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Conclusions & Recommendations - The intent of our effort here is to find out how useful it is for the modern world civilizations to use concrete with reinforcement as two of the fundamental building materials. This project contains reinforced concrete beam bending and strength analysis for 3 different concrete blocks and also gives background and research information about concrete. The comparison of concrete blocks includes different amounts of water / cement ratios and also different sizes of reinforcement. The concrete were tested after a curing period of 15 days. A hydraulic concrete-beam testing machine was used to test the strength performance of the blocks.
The maximum strength obtained was 10, 040 lbs for the second sample. This was a good result since after 14, 000 lbs of compression force concrete blocks are consider as high strength concrete in which the reinforcement rebar had a great contribution for increasing the summing strength. We take advantage of the existing hydraulic concrete-beam testing machine in the science department and began to make 3 concrete beams and test for their compression force. This machine would only test concrete-beam for its flexural force because concrete gives a very impressive amount of compressive strength and rebar gives a very good tensile strength. This hydraulic compression is acting on both ends of the beam on one side and another force acting in the middle of the beam on the other side. Therefore the compression force of the concrete will push against the bending rebar's, which it will contribute to the summing flexural strength.
The following figure on the right side is a hydraulic concrete-beam testing machine showing how it would compress the concrete to determine it's flexural strength. For us to get a sense of the strength of a concrete as well as how the reinforcements help contribute the flexural strength, we made 3 blocks of concretes under 2 different concrete mix proportions and 2 different sizes of rebar's as reinforcement. Concrete for the first block contains a ratio 1: 2: 3 (water: cement: fines with aggregates) and two rebar's with diameter 3 / 8 -inch. The second block has the same concrete mix and two larger rebar's with diameter 0. 5 -inch. Concrete for the last block contains a ratio 3: 1: 9 and two rebar's with diameter 3 / 8 -inch.
The actual curing period was 15 days before we test the ultimate samples. The resulting flexural strengths for these 3 blocks were 5, 980 lbs, 10, 040 lbs, and 5, 260 lbs respectively. Rounding up these results we can see that the magnitude of the flexural force that concrete with reinforcement can sustain is very huge that we can put trust on it when its used as the building materials. The real world usage and research of concrete is far more comprehensive than what we have done in this project. Therefore we included some interesting background and useful information about concrete that would help us understand more about the nature and application of concrete as we mention them through out the rest of this project. Our primary objective for this project is to find out how trustworthy it is to use concrete and reinforcement rebar as two of the fundamental building material.
We decided to accomplish this mission by testing the concrete beam to determine the magnitude of the flexural strength it can sustain where this strength may or may not be good enough for a range of real world building applications. Since our scope of work in this project does not contain a wider range of study and experiment for concrete and rebar's, we choose to have a secondary objective: include some interesting information about concrete and reinforcements and provide some interesting and must know information about concrete that would be useful for students to have a sense about the usage of concrete and rebar in modern society. Cement, as we know today, the product with less than 200 years of history. Some was used in Europe as a cementing material made by heating naturally accruing mixture of limestone and clay in 1700 's. Greek and Roman builders discovered how to build limestone's and make lime, which when we mix with water, formed cement that harden slowly.
The invention of reinforced concrete led to use of concrete in buildings. Around 1920, the importance of water cement ratio became known, and many users began specifying a limit of water content and slump. By 1977 the precast concrete industry represented a capital investment of $ 1. 1 billion in plants and facilities consuming thousand tons of cement annually and employing thousands of people. The familiar material that we know as concrete is actually a rather complex mixture of compounds, including Portland cement, sand, gravel or crushed rock, and water. When properly produced, the mixture gets hard and becomes a material with high strength, excellent durability, fire resistance, and water tightness. Cement and concrete are not the same.
The difference between cement and concrete is, cement is a dry powder, it becomes a paste that binds the aggregate (sand and gravel) particles in to the solid when mixed with water. The fresh concrete is concrete in a plastic state. The cement has not hydrated, or set. The concrete has no definite shape; it can be molded or shaped with ease. One of the most important properties of fresh concrete is workability, which can be defined as the ease with which the concrete can be handled and placed in the forms with a minimum loss of homogeneity. Cementitious Materials of Different Types Categorization of cementitious materials: Originally, concrete was made using a mixture of only three materials: cement, aggregate, and water; almost invariably, the cement was Portland cement.
Later on, in order to improve some of the properties of concrete, either to make it fresher or more hardened, small quantities of chemical products were added into the mix. These materials are called chemical admixtures. Other materials that are inorganic in nature were also introduced in the concrete mixture. The reason for the use of these materials was usually economic, since they were cheaper than Portland cement. Some of these materials were also byproducts or industrial wastes. Some of these materials are blast furnace slag, fly ash, and silica fume.
According to ASTM if cement consists of two or more inorganic constituents, which contribute to the strength gaining properties, it is called hydraulic cement. (ASTM C 1157 - 94 a) However, the American Concrete Institute does not use this terminology. Another terminology is that, if cement consists of Portland cement and one or more appropriate inorganic materials, it will be called blended cement. All of these materials called inorganic constituents or components have one in common that they contribute to the strength-gaining properties of the cement. All these cementitious materials are at least fine as the particles of Portland cement and sometimes even much finer. This is by far the most common cement that is used. About 90 % of all cement used in the United States is ordinary Portland cement.
Ordinary Portland (Type I) cement is admirably suitable for use in general concrete construction when there is no exposure to sulfates in the soil or groundwater. The standard requirements for this kind is that it is made from 95 to 100 percent of Portland cement clinker and 0 to 5 percent of minor additional constituents, all by mass, the percentages being those of the total mass except calcium sulfate and manufacturing additives such as grinding aids. (Refer to attachment 1) This cement comprises Portland cement subclasses of 32. 5 and 42. 5 Mpa as prescribed by BS 12: 1991. Rapid-hardening Portland cement (Type III), as its name implies, develops strength more rapidly, and should, therefore, be correctly described as high early strength cement. The increased rate of gain of strength of the rapid hardening is achieved by a higher C 3 S content (higher than 55 percent, but sometimes as high as 70 percent) and by a finer grinding of the cement clinker. (Refer to attachment 1) 3. Special very rapid-hardening Portland Cements: There exist several specially manufactured cements, which are particularly rapid hardening. One of these is so-called ultra high early strength cement.
This type of cement is not standardized but rather supplied by individual cement manufacturers. Ultra high early strength cement has been used successfully in a number of structures where early pre-stressing or putting into service is important. (Refer to attachment 1) The rise in temperature in the interior of a large concrete mass due to heat development by the hydration of cement, coupled with a low thermal conductivity of concrete, can lead to serious cracking. For this reason, it is necessary to limit the rate of heat evolution of the cement used in this type of a structure: a greater proportion of the heat can then be dissipated and a lower rise in temperature results. Cement having such a low rate of heat development was first produced for use in large gravity dams in the United States, and is also known as low heat Portland cement (Type IV). However, for some time now, Type IV cement has not been produced in the United States. (Refer to attachment 1) There is a reaction between C 3 A and gypsum and of the consequent formation of calcium self-aluminate. A second type of reaction is that of base exchange between calcium hydroxide and the sulfates, resulting in the formation of gypsum.
These reactions are known as sulfate attack. Sulfate attack is greatly accelerated if accompanied by alternating wetting and drying. The remedy lies in the use of cement with a low C 3 A content, and such cement is known as sulfate-resisting Portland cement. (Refer to attachment 1), (Picture 2) For architectural purposes, white concrete or a pastel color is sometimes required. To achieve best results it is advisable to use white cement with, of course, a suitable fine aggregate and, if the surface is to be treated, also an appropriate coarse aggregate.
White cement has also the advantage that it is not liable to cause staining because it has a low content of soluble alkalis. Cements of this name consist of an intimate mixture of Portland cement and ground granulated blast furnace slag. This slag is a waste product in the manufacture of pig iron, about 300 kg of slag being produced for each tone of pig iron. Chemically, slag is a mixture of lime, silica, and aluminum, that is, the same oxides that make up Portland cement but not in the same proportions.
Supersulfated cement is made by inter grinding a mixture of 80 to 85 percent of granulated blast furnace slag with 10 to 15 percent of calcium sulfate and up to 5 percent of Portland cement clinker. The cement has to be stored under very dry conditions as otherwise it deteriorates rapidly. Description of Cementitious Materials: Pozzolanas: On of the common materials classified as cementitious is pozzolana, which is natural or artificial material containing silica in a reactive form. A more formal definition of ASTM describes pozzonola as a siliceous and aluminium material, which in itself possesses 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. Fly ash, also known as pulverized-fuel ash, is the ash precipitated electro statically or mechanically from the exhaust gases of coal-fired power stations; it is the most common artificial pozzonola. (Attachment 5) Silica fume: This is a recent arrival among cementitious materials. It was originally introduced as a pozzonola.
However, its action in concrete is not only that of a very reactive pozzonola but is also beneficial in other aspects. It is a byproduct of the manufacture of silicon and ferrosilicon alloys from high-purity quartz and coal in a submerged-arc electric furnace. Silica in the form if glass is highly reactive, and the smallness of the particles speeds up the reaction with calcium hydroxide produced by the hydration of Portland cement. The very small particles of silica fume can enter the space between the particles of cement, and thus improve packing. (Attachment 5) Fillers: A filler is a very finely-ground material, of about the same fineness as Portland cement, which, owing to its physical properties, has a beneficial effect on some properties of concrete, such as workability, density, permeability, capillarity, bleeding, or cracking tendency. Fillers can be naturally occurring materials or processed inorganic mineral materials. What is essential is that they have uniform properties, and especially fineness. (Attachment 5) The wide variety of cement Types (in American nomenclature) and cement Classes (in European classification) and, above all, of cementitious and other materials used in blended cements, may result in a bewildering impression.
Which cement is best? Which cement should be used for a given purpose? There is no simple answer to these questions but a rational approach will lead to satisfactory solutions. No single cement is the best one under all circumstances.
Even if the cost is ignored, pure Portland cement is not the all-around winner. What is really important is that the appropriate cement should be used for a given purpose. More than one type or class of cement can be used. The choice depends on availability, on cost-that important element in engineering decision making- and on the particular circumstances of equipment, skilled labor force, speed of construction and, of course, on the exigencies of the structure and its environment. (Attachment 2) Because at least three-quarters of the volume of concrete is occupied by aggregate, it is not surprising that its quality is of considerable importance.
Not only may the aggregate limit the strength of concrete, as aggregate with undesirable properties cannot produce strong concrete, but the properties of aggregate greatly affect the durability and structural performance of concrete. Aggregate was originally viewed as an inert material dispersed throughout the cement paste largely for economic reasons. It is possible, however, to take an opposite view and to look on aggregate as a building material connected into a cohesive whole by means of the cement paste, in a manner similar to masonry construction. In fact, aggregate is not truly inert and its ph...
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Research essay sample on Blast Furnace Reinforced Concrete
