Description
CHAPTER ONE
1.0. INTRODUCTION
The importance of understanding various types of materials used in Civil
Engineering is widely recognized. There has been tremendous increase in the
latest research and practical achievement to improve on concrete technology.
Free exchange for technical knowledge at international conferences in many
countries and worldwide exchange of technical paper, upgrading of internet
information on how concrete can be improved in a situation where needed and
bulletins has led to a general polling and shifting of information and recently to
the publication of many new code and standard. Concrete
is a composite material which is formed by mixing in good proportion, cement,
water, fine aggregate and coarse aggregate, air and at times admixture. Freshly
prepared concrete is called Wet or Green concrete. Concrete is used in
substructure and superstructure work in civil engineering, for a meaningful
work to take place in a construction industry, concrete must be available.
However, the properties and performance of this concrete are being influenced
by the introduction of some materials called admixture.
Admixtures have been in use almost since the inception of the art of
concreting. It is reported that the roman builders used oxblood as an admixture
in their concrete and masonry structure. Research has shown that oxblood is an
excellent air entraining agent. During the early part of this century it was a
common practice to add gold dust, soap to concrete as water proofing agent.
Admixtures are materials other than water, cement, aggregate and additives
like pozzolana or slag and fibre reinforcement, used as an ingredient of concrete
or mortar and added to the immediately before or during its mixing to modify or
alter one or more properties of the concrete in the plastic or hardened state.
Admixtures can also be said to be substances introduced into concrete mixes
in order to alter or improve the property of the fresh or hindered concrete or
both in general.
Admixtures are classified as either mineral admixture which may be
introduced as blended materials such as fly-ash (FA), silicate fume (SF), ground
granulated blast furnace slag (GGBS), meta kaolin (MK), and rice husk ash
(RHA) or chemical admixture which are typically added during the mixing
process of concrete production, its include accelerators, retarders, air entrainer,
plasticizer or water reducer, water proofers and pigments (colourants).
In view of the above facts the project title “the effect of admixtureson the
properties of concrete” is carried out with the aim of knowing the effect of the
various types of admixture used on the properties of concrete, in term of the
workability of concrete, setting time of concrete, durability of concrete and the
concrete strength. The test also compared the effect of various admixtures on
the setting to the hardening time of concrete as well as the slump and trowel test
to know the degree of workability.
The test is limited to selected admixtures as a result of time factor, likewise
the properties of concrete on which the test are based are limited but the most
important and most interesting area are selected such as limestone powder(LP),
sugar, groundnut shell ash(GSA) and cow bone ash(CBA).
1.1. STATEMENT OF THE PROBLEM
Not all admixtures are economical to employ on a particular project. Also
some characteristic of concrete, such as low absorption, can be achieved simply
by consistently adhering to high quality concreting practices.
The chemistry of concrete admixture is a complex topic requiring in depth
knowledge and experience. A general understanding of the options available for
concrete admixture is necessary for acquiring the right product for the project
base on the climatic condition and project requirement.
1.2. AIM AND OBJECTIVES OF THE STUDY
The aim of this project is to determine the effects of limestone
powder(LP),sugar, groundnut shell ash(GSA)and cow bone ash(CBA)
admixtures on the properties of concrete.
The objectives of the study are alighted below:
i. To know how admixtures affect concrete in term of its workability, setting
time, durability and strength.
ii. To enable one to know the cost of using the various admixtures.
iii. To be able to compare concrete with admixture and concrete without
admixture in term of their strength, workability.
1.3. JUSTIFICATION OF THE STUDY
Admixture has been in use for a very long time, suchas calcium
chloride to provide a cold-weather setting concrete. Others are more recent and
represent an area of expanding possibilities for increased performance. These
types of admixtures are available in two forms, which are mineral or chemical
admixture. Admixture like fly-ash, silicate fume, slag comes in category of
mineral admixture, while chemical admixtures are super plasticizers,
accelerator, water reducer, retarder and air entrainer.
Admixtures are used to modify the properties of concrete such as to
improve workability, curing temperature range, setting time, increase strength,
retard or accelerate strength development, reduce segregation, decrease or
reduce permeability, increase bond of concrete to steel reinforcement, increase
durability or resistance to severe condition of exposure. Generally, an admixture
will affect more than one properties of concrete and its effect on all the
properties of the concrete must therefore be considered.
Admixture may increase or decrease the cost of concrete by reducing cement
quantity required for a given strength changing the volume of the mixture, or
reducing the cost of concrete placing and handling operations. Control of setting
time of concrete may result in decreasing waiting time, repetition in the
preparation of concrete in a large construction and therefore eliminating
construction joint.
1.4. SCOPE OF THE STUDY
The scope and limitation of this project is basically the effect of admixture on
the properties of concrete. In view of the above facts, the extent at which some
of the admixture hamper or enhances the properties of concrete is a motivating
factor on this project. In this project limestone powder(LP), sugar, groundnut
shell ash(GSA), cow bone ash(CBA) will be considered. The first three are
retarding admixtures and consistency test of cement such as sieve analysis,
slump, and compressive strength etc. would be carried out on the samples.