Know more about concrete
How is concrete made?
Concrete is a mixture of paste and aggregates (sand and rock). The paste, comprising Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. This hardening process continues for years meaning that concrete gets stronger as it gets older. In this process lies the key to a remarkable trait of concrete: it is plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why one material—concrete—can build skyscrapers, bridges, pavements, sidewalks, superhighways, houses and dams.
Are concrete and cement the same thing?
Of course no. The words concrete and cement are commonly used interchangeably, but cement is really an ingredient in concrete. Therefore, there is no such thing as a cement sidewalk, or a cement mixer. The proper terms are concrete sidewalk and concrete mixer.
What is a Portland cement?
Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete—just as stainless is a type of steel and sterling a type of silver.
What does “cure” concrete mean?
Curing is one of the most important steps in concrete construction because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period—from five to seven days after placement for conventional concrete—the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Why does concrete crack?
Concrete, like all other materials, will slightly change in volume when it dries. In typical concrete this is about 1/16 of an inch in 10 feet. The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes
due to shrinkage.
Concrete is a mixture of paste and aggregates (sand and rock). The paste, comprising Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. This hardening process continues for years meaning that concrete gets stronger as it gets older. In this process lies the key to a remarkable trait of concrete: it is plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why one material—concrete—can build skyscrapers, bridges, pavements, sidewalks, superhighways, houses and dams.
Are concrete and cement the same thing?
Of course no. The words concrete and cement are commonly used interchangeably, but cement is really an ingredient in concrete. Therefore, there is no such thing as a cement sidewalk, or a cement mixer. The proper terms are concrete sidewalk and concrete mixer.
What is a Portland cement?
Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete—just as stainless is a type of steel and sterling a type of silver.
What does “cure” concrete mean?
Curing is one of the most important steps in concrete construction because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period—from five to seven days after placement for conventional concrete—the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Why does concrete crack?
Concrete, like all other materials, will slightly change in volume when it dries. In typical concrete this is about 1/16 of an inch in 10 feet. The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes
due to shrinkage.
Replies
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sexy_engineeragree and thanks for the post dear......... -
maria flor
Thanks. Welcome to CE. Why don't you post a short introduction about yourself here: #-Link-Snipped-#sexy_engineeragree and thanks for the post dear......... -
maria florTypes of concrete failures
1. Cracking
2. Crazing and map cracking
3.low resistance to wear
4.dusting
5.scaling
6.popouts
7.blisters
8. Spalling
9. Ponding and inadequate slope to drain
10. Curling and warping
11. Carbonation
12. Freeze / thaw -
maria florConcrete Finishes
The finishes of concrete may be classified as either form finished or mechanically finished and they are the following:
1. HARD STEEL TROWELED (BURNISHED TROWELED)
2. LIGHT STEEL TROWELED
3. FLOAT TROWELED
4. BROOM FINISH
5. SPECIAL CONCRETE FINISHES
*DRY SHAKE SURFACE HARDENERS
*BONDED TOPPINGS -
CIVILPRINCESS1. concrete is graded as M25, M30, M40, M60... all based on the compressive strength. an M25 grade concrete will have a compressive strength of 25 MPa.
2. in 28 days of curing the concrete will attain the required strength (25 MPa or 40MPa or so on...)
in 7 days curing it must have gained 70% of the strength.
3. two types of mix design: (i) volume batching, (ii) weight batching. the second is more preferred. -
CIVILPRINCESStests on fresh concrete:-
there are many tests like
1. slump test
This test is used to determine the workability of fresh concrete, which would normally be undertaken at the point of delivery to ensure the concrete is of adequate consistency for placement.
2. compression test
Cubes of fresh concrete are made to test a variety of properties on the eventually cured and hardened concrete. Fresh concrete is subjected to a standard compaction regime in the cube mould and is then normally initially cured under specific laboratory conditions.
3. air contest testing
Air content of fresh concrete is normally measured, by the use of a special air meter, to assess whether the concrete contains the required amount of air. This would be measured when air’s entrapment or entrainment is required by the concrete design.
4.Bleeding
This test method is used to measure the amount of bleed water which may escape from a freshly compacted concrete sample.
5. setting time
This test is used to determine the elapsed time between batching of a concrete sample and when it is deemed by standard methods to have set.
6. temperature
Temperature of concrete at the time of placement is important to control and to avoid many possible difficulties. In hot climates, it is important to measure the temperature of the fresh concrete to ensure it is not too hot, which could cause flash setting and rapidly reducing workability. Measurements are generally taken at the point of placement.
of these the 1, 2, 5 are mostly done. -
CIVILPRINCESSnon destructive testings on concrete structures:-
- VISUAL INSPECTION
- HALF-CELL ELECTRICAL POTENTIAL METHOD
- SCHMIDT REBOUND HAMMER TEST
- CARBONATION DEPTH MEASUREMENT TEST
- PERMEABILITY TEST
- PENETRATION RESISTANCE OR WINDSOR PROBE TEST
- RESISTIVITY MEASUREMENT
- ELECTROMAGNETIC METHODS OF TESTING CONCRETE
- RADIOGRAPHIC TESTING
- ULTRASONIC TESTING
- INFRARED THERMOGRAPHY
- CORROSION RATE MEASUREMENT
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maria florFor centuries, concrete has been used as a durable building material. Since the turn of the century, with the advent of steel reinforcing, concrete has become the most widely used building
material in modern society. Durable and corrosion resistant, concrete can resist attack by sunlight, moisture, most microorganisms, and come chemicals. Concrete is capable of achieving compressive strengths of as high as 14,000 P.S.I., and yet has relatively low tensile and flexibly strengths. Depending on the availability of raw materials and alternative building products, concrete can be relatively inexpensive to produce and simple to form into complex building shapes. -
maria florWhen cement is mixed with water the resultant product is referred to as PASTE. This is if substance that binds all other ingredients together.
Aggregates are divided into two categories and are comprised of a large number of naturally occurring and manufactured products. The basic distinction is as follows:
Fine aggregate - #4 sieve to pan (1/4" to powder)
Coarse aggregate - 3/8" to 1-1/2"
The addition of fine aggregate to the PASTE transforms the product to a MORTAR. The subsequent addition of coarse aggregate results in CONCRETE. -
maria florPlastic shrinkage, thermal shrinkage, settlement, movement can caused damage in concrete structures..in order to prevent this concrete joints are required. There are 3 common types of concrete joints and they are the following:
1. Contraction (Control) Joints-are purposely installed joints designed to regulate cracking that might otherwise occur due to the unpredictable, unavoidable, contraction of concrete.
2.Construction Joints- are made before and after interruptions in the placement of concrete or through the positioning of precast units.
3. Expansion Joints-are designed to prevent the crushing and distortion of the abutting concrete structural units that might occur due to the transmission of compressive forces that may be developed by expansion, applied loads, or differential movements arising from the configuration of the structure or its settlement. -
maria florWhat’s involved in ordering concrete?
1. Grade Preparation- involves setting the grade elevation and creating a level and well-compacted surface. Compaction can be obtained using a compactor, sprinkler or both.
2. Placing the Concrete- You need to determine how the concrete will be placed, e.g. directly from the mixer truck into the prepared grade, a pump (trailer or boom) or a wheelbarrow. If pumping, Rinker Materials will need to know the size of the pump and the name of the pump company. Also keep in mind that a mixer truck is quite large and requires clearance of at least 14 feet in height and 10 feet in width to safely reach a job site.
3. Ordering- By using a concrete calculator, you can determine the amount of concrete needed. It is best to overestimate since a concrete finishing crew will likely be on site and another mixer truck may not be readily available. It is extremely important to order the right amount of concrete. Any excess concrete will be taken back to the plant and disposed of properly. -
maria florSome common and main types of concrete are:
Normal concrete
High Strength Concrete
High Performance Concrete
Air Entrained Concrete
Light Weight Concrete
Self Compacting Concrete
Shotcrete
Pervious Concrete
Roller Compacted Concrete -
RISHABH LALAStages of involved in making concrete -
1.Batching -involves weight and volume batching
2.Mixing
3.Transporting
4.Dumping
5.Compaction
6.Finishing
7.Curing -
AnreWhat is Concrete Cancer??
Alkali-Aggregate Reaction is called as concrete cancer. The alkali-aggregate reaction is an important phenomenon that influences the strength of the concrete structure, how big or small the structure is.
#-Link-Snipped-#
Fig.1.Bridge girders and piers after alkali - aggregate reaction
Some of the aggregates are not completely inert. Some contain reactive silica which will react with the alkalies present in the cement ( i.e. Sodium Oxide and Potassium Oxide). The failures of many structures like pavements, piers and sea wall may be due to the alkali-aggregate reaction.
Alkali -Aggregate reaction
The alkali-aggregate reaction is the reaction between the alkalies present in the cement and the reactive siliceous minerals in the aggregate. During the alkali-aggregate reaction, alkali silicate gels of unlimited swelling type are formed. Swelling of alkali silicate gels results in the disruption of concrete with the spreading of pattern cracks and eventual failure of the concrete structures.
For More Details on Alkali Aggregate Reaction in Concrete, refer the article:
#-Link-Snipped-# for Concrete Cancer
#-Link-Snipped-# for control measures of alkali aggregate reaction -
Kavi DesaiCommon Problem while Concreting: Segregation:
Segregation in concrete means separation of concrete ingredients as the concrete mix is not homogeneous.A good picture of cohesion of the concrete mix is obtained by flow test. If the concrete is not cohesive the larger particles of aggregate will separate out and will move towards the edge. Another form of segregation happen if concrete mix carried out on a sloppy surface. A cement particle tends to run away from the center of the concrete mix and leaving the coarser material behind. Segregation cannot be measured in qualitative terms but can be detected by an expert eye.
For tips on avoiding and reducing the segregation of concrete, refer the following article: #-Link-Snipped-#
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