The Composition Of Concrete Attributes Biology Essay

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Concrete has many different properties including strength, durability, pore structure, workability, and set time. There are many in situ and lab tests that can be performed to identify and measure these characteristics. The composition of concrete attributes varies depending on the design of concrete and its structural requirements.

Concrete properties are influenced by a variety of different production and installation conditions. The most common are aggregate type and size, water to cement ratio, curing conditions, and heat of hydration. The goal is to obtain the optimum balance that completely fits the specific design requirements. For example, increasing the w/c ratio for increased workability may result in a major decrease in concrete compressive strength. Admixtures are other materials that are used in concrete production in order to modify its properties and obtain desired results (Suchorski, 2007).

ACI 116R-00 defines admixtures as "a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementations mixture to modify its freshly mixed, setting, or hardened properties." There are many different admixtures used in different conditions and design requirements. The American Concrete Institute Committee states that the purpose of using admixtures is to modify compressive and flexure strength at all ages, decrease permeability and improve durability, inhibit corrosion, reduce shrinkage, accelerate or retard set, increase slump and workability, improve pumpability and finishability, increase cement efficiency, and improve the economy of the mixture. A full list of admixture functions determined by ACI 212-3R is given in Appendix A-1. The standards for each type of admixture are given in Appendix A-2. (Suchorski, 2007)

The 'Green Revolution' is reshaping the construction industry with a new trend of environmental, economic, and social sustainability. The production of concrete has changed and is still changing with the advent of new technologies and chemicals and minerals that strive to reduce both pollutants and asset footprints. Governmental, regional, and global construction codes aim to decrease the negative environmental effects of all construction activities.

The goal of this paper is to examine and identify alternative mineral admixtures that would increase production efficiency, decrease production costs, and reduce environmental damage. Studies and experiments analyzing the performance of new mineral admixtures are evaluated. This paper first focuses on conventional chemical and mineral admixtures and then concentrates on various admixture performance experiments that aim to promote sustainability while improving concrete.

Chemical Admixtures:

In this section, chemical admixtures are described with distinctions made parallel to the ACI admixtures specifications. There are advantages and disadvantages for each admixture, depending on structural and exposure conditions. Often, some properties are enhanced while other are reduced in order to comply with design specifications.

Air Entrainments

Air bubbles are produced during mixing and installation of concrete. They affect the porosity and permeability of concrete and cause easier ingression of aggressive agents and ions that lead to corrosion and concrete degradation. However, during 1930s, after rigorous experiments and research, it was found that an adequate amount and distribution of entrapped air reduced the risk of freeze/thaw deterioration and subsequently did not adversely affect concrete compressive strength until 28 MPa was reached (Suchorski, 2007)

Air entrainment occurs when admixtures are deliberately added to concrete during batching. These air bubbles stabilize during hydration and become part of the hardened concrete. There are capillary pores in concrete that connect the entrapped air. The relatively bigger entrained air bubbles make these capillaries discontinuous and they act as reservoirs that serve to mitigate the effects of ice expansion. As a result, the reduced tensile stresses prevent cracking in concrete. The amount of entrained air, size, and distribution is based on exposure conditions, design specifications, and aggregate size. The air entraining admixtures must comply with the ASTM Specification C 260 which details the spacing, size, and air content parameters. Placement, settlement, and finishing techniques may decrease the air content during installation. The factors that influence the performance of the air entraining admixtures are given in Appendix A-3(Suchorski, 2007).

Water Reducing and Set Controlling

Water reducing and set controlling admixtures are involved during the mixing process for the following purposes:

to improve durability

to ease placement

to modify the setting time

to ease finishing with less segregation between aggregates and paste

Due to the reduced water to cement ratio, there is a significant increase in cement strength and efficiency.

ASTM C 494, Standard Specification for Chemical Admixtures for Concrete, identifies seven different types of water reducing and set controlling admixtures. They are:

Type A: Water reducing admixtures

Type B: Retarding admixtures

Type C: Accelerating admixtures

Type D: Water reducing and retarding admixtures

Type E: Water reducing and accelerating admixtures

Type F: Water reducing, high range admixtures

Type G: Water reducing, high range, and retarding admixtures

Type A, water reducing

Type A admixtures are used typically to decrease water content by 5-12% (Suchorski, 2007). Higher dosages need to be used carefully as they cause excessive retardation of setting time. This retardation may be overcome by adding accelerating admixtures to the batch(American Coal Ash, 2004).

Type B and Type D, water reducing and retarding

Both types offset the effects of high temperature on concrete and increase workability during the placing and consolidation periods. The benefits derived from the retardation are flexibility, the prevention of cold joints, the ability to finish in hot water, and full deflection before initial set . The American Concrete Institute classifies Type B and D admixtures into two groups-conventional retarding admixtures and extended set admixtures. Extended set admixtures are newly developed as highly potent retarders with higher efficiencies. The extended set admixtures react with all major cement constitutes whereas conventional admixtures only react with some constitutes(Suchorski, 2007).

Type C and Type E, water reducing and accelerating

Type C and E admixtures shorten concrete setting time and accelerate its strength development. Reduced bleeding, improved exposure resistance, and earlier finishing are other outcomes of these admixtures. There are a number of standards and guidelines that regulate the use of these admixtures as they contain high amounts of calcium and other detrimental ions Failure to comply with these standards and guidelines may result in concrete deterioration and degradation(Suchorski, 2007).

High and mid-range water reducing admixtures

High range water-reducing admixtures (HRWR), often called super-plasticizers, may reduce concrete water content by 30% without causing excessive retardation. HRWR admixtures can be used to establish a higher workability/flowability of concrete at the same water level. HRWR admixtures must comply with Types F and G standards of the ASTM C 494.

The following are the overall advantages of HRWR admixtures: significant water reduction, reduced cement content, increased workability, reduced effort for placement, effective use of cement, rapid strength development, reduced permeability. The disadvantages are listed as follows: slump loss, air void, color blemishes on exposed and formed finish, increased cost of production. The mild water reducing admixtures provide moderate reduction without significantly delaying the setting time (Suchorski, 2007).

Corrosion Inhibitors

Reducing steel corrosion is vital for concrete durability. Steel corrosion causes cracking, spalling, increased permeability, and strength loss in concrete. Chlorides introduced from deicing salts, seawater, or concrete ingredients are the greatest cause of corrosion. Corrosion inhibitor admixtures added during batching delay the onset of corrosion and also reduce the rate of corrosion after initiation(Kessler, et al., 2003).

Shrinkage Reducing Admixtures

Concrete loses moisture during drying which causes volume contraction. This shrinkage results in cracking due to internal or external restraints. Decreasing the water content using good quality aggregates or changing the aggregate size and content can minimize cement contraction. Shrinkage reducing admixtures reduce the water tension in capillaries and thus reduce shrinkage (Holland, 1999).

Other Chemical Admixtures

Alkali-silica reactivity

Alkali silica reaction occurs between the alkalis in cement and silica in the aggregates which results in expansion causing cracks and fractures. The reaction depends on the amount of alkali, the reactivity of aggregates, and moisture content. Lithium based chemical admixtures are used to minimize the risk of expansion as they react with the already available silica in aggregates.

Under watering concrete

Placing structures under water may cause cement and aggregate washout. This leads to a loss of cement strength and integrity. Anti-washout or viscosity modifying (VM) admixtures are used to increase concrete cohesiveness which reduces washout, increases resistance to dilution, and preserves the integrity of concrete(Suchorski, 2007).

Bonding

Bonding admixtures increase the bond between new and old concrete.

Pumping

Pumping admixtures improve the pumpability, thicken the paste, and reduce separation and bleeding of concrete.

Pigments

Pigments cause a change in the color of concrete in order to increase its aesthetic appeal.

Mineral Admixtures

General Properties

Characteristics and classification

Mineral admixtures are fine-grained siliceous materials that have pozzolanic or latent hydraulic properties. They are added in relatively large amounts-20 to 70 % of the cementitious material-in order to improve concrete properties.

A mineral admixture can be pozzolanic, cementitious, or both. Pozzolanic materials do not have cementitious value but react with calcium hydroxide to form cementitious compounds (Mehta, 1987). Cementitious materials have properties that are similar to but stronger than regular cement. Producing one ton of Portland cement emits approximately 738 kg of carbon dioxide. Replacing cement with mineral admixtures would vastly reduce concrete's carbon footprint.

Mineral admixtures are classified as natural minerals or by-products based on their origin. Almost all natural mineral admixtures are derived from volcanic activity and the cooling of magma. These admixtures include volcanic glasses, volcanic tuffs, calcined clays or shales, and the presence of diatomaceous earth. By-product materials are mainly ashes formed from combustion processes, crop residues, silica fume produced from certain metallurgical operations, and granulated slag generated from metal industries(Mehta and Monteiro, 1993). The conventional mineral admixtures that are used extensively in the production of concrete are fly ash, iron blast furnace slag, silica fume, rice husk ash, and metakaolin.

Effect on concrete

Pozzolanic materials increase the strength of concrete. In concrete there are air voids, fractures, and micro cracks that appear at the interfaces between the aggregate and cement and the mineral admixtures are very fine particles that are able to fill these micro cracks and voids. The pozzolanic reaction converts the compact CSH phase with large cavities to low density CSH with smaller voids. Thus, the concrete structure becomes denser, has fewer cracks and voids, and exhibits increased compressive strength(Chan, et al., 1999).

As the cracks and voids are filled, permeability of the concrete structure decreases. The impermeable concrete has less water diffusion as well as increased resistance against damaging chemical agents and steel corrosion. Also, cohesiveness of mineral admixtures improves the workability and reduces the bleeding of concrete.

In addition, mineral admixtures increase the durability of concrete in many aspects. Lower heats of hydration reduce the thermal strains and cracking in concrete and the low permeability decreases the diffusion of chloride ions which reduces the risk of corrosion. Hydrated cement paste that is formed due to the presence of calcium hydroxides is not durable in acidic environments and as such the replacement of cement paste with mineral admixtures improves its resistance against harmful chemicals. With reduced amounts of C3A due to replaced cement, sulfate intrusion is also minimized. The amount of soluble alkalis in cement paste decreases due to the utilization of mineral admixtures and the alkali aggregate reaction is thus minimized(Chan, et al., 1999).

Conventional Mineral Admixtures

Fly ash (pulverized fuel ash)

Fly ash, a by-product of coal-fired plants, was produced in large amounts during the 19th and 20th centuries. Coal has different properties on every region depending on its depth, soil content, and moisture of formation. Thus, fly ash properties depend on the particular characteristics of coal.

Fly ash can be categorized into two classes. Class F is produced with the burning of harder, older, and bituminous coal. This class is pozzolanic and requires cement and the presence of water to become a cementitious compound. Class C is a by-product formed from the burning of younger lignite or sub-bituminous coal. Having pozzolanic characteristics that are similar to Class F, it also has cementing properties. Class C does not require water; however, it hardens and gains strength over time in the presence of water (Will).

Fly ash is commonly used as a substitute to Portland cement due to its pozzolanic properties and Class C fly ash is generally used as a replacement for Portland cement. Class F has volatile effects on the entrained air of concrete thus reducing its resistance to freeze/thaw damage. Fly ash dosage changes for every application but it is often 30% of Portland cement (American Coal Ash, 2004).

Fly ash affects the strength, chemical resistance, and durability of concrete depending on the type of fly ash and the dosage, concrete ingredients, and cement type. However, fly ash typically increases the final strength, chemical resistance, durability, and workability of concrete. The data and the experiments that demonstrate these properties can be found in the publication written by the American Coal Ash Association for the Federal Highway Administration of the United States (American Coal Ash, 2004). Fly ash contains approximately 65% of silica which reacts with lime during the hydration of the cement paste thus producing a gel. This gel fills the capillary pores and reduces the permeability and pore size of concrete (Chan, et al., 1999).

Utilization of fly ash as a replacement for Portland cement has many environmental benefits. Only 25% of all coal combustion residues are recycled whereas the rest are discarded in landfills or abandoned. Thus, using fly ash as a mineral admixture facilitates waste disposal and reduces adverse environmental effects (Will).

Blast furnace slag

Ground granulated blast-furnace slag is produced as a result of quenching molten iron slag which is a by-product of iron production. Quenching occurs from a blast furnace that uses water or steam. The glassy and granular product is dried and grounded to turn into a fine powder and the blast furnace slag is used to improve the quality of cement. The blast furnace slag content varies from 30% to 70% which produces Portland Blast Furnace Cement (PBFC) or High Slag Blast Furnace Cement (HSBFC).

The ground granulated blast furnace slag has many effects on cement and concrete. GGBS cement has higher set times but continues to gain strength over longer periods(Mehta and Monteiro, 1993). These characteristics vary depending on the GGBS amount, cement type, moisture, and curing conditions. Higher set times reduce the heat of hydration and decrease the temperature variation in concrete. Reducing thermal and shrinkage strains help to avoid cold joints. GGBS concrete reduces damage due to alkali-silica reaction and increases resistance to chloride, sulfate, and other damaging chemicals. This improvement in durability is due to the denser microstructure that results in lower permeability and the reduction in the release of alkalis from cement (Chan, et al., 1999).

Silica fume

Silica fume is a by-product of metallic silicon production. This cementitious material is added to concrete at different dosages depending on the intended purpose as either pumping aid or to produce high quality and high strength concrete (Ay and Topcu, 1995).

The powerful pozzolanic effect of silica fume increases the CSH in concrete. Reduced capillary pores and voids result in lower permeability and increased strength. Thus, silica fume improves the durability of the concrete structure. Also, pumpability and cohesiveness of concrete will be improved and bleeding will be minimal. However, with higher proportions of silica fume, super-plasticizers must be added to obtain the same workability. The table in Appendix A-4 taken from the Report on Concrete Admixtures for Waterproofing Construction shows how silica fume dosage changes the strength, water and chloride permeability , and slump of concrete (Chan, et al., 1999).

Rice husk ash

Rice husk ashes are shells that are produced during the de-husking of paddy rice. These husks, in which 200 kg is produced for every one ton of paddy rice, are an enormous disposal problem for centralized rice mills. The effect on concrete is similar to other mineral admixtures due to the high presence of pozzolanic properties. The Possibility of Adding the Rice Husk Ash to the Concrete report shows positive experimental results on compressive and tensile strengths, elastic modulus, and water absorption of rice husk ash concrete (Tashima, et al., 2004). Some of these results and graphs are given in Appendix A-5.

Metakaolin

High purity kaolinitic clays are calcined at low temperatures to keep the silica and alumina in an amorphous state. When pulverized to small particles, highly reactive pozzolanic metakaolin forms. The effect on concrete is similar to other mineral admixtures due to the high presence of pozzolanic properties. Its effect on reducing alkali silica reaction is significant due to reduced calcium hydroxide levels. Powerpozz, by Advanced Cement Technologies, underlines the importance of metakaolin in the reduction of ASR in concrete .

Modern Research and Results

Black liquor

Introduction and Methods

In Egypt, 10 million tons of rice straw and 3.5 million tons of bagasse were produced as agro by-products in 2006. These are used as feedstock for the pulp and paper industry which produces large amounts of black liquor. Black liquor has lignin in its structure that is not used efficiently. Lignin is a group of phenolic polymer that confers the rigidity to the woody cell wall and is highly reactive due to its chemical bonds and functional groups. Thus it can serve as binder, dispersant, and emulsifier (El-Mekkawi, et al., 2011).

Alkali lignin can be extracted from black liquor by filtration, evaporation, sulfonation, and drying. This process and the experiment conducted by Chang et al is detailed in the next section of this paper entitled 'straw pulp waste liquor.'

El-Mekkawi et al conducted an experiment using black liquor as an admixture for concrete. The following black liquor properties are obtained through lab devices and experiments: pH, specific gravity, total solid content, chloride content, sulfate content, chemical oxygen demand, biological oxygen demand, sugar content, carbohydrate content, ash content, lignin content (El-Mekkawi, et al., 2011).

Two different water cement ratios were used in the tests: 0.4 high strength concrete, 0.5 normal strength concrete. Details about the concrete material properties and test methods are outlined in the paper entitled, "Utilization of black liquor as concrete admixture and set retarder aid." Black liquor was added as a replacement for water so that the total liquid in the sample remained stable.

Test Results

The slump result for w/c=0.4 sample with no black liquor was found to be zero, making it not acceptable according to standards. The workability of concrete at 0.4 is very low which does not allow for desired mixing and compaction of concrete. Consequently, reduced compressive strength and slump occurs. Black liquor acts as a dispersing agent and neutralizes the electrostatic charges in cement which increases slump and the compressive strength of concrete. The other sample with w/c=0.4 and 15% black liquor showed the maximum slump. The graph (Table 1) below summarizes the results (El-Mekkawi, et al., 2011).

Increasing the black liquor above a certain limit may reduce the compressive strength of concrete. This is mainly due to the exceeding amount of charged ions that may recharge the solids thus reducing their ability to mix. This causes a reduction in both compressive strength and slump after the 15% replacement level, as seen in both water content samples. The graph (Table 2) below summarizes the results with respect to compressive strength. Similar trends are seen for tensile strength but are not mentioned in this paper.

Chlorine ions in concrete cause corrosion while sulfate ions may cause cracking. Chemical analysis is made on hardened concrete samples. The addition of black liquor does increase these values but they are still significantly below standards. This data is summarized in the table (Table 3) below (El-Mekkawi, et al., 2011).

Table 3: Chlorine and sulfate ions in 28 days hardened concrete

Concrete Mixes

Chlorine ions % (cement wt)

Sulfate ions % (cement wt)

w/c=0.4, 15% replacement

0.131

2.655

w/c=0.5, 5% replacement

0.119

2.138

w/c=0.5, 15% replacement

0.149

3.266

w/c=0.5, 25% replacement

0.159

3.3

Black liquor contains sugars which act as a retarder. The initial and final set times for black liquor concrete were appropriate according to standards. Table (Table 4) below shows the set times with different dosages (El-Mekkawi, et al., 2011).

Table 4: Effect of black liquor on cement paste setting time

Dose (%)

Initial Set Time (min)

Final Set Time (min)

0

18

37

10

49

55

20

27

3

30

54

46

El-Mekkawi et al also concentrated on bagasse as a replacement for black liquor. Bagasse as a mineral admixture will be analyzed in the following sections.

Conclusion

Black liquor has a minimal cost compared to other mineral admixtures used to increase workability and retard setting of concrete. The report entitled, 'Utilization of Black Liquor as Concrete Admixture and Set Retarder Aid', shows that black liquor gives the maximum performance at approximately 15% levels. It increases the workability noticeably and acts as a retarder due to its high sugar content. There is a gain in compressive strength in both 7- and 28-day results. Although black liquor increases the chemical content in concrete, the results are substantially below the chemical composition standards for chlorine and sulfate(El-Mekkawi, et al., 2011).

Straw pulp waste liquor

Introduction and Process

Chang et al conducted experiments on straw pulp waste liquor as a mineral admixture in their article entitled, 'Straw Pulp Waste Liquor as a Water-reducing Admixture.' This section summarizes their process, findings, and results.

Straw pulp waste liquor, a by-product of the paper making process, contains high amounts of lignin and cellulose. This environmentally degrading liquor is disposed into rivers without appropriate treatment. Utilizing this waste liquor as an admixture has many economic and environmental benefits (Chang and Chan, 1995).

The reactivity of lignin molecules is an important process in improving workability of concrete. The process to produce a surfactant substance from alkali lignin is sequenced as follows:

black waste liquor > filtration > evaporation > sulphonation > spray drying > product

The effect of sulphonation temperature on slump, w/c, and compressive strength is given in the tables below (Table 4 and 5).

Table 4: Effect of sulphonating temperature for the new admixture on strength of concrete

Sulphonation (oC)

Slump (mm)

w/c

3 day strength (MPa)

7 day strength (MPa)

28 day strength (MPa)

80

60

0.58

12.0

23.1

32.8

100

65

0.56

12.5

25.2

35.5

120

70

0.57

12.0

23.6

35.2

140

65

0.59

11.7

22.8

32.4

The properties of the new admixture at a sulphonation temperature of 100 oC are(Chang and Chan, 1995):

Table 5: Properties of new admixture

Moisture Content

1%

Specific Gravity

1.15

Bulk density

785 kg/m3

Fineness

0.315 mm , 4% residue

Insoluble residue

1.78%

Chloride ion

0.65%

Lignin

16.8%

Acidic precipitate

9.32%

Free alkali

Trace

Effects on Concrete Performance

Increasing the admixture dosage decreases the w/c and causes an increase in concrete compressive strength. However, when the dosage exceeds 0.3%, the early strength of concrete decreases due to retarding and the presence of air entraining ingredients. The 3-day, 7-day and 28-day strengths for different dosages are given in the graph (Table 6) below.

The slump of the concrete had to be kept at 60 mm. To retain the slump, the water content of the mixture was decreased by approximately 10% for every input dosage of 0.25%. The water bleeding rates for the control sample and for the sample with 0.25% straw pulp waste liquor were 2.8% and 1.67% respectively. This highlights a reduction of 40% in bleeding.

There is a decrease of 48 minutes and 60 minutes for the initial and final set times for the concrete with waste liquor. The loss of workability and standard compliance for the concrete with the new admixture are given below (Tables 7 and 8).

Table 8: Properties of concrete incorporating the new water reducing admixture

Property

Standard Requirements for Ordinary Admixtures

Test Results

1st class

Qualified

Water reducing rate, %

>8

>5

10

Water bleeding rate, %

<95

<100

60

Air content, %

<3

<4

3

Initial set time (min)

-60 to +90

-60 to+120

+48

Final Set time (min)

-60 to +90

-60 to +120

+60

Compressive Strength (MPa)

1 day

-

-

-

3 days

>115

>110

118

7 days

>115

>110

122

28 days

>110

>105

115

90 days

>100

>100

100

Shrinkage Rate (90 days), %

<120

<120

110

Corrosion of steel

None

None

None

The new admixture is produced from the waste liquor of straw pulp by an alkaline process. The admixture has a water reduction rate of about 8%, a compressive strength increase of 10%, and uses less cement . The new admixture has a decent overall performance while exhibiting many environmental and economic benefits.

Bagasse ash

Introduction

Sugar cane bagasse is a waste product of sugar mills that is dumped into open space. Aigbodion et al state that 1 ton of sugar produces 280 kg of bagasse ash(Aigbodion, et al., 2010). Pozzolanic materials such as bagasse ash affect concrete's resistance against corrosion in many different ways as explained previously. In their article entitled, "Evaluation of bagasse ash as corrosion resisting admixture for carbon steel in concrete," Ganesan et al investigate the effect of bagasse ash dosage on reinforcement corrosion and other concrete performance characteristics. In a similar fashion, Maslehuddin et al have concentrated on the effect of fly ash and Zhang et al have concentrated on the effect of rice husk ash on steel reinforcement. The experiment conducted by Ganesan et al investigates the transport species of chloride, sulfate, and carbon dioxide in order to correlate bagasse performance to corrosion resistance(Ganesan, et al., 2007).

Effects on Concrete Performance

Bagasse ash has been added to concrete as 5, 10, 15, 20, 25, and 30 weight percentages. The effects on concrete compressive strength are given in Table 9. The variation in corrosion rates and electrical potentials found by gravimetric method, linear polarization values, and impedance measurement values are given in Tables 10, 11, and 12 respectively (Ganesan, et al., 2007).

Table 9: Compressive strength and resistance to chloride ion penetration of bagasse ash concretes

Specimen

BA replacement

Compressive Strength (MPa)

Resistance to Cl penetration (C)

7 days

14 days

28 days

90 days

28 days

90 days

C

0

27.22

32.30

36.05

38.30

2775

2480

B1

5

31.11

34.60

41.30

44.00

2046

1605

B2

10

34.12

40.90

42.10

44.10

1854

1374

B3

15

34.09

39.90

41.21

43.00

1302

874

B4

20

33.90

37.60

39.80

40.70

1203

760

B5

25

32.57

33.10

33.60

36.70

1050

681

B6

30

29.56

30.40

30.80

31.60

2086

1289

Table 10: Gravimetric method of corrosion rate values of bagasse ash concretes

Specimen

BA replacement

Corrosion rate x 10-3 mmpy

Percentage reduction in CR

C

0

21.63

B1

5

15.42

28.71

B2

10

6.02

72.16

B3

15

8.12

62.45

B4

20

11.71

45.86

B5

25

16.24

24.91

B6

30

84.56

-290.91

Table 11: Linear polarization resistance value and corrosion rates of bagasse ash concretes

Specimen

BA replacement

Corrosion potential (mV SCE)

Rp kohms-cm2

Icorr uA/cm2

Corrosion rate x10-3 mmpy

% reduction in CR

C

0

495

14.943

1.74

20.14

B1

5

361

33.147

0.748

9.08

54.92

B2

10

321

110.91

0.234

2.71

86.54

B3

15

359

54.09

0.481

5.56

72.39

B4

20

430

31.63

0.822

9.51

52.78

B5

25

441

27.43

0.948

10.97

45.53

B6

30

490

6.681

3.89

45.05

-123.68

Table 12: Impedance measurement values and corrosion rates of bagasse ash concretes

Specimen

BA replacement

Corrosion potential (mV SCE)

Rct kohms-cm2

Icorr uA/cm2

Corrosion rate x10-3 mmpy

% reduction in CR

C

0

448

12.31

2.119

24.45

B1

5

353

19.56

1.334

15.38

37.10

B2

10

341

101.50

0.257

2.96

87.89

B3

15

359

34.89

0.745

8.63

67.70

B4

20

395

28.26

0.920

10.65

56.44

B5

25

449

16.50

1.575

18.24

25.39

B6

30

488

3.994

6.509

75.36

-208.22

The compressive strength of concrete is highest at 10 and 15 percentage replacement levels. This is due to the higher amount of silica in bagasse ash which causes additional CSH gel formation. However, higher levels cause a significant decrease in concrete strength. The corrosion rate (calculated by gravimetric method), linear polarization, and impedance all show a minimum rate at 10 to 15 % bagasse ash replacement levels. The additional CSH gel formation causes large permeable pores to turn into small impermeable pores thus increasing corrosion resistance. All of the results by K. Ganesan, K. Rajagopal, and K, Thangavel are given in Appendix A-5 (Ganesan, et al., 2007).

Waste paint

Latex paint wastes are disposed in landfills at substantial economic and environmental costs. These wastes are mostly made up of polymers which are active ingredients in polymeric admixtures. These admixtures increase the bond between cement and aggregate and increase workability and flow of cementitious materials. Improvements in workability enable settlement around congested reinforcement, fill small voids, and reduce the necessity for compaction and vibration. However, these polymeric admixtures are often too expensive. Utilizing waste paint as a polymeric admixture would decrease costs while reducing the negative environmental effects of cement formation (Almesfer, et al., 2012).

In their report, Almesfer et al conducted experiments in two stages. The first experiment included chemical admixtures along with waste paint in the concrete mixture. The second experiment excluded such admixtures and only incorporated waste paint. The first experiment resulted in excessive amounts of polymers and air entrainment. The second experiment was conducted solely for the purpose of determining the effects of waste paint on concrete properties. This paper focuses only on the second test. The following tables display the results for compressive strength (Table 13), yield shear stress (Table 14), viscosity (Table 15), and separation (Table 16)(Almesfer, et al., 2012).

It is apparent that compressive strength is not greatly affected by the inclusion of waste paint. The observations suggest that there is a threshold replacement level with the minimum compressive strength that must be avoided. There is a distinctive change in yield shear stress with the addition of waste paint. However, viscosity and separation percentages dropped immediately with the inclusion of waste paint-there are several reasons for this. The thickening agents that increase yield stress can lead to increased air content and viscosity reduction and waste paint can cause the neutralization of relatively strong electrostatic interactions within concrete. This further causes a reduction in the effectiveness of the bonds in concrete. Overall, 8-12% waste paint replacement resulted in maintained strength and improved workability in concrete. However, other criteria such as long-term durability must be investigated for a better understanding of this admixture and to ensure reliable performance (Almesfer, et al., 2012).

Lignite ash

In their article entitled "Utilization of Lignite Ash in Concrete Mixture," Demirbas et al studied the effect of lignite ash in terms of its different silica, alumina, and iron oxide constituents. Coal ash can be used similarly to fly ash or blast furnace slag. However, specifications must be present in order to limit silicon dioxide, aluminum oxide, and iron oxide concentrations. Lignite ash is preferred due to its high calcium oxide and magnesium oxide contents. The article draws attention to typical constituents of coal ash and proposes approximate fraction limits for SiO2, Al2O3, Fe2O3, CaO, MgO, TiO2, and Na2O+K2O (Demirbas, et al., 1995).

The experiment consists of eleven samples with different moisture, volatile material, fixed carbon, and ash contents. Chemical analysis is conducted on these samples in order to obtain the amounts of compounds listed above. These values are then compared with minimum and maximum values for Portland cement, fly ash, blast furnace slag, and international standards. Constitutes of the sample with highest compression strength are given below. The experiment shows that lignite ash can be used in concrete production and can replace Portland cement which will in turn reduce costs and environmental damage.

Lignite Code

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O+K2O

SO3

SiO2+Al2O3+ Fe2O3

LA-1

15.2

23.5

18.9

25.6

12.5

2.4

1.9

57.6

Thermosetting plastic waste

Thermosetting plastic cannot be melted due to its firmly bonded molecular chains. Such wastes are currently burned or buried which are costly and cause pollution. Various studies have been conducted on the application of thermosetting plastic wastes to construction materials. Rebeiz (1996) experimented on the effect of polyethyleneterphthalate (PET) plastic waste on concrete strength properties. Choi et al (2006) investigated how PET waste can reduce the weight of concrete by 2-6%. Our analysis is based on the paper written by Phaiboon and Mallika Panyakapo entitled "Reusing Thermosetting Plastic Wastes in Lightweight Concrete."

The study by Phaiboon and Panyakapo used melamine plastic which is made of three main components: alpha cellulose, melamine crystal, formaldehyde. The product has high breaking and temperature resistance, low thermal conductivity, low specific gravity, and is non-toxic. Its properties are given in Appendix 6. Melamine aggregates are coarse with a rough shape and surface texture. The mechanical interlocking of melamine contributed to the compressive strength of the mortar. Panyakapo et al conducted experiments with 6 different mix samples. These have variations in sand, water, fly ash, aluminum powder, and melamine plastic contents. Their results are summarized below (Panyakapo and Panyakapo, 2008):

Melamine plastic reduces concrete density due to its low specific gravity. However, compression strength also drops because of poor bonding between plastic particles and cement paste.

Fly ash can be used to increase compression strength of concrete. High temperature curing is needed.

Aluminum powder further reduces compressive strength due to increased porosity.

Concrete sample with thermosetting plastic admixture meets most ASTM C129-05 Type II standards for non-load bearing lightweight concrete.

Waste glass

Mixing recycled crushed glass in concrete reduces water absorption and drying shrinkage. However, it may trigger alkali silica reaction (ASR) in cementitious materials while reducing concrete strength by 5 and 27% for glass replacement levels of 5 and 30%. Common mineral admixtures that limit ASR are pulverized fuel ash, silica fume, and metakaolin.

Recycled fine aggregates used in concrete have high water absorption characteristics making them unsuitable for high-grade applications. Chi Sing Lam et al concentrated on using waste glass along with recycled fine aggregates to ameliorate the high absorption of recycled aggregates. Their experiments produced the following results(Lam, et al., 2007):

It is not feasible to use recycled crushed glass without ASR suppressants.

Pulverized fuel ash and metakoalin can minimize ASR expansion. However, PFA has high efficiency and lower cost. It is recommended that 10% by weight of total aggregate of PFA should be added to the mixture with RCG.

At 10% PFA content, concrete strength improved as RCG content is increased.

The water absorption of the recycled aggregate concrete decreased with increased RCG content.

Environmentally friendly concrete with 100% recycled material aggregate can be obtained with 50% RCG, 50% RFA, and 10% PFA.

Silicoferrochromium fume

Fume is collected in electrostatic filters in order to prevent environmental pollution during silicoferrochromium manufacturing. In the study conducted by Ay et al, silicoferrochromium fume that contained 85.5% SO2 was added to the mixture in order to assess concrete performance. Six different batches were prepared, each with different fume percentages ranging up to 4.76%.

Unit weight, ultrasound velocity, hardness, and compressive strength for each sample are calculated at 7 and 28 days. These results are presented below.

Specimen Code

Fume (%)

Unit Weight (kg/m3)

Ultrasound Vel (km/s)

Hardness

Compressive strength (MPa)

7 days

28 days

7 days

28 days

7 days

28 days

7 days

28 days

C30-K0

0

2.46

2.48

3.20

3.30

19.0

27

19.24

29.81

C30-K1

1

2.43

2.42

3.25

3.40

19.6

28

21.51

30.37

C30-K2

2

2.44

2.44

3.50

3.55

21.8

31

24.50

39.61

C30-K3

2.82

2.42

2.42

3.15

3.20

20.2

30

22.50

34.52

C30-K4

3.76

2.40

2.40

3.11

3.12

19.8

29

20.75

33.75

C30-K5

4.70

2.48

2.38

3.06

3.02

19.2

29

20.17

32.82

Ay et al concluded the following from their experiments(Ay and Topcu, 1995):

The ultrasound test, conducted to evaluate dynamic modulus of elasticity, shows an increase until a percentage level of 2%, and a decrease thereafter. This result is congruent with the findings for compressive strength of specimens. It should be noted that the sample with 2% replacement has a 33% higher compressive strength than the control sample.

Fume addition caused a decrease in the unit weight of concrete.

The decrease in K3, K4, and K5 sample performances are likely due to the lack of water or super plasticizers for these specimens.

Silicoferrochromium fume admixture performance is similar to silica fume. This by-product can be used to increase compressive strength in an economical manner.

Conclusion

Developed by US Green Building Council, Leadership in Energy and Environmental Design (LEED) rating system has brought many changes to the construction industry. There are five major credit categories in LEED, each related to potential environmental and social impacts of a building: Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Environmental Quality. Energy embedded in concrete, mainly steel and cement, is important while analyzing the Energy and Atmosphere aspects of a sustainable design. Nearly 0.9 tons of CO2 are emitted (12000 million calories) for every 1 tons of cement produced, excluding costs for transportation and installation (Rubenstein).

Admixtures have been widely used for their low cost and improved concrete performance in certain aspects. Bi-product admixtures, replaced with an amount of cement, reduce the total footprint, water consumption and raw materials of concrete. Furthermore, this green cement, which can also incorporate recycled materials, aids the disposal and management of residues from a number of manufacturing processes. Considering that cement production raise currently stands at 2.5% annually, incorporating green cement is of vital importance(Rubenstein).

The effects of various residues on concrete performance are experimented as the industry shifts towards sustainability. This paper analyzed successful researches in terms of admixtures effect on strength, durability, permeability, unit weight, viscosity, shrinkage and ion concentration. Further technical analysis is needed before applying these admixtures to fully understand their behaviors under sustained loads, creep and exposure conditions.

Some of the regional admixtures cannot be employed on a global scale due to lack of such bi-products in other regions, like the lignite ash in Turkey, and high transportation costs. This paper shows that there are numerous regional and global solutions to reduce energy in concrete. With a detailed analysis of benefits and costs, the feasibility of black liquor, waste paint, straw pulp waste and bagasse ash can be examined on a macro level. Adding Portland cement still stands as the easiest and fastest way to achieve desired results, but it is least sustainable. New trend in concrete industry is to use more environmentally friendly and energy efficient methods parallel to sustainability guidelines and regulations.

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