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Concrete is the one of the oldest construction materials created by human. It is used widely around the world in various forms, especially in building construction. Many people felt that concrete will be continued to be the primary building material for several decades.
Generally, the use of concrete as a building material is the most important element than other materials for most of building structures. The usage of concrete does have many advantages, either during the construction process until the use in the structures. This is because this material is easily available and can also provide a strong building structure as well as being effective in a cost construction.
However, the concrete as a building material has a certain disadvantages. Its physical characteristic which is brittle causes itself to be unable to meet the required strength in all conditions. Besides, concrete has a low tensile strength, low ductility, less stable volume, ratio of strength towards small weight, high permeability, high drying shrinkage and poor resistance to some chemicals.
Therefore, modifications must be made to improve the performance of concrete so that it can be used more effectively. In the line with current technology, there are many modifications being done to the concrete to improve and enhance the properties of concrete. The use of additives in the concrete mix is one of the technologies that have been used in the construction industry to improve the properties of concrete properties such as strength, workability, durability, bleed, creep and so on.
One of the attempts to improve these properties is to apply the polymer in the concrete. Concrete technological developments also give the different types of polymer additives that can affect the nature of concrete and its application.
Generally there are three types of polymerized concrete vary by method of production. The first group is polymer-modified concrete, the second group is polymer impregnated concrete, while the third group is polymer concrete. We will determine the characteristics of each of group of polymerized concrete.
To know about concrete and its characteristics
To know about polymer and its characteristics
To study about polymer that uses in concrete
To determine a group of polymerized concrete
INTRODUCTION TO CONCRETE
The usage of concrete today is the important element in a construction industry. In general, concrete is a material made from a mixture of cement, aggregates, sand and water at a specified rate or ratio designed. In certain event, an additive is mixed to produce a concrete with certain character. Mixture designs that commonly used, is defined as the compressive strength criteria in a period of 28 days and designed according to grade. For example, grade 30 of concrete has strength 30 N/mm2 at 28 days. (Blackledge, 1987)
Because of concrete is one of the most abundant materials used, manufacturing techniques of good quality concrete must be understood and carefully observed. The quality of concrete is dependent on the quality of the raw materials used, the mixture, the water-cement ratio, the way of mixing, the way to transfer, the way to piled (placing the concrete), how to compact the mixed concrete, the quality of the mold and the method of preservation.
If the raw materials used have low quality or the preparation which does not follow the rules that have been set, then as a result, concrete will be in low quality. Besides, it may result as the concrete cannot hold a load as expected. If this happens, the effect is very bad.
ELEMENTS IN CONCRETE
Cement is a material which has cohesive and adhesion properties that can bind rocks into a solid body. Cement is produced from a mixture of clay and limestone. In general, the production of cement is including clay and limestone that will be milled and heated up to be coal or clinker in the rotary burner. The clinker will be ground into fine dust and a little gypsum will be included at the end of mixing. (R.H Elvery, 1969)
There are many types of cement made in a factory for a particular purpose, and to meet the requirements of the course. The types of main cement are:
a. Ordinary Portland Cement
b. Modified Cement
c. Rapid Hardening Cement
d. Low Heat Cement
e. Sulphate Resisting Cement
The content ratio of chemical substances in various types of cement influences the properties and the name of the cement. Chemical composition of the Portland cement is shown in Table 1 and the major compounds of Portland cement are shown in Table 2. (M.S Shetty, 1986)
Table 1: Types of mixed oxide in Portland cement (Source: M.S Shetty, 1986)
Percentage from the net weight (%)
60.0 - 67.0
17.0 - 25.0
3.0 - 8.0
Iron oxide, Fe2O3
0.5 - 6.0
Magnesium oxide, MgO
0.1 - 4.0
Sulfur Trioxide, SO3
0.4 - 1.3
1.0 - 3.0
Table 2: Main compound in Portland cement (Source: M.S Shetty, 1986)
Name of chemical compound
Percentage of content (%)
Gypsum and others
Water is needed in concrete for hydration and workability of concrete. The water used must be free from excessive amounts of impurities because it will has an adverse effect on the process of hardening, volume stability, durability, discoloration and corrosion of reinforcement. Some of these impurities are acid, alkaline, sulfate, clay, chloride and others.
Different types of water available on earth are causing the need to find the water that can be used for concrete works. The water used for mixing concrete should be clean. It can be taken from any approved source. It should also be free from dirt and suspended solids, organic matter and sea salt. Water that containing algae is not suitable for concrete because algae is trap the air and high air content will reduce the strength of concrete. Increased algae from 0.09% to 0.23% will increase the air content of 10.6% and resulted in a reduction of concrete strength by 50%. (Mehta, 1991)
The use of sea water in reinforced concrete and prestressed concrete shall not be used. It will be a danger of corrosion of reinforcement due to chloride content in the water, even to the concrete as the friable disfigure work. (Mehta, 1991)
In the context of Malaysia, tap water can be used without problems because it is not only drinkable but assured quality and from an approved source.
Aggregate is an important ingredient in concrete. It also plays an important role in shaping the strong mixed concrete and resilient while reducing shrinkage and more economical. (M.S Shetty, 1986) In a concrete mix, gradation of aggregate not only limiting the strength of concrete, but the aggregate properties also have a significant effect on the durability, workability and behavior of concrete structures. (Neville, 1981)
There are two groups of aggregates which are the coarse aggregate and fine aggregate. Fine aggregate (sand) has a size less than 5 mm and coarse aggregate (usually called rock) has a size greater than 5 mm.
WORKABILITY OF CONCRETE
The strength of concrete at the rates specified mixture strongly influenced by the degree of compactness. Therefore, a very high workability of concrete is needed to produce a strong concrete. The term used is to describe the pleasures of workability of concrete that will be compacted. Cement content, an overall of aggregate grading and practical form of aggregates will affect the workability of concrete. (Blackledge, 1987)
The factors that affecting the workability of concrete are including cement, aggregates, water-cement ratio, additives, temperature and time. The tests that commonly used to measure the workability are debris test, compactness test and vee-bee test on consistency time (VB).
Workability of concrete can be said to be good if it fulfills the following characteristics:
Can be easily compacted to remove trapped air to achieve the strength and ruggedness.
Can be easily transported and placed by such methods as using trucks, carts and pumps.
Flow to every corner and fills the entire mold despite having the reinforcement structure closely.
Can produce a good finish during the mold was removed without having a blank spaces between the concrete like honeycomb.
STRENGTH OF CONCRETE
The strength of concrete is one of the important properties of concrete to provide a comprehensive overview on the quality of concrete because strength is directly related to the structure of hardened cement paste. (Neville, 1981)
In Figure 1, the strength of concrete increases with age and increase strength continues for some time. However, the concrete at 28 days old is used as a measure of strength. The increase in compressive strength of concrete is highly dependent on temperature and humidity during a level of hardening of concrete. Water-cement ratio is among the main factors that control the strength of the concrete.
Figure 1: Relationship between the strength of concrete and water-cement ratio
(Source: EngineeringIntro.com, 2012)
Besides taking into consideration the water-cement ratio, the strength of concrete is also very dependent on the method or process. For example, in the process of preparing the concrete, if there is a change in quality of ingredients that is mixed, then it will affect the strength of concrete produced which is same as concrete that add with additives.
TESTS ON CONCRETE
Tests on concrete are important in concreting work either before or after the concrete progress. Workability of concrete is very important in determining the strength and durability of concrete, as well as quality of materials used and the mixing ratio according to the specifications. The test that is usually done to measure the pleasure of work at construction sites and in the laboratory is debris test, compactness test and vee-bee consistency test (VB). (Civil Engineering Portal, 2012)
Meanwhile, to determine the strength of concrete, compressive tests were conducted on samples taken from the cube of concrete mix used for concreting work. The cubes of concrete are according to the specifications in the concrete compression testing procedure.
RELATIONSHIP BETWEEN COMPRESSIVE STRENGTH AND FLEXURAL STRENGTH OF CONCRETE
Compressive and tensile strength (bending) is associated closely linked. The ratio of compressive strength and tensile strength is dependent on the general level of the concrete strength. In other words, when the compressive strength is increased, flexural strength also increased but at a declining rate.
For Figure 2, the flexural strength generally is taken about one-tenth or 10% of the compressive strength but different aggregates cause this rate to change. Then the compression test is only a general guide to the strength of this tension or bending. There are several factors that may be associated with this condition. The tensile strength of concrete is more sensitive to the preservation of the less reasonable than the compressive strength of concrete.
Figure 2: Relation between flexural strength and compressive strength
(Source: A.K. Padmini, K. Ramamurthy, 2009)
Figure 3: Modulus of elasticity as a function of compressive strength
(Source: Federal Highway Administration (FHWA), 2006)
For Figure 3, compressive strength is also being expressed in modulus of elasticity of concrete. Few equations are considered to cover the whole data when many empirical equations for predicting modulus of elasticity have been proposed by many investigators. The mechanical properties of concrete are highly dependent on the properties and proportions of binders and aggregates which is one of the reasons that should be considered.
Polymers are the materials that most widely used in important technology in the 20th century. Besides, polymers also play an important role in daily life such as clothing, home appliances, automotive, communication technology and so on. Similarly, in metal and ceramic technology, the study of polymers has a concept of applications, which is to understand the concept in the manufacturing process, the structure of the physical and mechanical properties of the material formed.
In general, polymers are macromolecules that are formed when a large number of molecules or monomers that combines in such a chain. Monomers are acting in a small unit repeating the chemical reactions to form a long chain. A chain may occur in the form of linear or branched chain within three-dimensional.
STRUCTURE OF POLYMER
Polymer can be divided into several groups of structure such as linear polymer, branched polymer, star polymer, dendrimer polymer and cross-linked polymer. These structures are formed depending on the way carbon bond that owned by a polymer is formed.
C:\Users\Siti Rashidah\Desktop\solid state physics\LINEAR.gif
Figure 4: Linear polymer
Figure 5: Branched polymer
Figure 6: Cross-linked polymer
Figure 7: Star polymer
Figure 8: Dendrimer polymer
(Sources: Polymer Science Learning Center, 2005)
Figure 4 is showed a linear polymer. The monomeric units in linear polymer are linked linearly together but not in a long chain. For Figure 5, side chains of branched polymer are attached to the backbone of the molecular chain. Next, cross-linked polymer is a network of polymer chains which is in a formation of a 3D. In Figure 7, star polymer is a macromolecule having a small core of molecules (branch point) with branches radiating from the core. Lastly, in Figure 8, dendrimer polymer is a hyper-branched and mono-disperse molecules that give a good property due to its structure. (McGraw-Hill S&T Dictionary, 2012, Klajnert B. and Bryszewska M., 2001)
PROPERTIES OF POLYMER
Properties of the polymer mainly depend on the geometry of the polymer bond. There are three main types of polymer properties that have been identified as the thermoplastic properties, thermosetting and elastomeric.
Thermoplastic polymer is a polymer which must be diluted at a high temperature for processing and after cooling, the polymer material will retain to its shape. In addition, it also may be diluted again and formed into required shape without changing its original features. Usually it consists of a long chain linear polymer containing carbon atoms bond formed by covalent bonds. Many thermoplastic materials can be melted in the temperature range from 100 Â° C to 250 Â° C.
Elastomer polymer which is rubber is a polymer with elastic properties which can change its dimensions when subjected to tensile forces. When the tension is released, the polymer can be returned to its original dimensions. However, this elastic property will lose effect when subjected to high temperatures. Elastomeric polymer which first known is natural rubber latex extracted from the tropical rubber tree called as Hevea Brasiliensis through vulcanization with sulfur. This material consists of primary material which is poly (cis-isoprene) mixed with some other components, including proteins and fats. The structure of the repeat unit of poly (cis-isoprene) is shown in Figure 6.
Figure 9: Structure of repeat unit of poly (cis-isoprene)
(Source: Blackledge, 1992)
Thermoset polymer usually has a cross-bonding structure chain and it can be formed by reaction of heat or chemical. The nature of the thermoset polymers usually has a resistance to thermal reactions of stable and strong rigidity. However, thermoset polymers cannot melt at high temperatures but will rot and decompose.
POLYMER IN CONCRETE
There are three main groups of polymerized concrete. The main difference between the three groups is in terms of the preparation method. However, all of these three methods have the same objective which is to improve the general weaknesses in plain concrete. Besides, the advantages of the polymer itself are also the major selection criteria for this modifier agent. Polymer has good features such as the strength, elasticity, high adhesion properties and good durability. The main groups of the polymerized concrete are polymer concrete, polymer impregnated concrete and polymer modified concrete.
For this type of concrete, cement is replaced with the polymer material. Polymer concrete is made by adding a monomers or resin system together with aggregates. Polymerization reaction that occurs in the concrete will change monomers or resin system to a hardening of the polymer structure. It is also known as resin concrete. (Mehdi, 2011)
POLYMER IMPRAGNATED CONCRETE
Polymer impregnated concrete generated by absorbing the monomers into an already hardened concrete until it reached saturation in the concrete, in which all the pores, voids and cracks will be filled by the monomers. This process will be followed by the polymerization process. Porosity factor appearing in the concrete will influence the absorption of monomer.
The process of filling monomers into a concrete is done by means of concrete drying and heating to remove the water content in it. Later on, it is placed in a vacuum and submerged under certain pressure followed by a polymerization process with thermal catalytic method or gamma rays. (Fowler, 2012)
POLYMER MODIFIED CONCRETE
Polymer modified concrete is formed when Portland cement and aggregates are combined together during a mixing of polymer. Then, the concrete is cured in a moist chamber. Besides of being able to fill the pores of the air, it is able to form the polymer latex binder particles as well as in the role of the cement paste in concrete. This type of concrete as well is known as polymer Portland cement concrete (PPPC) and latex modified concrete. Usually, polymer modified concrete is always being used because of its method that is practical and easy to produce. (American Concrete Institute, 2009)
As a conclusion, we know about the concrete and its characteristics within its function in the construction as a main element/material. Besides, we also have studied about polymer, its characteristics, structures and as well as its role in the concrete as a modification to improve the strength and other characteristics of concrete. In addition, we have determined the types or group of polymerized concrete that have been created and their characteristics as well.