What is a pozzolana?
A pozzolan is a siliceous or siliceous and aluminous material that in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties.
Why is pozzolana added to cement?
As the definition implies, a pozzolan combines with calcium hydroxide in the concrete to form calcium silicate hydrate, similar to that produced by hydration of portland cement. Use of pozzolans may increase or decrease water demand depending on the particle shape, surface texture, and fineness. …
What is meant by pozzolanic reaction?
The pozzolanic reaction is the chemical reaction that occurs in portland cement upon the addition of pozzolans. The pozzolanic reaction converts a silica-rich precursor with no cementing properties, to a calcium silicate, with good cementing properties.
How Pozzolans are beneficial in cement manufacturing?
Typically pozzolans are used as cement replacements rather than cement additions. Adding pozzolans to an existing concrete mix without removing an equivalent amount of cement increases the paste content and decreases the water/cement ratio. In other words, adding more pozzolans to a mix changes the mix proportions.
Which is not pozzolanic material?
Which of the following is not a pozzolanic material? Explanation: Pozzolans are silicate based materials that form cementitious materials. Fly ash, silica fumes and slag are composed of oxide of silicon. Cinder is a coal residue.
What is known as clinker?
Clinker is a nodular material produced in the kilning stage during the production of cement and is used as the binder in many cement products. The lumps or nodules of clinker are usually of diameter 3-25 mm and dark grey in color.
Which cement is used in underwater construction?
Portland cement
Which cement is used in sewage and water treatment plant?
In the wastewater structures as the structures are in a corrosive environment the use of sulphur resisting cement (SRC) and Sulphur infiltrated concrete is very helpful in terms of DURABILITY parameter.
Which cement is used in coastal area?
Coastal+ is the cement specially designed considering the exposure conditions in coastal area, to provide complete protection to the structures from the aggressive environment. It also offers prompt technical services at all stages of construction.
Which cement is best for coastal areas?
Portland slag cement
Which cement is used in frost resistance concrete?
According to the results in the paper, air entraining cement (AEC) allows to get established air entraining degree of concrete mix, simultaneously providing required parameters of air void distribution and pore size, which is the condition of producing frost resistant concrete.
Where is M15 concrete used?
Regular grades of concrete are M15, M20, M25, etc. For plain cement concrete works, generally, M15 is used. For reinforced concrete construction minimum M20 grade of concrete is used.
How do you frost proof concrete?
Mixing frost-resistant concrete is primarily associated with two activities. The first one is to create a composite with a low water-cement ratio. While the second is adding thereto a special aeration admixture.
Is concrete frost resistant?
Concrete will suffer frost damage when saturated and subjected to freezing temperatures. Frost-durable concrete can be produced if a specialized surfactant, also known as an air- entraining admixture (AEA), is added during mixing to increase the volume of air voids.
How does Frost affect concrete?
If freshly placed concrete cools below 0ºC the water in the mix will freeze and expand. This could damage the concrete so much that it becomes useless and has to be removed. However, even after the concrete has reached 2 N/mm2 low temperatures will slow down the strength development.
What happens if concrete freezes?
If Concrete Freezes Too Soon Concrete that freezes when it is fresh, or before it has cured to a strength that can resist the expansion associated with the freezing water, will suffer a permanent loss of strength. Early freezing can reduce the final strength of the concrete by up to 50%.
What is freezing and thawing?
Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water. Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.
What are the three steps of freeze/thaw weathering?
Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through). Water enters cracks in the rock. When temperatures drop, the water freezes and expands causing the crack to widen. The ice melts and water makes its way deeper into the cracks.
How do you prevent freeze thaw?
The only way to prevent freeze/thaw damage is to treat your concrete with a quality concrete sealer. Siloxa-Tek 8500 or Siloxa-Tek 8505 are the best sealers to use to prevent freeze-thaw damage and prevent the incursion of water into the concrete.
What is the thawing process?
Thawing is the process of taking a frozen product from frozen to a temperature (usually above 0°C) where there is no residual ice, i.e. “defrosting”. Thawing is often considered as simply the reversal of the freezing process. However, inherent in thawing is a major problem that does not occur in the freezing operation.
Do not thaw before cooking?
Do: Cook Without Thawing You don’t have to thaw food. It just makes most meats cook quicker and more evenly. If it takes you 30 minutes to cook a thawed chicken breast, it’ll take you 45 to cook a frozen one. You also don’t have to thaw frozen vegetables: Just cook them straight from the package.
What are 3 acceptable methods for thawing food?
When thawing frozen food, it’s best to plan ahead and thaw in the refrigerator where it will remain at a safe, constant temperature — at 40 °F or below. There are three safe ways to thaw food: in the refrigerator, in cold water, and in the microwave.
What are 4 acceptable methods of thawing food?
There are four acceptable methods for thawing food: in a refrigerator, under cold running water, in a microwave, or as part of the cooking process.
Can I leave meat out overnight to thaw?
A lot of bacteria grows in the range of 40-100°F (4-38°C) (i.e. room temperature). It’s definitely not recommended to defrost meat at room temperature. In fact, you are not supposed to leave meat at room temperature for more than an hour. You grab a package of meat or chicken and use hot water to thaw it fast.
Can I leave chicken on the counter to thaw?
First, chicken should never be thawed or defrosted on the counter at room temperature or in a bowl of hot water. And whole chickens will take a very long time in a bowl of cold water. However, smaller cuts, and especially boneless cuts, do well with the cold bowl of water or microwave method.
Does meat thaw faster in cold water or hot water?
EVEN in kitchens where fresh is king, the freezer remains a handy tool. Thawing in cold water, 40 degrees or below, is safe and much faster — water transfers heat far more efficiently than air — but it can still take hours. …
How do you safely thaw frozen chicken?
Thawing chicken in the fridge is the best and safest way to defrost it, but it requires about a day of planning ahead, so if you need a faster solution, skip ahead. The day before you plan to cook your chicken, transfer it from the freezer to the fridge to let it thaw slowly, for at least 24 hours.