Effect Of Admixtures On Properties Of Concrete

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 admixtures on 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, such as 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.