Table of Contents
Chapter 1: 1.0 Introduction
Concrete used nowadays has enabled a man to reach the heights never imagined before in the area of construction. Various suspended structures, large and expansive pavement, reinforcement columns, highways, bridges, pillars and beams can be built by a man. Additionally, the service life of these structures have also increased. A standard bridge or a super highway constructed today in the developed world is expected to be used for fifty years. It is an amazingly expansive period of time. The government through various agencies has to constantly repair these structures in form of sealing of cracks so that the structure is durable. The cost of this maintenance structure is very high and may go up to 30% over a period of 50-60 years. This is a large sum of money that can be utilized for other developmental agendas.
On the other hand, there are numerous cases where slabs, columns, pillars, beams, suspended bridges made of concrete simply snap or dilapidate such that they can no longer be useful. Concrete is very brittle and snaps as soon as its elasticity limit is exceeded even if reinforcement does not withstand. Whenever the elasticity limit of concrete is exceeded only slightly, crack development is a common experience. If these cracks are not sealed off effectively and in advance, they alloy the corrosion of the reinforcement bars by oxygen and chlorine that weaken concrete, which can ultimately collapse. This means that concrete will always require maintenance, which is sometimes expensive. Additionally, sometimes the structures may dilapidate or just fail earlier than expected, which exposes the owners or governments to more costs.
1.1 Thesis Statement
The literature review explains the history and milestones made in the evolution of concrete over the years, as well as the results of these many years of evolution. The structure, composition, as well as strengths and limitations of concrete used nowadays has been highlighted in the following research. The following research will have an in-depth view of various aspects of concrete used nowadays (henceforth called concrete). The details, as well as circumstances that lead to cracking of concrete will be also researched.
Cracking will be discussed as the major limitation of concrete. The discussion will include how cracks develop in concrete and factors that aggravate this situation and how cracks affect the strength and durability of different concrete structures. Finally, there are various efforts that are used to react to cracks occurring on/within concrete structures. A set of technological advances have been applied to prevent crack formations and also repair them. On the other hand, some researchers have taken a proactive approach to crack formation and are researching on the materials that lead to concrete that will resist cracks in the first place. Others are working on the materials that will provide concrete with self-healing mechanisms. All these points will be discussed in this research.
1.2 History of Development of Concrete
Around 12 million years ago, the world sop what was probably the greatest natural fires of this time period. This happened at a place around the present days' Israel. This event is very important to the history of world’s cement, concrete, as well as architecture all together. It is believed that the first material that is close to modern day cement was found here. It was found as deposit occurred when spontaneous combustion took place due to reaction involving oil shale and limestone. It should be noted that cement as a binding material has been utilized in concrete in all ages. Advancement and further development of this material, including blending it with various materials, was made according to various uses that arose.
A specific date of when the use of concrete might have begun varies among researchers. The main reason for this is that there are many materials that can be referred to or are much related to concrete. The materials and composition of what has been known as concrete has varied over time (Concrete Society, 1967). The most ancient of these materials was obtained when limestone or gypsum was burned and then crushed to form what is considered the earliest form of cement. The resulting dust like material was mixed with water and was utilized for various purposes. In the southern part of the Middle East, this material was formed into a paste that was placed as a layer on different earthen structures. This material hardened after reacting with the environmental air. The, it formed an impermeable layer that protected the structures making them last longer. In Greeks and Romans, the following material was mixed to form mortar that was used for layering stones and bricks. It was also used in order to seal the joints between the stones.
In the Roman Empire, the new designs and architecture inspired the need for structural material. The same material was utilized to form mortar which was used to layer rubble which was molded to form various shapes and vaults to obtain various suspended structures. Over thousands of years, these materials were improved and combined with aggregates to form concrete used nowadays.
Over the years, the other components of concrete have gained importance. Initially, the binder (Cement) was coarse in formation, and there was no need for san. It was mixed with water, and the resultant substance was similar to the present day mortar. The material was coarse but still fine enough to provide an adequate surface area to react with the environmental air. This material would later be abandoned for hundreds of years, especially after the fall of the Roman Empire. It happened that since the fall of the Roman Empire in 400AD, nothing really happened in the development of either cement or concrete. There is no structure or activity involving concrete that took place until the 17th century.
The idea of concrete was reintroduced in 1768. It formed a basis for Industrialization and further development in the world. Joseph Moxon wrote a book that literally reminded the world about the successes that has been brought about by cement. Although the researcher did not do this literally, his book described the experiences of how concealed inferno in fiery lime appeared when the water was added. It was a process that resonated well, and as a result, the engineers and builders would start thinking about concrete.
John Smeaton was one of the engineers who later contributed to the evolution of concrete. This British engineer came up with hydraulic cement that had a widespread application in construction in and under water. He had conducted repeated research and trials under fresh and salt water until he achieved this milestone. Later in 1779, BRY Higgins obtained a patent for his hydraulic cement. It was traded under the name stucco. It found a widespread application for exterior use in that it was waterproof and protected structures from moisture.
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Another Briton named James Parker obtained a patent for hydraulic cement. This cement was obtained through natural means. The process was described as natural as it was obtained through calcining nodules of mixed limestone that contained a form of clay. The product was traded under the name Parker’s cement.
The period between 1812 and 1813 brought about advancement in the development of cement. This period saw a wide use of cement by French people. A French innovator Louis Vicat artificially prepared hydraulic cement through the use of limestone and clay which he calcinated. At that time, much refinement work was performed. Very little variation or refinement of any significance really happened. Later in 1818, another innovator Maurice St. Leger also obtained a patent for cement.
This is a period in which cement and concrete in general gained a lot of popularity in America. American engineers appreciated and utilized this technology effectively. Canvas White simplified the process of cement production greatly. He found a rock deposit in the county of Madison, New York, that required very little processing to form hydraulic cement. Other researchers, such as Abraham Chambers and John Tickel, also obtained patents for hydraulic cement. This happened in the year 1821. No pioneer work was conducted in the following years, and cement remained rather the same. The concrete made was also crude as rubble was layered with mortar. In the year 1924, the world came very close to the creation of cement in its most modern form. In England near the polish border in the town of Leads, Joseph Aspdin, who was a brick layer patented a form of cement he called Portland cement. He gave it this name because it resembled a rock that was very common in this place, especially off the British cost, in the Isle of Portland.
Large construction projects started in the US raised the demand for cement in a greatly way. An example of such projects is the Erie Canal. In the year 1928, there was a diversification in the use of cement and concrete altogether. It was seen as a builders or architects' material. However, in the year 1828, it was utilized for engineering purposes for the first time. IK Brunel used Portland cement to fix a section of the Thames tunnel that had a breach. This widened the imaginations of the engineers, architects and builders of the immense possibilities for the use of concrete in future.
In the 1850s, another use of cement was discovered or revisited. As Egyptians had used ancient forms of cement to join bamboo together into a boat, Jean-Louis Lambot was the first to use this new form for reinforcing boats. This also had an implication of acting as a pointer to various areas where cement could be put to in the future. By the year 1854, concrete close to what is in use was developed. It should be noted that, in the Western Europe and America, mortar was utilized for layering stones. However, William B. Wilkinson used concrete for walling for the first time in the modern history. He used concrete to erect servants’ cottages. This added a perspective in the evolution of cement and concrete, and it was another possibility that could be explored.
The ten year period leading to 1867 is very crucial to the development of cement/ concrete. It was the period when Portland cement was utilized to construct a sewer system in London. It was a test for permeability, as well as structural strength. It is crucial to note that it was utilized to form giant pipes that were laid on the ground. This gave people an opportunity to visualize and imagine how much more concrete would have done. This raised the acceptability of concrete as a structural material
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In the same year, concrete was utilized in a way similar to what is used today. Joseph Monier developed garden beams, posts and tubs by pouring concrete into molds. He proceeded and obtained a patent for his innovation. The idea of pouring concrete into mold to give it shape was realized here. The world has built and developed this concept immensely to date where structures are made by pouring concrete into the mould and later removing it. This increased the demand for concrete and cement. In the following year, the shipment of Portland cement to the US begun. This increase in demand for concrete happened, especially in the north Western Europe and North America, in over the next 10-15 years. In France, for instance, Francoise Coignet, who was a builder, popularized the use of concrete in France. He integrated concrete in his work, which made several builders of his time to follow his example. By the year 1871, the demand for cement and by extension concrete in the US had exceeded the amount that could have been supplied effectively through importation. The demand for Portland cement was enormous. David O. Saylor, an entrepreneur, started the earliest Portland cement factory in America. It was established in the town of Coplay.
In the 1875, one gigantic step was made towards in the development of concrete. At that time, the cement formulation was very fine compared to what was utilized in the Roman Empire. For this reason, the use of sand in concrete was widely accepted. Additionally, instead of rubble, stone was crashed to obtain gravel. The level of technology enabled engineers and builders to crash stone with the required strength in order to develop ballast. The use of ballast as an aggregate was adopted and utilized. It is referred to as crashed stone, gravel, or ballast. Even after concrete was developed from cement, sand and ballast, it was still very brittle and could shatter easily. An innovation was required to overcome this challenge. For instance, in the New York city in port Chester, Robert Mook who was an architect designed a house that was built in a ground breaking way. William E. Ward, who was a builder, used this reinforced concrete for the construction of this house. This was the pioneer work for the use of reinforced concrete.
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A formation and a proper method of reinforcing concrete were developed. This involved the use of twisted still bars that were placed inside the molds before concrete was poured. After curing of concrete, the mold would be removed leaving the steel bars embedded, which made the resultant structure to be less brittle by increasing its tensile strength. This method of production was patented by Earnest L. Ransom. It was the beginning of reinforced concrete and a pointer to much that would come in the future. Simultaneously, better methods of producing Portland cement were developed to cope with the great demand and the quality desired.
With this advancement in technology experienced above, the concrete similar to what is used today had been developed by the year 1889. Consequently, it was used for functions very similar to what concrete is used for today. The first reinforced concrete bridge was built in the year 1889. Since that day, the general improvement that has been made to concrete is minimal. There has not been much improvement in this form of concrete that is formed from Portland cement.
Ballast as a component of concrete used nowadays does not have a long history as the concrete does. Ballast does not have to react chemically; it is a bulk feeling material. The only evolution that has occurred is shifting from rubble that was layered by hand in the Roman Empire to the form utilized today. In the 17th, 18th and 19th centuries, ballast was made in a way that it is worked into a homogeneous mixture. This requires it to be a finer material. Additionally, a material with high stability and strength is required, which is crucial for building strong structures. It is obtained by crashing stones with the required strength to the required sizes. Some regions of the world use volcanic ash with the required properties.
On the other hand, sand as an aggregate has not undergone much evolution. It is utilized in its natural form in most cases. However, the use of sand has become popular in concrete since the 18th century. The form of ‘cement’ used in the Roman Empire was course enough and did not require the fine aggregate of sand.
Nowadays, various materials are used in the production of concrete. These are Portland cement, water, crashed stone and sand, which are referred to as aggregates. Other components and chemicals referred to as admixtures are utilized. These are added to boost properties of concrete, as well as make it resistant to numerous environmental extremes.
In 1300BC, the architecture of the Middle East changed significantly. Builders used a thin layer of damp crashed limestone to protect walls and clay structures. They later found out that this layer hardened over time after reacting with atmospheric air. Later on, the Romans and the Greeks improved this powdery limestone by the addition of sand and water.
The period between 300BC-476AD is a very important period in the evolution of concrete. During this period of nearly 800years, the use of concrete increased significantly (Hill, & National Ready Mixed Concrete Association 1989). The mixture used in that time was referred to as opus caementicium, which is known as Roman Concrete. It comprised pozzolana, quick lime and pumice and was utilized as concrete. This became a critical occurrence in the evolution of architecture and is what is now referred to as the Roman Architectural Revolution. It enabled the Romans to overcome challenges experienced when dealing with stone and brick. New forms that were complex and in construction and dimension could be constructed by people.
Modern tests reveal that this form of concrete matches the concrete used nowadays in terms of compressive strength. One major challenge of this form of concrete was and still is its very low tensile strength. The following strength of concrete would be boosted through reinforcement, and this technology was not available in those days. Concrete used nowadays is reinforced and is very high in tensile strength compared to opus caementicium. This makes the modern day concrete to be sufficiently strong and suitable for many functions that were previously impossible with opus caementicium. Concrete nowadays is structural and differs distinctively from Roman concrete in two ways. The first difference is that it is made as a homogeneous fluid and later poured into forms, whereas opus caementicium was layered using hand alongside aggregate that comprised mainly of rubble. The second difference is that today’s concrete is reinforced and is used for structural purposes.