Importance of Concrete Durability - Coursework Example

Durability of Concrete One of the nightmares for most of the homeowners is how they can get a durable roofing material. These home owners associate durability with a number of positive things, which include the ability of a given the roofing material to be waterproof, have some impact resistance, have some thermal resistance, to be rustproof, rot- proof, fire resistant and dust resistant. The search for the appropriate roofing material, which possess these durability features has therefore, ended in concrete roof tiles. The concrete roof tiles are made from natural materials, which include water, cement and sand. The concrete can therefore be seen as a more environmentally friendly material compared to other roofing materials like metal roofing or asphalt composition shingles. It is possible to recycle old roof tiles and use them in creating new tiles as well as other products. This brings the economic value of concrete when used as a material for making roof tiles. The concrete also has proven durability and structural integrity when used to make concrete roof tiles. This has made most of the best concrete roof tile makers give a fifty-year or short lifetime product warranties for the same. Therefore, durability of concrete has been responsible for its wide use in making the concrete roof tiles, which have turned to be very economical to the homeowners. Table of Contents 1.0 Abstract 2 Table of Contents 3 Literature Review 4 Case studies and examples 7 Life Cycle Cost Considerations 14 Conclusion 17 Introduction The focus of this paper is on the durability of concrete. The research paper will therefore, be divided into a number of sections so that it can address the topic clearly. The introductory section will give an overview of what the research paper entails. It will also highlight the aim of the research paper and the problems identified before the selection of the topic. The objectives of the research paper will also be laid down in the introductory section. The next section after introduction is the literature review section. This section will bear the research studies and findings that are related to the topic of the durability of concrete. Therefore, what other authors have said regarding the topic is going to be outline in the literature. In order to support the arguments of the research paper, there will be a section containing case studies, examples and problems. Finally, the cost economy of concrete is going to be highlighted. Literature Review Durability is a term that is used to describe the ability of a given product to endure. For instance, durable products are those products that have a long usable life. This term is often used in technology and safety to refer to the situation in which a product is waterproof, has some impact resistance, has some thermal resistance, and is rustproof, rot- proof, fire resistant and dust resistant. Therefore as far as the research on the durability of concrete is concerned, the main focus will be on such things as its tensile strength, indestructibility, permanence, changelessness and everlastingness. Tensile strength refers to the strength that the concrete can bear without being torn apart. Indestructibility refers to the strength of the concrete to resist destruction. Permanence refers to the concrete’s ability to exist for an indefinite time or duration. Persistence refers to the property of the concrete to have a connected and continuous period of time (DHIR, DYER & HALLIDAY, 2002). Therefore, focusing on the different meanings of durability, it is important to describe some of the characteristics of concrete, which are related to its durability. First, one of the areas where concrete is used widely is in roofing. In this case, there are concrete tiles that are used specifically for roofing purposes. Therefore, most of the durability features of the concrete are going to be discussed based on the concrete tile roofing. As far as this aspect is concerned, there are a number of important characteristics of concrete tiles (BRITO & SAIKIA, 2013). Over the past few years, the demand for having concrete tile roofing has risen at an alarming rate. There are plenty of reasons behind this. One of the main reason is the fact that roofing using concrete tile offers a good blend of durability, strength and stability. These features are important in the light that climatic conditions across the world have been changing drastically, leading to a rising need for a solid and durable concrete tile roofing so as to prevent houses and other structures from being damaged. With the prevalence of hurricanes and hailstorms in most areas of the world, the failure to have proper roof replacement in a particular building may result in serious damage to property and life. Therefore, the place of durable concrete in our buildings and other structures is undisputable. Concrete is best suited for roofing many structures because of a number of characteristics (GUERRA S., 2008). One of these characteristics is quality. Quality is very important. The kind of material used in concrete tile roofing is of high quality. This is because concrete is made by mixing concrete with sand as well as pigment. This high quality makes the concrete tiles to last for a hardwearing and beautiful roof for one’s home. Boral concrete can last for about 20 years, for instance without any defect. This is because it is manufactured from strong and durable concrete (SIMMONS, 2013). The other important quality of Boral concrete roof tiles is that it is salt safe when used for coastal homes. Roofing in coastal homes has never been without worries especially when iron sheets are used. This is because there are a lot of salt in the coastal waters. However, with the use of Boral concrete roof tiles, homeowners can have a reason not to worry. These concrete roof tiles can therefore, be used in coastal regions close to the breaking surf. Thirdly, concrete roof tiles have good thermal performance. This refers to the way it influences the temperature inside the house as well as the energy needed for maintaining the indoor temperature at a comfortable amount or level. The fact that concrete tiles are unaffected by heat or high temperatures, makes it capable to have this high thermal performance. It is therefore durable since it can withstand high temperatures or a lot of heat. In other words, it has high thermal resistance. Apart from being long lasting, salt safe and having high thermal resistance, Boral concrete roof tiles are fire resistant. This means that the concrete roof tiles are non-combustible. Therefore, they can be used easily and safely in areas that are prone to bushfires (DHIR, DYER & HALLIDAY, 2002). The application of concrete roof tile can be traced to many centuries ago. This is because concrete is sustainable, durable and dependable material that facilitates energy sufficient design. It also exhibit a distinct or unique architectural character. Recently, the concrete material has grown in popularity due to its great or superior strength it possesses, which is greater than that of other conventional roofing materials like asphalt or wood. Due to the long history of concrete tile, there has been a development of a large number if concrete roof tile shapes. Consequently, among these shapes are Roman tiles, which have a convex curve at one end and a concave curve at the other, so as to allow interlocking, flat tiles, barrel or semi-cylindrical Mission tiles and S-shaped pan tiles. The most common tile that comes to mind as far as concrete tile is the red-hued tile. The red hued tile is available in a wide variety of colors, designs and shapes. Concrete roof tiles are suitable for most of the types of residential styles, for instance Queen Anne home, Cape Cod, Spanish colonial and Craftsman bungalow. The concrete roof tile can also be used for churches, schools, commercial structures as well as for other types of buildings courtesy of its aesthetic design qualities and durability. The concrete roof tiles provide better insulation to a building against strong summer heat compared to the other roofing materials like wood shingles or asphalt shingles. In addition, the lifespan of concrete roof tiles is often 2 or even 3 times longer than that of the other traditional roofing materials. This makes it economical since the life cycle costs are normally evaluated during project budgeting against initial costs. There has been a boom in residential construction and design because od low interest rates experienced during the late 1990’s through 2005. Consequently, homebuilders have discovered that when the use such quality materials as concrete tile, they can increase the value of their projects and make them distinct from other countless projects. Case studies and examples As per the Tile Roof Institute, there are regional variations as far as the use of concrete roof tiles is concerned. In this case, majority of the homeowners residing in areas, which experience heavy snowfall mistakenly think or believe that the accumulation of snow on a roof tiled with concrete is dangerous. These homeowners therefore, often organize for snow removal. According to experts, this arrangement is, in most cases not necessary. In addition, the snow removal is potentially damaging and dangerous to the roof tiles. This is because snow serves as an effective insulator. In addition, snow guards placed across the surface of the roof can hold or confine snow on the roof safely until the snow melts in spring. Therefore, concrete roof tiles are very good in homes situated in snow areas (BRITO & SAIKIA, 2013). When it comes to humid areas like south Texas and south Florida, the architects that specify tiles have to be aware of the consequences of mildew and mold, which grow and thrive in moist and shady areas. In order to reduce this problem, there is need to put in place a proper roof orientation and proper roof drainage. These will expose the wet and shadowed areas to sunlight. In Florida, the humid conditions provide a good environment for the collection of fungus on roofs. The temperature in this place can never become cold enough to kill the fungus. The fungus is unsightly. Spores can therefore, be destroyed using five percent bleach solution without worrying about the concrete tiles because of its resistance to bleach chemicals. Other materials may be affected by these chemicals (GUERRA S., 2008). Factors Affecting the durability of Concrete Strength Cement aggregate, water, sometimes admixtures are the key components of concrete. The mixing of these materials in specified quantities yields concrete. Concrete but not cement alone is a building material. For a given acceptable aggregate and cement, the strength that can be formed by a workable and properly placed mixture of aggregates, water and cement (under same curing, testing and mixing conditions), is influenced by the (1) ratio of mixing water to cement (2) ratio of aggregate to cement, the bond between the coarse aggregate and the mortar, and the strength of the mortar (3) grading shape, surface texture, stiffness and strength of aggregate particles, and (4) maximum size of aggregate. Strength of concrete and the structure of a hydrated cement paste are directly related. Air inside concrete causes voids to be produced. Excess water in concrete often evaporates leaving the concrete with void. This causes the W/C ratio and the porosity of cement paste within the concrete to increase. Increase in porosity causes the compressive strength associated with the concrete to decrease. Strength of Cement versus the Strength of Concrete It can never be possible to design a high strength concrete mix with a low strength cement. Variations in the strength of cement are largely contributed by lack of uniformity in the initial raw materials that were used in manufacturing the cement between different quarries and different sources of supply. Differences in the detail of the manufacturing process and the variations in the coal’s ash content used in firing the kiln, also contributes to variations in commercial cement properties. Generally, the modern manufacturing process of cement is highly sophisticated. Up to1975, the production of cement in a country like India was OPC-33 Grade. It was difficult obtaining high strength concrete using this type of cement. Worldwide, consumers have been finding it difficult getting ensured and consistent supply of high-strength cement concrete with this kind of cement. Because of the existing variations in the strength of cement, concrete obtained from these cement always has variable strengths. In order to use a correct approach to the Concrete mix Design, the facility should be available at site with the necessary set of requirements, materials, and the site conditions. This would allow a concrete curve to be developed at the site. This will help achieve the required W/C ration versus compressive strength. Concrete Durability Problems in the gulf Region experiences The gulf region suffers from very severe durability problems. These problems are caused by sulfate attack and chloride induced corrosion. The following are the causes of these problems: Aggressive environmental conditions, which is characterized by high humidity, large fluctuation in the seasonal and diurnal temperature and high temperature (humidity (H = 40 to 100% and ∆T = 20 ºC during summer). Continuous and sudden fluctuations in humidity and temperature initiate the ever existing cycles of contractions/expansions and dehydration/hydration, which leads to damage due to mechanical and thermal stresses. Large differences in thermal coefficients of aggregate commonly used and hardened cement paste. Limestone, which is the aggregate that is predominantly used in the gulf region has a thermal expansion coefficient of 1×10 –6 /ºC. The thermal expansion coefficient for hardened paste is relatively higher (range between 10×10 –6 /ºC and 20×10 –6 /ºC). Because of this, the compressive and tensile stresses develop in the cement aggregates and paste with the decline in temperature. Poor quality of the local crushed aggregates of limestone, characterized as absorptive, porous, excessively dusty and relatively soft. Excess fines and dust causes high water demand. This results in greater shrinkage of concrete and lower strength. Besides, dust weakens the bond at the interface of the aggregate paste. Air, sabkha soil and water heavily contaminated with large quantities of salts. The chloride salt, which is admixed in the concrete by mixing aggregates and water, contributes by the penetration of chloride laden groundwater and penetration of the airborne chloride laden dew and mixture caused by capillary action makes the reinforcing steel to be corroded very severely. Sulfate within the soil causes the concrete to severely deteriorate. Effect of Sulfate attack and Chloride Sulfate attack usually manifest through the expansion of the concrete. This leads to cracking of the concrete. Sulfate attack can also be manifested in the form of the progressive loss of mass and strength of concrete. This is caused by deterioration in cement hydration product cohesiveness. There are various forms of sulfate attack namely, the expansive type, onion-peeling type and acidic type. Figure 01 shows the common forms of sulfate attack in the gulf region. Figure 01: Common forms of sulfate attack: (a) acidic type, (b) expansive type and (c) onion-peeling type. Main factors affecting sulfate and Chloride attack in the Gulf Region. The major factors that affect sulfate attack include the type and content of cement, flash addition, sulfate concentration and type, chloride ions, alongside other factors. Cement content and type The most vital mineralogical phases of cement affecting the intensity and magnitude of sulphate attack include C3S/C2S, C3A ratio and C4AF. Cements having low content of C3A are less vulnerable to attack by the sulfate. However, cements that contain low C3A have a relatively higher C3S/C2S. Any increase in the content of C3S of cement leads to a higher calcium hydroxide amount. Higher content of cement significantly causes the rate of attack of sulfate to reduce. Fly ash addition Addition of pozzolanic admixtures such as fly ash leads to the reduction in the content of C3A of cement. This has a beneficial impact of sulfate resistance Sulphate concentration and type The sulphate attack increases with the increasing concentration of solution sulphate up to some level. Chloride Ions Chlorides have negligible to general beneficial influence on surface resistance of type 1 and type 5 cements. Sulphate binding of cement decreases under the chloride ions. The expansion of a concrete caused by sulphate attack where chloride is present becomes retarded due to increased sulphate ettringite solubility in calcium and sodium solutions that it happens in water. Other Factors Other factors include the soli porosity and flow of the groundwater, the water table water and its associated seasonal variation, quality of concrete and the form of construction. Remedies and Control Measures Control measures to help maintain the durability of concrete in the gulf region include: The quality of the concrete used. A low permeability should be considered since provides the best protection against sulphate and chloride attack. The important factors that can cause low permeability should be addressed. The measures include maintaining high cement content, adequate concrete thickness, proper curing and compaction, and low w/c ratio. Other measures include the use of chloride/sulphate resistance cements. They give additional safety against chloride or sulphate attack. Life Cycle Cost Considerations When concrete roof tiles are compared to other materials used for roofing, the expenses of installing concrete roof tiles can be more substantial. However, because of the extreme durability if concrete roof tiles, the cost of having concrete roof tile can be comfortably and favorably be spread over a long or extended life cycle. Depending on the quality of installation and weather conditions, concrete tile are basically permanent roofs. This means that they can stay for fifty to hundred years or more. During this long or extended duration, metal, asphalt and wood can be replaced up to 3 times. Therefore, because of the proven durability and structural integrity of concrete roof tiles, most of the best concrete roof tile makers give a fifty-year or short lifetime product warranties for the same. Hill Foley Rossi and Associates, a firm involved in architectural designs, which is also based in Duluth, Georgia, specified a concrete roof tile, which was flat for their own offices. This kind of concrete was made to appear like a slate. This was done at a fraction of the actual cost. Regarding the same, Mike Rossi, a principal with this company said that despite having same features as authentic slate roof, the flat concrete roof tile was little less expensive. He argues that one can have a concrete roof tile on his or her building for fifty years minimum, which is very long and extended in comparison with other materials like modified bitumen, which needs replacement in twenty years. Therefore, in the long run, one saves a lot of money since he or she has little to no cost of maintenance with concrete roof tile (HORNBOSTEL, 1991). Photo courtesy of MonierLifetile: This home was roofed with concrete tile designed to resemble traditional split shake shingles. Also linked with the cost is the aspect of maintenance. In this regard, concrete roof tiles can be said to be pest-resistant. Apart from being pest resistant, they are not damaged by sunlight or heat; they do not rot when exposed to wet conditions or climates. They also resist harsh weather and fire than other kinds of roofing products, especially asphalt, which can become brittle when exposed to harsh sunlight. The harsh sunlight can also weaken the shingle adhesive of the asphalt, increasing the chances of the shingles blowing off or tearing in bad weather. It is true that all roofs need some amount of maintenance. In this case, many roofing systems need cleaning, painting and coating and or sealing most part of the roof surface. Under normal conditions or situation, concrete roof tiles need minimal maintenance mainly in such areas as venting, flashings and gutters. The replacement of a missing, cracked or broken tile is very occasional. When there is cracking or breakage of a tile, the damaged concrete roof tile can be removed before being replaced in the same way the other concrete tiles are attached to the roof. In case there has been the use of mechanical fasteners and the screw or nail have to be cut, enough caution has to be taken to ensure that the underlayment is not ripped (DHIR, DYER & HALLIDAY, 2002). As far as cost is concerned, it is also important to argue that concrete roof tiles are very sustainable. In this case, concrete roof tiles are made from natural materials, which include water, cement and sand. Therefore, because of this, concrete roof tile can be seen as a more environmentally friendly material compared to other roofing materials like metal roofing or asphalt composition shingles. It is possible to recycle old roof tiles and use them in creating new tiles as well as other products. Therefore, the less frequent replacement of concrete tiles does not only translate to a reduced life cycle costs for the consumer but it also represents a general reduction in the use of natural and energy resources (BRITO & SAIKIA, 2013). Conclusion From this discussion, it is very evident that concrete can be used a good roofing tile. In this case, homeowners have a lot of things to praise the concrete roof tiles for. Top in this list is the fact that concrete is durable. Durability in this case has been defined to refer to the ability of a material to possess an array of qualities. The qualities mentioned in this paper include the ability of a given product to be waterproof, have some impact resistance, have some thermal resistance, to be rustproof, rot- proof, fire resistant and dust resistant. Because concrete roof tiles possess all of these qualities, it has widely been used. The fact that concrete roof tiles are durable has ensured that it is also economical in terms of costs. The paper has mentioned that concrete roof tiles they are not damaged by sunlight or heat; they do not rot when exposed to wet conditions or climates, resist harsh weather and fire than other kinds of roofing products, especially asphalt, which can become brittle when exposed to harsh sunlight. It has also been argued that because of the proven durability and structural integrity of concrete roof tiles, most of the best concrete roof tile makers give a fifty-year or short lifetime product warranties for the same. References: DHIR, R. K., DYER, T. D., & HALLIDAY, J. E. (2002). Sustainable concrete construction: proceedings of the international conference held at the University of Dundee, Scotland, UK on 9 - 11 September, 2002, [during the 2002 International Congress Challenges of Concrete Construction, 5 - 11 September 2002]. London, Thomas Telford. MELVILLE, I. A., GORDON, I. A., & STEPHENSON, E. M. (1997). The repair and maintenance of houses. London, Estates Gazette. HORNBOSTEL, C. (1991). Construction materials: types, uses, and applications. New York, Wiley. BRYS, G. (1992). Fibre and micro-concrete roofing tiles. Geneva, International Labour Office. SIMMONS, H. L. (2013). Olins construction principles, materials, and methods. Hoboken, N.J., Wiley. http://rbdigital.oneclickdigital.com. BRITO, J. D., & SAIKIA, N. (2013). Recycled aggregate in concrete: use of industrial, construction and demolition waste. London, Springer. GUERRA SANTIN, O. (2008). Environmental indicators for building design: development and application on Mexican dwellings. Amsterdam, Netherlands, IOS Press. Read More