Free CT 1: Ratio and Proportion 10 Questions 16 Marks 30 Mins Explanation: Low Heat Portland Cement is the most suitable type of cement for mass concreting works. Hydration of cement is an exothermic process that produces a large quantity of heat. In mass concrete structures such as dams, retaining walls, bridge abutment, rafts, etc the rate of dissipation of heat of hydration from the surface is much lower than that generated.
|Type of cement
|Ordinary Portland cement
|General construction and masonry
|Rapid hardening cement (C 3 S is more)
|Rapid constructions like pavements
|Low heat cement (C3A is less at 5% and C2S is more at 46%)
|Mass concreting works
|Blast furnace slag cement (Slag is added)
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- 0.1 Why low heat cement is used in mass concreting?
- 1 What is the mass of concrete?
- 2 Where mass concrete is best used?
- 3 What is a mass concrete placement?
- 4 Which cement is used in mass concreting such as dams and nuclear power plants?
Why low heat cement is used in mass concreting?
Low Heat Cement is specially blended to provide a lower heat of hydration in concrete. This unique attribute makes it ideal for mass concrete pours where the rate of temperature rise and the maximum temperature achieved must be controlled in order to reduce the risk of thermal cracking.
What are the different type of cement used for concreting?
Types of Cement – The different types of cement come from adding various ingredients and changing the proportions of ingredients. These additions and changes allow cement to be used in everything from general construction work to sulfate-resistant applications like sewage systems. Portland cement is only one of five basic types of cement recognized by ASTM, the full list includes:
Type 1 is ordinary Portland cement (OPC), which is a general-use material. Type 2 has moderate sulfate resistance, and its MH variant is moderately resistant to heat of hydration. It’s used in structures that will come into contact with sulfate in water or soil. Type 3 cement is an extra rapid hardening cement. Most concrete takes about a month to get to its full strength after it is poured; this cement becomes harder more quickly. Type 4 is a low heat cement that radiates less warmth as it sets and dries. It’s used for applications where too much heat is undesirable. Type 5 cement is highly sulfate resistant, used for contact with high alkaline soil and water.
Other cement varieties you may run into include:
Types 1A, 2A, and 3A, which are variants of type 1, 2, and 3 cements. These types of cement have air-entraining materials mixed in to make them resistant to moisture damage. Types IL (Portland-limestone), IS (Portland-slag cement), IT (ternary blended), and IP (Portland pozzolana) cement, which are hydraulic and have special properties. IS cement, commonly known as slag cement, includes granulated blast furnace slag and is often used to replace a portion of the portland cement going into the concrete. Type GU, HE, MS, HS, MH, and LH cements, whose names refer to their properties. GU stands for general use, HE for high early strength, and MS and HS for moderate and high sulfate resistance. Similarly, MH and LH refer to cement types with moderate and high heat of hydration.
Across all of these cement types, the most commonly varieties of cement used include:
What is mass concrete used for?
🕑 Reading time: 1 minute Mass concrete is defined as heavy volume concrete work with large dimensions and boundary conditions that are prone to elevated temperatures due to a higher rate of the heat of hydration. The high temperature in concrete results in high thermal stresses, cracking, and reduced long-term strength gain. Mass Concreting for Dam Construction Image Credits: Brennan Mass concrete is a term associated with the large in-situ concrete poured structures like dams, bridge piers, foundations of a large building, and large concrete placements (minimum 1 m deep). This article explains the important features and composition of mass concrete as per the American Concrete Institute (ACI).
What is the mass of concrete?
Mass concrete is defined by the American Concrete Institute as: “any volume of concrete in which a combination of dimensions of the member being cast, the boundary conditions, the characteristics of the concrete mixture, and the ambient conditions can lead to undesirable thermal stresses, cracking, deleterious chemical reactions, or reduction in the long-term strength as a result of elevated concrete temperature due to heat from hydration.” (ACI 207.1R).
Mass concrete has been historically associated with large structures such as dams, bridge piers, and other large volume placements. However, due to the increasingly common use of fast-track construction practices and high-performance concretes with high cementitious contents, mass concrete issues are being experienced in typical bridge and building placements.
Understanding the causes of mass concrete issues (high internal temperatures and temperature-related cracking) is the key to producing a structure that provides many years of service. The resources below provide information pertaining to material selection, thermal control calculation methods, and construction practices for mass concrete placements.
Where mass concrete is best used?
Mass concrete is usually associated with large, poured in-situ concrete structures such as dams, bridge piers, foundations to very tall buildings and other large volume placements which are at least 1m-deep. In many cases, mass concrete is unreinforced and therefore strong in compression but weak in tension,
Construction of the Hoover Dam (pictured) on the Colorado River, USA, began in 1931, required enormous quantities of mass concrete (3.3 million cubic metres ) to construct its arch-gravity structure, It is 13.7m wide at the top and 201m-wide at the bottom.
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What is low heat cement used for?
Low Heat Cement – Low Heat Cement is designed to provide a lower ‘heat of hydration’ in concrete. This attribute makes it ideal for mass concrete pours where the rate of temperature rise and the maximum temperature achieved must be controlled in order to reduce the risk of thermal cracking.
What is the mix ratio for mass concrete?
1 : 3 : 6 and 1 : 4 : 8 for foundations and mass concrete works.
How do you treat concrete mass?
Curing Methods for Mass Concrete: – Mass concrete is a large volume cast-in-place concrete construction such as heavy footings, dams, piers, abutments and similar massive construction. The heat generated due to hydration process in these constructions are very high and require the proper heat control arrangements to control the cracking and volume change.
The effect of temperature rise is very high in case of high strength and high cementitious concrete. The recommendations for control of heat in mass concrete can be found in ACI 207.1R and ACI 207.2R. The curing of mass concrete in horizontal or sloping surfaces can be done by keeping it continuously wet by spraying of water, by using wet sand or by using the water-saturated fabrics.
For vertical surfaces water must be allowed to rundown from top to bottom inside the form by loosening the ties of top formwork. Immediately after striking of forms, these concrete surfaces can be covered with water-saturated fabrics or can be kept wet by continuous spray of water.
What is a mass concrete placement?
Mass placements are defined as placements with a least dimension greater than or equal to 5 ft., or designated on the plans.
What is the most commonly used type of concrete?
1. Normal strength concrete – Normal strength concrete, or “regular” concrete, is the most common type of concrete with a basic mix of cement, aggregates, and water. Normal concrete has a mixing proportion of 1:2:4 (one part cement, two parts aggregate, four parts water), however, the amount of water used will depend on the humidity of the location and the desired consistency of the concrete.
Which cement is used in mass concreting such as dams and nuclear power plants?
Free CT 1: Current Affairs (Government Policies and Schemes) 10 Questions 10 Marks 10 Mins Low Heat Portland Cement is particularly suited for making concrete for dams and many other types of water retaining structures, bridge abutments, massive retaining walls, piers and slabs etc.
- In mass concreting, there is often considerable rise in temperature because of the heat produced as the cement sets and hardens.
- The shrinkage which occurs on subsequent cooling sets up tensile stresses in the concrete, may result in cracking.
- The use of low heat cement is advantageous since it evolves less heat than OPC.
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Is PPC low heat cement?
Difference Between OPC and PPC Cement – The main differences in their characteristics and uses are –
Portland Pozzolana Cement is a variation of Ordinary Portland Cement. Pozzolana materials namely fly ash, volcanic ash, are added to the OPC so that it becomes PPC. Pozzolana materials are added to the cement in the ratio of 15% to 35% by weight.Both are ecofriendly materials but Pozzolana Cement uses natural and industrial waste thus reducing the environmental pollution.
|It has higher strength than PPC in the initial stage.
|The strength of PPC is good than OPC in long terms.
|It has high heat of hydration making it unfavorable for mass concreting.
|The hydration process is slower than OPC resulting low heat of hydration. Therefore, it is suitable for mass concreting.
|The presence of sulphates, alkalies, chlorides, etc. is higher and less resistant than PPC.
|It has low percentage of sulphate alkalis, chlorides, magnesia and free lime in its composition, which makes the concrete durable.
|OPC is not favorable in aggressive weather.
|Show greater resistance to aggressive weather.
|OPC cement are available in three grades, such as 33 Grade, 43 Grade, 53 Grade
|PPC is available in any specific grades.
|It is slightly costlier than PPC.
|Cheaper than OPC.
Conclusion: Both OPC and PPC are commonly used cements in construction. These days, PPC is used as a substitute of OPC. PPC is a variation of OPC which adds a mixture of a pozzolanic material that helps to enhance the strength of the concrete. PPC also brings down the amount of OPC requirement in making concrete.