Construction Materials 48352 Assessment Task 1: Materials Design Project Introduction to concrete Concrete is widely used in all types of construction due to its flexible nature. Concrete is utilized in various ways for example, in house walls and foundation, gutter and curb, driveway paving among other different applications. This report reveals the correct material specifications; steel selection and concrete mix design for a 100m wide steel arch bridge. The paper explicitly considers the specified parameters required for a proper concrete mix design. The concrete mixture is assumed to have the smallest slump of 100mm. besides, this report concludes that the necessary concrete strength is 40MPa and that the temperature of the steel mixture does not exceed 70˚ C. An overview about concrete What makes concrete more unique is its ability to withhold large compression forces. Nonetheless, concrete cannot stand on its own; therefore, it has to be reinforced with other high-tension materials. In this case, steel is an excellent material. Concrete portrays one horrific thing, and that's the inability to withstand massive forces. Cracks start to appear when the stress level is high. Concrete also displays small thermal expansion hence; every concrete structure at one point in time will develop cracks when exposed to prolonged tension and shrinkage forces. For this case, Portland cement is the best due to its new micro-silica, blast-furnace slag, polymers, aggregate, recycled concrete, fibres and fly ash among other additive mixtures. Any other type of cement can be used, as long as the resultant mass is of equal cementing quality. Concrete Mix Design Analysis The necessary strength is 40Mpa, but an additional tolerance of 5% is to be included to compensate for the resultant effects that can be brought about by the various components present in the used cement. It is also to ensure maximum safety for this design, Therefore a new tolerance calculated using permits for the new strength of 48MPa (see figure 1&2). The project involves two concrete mixtures. The first mixture has 30% fly ash while the second is to have fly ash with a slag percentage of 70%. But of what significance does fly ash and slag provide for the project? Fly ash also referred to as pulverised fuel ash from combustive coal product. Fly ash is particularly important due to its cementations nature that binds the concrete more firmly. On the other hand, Slag is also of extra cementations advantage and is important for the project due to its ability to afford extra strength. Slag can be small-sized rock pebbles. Nonetheless, both mixtures are to involve cement to water ratio of 0.45 that is to guarantee exceptional concrete strength (see figure 1&2). Since the highest internal temperatures are not to go beyond 70˚ C, moderately lower cement amounts are utilized to maintain the required temperature. Besides, Fly ash is a well-known temperature coolant and therefore helps to maintain cracking and shrinkage levels. Also, Fly ash can transform concrete into workable spherical particles that also move faster. Slag is combined with concrete to produce moderately higher characteristics. In this case, about 70% of the concrete is to comprise of Slag (see figure 1 & 2). Slag is used, to adequately compensate for the new tolerance strength of 48MPa. And the cement to water is maintained at 0.45 to achieve the maximum strength required. Average concrete shrink is expected to happen between 50 and 100mm. Therefore, GGBFS (Ground Granulated Blast Furnace Slag) are included to provide more impartibility and secondary strength. The concrete mix is kept almost air free, and the preferred cement has to be of the General Blend (BG) collections that incorporate Slag and Fly Ash. Slag or Fly Ash manufactured cement produces later age strength, enhanced durability and improved concrete workability and performance. The uncrushed Slag Aggregates also provide the necessary level surface area that increases workability and binding effect. Calculations for Mix design Fly Ash Mass Volume () Material Strength Fm = Fc + Ks 40 MPa _ Material compensation 40+(1.65*5) 48 kg/ _ Cement Boral GB 600x0.7 420kg/ 420/3150 = 0.133 Supplementary Cementitious Material 600x0.3 180kg/ 180/2250 = 0.089 Water content (free water) =420x0.45 189kg/ 189/1000 = 0.189 Cement paste volume =WC+SCM+Cement _ 0.133+0.089+0.189=0.411 Air volume assumed 1% _ _ 0.010 Total (air volume+ cement paste) _ _ 0.411+0.01=0.412 Coarse aggregates _ 980kg/ 980/2650=0.370 Fine Aggregates _ 640kg/ 640/2610=0.245 Superplasticizer 5L 5/1145 0.004 Total _ _ 1.000 Using Slag Mass Volume () Material Strength Fm = Fc + Ks 40 MPa _ Material compensation 40+(1.65*5) 48kg/ _ Cement Boral GB 600x0.3 180kg/ 180/3150 = 0.057 Supplementary Cementitious Material 600x0.7 420kg/ 420/2250 = 0.191 Free water content =170x0.45 76.5kg/ 76.5/1000 = 0.077 Cement paste volume =WC+SCM+Cement _ 0.057+0.191+0.077=0.325 Air volume assumed 1% _ _ 0.010 Total (air volume + cement paste) _ _ 0.325+0.01=0.335 Coarse aggregate _ 975kg/ 975/2650=0.368 Fine Aggregate _ 645kg/ 645/2610=0.247 Superplasticizer 7L 7/ 0.006 Total 1.000 Concern about hydration heat In a construction perspective, such heat might be transferred to air and soil medium that may alter the temperature equilibrium. Major building structures are the most affected by hydration temperature phenomenon because of their inability to release the constant heat build up. Under construction, Portland cement is the most preferable since it has enough slag to reduce the amount of concrete hydration heat. More slag residues mean that the hydration temperature is reduced even further. Fly ash is the primary reason why Portland cement is considered for the project. Fly ash can regulate its temperatures below 70˚ C hence it is a great addition to ensure that the temperature does not raise to maximum limits. Fly ash can also be seen as the exact concrete cement replacement that cures all the heat problems. More so, a large volume of the fly ash is used to control the concrete's latent hydration heat. Incorporating sufficient amount of Fly ash also reduces temperature build up by diffusing off the extra heat, hence the project guarantees extended strength possibilities. It is a particularly brilliant idea since massive concrete volumes tend to crack when exposed to the excessive rise of heat. Hence, fly ash would be my recommendation for the final construction as it is very effective and would meet the requirements of this project in the most effective and profound manner. The Effect of slag on concrete hydration Slag concrete mixture has enough slag that helps reduce the amount of concrete hydration heat. During the mixing of cement with water, some heat is released and is referred to as the hydration heat. It is usually an exothermic chemical reaction that occurs when any substances are combined. In this construction perspective, such heat might be transferred to air and soil medium that may alter the temperature equilibrium. Bridge structures are the most affected by hydration temperature phenomenon because of their inability to release the constant heat build up. The slag mixture in the concrete means that the hydration temperature is reduced even further, hydration temperature otherwise means that the bridge might collapse. The figure 3 below shows the normal amount of Portland cement’s hydration heat when compared to the specific hydration heat produced when the slag combination is changed. It is observed that with each slag increment, the hydration heat level also reduces. The portion covered by the curve stands for the overall generated heat; hence, 70% slag greatly benefits the project by reducing hydration heat. It is concluded that even though the slag temperature might increase in the long run, the temperature cannot reach great levels. Hence slag is a better component for any concrete mix. Hence figure 4 below shows the temperature effect on slag, it clearly shows when time progresses the temperature due to slag added in the mix rises, the more percentage slag cement in the concrete mix the less the temperature would be produced. The Effect of Fly ash on concrete hydration heat Fly ash concrete mix has the ability to regulate its internal concrete temperatures to below 70˚ C hence it is a great addition to ensure that the temperature does not raise to maximum limits. Fly ash mix can also be seen as the exact concrete cement replacement that cures all the heat problems. More so, a large volume of the fly ash is used to control the concrete's latent hydration heat. Incorporating sufficient amount of Fly ash also reduces temperature build up by diffusing off the extra heat, hence the project guarantees extended strength possibilities. It is a particularly brilliant idea since massive concrete volumes tend to crack when exposed to the excessive rise of heat. Figure 5 below shows the amount of heat released when fly ash is used in the concrete mix. It is observed that without addition of fly ash, concrete temperature continues to increase, but when fly ash is added, the temperature decreases. Alone, Portland cement cannot regulate its internal temperature. Using fly ash as the alternative for cement therefore results in reduction of maximum temperature. Substantial amount of fly ash presents exceptional benefits by controlling the concrete’s hydration heat. As seen in figure 5 fly ash does not exceed70˚ C, hence the greater the volume of fly ash it becomes advantages for temperature reduction. Design considerations for Chloride induced Corrosion. Some concrete construction cracks defects occur when the reinforcement steel is corroded. Corroded steel may cause gasses and liquids to infiltrate the concrete matrix. Most structural cracks occur due to this phenomenon and chlorides are the primary corrosion agents. Chloride corrosion usually occurs due to dissolved chlorides in the chemical and water mixtures used to make the concrete. Also, chlorides might come about due to pre-existing hardened chloride paste on the steel. Chlorides also diffuse into the concrete epicentre in vapour form. Typically, during corrosion of steel, the resultant rust occupies additional space that generates tension in the concrete matrix (see figure 6& 7). This force is the one responsible for delamination, spalling and cracking of concrete. Thinking in the perspective that any vapour or liquid entering the model could lead unwanted cracks, the idea is to make sure that the steel is free from any corrosion. It is a necessary step to prevent unnecessary expansion to build up of ferric oxides. As a professional engineer I need to consider all aspects while designing my project I must reassure the protection of reinforcement which concrete is considerably the element to protect the reinforcements from corrosion. There are two main types of protection chemical and physical protection. In terms of chemical protection Ca(OH)2 chemically reacts with the surface od steel forming a thin layer of ferric oxide which protects the reinforcement from corrosion. However, due to physical protection corresponds to cover depth and quality (concrete) depending the environmental nature. Material Specification-considering strength and durability requirements. Durable materials are that which can withstand prolonged deterioration. In this case, the power of concrete is evaluated on its ability to resist abrasion, chemical attack, and weathering action, while preserving the necessary engineering properties. Besides, durability is all about conservation of resources and the environment through replacement and repair environmental impact wastes. Most concretes display different sustainability degrees depending on the desired properties and environment exposure. Portland cement concrete is the most appropriate brand due to its superior prospective strength. Both mixes are also designed with a little water content, which is necessary for the required durability and strength. There is a need for secondary cementing that provides additional strength. Air content of the cement mixture is also maintained within moderate levels to prevent cracks. Temperature is the other significant factor to consider when preparing a concrete mix. Since the reinforced concrete is to be permanently stressed by compression, it is of great importance to improve strength qualities of the concrete. However, the reinforcement does not necessarily have to be steel; rather, it can be of any passively embedded bars. The support design is to offer extra tensile strength in specific locations that are prone to structural failure and cracking. The project can involve any modern reinforced concrete with other composite materials for example polymers or steel. Figure 1 & 2 shows that the water content being low, for Fly Ash WC=0.189 and for GGBFS WC=0.077 which is an advantage to the mix as it will reach its maximum strength. Hence, the temperature is less than 70˚ C seen in figure 3&4. Conclusion Afoot bridge is prone to experience high tensional forces; hence its concrete mixtures must ascertain some level of strength. Such a project has to involve two concrete mixtures. The first mixture should have 30% fly ash while the second is to have fly ash with a slag percentage of 70%. Both slag and fly ash concrete mixtures give enough to hold the bridge in place, while making sure that the concrete does not crack due to reinforced material. My personal selection is Fly ash as it can regulate its temperatures below 70˚ C hence it is a great addition to ensure that the temperature does not raise to maximum limits l corrosion and hydration heats. 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