Materials and Mix Proportioning

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CHAPTER 3

MATERIALS AND MIX PROPORTIONING

3.1 Introduction

A comprehensive review of the literature related to the synthesis of non-conventional binder composites for civil engineering applications by geopolymer technology and their performance evaluation was presented in the previous chapter. ‘Literature review’ being prelude to any research, facilitated identifying the areas and scope for further investigations in this field and objectives of present research.

Characterization is a process of determining the distinctive properties/ characteristics of the materials proposed to be used in the study. It is a salient activity undertaken to evaluate the relevant properties of the materials with reference to particular application.

Mix proportioning is the process of determining the right combination of component materials that will produce a concrete mixture with the desired characteristics at the lowest possible cost. Even with ordinary concrete the process is not easy because it involves the art of balancing various conflicting requirements. Extensive laboratory testing must often be carried out before a satisfactory proportion of materials are arrived at. Formulating GPC is a more complex operation than formulating conventional concrete because the number of parameters to be managed is larger. Various studies have been carried out to investigate the basic properties of different materials used in this investigation.

The processing operations can be arranged in the following series of steps.

  1. first, it is necessary to choose the constituents, making use of available local materials.
  2. One must then decide in what proportions the constituents of the concrete have chance of satisfying the specification.
  3. The granular skeleton must be optimized by empirical or theoretical methods.
  4. The binder(s) - admixture(s) system must be investigated.
  5. Finally, it is necessary to test the rheological behavior of the geopolymer concrete, then its mechanical characteristics and durability aspects.

3.2 Materials

The materials used for making fly ash-based geopolymer concrete specimens are low-calcium dry fly ash (class F), ground granulated blast furnace slag as the source material, aggregates, alkaline liquids (combination of sodium hydroxide and sodium silicate solutions), water and superplasticiser.

3.2.1 Fly ash

Fly ashes are the small particles collected by dedusting systems of coal burning power plants. Fly ash can have different chemical and phase compositions because they are exclusively related to the type and amount of impurities contained in the coal burnt in the power plant. ASTM classifies them as class F and class C fly ashes based on the chemical composition. Class F fly ash is usually produced in power plants burning anthracite or sub-bituminous coal and are characterized by low calcium content. Most fly ashes are pozzolanic materials. The CaO content is less than 10 % in class F fly ash and is about 15 to 35 % in class C fly ash. For the present investigation fly ash used was confirming to ASTM Class F obtained from Raichur Thermal Power Station, Shaktinagar, Karnataka. The physical and chemical properties of the fly ash are given in Table 3.1.

Table 3.1: Physical and Chemical properties of Fly ash

Properties

Experimental values

Values as per

IS:3812-2003 [72]

Physical Properties

Specific gravity

2.00

-

Bulk density, g/cc

1.20

-

Finesses, m2/kg

290

-

Colour

Cream white

Chemical Properties

Oxide composition (% by mass)

Silicon dioxide (SiO2)

58.52

70% min.

Ferric oxide (Fe2O3)

6.20

Aluminium oxide (Al2O3)

22.48

Calcium oxide (CaO)

5.90

-

Magnesium oxide (MgO)

0.81

5% max.

Titanium dioxide (TiO2)

0.27

-

Potassium oxide (K2O)

0.42

-

Sulphur trioxide (SO3)

0.55

-

Alkali oxide (Al2O3)

0.40

1.5% max.

Loss of ignition (LOI)

12% max.

3.2.2 Ground granulated blast furnace slag

GGBS is the byproduct of the manufacture of iron. Molten slag, a secondary product of sintering of the raw materials which when quenched under high pressure water jets, granulates. The granulated slag when ground to very fine powder or less than 45 micron with a (Blaine) specific surface of 400-600 m2/kg is GGBS. It is glassy, non-metallic material comprising mostly silicates and calcium oxide combined with other oxides/ bases. It possesses both cementitious and pozzolanic properties; further it is a latent hydraulic material which can directly react with water, but in the presence of an alkaline activator to initiate hydration. Due to its latent hydraulic properties, GGBS has considered as the most suitable material for cement replacement and for the synthesis of alkali activated cement/ inorganic polymer binder [73].

According to Mehta [74] nearly 70% of ash available is suitable for synthesizing cementitious systems. If the available fly ash and GGBS are utilized fully and effectively, it is possible to meet the projected cement demand without increasing the current installed capacity of cement plants [75]. For the present investigation GGBS was obtained from JSW steel plant, Bellary, Karnataka. The physical and chemical properties of GGBS are given in Table 3.2.

3.2.3 Coarse Aggregate

It is well known that the strength of OPC is dependent almost on the strength of the binder and the interfacial bond between the binder and the aggregate. Therefore the use of stronger aggregates does not improve the strength of the normal concrete significantly. However, in GPC, both the binder strength and the interfacial bond strength may either approach or exceed the strength of the aggregates. When the binder and interfacial bond strength exceeds that of the strength of the aggregates, the use of stronger aggregates can lead to a considerable improvement in the strength of the concrete. Aggregates play a vital role in the properties of both fresh and hardened GPC since aggregates (both fine and coarse) occupy about 75 to 80 percent of the total concrete volume.

For use as coarse aggregate, equi-dimensional particles obtained by crushing a dense limestone or plutonic type igneous rock (such as granite, basalt, syenite, diorite, and diabase), are usually satisfactory. There is some controversy regarding the choice of maximum size of aggregate (MSA). However, available data shows that larger than 25 mm MSA generally impairs the strength and impermeability of concrete. Hence 10 mm to 20 mm MSA may be considered optimum for GPC, which is similar to that of OPC.

Crushed basalt stone chips were used in the present investigation. The maximum size of the aggregate was 20 mm. The sample of aggregate confirms to IS:383-1970 [77]. The physical properties and sieve analyses of three types of aggregates are as given in Table 3.3.

Table 3.2: Physical and Chemical properties of Ground granulated blast furnace slag

Properties

Experimental values

Values as per

IS:12089-1987 [76]

Physical Properties

Specific gravity

2.86

Bulk density, kg/m3

1230

Finesses, m2/kg

400

275 Min.

Soundness

Le-Chatelier expansion (mm)

1.6

10 Max.

Setting time (minutes)

  1. Initial
  2. Final

170

308

Not less than OPC

Compressive strength MPa)

  1. 7 day
  2. 28 day

26.4

42.3

12 Min.

32.5 Min.

Chemical Properties

Oxide composition (% by mass)

Silica (SiO2)

43.4

70 min.

Ferric Oxide (Fe2O3)

1.3

Aluminium Oxide (Al2O3)

12.5

Calcium Oxide (CaO)

40.3

45

Magnesium Oxide (MgO)

1.5

5.5 Max.

Sulphide sulphur

1.93

2 Max.

Phosphorous

0.6

-

Alkali Oxide (Al2O3)

0.15

1.5 max.

Loss of ignition (LOI)

1.80

12 max.

Table 3.3 Properties of coarse aggregates

Physical property

Experimental values

Specific gravity

2.70

Bulk density (kg/m3)

1650

Fineness modulus

5.90

Aggregate crushing value (%)

15.78

Aggregate Impact Value (%)

15.41

Water absorption (%)

0.50

Fineness Modulus

6.8

Source

Crushed granite stone

3.3.4 Fine aggregate

The grading and particle shape of the fine aggregate are significant factors in the production of GPC. The particle shape and texture affect the mixing water requirements and compressive strength. Generally the coarser type of sand is used because the finer one will absorb more water from the concrete and another major reason is that GPC comprises of large quantity of finer particles in the form of fly ash and ground granulated blast furnace slag etc.

Locally available sand quarried from Krishna River was used. The sand used conforms to grading zone II of Table 4 of IS: 383-1970 [77]. The physical properties of fine aggregates used in the investigations are presented in Table 3.4

Table 3.4 Properties of fine aggregates

Physical property

Experimental values

Specific gravity

2.61

Bulk density kg/m3

1670

Fineness modulus

2.60

Silt content

0.6%

Grading Zone

II

Water absorption

1.20%

Source

River bed

3.3.5 Cement

Commercially available ordinary Portland cement of 43 grade (Ultratech cement) conforming to the relevant Indian standard code IS:8112-1989 [78] was used throughout the investigation. The physical and chemical characteristics of cement were determined as per IS: 4031-1988 (part 3 to part 6) [79, 80, 81, 82]are given in the Table 3.5. The

3.3.6 Water

Water used for mixing and curing should be free from deleterious materials as per clause 4.3 of Is:456-2000 [83]. Potable water (pH value between 7 and 7.5) is generally considered satisfactory for mixing and curing of concrete. The clause further requires that the pH value should not be less than 6. Potable tap water available in the laboratory was used in the present study.

3.3.7 Alkaline Liquid

The alkaline liquid used for the experimental investigation is a combination of sodium hydroxide and sodium silicate solution. It is seen that the geopolymers with sodium hydroxide solution exhibit better zeolitic properties than potassium hydroxide activated geopolymers. It has been confirmed that addition of sodium silicate solution to sodium hydroxide enhanced the reaction rate between source material and the alkaline solution. The sodium hydroxide solids (pellet form) and sodium silicate solution were obtained from Amar Chemicals Agency, Bangalore.

Table 3.5: Physical and Chemical properties of cement

Properties

Experimental

values

Values as per

IS: 8112-1989 [78]

Physical Properties

Specific gravity

3.12

3.15

Bulk density, g/cc

1865

Finesses, m2/kg

340

225 Min.

Normal Consistency (%)

30

Setting time (minutes)

  1. Initial
  2. Final

180

255

30 Min.

600 Max.

Soundness

Le-Chatelier expansion (mm)

2

10 Max.

Compressive strength (MPa)

  1. 3 days
  2. 7 days
  1. 28 days

38.40

46.60

60.20

23 Min.

33 Min.

43 Min.

Chemical Properties

0.86

0.66 Min.

1.02 Max.

Al2O3 / Fe2O3

1.17

0.66 Min.

Insoluble Residue (% by mass)

2.32

5.00 Max.

Magnesia (% by mass)

0.93

6.00 Max.

Sulphuric Anhydride (% by mass)

1.83

3.00 Max.

Total loss on Ignition (% by mass)

1.40

4.00 Max.

Total chlorides (% by mass)

0.006

0.10 Max.

3.3.8 Sodium hydroxide

The sodium hydroxides are available in solid state by means of pellets and flakes. It is called as caustic soda, which is hygroscopic and readily absorbs CO2 from the air and should be stored in an air tight container. It is soluble in water and is highly exothermic when dissolved in water. The cost of the sodium hydroxide is mainly varied according to the purity of the substance. The geopolymer concrete is homogeneous material and its main process is to activate sodium silicate, so it is recommended to use sodium hydroxide with marginally lower cost. The physical properties of sodium hydroxide solution are presented in Table 3.6.

Table 3.6 : Properties of sodium hydroxide solution

Appearance

Liquid (gel)

Colour

Light yellow liquid

Molecular weight

185.24

Specific gravity

1.16

Melting point

318 °C

Boiling point

1390 °C

Assay

97% Min

Storage

Air tight container

3.3.9 Sodium silicate

Generally sodium silicate is known as water glass or liquid glass, available in liquid (gel) form. It is used as raw material in detergents, pulp and paper, ceramic industry, passive fire protection, textile, automobiles and manufacture of titanium di oxide. In the present investigation sodium silicate 2.0 (ratio between Na2O to SiO2) is used. The physical properties of sodium silicate solution are presented in Table 3.7.

Table 3.7: Properties of sodium silicate solution

Chemical formula

Na2O.xSiO2

Na2O

15.80%

SiO2

31.58%

Water

52.62%

Appearance

Liquid (gel)

Colour

Light yellow liquid

Molecular weight

185.24

Specific gravity

1.57

3.3.10 chemical admixtures

In order to improve the workability of fresh concrete, high-range water-reducing naphthalene based super plasticiser Conplast SP-430 purchased from Fosroc Chemicals, was added to the mixture. The properties of super plasticizer are presented in Table 3.8.

Naphthalene based superplasticizers are sold as a brown liquid, with the total amount of solid particles generally between 40 and 42%. They are also available in solid form as a brownish powder. Both the liquid and solid form naphthalene superplasticizers are available as sodium or calcium salts, but more often as sodium salt. Naphthalene superplasticizers have higher solids content, so they are most cost effective to obtain a certain degree of workability. These are less expensive. In the present investigations, superplasticizer was mixed with alkaline solution and was then added to the dry materials. The dosage of superplasticizer was adjusted to achieve suitable workability.

Table 3.8: Properties of superplasticizer

Brand

Conplast SP-430 (FOSROC, Mumbai)

Density

1206 kg/m3

Base chemical

SNFC

Specific gravity

1.205

pH

8.03

Appearance

Brown liquid

Solid content

40%

Reference specifications

IS:9103-1999 [84]

3.3.11 Reinforcing Steel

The steel used for the beams in the present work was with Fe-415 confirming to IS:1786-1985 [85]. The rebars were tested in a universal testing machine (UTM) of 1000 kN capacity as shown in Fig. 3.1. The steel bars were cut into 1000 mm length and gripped in the jaws of the machine. To measure axial displacement an extensometer was used. The stress-strain curve, modulus of elasticity and yield stress at 0.2% proof stress were determined.

3.4 Design of concrete mixes

The main objective of a concrete mix design is to select the optimum proportion of the various ingredients of concrete. Such proportion shall yield concrete possessing the required plasticity when green and satisfying the required strength and durability requirements in the hardened state [44]. For the present investigation three types of mixes were designed, they are designated with the specific identification as given in Table 3.9.

. Table 3.9 Nomenclature used for design mix

Type of Mix

Identification

Source Materials used

Geopolymer concrete

GPC1

Fly ash (100%), CA, FA, Alkaline solutions

Geopolymer concrete

GPC2

Fly ash (60%), GGBS (40%), CA, FA, Alkaline solutions

Conventional concrete

OPC

Cement, CA, FA, Water

3.4.1 Design of geopolymer concrete mix

Geopolymer concrete is emerging field in concrete technology, since there are no available standards or codes for practice of GPC mixes, the current mix design method is based on the procedure given by Rangan, B.V [82]. The GPC mix comprising of coarse and fine aggregates was taken as 77% of entire mass. The density of geopolymer concrete is taken similar to that of OPC as 2400 kg/m3 [86]. The details of mix design and its proportions for different grades of GPC, GPC1 with varying molarities and alkaline ratios are presented in Appendix A.

3.4.2 Design of conventional concrete mix

To compare the results of geopolymer concrete it was planned to cast the mixes with different grades of concrete as per IS:10262-2009 [87]. The details of design mix and its proportions are presented in Appendix B.

3.5Summary

In this chapter physical, chemical, mineralogical and morphological characterization was carried out on the materials proposed to be used in the investigation. The results show that the proposed source materials to be used as binder components are suitable for making geopolymer composites. Results of test on different aggregates also indicate their suitability for use in the study. The fly ash corresponds to class F, GGBS and other marginal materials possessing desirable characteristics will be used in conjunction with fine aggregate to derive desirable performance of the ambient and heat cured geopolymer composites. Thus the material characterization is an important phase of the proposed experimental investigation.

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