center for by-products utilization cbu reports/rep-256.pdfcenter for by-products utilization and ......
TRANSCRIPT
Center for
By-Products
Utilization DEVELOPMENT OF MANUFACTURING
TECHNOLOGY FOR LOW-COST,
HIGH-PERFORMANCE, BLENDED CEMENTS IN
WISCONSIN
Vol. I: STATE OF THE ART ASSESSMENT
By Tarun R. Naik, Shiw S. Singh, and Scott J. Belonger
Report No. CBU REP-256
Department of Civil Engineering and Mechanics
College of Engineering and Applied Science
THE UNIVERSITY OF WISCONSIN - MILWAUKEE
DEVELOPMENT OF MANUFACTURING TECHNOLOGY
FOR LOW-COST, HIGH-PERFORMANCE,
BLENDED CEMENTS IN WISCONSIN
Vol. I: STATE OF THE ART ASSESSMENT
By
Tarun R. Naik, Director
Center for By-Products Utilization
Shiw S. Singh, Post-Doctoral Fellow
Center for By-Products Utilization
and
Scott J. Belonger, Graduate Student
University of Wisconsin - Milwaukee
Prepared for:
University of Wisconsin System
Applied Research Grant Program
Department of Civil Engineering and Mechanics
College of Engineering and Applied Science
The University of Wisconsin - Milwaukee
P.O. Box 784, Milwaukee, WI 53201
Ph: (414) 229-6904
FAX: (414) 229-6958
i
ABSTRACT
Portland cement is the most costly and energy intensive ingredient used in the
production of concrete. There are several industrial by-products currently
available which can be used to supplement portland cement, such as fly ash,
slag, rice husk, silica fume, etc. These materials can be used in manufacture of
cement with little or no additional processing. The resulting material is termed
as blended cement. The use of blended cement in concrete and other
cement-based materials not only provides economic, energy savings, and
ecological benefits, but also provides improvement in properties of materials
incorporating blended cements..
The major aim of this investigation is to develop blended cement technology
using industrial by-products. This report presents only state-of-the-art
information pertaining to the production technology of blended cement. The
report includes information on constituent materials and manufacturing
processes, and performance characteristics of blended cements made with
various supplementary materials as well as chemical additives.
Previous test data have revealed that industrial by-products such as fly ash, slag,
silica fume, etc. are suitable for use in production of blended cements.
ii
Performance of these materials can be enhanced through further processing
and/or additions chemical activators.
iii
ACKNOWLEDGEMENTS
The authors express their deep sense of gratitude to the University of Wisconsin
system for providing partial financial support for this project through its Applied
Research Grant Programs.
The authors would also like to thank the College of Engineering and Applied
Science and the Graduate School of the University of Wisconsin-Milwaukee for
providing facilities for conducting this research work.
The primary sponsors of the Center for By-Products Utilization are: Dairyland
Power Cooperative, LaCrosse, Wisconsin; Madison Gas and Electric Company,
Madison, Wisconsin; National Minerals Corporation, St. Paul, Minnesota;
Northern States Power Company, Eau Claire, Wisconsin; Wisconsin Electric
Power Company, Milwaukee, Wisconsin; Wisconsin Power and Light Company,
Madison, Wisconsin; and Wisconsin Public Service Corporation, Green Bay,
Wisconsin. Their continuing help and interest in the activities of CBU is
gratefully acknowledged.
iv
TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1
2.0 CONSTITUENT MATERIAL FOR BLENDED CEMENT
5
2.1 PORTLAND CEMENT 6
2.2 POZZOLANIC MATERIALS
7
2.2.1 Natural Pozzolans 8
2.2.2 Fly Ash 8
2.2.3 Condensed Silica Fume
9 2.3 Blast-Furnace Slag
10
2.4 INERT FILLER MATERIALS 11
2.5 CHEMICAL ADMIXTURES 11
3.0 MANUFACTURING PROCESSES 13
3.1 PRODUCTION OF PORTLAND CEMENT 13
v
3.1.1 Quarrying And Crushing
13
3.1.2 Grinding And Blending 14
3.1.3 Production of Clinker 14
3.1.4 Grinding of Clinker 15
3.2 PRODUCTION OF BLENDED CEMENTS 15
3.2.1 Performance of Grinding Systems 17
3.2.1.1 Ball mills
17
3.2.1.2 Roller mills
17
3.2.1.3 Jet mills
18
3.2.2 Incorporation of Blast-Furnace Slag
18
3.2.3 Incorporation of Fly Ash
19
3.2.4 Blending Techniques
19
3.2.5 Quality Control
20
4.0 PREVIOUS INVESTIGATIONS 21
vi
4.1 BLENDS CONTAINING SEPARATELY GROUND 21
PC, GGBS, FA, AND SF
4.2 HIGH-STRENGTH BLENDS CONTAINING SF AND 26
FINELY GROUND PC AND GGBS
4.3 BLENDS CONTAINING SF AND SEPARATELY GROUND 32
AND INTERGROUND FA
4.4 BLENDED CEMENTS CONTAINING FINELY GROUND 34
SAND AND LECA-BY-PRODUCTS
4.5 PARTIAL AND FULL INTERGRINDING OF CEMENT 37
CLINKER AND FLY ASH
4.6 ACTIVATION OF NATURAL POZZOLANS 38
4.7 GYPSUM ACTIVATED FLY ASH BLENDS 41
4.8 ACTIVATION OF SLAG BLENDS 43
4.9 BINDERS CONSISTING OF 100% ACTIVATED SLAG 44
4.10 DURABILITY OF MATERIALS CONTAINING BLENDED 45
CEMENT
4.11 FREEZING AND THAWING, RESISTANCE OF
48
BLENDED CEMENTS
4.12 RESISTANCE TO REINFORCEMENT CORROSION OF
49
CONCRETE MADE WITH BLENDED CEMENTS
4.13 SULFATE ATTACK AND ALKALI/AGGREGATE REACTION 50
vii
RESISTANCE OF BLENDED CEMENT CONTAINING
CONCRETE
5.0 SUMMARY AND CONCLUSION 51
6.0 REFERENCES 54
viii
LIST OF TABLES
4-1 Proportions of Blended Cement Containing Slag, Fly Ash and 22
Silica Fume
4-2 Compressive Strengths of Test Specimens Containing Slag, Fly Ash
23
and Silica Fume
4-3 Blended Cement Proportions Using Silica Fume, Finely Ground 27
Portland Cement, and Ground Blast-Furnace Slag
4-4 Compressive Strengths of Blended Cement Concrete Using Silica Fume,
28
Finely Ground Portland Cement and Ground Granulated Blast-Furnace
Slag
4-5 Strength of Mortar Cubes Made From Blended Cements Containing 33
Interground Fly Ash
4-6 Compressive Strengths of Mortar Cubes Produced Using Blended 35
ix
Cement Containing Finely Ground Sand and Leca-By-Product
4-7 Comparison of Compressive Strengths Attained by Partial and 37
Full Grinding
4-8 Compressive Strengths of Paste Mixtures Containing 70% Natural
39
Pozzolans, 30% Lime and Optimum Values of Four Activators
4-9 Compressive Strengths of Mortar Mixtures Containing Class F Fly Ash 41
and Gypsum
4-10 Compressive Strengths of Mortar Cubes Produced With Ground 43
Granulated Blast-Furnace Slag and Various Chemical Activators
4-11 Compressive Strengths of Mortar Cubes Containing Activated Slag 45
4-12 Results of Durability Testing of Blended Cements Containing Ground
47
Granulated Blast-Furnace Slag, Silica Fume, and Fly Ash
x
SECTION 1
INTRODUCTION
Cement is a binding material that is used to bind coarse aggregate and sand to produce
concrete. Portland cement is the primary cementing material used in the United States
today. The United States produces approximately 90 million tons of Portland cement
annually [1]. The manufacture of cement is quite energy intensive, consuming
approximately 3000 KJ/kg (1300 BTU/lb) of cement [2].
Large amounts of fossil fuels are burnt to meet the energy requirements in the
production of portland cement. Combustion of these fuels results in emissions of
particulate matters and gaseous pollutants such as SOx, NOx, etc.. Both SOx and NOx
contribute to the formation of acid rain when hydrolyzed in the atmosphere.
Additionally, combustion of the fuels emit large amounts of greenhouse gases,
especially CO2. It is estimated that 1 ton of CO2 gas is produced for every ton of
portland cement [1].
-2-
This large consumption of energy also makes cement the most expensive ingredient
used in the production of concrete. The current (1995) price of portland cement
purchased in bulk is approximately $70 to $90 per ton. In comparison, coarse
aggregate and sand, the other primary ingredients used to produce concrete, are
approximately $12/ton and $7/ton, respectively. Although cement represents only
approximately 15% of the raw material, by weight, in normal strength concrete, it
accounts for over 50% of the material cost. High-strength concrete normally contains
more cement, making this percentage even higher.
Although portland cement is the primary binding agent used in the production of
concrete, there are also several other materials, primarily natural and artificial
pozzolans, which display cementing properties similar to portland cement. The
cementing properties of pozzolans have been well known for many years. Over 2000
years ago, Roman and Egyptian builders utilized volcanic ash, a natural pozzolan, in
combination with lime to produce mortar. Pozzolanic properties of coal fly ash was first
identified and utilized in concrete by Davis in 1937 [3]. Blast-furnace slag, a
by-product of the manufacture of pig-iron, has also been identified to possess
cementitous properties. Much research has been conducted to determine the effect of
incorporating supplementary materials such as natural and artificial pozzolans in
concrete production.
In the United States, electric utility companies produce approximately 80 million tons of
coal combustion by-products annually, in form of fly ash, bottom ash, and slag. Of this
-3-
80 million tons, approximately 25% is utilized in the construction of pavement
base-coarses, subgrade fills, and back-fill and in the production of concrete, and other
cement-based materials. The remaining portion of this is disposed of in landfills and
impoundments. Disposal by these methods not only result in high disposal costs to the
producer, but also result in a loss of energy and resource recovery. Due to the above
problems and shrinking landfill space, it has become essential to find constructive uses
for such materials.
Use of by-product materials in the production of cement-based materials not only
provides energy saving, economic, and ecological benefits, but also several technical
benefits. These advantages include: increased strength, improved workability,
reduced heat of hydration, increased freeze/thaw durability, and increased resistance to
chemical attack [4, 5, 6, 7, 8, 9].
Despite the obvious and well-known technical, economic, environmental and
energy-saving benefits that can be obtained through the use of these by-products, they
are still underutilized. The low utilization rate of by-products may have been due to
several factors, including variability in quality of materials, uncertainty of their effects on
strength and durability, and insufficiently developed by-product utilization technology.
In addition, many concrete producers do not have the facilities to handle many different
supplementary cementing materials. For these reasons, it is more practical to add
these materials in the production of cement. This will allow better quality control of the
-4-
resulting cementing materials and will eliminate the need to handle several
supplementary cementing materials at the concrete production plant.
Blended cement was first produced in the USA in the 1950's, when blast furnace slag
was used. Then in 1970, blended cement using fly ash was produced. Since this
time, blended cement use has been slow to develop in the USA. Of the 90 million tons
of cement produced in North America, less than 2% is produced as blended cements.
The U.S. trails many European and Asian countries in the use of blended cement.
This is primarily the result of insufficiently developed production technology for blended
cements incorporating various types of by-products, and availability of the relatively
low-cost portland cement.
In light of the above information, it appears highly attractive to use industrial
by-products in the manufacture of low-cost blended cements. However, technology for
by-product use in blended cements needs to be established. Therefore, this research
was undertaken to develop manufacturing technology for manufacture of low-cost,
high-performance blended cements in Wisconsin. This report deals with only
state-of-the-art information related to blended cement production technology.
-5-
Section 2
CONSTITUENT MATERIALS FOR BLENDED CEMENT
ASTM C 595 [10] defines blended cement as "a hydraulic cement consisting of two or
more inorganic constituents (at least one of which is not portland cement or portland
cement clinker) which, separately, or in combination, contribute to the strength-gaining
properties of the cement (made with or without other constituents, processing addition
and functional additions, by intergrinding or other blending)." The performance of a
blended cement is controlled by the chemical and physical properties of the blend.
-6-
These properties are greatly dependant upon the raw materials used in the blend and
are also influenced by the manufacturing processes.
The most accepted and widely used materials in the production of blended cements are
portland cement, portland cement clinker, and pozzolans. Other materials such as
crushed limestone, finely ground silica sand, rice husk, and cement kiln dust, etc. are
also used. In addition to these materials, small amounts of chemical
admixtures/activators may also be used to improve performance.
ASTM C 595 has established the following classes of blended cement for both general
and special applications:
1. Type IS - Portland blast-furnace slag cement for use in general concrete construction with slag content ranging from 25% to 70%.
2. Type IP - Portland-pozzolan cement for use in general concrete
construction with pozzolanic content ranging from 15% to 40%.
3. Type P - Portland-pozzolan cement for use in concrete construction where high strengths at early ages are not required with pozzolanic contents varying from 15% to 40%.
4. Type S - Slag cement for use in combination with portland
cement in making concrete and in combination with hydrated lime in making masonry mortar with slag content exceeding 70%.
5. Type I (SM) - Slag modified portland cement for general
construction use with slag content less than 25%.
6. Type I (PM) - Pozzolan-modified portland cement for use in general construction with pozzolanic content less than 15%.
-7-
2.1 PORTLAND CEMENT
Portland cement is defined by ASTM C 150 [10] as "a hydraulic cement produced by
pulverizing clinker consisting essentially of hydraulic calcium silicates, usually
containing one or more of the forms of calcium sulfate as an interground addition."
Portland cement is truly hydraulic, and therefore requires only the presence of water to
develop its strength gaining properties.
Chemically, portland cement is composed mainly of calcium and silica oxides along with
alumina and ferrous oxides. Trace amounts of other oxides such as magnesium oxide,
titanium oxide, and sulfur trioxides are also present. These oxides are present in
compounds consisting primarily of tricalcium silicates, dicalcium silicates, tricalcium
aluminates, and tetracalcium aluminoferrites (abbreviated as C3S, C2S, C3A, and C4AF,
respectively). The properties of portland cement are controlled by the composition of
these compounds.
2.2 POZZOLANIC MATERIALS
Pozzolanic material is defined by ASTM C 618 [10] to be "a siliceous or siliceous and
aluminous material which, in themselves, possess little or no cementitious value but
will, in finely divided form and in the presence of moisture, chemically react with calcium
hydroxide at ordinary temperatures to form compounds possessing cementitious
properties." Pozzolans exist in both natural and man-made forms. Volcanic ash is
-8-
the most common form of natural pozzolans. The most effective and widely used
pozzolans are man-made pozzolans. These include fly ash, silica fume and other
combustion ashes.
When a pozzolanic material is combined with cement, the strength-forming C-S-H
compound is formed due to its reaction with calcium hydroxide (CH), which is a
by-product of the hydration of cement. This pozzolanic reaction occurs much more
slowly than the hydration reaction. In addition, because CH is a by-product of cement
hydration, cement hydration must occur before pozzolans can form C-H-S. For these
reasons, strength development is often slower in pozzolanic portland cement than
plain portland cement. However, the pozzolanic reaction consumes CH, it generally
produces a more dense, less permeable concrete. This leads to higher strengths and
better durability characteristics at later ages.
2.2.1 Natural Pozzolans
Ash produced as a result of volcanic activity is considered to be a natural pozzolan.
The chemical composition of most volcanic ash is quite similar to fly ash. Volcanic
ash, however, generally contains larger amounts of crystalline particles rather than
glassy particles. Crystalline particles are much less reactive than glassy particles.
Also, natural pozzolans generally experience a greater loss on ignition. For these
reasons, natural pozzolans are generally less effective in cement-based materials than
other pozzolans.
-9-
2.2.2 Fly Ash
Fly ash is a by-product produced by the combustion of pulverized coal. It is removed
from the combustion gases by particulate collecting devices such as cyclone
separators, electrostatic precipitators, fabric filters, etc. Physically, fly ash particles are
typically spherical in shape, with particle sizes ranging from 1 to 150 μm, with a
specific gravity varying between 2.1 and 2.8. Chemically, fly ash is composed of
mainly SiO2, Al2O3, Fe2O3, CaO, and MgO. The presence of high amounts of silica and
alumina in fly ash results in its major pozzolanic properties.
ASTM C 618 [10] has also broadly classified fly ash into the following two classes:
Class F: Low-lime fly ash is normally produced from burning anthracite or bituminous coal which contains less than 5% calcium oxide. This class of fly ash has pozzolanic properties.
Class C: High-lime fly ash is normally produced by burning lignite or sub- bituminous coal which may have lime contents exceeding 10%. This class fly ash also has pozzolanic as well as cementitious properties. The pozzolanic reaction of the ash results in formation of pozzolanic C-S-H, similar to
that formed by the hydration of cement. Thus, pozzolanic reaction contributes to
formation of the hardened concrete. In fact, it causes both pore and grain refinements
of the hardened concrete mass. For a given strength requirement, it is possible to
replace a part of the cement requirement with fly ash. The higher calcium content of a
Class C fly ash allows greater replacement rates of cement than that of a Class F ash.
-10-
2.2.3 Condensed Silica Fume
Condensed silica fume is a by-product of ferro-silicon alloys or silicon metal, which is
removed from SiO gases by oxidation. Condensed silica fume is composed of
particles which are spherical in shape, with a very high fineness. Typical particle sizes
are in the order of 0.1 μm. The SiO2 content of silica fume generally exceeds 90%.
Due to the high fineness and high reactive silica content of silica fume, it is a highly
active pozzolan, making it another suitable substitute for portland cement in
high-strength concrete. Silica fume is quite effective in increasing the pore structure
density of concrete, making strengths exceeding 140 MPa (20,000 psi) attainable. The
large specific surface area of the silica fume also increases the water demand greatly,
by about one pound of water per pound of silica fume must be added. For this reason,
utilization rates of silica fume are typically limited to less than 10% [7].
The supply of silica fume is relatively small compared to that of fly ash or blast-furnace
slag. The United States produces approximately 130,000 tons annually, of which
nearly all is utilized [7]. Due to the relatively small rate of production and high demand,
condensed silica fume is relatively expensive, at prices in the order of $1000/ton. For
this reason, silica fume is used primarily to produce high-strength or high-performance
concrete.
2.3 Blast-Furnace Slag
-11-
Blast-furnace slag is a by-product of the manufacture of pig iron. The molten slag can
either be slowly cooled to a crystalline form or rapidly cooled to a granulated glassy
form. Although the crystalline slag has no hydraulic properties, the granulated slag
contains chemical compounds similar to portland cement, and when ground, the
granulated slag displays latent hydraulic properties. ASTM C 989 [10] defines
granulated blast-furnace slag as "the glassy granular material formed when molten
blast-furnace slag is rapidly chilled by immersion in water."
The granulated blast-furnace slag is produced in form of small-grained particles, similar
to fine aggregate. Granulated slag must be dewatered, dried, and ground in a process
similar to that used for cement clinker. The slag is less reactive than portland cement.
It is normally ground finer than portland cement to improve its activity. The specific
gravity of slag is also similar to that of portland cement, making the homogenous
blending of the two materials easier.
The latent hydraulic properties of ground granulated blast-furnace slag make it an
appropriate substitute for portland cement. Ground granulated blast-furnace slag has
only latent hydraulic properties and therefore must be used in combination with portland
cement, or alkaline activators to gain sufficient strength for structural applications.
2.4 INERT FILLER MATERIALS
Other inert materials may be used as filler material in blended cements, in order to
reduce the total amount of portland cement content. These materials include finely
-12-
ground silica sand, limestone, and kiln dust from clay brick or cement clinker
manufacturing. The effects of utilizing these materials vary, depending on properties
of individual materials. Some materials, not contributing to strength development, are
used primarily to reduce the cost of the blend. Several other materials have also been
found to increase performance within a limited rate of utilization.
2.5 CHEMICAL ADMIXTURES
Small amounts of additional chemical admixtures can be used to increase performance
of blended cements. It is known that pozzolans and slag contain large amounts of
glassy phases. The addition of alkaline admixtures can increase the solubility of
these glassy phases. It has been observed that both alumina and silica, the primary
compounds present in pozzolans, become soluble at a pH of 13.3 or greater.
Therefore, activation can be achieved by the use of chemical admixtures which will
increase pH of the mixture. Salts of weak acids and strong bases are the most
effective activating agents [11].
The following are the most commonly used alkaline admixtures for blended cement:
(1) Calcium Hydroxide (Ca(OH)2 or CH),
(2) Sodium Hydroxide (NaOH),
(3) Sodium Sulfate (NaSO4),
(4) Gypsum (CaSO4),
-13-
(5) Calcium Chloride (CaCl2),
(6) Sodium Carbonate (Na2CO3 ), and
(7) Sodium Silicate (Na2O-SiO2).
-14-
Section 3
MANUFACTURING PROCESSES
The manufacturing process used to produce cement has a great influence on both its
performance and cost. For portland cement, kiln-firing temperatures and technique of
firing can influence the chemical composition of the cement, as well as the amount of
energy consumed in production. The grinding and blending techniques used in
production of both portland cement and blended cements can also affect their quality,
performance, and cost. Due to these reasons, the cement manufacturing process
must be optimized with respect to both performance and economy.
3.1 PRODUCTION OF PORTLAND CEMENT
The production of portland cement can be divided into the following four basic steps:
1. Quarrying and crushing raw materials
2. Grinding and blending raw materials
3. Firing of materials to produce clinker
4. Grinding of clinker to produce cement
3.1.1 Quarrying And Crushing
Portland cement is made from ground material consisting primarily of calcium
carbonate and aluminum silicate. Limestones, clays, and shales provide abundant
sources of these materials. These materials are quarried from open-pit mines. Care
-15-
must be taken to assure that the chemical composition of these raw materials is fairly
consistent. These materials are quarried and transported in large pieces, normally
several feet in diameter. These large pieces of raw material are then crushed in two
stages, firstly the size is reduced to six to ten inches, and then to approximately one
inch. Until this point, each raw material is handled and stored separately.
3.1.2 Grinding And Blending
The crushed materials are then ground and blended. At this stage, the one inch raw
materials are ground finer than 0.1 mm (0.025 inch). After grinding, any particles not
ground to the desired fineness are returned to be reground. Blending may occur
before, during, or after grinding. Care must be taken to assure proper proportioning of
the raw materials in order to obtain a homogeneous blend. Also, water may be added
to the material before grinding. This water aids the grinding process and provides a
more uniform mixture. However, additional energy is required to remove the water in
the next phase of production.
3.1.3 Production of Clinker
The finely ground and blended materials are then fired to produce clinker. The ground
materials first enter a preheater. In the preheater, exhaust fumes are used to heat the
materials to approximately 1700 F, at which the moisture is removed. Once the
material is dried and preheated, it is fed to the rotary kiln where it is heated, by the
combustion of coal, to a temperature in the range of 2600 - 2700 F. At this
-16-
temperature, fusion occurs, which causes the material to transform into the reactive
calcium silicate and calcium aluminate com- pounds[12]. At this point, the
material is quickly cooled, causing the formation of the round, marble-sized, glass-hard
clinker.
3.1.4 Grinding of Clinker
After the clinker is produced, it is then ground to form the final product, portland
cement. When the clinker is ground, a small amount of gypsum is also added to slow
the initial setting time of cement. It is well known that the strength development of
portland cement is greatly influenced by particle size [13]. Therefore, particle size is
closely monitored to assure that the desired size distribution is attained. The particles
which are not ground fine enough are returned for additional grinding.
3.2 PRODUCTION OF BLENDED CEMENTS
Although the raw materials used to produce portland cement are widely available and
relatively inexpensive, the handling and processing required to make these materials
into portland cement is quite energy intensive. Therefore, the energy consumed in
portland cement production accounts for much of its expense. Additionally, increased
use of energy causes several environmental problems, as discussed before. It would
be beneficial to produce a cement which would require less handling and processing,
thereby reducing the energy consumption, reducing the emission of pollutants, and
increasing the economy of production. This can be accomplished by producing
-17-
blended cements using by-product materials, which exist in reactive forms with little or
no additional processing.
There are many possible ways to incorporate by-products in manufacturing of blended
cements. By-product materials can be blended with raw materials for portland cement
before clinker production. However, this does little to reduce the energy requirement,
with little or no increase in performance. For this reason, it is much more desirable to
add by-product materials after the firing of raw materials, thereby reducing the energy
consumption. The most desirable technique involves by-product addition after the
clinker is produced. By-product materials can be interground with clinker, ground
separately and blended with the finished portland cement, or simply blended in the "as
received" form with the finished portland cement. There are also several grinding
systems available for grinding of these materials, including ball mills, roller mills,
impeller mills, and jet mills. The effectiveness of the grinding process or system to be
used is determined by the grindability and interaction of the different materials, as well
as the desired performance and production rate.
Like portland cement, by-product materials such as fly ash and ground granulated
blast-furnace slag display increases in activity with increased fineness. This is the
result of the morphological, physical and chemical changes caused by grinding [14].
Grinding may destroy portions of the original crystal lattice, increasing the activity of the
alumina and silica. For these reasons, it may be desirable to grind these materials, to
optimize the performance of each component of the blend. However, the energy
required to sufficiently reduce the particle size of many materials may not be justified by
-18-
the increase in performance. Grinding also causes a breakdown of the natural
spherical shape of the fly ash particles, which decreases workability of the mixture [13].
3.2.1 Performance of Grinding Systems
There are many grinding systems available which can be used to produce blended
cements. Chopra and Narang [13] conducted an investigation on various grinding
systems used to produce blended cements. These include ball mills, roller mills,
impeller mills, and jet mills. The overall efficiency and effectiveness of reducing
particle size was studied.
3.2.1.1 Ball mills
Ball mills grind materials by the impact of falling balls. The ball mill is the simplest and
most widely used grinding system in the production of portland cements. In this
investigation, a ball mill designed for LA abrasion test for aggregates was used for
producing blended cement. This system was found to be ineffective for producing
blended cement. The ball mills are most efficient at low levels of fineness and for
materials having good grindability. A large amount of grinding energy is lost due to
particle interaction. Beyond intermediate levels of fineness, additional grinding can lead
to agglomeration of particles, which can actually increase particle size. The ball mills
also provide little control of particle size distribution, yielding a large range of particle
sizes.
-19-
3.2.1.2 Roller mills
Roller mills grind materials by the slow compression of materials between rollers. The
roller mill shows distinct advantages over the other systems considered in this
investigation. They provide much greater control of particle size, delivering particles
within a narrow range if desired. The mills also require much less energy for the same
amount of size reduction.
3.2.1.3 Jet mills
The jet mill is a new type of grinding system which uses a high velocity stream of air to
collide particles together, causing a reduction in particle size [14]. The particle size
distribution is controlled by the velocity of the collision. The results of an investigation
of the use of jet mills for grinding of cement clinker suggests that the jet mill provides a
good control of particle size distribution and increased hydraulic activity of the cement
due to morphological changes caused by the collision of particles. Agglomeration of
particles is also greatly reduced in this system. The drawback of this system is its
limited output. The largest jet mills are limited to a few tons of output per hour.
3.2.2 Incorporation of Blast-furnace Slag
Granulated blast-furnace slag exists in sand-sized glassy nodules. At this grain-size,
the materials is unreactive. Therefore, grinding of the granulated slag must be done to
realize its full hydraulic potential. The slag is less reactive than portland cement.
Therefore, it would be desirable to grind the slag finer than the portland cement. The
granulated slag, however, is much harder and less grindable than cement clinker.
-20-
When interground, the cement clinker is likely to be ground much finer than the slag.
Therefore, it is impossible to achieve the desired fineness of individual components.
Excessive grinding is required to achieve the desired fineness of the slag, at which
point the fineness of the clinker may exceed optimum value. Investigations of
intergound the slag and clinker have shown a disproportionate grinding of clinker
compared to the slag [13]. For this reason, separate grinding is more efficient and
provides a better control of particle size than intergrinding for most combinations of
cement clinker and the granulated slag.
3.2.3 Incorporation of Fly Ash
Fly Ash, in its as received form, is made up of primarily spherical shape particles, with
particle size typically varying in the range of 1 - 150 μm. It is generally finer than
portland cement. Fly ash also displays pozzolanic activity in this form, therefore, very
little or no additional processing is required to utilize it. Fly ash, however, like cement
and blast-furnace slag, will often display increased activity with increasing fineness.
Therefore, it may be advantageous to grind fly ash when using it to produce blended
cement. Unlike blast-furnace slag, fly ash tends to be softer than cement clinker.
Small doses of fly ash (10%) tend to act as a grinding aid for cement clinker when
interground, but at larger doses, the presence of fly ash may hinder the grinding of
clinker [13]. This problem may be overcome by first partially grinding the clinker then
adding fly ash and interginding. Since fly ash is reactive in its natural form, additional
grinding should be evaluated to assure that any increase in energy required for
-21-
production of blended cement is justified by corresponding increase in its performance.
In many cases, the most economical production technique may be simple blending.
3.2.4 Blending Techniques
Ingredients of blended cements must be blended to attain a homogenous mixture.
This can be done in the intergrinding process, if intergrinding is performed. For
separate grinding or simple blending, materials can be blended in a continuous
blending process, where materials are continually fed and blended or discontinuous
batch blending, where specific proportions of materials are fed into a silo and
mechanically blended.
3.2.5 Quality Control
The production of blended cement must be closely monitored to assure that the end
product is of consistent quality. Quality control begins with monitoring of raw materials.
An hourly chemical analysis of both clinker and by-products should be performed to
assure that the raw materials meet the required specifications. Feed rates of these
materials should be monitored and recorded to assure that proper proportions are
maintained. After each grinding, oversized particles are separated, normally by the
-22-
use of an air separator and returned for further grinding. A chemical analysis of the
final product is also performed to verify that the blend is homogenous and meets the
desired specifications. Several methods of evaluating the pozzolanic content of
blended cements are available. An evaluation of these methods has determined that
the most effective and efficient method is by X-ray diffraction (XRD) [15].
-23-
Section 4
PREVIOUS INVESTIGATIONS
The economic, environmental and technical benefits of blended cement use have
inspired much research in this area. Numerous investigations [16-33] have been
conducted to determine the effects of various raw materials and manufacturing
techniques on performance characteristics of blended cements in mortar and concrete.
This report provides a brief description of results from previous investigations pertaining
to blended cement technology.
4.1 BLENDS CONTAINING SEPARATELY GROUND PORTLAND CEMENT,
GROUND GRANULATED BLAST-FURNACE SLAG, FLY ASH AND SILICA
FUME
Hinczak, et al. [16] conducted an investigation of ternary and quaternary cement
systems containing portland cement, blast-furnace slag, Class F fly ash, and silica
fume. In this investigation, various combinations of these materials were used to
produce concrete (Table 4-1). The portland cement and blast-furnace slag were
ground separately. The fly ash and silica fume were not ground/interground. The
parameters such as compressive strength, drying shrinkage, water requirement and
heat of hydration were measured to evaluate the performance of the cements.
The compressive strength results showed that the mixture containing 95% portland
cement and 5% silica fume outperformed the control mixture at all ages. All other
-24-
blends had significantly lower strengths at 3 and 7 days. At 28 days and beyond,
strength of Mixture 4 containing 40% slag and 15% fly ash was comparable to that of
the control mixture. After 90 days, all blends developed strengths comparable to the
control mixture (Table 4-2).
Table 4-1: Proportions of Blended Cement Containing Slag, Fly Ash and Silica Fume [16]
Mixture
Portland Cement
(%)
Slag (%)
Fly Ash
(%)
Silica Fume
(%)
1
100
---
---
---
2
95
---
---
5
3
55
30
15
---
4
45
40
15
---
5
40
40
20
---
6
45
35
15
5
7
40
40
15
5
-25-
This study did not show significant differences in drying shrinkage among the various
mixtures tested. However, a direct relation between strength development and heat of
hydration was observed. The mixtures with the highest strength also produced the
highest amount of heat. The highest heat of hydration was produced by Mixture 2
followed by Mixture 1. The rest of the mixtures produced similar heat of hydration,
approximated one third to one half less than Mixture 1 and Mixture 2 at all ages.
Water required for consistent slump varied between mixtures (Fig. 4.1).
The authors concluded that ternary and quaternary cement blends allow production of
concrete with performances similar to that of ordinary portland cement, with the
exception at early ages. (Fig. 4.2 through 4.4). These blends can also be used to
significantly reduce heat of hydration.
Table 4-2: Compressive Strengths of Test Specimens Containing Slag, Fly Ash and
Silica Fume [16]
Mixture
Compressive Strength (MPa)
3-Day
7-Day
28-Day
90-Day
180-Day
1
17.5
24.0
34.0
37.0
39.0
2
21.5*
28.5*
45.0*
49.5*
48.5*
3
7.5
14.0
25.5
37.5*
43.0*
4
6.2
11.5
26.0
37.5*
43.0*
-26-
5
5.0
10.5
24.0
33.5
40.0*
6
7.5
14.0
32.1
39.5*
43.0*
7
6.5
12.0
27.5
37.0*
39.0*
* Compressive strength equal to or exceeding control
Figure 4.1: Effect of cement composition on water:binder ratio at constant
slump and binder content [16]
-27-
Figure 4.2: Effect of cement composition on compressive strength of concrete
at constant slump and binder content [16]
Figure 4.3: Effect of ternary and quaternary cements on drying shrinkage
of concrete [16]
-28-
Figure 4.4: Heat of hydration of ternary and quaternary cements [16]
-29-
4.2 HIGH-STRENGTH BLENDS CONTAINING SILICA FUME, AND FINELY
GROUND PORTLAND CEMENT AND GRANULATED BLAST-FURNACE
SLAG Shizawa et al. [17] studied properties of blended cement for use in ultra-high strength
concrete. In this investigation, blended cements containing finely pulverized portland
cement, finely pulverized blast-furnace slag, and silica fume were produced. These
cements were then used to produce concrete. Strength, workability, and heat of
hydration of a number of blends of these materials were then studied.
The cement blends were prepared by first separately grinding the cement and
blast-furnace slag to a specific fineness using a vibrational mill. The separately ground
materials were then blended. Portland cement with Blaine fineness of 335 and 644
m2/kg, (designated as N-OPC and H-OPC, respectively) and blast-furnace slag with
Blaines fineness of 415, 805, and 1163 m2/kg (designated as PBFS B04, PBFS B08,
and PBFS B12, respectively) were prepared. These materials were then blended in
the proportions according to Table 4-3 . These blends where used to produce
concrete at a constant water to cementitious materials ratio of 0.30. Superplasticizers
(SP) were used to maintain the desired level of workability. The results of the
investigation are presented in Table 4.4, and in Fig. 4.5 through 4.9.
The results showed that the increased fineness of the portland cement did not significantly increase the early strength development of the mixtures (Table 4.4). In fact, the increased
-30-
fineness of the cement reduced the early age strength in many cases. This may be partly attributed to the increased use of the superplasticizer to account for the loss of slump
due to the
increased fineness. The increased fineness of the blast-furnace slag increased
one-day strength
of the test mixtures. However, after one day, the slag with intermediate fineness
exhibited the
best performance. In general, an increase in fineness caused decreased workability of the concrete. Most mixtures containing slag were more workable than the control
mixtures. The
mixtures containing silica fume showed slight improvements in performance at later
ages, and
comparable performances at earlier ages.
Table 4-3: Blended Cement Proportions Using Silica Fume, Finely Ground Portland
Cement, and Ground Granulated Blast-Furnace Slag [17]
Mix Number
Quantity per Unit Volume (kg/m
3)
N-OPC
H-OPC
PBFS B04
PBF B08
PBFS B12
Silica Fume
SP
N-OPC
550
1.65
N-B04
330
220
1.65
N-B08
3 30
220
1.65
-31-
N-B12 330 220 1.65
N-SF
495
55
1.65
H-OPC
550
3.50
H-B04
330
220
3.50
H-B08
330
220
3.50
H-B12
330
220
3.50
H-SF
495
55
3.50
0
Table 4-4: Compressive Strengths of Blended Cement Concrete Using Silica Fume, Finely Ground Portland Cement and Ground Granulated Blast-Furnace Slag [17]
Mixture
Compressive Strength (MPa)
Slump
(mm)
1-Day
3-Day
7-Day
28-Day
91-Day
N-OPC
180
21.7
51.4
69.1
82.1
88.3
N-B04
249
4.1
33.3
55.6
79.9
88.4
N-B08
230
6.9
41.1
65.7
89.6
96.0
N-B12
127
12.8
36.8
53.8
65.1
73.7
N-SF
195
22.1
47.0
65.1
86.5
98.2
H-OPC
189
13.2
53.8
64.7
76.1
81.4
H-B04
247
---
30.5
53.3
72.5
83.0
-32-
H-B08 248 --- 30.4 58.6 80.6 87.6
H-B12
211
7.4
43.6
63.0
76.0
79.4
H-SF
210
14.9
49.1
62.1
76.0
92.9
Heat of hydration measurements were also made on six different cements, three
normal fineness (ordinary, moderate heat, and high early strength), and three high
fineness cements. As expected, increased fineness increases the heat of hydration (fig.
4.8). Heat of hydration measurements were also made on several blended cements
(fig. 4.9). In general, decreased portland cement content of the blend caused
decreased heat of hydration. Silica fume was particularly effective in reducing
hydration heat.
Fig. 4.5: Compressive strength of mortar of portland cement [17]
-33-
Fig. 4.6: Compressive strength of concrete (base cement: N-OPC) [17]
-34-
Fig. 4.7 Compressive Strength of Concrete (base cement: H-OPC) [17]
Fig. 4.8: Heat liberation of portland cement [17]
-35-
Fig. 4.9: Heat liberation of blended cement [17]
-36-
4.3 BLENDS CONTAINING SILICA FUME AND SEPARATELY GROUND AND
INTERGROUND FLY ASH
Giergiczny and Werynska [18] investigated the effects mechanical activation (grinding)
on performance of both Class C and Class F fly ashes in blended cement. The fly
ashes were ground separately in a laboratory ball mill for 15, 30, and 60 minutes. The
ground fly ash was then blended with portland cement. Blends containing either 30% fly
ash and 70% cement or 70% fly ash, and 30% cement were prepared. Additional
blends produced by intergrinding Class C fly ash and cement clinker were also
prepared. These blends were used to produce mortar cubes which were tested for
compressive strength. The compressive strength results indicated that Class C fly
ashes had a much greater potential for mechanical activation than Class F fly ashes
(Table 4.5). The ground Class C ash displayed increased strengths at all levels of
increased fineness, although the best performance was achieved at the intermediate
fineness of 559 m2/kg. The performance of the 30% Class C blend at this fineness
was comparable to the plain portland cement. The grinding of Class F fly ash showed
very little effect on compressive strength. The strength of the mortar containing Class
F fly ash was maximum at an intermediate fineness of 543 m2/kg.
The blends containing 70% interground Class C fly ash exhibited compressive
strengths comparably to the control mixture. The blends containing 50% Class C fly
ash outperformed the control mixture by approximately 20% at all ages when ground to
a fineness of approximately 450 m2/kg. This increase in strength may be attributed, at
least in part, to an increase in fineness of the portland cement particles. It was also
-37-
found that gypsum is not needed to control the setting time of these blends as is
needed for portland cement.
Table 4-5: Strengths of Mortar Cubes Made from Blended Cements Containing Intergound Fly Ash [18]
Composition (%) Blaines Fineness of Ash (m
2/kg)
Compressive Strength (MPa)
Portland Cement
Class C Fly Ash
Class F Fly Ash
7-Day
28-Day
91-Day
100
0
0
305*
24.1
40.5
49.3
70
30
0
233*
10.6
17.7
25.6
70
30
0
464
12.2
27.8
37.1
70
30
0
559
23.2
38.7
48.5
70
30
0
744
20.7
37.5
47.8
30
70
0
599
18.5
32.4
39.7
30
70
0
346†
14.6
29.3
33.8
30
70
0
447†
30.3‡
42.6‡
48.7
50
50
0
337†
20.3
34.5
39.3
50
50
0
472†
30.3
48.7‡
59.0‡
70
0
30
295*
16.2
24.9
41.2
70
0
3
388
13.5
23.8
47.0
70
0
30
543
16.5
31.0
49.9‡
70
0
30
640
14.3
25.3
45.2
30
0
70
543
3.8
9.7
25.2
* Materials unground
-38-
† Interground with portland cement clinker rather than portland cement, fineness represents fineness of ground clinker and fly ash
‡ Compressive strength exceeding control mixture strength
The authors concluded that grinding is an effective way to increase pozzolanic activity
of Class C fly ash. This was primarily attributed to the increased surface area of the
CaO grains. This probably led to an increase in hydration within the cement matrix due
to the formation of ettringite on the surface of the fly ash particles. The blended
cements produced by separate grinding or intergrinding were capable of producing
mortar strengths comparable to or greater than that achieved by mortar made with
portland cement.
4.4 BLENDED CEMENTS CONTAINING FINELY GROUND SAND AND
LECA-BY- PRODUCTS
Dubin [19] studied the effects of the replacing portland cement with finely ground silica
sand and LECA-by-product (dust derived from the manufacture of expanded clay). In
this investigation, various amounts of portland cement were replaced with these filler
materials. These materials were either interground or simply blended and used to
produce mortar cubes. A naphthalene-based superplasticizer was added to some
mixtures to reduce the water requirement. Compressive strengths of mortar cubes
made with the blended cement are shown in Table 4-6 and Fig. 4.10.
The results revealed that intergrinding can greatly improve the performance of blended
cements produced with sand, especially at early ages. The 30% interground sand
blend exhibited compressive strength values comparably to the control mixture at 28
-39-
days and exceeded the comparable unground blend by over 30% at all ages. Even
the blend containing 50% interground sand showed strengths which were comparable
to the control mixture after 180 days. The blend containing 30% LECA-by-product
showed the best results, with compressive strengths exceeding the control at 28 and
180 days.
The author concluded that both sand and LECA-by-product can be used to replace
30% or more of the portland cement to produce high strength concrete without reducing
the mechanical properties, provided that the blend is ground to a proper fineness.
Table 4-6 : Compressive Strengths of Mortar Cubes Produced Using Blended Cement Containing Finely Ground Sand and LECA-By-Product [19]
Mixture Number
Composition of Binder
Quantity (%)
W/B
Flow
Compressive Strength (MPa)
1-Day
28-Day
180-Day
1*
PC Filler-sand Superplast.
100.0 0.0 2.0
0.31
116
45.0
67.4
87.8
2*
PC Filler-sand Superplast.
70.0 30.0 1.4
0.32
108
19.6
43.2
65.0
3
PC Filler-sand Superplast.
69.0 29.6 1.4
0.31
116
34.5
61.9
85.6
4
PC Filler-sand Superplast.
49.5 49.5 1.0
0.28
116
28.1
57.5
82.5
5
PC Filler-LECA Superplast.
69.0 29.6 1.4
0.31
125
35.4
69.5
101.3
6*
PC Superplast.
100.0 0.0
0.41
112
31.3
53.9
72.0
-40-
7
PC Superplast.
98.0 2.0
0.28
106
57.2
88.0
-----
* Materials were not interground
-41-
(a) Real
(b) Relative
Fig. 4.10: Real and relative compressive strength: (a) Real; (b) Relative;
(Numbers of curves and bars are corresponding to numbers of
compositions in Table 4.6) [19]
-42-
4.5 PARTIAL AND FULL INTERGRINDING OF CEMENT CLINKER AND FLY ASH
Popovic and Tkalcic-Ciboci [20] studied the effect of partial and full intergrinding of
portland cement clinker and fly ash. Two grinding processes were compared. The
first method involved intergrinding the full amount of fly ash with cement clinker
(Process A). In the second method, the fly ash was first fed into an air separator, where
material finer than 45 μm, about 70% of the fly ash, was removed and added after
intergrinding the remaining coarse portion with the cement clinker (Process B). These
blends were ground to a Blaines fineness of 3550 ±100 cm2/g. The strength of these
blends were then evaluated according to Yugoslav (RILEM/ISO) standards. The
results are presented in Table 4-7.
Table 4-7: Comparison of Compressive Strengths Attained By Partial and Full
Grinding [20]
Blend
Proportions
Grinding Process
Blaines Fineness (cm
2/g)
Compressive Strength (MPa)
3-Day
7-Day
28-Day
Clinker Only
----
3530
39.3
48.1
57.1
20% Fly Ash
A
3590
32.8
41.3
47.2
50% Fly Ash
A
3620
19.1
24.3
32.9
20% Fly Ash
B
3575
32.2
43.0
46.8
-43-
50% Fly Ash B 3450 19.5 23.0 28.8
The results showed little difference in performance between the two grinding processes
used. However, it is estimated that the partial intergrinding process consumes 11% to
26% less energy compared to the full grinding. This is attributed to a more efficient
comminution of the clinker particles in the partial intergrinding process. The softer and
finer fly ash particles available in the full intergrinding process are thought to interfere
with the grinding of the clinker. For this reason the author concluded that partial
intergrinding can increase economy of the production process without sacrificing
performance.
4.6 ACTIVATION OF NATURAL POZZOLANS
Shi and Day [21] studied the effect of activation of blended cements made with lime
and natural pozzolans on strength of paste mixtures. The paste mixtures consisted of
80% natural pozzolan, 20% lime, and chemical activators. The natural pozzolan used
was a volcanic ash from La Paz, Bolivia. The lime was a commercial high-calcium
hydrated lime. The activators used were sodium sulfate (Na2SO4), flake calcium
chloride (CaCl2.2H2O), hemihydrate gypsum (CaSO4.0.5H2O), and sodium chloride
(NaCl). The authors designed an experimental program to obtain optimum
concentrations of these activators in blended cement. The concentration of the
activators varied in the range of 0-10%. An optimum dosage of 4% for sodium sulfate,
calcium chloride, and sodium chloride, and 6% for calcium sulfate was observed. (Table
4-8)
-44-
The mixture containing Na2SO4 (4%) showed the highest early strength development.
(Table 4-8). This mixture attained compressive strengths nearly three times that of
the control mixture at 3 days. At 180 days, the 4% Na2SO4 mixture attained a strength
of over 13.2 MPa, exceeding the control mixture by more than 50%. (Fig. 4.11) The
effect of the calcium chloride
(4%) was insignificant at 3 days, but after 28 days, the mixture containing 4% calcium
chloride showed the best performance of the four activators tested (Table 4-8).
Table 4-8: Compressive Strengths of Paste Mixtures Containing 70% Natural
Pozzolans, 30% Lime and Optimum Values of Four Activators [21]
Activator Used
Compressive Strength (MPa)
3-Day
7-Day
28-Day
90-Day
180-Day
None (control)
2.80
5.20
6.60
8.10
8.90
4% Sodium Sulfate
7.80
9.10
12.40
13.00
13.20
4% Calcium Chloride
2.70
8.00
15.20
15.60
16.20
6% Calcium Sulfate
------
4.00
10.90
14.00
15.80
4% Sodium Chloride
------
4.90
7.20
9.20
10.00
The mixture containing blended cement with 6% calcium sulfate did not attain sufficient
strength to be tested until after 7 days. The rate of strength gain was slow due to
addition of this activator. The effect of inclusion sodium chloride as activator was found
to be small compared to the activators tested (Table 4-8). In addition, several mixtures
-45-
including various combinations of two or more activators were also tested. However,
no combination of activators proved to be as effective as the activators used
individually. Based on the results obtained, the author recommended a dosage of 4%
for both sodium sulfate and calcium chloride activators to obtain the best results. The
sodium sulfate was found to be the most effective at early ages, where as the calcium
chloride showed the best results at later ages.
-46-
Fig. 4.11 Effect of Na2SO4 dosage on strength development of LP pastes [21]
4.7 GYPSUM ACTIVATED FLY ASH BLENDS
Aimin [22] and Sarkar investigated the influence of gypsum (CaSO4) activation on
portland cements containing fly ash. In the study, two mortar mixtures containing
portland cement, Class F fly ash, and gypsum were compared to a control mixture as
well as mixtures containing portland cement and Class F fly ash without gypsum, see
Table 4-9. The fly ash mixtures containing gypsum outperformed the mixtures without
gypsum at two replacement levels tested (Table 4-9). However, the control mixture
showed higher strength than the mixtures tested with or without gypsum (Table 4-9).
The authors concluded that the addition of gypsum is beneficial, but further evaluation
of proportions and composition should be performed in order to derive better results.
Table 4-9 : Compressive Strengths of Mortar Mixtures Containing Class F Fly Ash
and Gypsum
Mixture
Compressive Strength
1-Day
3-Day
7-Day
28-Day
100% PC
9.10
20.20
27.50
38.5
70% PC and 30% FA
6.10
14.80
22.50
31.2
70% PC, 30% FA, and
6.20
14.90
19.80
35.5
-47-
3% G
40% PC and 60% FA 2.10
7.60
10.00
16.20
40% PC, 60% FA, and
6% G
1.90
4.60
6.80
21.00
Figure 4.12: Compressive strength of mortar containing portland cement (c), Fly
Ash (F) and Gypsum (G) [22]
-48-
4.8 ACTIVATION OF SLAG BLENDS
Wu et al. [23] studied the activation of slag cements using sodium sulfate (Na2SO4),
potassium aluminum sulfate (KAl(SO4)2.2H20), and calcium aluminate cements (AC).
In the study, mortar mixtures containing 30% slag, 70% portland cement, and various
chemical activators were compared to a similar unactivated slag mixture and a control
mixture containing only portland cement. The results revealed that at early ages, a
combination of 2% calcium aluminate cement and 2% sodium sulfate provided the best
activation. This mixture attained compressive strengths nearly equal to the control
mixture at 1 day and exceeded the control mixture strength at 3 days. At 7 days and
beyond, 1.5% sodium sulfate and 0.5% potassium aluminum sulfate provided the best
activation, with strengths exceeding the control mix at all ages beyond 7 days. All
other activated slag mixtures tested exceeded the strength of the control mixture at and
beyond 28 days (Table 4-10).
Table 4-10: Compressive Strengths of Mortar Cubes Produced with Ground Granulated Blast-Furnace Slag and Various Chemical Activators [23]
Mixture
Compressive Strength (MPa)
-49-
1-Day
3-Day
7-Day
28-Da
y
90-Day
100% OPC
25.40
27.17
31.80
36.39
41.24
70% OPC and 30% BFS
18.62
23.76
30.69
40.00
43.64
70% OPC, 30% BFS,
1.5% Na2SO4, and 1.5% KAl
22.82
25.78
35.95
41.99
52.23
70% OPC, 30% BFS,
2% AC, and 2% Na2SO4
24.89
28.07
32.71
41.50
46.51
4.9 BINDERS CONSISTING OF 100% ACTIVATED SLAG
Douglas and Brandstetr [24] conducted research on the activation of ground granulated
blast-furnace slag in an attempt to completely eliminate the need for cement in the
hydration process. In their study, strengths of mortar cubes made with 100% portland
cement were compared to activated slag mixtures using no portland cement. All the
slag mixtures were activated with a sodium silicate solution. The following additional
activators and supplementary materials were also used in an attempt to increase
performance: calcium hydroxide (Ca(OH)2), sodium sulfate (Na2SO4), portland
cement, lime, and silica fume. The test results are presented in Table 4-11.
The slag mixture activated by only sodium silicate (Mix 2) showed 28-day strengths
exceeding the control mixture by more than 150%, but did not attain sufficient strength
to be evaluated at 1 and 7 days (Table 4-11). The sodium silicate activated slag
mixtures incorporating 8% silica fume and 2% Ca(OH)2 (Mix 3) and the 5% portland
-50-
cement mixture (Mix 4) displayed improved strengths. However, 1-day strengths of
these mixtures were considerably lower than the control mixture (Table 4-11). The
sodium silicate activated slag mixture containing 2% lime and 1% sodium sulfate (Mix
5) exhibited an improved 1-day strength, nearly equal to the control mixture. This
mixture, with the addition of 8% silica fume (Mix 6), showed the highest early
compressive strength. This mixture attained one day strength of 17.2 MPa, exceeding
the control mixture by 20%. The 28-day strength of this mixture was lower than the
other activated mixtures, but still outperformed the control mixture.
-51-
Table 4-11 : Compressive Strengths of Mortar Cubes Containing Activated Slag [24]
Mix No.
Mixture Content
Compressive Strength (MPa)
1-Day
7-Day
28-Day
1
100% Portland Cement
14.1
31.4
38.9
2
100% Slag
-----
----
65.2
3
100% Slag + 8% Silica Fume
+ 2% Ca(OH)2
8.5
48.9
74.3
4
100% Slag + 5% Portland
Cement
2.4
35.9
59.3
5
100% Slag + 2% Lime +
1% Na2SO4
12.0
43.9
62.0
6
100% Slag + 2% Lime + 1% Na2(SO)4 + 8% Silica
Fume
17.2
29.9
47.0
* All slag mixtures were activated with a sodium silicate solution consisting of
10.6% Na2O and 25.6% SiO2., with 6.9g Na2O per 100g of binder.
4.10 DURABILITY OF MATERIALS CONTAINING BLENDED CEMENT
Al-Amoudi et al. [25] studied the performance of plain and blended cements in high
chloride-sulfate environments. Performance of blends containing either 20% Class F
fly ash, 60% ground granulated blast-furnace slag or 10% silica fume were compared to
ordinary portland cement. Using the above cements, mortar cubes were cast to
evaluate strength loss when exposed to the high chloride-sulfate environments.
-52-
Concrete specimens were also prepared to evaluate steel reinforcement corrosion.
These specimens were exposed to two sulfate-chloride solutions, one with low sulfate
concentration with 0.55% sulfate and 15.7% chloride and the other with high sulfate
concentrations with 2.1% sulfate and 15.7% chloride. The compressive strengths of
mortar cubes were evaluated at the ages of 3 and 6 months. The reinforcement
corrosion in the concrete specimens was monitored monthly by running a polarization
scan in the range of ±250 mV of the free potential. The results are represented in
Table 4-12 and Figures 4.12 and 4.13.
As can be seen from Table 4.12 , each of the blended cements exhibited better results
compared to Type I portland cement. The least amount of strength reduction due to
sulfates was experienced by the silica fume blend at low sulfate-chloride concentrations
and by the Class F fly ash at high concentrations. The silica fume blends exhibited the
least amount of corrosion of reinforcement among all the blends tested. The fly ash
and ground granulated blast-furnace slag blends also outperformed the ordinary
portland cement. It should also be noted that mortar cubes containing both FA and SF
achieved higher strengths than those containing only PC after 28 days when cured
under normal conditions.
The authors concluded that blended cements containing Class F fly ash, silica fume or
ground granulated blast-furnace slag can provide increased durability when exposed to
sulfate-chloride environments. The silica fume blends were found to be exceptionally
effective in reducing corrosion of reinforcing bars.
-53-
Table 4-12: Results of Durability Testing of Blended Cements containing Ground
Granulated Blast-Furnace Slag, Silica Fume, and Fly Ash [25]
Material
Utilization Rate, %
Reduction in Strength, %
Corrosion Rate
(μm/year)
Low
Sulfate/Chlorid
e
High
Sulfate/Chlorid
e
Low
Sulfate/Chlorid
e
High
Sulfate/ Chloride
Portland Cement
100
21.3
19.8
83.57
54.1
Blast-Furnace Slag
60
9.91
15.0
19.05
17.83
Class F Fly Ash
20
12.18
10.92
22.81
22.7
Silica Fume
10
9.50
13.7
0.64
0.78
-54-
Fig. 4.13 Reduction in strength due to immersion in low sulfate-chloride [25]
-55-
Fig. 4.14 Reduction in strength due to immersion in high sulfate-chloride
solution [25]
-56-
4.11 FREEZING AND THAWING, RESISTANCE OF BLENDED CEMENTS
Investigations of freezing and thawing resistance of concrete containing blended
cements have yielded mixed results. Marzouk [26] reported that blended cements
containing 12% Class F fly ash and 8% silica fume produced concrete with excellent
freezing and thawing resistance. In his investigation, nearly 500 cycles were applied
before a considerable reduction in the dynamic modulus of elasticity was observed.
ASTM C 666 considers a dynamic modulus of elasticity reduction of 40% after 300
cycles to be acceptable. Nasser and Lai [27], however, reported that blended cements
incorporating 50% Class C fly ash displayed greatly reduced resistance to freeze-thaw
degradation, despite decreased permeability of concrete. Johnson [28] suggested that
blends containing 42% Class C fly ash and 15% micro silica exhibit performance
comparable to ordinary portland cement concrete, provided that adequate air
entrainment, and a good quality aggregate are used.
4.12 RESISTANCE TO REINFORCEMENT CORROSION Of CONCRETE MADE
WITH BLENDED CEMENTS
In general, studies have shown improved resistance to reinforcing corrosion when
mineral admixtures are used. The same effect is anticipated due to the use of blended
cement made with these admixtures. Torii and Kawamuru [29] reported improved
corrosion resistance of concrete made with fly ash, blast-furnace slag, or silica fume.
This was attributed to a reduction in permeability, which restricted the infiltration of
water, air and chloride ions in concrete, all of which are required for corrosion.
Maslehuddin et al. [30] also reported similar results. Their investigation demonstrated
that for a given strength level blends incorporating blast-furnace slag, Class F fly ash, or
-57-
natural pozzolans provided improved resistance to reinforcement corrosion compared
to concrete made with portland cement alone.
4.13 SULFATE ATTACK AND ALKALI/AGGREGATE REACTION RESISTANCE
OF BLENDED CEMENT CONTAINING CONCRETE
Numerous investigations [23,27,31] have been performed to evaluate concrete
resistance to sulfate attack when fly ash and blast-furnace slag are added to concrete.
It is well accepted that these materials can greatly improve resistance to sulfate
attack. This increased sulfate resistance is primarily attributed to the decreased
availability of the calcium hydroxide ions in the cement paste matrix to react with the
alumina-containing hydrates (C-S-H products). Also, decreased permeability
decreases the penetration of the sulfate ions into concrete. Class F ashes are
particularly effective in reducing sulfate attack due to their higher rate of consumption of
calcium hydroxide ions caused by their low-calcium content [23,27,31].
The use of blended cements also has a considerable potential to reduce the effects of
alkali/aggregate reaction. Like deterioration due to sulfate attack, alkali/aggregate
reaction is slowed by a reduction of available calcium hydroxide and decreased
permeability [32, 33].
-58-
Section 5
SUMMARY AND CONCLUSIONS
The production of portland cement consumes large amounts of energy. This energy
consumption adds to its production cost and is responsible for the emissions of large
amounts of air pollutants. The production of blended cements incorporating industrial
by-products will reduce the need of portland cement. This, in turn, provides many
economical and environmental benefits. Use of by-product materials in production of
blended cements not only provides these benefits, but also improves properties of
portland cement to a signification extent. Therefore, this research project was
undertaken to develop manufacturing technology for production of low-cost,
high-performance, blended cement incorporating industrial by-product materials. This
manuscript includes only the state - of - the - art information on blended cements.
The by-product materials such as fly ash, silica fume, slag, finely ground silica sand,
etc. can be used to produce blended cements. Of these materials, blast furnace slag
offers the greatest rate of utilization, with feasible cement replacement rates exceeding
70%. The production of useable slag, however, provides less energy savings than
most other supplementary materials. Silica fume provides excellent performance, but
due to its high cost and increased water requirements, it is only used in small amounts,
generally less than 10%. Coal combustion by-products including fly ash are relatively
abundant, and requires little or no additional processing when used. Fly ash is
generally less effective than slag. Utilization rates can range between 15% and 50%.
-59-
The properties of fly ash from vary depending upon source and type of fly ash. There
are many other supplementary materials utilized in blended cements including finely
ground silica sand and other inert filler materials. Additionally, chemical activators,
generally salts of weak acids and strong bases, can be used to increase performance
of these materials to a marked extent. These may include calcium hydroxide ( Ca
(OH)2), sodium hydroxide (Na OH), sodium sulfate (Na SO4), calcium chloride (Ca Cl2),
sodium carbonate (Na2 CO3), sodium silicate (Na2O - SiO2), etc. Past investigations
[22,23,24] have shown optimum concentrations for some activator such as Na2SO4,
CaCl2 2 H2O, CaSO4, and CaCl2, 2H2O in blended cement in the range of
4 - 6%.
The performance characteristics and cost of blended cements are also influenced by
the method of production used. Ingredients of blended cement can be interground,
separately ground, and blended, or simply blended. Several grinding techniques are
also available, including ball mills, roller mills, and jet mills. The manufacturing
technique which provides optimum performance and economy is dependent upon the
performance and interaction characteristics of the combination of materials used.
Hinczak et al. [16] concluded that concrete mixtures made with ternary and quaternary
cement systems, consisting of combinations of portland cement, blast furnace slag, fly
ash, and silica fume showed lower amounts of heat of hydration compared to control
mixture containing only portland cement.
-60-
Numerous studies have also shown that properly produced and utilized blended
cements can also provide increased durability of concrete and mortar containing them.
The use of blended cements in concrete generally produces a more dense, less
permeable concrete structure compared to the concrete containing portland cement
alone. In general, concrete made with blended cement exhibit reduced permeability
and increased resistance to freezing and thawing, sulfate attack, corrosion of the
reinforcement, alkali - aggregate reaction, etc.
-61-
Section 6
REFERENCES
6.1 References Cited 1. Davidovits, J., "CO2-Greenhouse Warming! What future for Portland Cement?",
Proceedings-Emerging Technologies Symposium on Cement and Concrete in the Global Environment, Portland Cement Association, Chicago, IL, 1993.
2. Schmidt, M., "Reduction of Energy Consumption and Emissions by Using High
Quality Blended Cements for Concrete",Proceedings of the Emerging Technologies Symposium on Cement and Concrete in the Global Environment, Portland Cement Association, Chicago, IL, 1993.
3. Lea, L. M., "The Chemistry of Cement and Concrete", Bell and Blaine Ltd., Great
Britain, 1970, 727 pages. 4. Ramme, B., "Ash Utilization at Wisconsin Electric", Proceedings of the
CBU/CANMET International Symposium on the Use of Fly Ash, Silica Fume, Slag, and Other By-Products in Concrete and Construction Materials, Milwaukee, WI, 1992.
5. Luther, M. and Mikols, W., "Ternary and Quaternary Concrete Mixtures
Containing GGBF Slag", Proceedings of the CBU/CANMET International Symposium on Concrete Technology for the 21st Century, Milwaukee, WI, 1992.
6. Lessard, S., Aitcin, P. C., and Regourd, M., "Development of a Low Heat of
Hydration Blended Cement", ACI SP 79, 1986, pp 747-763. 7. Malhotra, V. M., "The Use of Fly Ash, Slag, Silica Fume, and Rice-Husk Ash in
Concrete: A Review", CANMET, Mineral Sciences Laboratories Division Report MSL 92-70, September 1992.
8. Eldarwish, I. A., "The Use of Blended Cement in Concrete", Proceedings of a
Symposium Appropriate Building Materials for Low Cost Housing, African Region : Held in Nairobi, Kenya, 1983.
9. Loedolff, G. F., "Partial Replacement of Cement with Fly Ash - Optimum Blends",
Ash: A Valuable Resource, Vol. 2, February, 1987, pp. 1-9. 10. American Society for Testing and Materials, "Annual Book of ASTM Standards",
Vol. 04.01, Philadelphia, PA, 1993. 11. Ramachandran, V. S., and Mailvaganam N. P., "New Developments in Chemical
Admixtures", CANMET, Advances in Concrete Technology, 1992, pp. 859-898.
-62-
12. Mantel, D. G., "The Manufacture, Properties and Applications of Portland Cements, Cement Additives and Blended Cements", The Penrose Press, 1991, pp. 4-14.
13. Chopra, S. K., and Narang, K. C., "Blended Cements-Manufacturing Process
Technologies", Chemical Age of India, Technical Press Publications, Bombay, India, 1982.
14. Juhasz, A. Z., "Mechanical Activation of Minerals by Grinding: Pulverizing and
Morphology of Particles", Halsted Press, New York, 1990, pp. 241. 15. Suprenant, B., and Papadopolous, G., "Phase I - Evaluating Fly Ash Content of
Portland-Pozzolan Interground Cement", Report # FL/DOT/RMC/0422-2580, College of Engineering, University of South Florida, September, 1989.
16. Hinczak, I., Roper, H., and South, W., "Ternary and Quaternary Cement
Systems", Supplementary Papers, Fourth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, 1992, pp. 33 - 44.
17. Shizawa, M., Joe, Y., Kato, H., and Morita, T., "Study on Hydration Properties of
Blended Cement for Ultra-High Strength Concrete", Supplementary Papers, Proceedings of the Fourth CANMET/ACI International Conference on the use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, 1992, pp. 987-1003.
18. Giergiczny, Z., and Werynska, A., "Influence of Fineness of Fly Ashes on Their
Hydraulic Activity", Proceedings of the Third International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, ACI SP-114, Vol. 1, 1989, pp.97 - 115.
19. Dubin, J., "Binder with Low Portland Cement Content for High Performance
Concrete", Proceedings of the ACI International Conference on High Performance Concrete, ACI SP 149, Singapore, 1994, pp. 283-295.
20. Popovic, K., and Tkalcic-Ciboci, B., "Separate Grinding of PC Clinker Versus
Intergrinding with Fly Ash", Supplementary Papers, Proceedings of the Third CANMET/ACI International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Trondheim, Norway, 1989, pp. 252 - 258.
21. Shi, C., and Day, R., "Chemical Activation of Blended Cements Made with Lime
and Natural Pozzolans", Cement and Concrete Research, Vol. 23, No. 6, November 1993, pp.1389-1396.
-63-
22. Aimin, X., and Sarkar, S.L., "Microstructural Study of Gypsum Activated Fly Ash Hydration in Cement Paste", Cement and Concrete Research, Vol. 21, No. 6, November 1991, pp. 1137-1147.
23. Wu, X., Jiang,W., and Roy D., "Early Activation and Properties of Slag Cement",
Cement and Concrete Research, Vol. 20, No. 6, November 1990, pp. 961-974. 24. Douglas, E., and Brandstetr, J., "A Preliminary Study on the Alkali Activation of
Ground Granulated Blast-Furnace Slag", Cement and Concrete Research, Vol. 20, No. 5, September 1990, pp. 748-756.
25. Al-Amoudi, O., Rasheeduzzafar, Abduljauwad, S. N., and Maslehuddin, M.
"Performance of Plain and Blended Cements in High Chloride-Sulfate Environments", Supplementary Papers Proceeding of the Second CANMET / ACI International Conference on Durability of Concrete, Ottawa, 1991.
26. Marzouk, H., "Durability of High-Strength Concrete Containing Fly-Ash and Silica
Fume ", Serviceability and Durability of Construction Materials, American Society of Civil Engineers, New York, 1990, pp. 1026-1038.
27. Nasser, K. W., and Lai, P. S. H., "Effect of Fly Ash on the Microstructure and
Durability of Concrete", Serviceability and Durability of Construction Materials, American Society of Civil Engineers, New York, 1990, pp. 688-697.
28. Johnson, C., "Effects of Micro silica and Class C Fly Ash on Resistance of
Concrete to Rapid Freezing and Thawing and Scaling in the Presence of Deicing Agents", Proceedings of the Katharine and Bryant Mather International Conference on Concrete Durability, ACI SP-100, Vol. 2, Detroit, MI, 1987, pp. 416-428.
29. Torii, K., and Kawamura, M., "Chloride Corrosion of Steel Bars in Concretes
Containing Various Mineral Admixtures", Blended Cements in Construction, London, G.B.: Elsevier Applied Science, 1991.
30. Maslehiddin, M., Shamim, M., Al-Mana, A., and Saricimen, H., "Long-Term
Corrosion Resistance Characteristics of Concrete Made with Blast Furnace Slag", Fly Ash and Natural Pozzolans, Supplementary Papers-Third CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Ottawa, 1989.
31. Mehta, K. P., "Concrete Structure, Properties and Materials", Prentice-Hall, Inc.,
Englewood Cliffs, New Jersey, 1986. 32. Dunster, A. M., Dawano, H., and Nixon, P.J., "The Effect of Silica Fume to
Reduce Expansion due to Alkali/Silica Reaction in Concrete", Durability of Building Materials and Components, Proceedings of the Fifth International Conference, Brighton, U.K., Nov. 1990.
-64-
33. Lee, C., "The Effect of External Alkalies on Alkali-Silica Reaction", Supplementary Papers, Proceedings of the Third CANMET / ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Ottawa, Ontario, 1989.
ADDITIONAL REFERENCES
Taylor, H. F. W., "The Chemistry of Cements", Academic Press, London and New York, 1964. Davidovits, J. "High-Alkali Cements for 21st Century Concretes", Concrete Technology: Past, Present, and Future, Proceedings of V. Mohan Malhotra Symposium, ACI SP-144, 1994, pp. 447-482. Nagasaki, S., "Mineral Admixtures in Concrete: State of the Art and Trends", Concrete Technology: Past, Present, and Future, Proceedings of V. Mohan Malhotra Symposium, ACI SP-144, 1994, pp. 447-482. Berry, E. E., and Malhotra, V. M., "Fly Ash for Use in Concrete - A Critical Review", ACI Journal, March/April, 1980, pp. 59-73. Marsh, B. K., and Day, R. L., "Pozzolanic and Cementitious Reactions of Fly Ash in Blended Cement Pastes", Cement and Concrete Research, Vol. 18, 1988, pp. 301-310. ACI Committee 226, "Ground Granulated Blast-Furnace Slag as a Cementitous Constituent in Concrete", ACI Materials Journal, July-August, 1987, pp. 327-342. Duda, A., and Bauwesen, A,, "Hydraulic Reactions of LD Steelwork Slags", Cement and Concrete Research, Vol. 19, 1989, pp. 793-801. Mantel, D. G., "Investigation into the Hydraulic Activity of Five Granulated Blast Furnace Slags with Eight Different Portland Cements", ACI Materials Journal, September-October, 1994, pp. 471-477. Cairnes, T. H., Pitman, F. S., and Crawford, M. S., "Ordinary Portland Cement and Blended Slag Cement Concretes - A Field Comparison", Symposium on Concrete, 1983 : "The Material for Tomorrow's Demands", Perth, W.A., 1983, pp. 29-36. Regourd, M., and Mortureux, B., "Use of Condensed Silica Fume as a Filler in Blended Cements", ACI SP 79-46, Vol. 2, 1983, pp. 848-865.
-65-
Larbi, J. A., Fraay, A. L. A., and Bijen, J. M., "The Chemistry of the Pore Fluid of Silica Fume-Blended Cement Systems", Cement and Concrete Research, Vol. 20, No. 4, 1990, pp. 506-516. Grutzeck, M. W., Atkinson, S., and Roy, M. R., "Mechanism of Hydration of Condensed Silica Fume in Calcium Hydroxide Solutions", ACI SP 79-33, Vol 2., 1983, pp. 643-664. Wang, M. L., and Ramakrishnan, V., "Evaluation of Blended Cement, Mortar and Concrete Made from Type III Cement and Kiln Dust", Construction & Building Materials, Vol. 4, No. 2, June 1990, pp. 78-85. Ambroise, J., Dejean, J., Foumbi, J., and Pera, J., "Metakaoline Blended Cements Improve GRC Durability and Ductility", Construction and Building Materials, Vol. 3, No. 2, 1989, pp. 73-77. Caldarone, M., Gruber, K., and Burg, R. G., "High-Reactive Metakaolin: A New Generation Mineral Admixture", Concrete International, November 1994, pp. 37-40. Osback, B., "On the Influence of Alkalis on Strength Development of Blended Cements", The Chemistry and Chemically-Related Properties of Cement, British Ceramic Society, 1984. Huizer, A., Day, R. L., and Shi, C., "Activation of Natural Pozzolanas for Increased Strength of Low-Cost Masonry Units", Proceedings of the 6th Canadian Masonry Symposium, University of Saskatchewan, June 15-17, 1992, pp. 499-507. Fidjestol, P. and Frearson, J., "High-Performance Concrete Using Blended and Triple Blended Binders", Proceedings - High Performance Concrete, ACI International Conference, Singapore, 1994, pp. 135-160. Blair, J. B., Hollingsworth, D., Hopkins, D. S., Hunter, C., Munro, R. E., Dewal, J., "Blending of Slag Cement with Type C and Type F Fly Ash for Concrete", Proceedings from CBU/CANMET International Symposium, November 5 and 6, 1992. Comta, R. U., Massazza, F., "Some Properties of Pozzolanic Cements Containing Fly Ashes", SP 79, Vol. 1, 1986, pp. 335-353. Bernshausen, H., "Pfa in Blended Cement - Its Production and Application", World Cement, Vol. 19, No. 6, 1988, pp. 250-255. Neville, A. M., "Properties of Concrete", Halsted Press, New York, 1973. Woods, H., "Durability of Concrete Construction", American Concrete Institute, Detroit, MI, 1968. rep-256