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Write a summary about self-compacting concrete that is a liquid/fluid often used in structures that have congested reinforcement and those, which do not require vibration.
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Self-compacting concrete is a liquid/fluid often used in structures that have congested reinforcement and those, which do not require vibration. In the development of self-compelling concrete, one needs to strike a state of equilibrium for both deformability and stability. As Okamura and Ozawa (1995, p. 120) confirm, "the quality or characteristics of materials and the proportions of the mixtures also affect the compatibility of the self-compacing concrete".
human
Provide an essay about self-compacting concrete that is a liquid/fluid often used in structures that have congested reinforcement and those, which do not require vibration. Exapnd on the summary above.
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#Self-Compacting Concrete, Characteristics of SCC Research Paper
##Introduction
Self-compacting concrete (SCC) is a liquid /fluid often used in structures that have congested reinforcement and those, which do not require vibration. In the development of self-compacting concrete, one needs to strike a state of equilibrium for both deformability and stability. As Okamura and Ozawa (1995, p. 120) confirm, “the quality or characteristics of materials and the proportions of the mixtures also affect the compatibility of the self-compacting concrete”. Therefore, it is necessary for the evolution of procedures for designing these self-compacting concrete mixtures to ensure the longevity of structures. One of the surest ways to increase the stability of cohesiveness of the concrete is to use fine materials in these mixes. Despite the several investigations carried on this concrete, many large companies in Japan and around the world continue to use it because of its benefits. The paper presents a brief history of SCC followed by its characteristics besides showing how it works in relation to the ordinary concrete, amongst other details.
Historical background of the self-compacting concrete
Professor Okamura proposed the self-compacting concrete in 1986. This was after “several years beginning from 1983 in Japan when the durability of the concrete structure” (Okamura & Ozawa1995, p. 99) was at stake. Coming up with long-lasting constructions called for enough compaction, which again needed experienced personnel. Construction Company in Japan was facing a shortage of skilled workers, which contributed to a reduction in the quality of building and construction works (Deeb, Ghanbari, & Karihaloo 2011, p. 185). Maekawa and Ozawa in the University of Tokyo carried out further studies on self-compacting concrete. The studies bore fruits in 1988 when the model of SCC was finished with the use of locally available resources.
Countries that use SCC
The concept of self-compacting concrete manifested itself in Europe in the mid-1990s in most of the civil works. Most of the Sweden transportation networks relied on this concrete in their construction (Walraven 2002, p 356). Furthermore, the European Commission supported it by funding a multinational company specializing in the lead on self-compacting concrete in the late 1990s. Since then, many European construction companies have embraced this concrete using it in their building and construction work. Japan was one of the first countries in the world to begin using self-computing concrete in its construction work. The first application of concrete was in 1990. Then, it was used to make towers of concrete cable-stayed bridges in 1991(Guneyisi, Gesoglu & Ozbay 2011, p. 160). Lightweight SCC came in handy in the construction of beams of these bridges. Henceforth, other people have begun using this concrete in their construction work. Nowadays, the reason why many people prefer to use self-compacting concrete to traditional concrete is that it is easy, and it shortens the time of construction. It also guarantees compaction in the constructions, especially in the restricted regions.
##Benefits of SCC
Because most of the concretes that existed were poor in their compatibility, it was necessary for the introduction of self-compacting concrete. The concrete solved the problem of inadequate compaction that had earlier been experienced by the workers in the construction. Furthermore, the self-compacting concrete was designed in a manner that allowed uniformity in the quality of the concrete (Angel, Jaime, Galit 2011, p. 3420). The fact that it did not require any external vibration for its compaction made it a favorite for people. At the time, Japan was facing a problem in compaction. This concrete was to be a solution. In most cases, this problem-emanated from the increased rate of loses of skilled workers and complexities in the architectural designs and details that were in the reinforcement in the modern structures (Hassan, Hossain & Lachemi 2008, p. 12).
The main concern for creating this concrete was its durability. The concrete also provided satisfactory consolidation without having to consider the need for vibration. The concrete fulfilled this through its new state properties. For instance, “in the plastic state, the concrete flows under its own weight at the same time maintaining homogeneity besides filling any formwork that ensures congested reinforcement of structures” (Burcu & Mehmet 2011, p. 287). The homogeneity of the concrete is maintained even during placement, transportation, and providing long-term durability. It guarantees structure performance. In the hard state, it surpasses the standard concrete in terms of its durability and strength (Kim, Trejo, Hueste, & Kim 2001, p. 130). Even though the new concrete- self-compacting concrete has gained dominant use in Europe and Japan, other countries in the world have not overwhelmingly embraced it. Therefore, this has resulted in less development in terms of local materials. According to Aggarwal, Siddique, Aggarwal, and Gupta, (2008, p. 20), this concrete flows under its own weight through restricted sections without bleeding or segregation. Therefore, the concrete has a low-yielded value that gives it a high-flow ability. It has a reasonable thickness that enables it to stand firm against separation and bleeding.
When this self-compacting concrete is well developed, it ensures that both stability and deformability in the constructions are in an equilibrium state. Various researchers have outlined guidelines for proper mixture proportion of the concrete. These guidelines include reduction of the volume ratio of the concrete aggregate to cementitious material in the ratio of one to two and the increment of paste volume and that of the water-cemented ratio. They also include controlling the maximum coarse aggregate of the size of the particles and the total volume, and finally the use of diverse viscosity-enhancing admixtures (Naji, Hwang, & Khayat, 2011, p. 422).
##Characteristics of SCC
Self-compacting concrete is different from normal or rather conventional concrete. One of the characteristics that differentiate this concrete from conventional concrete is that it has the ability to flow. It has no segregation characteristics, as opposed to its non-blocking tendency (Okamura & Ozawa1995, p. 120). An increase in its flowing ability lowers the risk of separation. This, therefore, means that it is important to use proper mix design when making the concrete
Procedure for making SCC
According to Okamura and Ouchi (2003), using super plasticizers is necessary when high mobility of the self-compacting concrete is preferred (p. 16). On the other hand, separation can be curbed when “large amounts of powdered materials or viscosity modifying admixture” (Okamura & Ozawa1995, p. 120) are used. These powdered materials that are mostly used in making the self-compacting concrete include “silica fume, fly ash, limestone powder, quartzite filler, and glass filler” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 19) among others. Because the “proportions of the mixture and the characteristic of the materials affect self-compactibility, it has become necessary to come up with a procedure that mixes its design” (Burcu & Mehmet, 2011, p. 287). Ozawa and Okamura have come up with a style of doing a mix proportioning. In their mix proportion, the fine and coarse aggregate contents are fixed. The self-compatibility is realized by changing the “super plasticizer dosage and water to power ratio” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 15). The composition of the coarse aggregate present in the concrete is placed “at 50 percent of the total amount of solid volume while the fine aggregate contents are fixed at 40 percent of the total amount of motors” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 19). On the other hand, the water to powder ratio is estimated at around 0.9-1.0 by volume. This relies on the characteristics of the super plasticiser amount and the powder. Determining the right volume of water/ powder is reached through a number of trails. Therefore, self-compacting concrete has this limitation- mix design procedures has not yet been established.
Universal Testing Method: Aim of Every Test
According to Okamura and Ouchi (2003), universal testing methods of self-compacting concrete are not much (p. 15).Therefore, this has contributed to some resistance by a number of countries to embrace this concept. One country that has resistance adoption of this concrete construction is Australia. However, the current and preferred methods of testing that meet European standards include slump flow test, also called total spread and T50 time, L-box test, J-ring test, and sieve stability test (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 20).
Universal Standards of Testing SCC
Sieve stability test is used to assess segregation resistance, site use, and suitability for laboratory use. J-ring test is used to primarily evaluate the ability of the concrete to allow water passage. It is suitable for the site and laboratory use. On the other hand, L-box test is used for assessment of passing ability. It is suited for laboratory use. Finally, yet important, is the slump test, which is appropriate for assessing filling ability (Aslani, & Shami, 2012, p. 360). Like the other test, it is also used on site and in the laboratory. Furthermore, European standards recommend other three alternative methods for testing SCC. These methods include V-funnel test, Orimet test, and penetration test. V –funnel test is used to partially indicate the ability of filing and blocking, Orimet test functions are similar to that of v-funnel test. While penetration test is adopted, it is used to assess segregation, and in most cases, in combination with sieve stability test. It is also used in the laboratory.
Slump test
Slump flow test evaluates the free movement of self-compacting concrete on a level plane that has no obstacles. The concrete moves “when a slump cone filed with concrete is lifted” (Attiogbe, See, & Dazkco 2007, Para. 5). The filling aptitude of the concrete is determined by the standard span of the concrete ring. The time T 50cm is another indication of the flow of the concrete. This determines the period spent in seconds from the moment the cone is hoisted “until the flow of the concrete reaches the diameter of 500mm” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 22). This slump test therefore checks the spreading ability and filling with self-compacting concrete. The first test indicates the spread and viscosity [deformity] while the second tests how fast the mixture is gong to spread on the expected and/or defined distance.
T50 and slump flow test are some of the most used universal tests that show the best association concerning key parameters on plastic viscosity and yield value (Okamura, & Ouchi, 2003, p. 15). The parameters are used to determine the filing capabilities of SCC. The T50 is one of the tests that show association. It has the ability to be repeated and reproduced easily. One of the advantages of these tests is their universal acceptance as well as being simple to complete. These advantages have made the test likeable by many countries given that it has been recommended by the European standardisation.
The Orimet
The Orimet and V-funnel tests have been cited as the second preferred tests after T50 /slump flow test. V-funnel flow time test is the time that a specific volume of SC takes to pass through an opening. This test helps to give an indication of the capabilities of the filing of SCC if segregation and blocking is not occurring (McSaveney, Papworth, & Khrapko 2003, p. 6). The time that it takes for the concrete to pass through such opening is associated with the level of plastic viscosity of the mixture.
##L-BOX and J-Ring
When it comes to testing the passing ability of fresh self-compacting concrete, the frequently used test includes L-box and J-ring. These tests can also be repeated and reproduced. L-box tests are most suited in laboratory environments while J-ring tests can be used in both laboratory and sites. L-box test has been found good in terms of blocking behaviour, as well as in real construction work. The idea behind using J-ring test is to find the difference between obstructed flow and the flow when a ring of bars used to act as reinforcement does not impede it. The test determines/shows the passing ability of fresh SCC.
Penetration and sieve stability test
Penetration test and sieve stability tests are used for testing the level of resistance to segregation. Between the two methods, sieve stability test gets the first priority because it is easy to use, reproduce, and even repeat the tests (Guneyisi, Gesoglu & Ozbay 2011, p. 160). Furthermore, this test helps to provide a good association with real constructions situations. It is also a very simple method that can be used for testing. Penetration method is likewise used in testing, but comes second after sieve stability tests. When using this method, a sample cylinder of fresh SCC is allowed to penetrate upon applying certain amounts of weight. The depth of penetration shows the stability of the mixture. This method is somewhat difficult to use in reproducing tests hence second priority.
##Invention of SCC
The invention of self-compacting concrete has solved the historical problems that are associated with regular concrete. Structures with large volumes of steel reinforcement can be put up easily when self-compacting concrete is used. For instance, one common problem that regular concrete has is that it requires excessive vibration. This leads to bleeding and segregation of the concrete. Furthermore, it leads to blockage of passages through which particles of concrete are supposed to pass. In addition, using regular concretes in areas that have large volumes or many reinforcements is difficult. Therefore, it requires skilled workers to use mechanical vibrators in building structures (Khayat, Bickley, & Lessard 2000, p. 382). On the other hand, using SCC has a number of advantages including its capability of reducing the labour costs that result from the vibration needs. Secondly is that SCC has potential of reducing instances of bleeding and segregation when putting up structures. Furthermore, self-compacting concrete has a lower viscosity, which allows workers to pour it into formwork, which then spreads under its own weight. While it spreads, the concrete is able to fill spaces and all corners of formwork producing a durable structure that can last long. The concrete fills and levels itself because of the forces of gravity. Hence, no segregation occurs. Vibrators are not needed to complete its consolidation
Low viscosity of SCC is an advantage that is not experienced in the conventional concrete. Therefore, this advantage allows the concrete to be pumped at a greater flow rate compared to the conventional concrete. This pumping requires low pressure and helps to elongate the life span of pumps since they are not exposed to great risks of wear and tear (Hughes 2001, p. 260). Another advantage of self-compacting concrete is that it cuts the costs that would have been incurred in the transportation of concrete in buckets to the sites of constructions. The use of self-compacting concrete can also reduce the period of construction, as well as the labour that is required to a significant margin. The longest bridge in the world- Akashi-Kaiyo- was constructed using self-compacting concrete using 290,000m3. The duration of its construction was shortened by twenty percent.
Impact of corrosion of durability
Durability of concrete is usually affected by corrosion of steel reinforcement. Chloride ions usually penetrate into concrete in those environment rich in chloride, these ions penetrate to the steel reinforcement corroding them. Low permeability concrete that has dense microstructures interferes with the process of diffusion of chloride ions into the concrete hence reducing the rate at which corrosion affects the steel reinforcement. Due to its better resistance to segregation and bleeding, SCC has less permeable microstructure (Mehta, & Monteiro 1996, p. 9). The fact that Self-compacting concrete is made from a number of materials including water, super plasticisers, and other supplementary cement materials helps to increase concrete corrosion resistance. High range water used in the making of SCC disperses cement particles present in the mixture hence reducing permeability of the concrete. Therefore, these elements help in making the SCC concrete one of the best construction materials in the world resulting to its continued acceptance by constructors.
Criticism of self-compacting concrete
Even though various studies on the durability of self-compacting concrete have been done using various components such as water permeation, chloride permeability, freezing and thawing, sulfate resistance, and salt resistance tests, they did not consider the durability of self-compacting concrete with respect to cracking and corrosion performance. This gap left the question on whether SCC is vulnerable to cracking or not. Therefore, this issue should be considered before a conclusion on its durability is made. Furthermore, the various specimens used in this study were presumably small: there durability properties may not be able to ensure durability or uniformity in performance in large-scale situations. Effects of segregation and bleeding are manifest in large-scale situations like beams compared to small samples. Moreover, coasting techniques and conditions, as well as rebar, may differ leading to variations. The quality of the concrete below the lowest horizontal reinforcement bars in large-scale situations is likely and or is expected to be more porous and weak because of inadequate compaction. Likewise, this scenario may be manifested in larger scale situations than in lab samples hence affecting corrosion and durability of the reinforcement bars used in making structures (Sheasby, Alexander & Cao 2001, p. 5). With reference to this, it is advisable for the test to be conducted on large-scale situations, as opposed to small samples because this is the surest ways to determine the durability and corrosive nature of the self-compacting concrete. Testing on these large situations will ensure that such instances are noted down. This can help in evaluating the durability and the benefits of these concrete with the conventional one.
The future of SCC
Since most of the tests conducted have suggested that self-compacting concrete is appropriate for construction, there is still a need to promote the techniques for its production and its use in construction work. According to Marsh (2005), there is the need for rational training and qualification systems /mechanisms to be put in place for engineers (Para. 6). Furthermore, introduction of new structural designing and construction systems that use self-compacting concrete should be done. This will see more people begin to use the concrete for their construction work (Marsh 2005, Para. 6). The self-compacting concrete should become a typical concrete instead of an exceptional one. This can only be achieved when it is widely used. It is a durable and a reliable concrete that makes durable structures besides having very little maintenance work compared to other conventional concrete.
Concrete Products
Over the years, as Turcry, Loukili, and Haidar (2011, p. 301) confirm, “the use of self-compacting concrete has been gradually increasing”. This increase has resulted from the durability and its various advantages. This concrete is now used to make various products because of its eliminated vibration noise. This concrete has contributed to beautification of various working environments in the urban centers as various products used for plants are made from these concrete. Another importance of this concrete is that it elongates the life span of products. This therefore helps to reduce the cost, which could have incurred through replacement and repair.
Benefits of self-computing concrete
According to Guneyisi, Gesoglu, and Ozbay (2011), self-computing concrete has a number of advantages including its high performance when it is fresh and hard (162). This ensures that the structure is durable. The concrete has some economic benefits or efficiency since it shortens the construction time, reduces labour in terms of the number of people required to engage in construction beside the low cost of equipment required. The concrete has the potentiality of improving the working and living condition of people, as it leads to high consumption of industrial by-products, reduces the amount of noise during construction, and curbing health hazards. Lastly, the concrete enhances or promotes automated construction processes since the concrete is portable and can be used with machines (p. 150).
Coloured SCC
According to Lopez, Tobes, Giacco, and Zerbino (2010), the development or design of colored compacting concrete has opened a new field of application (7). This is because it has added level of attractiveness and alternatives to various challenging architectural works in terms of color and shape to the already available varieties of aesthetic characteristics of the conventional concrete (Lopez, Tobes, Giaccio, & Zerbino, 2009, p. 6). In the coloured SCC, viscosity and fluidity of the matrix is used in modifying the spreading of pigment particles. Furthermore, there is a need for the colour to be homogeneous. The surface finishing should be used as a guide towards the selection of molding and de-molding agents. In colored self-computing concrete, mortar test design is conducted to find out the type and dosage of a pigment. In the making of design fixes for a coloured self-computing concrete, it is required that water/cement ratio be used in the initial stage to provide strength while the pigment/cement ratio is used as a function on the intensity of the colour. The contents of the pigments are required to be five percent of the weight of the cement (Lopez, Tobes, Giaccio, & Zerbino 2009, p. 6). After preparation of these, a series of mortars are prepared aiming at obtaining a right dosage of super plasticiser, the sand/cement, and cement/filer proportions. Since pigments are fine powders upon their incorporation in self-computing concrete, it allows one to arrive at the calcareous filler content.
Accepting test at the job site
The degree of compaction of any structure depends on the SCC. Therefore, poor SCC cannot be compensated. It is therefore important for the self-computing concrete to be checked. The whole amount needs to be checked before any casting is started at a construction site. Most of the conventional testing methods require sampling though this might take a considerable amount of time in circumstances that self-compatibility acceptance test is to be done on the whole amount of concrete. Therefore, Ouchi developed an appropriate acceptance test method by first installing “the apparatus between agitator trucks with its pump at the site” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 20). Moving of the concrete through the equipment is a sure way of testing for self-compatibility of the structure. However, it fails the test. Therefore, the mixture proportion has to be adjusted. In fact, “the apparatus was used at a site in Osaka Gas LNG tank, and was able to save a considerable amount of acceptance test work” (Persson 2001, p. 193).
Apart from this location, self-compacting concrete is used in many other ways. These include construction of bridges i.e. girder, anchorage, arch, tower, joint between the beam and girder, and pier. It is also used in building, construction of box culverts, concrete filled either steel column, tunnels [lining, fill of survey tunnel, immersed tunnel], dams [concrete around the structure], and concrete products such as water tanks, slab, block, culvert, and segment.
Durability and long-term properties
##Shrinkage
Long-term shrinkage is an issue of concern by many SCC press applications. Studies on shrinkage have tended to depict similarities in the shrinkage between the SCC and traditional concrete. For instance, Turcry et al (2002) asserted that, after duration of 150 days, the shrinkage that developed in both SCC and conventional concretes was the same (p.41). Likewise, in a study by Person [2001], they found out the same results after carrying out their tests for the duration of one and half years. However, Raghavan et al. (2002) came out with different results after carrying out his studies. He found out that SCC mixes recorded or experienced twenty-five percent lower than conventional concrete in terms of shrinkage (Para. 2). He however did not provide duration of his study thus leading to questioning of whether the study was authentic. Regardless of these findings, it clearly demonstrates that the shrinkage level of the SCC and conventional concrete is more or less the same with minor disparities between them.
Characteristic of SC in a fresh state
Peterson et al. (2003) identifies the main characteristics of SCC when in a fresh state as filling ability, passing ability, and resistance and segregation ability. Filling aptitude is the capability of the concrete to move on its own with its weight vertically, as well as horizontally without forming any shape in a given corner or place. Passing ability is the ability of the concrete to flow freely through dense but not reinforced with blocks places. Resistance and segregation is the ability of the self-computing concrete to maintain a uniform mix during and after placement without separating of its aggregate from paste and or water from solid (Horta, 2005, p. 9).
Sorptivity index
This test is based on water that flows into concrete through its large connected pores. The test measures permeability. Plain concretes have a high Sorptivity implying that they are permissible than the SCC. Addition of mineral admixtures decreases the Sorptivity of SCCs. Hence, this test is used to determine the permeability of concrete. It also indicates that SCCs have less permeability level than conventional concrete (Horta 2005, p. 56).
##Conclusion
In conclusion, from the discussion, it is evident that self-computing concrete has come along way and still has a long way to go. Even though it proved to be advantageous compared to the conventional one, a number of countries are yet to adopt and use SCC in their construction. A lot of sensitising and production is required to sensitise people on its benefits. Most of the investigations have sought to find varied ways in which the self-compacting concrete can become a standard concrete. Some of the methods used in testing include the rational mix design method among others.
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#Self-Compacting Concrete, Characteristics of SCC Research Paper
##Introduction
Self-compacting concrete (SCC) is a liquid /fluid often used in structures that have congested reinforcement and those, which do not require vibration. In the development of self-compacting concrete, one needs to strike a state of equilibrium for both deformability and stability. As Okamura and Ozawa (1995, p. 120) confirm, “the quality or characteristics of materials and the proportions of the mixtures also affect the compatibility of the self-compacting concrete”. Therefore, it is necessary for the evolution of procedures for designing these self-compacting concrete mixtures to ensure the longevity of structures. One of the surest ways to increase the stability of cohesiveness of the concrete is to use fine materials in these mixes. Despite the several investigations carried on this concrete, many large companies in Japan and around the world continue to use it because of its benefits. The paper presents a brief history of SCC followed by its characteristics besides showing how it works in relation to the ordinary concrete, amongst other details.
Historical background of the self-compacting concrete
Professor Okamura proposed the self-compacting concrete in 1986. This was after “several years beginning from 1983 in Japan when the durability of the concrete structure” (Okamura & Ozawa1995, p. 99) was at stake. Coming up with long-lasting constructions called for enough compaction, which again needed experienced personnel. Construction Company in Japan was facing a shortage of skilled workers, which contributed to a reduction in the quality of building and construction works (Deeb, Ghanbari, & Karihaloo 2011, p. 185). Maekawa and Ozawa in the University of Tokyo carried out further studies on self-compacting concrete. The studies bore fruits in 1988 when the model of SCC was finished with the use of locally available resources.
Countries that use SCC
The concept of self-compacting concrete manifested itself in Europe in the mid-1990s in most of the civil works. Most of the Sweden transportation networks relied on this concrete in their construction (Walraven 2002, p 356). Furthermore, the European Commission supported it by funding a multinational company specializing in the lead on self-compacting concrete in the late 1990s. Since then, many European construction companies have embraced this concrete using it in their building and construction work. Japan was one of the first countries in the world to begin using self-computing concrete in its construction work. The first application of concrete was in 1990. Then, it was used to make towers of concrete cable-stayed bridges in 1991(Guneyisi, Gesoglu & Ozbay 2011, p. 160). Lightweight SCC came in handy in the construction of beams of these bridges. Henceforth, other people have begun using this concrete in their construction work. Nowadays, the reason why many people prefer to use self-compacting concrete to traditional concrete is that it is easy, and it shortens the time of construction. It also guarantees compaction in the constructions, especially in the restricted regions.
##Benefits of SCC
Because most of the concretes that existed were poor in their compatibility, it was necessary for the introduction of self-compacting concrete. The concrete solved the problem of inadequate compaction that had earlier been experienced by the workers in the construction. Furthermore, the self-compacting concrete was designed in a manner that allowed uniformity in the quality of the concrete (Angel, Jaime, Galit 2011, p. 3420). The fact that it did not require any external vibration for its compaction made it a favorite for people. At the time, Japan was facing a problem in compaction. This concrete was to be a solution. In most cases, this problem-emanated from the increased rate of loses of skilled workers and complexities in the architectural designs and details that were in the reinforcement in the modern structures (Hassan, Hossain & Lachemi 2008, p. 12).
The main concern for creating this concrete was its durability. The concrete also provided satisfactory consolidation without having to consider the need for vibration. The concrete fulfilled this through its new state properties. For instance, “in the plastic state, the concrete flows under its own weight at the same time maintaining homogeneity besides filling any formwork that ensures congested reinforcement of structures” (Burcu & Mehmet 2011, p. 287). The homogeneity of the concrete is maintained even during placement, transportation, and providing long-term durability. It guarantees structure performance. In the hard state, it surpasses the standard concrete in terms of its durability and strength (Kim, Trejo, Hueste, & Kim 2001, p. 130). Even though the new concrete- self-compacting concrete has gained dominant use in Europe and Japan, other countries in the world have not overwhelmingly embraced it. Therefore, this has resulted in less development in terms of local materials. According to Aggarwal, Siddique, Aggarwal, and Gupta, (2008, p. 20), this concrete flows under its own weight through restricted sections without bleeding or segregation. Therefore, the concrete has a low-yielded value that gives it a high-flow ability. It has a reasonable thickness that enables it to stand firm against separation and bleeding.
When this self-compacting concrete is well developed, it ensures that both stability and deformability in the constructions are in an equilibrium state. Various researchers have outlined guidelines for proper mixture proportion of the concrete. These guidelines include reduction of the volume ratio of the concrete aggregate to cementitious material in the ratio of one to two and the increment of paste volume and that of the water-cemented ratio. They also include controlling the maximum coarse aggregate of the size of the particles and the total volume, and finally the use of diverse viscosity-enhancing admixtures (Naji, Hwang, & Khayat, 2011, p. 422).
##Characteristics of SCC
Self-compacting concrete is different from normal or rather conventional concrete. One of the characteristics that differentiate this concrete from conventional concrete is that it has the ability to flow. It has no segregation characteristics, as opposed to its non-blocking tendency (Okamura & Ozawa1995, p. 120). An increase in its flowing ability lowers the risk of separation. This, therefore, means that it is important to use proper mix design when making the concrete
Procedure for making SCC
According to Okamura and Ouchi (2003), using super plasticizers is necessary when high mobility of the self-compacting concrete is preferred (p. 16). On the other hand, separation can be curbed when “large amounts of powdered materials or viscosity modifying admixture” (Okamura & Ozawa1995, p. 120) are used. These powdered materials that are mostly used in making the self-compacting concrete include “silica fume, fly ash, limestone powder, quartzite filler, and glass filler” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 19) among others. Because the “proportions of the mixture and the characteristic of the materials affect self-compactibility, it has become necessary to come up with a procedure that mixes its design” (Burcu & Mehmet, 2011, p. 287). Ozawa and Okamura have come up with a style of doing a mix proportioning. In their mix proportion, the fine and coarse aggregate contents are fixed. The self-compatibility is realized by changing the “super plasticizer dosage and water to power ratio” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 15). The composition of the coarse aggregate present in the concrete is placed “at 50 percent of the total amount of solid volume while the fine aggregate contents are fixed at 40 percent of the total amount of motors” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 19). On the other hand, the water to powder ratio is estimated at around 0.9-1.0 by volume. This relies on the characteristics of the super plasticiser amount and the powder. Determining the right volume of water/ powder is reached through a number of trails. Therefore, self-compacting concrete has this limitation- mix design procedures has not yet been established.
Universal Testing Method: Aim of Every Test
According to Okamura and Ouchi (2003), universal testing methods of self-compacting concrete are not much (p. 15).Therefore, this has contributed to some resistance by a number of countries to embrace this concept. One country that has resistance adoption of this concrete construction is Australia. However, the current and preferred methods of testing that meet European standards include slump flow test, also called total spread and T50 time, L-box test, J-ring test, and sieve stability test (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 20).
Universal Standards of Testing SCC
Sieve stability test is used to assess segregation resistance, site use, and suitability for laboratory use. J-ring test is used to primarily evaluate the ability of the concrete to allow water passage. It is suitable for the site and laboratory use. On the other hand, L-box test is used for assessment of passing ability. It is suited for laboratory use. Finally, yet important, is the slump test, which is appropriate for assessing filling ability (Aslani, & Shami, 2012, p. 360). Like the other test, it is also used on site and in the laboratory. Furthermore, European standards recommend other three alternative methods for testing SCC. These methods include V-funnel test, Orimet test, and penetration test. V –funnel test is used to partially indicate the ability of filing and blocking, Orimet test functions are similar to that of v-funnel test. While penetration test is adopted, it is used to assess segregation, and in most cases, in combination with sieve stability test. It is also used in the laboratory.
Slump test
Slump flow test evaluates the free movement of self-compacting concrete on a level plane that has no obstacles. The concrete moves “when a slump cone filed with concrete is lifted” (Attiogbe, See, & Dazkco 2007, Para. 5). The filling aptitude of the concrete is determined by the standard span of the concrete ring. The time T 50cm is another indication of the flow of the concrete. This determines the period spent in seconds from the moment the cone is hoisted “until the flow of the concrete reaches the diameter of 500mm” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 22). This slump test therefore checks the spreading ability and filling with self-compacting concrete. The first test indicates the spread and viscosity [deformity] while the second tests how fast the mixture is gong to spread on the expected and/or defined distance.
T50 and slump flow test are some of the most used universal tests that show the best association concerning key parameters on plastic viscosity and yield value (Okamura, & Ouchi, 2003, p. 15). The parameters are used to determine the filing capabilities of SCC. The T50 is one of the tests that show association. It has the ability to be repeated and reproduced easily. One of the advantages of these tests is their universal acceptance as well as being simple to complete. These advantages have made the test likeable by many countries given that it has been recommended by the European standardisation.
The Orimet
The Orimet and V-funnel tests have been cited as the second preferred tests after T50 /slump flow test. V-funnel flow time test is the time that a specific volume of SC takes to pass through an opening. This test helps to give an indication of the capabilities of the filing of SCC if segregation and blocking is not occurring (McSaveney, Papworth, & Khrapko 2003, p. 6). The time that it takes for the concrete to pass through such opening is associated with the level of plastic viscosity of the mixture.
##L-BOX and J-Ring
When it comes to testing the passing ability of fresh self-compacting concrete, the frequently used test includes L-box and J-ring. These tests can also be repeated and reproduced. L-box tests are most suited in laboratory environments while J-ring tests can be used in both laboratory and sites. L-box test has been found good in terms of blocking behaviour, as well as in real construction work. The idea behind using J-ring test is to find the difference between obstructed flow and the flow when a ring of bars used to act as reinforcement does not impede it. The test determines/shows the passing ability of fresh SCC.
Penetration and sieve stability test
Penetration test and sieve stability tests are used for testing the level of resistance to segregation. Between the two methods, sieve stability test gets the first priority because it is easy to use, reproduce, and even repeat the tests (Guneyisi, Gesoglu & Ozbay 2011, p. 160). Furthermore, this test helps to provide a good association with real constructions situations. It is also a very simple method that can be used for testing. Penetration method is likewise used in testing, but comes second after sieve stability tests. When using this method, a sample cylinder of fresh SCC is allowed to penetrate upon applying certain amounts of weight. The depth of penetration shows the stability of the mixture. This method is somewhat difficult to use in reproducing tests hence second priority.
##Invention of SCC
The invention of self-compacting concrete has solved the historical problems that are associated with regular concrete. Structures with large volumes of steel reinforcement can be put up easily when self-compacting concrete is used. For instance, one common problem that regular concrete has is that it requires excessive vibration. This leads to bleeding and segregation of the concrete. Furthermore, it leads to blockage of passages through which particles of concrete are supposed to pass. In addition, using regular concretes in areas that have large volumes or many reinforcements is difficult. Therefore, it requires skilled workers to use mechanical vibrators in building structures (Khayat, Bickley, & Lessard 2000, p. 382). On the other hand, using SCC has a number of advantages including its capability of reducing the labour costs that result from the vibration needs. Secondly is that SCC has potential of reducing instances of bleeding and segregation when putting up structures. Furthermore, self-compacting concrete has a lower viscosity, which allows workers to pour it into formwork, which then spreads under its own weight. While it spreads, the concrete is able to fill spaces and all corners of formwork producing a durable structure that can last long. The concrete fills and levels itself because of the forces of gravity. Hence, no segregation occurs. Vibrators are not needed to complete its consolidation
Low viscosity of SCC is an advantage that is not experienced in the conventional concrete. Therefore, this advantage allows the concrete to be pumped at a greater flow rate compared to the conventional concrete. This pumping requires low pressure and helps to elongate the life span of pumps since they are not exposed to great risks of wear and tear (Hughes 2001, p. 260). Another advantage of self-compacting concrete is that it cuts the costs that would have been incurred in the transportation of concrete in buckets to the sites of constructions. The use of self-compacting concrete can also reduce the period of construction, as well as the labour that is required to a significant margin. The longest bridge in the world- Akashi-Kaiyo- was constructed using self-compacting concrete using 290,000m3. The duration of its construction was shortened by twenty percent.
Impact of corrosion of durability
Durability of concrete is usually affected by corrosion of steel reinforcement. Chloride ions usually penetrate into concrete in those environment rich in chloride, these ions penetrate to the steel reinforcement corroding them. Low permeability concrete that has dense microstructures interferes with the process of diffusion of chloride ions into the concrete hence reducing the rate at which corrosion affects the steel reinforcement. Due to its better resistance to segregation and bleeding, SCC has less permeable microstructure (Mehta, & Monteiro 1996, p. 9). The fact that Self-compacting concrete is made from a number of materials including water, super plasticisers, and other supplementary cement materials helps to increase concrete corrosion resistance. High range water used in the making of SCC disperses cement particles present in the mixture hence reducing permeability of the concrete. Therefore, these elements help in making the SCC concrete one of the best construction materials in the world resulting to its continued acceptance by constructors.
Criticism of self-compacting concrete
Even though various studies on the durability of self-compacting concrete have been done using various components such as water permeation, chloride permeability, freezing and thawing, sulfate resistance, and salt resistance tests, they did not consider the durability of self-compacting concrete with respect to cracking and corrosion performance. This gap left the question on whether SCC is vulnerable to cracking or not. Therefore, this issue should be considered before a conclusion on its durability is made. Furthermore, the various specimens used in this study were presumably small: there durability properties may not be able to ensure durability or uniformity in performance in large-scale situations. Effects of segregation and bleeding are manifest in large-scale situations like beams compared to small samples. Moreover, coasting techniques and conditions, as well as rebar, may differ leading to variations. The quality of the concrete below the lowest horizontal reinforcement bars in large-scale situations is likely and or is expected to be more porous and weak because of inadequate compaction. Likewise, this scenario may be manifested in larger scale situations than in lab samples hence affecting corrosion and durability of the reinforcement bars used in making structures (Sheasby, Alexander & Cao 2001, p. 5). With reference to this, it is advisable for the test to be conducted on large-scale situations, as opposed to small samples because this is the surest ways to determine the durability and corrosive nature of the self-compacting concrete. Testing on these large situations will ensure that such instances are noted down. This can help in evaluating the durability and the benefits of these concrete with the conventional one.
The future of SCC
Since most of the tests conducted have suggested that self-compacting concrete is appropriate for construction, there is still a need to promote the techniques for its production and its use in construction work. According to Marsh (2005), there is the need for rational training and qualification systems /mechanisms to be put in place for engineers (Para. 6). Furthermore, introduction of new structural designing and construction systems that use self-compacting concrete should be done. This will see more people begin to use the concrete for their construction work (Marsh 2005, Para. 6). The self-compacting concrete should become a typical concrete instead of an exceptional one. This can only be achieved when it is widely used. It is a durable and a reliable concrete that makes durable structures besides having very little maintenance work compared to other conventional concrete.
Concrete Products
Over the years, as Turcry, Loukili, and Haidar (2011, p. 301) confirm, “the use of self-compacting concrete has been gradually increasing”. This increase has resulted from the durability and its various advantages. This concrete is now used to make various products because of its eliminated vibration noise. This concrete has contributed to beautification of various working environments in the urban centers as various products used for plants are made from these concrete. Another importance of this concrete is that it elongates the life span of products. This therefore helps to reduce the cost, which could have incurred through replacement and repair.
Benefits of self-computing concrete
According to Guneyisi, Gesoglu, and Ozbay (2011), self-computing concrete has a number of advantages including its high performance when it is fresh and hard (162). This ensures that the structure is durable. The concrete has some economic benefits or efficiency since it shortens the construction time, reduces labour in terms of the number of people required to engage in construction beside the low cost of equipment required. The concrete has the potentiality of improving the working and living condition of people, as it leads to high consumption of industrial by-products, reduces the amount of noise during construction, and curbing health hazards. Lastly, the concrete enhances or promotes automated construction processes since the concrete is portable and can be used with machines (p. 150).
Coloured SCC
According to Lopez, Tobes, Giacco, and Zerbino (2010), the development or design of colored compacting concrete has opened a new field of application (7). This is because it has added level of attractiveness and alternatives to various challenging architectural works in terms of color and shape to the already available varieties of aesthetic characteristics of the conventional concrete (Lopez, Tobes, Giaccio, & Zerbino, 2009, p. 6). In the coloured SCC, viscosity and fluidity of the matrix is used in modifying the spreading of pigment particles. Furthermore, there is a need for the colour to be homogeneous. The surface finishing should be used as a guide towards the selection of molding and de-molding agents. In colored self-computing concrete, mortar test design is conducted to find out the type and dosage of a pigment. In the making of design fixes for a coloured self-computing concrete, it is required that water/cement ratio be used in the initial stage to provide strength while the pigment/cement ratio is used as a function on the intensity of the colour. The contents of the pigments are required to be five percent of the weight of the cement (Lopez, Tobes, Giaccio, & Zerbino 2009, p. 6). After preparation of these, a series of mortars are prepared aiming at obtaining a right dosage of super plasticiser, the sand/cement, and cement/filer proportions. Since pigments are fine powders upon their incorporation in self-computing concrete, it allows one to arrive at the calcareous filler content.
Accepting test at the job site
The degree of compaction of any structure depends on the SCC. Therefore, poor SCC cannot be compensated. It is therefore important for the self-computing concrete to be checked. The whole amount needs to be checked before any casting is started at a construction site. Most of the conventional testing methods require sampling though this might take a considerable amount of time in circumstances that self-compatibility acceptance test is to be done on the whole amount of concrete. Therefore, Ouchi developed an appropriate acceptance test method by first installing “the apparatus between agitator trucks with its pump at the site” (Aggarwal, Siddique, Aggarwal & Gupta 2008, p. 20). Moving of the concrete through the equipment is a sure way of testing for self-compatibility of the structure. However, it fails the test. Therefore, the mixture proportion has to be adjusted. In fact, “the apparatus was used at a site in Osaka Gas LNG tank, and was able to save a considerable amount of acceptance test work” (Persson 2001, p. 193).
Apart from this location, self-compacting concrete is used in many other ways. These include construction of bridges i.e. girder, anchorage, arch, tower, joint between the beam and girder, and pier. It is also used in building, construction of box culverts, concrete filled either steel column, tunnels [lining, fill of survey tunnel, immersed tunnel], dams [concrete around the structure], and concrete products such as water tanks, slab, block, culvert, and segment.
Durability and long-term properties
##Shrinkage
Long-term shrinkage is an issue of concern by many SCC press applications. Studies on shrinkage have tended to depict similarities in the shrinkage between the SCC and traditional concrete. For instance, Turcry et al (2002) asserted that, after duration of 150 days, the shrinkage that developed in both SCC and conventional concretes was the same (p.41). Likewise, in a study by Person [2001], they found out the same results after carrying out their tests for the duration of one and half years. However, Raghavan et al. (2002) came out with different results after carrying out his studies. He found out that SCC mixes recorded or experienced twenty-five percent lower than conventional concrete in terms of shrinkage (Para. 2). He however did not provide duration of his study thus leading to questioning of whether the study was authentic. Regardless of these findings, it clearly demonstrates that the shrinkage level of the SCC and conventional concrete is more or less the same with minor disparities between them.
Characteristic of SC in a fresh state
Peterson et al. (2003) identifies the main characteristics of SCC when in a fresh state as filling ability, passing ability, and resistance and segregation ability. Filling aptitude is the capability of the concrete to move on its own with its weight vertically, as well as horizontally without forming any shape in a given corner or place. Passing ability is the ability of the concrete to flow freely through dense but not reinforced with blocks places. Resistance and segregation is the ability of the self-computing concrete to maintain a uniform mix during and after placement without separating of its aggregate from paste and or water from solid (Horta, 2005, p. 9).
Sorptivity index
This test is based on water that flows into concrete through its large connected pores. The test measures permeability. Plain concretes have a high Sorptivity implying that they are permissible than the SCC. Addition of mineral admixtures decreases the Sorptivity of SCCs. Hence, this test is used to determine the permeability of concrete. It also indicates that SCCs have less permeability level than conventional concrete (Horta 2005, p. 56).
##Conclusion
In conclusion, from the discussion, it is evident that self-computing concrete has come along way and still has a long way to go. Even though it proved to be advantageous compared to the conventional one, a number of countries are yet to adopt and use SCC in their construction. A lot of sensitising and production is required to sensitise people on its benefits. Most of the investigations have sought to find varied ways in which the self-compacting concrete can become a standard concrete.