Free CT 1: Building Materials (Building Stones) 10 Questions 10 Marks 7 Mins Vacuum concrete: It is the type of concrete in which the entrained air and excess water is removed for improving concrete strength. The water is removed by use of vacuum mats connected to a vacuum pump.
Lightweight concrete: It can be defined as a type of concrete which includes an expanding agent in it, so that it increases the volume of the mixture while giving additional qualities such as lessened the dead weight. Pre-stressed concrete: It is a form of concrete where initial compression is given in the concrete before applying the external load so that stress from external loads are counteracted in the desired way during the service period.
Air entrained concrete: It has effects on compressive strength of concrete and its workability. Air entrained concrete increases the workability of concrete without much increase in water-cement ratio. To maintain the desired compressive strength and workability of concrete together, generally in the case of higher strength concrete, admixtures are used.
- Air entraining agent is one such concrete admixture to increase the workability without affecting much reduction in compressive strength.
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- 1 What is air-entrained water?
- 2 Where is air-entrained cement used?
- 3 How is air entrained concrete made?
- 4 What causes entrained air?
- 5 Which one is not used as air-entraining agent?
- 6 What is Type 1 and Type 2 concrete?
- 7 Which type of cement is commonly used in Belize?
What type of cement is an air-entraining cement?
Air Entraining Cement is essentially ordinary portland cement in which air entraining agent is added during grinding of cement clinkers. Hence, it is also called Air Entraining Portland Cement as it is modified portland cement.
What is air-entrained concrete?
Entrained air refers to microscopic air bubbles intentionally incorporated into concrete during mixing, usually by use of a surface-active agent. These bubbles are spherical with diameters between 0.0004 and 0.04 in. (0.01 and 1 mm).
What is air-entrained water?
DISCUSSION – Air entrainment, or free-surface aeration, is defined as the entrainment/entrapment of un-dissolved air bubbles and air pockets that are carried away within the flowing fluid. The resulting air–water mixture consists of both air packets within water and water droplets surrounded by air.
It includes also spray, foam and complex air–water structures. In turbulent flows, there are two basic types of air entrainment processes ( Chapter 17 ). The entrainment of air packets can be localized or continuous along the air–water interface. Examples of local aeration include air entrainment by plunging jet and at hydraulic jump ( Fig.11.11(f) right ).
Air bubbles are entrained locally at the intersection of the impinging jet with the surrounding waters. The intersecting perimeter is a singularity in terms of both air entrainment and momentum exchange, and air is entrapped at the discontinuity between the high-velocity jet flow and the receiving pool of water.
Where is air-entrained cement used?
What is Air Entrained Concrete? Air entrained concrete contains microscopic air bubbles that help alleviate internal pressure on the concrete by providing small pockets for water to expand into when exposed to freeze-thaw conditions. Without these pockets water has no place to escape, leading to cracks and/or scaling in concrete that greatly diminish the lifespan of a structure.
Air is applied into a concrete mix via an air entraining admixture otherwise known as AEA. The amount of air in a mix can be adjusted to meet the specifications of the job at hand. Why do we use Air Entrained Concrete? It is beneficial to use air entrained concrete when placing concrete in areas with freeze-thaw conditions.
Freeze-thaw conditions occur when the temperature of an environment fluctuates between above freezing temperatures and below freezing temperatures. Additionally, air entrained concrete provides scaling resistance and a prolonged service life. It is important to use air entrained concrete to avoid cracks in the concrete which later leads to increased deterioration of the structure.
Technical Information: For freeze-thaw protection, the air content of a concrete mix will typically be in the 5-7% range. Depending on the amount of air specified, it will then be necessary to increase the cement content to achieve desired strengths. Although these air bubbles are microscopic, when the amount of air in a concrete mix is increased it will weaken the concrete.
Generally, the use of air entraining admixtures will lead to a strength reduction of about 5% for each 1% increase in the volume of air voids in a mix. The reason why this occurs is because as more air is introduced to the mix the concrete becomes less dense as well as more of the concrete being air.
With more cement (the “glue” in concrete) a concrete mix will have more strength. Therefore, if a concrete mix requires air entrainment there will typically be more cement in the mix to compensate for the strength loss. Advantages of Air Entrained Concrete: Air entrained concrete is key to freeze-thaw resistant concrete.
• Increased resistance to freeze-thaw conditions • Increased workability • Increased durability • Increased resistance to chemical attack • Increased cohesion Disadvantages of Air Entrained Concrete: • Strength loss • Decreases in unit weight • Potential honeycombing Folsom Ready Mix provides consistent, high-quality concrete.
Is Type 1 cement air-entrained?
Type I This is a general-purpose cement that is suitable for all uses where the special properties of other types of Portland cement are not required. Type IA Same as Type I except an air entraining admixture has been added during the manufacturing process.
Which of the following can be used as air entraining admixture?
2 Air Entraining Admixture – Air entraining admixture refers to the admixture that entrains a large number of uniform, stable and closed tiny bubbles in the process of mixing concrete to reduce the segregation of concrete mixture, improve the workability, and also enhance anti-freeze ability and durability of concrete.
It is a kind of surfactant, too. It has influences on concrete as follows: 1) It can improve the workability of concrete mixtures. The closed bubbles are like balls that can reduce the friction among cement particles to improve the mobility. Meanwhile, the bubble film can play a role of water conservation.2) It can enhance impermeability and frost resistance.
The closed stomata entrained by air entraining admixture can effectively cut off the capillary porosity ducts and reduce pores caused by segregation to enhance impermeability. Meanwhile, the closed pores entrained can be an effective buffer for the expansion caused by water freeze to improve frost resistance.3) It can reduce strength.
If the air content in concrete increases by 1%, its compressive strength will decrease by 4% ~ 6%. Thus, the adding amount of air entraining admixture should be appropriate. Air entraining admixture usually contains rosin resin, alkyl sulfonate, aliphatic alcohol sulfonate, protein salt and petroleum sulfonate, among which rosin resin is widely used.
Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781845699550500050
How is air entrained concrete made?
Air-entrained concrete is made by adding a detergent (an air-entraining admixture) to stabilize air bubbles trapped during mixing. In fresh concrete, the air bubbles reduce the water demand of the concrete and make the mix stickier, which helps to reduce segregation and reduces bleeding when air content is around 3%.
When was air entrained concrete first used?
Size – The air bubbles typically have a diameter of 10 to 500 (0.0004 to 0.02 ) and are closely spaced. The voids they create can be compressed a little, acting to reduce or absorb stresses from freezing. Air entraining was introduced in the 1930s and most modern concrete, especially if subjected to freezing temperatures, is air-entrained.
What causes entrained air?
Top 10 Causes Of Entrained Air Air entrainment occurs when the fluid contains air bubbles before it is pumped. Air entrainment can also be caused when liquid from an elevated point splashes into a wet well, causing turbulence and air bubbles to form. These air bubbles can get picked up and suctioned into the pump during operation.
- While air entrainment in miniscule amounts can be used to combat cavitation, just 1 or 2 percent air entrainment can cause pump performance to decrease.
- Result of air entrainment As air bubbles become trapped at the pump suction, they block the flow of fluid, leading to a gradual deterioration in pump performance.
As flow rate decreases, the developed head will drop off. This leads to an overall decrease in efficiency. Risks of trapped air Air entrainment causes increased vibration which leads to bearing failure. Entrained air can also collect in the seal chamber and cause mechanical seals to run dry.
A squeal at the start the pump can indicate entrained air when seal faces run dry. Entrained air can lead to the breaking of pump shafts as the pump may stall one second na pump the next in an endless loop. By introducing unwanted oxygen into the system, air entrainment can result in stress corrosion.
It can also cause a pump to lose its prime. The numbers speak for themselves:
Just 2% air entrainment can lead to a 12 % reduction in pump performance. Just 4% entrainment can lead to a 40 % reduction in pump performance At 10 % air entrainment, it’s quite likely your pump will stall completely.
Main causes of air entrainment: 1. Vortexing is the most common cause of entrained air. This happens to submersible pumps or pumps in suction lift applications when fluid levels in the tank or pit meets a certain level or when the static height of the fluid above the suction inlet is inadequate 2.
- Liquid is discharged from an elevated point into the pit or tank and free falls onto the fluid surface, dragging air into the suction line 3.
- Pumps and tanks had air in them to begin with and were not properly filled or vented during start up 4.
- Suction systems operated at a pressure below atmospheric (vacuum) can cause air to leak in at several places, (but when static, fluid will not leak out) 5.
Leaky suction line 6. Mixers and agitators add air into the process 7. Air and gases purposefully injected into the fluid (such as to prevent cavitation) used in excess 8. A chemical reaction, creating air or gases 9. Improper design of suction pipe geometry/arrangement with unvented high points that will not dissipate or reduce the air and gases present.10.
- The product contains entrained air, such as paper and pulp stock, as these companies often inject air in stock/slurry mixes.
- If you’d like to find out more about what could be causing entrained air in your pump (and what to do about it) call our toll-free number at 1-800- 367-4180.
- We have experts on hand to help you choose, install, and maintain a variety of equipment.
: Top 10 Causes Of Entrained Air
What are the types of admixtures in concrete?
Five Functions – Admixtures are classed according to function. There are five distinct classes of chemical admixtures: air-entraining, water-reducing, retarding, accelerating, and plasticizers (superplasticizers). All other varieties of admixtures fall into the specialty category whose functions include corrosion inhibition, shrinkage reduction, alkali-silica reactivity reduction, workability enhancement, bonding, damp proofing, and coloring.
- Air-entraining admixtures, which are used to purposely place microscopic air bubbles into the concrete, are discussed more fully in Air-Entrained Concrete.
- Water-reducing admixtures usually reduce the required water content for a concrete mixture by about 5 to 10 percent.
- Consequently, concrete containing a water-reducing admixture needs less water to reach a required slump than untreated concrete.
The treated concrete can have a lower water-cement ratio. This usually indicates that a higher strength concrete can be produced without increasing the amount of cement. Recent advancements in admixture technology have led to the development of mid-range water reducers.
- These admixtures reduce water content by at least 8 percent and tend to be more stable over a wider range of temperatures.
- Mid-range water reducers provide more consistent setting times than standard water reducers.
- Retarding admixtures, which slow the setting rate of concrete, are used to counteract the accelerating effect of hot weather on concrete setting.
High temperatures often cause an increased rate of hardening which makes placing and finishing difficult. Retarders keep concrete workable during placement and delay the initial set of concrete. Most retarders also function as water reducers and may entrain some air in concrete.
Accelerating admixtures increase the rate of early strength development, reduce the time required for proper curing and protection, and speed up the start of finishing operations. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather. Superplasticizers, also known as plasticizers or high-range water reducers (HRWR), reduce water content by 12 to 30 percent and can be added to concrete with a low-to-normal slump and water-cement ratio to make high-slump flowing concrete.
Flowing concrete is a highly fluid but workable concrete that can be placed with little or no vibration or compaction. The effect of superplasticizers lasts only 30 to 60 minutes, depending on the brand and dosage rate, and is followed by a rapid loss in workability.
As a result of the slump loss, superplasticizers are usually added to concrete at the jobsite. Corrosion-inhibiting admixtures fall into the specialty admixture category and are used to slow corrosion of reinforcing steel in concrete. Corrosion inhibitors can be used as a defensive strategy for concrete structures, such as marine facilities, highway bridges, and parking garages, that will be exposed to high concentrations of chloride.
Other specialty admixtures include shrinkage-reducing admixtures and alkali-silica reactivity inhibitors. The shrinkage reducers are used to control drying shrinkage and minimize cracking, while ASR inhibitors control durability problems associated with alkali-silica reactivity.
Which one is not used as air-entraining agent?
Concrete Technology Questions and Answers – Mix Design of LWC, Aerated Concrete This set of Concrete Technology Quiz focuses on “Mix Design of LWC, Aerated Concrete”.1. What is the amount of mixing water used to make LWC? a) 1/2 b) 2/3 c) 1/4 d) 1/3 View Answer Answer: b Explanation: The general practice for structural light-weight concrete is to mix the aggregate and about 2/3 of the mixing water for a period upto one minute prior to the addition of cement and the balance mixing water.2.
- What is the normal time to get uniform mixing? a) 30 seconds b) 2 or more minutes c) 1 minutes d) 24 hours View Answer Answer: b Explanation: Mixing is done continuously as required for homogeneity.
- Usually, 2 or more minutes are required to get uniform mixing.3.
- The strength of the resulting concrete is _ % lower than when dry aggregate is used for the same content.
a) 5-10 b) 10-15 c) 15-20 d) 0-5 View Answer Answer: a Explanation: It has been seen that the strength of the resulting concrete is about 5 to 10 percent lower than when dry aggregate is used for the same content and workability. Note: Join free Sanfoundry classes at or 4.
The density of concrete made with saturated aggregate is _ a) High b) Low c) Very high d) Very low View Answer Answer: a Explanation: Moreover, the density of concrete made with saturated aggregate is higher and the durability of such concrete, especially its resistance to frost is lower.5. The light-weight concrete is prepared by _ a) Mixing Portland cement with sawdust in specified proportion in the concrete b) Using coke-breeze, slag as aggregate in the concrete c) Mixing Al in the concrete d) Mixing Fe in the concrete View Answer Answer: b Explanation: The light-weight concrete is prepared by using coke-breeze, cinder or slag as aggregate in the concrete.6.
Aerated Concrete is _ a) Very heavy weight b) Heavy weight c) Medium weight d) Light weight View Answer Answer: d Explanation: Aerated concrete is also referred to as gas concrete, foam concrete, cellular concrete. In India we have at present a few factories manufacturing aerated concrete.7.
Air contents should be _ % by volume. a) 1-2 b) 2-3 c) 3-4 d) 4-5 View Answer Answer: c Explanation: This type of cement was first of all developed in U.S.A. It is recommended that air contents should be 03-04 % by volume.8. Which one is not used as air entraining agents? a) Alumina b) Natural resins c) Fats d) Oil View Answer Answer: a Explanation: Natural resins, fats, oils are used as air entraining agents not alumina.9.
Entrainment of air while applying cement, increases resistance to frost action. a) True b) False View Answer Answer: a Explanation: It is found that entrainment of air or gas bubbles while applying cement, increases resistance to frost action.10. Aerated concrete is made in the density of approx.
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What are the properties of air-entraining cement?
In cement: Types of portland cement Air-entraining cements are made by the addition on grinding of a small amount, about 0.05 percent, of an organic agent that causes the entrainment of very fine air bubbles in a concrete. This increases the resistance of the concrete to freeze-thaw damage in cold climates.
Which of the following types of cement is used in marine structures?
Free 20 Questions 20 Marks 20 Mins The blast furnace slag cement has very low permeability and provides good resistance to chloride and sulphate attack which is present in seawater. The blast furnace slag cement is widely used in the marine structure.
- Blast furnace slag cement other uses: Used for structures meant for water retaining such as retaining wall, rivers, ports, tunnels for improvement in impermeability.
- Used in mass concreting works such as dams, foundations which require low heat of hydration.
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What is Type 1 and Type 2 concrete?
Type I is a general purpose portland cement suitable for most uses. Type II is used for structures in water or soil containing moderate amounts of sulfate. Type II(MH) is a moderately sulfate resistant cement that also generates moderate heat during curing.
What is Type A cement?
TYPES OF CEMENT AND WHAT THEY DO – Portland Cement is a type of cement, not a brand name. Many cement manufacturers make Portland Cement. It is a basic ingredient of concrete, made using a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete.
- The Portland Cement Association’s How cement is made provides detailed information of the process.
- To find out more about what concrete is made of, concrete mix designs, admixtures, and water to cement ratios, read our section ” What Is Concrete ?” Type 1 – Normal portland cement.
- Type 1 is a general use cement.
Type 2 – Is used for structures in water or soil containing moderate amounts of sulfate, or when heat build-up is a concern. Type 3 – High early strength. Used when high strength are desired at very early periods. Type 4 – Low heat portland cement. Used where the amount and rate of heat generation must be kept to a minimum.
- Type 5 – Sulfate resistant portland cement.
- Used where the water or soil is high in alkali.
- Types IA, IIA and IIIA are cements used to make air-entrained concrete.
- They have the same properties as types I, II, and III, except that they have small quantities of air-entrained materials combined with them.
Types IL, IS, IP and It are blended hydraulic cements that offer a variety of special performance properties. A cement factory (Juan Enrique del Barrio / Shutterstock). These are very short descriptions of the basic types of cement. There are other types for various purposes such as architectural concrete and masonry cements, just to name two examples. Your ready mix company will know what the requirements are for your area and for your particular use.
Which type of cement is commonly used in Belize?
Belize Imports from Guatemala of Portland Cement, Aluminous Cement, Slag Cement, Supersulfate Cement & Similar Hydraulic Cements was US$7.63 Million during 2021, according to the United Nations COMTRADE database on international trade. – Trading Economics members can view, download and compare data from nearly 200 countries, including more than 20 million economic indicators, exchange rates, government bond yields, stock indexes and commodity prices.