This article provides information regarding formation of concrete. Portland cement is produced by combining calcium silicates, aluminates, and aluminoferrite. Clinker is made by mixing together minute quantities of limestone, clay, and other minerals. Cement that is older than three months ought to first be put through a series of strength examinations before being put to any practical use at all. Portland Pozzolana Cement (PPC) is obtained in one of two ways. It can be made by intergrinding a pozzolanic material with clinker and gypsum. The amount of time it takes for the concrete to set can be accelerated or slowed down depending on the salts, chemicals, clay, and other elements mixed inadvertently with the sand, aggregate, and water. Aggregates, before being used, should go through the required screening procedure and, if necessary, be cleaned by washing. It is crucial to keep in mind that fine aggregates must be free of coagulated lumps. Increasing the water-to-cement ratio leads to a reduction in the compressive strength of concrete. Mixing water should not contain any substances that have the potential to have a significant negative effect on the strength (i.e., on the process of hydration) or durability of the concrete. Water that is safe for consumption can also be used for mixing without requiring any major adjustments. High alumina cement contains more alumina than ordinary Portland cement. Water that contains free carbonic acid is water that should not be used in the manufacturing of concrete. The quality of concrete suffers when it is mixed with water that has a sulphate concentration greater than 1%.
Abstract:
This article provides information regarding formation of concrete. Portland cement is produced by combining calcium silicates, aluminates, and aluminoferrite. Clinker is made by mixing together minute quantities of limestone, clay, and other minerals. Cement that is older than three months ought to first be put through a series of strength examinations before being put to any practical use at all. Portland Pozzolana Cement (PPC) is obtained in one of two ways. It can be made by intergrinding a pozzolanic material with clinker and gypsum. The amount of time it takes for the concrete to set can be accelerated or slowed down depending on the salts, chemicals, clay, and other elements mixed inadvertently with the sand, aggregate, and water. Aggregates, before being used, should go through the required screening procedure and, if necessary, be cleaned by washing. It is crucial to keep in mind that fine aggregates must be free of coagulated lumps. Increasing the water-to-cement ratio leads to a reduction in the compressive strength of concrete. Mixing water should not contain any substances that have the potential to have a significant negative effect on the strength (i.e., on the process of hydration) or durability of the concrete. Water that is safe for consumption can also be used for mixing without requiring any major adjustments. High alumina cement contains more alumina than ordinary Portland cement. Water that contains free carbonic acid is water that should not be used in the manufacturing of concrete. The quality of concrete suffers when it is mixed with water that has a sulphate concentration greater than 1%.
1. CEMENT
Calcium silicates, aluminates, and aluminoferrite are the three primary components that combine to produce Portland cement. Aluminoferrite is also a contributing component 1. Clinker is made by mixing together minute quantities of limestone, clay, and a variety of other minerals in very specific proportions. Following the pulverisation step, this mixture is next heated to high temperatures (about 1500 degrees Celsius) and subjected to high temperatures 2. After that, the clinker is ground into a fine powder, and regular Portland cement is produced by combining it with a little amount of gypsum in a reasonably constant ratio (OPC) 3. When mixed with water, sand, and stone, and then allowed to go through a slow chemical reaction with the water, it results in the formation of a brittle mass that is known as concrete 4. Cement is a hygroscopic material, which implies that it is capable of collecting moisture and is therefore classified as a hygroscopic material 5. Hydration is the name given to the chemical reaction that takes place when it is exposed to moisture 6. Hydration takes place when anything is exposed to water 7. The conclusion that can be drawn from this is that cement will remain in good condition provided that it does not come into touch with any kind of moisture 8. Cement that is older than three months ought to first be put through a series of strength examinations before being put to any practical use at all 9.
According to the findings of the Bureau of Indian Standards (BIS), OPC can be separated into three main classes 10. The compressive strength of mortar cubes, which are formed of cement and sand and have a face area of fifty square centimetres, is the most important factor that is considered during classification 11. The ratio of water to cement is established through a procedure that has been predetermined, and the proportion of cement to sand, measured in terms of weight, is one part cement to three parts standard sand 12. The grades are as follows: (i) 33 grade (ii) 43 grade (iii) 53 grade 13.
The grade number provides an indicator of the minimum compressive strength in N/mm2 of cement sand mortar after it has been allowed to cure for a period of 28 days, as determined by the testing method that was presented earlier 14.
Portland Pozzolana Cement (PPC) is obtained in one of two ways: either by intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement 15. Both methods result in the same finished product 16. Both of these approaches wind up producing the same effect in the end. In the modern world, thermal power plants generate fly ash, which can afterwards be processed and used in the manufacturing of PPC after going through the appropriate steps 17. This fly ash is of an exceptionally high calibre 18.
2. ADVANTAGES OF USING PORTLAND POZZOLANA CEMENT OVER OPC
When water is added to cement, the pozzolana in the cement combines with the lime and alkali to produce compounds 19. These compounds can then be used in the cement manufacturing process 20. These chemicals make a contribution to the cement's strength, as well as its impermeability and resistance to sulphate 21. In addition to this, it helps make the material more workable, it decreases bleeding, and it limits the destructive expansion that is induced by the reaction between alkali and aggregate 22. This effect is achieved via a reduction in the heat required for hydration, which in turn controls temperature differentials 23. Temperature differences are what cause thermal strain, which in turn causes cracking in mass concrete structures like dams 24. Examples of these types of constructions include tunnels and dams 4. The pozzolanic ingredient that is utilised in the manufacturing process of PPC is the source of the product's distinctive colour 9. Invariably, the PPC that uses fly ash as a pozzolana will exhibit a colour that is different from that of the OPC. This is because fly ash is a pozzolanic material 11. It is important to keep in mind that the colour of the cement has no bearing on the quality of the product; rather, the quality of the cement is determined by the raw materials that are used in its production as well as the quality control methods that are put into place throughout that production 22. It is important to keep in mind that the colour of the cement has no bearing on the quality of the product 17. The nature and colour of the raw materials that are used to create cement are the primary contributors to the colour of the finished product 10. The type and colour of the raw materials that are used to make cement will differ from factory to factory, and may even change between batches of cement made by the same manufacturer 21. This is because cement is made from a variety of different components 6. Additionally, the colour of the aggregates, as well as, to a lesser extent, the colour of the cement, can have an impact on the final colour of the concrete once it has been completed 13. To offer preference to one particular cement over another only on the basis of colour would, from a theoretical standpoint, be improper 19.
3. SETTLING OF CEMENT
When water and cement are mixed together, a paste is generated that, for a limited amount of time, is able to keep its pliability and flexibility despite the drying process 24. During this period, you do not need to worry about any detrimental effects developing as a result of moving the paste around or reapplying it because there will not be any at this point 4. When the interaction between the water and cement is allowed to continue for a longer period of time, the paste loses its ability to be flexible 8. The "setting" stage is the first step in cement's transition into a more solid substance, and it's given that name because of how it happens 10. As soon as the initial setting of the cement paste has taken place, it has grown noticeably more rigid and has lost its ability to be flexible 19. When the paste has become more solid and is able to withstand some light load, this marks the completion of the setting process 21. Both of these points are completely arbitrary; the only ones that count are the ones that are determined by the Vicat needle penetration resistance 5.
In the vast majority of instances, the type of cement used is what decides how soon or how slowly it will set 22. There is also the possibility that the issue is the result of factors that are unconnected to the cement itself 11. The conditions of the surrounding environment play a vital role in this 17. The sun goes down earlier in the summer when it is hotter outside, but it goes down later in the fall and winter when it is cooler 15. The amount of time it takes for the concrete to set can be sped up or slowed down depending on the sorts of salts, chemicals, clay, and other elements that are mixed inadvertently with the sand, aggregate, and water 19.
4. The retrieval and storage of cement
It demands special attention since, if it isn't given, it can lead to a loss not just in terms of monetary loss, but also in terms of a loss in the product's quality. Both of these outcomes are undesirable 2. The following is a list, in the opinion of the recommendation, of things that should not be done 1:
a) Never store bags in a building or a godown that does not have completely waterproof walls, roof, and floors 1.
b) Do not store bags in a brand-new warehouse before the interior has had sufficient time to become totally dry. This guideline applies in any circumstance, including when the storage facility was just built 16.
c) You should not be content with doors and windows that do not fit properly; rather than settling for this, you should check to see that they do fit properly and then take steps to ensure that they remain closed 9.
d) Under no circumstances should you stack the bags against the wall. In a similar vein, you shouldn't stack them on the floor unless it's a concrete floor that's entirely dry, unless it's a concrete floor that's completely dry. If this is not possible, the bags should be placed on wooden sleepers or planks 21.
e) It is imperative that the bags be stacked in a compact way; this point should not be overlooked 23.
f) The height of a stack shall not exceed 15 bags to its maximum capacity, and the bags should be put in a header-and-stretcher formation 16.
g) Refrain from disturbing the cement that has been kept until it is appropriate to take it out of storage and start using it 19.
h) You are not permitted to take items out of only one layer at a time when removing baggage. Take a step or two or three in the opposite direction 21.
i) Do not keep dead storage. When retrieving bags from storage, it is essential to follow the "first-in, first-out" protocol. This means that the most recently stored bags should be removed first 7.
j) If you have to temporarily store bags at the job site, do not stack them on the ground. Instead, find a safe place to put them. Put them in a heap on an elevated platform that is free of moisture, and then cover the heap with a tarp or a sheet made of polythene 10.
5. AGGREGATES
In order to fulfil the requirements for the coarse aggregate, the construction project must employ river gravel or crushed stone. It should be firm, sturdy, dense, and long-lasting, and it should not contain any clay or loamy admixtures, quarry refuse, or vegetal matter 12. Also, it should not contain any clay. In addition to that, it needs to be tidy 20. The components that go into making up the aggregate should have a shape that is either cube-like or rounded, and the surfaces of those components should either be granular, crystalline, or smooth (but not shiny), with the proviso that they should not have the appearance of being powdered 9. Aggregates, before being used, should go through the required screening procedure and, if necessary, be cleaned by washing. This is to ensure that they are of the highest quality 24.
It is recommended that coarse aggregates be thrown away if they contain mica or shards that are flat, elongated, or flaky 1. This is because mica is a very fragile mineral 3. When grading coarse aggregates, it is suggested that the specifications of IS-383 be followed as closely as possible 23. After being submerged in water for twenty-four hours, a sample of the coarse aggregate that had been dried out earlier should not experience a gain in weight that is greater than five percent 8. When one stores aggregates, they should do so in such a way as to keep the sizes from becoming separated and to avoid contaminating the material with particles 11. This can be accomplished by storing the aggregates in an airtight container 24.
Fine aggregate is defined as aggregate that can pass through a sieve with a size of 4.75 International Standards Units 1. This size of sieve is used to define fine aggregate 21. The incorporation of fine aggregate into concrete serves to enhance the material's workability and puts the mixture one step closer to being homogenous 16. Whenever fine aggregate is required for construction projects, it is common practise to source sand from natural rivers 17. It is crucial to keep in mind that fine aggregates must be free of coagulated lumps 8. This is one of the most important things to keep in mind 19. When grading fine aggregates, also known as natural sand or crushed stone, the process must be carried out in such a way that not more than 5 percent of the particles can be larger than 5 millimetres, not more than 10 percent of the aggregate must pass IS sieve No. 150, not less than 45 percent nor more than 85 percent of the aggregate must pass IS sieve No. 1.18 millimetres, and not less than 25 percent nor more than 60 percent of the aggregate must pass IS sieve No as per protocol 9.
6. WATER
The strength of concrete suffers when the water-to-cement ratio is altered in any direction, regardless of which direction it is changed from 15. The compressive strength of concrete suffers when the water-to-cement ratio is increased, while the workability of concrete suffers when the ratio is decreased 6. Increasing the water-to-cement ratio leads to a reduction in the compressive strength of concrete 1. When it comes to the manufacture of cement and concrete, water is one of the most crucial components 22. As a consequence of this, the ratio of water to cement needs to be adequate in line with the regulations, and it needs to be correct 10.
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- Anónimo,, 2022, Concrete formation. Strategies to prepare good standard concrete, Múnich, GRIN Verlag, https://www.grin.com/document/1286517
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