Concrete material


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Concrete Introduction in Building

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Concrete material

  2. 2. CONCRETE is made by mixing WATER COARSE AND FINE AGGREGATES CEMENT The aim is to mix these materials in measured amounts to make concrete that is easy to: 1.TRANSPORT 4. FINISH 3. COMPACT 2. PLACE
  4. 4. CEMENT-The cement powder, when mixed with water, forms a paste.-This paste acts like glue and holds or bonds the aggregates together.
  5. 5. AGGREGATES• Aggregates are of two basic types:1. COARSE: crushed rock, gravel or screenings.2. FINE : fine and coarse sands and crusher fines. Sand should be concreting sand and not brickies sand or plasterers sand. Aggregates should be:1.STRONG and HARD - A stronger, harder aggregate will give a stronger final concrete. Never use a crumble or flakey rock like sandstone.2. DURABLE to stand up to wear and tear and weathering.3. CHEMICALLY INACTIVE so the aggregates don’t react with the cement.
  6. 6. WATER• Water is mixed with the cement powder to form a paste which holds the aggregates together like glue.• Water must be clean, fresh and free from any dirt, unwanted chemicals or rubbish that may affect concrete.• Many concrete plants now use recycled water.• Always check bore water before use.• Don’t use sea water as it may rust the steel reinforcement in the concrete.
  7. 7. ADMIXTURES• Admixtures are mixed into the concrete to change or alter its properties. Example, the time concrete takes to set and harden, or its workability.• HOW THE PROCESS WORKS Measured amounts of the coarse and fine aggregates are mixed together. A measured amount of cement is added and mixed in.• Enough water is added to make the mix workable. All the materials are then mixed together well. The cement powder and water form a paste which bonds the aggregates together like glue.
  8. 8. CONCRETE PROPERTIES • The four main properties of concrete are: COHESIVENESS DURABILITYWORKABILITY STRENGTH • Concrete has three different states: PLASTIC SETTING HARDENING In each state it has different properties .
  9. 9. CONCRETE STATES1. Plastic State When the concrete is first mixed it is like bread dough. -It is soft and can be worked or moulded into different shapes. In this state concrete is called PLASTIC. Concrete is plastic during placing and compaction. -The most important properties of plastic concrete are workability and cohesiveness2. Setting State. -Concrete then begins to stiffen. The stiffening of concrete, when it is no longer soft, is called SETTING. - Setting takes place after compaction and during finishing. -Concrete that is sloppy or wet may be easy to place but will be more difficult to finish.
  10. 10. • Hardening State After concrete has set it begins to gain strength and harden. The properties of hardened concrete are strength and durability.• Hardened concrete will have no footprints on it if walked on
  11. 11. CONCRETE TESTING• There are two main tests to be done on concrete:1. SLUMP test. SLUMP test shows the WORKABILITY of concrete.• Workability measures how easy the concrete is to place, handle and compact.2. The COMPRESSION test. The COMPRESSION test shows the best possible strength concrete can reach in perfect conditions. The compression test measures concrete strength in the hardened state. Testing should always be done carefully. Wrong test results can be costly.
  12. 12. • SAMPLING• The first step is to take a test sample from the large batch of concrete. This• should be done as soon as discharge of the concrete commences. The sample should be• representative of the concrete supplied.• The sample is taken in one of two ways:-For purposes of accepting or rejecting the load: Sampling after 0.2 m been poured.-For routine quality checks: Sampling from three places in the load.
  13. 13. SLUMP TEST• The slump test is done to make sure a concrete mix is workable.• The measured slump must be within a set range, or tolerance, from the target slump.Tools• Standard slump cone (100 mm top diameter x 200 mm bottom diameter x 300 mm high)• Small scoop• Bullet-nosed rod• (600 mm long x 16 mm diameter)• Rule• Slump plate (500 mm x 500 mm)
  14. 14. METHOD1.Clean the cone. Dampen with water and place on the slump plate. The slump plate should be clean, firm, level and non-absorbent.2.Collect a sample.3. Stand firmly on the footpieces and fill 1/3 the volume of the cone with the sample. Compact the concrete by rodding 25 times. Rodding Rodding means to push a steel rod in and out of the concrete to compact it into the cylinder, or slump cone. Always rod in a definite pattern, working from outside into the middle.4. Now fill to 2/3and again rod 25 times, just into the top of the first layer.
  15. 15. 5. Fill to overflowing, rodding again this time just into the top of the second layer. Top up the cone till it overflows.6. Level off the surface with the steel rod using a rolling action. Clean any concrete from around the base and top of the cone, push down on the handles and step off the footpieces. 7. Carefully lift the cone straight up making sure not to move the sample. 8.Turn the cone upside down and place the rod across the up-turned cone.
  16. 16. 9. Take several measurements and report the average distance to the top of the sample.10. If the sample fails by being outside the tolerance (ie the slump is too high or too low), another must be taken. If this also fails the remainder of the batch should be rejected.
  17. 17. THE COMPRESSION TEST• The compression test shows the compressive strength of hardened concrete. The testing is done in a laboratory off-site. The only work done on-site is to make a concrete cylinder for the compression test. Tools• Cylinders (100 mm diameter x 200 mm high or 150 mm diameter x 300 mm high)• (The small cylinders are normally used for most testing due to their lighter weight)• Small scoop• Bullet-nosed rod (600 mm x 16 mm)• Steel float• Steel plate
  18. 18. METHOD1. Clean the cylinder mould and coat the inside lightly with form oil, then place on a clean, level and firm surface, ie the steel plate.2. Collect a sample.3. Fill ½ the volume of the mould with concrete then compact by rodding 25 times. Cylinders may also be compacted by vibrating using a vibrating table.
  19. 19. 4. Fill the cone to overflowing and rod 25 times into the top of the first layer, then top up the mould till overflowing. 5. Level off the top with the steel float and clean any concrete from around the mould.6. Cap, clearly tag the cylinder and put it in a cool dry place to set for at least 24 hours. 7. After the mould is removed the cylinder is sent to the laboratory where it is cured and crushed to test compressive strength.
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