on the part of Architects and Engineers to design for and to demand the production of more sustainable concrete i.e. concrete made using waste materials. Engineers and Architects need to take up the cause of using and producing sustainable concrete and should be at the forefront through their various associations ,ICE, ASCE etc., to sensitising builders and property owners that using sustainable concrete could produce a product which is "greener" and which can perform as well or better than using natural aggregates.