CONTENTS No.
Content
Page
Introduction Chapter (1) Cement manufacture and blended cement 1.1 Ordinary Portland Cement composition, types and manufacturing manufacturing 1.2 Blended cement
2 3 4
Chapter (2) 2.1 2.2 2.3
Characterization of pozzolana Definition Types and their composition Difference between pozzolanic cement and pozzolana cement
8 9 9 19
Chapter (3) 3.1 3.2 3.3 Chapter (4) 4.1 4.2 4.3 Chapter (5) 5.1 5.2
Lime and pozzolana mixtures Pozzolanic reactions Thermal treatment of pozzolana Reaction products Properties of pozzolana mixtures Microstructure and porosity of pozzolana cement Properties of pozzolana containing mortars Effect of pozzolana on durability Experimental Results Determination of free lime procedures Results and discussion List of tables List of figures References
20 21 23 24 27 28 34 37 49 50 51 53 45 55
1
6
Introduction
Pozzolana is one of the mineral admixtures blended with the Portland cement clinker in an attempt to improve mechanical and physical properties for produced concrete. Pozzolana also reduces cost of cement manufacture where it replaces a part of clinker which production cost is high. Most importantly the role of pozzolana in improving durability of concrete has provoked an increase in use of pozzolanic materials in cement manufacture. This research will include a simple characterization of pozzolana and a study of its effect on properties of cement.
2
Cement Manufacture and Blended Cement
Ch. (1): Introduction 3
1-1. Ordinary Portland Cement Portland cement is a hydraulic binding material most used in building and structures. 1-Composition: It is composed of clinker which is a ground burnt mixture of raw materials, limestone and clay, and other additives that are used to improve quality and properties of clinker such as gypsum which control setting time of cement, mineral admixtures are added up till 15% of the total amount. A] Chemical composition Lime stone is composed of two oxides, CaO and CO2 , while clay is composed of SiO2, Al2O3 and Fe2O3; CO2 is removed by burning and the remaining four oxides are the main constituents of clinker in the following percentages: CaO 62-68% SiO2 21-24% Al2O3 4-8% Fe2O3 2-5% There are also other minor oxides that can affect quality of the clinker such as; MgO when it exist in percentage above above 5% it is burned burned at 1500°c and slakes very slowly causing cracks in hardened concrete. Alkali oxides like Na2O or K 2O in percentage above 1% cause failure in concrete. These oxides are not free in clinker, they exist in form of combined materials, and the main four compounds are: 3CaO.SiO2 (alite) 45-65% 2CaO.SiO2 (belite) 15-35% 3CaO.Al2O3 (celite) 4-14% 4CaO.Al2O3.Fe2O3 (celite) 10-18% Free CaO are not supposed to exist in clinker because it has the same effect of MgO but in wider range. B] Mineral composition Knowing the minerals in clinker allow us to pre determine its physical and mechanical properties. Minerals in clinker are subdivided into High alite C3S >60% Low alite C3S >50-60% Belite C2S >35% Aluminate C3A >12% Aluminoferrate C4AF >18% Varieties of OPC have altered percentages of each mineral according to the cement type. 2- Types of OPC: 4
Different types of Portland cement are manufactured to meet different physical and chemical requirements for specific purposes, such as durability and high-early strength. Eight types of cement are covered in ASTM C 150. More than 92% of Portland cement produced is Type I and II (or Type I/II); Type III accounts for about 3.5% of cement production. Type IV cements is only available on special request, and Type V may also be difficult to obtain (less than 0.5% of production). Although IA, IIA, and IIIA (air-entraining cements) are available as options, concrete producers prefer to use an air-entraining admixture during concrete manufacture, where they can get better control in obtaining the desired air content. However, this kind of cements can be useful under conditions in which quality control is poor, particularly when no means of measuring the air content of fresh fresh concrete is available. available. If a given type type of cement is not available, comparable results can frequently be obtained by using modifications of available types. High-early strength concrete, for example, can be made by using a higher content of Type I when Type III cement is not available, or by using admixtures such as chemical accelerators or high-range water reducers (HRWR). The common types of OPC are listed in the table bellow. Table (1-1) Cement Use type General purpose cement, when there are no I1 extenuating conditions Aids in providing moderate resistance to sulfate II2 attack III When high-early strength is required When a low heat of hydration is desired (in massive IV3 structures) V4 When high sulfate resistance is required A type I cement containing an integral air-entraining air-entraining IA4 agent A type II cement containing an integral air-entraining IIA4 agent A type III cement containing an integral airIIIA4 entraining 3- Manufacturing: Manufacturing: •Raw materials must contain 75-78% CaCO3 and 22-25% of clayed materials, since there are no natural rocks with that composition, a mixture of limestone and clay is used in addition to the correcting admixtures to 5
compensate for oxides not exist in raw materials. For example insufficient in SiO2 calls for introduction of high silica materials such as (opoka or diatomite) •Also there is wide use in cement industry for waste and by-products of other industries such as blast furnace, slag or nepheline slime. •The fuel used is pulverized coal, fuel oil and natural gas. Steps of manufacturing flow sheet: •Quarrying lime stone and clay •Preparing raw materials and blending them •Burning mixture •Grinding with gypsum to fine powder with addition Techniques of manufacturing: •Dry method: raw materials are mixed, ground and burned dry with out water •Wet method: raw materials are mixed with water then ground and burned. •Combined method: to acquire advantages of both methods, raw materials are mixed with water, ground then dewatered before drying as granules.
1-2. Blended Portland Cements Blended cement is a mixture of Portland cement and blast furnace slag (BFS) or a mixture of Portland cement and a pozzolana. The use of blended cements in concrete reduces mixing water and bleeding, improves finish ability and workability, enhances sulfate resistance, inhibits the alkali-aggregate reaction, and lessens heat evolution during hydration, thus moderating the chances for thermal cracking on cooling. Blended cement types and blended ratios are presented in table bellow. Table (1-2) Type IP I(PM) P IS I(SM) S
Blended Ingredients 15-40% by weight of pozzolana (fly ash) 0-15% by weight of Pozzolana (fly ash) (modified) 15-40% by weight of pozzolana (fly ash) 25-70% by weight of blast furnace slag 0-25% by weight of blast furnace slag (modified) 70-100% by weight of blast furnace slag
The advantages to using mineral admixtures admixtures added at the batch plant: Mineral admixture replacement levels can be modified on a day-today and job-to-job basis to suit project specifications and needs.
•
6
Cost can be decreased substantially while performance is increased (taking into consideration the fact that the price of blended cement is at least 10% higher than that of Type I/II cement [U.S. Dept. Int. 1989]). GGBFS can be ground to its optimum fineness. Concrete producers can provide specialty concretes in the concrete product markets. •
•
•
Precautions must be considered when mineral admixtures are added at the batch plant: Separate silos are required to store the different hydraulic materials (cements, pozzolanas, and slags). This might slightly increase the initial capital cost of the plant. There is a need to monitor variability in the properties of the cementitious materials, often enough to enable operators to adjust mixtures or obtain alternate materials if problems arise. Possibilities of cross-contamination or batching errors are increased as the number of materials that must be stocked and controlled is increased. •
•
•
7
Characterization of Pozzolana
Ch. (2): Characterization of Pozzolana 2-1. Definition 8
The term Pozzolana has two meanings; the first is that pyroclastic rocks mainly glassy or zeolitised which occur near Pozzuoli (ancient Puteoli, Italy) or near Rome. The second meaning is those artificial or natural materials that harden when mixed with water in presence of lime or any material that release calcium hydroxide (Portland cement). The interest here will be of the latter definition since it is more general. For along time the interest in Pozzolana was restricted to Italy where natural Pozzolana was found. In other countries that interest is rather recent, arises from the need to reuse waste materials such as fly ash and silica fume. Many studies have confirmed that pozzolanic cement yield concrete showing a high ultimate strength and great resistance to aggressive attacks. Establishing a classification for pozzolanic materials has proven difficult since that name include materials of different composition and mineralogical and geological origin. The more common classification is of the origin of Pozzolana, a subdivision to natural and artificial pozzolanas. This division is not very well defined since there are materials that originally pozzolanic but contain other components which takes on clear pozzolanic action only by firing.
Types & Their Composition .2-2 Volcanic origin Sedimentary Mixed ------------origin origin Incoherent Tuffs Fly ash Burned clays Micro Other Artificial silica materials (Class (F (Class (C and shale (Table (2-1 Natural pozzolana origin : (a) Volcanic origin: Pyroclastic rocks result from explosive volcanic eruptions. Rapid pressure decrease during eruption causes the gases dissolved in liquid magma to be released forming microscopic bubbles in particles, forming a micro porous structure. At the same time particles are subjected to quenching process responsible for the glassy state. The material can be deposited on ground or in water, ground deposits are loose and heterogeneous, they are composed of ashes mixed with ducts fragments. Non explosive eruptions produce weak quenching which is not sufficient to prevent crystallization which give no or little pozzolanic effect. Natural
9
1- Incoherent materials; glassy volcanic pozzolanas. Most common example is Italian pozzolana form Campania. The following table shows the chemical composition of some incoherent volcanic pozzolana by percentage. Pozzolana
SiO2
Al2O3 Fe2O3 CaO
MgO Na2O
K 2O TiO2
SO3
Bacoli
53.08
17.89
4.29
9.05
1.23
3.08
7.61 0.31
0.65 3.05
Barlie
44.07
19.18
9.81
12.25
6.66
1.64
1.12 0.79
.Tr
4.42
Salone
46.84
18.44
10.25
8.52
4.75
1.02
6.35 0.06
.Tr
3.82
Vizzini
50.48
16.44
11.59
4.86
5.24
0.87
0.17 0.08
0.15 9.68
Volvic
54.3
14.5
4.47
2.6
65.1
19.53
5.5
3
1.1
58.91
15.89
2.85
2.48
1.33
65.74
14.56
2.54
3.35
69.34
14.56
1.02
2.61
71.77
11.46
1.14
1.1
Santorin earth Rhine tuffash Rhyolite Pumicite Furue shirasu Higashi Matsuyama
LOI
3.5 6.12
4.53
2.21
4.97
1.92
3.43
1.33
3
2.39 0.25
1.85
0.54
1.53
2.55 0.14
6.5
(Table (2-2 LOI: loss on ignition The mineralogical composition of some in coherent volcanic pozzolanas is .shown below in the table Pozzolana Country Active Phase Inert Phase Bacoli Italy Glass ,Quartz, feldspar, augite Partially decomposed Pyroxene, olivine, mica, Barlie Italy glass analcime Leucite, Pyroxene, alkali Salone Italy Glass, analcime feldspare, mica Feldspare, quartz, olivine, Vizzini Italy Glass clay Volvic France Glass Andesine, quartz, diopside Quartz, anorthite, Santorin earth Greece Glass labradorite Quartz(9%), Rhine trass Germany (Glass (55-60% (feldspar(15% (Glass (62-67% Quartz(19%), Bavaria trass Germany (Chabasite(3% (feldspar(15% (Analcime(5% 10
Rhyolite Pumicite
USA
(Glass (80%
Furue shirasu
Japan
(Glass (95%
Higashi Matsuyama
Japan
(Glass (97%
Clay(5%), calcite, quartz, feldspar Quartz(1%), (anoethite(3% Quartz(1%), (anoethite(1%
(Table (2-3 (2) Compact materials (tuffs); the deposits of volcanic pozzolana could contain compact layers as a result of weathering, which can cause zeolitisation or agrillation. Zeolitisation increase pozzolanic activity and agrillation cause decrease in it. Chemical composition of some tuffs is shown in the following table. Pozzolana
SiO2
Al2O3
Fe2O3
CaO
MgO Na2O
Bacoli
52.12
18.29
5.81
4.94
1.2
1.48
5.06
11.1
Barlie
62.45
16.47
4.41
3.39
0.94
1.91
2.06
7.41
Salone
55.69
15.18
6.43
2.83
1.01
0.26
16.33
Vizzini
73.01
12.28
2.71
2.76
0.41
0.1
6.34
Volvic Santorin earth Rhine tuffash Rhyolite Pumicite Furue shirasu Higashi Matsuyama
54.68
17.7
3.82
3.66
0.95
67.7
11.32
2.66
3.73
1.64
40.9
12
14
14.6
1.45
71.63
10.03
4.01
1.93
1.22
71.65
11.77
0.81
0.88
0.52
1.8
3.44 0.34
9.04
71.11
11.79
2.57
2.07
0.15
1.66
1.66 0.27
9.5
3.43
K 2O
SO3
6.38
LOI
9.11 0.18
7.27 12.06
2.35
3.05
(Table (2-4 In some deposits transformation of pozzolana and incoherent glassy layers into compact tuffs is evident. Pozzolana in common is separated from tuffs with an intermediate layer. The composition of those three layers is shown in the following table. Pozzolana Intermediate layer Yellow tuffs SiO2 56.04 54.3 51.36 TiO2 0.42 0.42 0.42 ZrO2 0.03 0.05 0.03 Al2O3 17.79 17.4 16.84 Fe2O3 2.07 2.65 3.9 11
FeO MnO MgO CaO BaO K 2O Na2O Cl2 SO3 P2O5 CO2 H2O + H2O Total
2.8 0.12 1.19 3.47 0.06 7.43 4.17 0.05 0.05 0.1
2.12 0.15 0.92 3.61 0.08 6.93 3 0.06 0.05 0.08
0.6 3.79 100.18
0.84 0.14 0.99 3.47 0.05 6.57 2.57 0.09 0.04 0.13 0.44 4.96 7.55 100.39
2.65 5.7 100.17 (Table(2-5 The relation between loose pozzolana layer and layer of tuffs is proved by reproducing the (pozzolana yellow tuffs) transition. Bucoli pozzolana underwent hydrothermal treatment resulting in a material similar to yellow tuffs. Chemical composition does not change but the original component was transformed into zeolitic materials confirming the large capacity of pozzolana for zeolitisation. Rate of transformation and type of mineral resulting depend on autoclaving conditions and chemical activator used. The table shows the mineral composition of transformed transformed materials. (%)Contents Tokay Heulandite Mineral Zaloska tuffs Gorenje tuffs mountain form tuffs theigarhorn Clinoptilolite 62±3 68±3 Heulandite 18±1 11±1 100 Analcime 45±2 α-Quartz 19±1 28±2 15±1 Cristobalite 5±1 Montmorillonite Traces Illite Traces Andesine 24±1 Chlorite Traces (Table (2-6 →
origin : (b) Sedimentary origin: 12
Clays and diatomaceous earths are sedimentary rocks capable of combining with lime. Clays originate from alternation of igneous rocks. Diatoms originate from siliceous skeletons of microorganisms deposited in water. Both clays and diatoms occur mixed together. Clay minerals alone can react with lime but can not be used as pozzolana due to increased water demand and lowering of strength. Diatomaceous earths, also called moler, consist of mixture of montmorillonite montmorillonite and amorphous opal, used either as it is or calcined to improve pozzolanic properties. Chemical composition of some diatoms is shown in table: Pozzolana
SiO2
Al2O3
Fe2O3
CaO
MgO Na2O
K 2O SO3
Moler
75.6
8.62
6.72
1.1
1.34
0.43
1.42 1.38 2.15
Diatomite
85.97
2.3
1.84
.Tr
0.61
0.21
0.21
Diatomite
60.04
6.3
5.8
1.92
2.29
LOI 8.29 11.93
(Table (2-7 :c) Mixed origin ) In north Rome there are some deposits composed of materials of different origin. Chemical composition of some of those materials is presented in the table below: Pozzolana
SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO Na2O
K 2O
SO3
Sacrofano White eartha White earth b Whit earth-c White earthd Beppu white clay Gaize
85.5
3.02
0.44
1.22
0.58
0.16
0.26
0.77 7.94
90
2.7
0.7
0.2
6.1
84.25
4.5
1.55
2.4
8.4
78.4
12.2
1.5
1.55
8.6
56.8
21.4
1.7
2.35
7.5
87.75
2.44
0.41
79.55
7.1
3.2
1.1
0.19
0.23
2.4
1.04
0.11
LOI
0.11 0.86
5.9
(Table (2-8 The presence of diatoms with fragments of volcanic rocks shows that these deposits originate from deposition of materials of different origin in stagnant water followed by acid attack.
Artificial pozzolana :a)Fly ash ) 13
It consists of finely divided ashes produced by burning of pulverized coal in power plants. Owing to high temperature reached in burning, most minerals of coal are melted to small drops, sudden cooling transforms them into spherical glass particles. Chemical composition of bituminous fly ash(class F), low lime, is shown in table below: Country
SiO2
Al2O3
Fe2O3
CaO
MgO Na2O
K 2O
SO3
C
France
51.68
27.01
6.25
1.72
1.88
0.54
4.49
4.7
France
48.1
24.68
6.5
1.41
1.82
0.56
4.06
11.7
Belgium
55.74
24.41
6.02
2.47
2.22
Taiwan
48.75
23.21
4.15
3.93
1
0.24
1.1
10.39
UK
50.09
28.1
11.7
1.62
1.54
0.28
0.62
1.27
Poland
50.8
23.9
8.6
3.6
2.8
0.8
2.9
0.8
2.9
Denmark
53.98
22.27
11.6
3.95
1.97
2.71
.Eq
0.73
2.13
Netherlands
50.46
25.74
6.53
4.32
2.24
2.04
4.43
Canada
47
17.7
25.3
2.1
1
0.7
2.3
0.3
2.4
Japan
57.5
26.1
4
5.1
1.3
1.5
1.35
0.4
1.6
UK
48
38.2
4.5
3.3
1.5
0.3
1.7
0.37
2.3
Japan
53.53
23.55
6.23
5.85
1.6
2.2
1.75
USA
52.24
19.01
15.71
4.48
0.89
0.82
2.05
1.34
0.92
Canada
43.8
22.1
16.2
3.5
0.8
4.4
.Eq
1.1
5
Germany
51.2
29.6
6.8
3.4
1.2
0.6
3.1
0.5
3.3
1.04
LOI
2.74
3.95
2.14
3.44
(Table (2-9 Class F fly ash has few mineral phases, beside the prevailing vitreous ground mass, only four compounds are present: quartz, mullite, hematite and magnetite. The mineral composition of this class is presented in the following table: Flay ash source Dunston
Quartz
Mullite Hematite
Magnetite
Carbon
Glass
4.5
11
2.7
1.4
3.1
77
Ferrybridge
2.8
6.5
1.6
1.9
1.5
86
Hams hall
3.5
10
2.1
1.2
0.6
83
Rye house Skeleton Grange Northeast P26 Northeast
8.5
14
2.4
2.5
2.4
71
4.1
10
9
2.6
2.1
79
7
28
7
7
4
45
2
9
7
3
70
14
Anhydrite
P27 EFA
1.8
2.1
0.7
95.4
LM
5.1
22.8
0.5
71.6
Lubbenan
17.1
10.4
2.7
75.8
11.4
Eophenhain Swarze Pumpe Vackarode
1.4
1.9
3.8
74.3
12.9
2
5.7
1
74.3
16.9
2
6.2
2.2
80.2
9.4
Hagenwerder
0.3
5.1
6.1
85.1
3.3
Hershfeld
1.8
3.8
5.1
93.6
0.7
(Table (2-10 The microprobe analysis of types of class F fly ash show chemical [(heterogeneity of particles. This is shown shown in the following following table; [Table(2-11 No .
SiO2
Al2O3
Fe2O3
CaO
1
58
36.1
3
2
2
53.1
33.1
6.3
3
51.1
42.9
5.1
4
43.5
24.2
9.6
18.4
5
42.5
30.2
12.9
7
6
42.1
29.3
17.9
4.6
7
42.1
24.2
26.8
8
42
29.5
20.8
Ash particles classification is shown in the following table: Type shape colour texture Size a- glassy, clear, solid b-glassy with 0-20 Spherical bubbles 1 Colorless & round c-glassy with trace crystalline d-most 10-50 crystalline, solid Spherical Light brown Light color are 2 5-30 & round to black glassy, all solid 3
Rounded
White
4
Irregular Light brown
Glassy, spongy
10200
Partially crystalline, solid
10100
15
comments
Deep color indicate iron Bubbles give foam or cenospheres Irregularity very marked
Agglomerated particles contain red areas Partially burnt coal contain some minerals
5
Irregular
Varicolored
Partially crystalline, solid
50500
6
Irregular
Black
Solid or porous
20200
7
Angular
Colorless
crystalline, solid
10100
May be quartz
8
Angular
Red
crystalline, solid
5-50
May be hematite
(Table (2-12 There is another type of fly ash, Class (C) which has high lime content, this is resultant from sub bituminous coal and lignite combustion. The chemical composition of this class is shown in the table below:
Country
SiO2
Al2O3 Fe2O3
CaO
MgO Na2O
Saudi Arabia
52.3
25.2
4.6
10
2.2
Poland
44.4
16.4
6
22.1
1
0.1
Canada
38.67
18.56
5.89
22.96
4.99
Spain
49.8
17.3
8.7
24.9
Greece
26
10.6
6.59
USA
51.3
20.9
USA
44.6
USA
K 2O
Free lime
SO3
LOI
0.6
0.4
0.5
4.6
3.9
1.74
0.41
1.87 6.26
1.9
0.3
1.7
4.3
42.1
1.84
0.17
0.8
5.57 4.55
6
7.98
1.05
b
15.5
7.7
20.9
32.8
22.9
5.1
27.4
4.82
Turkey
27.4
12.8
5.5
47
2.5
0.2
0.2
6.2
2.4
18.6
Turkey
40.6
9.1
7.7
19.9
8.1
0.9
0.7
10.6
1.4
5.5
Turkey
39.9
22.3
4.4
25.4
1.9
0.1
0.4
4.8
0.4
9.8
Italy
55.42
23.41
7.71
3.16a
3.82
0.9
2.87
0.18 1.06
Canada
47.9
21.9
4.91
13.3
2.92
6.05
0.96
1.16 0.14
0.25
0.89 b b
1.56
2.3
11.4 10
0.52 0.17 1.5
0.05
2.21 0.53
(Table (2-13 a: Low-lime lignite b: Na2O equivalent Unlike class F, class C has many mineralogical mineralogical phases due to variable chemical composition. By XRD analysis we can identify: quartz, lime, periclase, anhydrite, ferrite, spinel, merwinite, alkali sulfate, melilite, sodalite and hematite. 16
The mineralogical composition of this class is presented in the following table: Mineral HL1 HL2 HL3 Quartz 4.5 5.6 5.1 Lime 18.6 5.5 9.8 Anhydrite 12.2 9.3 7.4 Plagioclase 28~ 15~ 20~ Hematite 4 6 2 Magnetite 0.8 2.5 0.6 Mullite 1 1.2 4.3 Amorphous and 30~ 50~ 50~ glass (Table (2-14 The difference between class F and class C fly ash concerns the chemical and mineral composition and the structure of the glass. These differences are highlighted by the change in X-ray diffraction background induced by the glass. The relation between content of CaO and the position of maximum of X-ray in background is shown in the figure:
Figure (2-1) (b) Burned clay and shale: Clay gains a pozzolanic activity when burned at temperature between 600900°c. Theses artificial pozzolanas are composed mostly of silica and alumina. The loss of combined water at burning cause the crystalline structure to be destroyed, silica and alumina become in a messy and unstable amorphous state. Heating does not affect on anhydrous minerals, so the pozzolanic activity depends on the clay minerals and the thermal treatment conditions. The chemical composition varies according to the origin. Silica content can vary between 22-42%, and lime can vary between 22-55%. 17
Burned shales have more complicated mineral composition than burned clays depending on the chemical composition and temperature and duration of burning. For example a burned shale at 750-840°c contain minerals already exist in shale like: β-quartz, α-cristobalite, α-cristobalite, calcite, α-ferric oxide and muscovite; and other minerals formed by burning like: gehlenite, anorthite, wollastonite, orthoclase, anhydrite, β-C2S, CA and CaO. (c) Micro silica or silica fumes: The manufacturing process of silicon metal and ferrosilicon ferrosilicon alloy in electrical arc at temperature up to 2000°c generate fumes containing spherical micro particles of amorphous silicon dioxide due to the reduction of quartz to silicon. The gaseous silicon dioxide is transported by combustion gases to lower temperature zones where it is condensed to tiny particles. The main properties of micro silica are the high silica content, high specific surface area and amorphous structure. The chemical composition of the micro silica is shown in the table below: Si metal manufacture FeSi 75% SiO2 97-98 86-90 C 0.2-1.3 0.8-2.3 Fe2O3 0.02-0.15 0.3-1 Al2O3 0.1-0.4 0.2-0.6 CaO 0.08-0.3 0.2-0.6 MgO 0.3-0.9 1-3.5 Na2O 0.1-0.4 0.8-1.8 K 2O 0.2-0.7 1.5-3.5 S 0.1-0.3 0.2-0.4 LOI 0.8-1.5 2-4 (Table (2-15 Micro silica particles are spherical and have average diameter of 0.1μm. The specific surface area ranges from 15 to 25 m2/g. It may contain traces of quartz, low-lime silica fume shows a high degree of condensation of silicate ions since it is formed by polymeric species.
2-3. Difference between pozzolanic cement and pozzolana po zzolana cement When pozzolana is mixed with Portland cement and water, it reacts with calcium hydroxide formed during hydration of calcium silicates. As a result the final portlandite content in hydration products is always lower than it is in 18
Portland cement alone. The simultaneous existence of cement and pozzolana modifies the hydration products. Pozzolanic cements are mixes of pozzolana and cement that if dispersed in excess water under certain conditions give rise to unsaturated calcium hydroxide solution. Pozzolana cement do not comply with this requirements, as their pozzolana content is insufficient to combine all portlandite formed during hydration of calcium silicates to give unsaturated lime solution. Hardened pozzolanic cement lack for free lime, while pozzolana cement does not. Portlandite content depends on the activity of pozzolana, amount of lime released and pozzolana/cement ratio. Pozzolana can be added at the plant or at the building site. In the first case, pozzolana undergoes either grinding with clinker and gypsum or separate grinding followed by mixing and homogenization. homogenization. In the latter case, pozzolana is introduced into concrete mixer along with Portland cement. This procedure improves quality in term of strength and stability, but it causes certain decline in properties of concrete when pozzolana is added as partial replacement for Portland cement. Yet, this procedure is not recommended for the following reasons: •degree of homogenization reached is lower •replacing large part of Portland cement with pozzolana reduces early strength •building yards rarely have personnel, equipment and time required for checking properties of pozzolana and mixes.
19
Lime and Pozzolana Mixtures
Ch (3): Lime and Pozzolana mixtures 3-1. Pozzolanic reactions Pozzolanic activity covers all reactions occurring between active constituents of pozzolana, lime and water. There is great difficulty in evaluating pozzolana's active phases so, the progress of reaction is followed in term of 20
diminution in free lime in system or the increase in silica+ alumina soluble in acid using the Florentin attack method. The activity of pozzolana includes two parameters, the maximum amount of lime that pozzolana can combine and the rate at which this combination occur. The heterogeneity of pozzolana and the complexity of hydration phenomena do not allow a model of pozzolanic activity only enables a general trend identified.
Figure (3-1) From the figure above, when water is in excess, amount of combined lime vary according to type of pozzolana. After 180 days pozzolanas have combined 45-75% of lime. In pastes, lime combination is lower than it is in hardened mass. The factors affecting amount of combined lime: 1- Different pozzolanas have different capabilities to combine lime, as shown in the table below; Mineral component Rhenish trass Quartz Feldspar Leucite Analcime Kaolin Glass phase
Free alkali
Average amount in trass
Calculated lime reaction
0.4
13
5.5
0.2 1.8 3 2.1 24
15 6 7 2 55
17.5 5.4 13.3 0.7 200
Lime reaction
Na2O
K 2O
43
1.5
117 90 190 34 364
1.1 1.3 10.7 0.3 18
21
Total Glass phase Bavarian Obsidian glass
-------
-------
-------
98
242.5
272
6
6
66
179
176
3.7
3.1
-------
-------
Table (3-1) 2- The larger the amount of combined lime, the higher the content in the active phase and the lower the content in the inert phase. 3- The amount of combined lime is related to the SiO2 content in the active phase which ranges between 45-75% in volcanic glass and fly ash but reach 95% in active amorphous micro silica. 4- Within certain limits the amount of combined lime increase as lime/pozzolana ration increase, as shown in figure below;
Figure (3-2) 5- Combined lime also depends on curing time, but the rate varies between types of pozzolana. The following figure illustrates effect of curing time on the combination amount.
22
Figure (3-3) 6- Short term activity depends on the specific surface area (BET) of pozzolana, while long term activity better referred to the chemical and mineralogical composition of pozzolana. 7- The larger the amount of water the higher the rate of combination, thus the pozzolanic reaction is slower in paste. 8- The rate of pozzolanic reaction increase by the increase in temperature, as seen from the following graph;
Figure (33-4)
3-2. Thermal treatment of pozzolanas When heated, pozzolana undergoes chemical and structural transformation that may change, to a positive or negative extend. The resulting effect, an increased or decreased pozzolanic activity, depends on type of pozzolana, temperature and duration of heating. The negative effect induced by temperature explains the apparent contradiction that occurs in some materials. 23
If temperature is raised step by step, combined lime increase then decreases. The following figure shows this effect, it also shows that heating is followed by a decrease in specific area.
Figure (3-5) This means that optimum thermal treatment must be defined for each pozzolana by means of testing. For most pozzolanas the heating is done at 70800°c, higher temperature improve deverification, crystallization and densification and formation of more stable phases. Micro structural changes by calcinations are evident in natural pozzolana due to the variation in refraction index.
3-3. Reaction products Reaction of lime and pozzolana give similar products to those found in hydration of Portland cement since the overall chemical composition of both mixes falls in the same field. For the same reason different types of pozzolana give the same products. The table below shows the difference between hydration products in pastes and in hydration in excess water. Bacoli C-S-H C2ASH8 C4AH13 C3A.CO3.H1
Dehydrate d Kaolin a b + + + + -
Sengi
Neapolitan yellow tuffs a b + + + + + -
Rhine trass a b + + + + + +
a + + -
b + + -
a + + -
b + + -
-
+
+
+
-
-
-
+
-
-
-
-
+
-
-
-
-
-
-
-
2
C3AS3 C3AH6
a: reaction time in water=90 days b: w/s ratio=0.4 ; pastes cured for 5 years Table (3-2)
24
Excess water accelerates final stage of reaction. The hydration products formed in pastes are smaller in size and more irregular. By extending reaction time between lime and pozzolana in solution, there are some compounds are recognizable such as hex. Ca-aluminate, ca-silicate hydrate, carboaluminate, gehlenite hydrate and hydrogarnet. The following table shows nature and amount of hydrated compounds; Pozzolana Furue Shirasu
Higashi Matsuyam a Tuff(G)
Kanto (Hachoiõji) Loam(R) Beppu white Clay(V)
Tominaga Masa soil(M)
Takehara Fly ash (T)
Curing temp. 20,40,6 0 20,40,6 0 20
Ag e 7
CC3AH6 C3A.CaCO3.H12 C2ASH8 S-H C3AS2H2 C4AH13 +
20
180
40
7
40
180
60
7
60
180
20 20 40 40 60 60 20,40,6 0 20,40,6 0 20 20 40
7 180 7 180 7 180
++ + ++ + (+) ++ + + ++ + (+) (+) (+) (+) +
7
+
180 7
-
+
-
(+)
+++
(+)
-
(+)
-
-
+
-
-
(+)
-
-
(+)
-
-
-
-
-
-
-
(+) +++ +++++ ++++
+++ +++ + (+) (+) -
+ +++ (+) (+) -
-
-
-
-
-
-
7 180 7
++ + -
(+) (+)
+++ ++ +
-
40
180
-
++
+
-
60 60 20,40,6 0 20,40,6 0
7 180
(+)
+ +++
+ (+)
-
7
+
-
-
-
180
++
-
+
(+)
180
Table (3-3) When gypsum occurs in the paste, ettringite can be formed, formation of ettringite causes paste to crumple. 25
The C/S ratio in C-S-H is variable and depends on the type of pozzolana, time and temperature of curing, the lime/pozzolana ratio and analytical method used. The variability of C/S ratio is attributed to non-staichiometry of C-S-H, depending on chemical composition of the pore solution. The progress of pozzolanic reaction is marked by changes in distribution of silicate ions in the reaction products. SO4- in low lime fly ash dissolves in lime and water and cause ettringite and gypsum to precipitate. The rate of ettringite formation depends on rate of alumina dissolution. If ash is washed with water the sulfate occur in soluble form and both ettringite and gypsum gypsum are not formed. formed. Low lime fly ash mixed with water water and lime form C-S-H, C 4AH13 and C2SAH8 and some times ettringite. High lime fly ash which contain high amount of free lime when mixed with water transform to Ca(OH)2so it doesn't need any lime addition, so they corresponds to artificial hydraulic limes. High lime fly ash may contain C2S, in this case hardening occur due to pozzolanic reaction and hydration of hydraulic components. In any case C-S-H, C4AH13, carboaluminate, gehlenite hydrate and ettringite are formed. If lime combine with Al 2O3 and SiO2 there will be no pozzolanic action. The reaction of silica fumes fumes and Ca(OH)2 is very rabid and causes a phase to precipitate on silicon peroxide, this layer is unstable and turns to C-S-H rabidly. In pastes, owing to high reactivity of silica fume, free lime disappear generally generally between7 and 28 days. In all hydrations hydrations the product C-S-H is more crystalline than that found in Portland cement.
26
Properties of Pozzolana and Cement Mixture
Ch (4): Properties of pozzolana mixtures 4-1. Microstructure and porosity of pozzolana cement Porosity of pozzolana-containing pozzolana-containing pastes; 27
It is an intrinsic property of cement which can be limited but not eliminated. It influences the strength and permeability of paste, mortars and concretes. All aspects of strength are related to total porosity where permeability depends on structure and size distribution of the pores. Porosity depends on : 1- decr decrea ease se by decr decrea ease se in wate waterr ratio atio 2- decr decrea ease se by incr ncreasi easing ng cur curing perio eriod d 3incr increa ease se by incr increa easi sing ng curi curing ng temp temper erat atur uree 4- dif differs ers acc acco ordin rding g to type type of cem cement ent Correct determination of porosity and pore size distribution is a difficult target. Difficulties come from structure alternation that method of sample preparation and determination induces. Determination Determination involves preliminary removal of water from pores of the paste and filling the same pores with a suitable fluid. Water removal obtained by: 1Oven drying 2D-dr D-dryi ying ng(( und under er vacu vacuum um over over a dry dry ice ice tra trap) p) 3P-dr P-dryi ying ng(( und under er vac vacuu uum m ove overr mag magne nesi sium um per per chl chlor orat atee hydr hydrat ate) e) 4Sublimation 5Solvent re replacement Methods of porosity determination are: 1- mercu ercurry intr intrus usiion unde underr pres pressu surre 2- hel helium disp displlace acement ent at at low low press ressu ure 3- metha ethano noll di displ splacem acemen entt at at low low pres pressu surre 4water intrusion 5nitrogen so sorption The relevant distribution curve allows calculation of: 1- Thre Thresh shol old d diame diamete terr (TD): (TD): por poree diam diamet eter er at whi which ch cont contin inuo uous us mercury intrusion begins 2- Maxi Maximu mum m conti continu nuou ouss diame diamete terr (MCD (MCD): ): max maxim imum um pore pore dia diame mete ter r corresponding to the main pore frequency 3- Main Main peak peak intens intensity ity (PI): (PI): freque frequency ncy of pore pore corr corresp espond onding ing to MCD MCD Influence of drying procedure on porosity and pore size distribution is illustrated in the following figure:
28
Figure(4-1) These results show: 1Oven Oven dry dryin ing g resu result lt in in part partia iall dist distri ribu buti tion on of of pore pore str struc uctu ture re due due to to stresses induced by receding water meniscuses on drying. 2Solv Solven entt repl replac acem emen entt tend tendss to pre prese serv rvee orig origin inal al por poree stru struct ctur ure. e. The table below shows the effect of solvent type in solvent replacement technique: Pore Heat Time of Pore vol Total Sample drying preheating TD vol At solvent At pore no. with vacuum (µm) 0.1 0.01 volume vacuum treatment µm µm A 0 Methanol 0 .5 16 37.5 51 B 5 Methanol 0.59 19 38.2 52 C 16 Methanol 0.59 16 36 50.5 D 24 Methanol 0.25 13.6 36 49 20h,100˚c H 0 Isopropanol 0.35 12 35 49.8 J 5 Isopropanol 0.35 12 35 49.8 L 16 Isopropanol 0. 0.35 12 35 49.8 M 24 Isopropanol 0.59 19 41.5 49.8 (For CEMI)
Table (4-1) 29
When Portland cement pastes are prepared with the same drying procedure, the porosity values found by mercury intrusion or helium pycnometry are the same. But this is different in case of pozzolana containing cement. Since values of porosity obtained by helium are confirmed by using methanol saturation, we can say that mercury can not occupy the entire space accessible to helium and methanol. When total porosity of pozzolanic cement is assessed by mercury intrusion, it turns out to be higher than that of Portland cement. The table below shows these results for natural pozzolana and containing cement:
sample CEM I Filler Fly ash Vizzini pozzolana Qualiano pozzolana Casteggio pozzolana Barile pozzolana Sengi pozzolana Bacoli pozzolana
Porosity Portland Blending 28 days curing cement% component% Rabid Slow 100 0 17 14.7 70 30 17.8 21.4 70 30 21.8 21.3
7 months curing Rabid Slow 13.1 10.6 15.3 13.8 17.4 16.4
70
30
18.7
21.6
14.3
12.9
70
30
20
18.8
11.3
10.7
70
30
17.8
16.3
13.6
11.6
70
30
17.7
17.9
13.5
12.7
70
30
17.5
19.3
13.4
34.2
70
30
17.8
18.7
13.3
11.4
Table (4-2)
30
As for silica fume and fly ash containing cement: paste
Ag e
Total pore are 38.3 53.4 53.9 50.7 28.8 48.4 50.4 50.7 24.4 43.2 50.7 55.9 32.9 43.3 53.9 55 41 49 50 36.9
Av. Bulk Skeletal por poros osit ity y Perm Permea eabi bili lity ty Pore density density diameter Control 1 0.036 1.37 2 .6 47.4 1.2×10-7 3 0.022 1.46 2.54 42.5 4.9×10-10 7 0.019 1.47 2.39 38.4 6.5×10-10 28 0.018 1.51 2.33 35 6.2×10-12 4515 1 0.045 1.43 2.65 46 1.1×10-7 3 0.026 1 .4 2.48 43.6 2×10-8 7 0.023 1 .4 2.32 39.7 1.3×10-8 28 0.02 1 .5 2.39 37.4 1.3×10-11 4530 1 0.061 1.32 2.57 48.6 7.1×10-7 3 0.031 1.42 2 .7 47.5 4.7×10-8 7 0.026 1.32 2 .3 42.8 5.6×10-9 28 0.02 1.43 2.42 40.9 1×10-12 1015 1 0.041 1.37 2.54 46.3 6×10-8 3 0.028 1.41 2.46 42.7 6.4×10-9 7 0.022 1.42 2.43 42.1 6.1×10-10 28 0.019 1.47 2.36 37.9 2.9×10-12 1030 1 0.039 1.29 2.62 50.9 1.6×10-7 3 0.03 1.35 2.66 49.3 2.3×10-8 7 0.026 1.36 2.43 44.3 1.9×10-9 28 0.02 1.35 2.35 42.4 5.3×10-13 Table (4-3) What ever was the type of pozzolana, porosity decrease with time but it still higher than porosity of Portland cement. Porosity increases by increasing fly ash but decrease by increasing rice husk. Porosity of blended cement paste depends on method of determination through all range of porosities. Porosity measured by methanol or helium pycnometry appears to be lower than by mercury intrusion, as shown in figures below:
31
Figure (4-2)
Figure (4-3) 32
So, basically we can say that; Mercury porosity is higher than helium porosity • Helium porosity is higher for oven dried samples than for solvent • replacement The damage caused by mercury intrusion in fly ash containing pastes is demonstrated by subjecting samples to two following intrusions. Repeated intrusions showed that in Portland cements pores size distributions did not change much except for an increase in threshold diameter, but blended cement differs a lot. The figure here shows that curve has changed from convex to convex.
Figure (4-4)
33
Since the two methods give comparable results with Portland cement pastes, it can be assumed that the pore structure of pozzolana cement pasties different and the pore system is more segmented.
4-2. Properties of pozzolana containing Mortars Mechanical properties 1. Setting: Setting time does not change greatly from Portland cement when using natural pozzolana. As for fly ash, it delays initial and final setting times. Silica fumes prolong setting times but, it is usually used with plasticizers which make it difficult to differentiate the delay resultant by silica fume from the one of the admixtures. 2. Strength: Pozzolana starts reacting slowly with calcium hydroxide and initially behaves as an inert material diluting the Portland cement. Pozzolana accelerates early hydration of clinker after 8hours after mixing with water. Partial replacement of pozzolana for Portland cement reduce initial rate of hardening but at greater ages this situation is reversed and pozzolana cement can attain the same or even higher strength than Portland cement. The following figure shows that 30% replacement of fly ash can reduce strength by 50%, difference in strength decrease by time till it disappears or reverse sign.
Figure (4-5) 34
The moment of recovery depend on fineness of Portland cement and pozzolana and activity of pozzolana. The effect of pozzolana on strength depends on: Pozzolana content and type • The figure below shows an optimum level of replacement which is dependent on type of pozzolana used.
Figure (4-6) The strength of pozzolana cement depends on characteristics of pozzolana used as shown in figure below.
35
Figure (4-7) Particle size distribution of pozzolana • The figure below shows that the negative effect on strength increases with particle size and decrease with time only for fine fractions.
Figure (4-8) Grinding promotes activity of fly ash but if fineness exceeds certain limits compressive strength decrease instead. That is due to decrease in combined lime which is ascribed to decrease in permeability of paste which hinders mobility of ions. 36
Properties of Portland cement The influence of 8fly ashes and 4portland cements on relative compressive strength. •
Figure (4-9) Difference in strength between blended and Portland mortars have been attributed to different content of alkalis in Portland cements among other factors. Shrinkage Normal percentage of pozzolana does not affect drying shrinkage or expansion in water. The following table shows that shrinkage in air for Portland cement and pozzolana cement is the same. Curing period Cement 7 28 90 CEM I 32.5 427 755 890 CEM I 42.5 396 733 873 CEM I 52.5 453 842 1043 CEM I 32.5 329 653 793 CEM I 42.5 381 725 904 CEM I 52.5 434 797 991 CEM I 42.5 430 685 810 CEM I 52.5 461 770 988 CEM IV 32.5 428 784 943 CEM IV 42.5 420 743 915 CEM IV A 393 737 889 CEM IV B 32.5 440 765 900 CEM IV A 42.5 425 706 890 Table (4-4)
37
The next table shows that shrinkage of mortars is affected by the fineness of clinker more than by fineness of fly ashes. Fineness(cm2/g) Fly ash Curing period Clinker Fly ash content 7days 28days 90days 1year 5years 2540 0 430 500 650 750 750 2880 40 400 460 500 500 550 8200 40 400 500 560 600 630 3580 0 500 650 780 1000 1100 2880 40 400 530 590 680 720 8200 40 400 530 620 750 780 5130 0 700 870 1060 1340 1450 2880 40 460 590 720 840 870 8200 40 440 590 720 840 870 Table (4-5)
4-3. Effect of pozzolana on durability Durability defines the suitability of concrete to preserve structural performance, fixed by designer, over the time; it plays an important role in .determining the service life of the structure ; Influence of environment (1) H2O effect: Water can decompose any hydrated compound in cement and leach lime leaving a residue made of SiO2.xH2O,Al2O3.yH2O and Fe2O3.zH2O. The residue acts as a protective layer against leaching on account of the gel-like nature of its compounds. The rate of leaching is high for porous concrete in excess presence of water or its renewal. It slows down when concrete is compact and strong. Leaching increases porosity and permeability which decreases strength and durability. The methods for assessing resistance of leaching based on water percolation through more or less porous concrete followed by determining leached lime or loss of mass. The amount of leached lime by distillated water from porous pozzolana cement is less than released by Portland cement and decreases as pozzolana/clinker ratio increase as shown in the following figure.
38
Figure (4-10) When compared to pozzolanic cement, Portland cement showed; Thicker corroded layer • Diffuse porosity decreasing form the surface to the • inside Deposit on the surface of gel like layer crossed by • small channels The mass loss of prism cured for28 days stored in soft water and brushed increase by substituting 30-40%of fly ash for Portland cement. That loss is related to the decrease in strength caused by partial replacement in initial setting period. Acid water increase rate of leaching, but pozzolanic cement shows better resistance than Portland cement as illustrated in the table below: Mix composition Mix105 Mix109 OPC(kg/m3) 170 312 Fly ash(kg/m3) 170 Water/binder 0.35 0.6 28 days compressive 78.4 43.2 strength Cumulative mass loss(g/kg) 5.8 7.8 Brushed 39
Un brushed
2.5 3.4 Table (4-6) The reasons that hard pastes of pozzolanic cement are more resistant to leaching more than Portland ones are: They contain 3-6%Ca(OH)2 compared to 20-22% of Portland cement They contain more calcium silicate hydrates • The C/S ratio of C-S-H is lower • They have lower permeability • •
(2)SO4-2 effect: Sulfate can be dangerous to concrete due to expansive nature of them or the products of their reaction with cement. CaSO 4 reacts on calcium aluminates hydrates forming expansive ettringite (3CaO.Al2O3.3CaSO4.32H2O) Na2SO4 react on calcium hydroxide forming gypsum which in presence of aluminates gives ettringite. MgSO4 react on all cement compounds forming Mg(OH)2 (brucite) and gypsum. Conditions enhancing formation of expansive compounds are: Occurrence of both aluminates hydrates and • calcium hydroxide, the following figures illustrate the positive effect of natural pozzolana
Figure (4-11) 40
Figure (4-12) Characteristics of mortar and concrete • (strength, porosity and permeability) The figure below shows the expansion of Portland cement mortars by increasing w/c ratio, i.e. by increasing porosity and permeability.
•
Figure (4-13) PH range, the range between 6-11.5 is less aggressive 41
Volume/surface area ratio of concrete. In the figure below we can see that positive effect by pozzolana is enhanced by increasing the size of the sample. •
Figure (4-14) Na2SO4 attack; natural pozzolana increase the sulfate attack resistance of cement. Also artificial pozzolana improves sulfate resistance to the attack by sodium sulfate. The sulfate resistance of pozzolana increases as curing time increases. Pozzolana only delays the performance failure but not eliminate it. They can prolong the life expectancy of concrete as shown in the figure below.
42
Figure (4-15) The next figure shows the improvement improvement in resistance to sulfate attack caused by increase cement dosage.
Figure (4-16) Silica fumes increase resistance to sodium sulfate attack, the higher the replacement level the lower the expansion. The grade of silica play an important role, since 10% replacement of good silica fume are enough to keep expansion below0.1% while for the same level of protection 15% of poor quality silica fume replacement is required. The physical and chemical properties of 28 days fly ash and silica fume mortars are explained in the table below through the pore volume of both when immersed for one year. w/c ratio Plain mortar Fly ash
Si fume
0.55
28 days Comp. strength 45.3
Total pore vol 39.8-17.6
10%
0.54
37.1
22.4-23.6
30%
0.52
35.8
44.5-15.1
50%
0.5
23.8
42.8-16.5
70%
0.48
11.7
62.2-34.6
5%
0.55
44.4
50.7-13.8
10%
0.54
45.1
36.1-11.6
20%
0.54
46.6
29-20.7 43
1year pore volume water 10% Na2SO4 33.8 94.8 (11.1) (83.3) 26.3 (34.6) 33.2 27.7 (15.4) (20.9) 38.6 (13.2) 85.5 (10.6) 30.1 (11.6) 44.7 46.8 (22.6) (24.6) 33.8 (17.8)
10% MgSO4 52.2 (36.1) 25.8 (32.9) 22.9 (38.4) 19.9 (42.7) 43.5 (19.5) 45.6 (28.9) 22.4 (21.4) 55.7 (57.6)
30%
0.53
50.2
28.4-21.1
17.8 (36.5)
27.2 (31.2)
68.6 (87.5)
Table (4-7) Linear expansion, weight gain and sulfate consumption of concrete exposed to 5% sodium sulfate were strongly reduced when silica fume used in 10% replacement. Inter grounding of pozzolana with gypsum reduce the effect of sulfate attack more than when it is just mixed with clinker and gypsum. MgSO4 attack; It is considered to be more severe than sodium sulfate attack. Natural and artificial pozzolana can enhance resistance of mortars to magnesium attack but some times they can worsen the performance. That performance seems to be dependent on type of pozzolana used. OPC containing 25% of fly ash behaves like sulfate resisting in weak MgSO4 but it is of low performance in concentrated solutions. The table below shows the loss of strength and resisting properties in Portland and pozzolana mortars through time. Type Type Compressive strength of of MPa % of water cured samples mortar cement 90 d 180 d 1 y 2y 90 d 180 d 1 y 2y Plain OPC 37.8 12.8 17.4 7 107 61 40 16 SPC 36.7 20.2 8 .5 116 61 23 SRPC 40.7 36.6 33.9 32.2 110 93 83 72 15%Si OPC 29.1 22.1 12 63 46 21 fume SPC 36.3 20.4 12.5 99 48 29 SRPC 46.8 17.7 11.7 103 39 23 Table (4-8) OPC= ordinary Portland cement SPC= slag Portland cement SRPC= sulfate resisting Portland cement Level of effectiveness of pozzolana don't depend much on type of cement used, it depends more on level of replacement, the following figure prove that.
44
Figure (4-17) Influence of aggregates; Alkali-silica reaction; this reaction forms a more or less viscous gel made up of alkali- and alkaline earth silicates which tend to absorb water from the environment and expand. Conditions essential for alkali-silica reaction: • High alkali content of cement • Only a part of aggregates is reactive • High humidity Influence of pozzolana; there were cases where pozzolanas were not effective in preventing expansion of alkali-silica reaction which is ascribed to insufficient quantity or poor quality of pozzolana. The expansion of mortars varies with the proportion of reactive aggregates and it reaches maximum at a certain level "Pessimum effect". The addition of pozzolana reduces this effect but some times give a similar effect as shown in the following figure.
45
Figure (4-18) Generally, partial replacement of high alkali cement with pozzolana produces great reduction in expansion. However, some fly ashes give a pessimum effect as shown in the figure.
46
Figure (4-19) This is not a general rule since in some fly ashes this peak doesn't appear as shown in the figure below.
Figure (4- 20) Addition of pozzolana increase total alkali content but the availability of these alkalis depends on progress of pozzolanic reaction. The next figure show that expansion reduction due to alkali-silica reaction depends on the source of pozzolana which when differ it varies specific surface area of pozzolana.
47
Figure (4-21) In conclusion, all laboratory tests and field experience have shown that pozzolana reduce expansion provided that replacement is sufficient. Factors reducing expansion • Lower permeability • Lower alkalinity • High alkali content • Low portlandite content • Low C/S ratio for C-S-H
48
Experimental techniques
Ch. (5): Experimental 49
5.1- Determination of free lime in pozzolana procedures Reagents; •
Solvent: One part by volume pure glycerol to 5 volumes absolute
ethyl alcohol. •
Indicator: Indicator : 0.18 g of phenol phthaline was dissolved in 2160 ml of
the previous mixed solvent. •
Standard ammonium acetate titrante :
16 g dry crystalline crystallin e
ammonium acetate was dissolved in 1 liter of distillated water. Pozzolanas; 1-
Standard si silica fu fume
2-
Standard Homra
Procedure 1- Sample preparation
To obtain CaO we burn Ca(OH)2 at 900˚c for 1 hour To prepare testing samples we mix (8:2 lime : pozzolana) and cure them for 24 hours at 50˚c. 2- Standardization Standardization
0.5 g of freshly ignited CaO was placed in 200 ml Erlenmeyer flask, about 60 ml of glycerol-ethyl alcohol solvent were added. A reflux condenser was fitted then the mixture was boiled for 5 – 20 minutes and then titrated while still nearly boiled with ammonium acetate solution until the pink color disappears. The boiling continued for 5-20 minutes and the mixture titrated again, this process was continued till the free CaO content does not exceed than 0.05 % after 2 hours boiling where no further pink coloration appears.
3- Samples 50
Exactly 0.5 g of sample was put in 200 ml Erlenmeyer flask, 40 ml of glycerol-ethyl alcohol solvent were added and proceeding as in standardization of ammonium acetate solution .
5.2- Results and discussion Percentage of free lime is calculated by the law: %CaO
Where: W1
=
W 1 × V 2 W 2
× 100
× V 1
weight of freshly ignited CaO (standard).
V1
ml of ammonium acetate required for ignited CaO.
W2
weight of sample taken
V2
ml of ammonium acetate required for sample.
No. Sample
1 Fresh
2 2g Silica
ignited CaO
fume+8g CaO Results
3 2g Homra+8g CaO
V1 = 74.5 ml V2 (Homra) = 65 ml V2 (Si.fume) = 62.5 ml In Homra %CaO
=
0.5 × 74.5 0.5 × 65
× 100 =
87.2%
In silica fumes %CaO
=
0.5 × 74 .5 0.5 × 62 .5
×100 = 83 .8%
Discussion: From the results shown the percentage of free lime after 24 h curing for (8:2 lime: pozzolana) sample is as follows 51
Pozzolana %CaO
Homra 87.2%
Silica fumes 83.8%
The higher percentage in case of using homra indicates that silica fume react with lime at a higher rate Then the pozzolanic reaction of silica fume is some what faster than that of homra.
List of tables No. 1-1 1-2 2-1 2-2 2-3
Table Cement types and uses Ingredients of blended cements Types of pozzolana Chemical composition of incoherent volcanic pozzolana Mineralogical co composition of of coherent vo volcanic po pozzolana 52
2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 2-15 3-1 3-2 3-3 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8
Chemical composition of tuffs Composition of the three layers in tuffs Mineralogical co composition of of tr transformed ma materials Chemical composition of diatoms Chemical composition of mixed origin pozzolana Chemical composition of bituminous fly ash(class F) Mineral composition of of bituminous fl fly ash(class F) F) Chemical heterogeneity of fly ash (class F) Ash particles classification of class F Chemical composition of fly ash (class C) Mineralogical composition of fly ash (class C) Chemical composition of micro silica Pozzolana combination with lime Hydration products in pastes and excess water for pozzolana cement Nature and amount of hydrated compounds in excess water solution of pozzolana-lime pozzolana-lime mixture Effect of solvent in solvent replacement water removal of pastes on porosity Porosity results by mercury intrusion for Portland and blended cement Porosity results by mercury intrusion for silica fume and fly ash cement Comparison of shrinkage between Portland and pozzolana cements The relation between shrinkage and fineness of cements Resistance of cements to water leaching The physical and chemical properties of 28 days fly ash and silica fume mortars Loss of strength and resisting properties in Portland and pozzolana mortars through time.
List of figures No. 2-1 3-1 3-2 3-3
Figure The relation between content of CaO and the position of maximum of X-ray in background Relation between specific surface area and pozzolana/lime ratio for different water content Relation between amount of combined lime and pozzolana/lime ration Relation between amount of combined lime and time of curing 53
3-4 3-5 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12 4-13 4-14 4-15 4-16 4-17 4-18 4-19 4-20 4-21
Relation be between te temperature an and ra rate of of pozzolanic re reaction Thermal treatment of pozzolana Effect of drying method on porosity and pore size distribution Difference in porosity measured by methanol or helium and that measured by mercury Damage caused by mercury intrusion in fly ash containing samples The relation between compressive strength and time for mortars Effect of pozzolana content on strength of mortar The effect of pozzolana type on strength on mortar Effect of pozzolana fineness on compressive strength Influence of Portland ce cement properties on on mortar strength The amount of leached lime by distillated water from porous pozzolana cement and Portland cement. Effect of occurrence of both aluminates hydrates and calcium hydroxide on formation of expansive compounds in concrete Variation of expansion rate according to w/c ratio Effect of size of sample on expansion of concrete Effect of pozzolana content on strength Improvement in resistance to sulfate attack caused by increase cement dosage Effect of cement type on expansion Effect of pozzolana addition on expansion "pessimum effect" Pessimum effect in some fly ashes Fly ashes that don't give pessimum effect Expansion reduction due to alkali-silica reaction dependant on the source of pozzolana
References 1. A.Komar Chapter (V)- B- Hydraulic binders Building materials and components, 135-185 (1979- second edition 1987) 2. Lea Chapter (10)- Pozzolana and pozzolanic cements (Franc Massazza) Chemistry of cement and concrete, 471-602 ( 1998 )
54
