Essay: Use of fine green crushed glass (FGCG) and crumb rubber (CR) in concrete

Introduction
This chapter deals with the background and motivation for the use of waste glass and tyres in the form of fine green crushed glass (FGCG) and crumb rubber (CR) in concrete. The use of these wastes will be to reduce the amount of raw materials used for aggregate and cement production that has an effect on the environment. The environmental problems caused by glass and tyres needs to find an economically viable solution, primarily in the construction industry.
Background and Motivation
Over the last few decades there has been an increase in pollution in not only South Africa, but globally. This is due to the increase in population that inevitably leads to more waste being generated. Wastes such as tyres are a concern at landfill sites, also referred to as Waste Disposal Facilities (WDFs) in South Africa (SA), as they cause pollution to the environment, create hazards and become a breeding ground for vermin and mosquitoes, which may lead to the spreading of diseases.
In addition, according to the Recycling Economic Development Initiative of South Africa (REDISA) , the legislative authority for the recycling of waste tyres in SA, it is estimated that in SA there are approximately 10 million tyres being disposed of at waste disposal facilities and by means of dumping each year.
The problem with glass found at WDF’s can be considered to have a lesser impact on the environment compared to the impact which tyres have on the environment. Waste Glass (WG) found at Material Recover Facilities (MRFs) where it follows the process of reduce, re-use and then recycle (Batayneh, Marie & Asi, 2007) needs to find a solution where recycling is considered a last resort. That said, the excess glass from the MRFs or where there are no MRFs, glass will be dumped at WDFs. As the very long lifespan of glass is unknown it takes up space at the waste disposal facilities where it could be used to better effect and thereby reduce impact on the environment.
Adding to the reduction of waste that is required in SA, Muigai et al. (2013) determined that in SA 39.7 Mt of raw materials are used per year for the production of concrete. Where 32.1 Mt were used for the production of aggregate and 7.6 Mt for the production of cement. This indicates that the end use which is concrete has a major effect on the natural resources. The production of cement also contributes to 94.7% of carbon dioxide emissions of the concrete industry (Muigai et al., 2013).
The aforementioned effects glass and tyres has in the environment and the impact cement and aggregate has on the natural resources gives rise to a more sustainable use of raw materials. The glass and tyres could be used to partially replace aggregate in concrete.
Research problem
Recyclable FGCG and CR as a partial replacement for fine aggregates, fresh and hardened properties of concrete have been investigated separately. No investigations on the fresh and hardened properties of recyclable FGCG combined with CR in concrete have been officially investigated in literature.
Research Question
What effect will recyclable fine green crushed glass and crumb rubber have as a partial replacement for fine aggregate on concretes fresh and hardened properties?
Objectives and outcomes
The aim of this work is to evaluate the fresh and hardened properties of concrete containing waste glass and tyres with conventional cement binders. The glass used in this study will be fine green crushed glass (FGCG) and the tyres will be in the form of crumbed rubber (CR) as a partial replacement for fine aggregate in concrete. In order to achieve this, the following objectives will be achieved:
To establish through tests the fresh and hardened properties of concrete containing aggregates of a combination of FGCG and CR compared to conventional concrete.
The percentage of partial replacement of a combination of FGCG and CR that yields the minimum allowable strength of concrete used in practice.
To determine whether or not it is economically viable to use glass and tyres combined in the form of FGCG and CR as a partial aggregate replacement for uses in concrete.
The main expected outcome would be to establish the fresh and hardened properties of FGCG and CR combined in a mix and compared to conventional concrete using the same mix design.
Establish the workability and compressive strength of concrete containing different percentages of a combination of FGCG and CR as a partial replacement in concrete.
The percentage of partial replacement of a combination of FGCG and CR that yields the maximum strength at 28 days.
Relate the economic viability of the use of such partial replacements aggregates in concrete.
Significance
This study falls into the disciplines of Material Science in Civil Engineering and Environmental Engineering.
The material science discipline is significant as it will investigate the behaviour and the nature of the concrete containing glass and tyres in the form of FGCG and CR combined, with special reference to the workability and compressive strength. The Environmental Engineering aspect will involve the use of the recyclable material and the impact it will have on the environment. The practice of sustainable engineering design in the manufacturing of concrete are considered in order to reduce the negative impacts on the environment.
Delineation
The study will be focussed on the fresh and hardened properties of concrete .The slump test, fresh and hard density, dry shrinkage and compressive strength tests will be conducted in accordance with The South African National Standards (SANS, 2006) specifications using different partial aggregate percentage replacements of a combination of FGCG and CR and conventional concrete mix. The focus in this study will be around the amount of FGCG and CR used to achieve optimum results. The study will not evaluate flexural, tensile strength, creep, durability and immersion tests. Also modulus of elasticity, toughness and impact resistance will not be investigated.
Methodology
All tests were conducted according to SANS (2006) specifications and conducted at the concrete laboratory at Cape Peninsula University of Technology (CPUT), Bellville Campus. Materials will be gathered around the Western Cape.
The slump test will be conducted once mixing of the concrete has been completed. Fresh and dry densities will be recorded. Dry shrinkage tests will be conducted and compressive strength tests after 7 and 28 days of curing.
Comparisons will be made in terms of workability, fresh and hard densities, shrinkage and compressive strength with the partial replacements with the conventional concrete mixes and the tests previously done in literature.
Also a brief cost analysis will be conducted where the pricing of all materials will be compared to evaluate which concrete mix is the most economically viable and whether or not the use of the partial replacement of FGCG and CR can be used on large scale will be determined as a result.
Organisation of dissertation
The motivation and background as to what the problem is and possible solutions to the problem are presented in Chapter 1.Then also, specifying what testing will be conducted.
The literature review and theory that forms Chapter 2 will evaluate previous tests conducted including the materials used and also compare the information of different authors found in literature. It also includes the properties of concrete and considerations to be noted when using glass and tyres in concrete.
Chapter 3 will present how tests were conducted, the materials used and how equipment was used during the testing of slump, compressive strength and dry shrinkage tests. Furthermore this chapter will also include how the mixing, curing as well as the fresh and hardened densities processes were conducted.
The results of the fresh and hardened properties will be displayed in Chapter 4 as well as the cost of the materials obtained.
The results of this study will be evaluated, discussed and also compared to that found in literature in graphs and tables, this will form Chapter 5.
Finally, conclusions of the study will be drawn and then ending off of the research with recommendations on how to improve or how evaluating the objectives can be done differently in order to improve the fresh and hardened properties.
Literature review and theory
This chapter will present the research conducted with regards to waste used in concrete but particularly the use of glass and tyres in concrete. Also the various reviews of previous studies, discoveries and test methods will be reviewed and summarised.
Introduction
The increasing amount of waste being disposed of each year is taking up both landfill air space and land space that can be used more efficiently. Both glass and tyres are contributing significantly to this problem. As glass have an unknown lifespan and tyres are difficult to compact and breakdown.
A view is shared by Gautam, Srivastava and Agarwal (2012) where they state that there is a huge potential for waste glass has in the concrete construction sector. The use of waste tyres in concrete is a possible disposal solution when used in concrete (Khaloo, Dehestani & Rahmatabadi, 2008). Siddique and Naik (2004) states that concrete containing tyre rubber can form a workable concrete mix.
Shayan and Xu (2004) is in agreement with the aforementioned authors regarding glass as they specify that glass can be used as a fine or coarse aggregate or supplementary cementitious material in concrete. Also Ganjian, Khorami and Maghsoudi (2009) states that studies have been conducted on crumb rubber as an aggregate replacement but shares the view that very little studies of the potential of crumb rubber as a cementitious filler has been conducted and that there is a potential for the research to be expanded.
The objective of this literature review is to determine the effect fine green waste glass and crumb rubber has on the fresh and hardened properties of concrete, the impact these two potential aggregates and/or cement replacements has on the environment before considering its application in concrete. This chapter will elaborate on the following areas:
‘ Composition of concrete
‘ Properties of fresh concrete
‘ Properties of hardened concrete
‘ Environmental impacts of concrete
‘ Glass and tyres in the environment
‘ Fresh properties of glass and tyres in concrete
‘ Hardened properties of glass and tyres in concrete
‘ Existing literature using glass and tyres in concrete
‘ Considerable parameters
Composition of concrete
Concrete can be simply defined as mixture that consists of cement, aggregates; stone (coarse aggregate), sand (fine aggregate) and water. The mixture is significantly broken up into two parts namely a mortar and paste. The cement, water and sand make up the mortar, the cement and water which forms the paste binds all the material together which ultimately give the concrete its strength.
Cement
The most common cement used in concrete around the world is Portland cement and in SA it is used on its own or added with a cement extender. Portland cement is derived from three broad raw material categories. Calcareous derived from limestone, calcrete or chalk; argillaceous made up of clay or shale and iron oxide that is derived from natural iron oxide (van Amsterdam, 2000).When these raw materials are heated in a kiln at very high temperatures and grinded it then forms a fine mineral powder that is usually found to be grey in colour (Addis, 1998).
Cement can be in either its soft or plastic state and as time goes by it hardens and assist in binding the other constituents that make up concrete.
Aggregates
Aggregates are divided into two categories, coarse and fine. The coarse aggregate is made up of stone and fine aggregate made of sand.
The aggregates make up 70% of concrete generally and should be strong and hard, durable, chemically inactive, clean and well graded (Addis, 1998).
Aggregates are the products of rocks that have been blasted and rocks that had been crushed at quarries. The fine and coarse aggregates are determined by its size passing through sieves. The 4.75mm sieve that retains aggregate is considered as coarse and the aggregates passing through the 4.75mm sieve is considered as fines. The coarse aggregate which is the stone reduces the paste content and improves the stability of the concrete. The fine aggregate which is the sand fills up the void that exists between the cement and stone (Van Amsterdam, 2000).
When aggregates do not have the favourable characteristics in a concrete mix and has not been used in practice, the aggregates should be tested in a laboratory before applying it (Addis, 1998).
Taking the above into account, laboratory tests on aggregates that are not commonly used in concrete should be tested and the results will determine the viability of its application.
Water
The water used in concrete should be clean, free from dirt and impurities and also unwanted chemicals that can make the concrete unfavourable for use. When using water from boreholes and naturals sources the quality of the water should first be monitored before usage. As water is a scarcity other natural waters such as sea water may be considered. Many authors indicate that sea water may not be used in reinforced concrete and can be used to a certain extent in unreinforced concrete.
Water not only makes the concrete workable but it also mixes with cement to give concrete its strength (Addis, 1998). A chemical reaction, hydration takes place with the strengthening of the cement as the fibres of the cement particles grow into the water interlocking with other fibres form cement particles which acts as a binder of the mix (Van Amsterdam, 2000).
Admixtures
The use of admixtures in concrete is not a requirement of the mix but is used to improve its strength and properties. The admixtures such as plasticizers or water reducing agents (WRA), superplasticizers or high range water reduces (HRWR), retarders, accelerators and air-entraining agents (AEA) are mixed into concrete mixes that contain cement, aggregate and water (Van Amsterdam,2000). These admixtures should be correctly added to the concrete mix to ensure the correct specifications are met.
Properties of fresh concrete
Concrete is in its fresh state when it can be moulded and compacted thus changing its shape.
The properties of concrete in its fresh state are important as it has an influence on the long term behaviour, ultimate strength, elastic modulus, creep and its durability. The properties of concrete in its fresh state can be assessed according to its consistence, workability, settlement and bleeding as well as plastic shrinkage.
Consistence
The consistency of concrete is the measurement of how wet the concrete is when mixed. Consistence of a mix is used to control the amount of water used in the mix, thus measures the sloppiness or stiffness of the mix (Addis, 1998). The sloppiness or stiffness of the mix won’t have an effect on the strength of the concrete if the proportions of the mix are mixed correctly (van Amsterdam, 2000). A slump test in accordance with the method SANS 5862-1:2006 is a common standard used for measuring the consistence. The slump test follows the procedure as shown in Figure 2.1 where the concrete mix is removed from the mould. Figure 2.2 indicates how the slump is measured and Figure 2.3 indicates the different types of slumps that can be found.
A shear or collapsed slump occurs due to lack of cohesiveness, low cement content or tamping has not been done evenly (Addis, 1998). When shear or collapsed slump occurs then testing of the consistence should be redone.
Workability
The workability of concrete cannot be measured. However the slump test is a good measurement to determine the workability and assess the properties of the concrete. The workability of a concrete mix is determined by the ease it can be placed, compacted and finished without separation or segregation of the constituents of the concrete. The constituents of concrete influence the workability as the smaller the size of the stone the concrete will be produce a better workability. When sand fines in a concrete mix are to low or in excess, the form will lack cohesion and the latter create a sticky concrete. Increasing the cement content will create a cohesive concrete mix that is sticky and will make concrete unworkable (Addis, 1998).
Settlement and Bleeding
Settlement and bleeding occur at the same time. As concrete and aggregate settle downwards and displace water, bleeding occurs as water moves upwards. This continues until the concrete is set (Addis, 1998).Some bleed water may be found under aggregates, this reduces the bond of the mortar and stone and creates a concrete that has less strength compared to that if the bleeding had been reduced (van Amsterdam, 2000).According to van Amsterdam (2000) bleeding of concrete can be reduced by using less water, finer material, also an expensive method to reduced bleeding is when the cement content can be increased of a mix.
Plastic Shrinkage
Plastic shrinkage occurs due to the conditions in the environment such as the heat and wind that causes water in the concrete to evaporate quickly. According to Addis (1998) that when plastic shrinkage occurs cracks start and appear at the surface of the concrete and then cracks further down the concrete. Plastic shrinkage can be prevented if measures such as covering concrete with plastic sheeting or fog spray is used (Addis, 1998).This can be seen as a means to keep concrete moist. The plastic shrinkage cracks that appear at the surface of the concrete can be closed before the concrete sets by revibrating (Addis, 1998).
Properties of hardened concrete
Once concrete has set and cured for the required number of days the hardened properties of concrete may be assessed. The hardened properties of concrete may be assessed by testing its compressive and tensile strength.
Forms of strength
2.4.1.1 Compressive strength
The most common way of assessing the hardened properties of concrete is by conducting the compressive strength test. An Addis (1998) state that if concrete does not have the required strength it is of no use, also that when concrete is too strong it is too expensive. The aforementioned statement is agreed with as the appropriate concrete strength should be used for its intended application and also to avoid excess materials that give rise to cost. In SA the strength of concrete is monitored whereby concrete cubes are tested (Addis, 1998).The water: cement (w: c) ratio has the biggest effect on the strength of the concrete (van Amsterdam, 2000).Taking the above into account it is clear that the amount of water added to the concrete mix plays a big role and that cubes have to be tested according to the appropriate method of SANS 5863:2006.
Compressive strength is calculated with the following formula:
”c (2.1)
Where
”c = compressive strength (MPa)
F = load at failure (KN)
A = cross sectional area (m2)
2.4.1.2 Tensile strength
The tensile strength of a concrete specimen is tested where by the specimen is loaded at midspan or at third points. The testing of the specimen under goes stress; the maximum amount of stress that the concrete specimen fails at determines its ultimate strength. The test is also known as the Ultimate Strength Test (UTS).According to (Addis, 1998) the test is only conducted on concrete specimens that will be used for floors on the ground or pavements. The method of testing concrete specimens should be according to the method of SANS 5864:2006.
.
Flexural strength is calculated with the following formula:
For two-point loading (at third points)
ff (2.2)
For mid-span loading (at centre-point)
ff (2.3)
Where
ff = flexural strength(MPa)
P = breaking load (KN)
L = distance between axes of supporting rollers (mm)
b = width of specimen (mm)
d = depth of specimen (mm)
Forms of deformation
Concrete deforms when a load is applied on it. In some case the deformation is temporary and other cases deformation is permanent. The following forms of deformation will be covered namely shrinkage, elastic deformation and creep.
2.4.2.1 Shrinkage
According to Addis (1998) shrinkage in concrete occurs due to the loss of moisture in the environment. A similar view is shared by van Amsterdam (2000) where he states that the occurrence of shrinkage is dependent on factors such as the thickness of the concrete, the moisture in the environment and the concrete mix. These factors mentioned will occur after curing as concrete loses its moisture and the environment concrete is exposed to do not have the moisture that was available during the period of curing. The method of testing concrete specimens should be according to the method of SANS 6085:2006.
Dry shrinkage is calculated with the following formula:
Dry Shrinkage % (2.4)
Where
L1 = measurement after initial curing (mm)
L2 = measurement after drying (mm)
L0 = distance between the inner most anvils (mm)
2.4.2.2 Elastic deformation
The elastic deformation can be easily understood by its name. The concrete specimen will deform but has an elastic effect whereby it will return to its shape that it had before it had deformed. A view is shared by (Addis, 1998) where he states that concrete will have an elastic reaction if concrete is loaded for a short time. Thus meaning that concrete that is loaded for a long period of time will not have elastic characteristics. The method of testing concrete specimens elastic stiffness has no SANS: 2006 standard.
Modulus of elasticity can be calculated with the following formula:
E (2.4)
Where
E = modulus of elasticity
Stress = load ” cross sectional area (P/A)
Strain = change in length ” original length (”L/L)
2.4.2.3 Creep
Creep occurs under two conditions basic creep where there is no drying taking place and drying creep where loaded concrete is drying. According to (Addis, 1998) creep occurs when there is an increase in strain on a specimen when the specimen is under a constant or controlled stress. He also states that creep has both beneficial and detrimental effects on a structure. This being said creep may be permanent in some cases and in others temporary. The method of testing concrete specimens specific creep has no SANS: 2006 standard. Creep can however be measured in accordance with the ASTM C512-87 (1994) and RILEM CPC-12 (1983) standards (Addis, 1998).
Specific creep can be calculated with the following formula:
Cc (2.5)
Where
Cc = specific creep
”c = creep strain
” = stress
Environmental impacts of concrete
According to Meyer (2009) the concrete industry has a huge impact on the environment. The view is that natural resources from the environment produce aggregates and cements which are required for the manufacturing of large amounts of concrete. Muigai et al. (2013) states that 39.7 Mt of raw materials are used per year for producing concrete and can be broken down where 32.1 Mt come from raw materials used for aggregates and 7.6 Mt of raw materials used to produce cement binders.
Cement
As previously mentioned raw materials are heated to produce cement which give rise to CO2 emissions, in SA the annual cement sales are high Muigai et al. (2013).That said, cement sales are high due to it being one of the main materials in concrete production. Figure 2.4 shows the cement sales from 2005 to 2008, this information had been retrieved from (C&CI, 2008).
With reference to Figure 2.4, the production of Portland cement and the cement binders are approximated that 20.4 Mt of raw materials were used per year to produce cementitious materials (Muigai et al., 2013).This is a huge amount taking into account the small amount SA’s concrete industry produces when in comparison with the world. The CEMBUREAU (2009) that is cited by (Muigai et al., 2013) states that SA only produces 0.58% of the estimated 12 billion m3 of concrete produced annually worldwide. This being said, raw materials globally are being used in abundance.
The average sales of cement binders are indicated in Figure 2.4, approximately 37% (4.73 Mt) of those binders are for the production of concrete and according to Table 2.1 that indicates the amount of CO2 on average that comes from the concrete industry in SA (Muigai et al., 2013).This information had been retrieved from (InEnergy Report 2010) as cited by (Muigai et al., 2013).
It should be noted that cement production utilises a considerable amount of natural resources in not only SA, but globally. The use of these natural resources in the concrete industry contributes significantly to the amount of CO2 that is emitted from the cement and aggregate industry.
Aggregates
Muigai et al. (2013) reported that the calculation of sales of aggregates in SA had been conducted by the Aggregate and Stone Producers Association of South Africa (ASPASA) and the Department of Mineral Resources (DMR). A difference in the sales can be seen in Figure 2.5 as the calculations of aggregates conducted in the same year by ASPASA and DMR were different. Muigai et al. (2013) makes reference to the difference in averages of aggregate volumes as ASAPAS based averages on conversion factors of cementitious materials that go into the production of concrete and DMR base averages on sales reported by registered operating quarries and sand extractions in SA. Muigai et al. (2013) states that it is estimated that 30% of aggregates and sand that has been produced (2005-2008) is used for the production of concrete and averages to 32.1 Mt for the period mentioned, which can be considered high.
The CO2 emissions with reference to the data gathered by ASPASA shows an in increase in the emissions from 2005 to 2008 as seen in Table 2.2.Taking into account the need for concrete these CO2 emissions looks likely to increase if a suitable solution for a replacement of aggregates in concrete is not found in the near future.
Glass and tyres in the environment
Impact of glass and tyres in the environment
The life span of glass is unknown and takes up space at MRF’s and WDF’s and tyres are difficult to compact and breakdown and take up landfill air space as well as land space that can be used for disposal of other wastes that are biodegradable. Both tyres an glass have a significant impact on the environment due to the large amounts generated globally annually.
Glass
Shi and Zheng (2007) state that not all waste glass that has been used can be can be recycled into new glass due to the impurities it possesses as well as the cost associated with the recycling process. Shao et al. (2000) states that disposing of glass at waste disposal facilities is not environmentally friendly as waste glass is not a biodegradable product. Topcu and Canbaz (2004) share a similar view as they regard glass as being imperishable and harmful to the environment.
Tyres
Khaloo, Dehestani and Rahmatabadi (2008) is of the view that the management of waste tyres found in the environment is not only a concern but a health problem. An agreement to his view has been taken as tyres found at WDF’s attract rats, mice and mosquitoes are only a few of the problems mentioned, that can spread diseases. The health impact is not the only impact it has as Ganjian, Khorami and Maghsoudi (2009) state that scrap tyres are not biodegradable and have a bad effect on the environment itself.
Reducing the impact of glass and tyres in the environment
Many methods are used to reduce the impact glass and tyres have on the environment. However not all the methods are economically viable and further methods are needed to reduce the impact of the wastes such as glass and tyres that are not biodegradable.
Glass
Jin, Meyer and Baxter (2000) state that waste glass can be used as a suitable aggregate in concrete as this has been proven by research at Columbia University. Aggregate being suitable for the use in concrete may reduce the impact glass has on the environment but the economic viability has to be taken into account in order to expand on the use of glass in concrete. The use of waste glass in concrete is a viable secondary market as it is economically feasible (Meyer, 2009).
Tyres
Many methods of recycling or use of scrap tyres have been identified globally such as the burning of tyres to produce electricity or as a fuel in cement kilns. According to Meyer (2009) the aforementioned use of scrap tyres have been successful but result in too much loss in value or volumes are too small to lessen the impact of stockpiled tyres at WDF’s. This creates a need for an alternative use for scrap tyres that can have a considerable impact in reducing tyres that are taking up air space at WDF’s. Meyer (2009) further suggests that tyre rubber used in concrete as an aggregate is a viable solution to recycle tyres when taking into account its economic viability.
The concrete containing glass and tyres would have to be compared to conventional concrete mixes to determine its economic viability and also the concretes properties in its fresh and hardened and states. Thus will indicate if tyres and glass in concrete can reduce the impact it currently has on the environment.
Existing literature using glass and tyres in concrete
Tests conducted using glass
In the 1960’s many studies were conducted for the use of WG as an aggregate for cement concrete, however many of these concretes containing glass aggregates had cracked (Shi & Zheng, 2007). Shi and Zheng (2007) also states that since 1997, which referred to as the past 10 years prior to 2007, glass used in cement concrete has gone through many investigations due to the costs and environmental regulations that it has.
Topcu and Canbaz (2004) conducted an investigation where domestic WG was evaluated in concrete that had gone through the recycling process. Both fresh and hard concrete specimens were analysed. The WG used was print silk that was a result of the crushing of coloured soda bottles, before crushing the soda bottles, they were kept in water in order for easy removal of the label. The WG was used as a partial replacement for stone. Four samples of different volumes of WG; 15%, 30%, 45% and 60 % were used as a partial replacement in concrete. PKC_/B 32.5R type Portland cement was used, crushed green soda glass was used as a coarse aggregate with a water to cement (w/c) ratio of 0.54. Fifteen cylindrical shaped concrete specimens were tested that had a diameter (”) of 150mm and a height of 300mm. These concrete specimens were cured for 28 days in lime-saturated water at 22”C before the hardened concrete tests were conducted. Tests such as unit weight, slump, compressive and flexural strength as among other tests were conducted.
They suggested that WG used as a partial replacement for fine aggregate would mean an improvement in results compared to the partial aggregate replacement of stone, meaning that the concretes characteristics would also be better. It should be noted that they go a step further by stating that if the fine aggregate is used as a partial replacement in concrete, if the geometry of the WG is more spherical in shape, results will further improve.
Batayneh Marie and Asi (2007) tested concrete specimens with partial replacement of glass, plastic and crushed concrete. The performances of concrete containing these recycled materials were tested using Ordinary Portland Cement (OPC). An investigation was conducted on the different effects these recycled materials would have on concrete. The concrete specimens used for testing were of various size moulds; cubes of (100mm x 100mm x 100mm), cylindrical shapes of 150mm ” and 300mm height and a beam size of (100mm x 100mm x 400mm). Different volumes of glass, plastic and crushed concrete were used in the investigation.
The concrete specimens of concrete waste glass (CWG) that replaced the fine aggregates of 5%, 10%, 15% and 20% of the total volume of concrete.
They gathered that the strength of the concrete improved by partial replacement of fine aggregate using CWG and that consequently the alkali contents of aggregate would affect the long term durability and strength, which requires a long term investigation.
Ismail and AL-Hashmi (2009) conducted tests evaluating the strength and the alkali-silica-reaction (ASR) properties of concrete specimens containing different volumes of partial replacement of WG of fine aggregate in concrete. Three different volumes of partial replacement of WG for sand were tested, with volumes of 10%, 15% and 20%. The concrete specimen sizes were in moulds where three 50mm layers would each be compacted before the next layer of concrete was added. The concrete mix consisted of Portland Cement, natural sand that was no larger than 4,75mm, coarse aggregate of crushed stone that had a size of 20mm maximum diameter size and a w/c ratio of 0.53. WG from bottles jars and windows were used as a partial replacement for sand. The concrete specimens were dried for 24 hours and then cured for 28 days before testing had commenced. They deduced from the tests conducted that the partial replacement of sand with CWG reduces ASR expansion and that no notable changes were found in the concrete specimens.
Gautam Srivastava and Agarwal (2012) conducted compressive strength tests on 66 concrete specimens. The specimens were in cubes (100mm x 100mm x 100mm), where Ordinary Portland cement was used combined with potable water. The mix design for the concrete specimens was 1:1.67:3.33 and was cured for 7 and 28 days respectively before testing commenced. An observation that should be noted was that a marginal decrease in strength of the specimens at 30% replacement of WG with aggregates was found.
Tests conducted using tyres
According to Bravo and de Brito (2012) studies on concrete specimens containing rubber aggregate (RA) started in the 1990’s. Bravo and de Brito (2012) further states that Eldin and Senouci (1993) were the first to study and perform tests on concrete tyre aggregate (CTA). They deduced that CTA had a low workability, compressive and tensile strength. According to Eldin and Senouci (1993) the compressive strength decreased with the increase in size of tyre aggregate (TA).
Toutanji (1996) conducted tests on the compressive and flexural strengths of concrete specimens. Four different volumes of TA; 25%, 50%, 75% and 100% of the total volume of concrete specimens were tested. The specimens were cylindrical in shape with a diameter (”) of 100mm and height of 200mm.It should be noted the volumes of TA were free of steel wires and no minerals or admixtures were added to the TA. The testing was conducted after 28 days of curing of the concrete specimens.
He concluded that the relationship between the strength of the concrete and volume of the tyre aggregate is non-linear. This indicates a difference in observations between Toutanji (1996) and Eldin & Senouci (1993). The former indicates no relationship and the latter says that there is a relationship, as the CTA decreases in compressive strength, with the increase in size.
Khaloo, Dehestani and Rahmatabadi (2008) conducted compressive strength tests on concrete specimens. Khaloo, Dehestani and Rahmatabadi (2008) tested four different volumes of TA. Thus they used a similar method of testing as Toutanji (1996). Khaloo, Dehestani and Rahmatabadi (2008) went a step further by testing TA, CR and a combination of TA and CR to replace aggregates. The volumes of TA and CR that was used as a total volume of the concrete specimens were 12.5%, 25%, 37.5% and 50%. The concrete specimens were cylindrical in shape with a 150mm ” and height of 300mm.The materials used were; Type I Portland cement, Coarse aggregate of 20mm and fine aggregate of a maximum size of 4.75mm.
They gathered that fresh rubberized concrete properties were better compared to conventional plain concrete as it had a lower unit weight and an acceptable workability. A decrease in brittle behaviour was also found when the amount of rubber was increased.
Ganjian, Khorami and Maghsoudi (2009) performed mechanical tests in the form of compressive, tensile, flexural strength tests, modulus of elasticity as well as durability tests. Ganjian, Khorami and Maghsoudi (2009) conducted tests on three different volumes of CR and TA. The volumes were 5%, 10% and 15% of the total volume of concrete. It should be noted that during the tests TA was used as a replacement for coarse aggregate and CR as a replacement for cement where the same percentage was used. The specimens were in the form of a 150mm shaped cube, the materials consisted of Portland cement, coarse aggregate of maximum of 25mm in size and drinking water was used for the concrete mix.
He gathered that there are two main factors dependant on the compressive strength of a specimen, which is the size of the rubber replacing the aggregate and the percentage of rubber replacing aggregate.
Bravo and de Brito (2012) conducted tests on concrete specimens where they evaluated fresh and hard characteristics. They replaced natural aggregate (NA) with TA of 5%, 10% and 15% of total volumes of concrete. They tested 13 concrete specimens where aggregates that passed through the 4mm sieve were taken as fines and the aggregate retained was said to be coarse.
They concluded that compressive strength of the concrete tested had lost half its strength when 15% of the total volume of concrete’s NA was replaced with 15% TA.
Glass and tyres in concrete pavements
Literature indicates that glass as a partial replacement of 20% exhibited high strength and the addition of the same partial replacement of tyres showed a considerable decrease in strength. The main negative with high amounts of tyre as partial replacement is its decrease in strength. However Ganjian, Khorami and Maghsoudi (2009) state that although concrete strength does decrease the concrete that has tyre rubber as a partial replacement, it has an increase in toughness and impact resistance when compared to conventional concrete.
That said, Shayan and Xu (2004) achieved a VicRoads 32MPa strength grade concrete for the use in concrete pavements. It should be noted that they conducted a number of tests before achieving a suitable concrete mixture. The strength was also achieved with the addition of an admixture. The dry shrinkage of the 32Mpa concrete mix was below the Australian Standards AS 3600 of 0.075%, which is a good sign.
Taking the aforementioned into account a mix with high impact resistance, toughness and strength could possibly be achieved with the addition of glass and tyres as a partial replacement in the same concrete mixture. The mixture should be compared to that containing glass, tyre rubber and a combination of glass and tyre rubber .The mixture should be considered without the use of an admixture due to the additional cost of the concrete mixture. The benefits of the mixture could possibly improve the fresh and hardened properties, de Castro & de Brito (2013) states that glass in concrete pavement deflects nocturnal light that allows better visibility which also improves traffic safety.
Fresh properties of glass and tyres in concrete
The use of glass and tyres in concrete has undergone considerable research with reference to their properties. The fresh properties will have to firstly be assessed before considering the properties containing glass and tyres in their hardened state.
Slump
Glass
Terro (2006) assessed the workability of concrete using fine waste glass (FWG), crushed waste glass (CWG) and fine crushed waste glass (FCWG) as seen in Figure 2.6. An observation was made where the slump increased when the percentage of waste glass increased. FCWG showed to have the best slump as the glass content increased. Terro (2006) states that the FCWG increase in slump is due to the lower specific surface and the smooth surface of the coarse glass.
Batayneh, Marie and Asi (2007) tested the workability of concrete containing glass, plastic and crushed glass. The different percentages of glass ranging from 0% – 20% that had been crushed in a laboratory was found not to affect the workability of the concrete as seen in Figure 2.7.Also it can be noted that of the three wastes used glass had the best workability.
Ismail and AL-Hashmi (2009) found that when assessing the workability of different percentages waste glass that there is a decrease in slump when there is an increase in the ratio of the waste glass as seen in Figure 2.8.They also state that the decrease in slump is due to the poor geometry of the glass used and even though a decrease in slump was observed the slump was still deemed to be workable.
Tyres
Aiello and Leuzzi (2010) tested the workability of the concrete replacing tyre rubber particle (TA) with aggregates. The tests were conducted in two sets, the one set replaced TA with coarse aggregate of a maximum size of 20mm and the other replaced fine aggregate where the size ranged between 10-15mm. A better workability was observed with the TA replacing the aggregates compared to that of the control mixture.
Khatib and Bayomy’s (1999) assessment of the concretes workability was conducted as shown in Figure 2.9 in three groups: Group A where CR replaced sand, Group B Tyre chips replaced coarse aggregate and Group C a combination of CR and Tyre chips used. It was observed that when the replacement volume by total aggregate reached 40% the slump value was near zero and the concrete was not workable.
Khaloo, Dehestani and Rahmatabadi (2008) assessed workability with three mixes of tyre aggregate; coarse, fine and a combination of the two. For the fines mixture with reference to Figure 2.10 at 15% of the total aggregates used the maximum slump is reached and decreases with the increase in tyre aggregate. The coarse mixture decreases to a minimum value at 15% concentrations and the combined concentration slump is better than that of the coarse concentrations. Its concluded by Khaloo, Dehestani and Rahmatabadi (2008) that rubberised concretes workability is acceptable with the characteristics it poses such as the ease it can be handled, placed and finished.
Bravo and de Brito (2012) conducted the assessment of the workability of concrete in four sets as seen in Figure 2.11.He observed that all the concrete mixes have a similar workability as the target value for the slump was 80mm with a tolerance of ”15mm and all the sets examined fell in the range. He concluded that the difference found in the slump was mainly due to the different shape of the TA.
Concrete mixtures containing fine crumb rubber is more workable than mixes with coarse tyre chips or mixes that have both crumb rubber and tyre chips (Siddique & Naik, 2004).
Fresh density
Glass
Taha and Nounu (2008) observed similar findings to Ismail and AL-Hashmi (2009) where the fresh density decreased with the increase in the glass content, when compared to the conventional concrete mix. The contents of glass was recycled glass sand (RGS) that can be seen in Table 2.3,where mix called M1 contained 100% Portland Cement,M2 60% of ground granulated blast furnace slag replacing Portland cement,M3 contained 10% metakaolin partially replacing cement and M4 contained 20% pozzolanic glass powder partially replacing cement.
According to Taha and Nounu (2008) bleeding and segregation was observed when the glass content was at 50% due to the glasses sharp edges and texture that resulted in a week bond of the concrete mixture.
Ismail and AL-Hashmi (2009) measured the fresh densities of concrete containing glass of 10%, 15% and 20%.The measurements were compared to that of the conventional concrete mix. It was noted that as the glass content increased the fresh density of concrete decreased as seen in Figure 2.4. Ismail and AL-Hashmi (2009) states the decrease in the fresh density of the concrete containing glass can still be compared to the conventional concrete mixture.
Tyres
Khatib and Bayomy (1999) states that the air content of the concrete increased when the unit weight of the concrete is in its fresh state decreased.A unifirom loss in weight can be seen n Figure 2.12.Khatib and Bayomy (1999) also suggests that concretes unit weight may be decreased up to 75% of the normal concrete mix. What should be noted is that the three groups tested consisted of the following; Group A where CR replaced sand, Group B Tyre chips replaced coarse aggregate and Group C a combination of CR and Tyre chips replaced aggregates.
Bravo and de Brito (2012) measured the fresh density of four sets of concrete containing TA as seen in Figure 2.13.It can clearly be observed that with the increase in TA the fresh density decreases. Bravo and de Brito (2012) deduced that the change in the concrete density is due to the difference between NA and TA. Also that the when the TA size decreases the density of the concrete containing TA will result in a lower fresh density. This indicates that that smaller the tyre aggregate particles the lighter the weight of the concrete.
Khaloo, Dehestani and Rahmatabadi (2008) measurements resulted in the same characteristics as Bravo & de Brito (2012) where the increase in tyre content, resulted in the fresh density becoming less as seen in Figure 2.14. Also the finer the tyre particles the lighter the concrete when the finer particles have the same content of particles as the bigger TA. Khaloo ,Dehestani and Rahmatabadi (2008) deduced that tyre particles have high water absorption thus results in when fresh density becomes hardened density using tyre rubber in concrete is greater than plain concrete. Thus concluding that concrete containing tyre rubber is more porous than plain concrete.
Hardened properties of glass and tyres in concrete
Compressive Strength
Glass
Batayneh, Marie and Asi (2007) deduced that concretes strength in all respects increased considerably over all strength tests and that the strength increase is due to the surface texture of the glass that is better than that of sand. It can be seen in Figure 2.15 that as the glass increased so did the compressive strength.
Gautam, Srivastava and Agarwal (2012) concluded from his study that at 28 days that concrete using waste glass as a fine glass replacement increase the strength up to 20% and a decrease in strength is noted with further addition of glass strength decreases as seen in Figure 2.16. Waste glass can be used as a replacement for fine aggregate (Gautam, Srivastava & Agarwal 2012).The most strength with glass as a replacement from this study was glass at a partial replacement for aggregate at 10% as seen in Figure 2.16.
Shao et al. (2012) found that when measuring the compressive strength of concrete containing glass that one of the measurements was more than the control mixture at 90 days. The glass content that had a higher compressive strength than the concrete control mixture was the mixture that the glass particles were 38 um as seen in Figure 2.17. Shao et al. (2012) concluded that the smaller the size of the glass used in concrete the higher compressive strength will be found.
Tyres
Khatib and Bayomy (1999) during his study where crumb rubber replaced sand (Group A),tyre chips replaced coarse aggregate (Group B) and both crumb rubber and tre chips replacing coarse and fine aggregate (Group C) the different strengths can been observed in Figure 2.18.It can be seen that as the tyre content increased,the strength decreased.He concluded that the reduction of strength has a negative effect on the concrete but the rubber in concrete had a much higher deformation when compared to the normal concrete mix.
To illustrate what replacement is more favourable Bravo and de Brito (2012) used Figure 2.19 to achieve this. The Figure had been retrieved from Valadares (2009).The study revealed that the shredding process of the rubber had no effect on the properties of the concrete. According to Bravo & de Brito (2012) concrete strength loss is greater when fine aggregate is replaced in concrete compared to coarse aggregate.
Dry Shrinkage
Dry shrinkage is one of the hardened properties of concrete that occurs due to los of moisture in the environment concrete is in and also due to the composition of the concrete mixture. The dry shrinkage of concrete containing glass and tyres were assessed.
Glass
Limbachiya (2009) conducted tests on the dry shrinkage properties of glass replacing sand of 5%, 10%, 15%, 20%, 30% and 50% of the concretes weight. He found that there was no dry shrinkage for the partial replacement of glass up until 20% and that there was a reduction in shrinkage with the increase of the glass replacement.
Penacho, de Brito and Veiga (2014) conducted a study on glass of 50% and 100% replacing sand in concrete and compared it to the conventional concrete mix. The shrinkage results are depicted in Figure 2.20. It is visible that the shrinkage of the control mix and the concrete mix containing 50% glass has similar properties of shrinkage. Penacho, de Brito and Veiga (2014) states that a reduced shrinkage will be found as the glass content increases.
Rashad (2014) states that glass as a replacement for sand is and advantages as it reduces the shrinkage as shrinkage is one of the main causes of cracks occurring in concrete. Thus it can be noted that glass reduce cracks in concrete when the correct partial replacement is used in concrete.
Tyres
According to Siddique and Naik (2004) limited literature is found with regards to assessing the plastic shrinkage properties when rubber particles are used in concrete.
Bravo and de Brito (2012) reported on the study that he conducted in 2009 where he found that shrinkage had increased with the use of tyre particles compared to the normal concrete mix. He also states that the increase in shrinkage is due to the higher w/c ratio used. From Figure 2.21 it was noted that the increase in TA was not significant to the increase in shrinkage. According to Bravo & de Brito (2012) shrinkage is increased by the shape of the replacing and aggregate and not the size.
Bravo and de Brito (2012) proves that Siddique and Naik (2004) were correct when they concurred that there was limited research on dry shrinkage in literatures as Bravo and Brito (2012 were not able to compare the results of the study in 2009 to previous research in literature.
Practical Considerations
These parameters need to be considered before using certain materials as replacement aggregates in concrete.
The alkali-silica reaction in concrete containing glass
The applications where glass can be used in concrete are limited due to damaging expansions. These damaging expansions are caused from the high-alkali pore water in cement pastes and the reactive silica that WG possesses. The combination of the cement pastes and WG causes an ASR (Gautam, Srivastava & Agarwal, 2012).
A silica gel forms between Portland cement and aggregates that causes cracks upon expansion, weakens the concrete and also shortens the concrete’s lifespan (Swamy, 2003). An ASR does not only occur in glass concrete, but also in conventional concrete mixes as aggregates contain certain siliceous rocks and minerals. For an ASR to occur three factors need to be present; alkali, silica and moisture (Meyer, Egosi & Andela, 2001). They further state that adding mineral admixtures that suppress ASR, making glass resistant by coating it with zirconium and sealing the concrete by protecting it by moisture and using special ASR-resistant cements are the few of the measures found that can be used to avoid ASR from occurring.
A simple yet effective method for using WG in concrete for testing can be used that will avoid ASR from occurring. Two components of WG glass should be considered such as: the colour of the glass and its size. Bazant, Zi and Meyer (2000) and Batayneh Marie and Asi (2007) who cite Blumnetsyk (2003) found similar ideas. Bazant, Zi and Meyer (2000) states that if the glass particles are small enough, over time ASR will be eliminated. Batayneh Marie and Asi (2007) who cite Blumnetsyk (2003) states that WG from green bottles (GWG) mitigates ASR due to the green colour derived from chromium oxide.
The type of tyre aggregate used in concrete
Studies indicate different tests that have been conducted on tyres recycled in different forms and also analysis made on the size and shape of the tyres in its recycled form.
Topcu (1995) studied the performance of concrete with partial replacement of both fine and coarse aggregates with TA in concrete. He confirmed that the strength of concrete had decreased with the increase in size of TA.
Gesoglu and Guneyisi (2007) found that when the volume TA increased concrete became less resistant to chloride ions ingressing into the concrete.
One of the requirements for corrosion to take place is that of chloride penetrating through concrete (Bohni, 2005). Thus when TA volume is increased, this could lead to favourable conditions for corrosion initiation. Furthermore, the size of the aggregate has a considerable effect on the strength of the concrete, meaning that smaller aggregates may be a better replacement in the form of CR.
Conclusion
In summary with regards to WG being a partial replacement in the total volume of concrete, WG as a partial fine aggregate replacement produces better properties in concrete when compared to WG being used as a partial replacement for coarse aggregate. According to Topcu and Canbaz (2004) WG cannot be used as an aggregate within concrete without considering the ASR properties.
Bazant, Zi and Meyer (2000) state that the effect of ASR will be eliminated as time goes on if particle sizes are small enough. Batayneh Marie and Asi (2007) who cite Blumnetsyk (2003) found that glasses from green bottles tend to mitigate ASR due to the existence of chromium oxide found in the green glass. What should also be noted is that, WG as an aggregate found in concrete with a volume of more than 20%, caused a noteworthy decrease in the compressive strength of the concrete (Topcu & Canbaz, 2004).
It is evident that the strength of concrete containing TA is less than that of conventional concrete. Bravo and de Brito (2012) states that many authors advise against the partial replacement of NA with TA that is more than 25% due to excessive loss in the strength that will be found in the concrete specimen. Khaloo, Dehestani and Rahmatabadi (2008) agrees that partial replacement of 25% of aggregate is not recommended mainly due to the decrease in the ultimate compressive strength of the concrete. Ganjian, Khorami and Maghsoudi (2009) used total volumes of 5%, 7.5% and 10% of discarded tyre rubber as partial replacement for aggregate in concrete. He also stated that increasing the volume of each of the partial replacements will have no major changes on the concrete.
Research methodology
The aim of the research design will be to assess the fresh and hardened properties of green waste glass from green glass bottles and crumb rubber from tyres as a partial replacement for aggregate.
The objective of the tests to be carried out will be to assess the properties of concrete containing partial replacements of a combination of FGCG and CR for fine aggregates in concrete and compare it with conventional concrete mixes and similar mixes in literature.
The fresh and hardened properties of concrete will be investigated. The following percentage will be used as a partial replacement for fine aggregate in the respective batches:
Control mix (conventional concrete)
Mix 2 (20% FGCG partially replacing fine aggregate)
Mix 3 (20% FGCG and 5% CR partially replacing fine aggregate)
Mix 4 (20% FGCG and 10% CR partially replacing fine aggregate)
Mix 5 (20% FGCG and 15% CR partially replacing fine aggregate)
Research design
This dissertation shall be an experimental and comparative one. The experimental work had been conducted in the concrete laboratory at the Cape Peninsula University of Technology (CPUT); Bellville Campus. The tests were conducted under the supervision of the Laboratory Technician. The tests that were conducted were in accordance with SANS. The following tests were conducted:
Slump Test -SANS 5862-1: 2006
Density of Fresh concrete: -SANS 6250: 2006
Density of Hardened concrete -SANS 6251: 2006
Dry Shrinkage -SANS6085: 2006
Compressive Strength -SANS 5863: 2006
A brief cost analysis will also be conducted with the different batch mixes. The batch mixes will be compared to establish what the most cost effective batch is.
Research methodology
The tests and calculations that were done on the FGCG and CR partially replacing fine aggregates focused namely on; fresh density, slump, hardened density, shrinkage and compressive strength. Moulds in the shape of cubes and beams will be used for casting. The concrete cubes will be used to test the compressive strength and the beams used to test the shrinkage.
Data
The following materials are required for the casting and testing to be conducted:
Type of partial aggregates: FGCG and CR were 2mm or smaller
Type of coarse aggregate: maximum stone size of 19mm
Type of cement: CEM 42.5 Portland cement
Type of sand: Malmesbury sand
Type of water: Potable water
Quotations: The different materials and the cost of each
Research equipment
All machinery and equipment was checked and calibrated beforehand and the required clothing was worn to prevent health hazards or injury. The following research equipment was used:
3.2.2.1 Mixing of concrete
Prior to the mixing of materials such as cement, sand, stone, fine green crushed glass, crumb rubber as well as water, the mass of each material was weighed on the weigh scale.
The mixing was conducted on an impermeable surface in the laboratory. The mixing of concrete was in accordance with SANS 5861-1:2006. A spade was used to mix fine aggregate with cement as seen in Figure 3.1.
Once the fine aggregate (sand, CR and FGFG) was well mixed with the cement, coarse aggregate was added to the batch as seen in Figure 3.2.
After the coarse aggregate was mixed thoroughly with the fine aggregates and cement, water was added to the mix and the slump test was conducted.
3.2.2.2 Slump Test
The slump test was conducted once concrete was thoroughly mixed and a homogenous mix was evident. The slump test was conducted in accordance with SANS 5862-1:2006
The slump cone was placed on the base, and then filled with concrete approximately 100mm high and 25 blows were applied with the rod. Another 100mm of concrete was added and another 25 blows was applied, this continued for a third time.
The top of the cone was smoothed out with the rod. Then finally the cone was removed and the slump was measured as seen in Figure 5.3. Once the slumps of the different batches were recorded the fresh density was recorded.
3.2.2.3 Fresh Density
The fresh density of concrete was recorded once concrete was placed in cubes while concrete was still in its fresh state. The fresh density of concrete was done in accordance with SANS 6250:2006.The concrete sample was placed on the weigh scale while still in its mould to determine its mass. The mass of the mould was recorded before the concrete sample was filled with concrete in order to get an accurate weight. After the sample had been recorded in its fresh state it was then placed at room temperature as seen in Figure 3.4 to dry for 24 hours.
After 24 hour of drying, the concrete samples mould were removed and then placed in the curing tank as seen in Figure 3.5.The curing of the concrete cubes was in accordance with SANS 5861-3:2006.The concrete cubes were cured for 7 and 28 day respectively before the compressive strength could be tested.
3.2.2.4 Hardened Density
After concrete cubes had been cured for 7 and 28 days respectively excess water was then removed from the cubes. The hardened density of concrete was in accordance with SANS 6251:2006.The cubes were then placed on a weigh scale where there masses were recorded. After the masses were recorded the compressive strength tests were conducted.
3.2.2.5 Compressive Strength
The compressive strength was conducted after the hardened concrete cubes masses were recorded on the weigh scale. The compressive strength machines plates were cleaned and the cubes were placed in the machine as seen in Figure 3.6.
What should be noted is that cubes were placed opposite to the way in which they were casted as specified in SANS 5863:2006.The concrete cubes force at failure was recorded once cube was crushed and machine beeped.
3.2.2.6 Dry Shrinkage
The dry shrinkage was tested on beams as required in SANS 6085:2006, where anvils in the form of nails were placed on the outer ends of the beams while being casted. The anvils are where readings will be taken from. The beams were cast and then allowed to dry for 24 hours. The beams moulds were removed and then measured with a measuring device as L0 that measure up to 2um and placed in a curing tank to cure for 7 days.
Then a measurement was taken after 7 days of curing as seen in Figure 3.7.The measurement recorded on day 7 of curing was recorded as L1.
After curing and reading L1 was recorded the beams were placed in a oven at 50” C for 7 days as seen in Figure 3.8.The beams readings were recorded after 7 days of being dried in the oven.
After 7 days of curing and 7 days of oven drying, the dry shrinkage was recorded as day 14.The readings were then taken at day 16, 18, 20 and 22 until the same reading was recorded in the beams for 2 consecutive reading days in a row. This reading was recorded a L2.
Analysis and presentation of results
The fresh and hardened properties results will be presented and then finally a cost analysis will be conducted.
‘ Fresh Properties
The slump of the different partial replacements will be compared and plotted on graphs. Then comparisons will be made with slumps of each mix. The average fresh density of the mixes of partial replacements will be tabulated, displayed on graphs and compared to the conventional concrete mix.
‘ Hardened Properties
The beams dry shrinkage of different partial replacements will be measured to determine the shrinkage and will be compared to the conventional concrete mixes beams. The information will be displayed in tables and on graphs then analysed further.
The concrete cubes hardened density will be recorded and comparisons of the partial replacement mixes as well as the conventional concrete mixes will be made. The compressive strength at 7 and 28 days of the cubes will be compared to those in literature and the cubes cast in this experiment. These results will be analysed on a graph to determine if the partial replacements hardened properties are better than that of the conventional concrete mix.
‘ Cost Analysis
The cost analysis will be conducted on all the batches. The materials will be priced according to the amount used per batch mix. The cost of each mix will be evaluated to determine the economic viability and determine the most viable mix.
Results
This chapter will discuss the results of tests conducted from the 27 June to the 26 July 2015.Five batches of concrete were mixed and tested to evaluate the effects of partial replacement of sand with 20% fine green crushed glass with increasing percentages of crumbed rubber. It should be noted that all the batches contain the same amount of cement, stone and water. The fine aggregate, that is the sand, had been partially replaced by fine green crushed glass and crumb rubber by different percentages. Table 4.1 shows how the fine aggregates partial replacement of the sand in their respective batches.
Slump tests
The slump test was measured when concrete was in its fresh state, indicating the consistency and workability of the concrete. The different slumps obtained in their respective batches are shown in Table 4.2.
The slumps obtained ranged from 55 mm to 85 mm and is shown in Figure 4.1.
The control mix and mix 2 obtained the same slump of 85mm.Mix 3 obtained a slump of 70mm,mix 4 a slump of 65mm and mix 5 recorded the lowest slump of 55mm.An acceptable slump would be between 55mm to 105mm as the target slump was 80mm as Van Amsterdam (2000) sets the limit for the slump 25mm above and below the required slump designed to be acceptable.
Fresh concrete density
The fresh concrete density was recorded when concrete cubes were in its fresh state and in there moulds. The results displayed the average of five batches of freshly mixed concrete. It should be noted that for each batch six cubes were used. The cubes that would be crushed on day 7 and day 28 were grouped together in order to elaborate on the results in the following chapter. Table 4.3 below indicates the average fresh mass of the 7 day and 28 day samples.
Figure 4.2 and 4.3 shows the range of the day 7 and day 28 samples fresh mass respectively for each mix.
The ranges of the average fresh densities were from 2440 to 2500 kg/m3.The density and mass of the batches gets less with the increase in partial replacement of sand.
Hardened concrete density
The hardened concrete density was recorded when concrete cubes were in its hardened state. The concretes cubes hardened density was recorded after cubes had been cured for 7 and 28 days respectively. The results will display the average of five batches. It should be noted that for each batch six cubes were used, three for the 7 day and three for the 28 day sample. Table 4.4 indicates the average mass of the 7 day and 28 day samples when concrete were in its hardened state.
Figure 4.4 and 4.5 shows the range of the day 7 and day 28 samples hardened density respectively before they were crushed.
The ranges of the average hardened densities of the 7 day sample were from 2346.67 to 2500.74 kg/m3 and the 28 day hardened density was in the range 2352 to 2492.44 kg/m3.An increase in density was observed from the day 7 to day 28 curing.
Compressive strength in concrete
The compressive strength test produced the data of the maximum load cubes can withstand under compression. The average load of cubes crushed at a force of 345KN/min is shown in Table 4.5 at 7 days and 28 days respectively.
The average loads of failure for the day 7 samples was in the range of 514.47 to 305.47 KN and the loads of failure of the 28 day samples were 782.60 to 484.93 KN. Figure 4.6 and 4.7 show the strength of the concrete.
The compressive strength of concrete of the 7 day sample was in the range of 13.58 to 22.87 MPa and for the 28 day samples range 21.55 to 34.78 MPa. The strength increase in all batches from day to day 28 as expected.
Dry shrinkage
The dry shrinkage test was conducted on beams over a period of 20 days. The first reading taken was L0 measured after the beams moulds were removed. The second reading L1 was obtained after curing and the third reading L2 was obtained after the beam had been oven dried on day 14 and readings were taken on 16,18 and 20 days. Once the same reading was observed on consecutive measurement days L2 was recorded. Equation 2.4 was used to obtain the results of shrinkage shown in Table 4.6.
Dry Shrinkage % (4.4)
The average shrinkage was found between 0.040 to 0.017% ranges. The results varied with the total percentage of sand that was partially replaced.
Cost analysis
A cost analysis was conducted on the 30Mpa mix design used during the investigation as mentioned in chapter 3.The cost analysis is brief as transportation and availability of materials were not taken into account. The cost analysis is based on the materials used for the mix design. Table 4.7 indicates the material costing layout of material used.
The cement, fine aggregate and coarse aggregate costs were obtained from different sources in the Western Cape and South Africa, therefore transport costs were not considered as an accurate transport fee would vary. Cement, sand, stone and crumb rubber represents mean costs of different sources and the glass cost was obtained from a single source.
The cement and crumb rubber showed the highest cost per kg where the glass and san showed similar costs that were the lowest of the materials used. Water was not considered in the pricing of materials as it is readily available and in industry water costs are overlooked.
Conclusions drawn from results
The results obtained for the five mixes prepared with20% FGCG, sand ranging from 100% to 65% and CR content increasing from 0% to 15%.These results included slump obtained, fresh and hardened concrete density, compressive strength, dry shrinkage and a cost analysis. These results will be analysed and elaborated on in chapter five that follows.
Discussion
This chapter will discuss the fresh and hardened properties of the various concrete mixes in depth that have been tested. Also, it will include a brief cost analysis as well as a comparison made with similar tests that have been conducted in previous studies.
Analysis of fresh properties of concrete
The fresh properties that will be analysed and compared to similar studies are the slump test and the fresh densities of the concrete mixes. Comparisons will be made with existing literature where literature only contains partial replacement of crumb rubber compared to this study that has partially replaced crumb rubber and fine green crushed glass combined.
Slump test analysis
A decrease in slump was observed as the increments of crumb rubber partially replacing fine aggregate had been increased. What should be noted is that the conventional concrete mix and the mix that has sand partially replaced by 20% FGCG had the same slump. This showed the concretes workability is not affected when fine aggregate is partially replaced up to 20% with FGCG.
While conducting the slump test an observation was made that both the fine green crushed glass and crumb rubber mixed well and no colour changes were observed in the concrete. Both partially replaced elements cannot be seen with the eye once mixed. The relationship between crumb rubber and fine green crushed glass partially replacing sand can clearly be seen in Figure 5.1.
The slump ratio shows a steady decrease in the slump ratio with the increase in crumb rubber. The more crumb rubber added the less workable the concrete becomes as observed during the study in Figure 5.1.
Khatib and Bayomy (1999) had similar results to this study even though this study partailly replacing 25%, 30% and 35% of the total volume of fine aggregate.
Khaloo,Dehestani and Rahmatabadi (2008) and Bravo and De brito (2012) had staggering results with the increase in partially replacing fine aggregate with CR as seen in Figure 5.2. What should be noted is that when crumb rubber was added to the mixes the, workabality did not necessarily increase in all the slumps, but the workability was not affected as it was still in the required slump range.
This could be due to the crumb rubber not absorbing as much water as the sand,resulting in a better workability.
The workability of the concrete in this study was found to be acceptable as the fine green crushed glass when added to the crumb rubber in the mix did not decrease as much as the slump of that found in Khatib and Bayomy(1999) study.
This is an indication that the fine green crushed glass when combined with crumbed rubber partially replacing fine aggregate improves the workability. Khatib and Bayomy (1999) study differed where a decrease in slump was observed due to only partially replacing fine aggregate with CR.
Analysis of fresh density of concrete
The fresh concrete density of this study in Figure 5.3 shows the day 7 and Day 28 samples respectively. The densities of the samples were recorded as further analysis of the hardened density will be conducted when compared to the hardened density at 7 and 28 days.
The decrease in concrete density is shown with the increase in partial replacement of fine aggregate in Figure 5.3.The decrease in density trend can also be observed in the day 7 sample that shows a density of between 2480.89 kg/m3 to 2331.56 kg/m3, which shows a less dense mix than that of the conventional concrete mix. The 28 day sample shows similar results as expected as the decrease in weight is between 2473.48 kg/m3 to 2332.74 kg/m3.
The percentage of the fresh density of the partially replaced mixes when compared to the conventional concrete mix is illustrated in Figure 5.4 where the percentage indicates how much lighter the mixes are. Mix 3, mix 4 as well as mix 5 shows a drop in density which is a positive as light weight concretes with the desired strength can be advantageous in the construction industry.
mix.
Mix 3 of this study containing 20% fine green crushed glass and 5% crumb rubber as a partial replacement showed a lighter density when compared to Bayomy (1999) and De Brito (2012) that only partially replaced crumb rubber by 5%.With reference to Figure 5.5 Bayomy (1999) and De Brito (2012) a decrease in density of 0.21% and 2.48% was observed respectively. Similar results were observed with mix 4 when compared to aforementioned authors’ studies. Mix 5 differed as both the authors had a higher percentage of density drop compared to this study.
These less dense mixes are desirable in the construction industry as transportation of concrete could be easier and when considering using the concrete in pre-cast form is an added advantage if the lightweight concrete fulfils the strength requirement that will be analysed in section 5.2.2.
Analysis of hardened properties of concrete
The hardened properties that will be analysed and compared to similar studies are the hardened density, compressive strength test and the dry shrinkage test. It should be noted that all hardened properties analysed samples were only tested after a minimum of 7 days.
Analysis of hardened density of concrete
The hardened density of concrete samples will analyse the densities recorded on day 7 and day 28 respectively. The general assumption was that due to a decrease observed in the fresh density of concrete with the increase of partially replacing aggregate the same trend could be expected in the hardened density. The hardened density of both the 7 and 28 day samples are displayed in Figure 5.6.
The decrease in density observed was due to the increase in crumb rubber added to the respective batches, which was observed in the fresh and hardened density. The decrease in density is shown in Figure 5.6 for the hardened density. Though there is a decrease in density, the decreases is not constant as it varies.
The 7 day sample shows a much greater loss in density compared to the 28 day sample when making a comparison to mix 2.When comparing mix 2 and mix 3 of the 28 day sample a notable decrease in density is observed, however in the 7 day sample no notable decrease in density is seen when making comparison between mix 2 to mix 3 in Table 5.1 below that shows the difference in the hardened density from mix to mix.
An observation worth mentioning was that the density of the concrete shows a large decrease in density in mix 4 when compared to the other mixes in both the 7 and 28 day samples and in the 7 day sample between mixes 2 to mix 3. The density difference in mix 4 to mix 5 was minor when taking into context the decrease in density between the batches analysed in Table 5.1.
Analysis of compressive strength
The compressive strength of concrete samples at 7 and 28 days showed a similar trend to that of Khatib and Bayomy (1999) and Bravo and de Brito (2012).The trend indicated that with the increase of crumb rubber partially replacing sand the compressive strength decreased. The addition of fine green crush glass affected the compressive strength as even though a decrease in strength was observed one batch containing CR still met the design requirements of a 30 MPa mix.
Figure 5.7 shows the trends of the 7 and 28 day compressive strengths respectively. An observation that was a positive of the study was that similar strengths were shown to the control mix in both mix 2 and mix 3.At this early stage of 7 days the compressive strengths for the control mix, mix 2 and mix 3 were 22.87 MPa, 22.56Mpa and 21.57Mpa.This was a positive in terms of no notable compressive strength loss was found as they were similar. With regards to mix 4 and mix 5 clear strength losses were observed.
The final compressive strength at 28 days showed similar trends to that recorded in day 7 as shown in Figure 5.7.The design mix of 30 MPa was met by the control mix, mix 2 as well as mix 3.This was a positive as the design requirements have been met. Mix 4 and mix 5 did not meet the design requirement of 30 MPa. This could be due to the fact that 25% partially replacing sand with crumb rubber and fine green crushed glass is the optimum replacement that may occur.
The strength gained from day 7 to day 28 is shown in Table 5.2.The strength increases was in the range of 63.02% in mix 5 which was the lowest to 68.02% of mix 3 which was the highest strength increase of this study. The strength increase of Khatib and Bayomy (1999) was in the range of 50% to 57.69% from day to day 28.
The control mix, mix 2 and mix 4 showed similar strength increases. Thus indicating that the strength increase percentage from day 7 to day 28 is not dependant on the amount of fine aggregate replaced.
Though there were strength increases were observed in Table 5.2 as expected from day 7 to day 28.The decrease in strengths when compared to the control mix in day 7 and day 28 respectively were observed in Figure 5.8.
The decrease compressive in strength when compared to the conventional mix on day 7 was observed in all the batch mixes. A similar strength decrease was observed for the 28 day compressive strength. The notable decreases in strength were observed in mix 4 and mix 5 that had a loss in compressive strength of 28.82% and 40.62% respectively. This loss in strength is high and as concrete reaches 70-80% of its strength after 7 days of curing the gain in strength at 28 days would therefore not be considered high.
At 28 days the compressive strength of concrete a decrease in strength was again observed in all mixes when compared to the control mix. The loss in strength did not affect mix2 and mix 3 in reaching the design requirement of 30 MPa as both mixes fulfilled the design requirement. Mix 3 results were a positive for this study where the strength was obtained.
What should be considered is that Addis (1998) indicates that the strength gain of concrete still occurs after 28 days if the curing period is extended. This gives rise to contemplate whether the strength gained in mix 5 was high but the design required strength was not reached. If mix 5 was cured for a longer period of time the mix strength could possibly increase and reach the design requirement of 30 MPa.
The study was further analysed by comparing the compressive strength at 7 days to that of Khatib and Bayomy (1999).A higher strength was observed in all mixes at 7 days showing that the addition of fine green crushed glass improved the strength when mixed with crumb rubber as seen in Figure 5.9.
A similar trend was observed at 28 days where all the strengths of concrete containing a partial replacement of fine green crushed glass and crumb rubber had a higher strength than Khatib and Bayomy (1999) except for mix 3 where the mix was 1.20 MPa less than that of Khatib and Bayomy (1999).Figure 5.10 shows this as well as a strength decrease with the increase of fine aggregate partially replaced.
The addition of fine green crushed glass and crumb rubber improved the strength characteristics when compared to Khatib and Bayomy (1999), which is a positive for this study. Though a decrease in strength is observed, mix 3 reduction in strength is acceptable as the design strength was met.
Analysis of dry shrinkage
The dry shrinkage in concrete is related to the moisture in the cement pastes and also the environment in which concrete is found. Concrete shrinkage will occur in conditions other than when permanently saturated in water.
Bravo and de Brito (2012) indicated in Figure 2.25 that the shrinkage of concrete increase with the increase of partial replacement of crumb rubber for fine aggregate. The dry shrinkage can only occur once concrete has hardened, then only can it be analysed. Figure 5.11 displays the shrinkage in the different batches tested.
Mix 2 which consists of fine green crushed glass partially replacing 20% of fine aggregate shows a considerably high increase in shrinkage. All the mixes that had the addition of crumb rubber showed a decrease in shrinkage in comparison with that only consisting of fine green crushed glass.
However the mix containing 5% CR and 10% CR were similar to tests conducted by Bravo and de Brito (2012) as it showed an increase in shrinkage.
The notable change from the 15% CR that Bravo and De Brito (2012) used during his study and this study was that the mix that contained 15% crumb rubber combined with 20% fine green crushed glass reduced the shrinkage of the beams when compared to the conventional concrete mix.
The decrease in shrinkage usually occurs when the aggregates in concrete has a high stiffness characteristic Addis (1998). Sand does not have the stiffness characteristics that crumb rubber and fine green crushed glass possess.
Cost analysis
As previously mentioned in chapter 2 by Muigai et al. (2013) natural resources need to be preserved for future uses. This gave rise the cost comparison with that of conventional concrete and partially replacement of fine aggregate with the crumb rubber and fine green crushed glass in concrete. Table 4.7 showed the cost of the materials used in the concrete mixes. In Table 5.3 the different batch prices are displayed.
The cost comparison in Table 5.3 shows the cost on a small scale as this study was not conducted in practice but in a laboratory in order for it to be used in industry. The cost shows variations from the conventional concrete mix where only mix 2 had a similar cost comparison.
In industry concrete is used per m3 and is also sold per m3.Figure 5.12 shows the cost comparison of the different batch mixes priced per m3 of concrete.
It is clearly illustrated that the concrete containing 15% crumb rubber is the most expensive batch. A gradual decrease in cost is observed with the decrease in crumb rubber partially replacing fine aggregate.
The batches containing crumb rubber has a much higher cost than that compared to the conventional concrete mix, mainly due to the high cost of the crumb rubber in South Africa. Mix 2 containing no crumb rubber but has fine green crushed glass partially replacing fine aggregate was at a lower cost than that of the conventional concrete mix.
Conclusion
In summary the slump of this study that contained 20% FGCG combined with 5%, 10% and 15% CR showed decrease in slump with the addition of CR. Compressive strength also decreased with the more sand that was partially replaced. Figure 5.12 illustrates a summary of the tests conducted in order to obtain the objectives set out in chapter 1.
It is clear that the cost of the different mixes increases with the decrease in sand and when combining FGCG and CR as a partial replacement.
The dry shrinkage shows that the less sand used in the mix the less dry shrinkage is found however the cost is still higher when compared to the conventional concrete mix.
Conclusions and recommendations
In Summary this chapter will provide conclusions on the study that has been completed and certain recommendations will also be made on how to improve the study in future.
Conclusions
The following conclusions were drawn from the five batch mixes fresh and hardened properties analysed as well as the cost analysis conducted:
The workability of the conventional concrete and that of mix 2 (partially replacing 20% fine green crushed glass with fine aggregate) were found to be the same indicating that partially replacing sand up to 20% does not affect workability. The workability was still within an acceptable limit with the addition of crumbed rubber but was much lower than the control sample.
Both the fresh and hardened properties of the concrete batches are affected when sand is partially replaced with fine green crushed glass and crumb rubber as they show similar trends. The more sand is partially replaced the lesser the density of the batches. The density decreased with the increased replacement of sand.
The compressive strength of mix 2 and mix 3 met the design requirement of 30 MPa along with the conventional concrete mix. The increase in crumb rubber to the batch mixes caused a decrease in strength observed. That said, mix 5 with the highest amount of crumb rubber had the highest strength gain from day 7 to day 28.However this strength gain was 2.74% more than that of the conventional concrete mix.
Dry shrinkage indicated that partially replacing sand with fine green crushed glass up to 20% was the highest of all batch mixes evaluated. The addition of crumb rubber to the mixes containing 20% fine green crushed glass replacing fine aggregate showed a decrease in shrinkage. The decrease in shrinkage when compared to the conventional concrete mix was that crumb rubber up to 15% was the only mix that had less dry shrinkage than that recorded on the conventional concrete mix.
The cost analysis indicated that partially replacing sand up to 20% with fine green crushed had the lowest cost per/m3 as it was R 3 less per/m3.The addition of crumb rubber increasing also showed an increase in the cost. The highest cost of concrete was in mix 5 where a R 151 more per/m3 was found making comparison to the conventional concrete mix.
Considering all the mixes evaluated, the mix containing 5% CR and 20% FGCG replacing sand was found to be the optimum mix when making comparison to the conventional concrete. This is due to the strength requirement meeting the 30 MPa design and the shrinkage was slightly more than the conventional concrete mix. The slump was also in the required range however the cost was significantly higher than that of the conventional concrete mix when measured in R/m3.
Recommendations
In terms of the conclusions drawn the following recommendations have been identified for future research regarding the improvement of this study:
Fine green crushed glass and crumb rubber of 1 mm or smaller as the finer material improves the workability.
Mixes partially replacing aggregates such as fine green crushed glass combined with crumb rubber should be cured for a period longer than 28 days before testing the compressive strength.
A study having the same increments of fine green crushed glass and crumb rubber as this study should be added to conventional concrete instead of partially replacing fine aggregate and then evaluate the properties.
Tests such as durability, flexural, tensile splitting strength and alkali-silica reaction should be conducted with the same mix design as this study.
Admixtures should be added to the concrete batches that have the same design as this study to assess the properties.