Instrumentos para identificar las Habilidades científicas

The raw materials used in this project have been the following: general use portland cement, blast furnace slag, class F fly ash from coal combustion, metakaolin and glass powder.

53 General Use portland cement (OPC) is the most classical cement, without additions, usually used in ordinary mortars and concretes. OPC has been chosen in this project for comparative purposes in phase 1, in order to establish a direct relationship between test methods and results.

The OPC used in this project was supplied by the company “CRH”, in the Province of Québec, Canada. The physical properties of the cement are shown in table 3.1 and figure 3.2, as well as the other raw materials used in this project. The density of all materials was measured by means of a Helium pycnometer (chapter 3.6.1), the fineness by means of the Blaine method (chapter 3.6.2) and the granulometry by means of laser diffraction technique (chapter 3.6.3).

Table 3.1 Physical properties of the raw materials

Density (kg/m3₎

Blaine (cm2_/g)

General use portland Cement 3.15 ± 0.00 3820 ± 15 Blast furnace slag 2.97 ± 0.01 6422 ± 56 Class F Fly Ash 2.59 ± 0.00 3723 ± 39

Metakaolin 2.75 ± 0.01 18898 ± 32

Glass Powder 2.57 ± 0.01 5124 ± 97

a) Between b) Above

Figure 3.2 Particle size distribution of the raw materials measured by laser diffraction. a) Between particles sizes, b) Above particles sizes

The chemical composition of the cement was measured by X-ray fluorescence (chapter 3.6.4), and the results are shown in the table 3.2:

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Table 3.2 Chemical composition of the raw materials

SiO2 Al2O3 Fe2O3 CaO Na2O K2O MgO SO3 LOI 1

General use portland Cement 19.5 4.6 2.3 62.5 0.2 0.8 2.0 3.0 5.2 Blast furnace slag 35.1 10.8 0.4 42.0 0.2 0.3 7.9 1.1 1.7 Class F Fly ash 45.9 23.2 16.9 4.5 1.3 1.9 1.0 0.1 4.2

Metakaolin 55.2 41.5 0.4 0.0 0.2 0.1 0.0 0.0 0.5

Glass Powder 71.8 1.4 0.4 12.0 12.3 0.5 1.1 0.1 0.0

1. LOI: Lost on ignition

The mineralogical composition of the cement, obtained by X-ray diffraction (chapter 3.6.5), is shown in the figure 3.3. It can be seen that the cement is composed by crystal phases of alite (A), ferrite (F) and aluminate (C). The Bogue composition of this cement has been found to be: 65.9% C3S, 6.3% C2S,

7.4% C3A and 7.1% C4AF.

Figure 3.3 Mineralogical composition of the General use Portland cement. A: C3S, C: C3A, F: C4AF

3.2.1.2 Blast furnace slag

Blast furnace slag is a by-product from iron production process. It is generated in a blast furnace in which, after the melting process of all the raw materials (iron ore, coke, limestone, dolomite...), molten iron slag product is separated by decantation. Thus, steel with higher density is extracted from the bottom, and the rest (slag), is extracted from the top. In order to get a highly reactive slag, the molten slag is rapidly quenched to get a glassy product that is then dried. Depending on the cooling process, different types of slag products can be obtained. When it is cooled by water, a granular slag is obtained. This slag is then grounded to finally get the ground granulated blast furnace slag.

55 The ground granulated blast furnace slag used in this project was supplied by the company “GRANCEM”, in the state of New Jersey, United States. The physical properties of the slag are shown in table 3.1 and figure 3.2 and the chemical composition is shown in the table 3.2. The slag is mostly composed of CaO (42%) and SiO2 (35.1%), with an important content in Al2O3 (10.2%) and other

minor phases. The mineralogical composition (figure 3.4) shows that the slag is an amorphous material.

Figure 3.4 Mineralogical composition of the blast furnace slag.

3.2.1.3 Class F fly ash

The fly ash used in this project is a residue from the coal combustion of coal-fired power plants. During this process, coal is burned in a boiler at elevated temperatures. The ash that is driven out of the boiler with the flue gases is recovered in filters (electrostatics, bags or cyclones) in order to clean these gases before they reach the chimneys. This ash is then called fly ash. When the ash is suspended in the flue gasses, it is rapidly cooled and solidifies in spherical shape. Fly ashes are mainly glassy but during the cooling process, some minerals are able to crystallize (mullite, magnetite, etc.), doing fly ash a heterogeneous material. Depending on the coal used for the combustion, the composition of the fly ash will vary. Thus, according to ASTM C618, fly ash is divided in two classes depending on its calcium, silicon and aluminum content:

- Class F fly ash: when SiO2 +Al2O3 + Fe2O3 ≥ 70%, SO3 ≤ 5%, moisture content ≤ 3% and the

loss of ignition (LOI) ≤ 6%.

- Class C fly ash: when SiO2 +Al2O3 + Fe2O3 ≥ 50%, SO3 ≤ 5%, moisture content ≤ 3% and the

loss of ignition ≤ 6%.

The class F fly ash used in this project was supplied by the company “CRH”, located in Montreal, Quebec, Canada. The physical properties of the class F fly ash are shown in table 3.1 and figure 3.2

56 and the chemical composition is shown in the table 3.2. The chemical composition shows that effectively the fly ash is of type F and the summation of SiO2 +Al2O3 + Fe2O3 of 85.9% is higher than

70%. Else, SO3 content is quite below 5% (0.1%) and the LOI of 4.2%, below 6%.

The mineralogical composition of the fly ash is shown in the figure 3.5. It can been seen the amorphous characteristic of the fly ash, represented by a broad halo between 15 and 35 degree 2, as well as the typical crystalline products of class F fly ashes, such as mullite (M), magnetite (N) and quartz (Q).

Figure 3.5 Mineralogical composition of the fly ash.

3.2.1.4 Metakaolin

Metakaolin is a product obtained from the calcined kaolin. Kaolin is a hydrated aluminosilicate material (Al2Si2O5(OH)4). It is a layered material, with tetrahedral sheets of SiO4 linked to octahedral sheets of

AlO6 through the oxygen atoms. When it is heated between a wide ranges of temperatures (normally

550-850ºC) kaolin dehydroxilates to get metakaolin, a disordered amorphous, highly pozzolanic material.

The metakaolin used in this project was supplied by the company UNICAL. In this case, metakaolin was obtained by calcination of kaolin at 700ºC. The physical properties of the metakaolin are shown in

table 3.1 and figure 3.2 and the chemical composition is shown in the table 3.2. It can be seen that it

is composed mainly by silica (55.2%) and alumina (41.5%). It is a very fine material, with a Blaine of 18898 cm2_{/g. The mineralogical composition (figure 3.6) shows that it’s an amorphous material with}

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Figure 3.6 Mineralogical composition of the Metakaolin.

3.2.1.5 Glass Powder

Glass powder is an amorphous silica-rich material obtained by grinding the mixed colored glass waste of the sorting plants. The mixed colored glass waste, due to the difficulties of revalorizing it to produce new glass, is ground to obtain a glass powder. This glass powder, due to its composition (silica-rich material), possesses pozzolanic properties and thus can be used as a SCMs.

The glass powder used in this project was supplied by one of the sorting plants of the company “Tricentris”, located in the Province of Quebec, Canada. The physical properties of the glass powder are shown in table 3.1 and figure 3.2 and the chemical composition is shown in the table 3.2. It can be seen that this material possesses a high fineness (higher than OPC and FA). The mineralogical composition of the glass powder (figure 3.7) shows an amorphous material without presence of crystalline phases.