This document discusses pozzolanic materials and fly ash. It defines pozzolanic materials as finely powdered materials that can be added to lime or cement mortar to increase durability through chemical reactions. The document outlines various natural and manufactured sources of pozzolanic materials including volcanic ash, burnt clay, slag, ashes of organic origin, and certain sands. It also discusses the properties and reactivity of pozzolans and their effects on mortar and concrete qualities like strength and stiffness. Additionally, the document defines fly ash as a byproduct of burning coal used in concrete for its cementitious properties. It notes the two main types of fly ash, Class C and Class F, and outlines fly ash's

1. POZZOLANIC AND FLY ASH
MODULE
ME CIVIL (REGULAR)
(CONSTRUCTION TECHNOLOGY AND MANAGEMENT)
Course Coordinator:
Dr Hemant Sood
Submitted by:
Ankaj Kumar
Roll No- 202304

2. POZZOLANIC MATERIALS AND FLY ASH
1.1 INTRODUCTION
A simple everyday definition of 'pozzolan' could be 'a finely powdered material which can be
added to lime mortar (or to Portland cement mortar) to increase durability. A more formal
definition is given by ASTM C618-84 as 'a siliceous or siliceous and aluminous material which,
in itself, possesses little or no cementitious value but which will, in finely divided form in the
presence of moisture, react chemically with calcium hydroxide at ordinary temperature to form
compounds possessing cementitious properties.
1.2 MODULE OUTCOME
 To know about the pozzolanic material importance in civil engineering.
 To know various types of pozzolanic materials.
 To about importance of fly ash in civil engineering field.
1.3 SOURCES AND TYPES OF POZZOLANIC MATERIALS
(a) Natural, very finely divided, Highly Reactive Materials of Volcanic Origin
These materials are formed from a combination of minerals, (mainly consisting of silica and
alumina with smaller and variable quantities of other minerals containing calcium, magnesium,
iron, potassium, and sodium), ejected from volcanoes in the form of very finely divided
vitreous material. Other vitreous volcanic material, such as basalt, may have mild pozzolanic
properties if very finely ground.
(b) Low Temperature Calcined Products in Various forms
Pozzolanic additives derived from lightly fired and finely crushed clay products, such as clay
tile or brick, were used by the Romans and combinations of non-hydraulic lime and low
temperature brick dusts have been used over a long period of time. Similar specifications are
successfully employed in modern conservation practice where additional set and durability are
required without seriously reducing the permeability and flexibility of the mortar.
Bodies such as English Heritage have promoted the use, particularly for conservation work, of
low temperature clay pozzolans in non-hydraulic mortars. Current advice is that the material
should be derived from clay fired at temperatures below 950 °C, and ground to a range of
particle sizes between 38 and 600 microns.Modern sources of potentially suitable material
include reject bricks and tiles from traditional producers, which can be crushed in a roller pan

3. mill. Some manufacturers also produce low temperature purpose-made dusts for sale as
pozzolans.
(c) Clay or Kaolin Products specially Manufactured as Pozzolans
These are produced primarily for use with Portland cement and all currently available technical
and performance data relates to their use in that context. These materials are highly reactive
and combine readily with calcium hydroxide to form calcium silicate hydrates and calcium
alumino-silicate hydrates. Their effect on the performance and characteristics of lime mortars
is not currently known but, subject to adequate investigation and trials, it is possible that their
use could be extended into this field.
Also falling into the category of fired clays is the material known as HTI (high temperature
insulation) powder. This was widely specified in the 1980s but has now largely been
superseded by lower temperature materials which are thought to be more consistent in their
performance.
(d) Mineral Slag
Furnace slag is a vitrified material, produced as a by-product of processes such as smelting,
and requires grinding to convert it to a reactive material. It contains silica, alumina, lime and
other minerals in various proportions and, in modern practice, is more commonly used as an
additive in Portland cement concretes. Historically, forge scale and iron-rich slag, known as
minion, were also used.
(e) Ashes of Organic Origin
Coal cinders generally have an acceptable balance of silica and alumina, and have been used
historically as a pozzolanic additive, but their physical structure tends to weaken the mortar
and to absorb excessive water. Coal ash is widely used, in the form of PFA (pulverised fuel
ash) as an additive to cementitious mortars and in lime-based grouts. The use of coal-based
products carries a risk of sulphate contamination and the materials should always be selected
from low sulphate coals. The residue of fuels from lime burning, whether from coal-, coke-, or
wood-fired kilns, known as lime-ash, is well known historically as a pozzolan and is still
available. Other vegetable ashes, such as rice husk ash, are used as pozzolans in other parts of
the world. Bone ash is also known to have been used.
(f) Certain Natural Sands and Crushed Rock Products
Certain types of sand, such as argillaceous (clayey) sands containing high proportions of schist,
basalt, feldspar and mica, can have mildly pozzolanic properties. Whilst these sands are not
generally specified for modern lime-based mortars it may be useful to recognize that,
historically, in certain localities, their use could have influenced the nature of local lime

4. mortars. Finely crushed rock products from sources containing an appropriate balance of
minerals may also produce a mild pozzolanic effect. Traditionally, mortars were often
produced using techniques which brought the sand into contact with hot slaking lime, and it is
possible that this heat would have encouraged any potential for a mild pozzolanic reaction
between sand and lime.
1.4 Properties and reactivity of pozzolans and their influence on
the quality of mortars and concrete
Industrial and agricultural waste with pozzolanic properties is used as partial binder
replacement in building materials to enhance sustainability and improve the service life of
structures. This leads to economic and environmental benefits such as recycling waste, whose
disposal threatens the environment, and reducing cement/lime content, with the subsequent
drop in energy consumption, non-renewable raw material consumption and CO2 emissions.
Pozzolan properties including particle size, specific surface, chemical and mineral
composition, amorphousness and water demand affect their reactivity, and consequently the
setting and strength of composites. Pozzolanic reaction is not as slow as it is generally believed;
and that hydrates are clearly present only after 24 hours of curing, forming continuous networks
throughout the paste after 14 days. It was also evidenced that pozzolans enhance the modulus
of elasticity making lime mortars progressively stiffer however, unlike most building materials,
enhanced stiffness and larger elastic regions are not coupled to increased brittleness, and the
mortars remain plastic, undergoing significant strain before failure even at high pozzolan
contents. The work has also evaluated and established a correlation between techniques that
measure reactivity (chemical and physical indices and portlandite consumption) and carried
out a comprehensive, comparative study of setting times and water demand for a range of
pozzolans.
1.5 FLY ASH
Fly ash is a byproduct from burning pulverized coal in electric power generating plants. During
combustion, mineral impurities in the coal (clay, feldspar, quartz, and shale) fuse in suspension
and float out of the combustion chamber with the exhaust gases. As the fused material rises, it
cools and solidifies into spherical glassy particles called fly ash. Fly ash is collected from the
exhaust gases by electrostatic precipitators or bag filters. The fine powder does resemble
portland cement but it is chemically different. Fly ash chemically reacts with the byproduct
calcium hydroxide released by the chemical reaction between cement and water to form

5. additional cementitious products that improve many desirable properties of concrete. All fly
ashes exhibit cementitious properties to varying degrees depending on the chemical and
physical properties of both the fly ash and cement. Compared to cement and water, the chemical
reaction between fly ash and calcium hydroxide typically is slower resulting in delayed
hardening of the concrete. Delayed concrete hardening coupled with the variability of fly ash
properties can create significant challenges for the concrete producer and finisher when placing
steel-troweled floors.
Types of Fly ash
Two types of fly ash are commonly used in concrete: Class C and Class F. Class C are often
high-calcium fly ashes with carbon content less than 2%; whereas, Class F are generally low-
calcium fly ashes with carbon contents less than 5% but sometimes as high as 10%. In general,
Class C ashes are produced from burning sub-bituminous or lignite coals and Class F ashes
bituminous or anthracite coals. Performance properties between Class C and F ashes vary
depending on the chemical and physical properties of the ash and how the ash interacts with
cement in the concrete. Many Class C ashes when exposed to water will react and become hard
just like cement, but not Class F ashes. Most, if not all, Class F ashes will only react with the
byproducts formed when cement reacts with water. Class C and F fly ashes were used in this
research project.
Application of Fly ash
Fly ash can be a cost-effective substitute for Portland cement in many markets. Fly ash is also
recognized as an environmentally friendly material because it is a byproduct and has
low embodied energy, the measure of how much energy is consumed in producing and shipping
a building material. By contrast, Portland cement has a very high embodied energy because its
production requires a great deal of heat. Fly ash requires less water than Portland cement and
is easier to use in cold weather. Other benefits include:
 Produces various set times
 Cold weather resistance
 High strength gains, depending on use
 Can be used as an admixture
 Considered a non-shrink material
 Produces dense concrete with a smooth surface and sharp detail
 Great workability
 Reduces crack problems, permeability, and bleeding

6.  Reduces heat of hydration
 Allows for a lower water-cement ratio for similar slumps when compared to no-fly-ash
mixes
 Reduces CO2 emissions
Disadvantages of Fly ash
Smaller builders and housing contractors may not be familiar with fly ash products, which can
have different properties depending on where and how it was obtained. Additionally, fly ash
applications may face resistance from traditional builders due to its tendency to effloresce along
with concerns about freeze/thaw performance. Other concerns about using fly ash in concrete
include:
 Slower strength gain
 Seasonal limitation
 Increased need for air-entraining admixtures
 Increase of salt scaling produced by higher proportions of fly ash
1.6 REFERENCES
[1] https://www.aboutcivil.org/sources-of-pozzolanic-materials.html
[2] https://www.tcd.ie/civileng/research/structures/materials/pozzolans.php
[3] https://www.concreteconstruction.net/how-to/materials/what-is-fly-ash_o
[4] Concrete Technology by M L Gambhir