Short notes on :
Light Weight Concrete:- The most significant property is reduced weight at no sacrifice in strength. Structural lightweight concrete available today are rotary kiln expanded shale, clay or slate (roughly 80% of structural use) and sintered expanded shale or clay (20%) provides the same compressive strength as normal weight aggregates with approximately the same cement content.
If the lightweight concrete is comparable in compressive strength to normal weight concrete, the shear capacity (or, more correctly, the bearing capacity) of the connectors should be comparable. Pushout tests on shear connectors in lightweight concrete have indicated comparable value. In some areas, lightweight structural concrete is being specified because it has less shrinkage cracking potential than normal weight concrete. Although there are no definitive values available, the feeling exists with some researchers that lightweight concrete under test performs better in composite design, possibly because the slightly higher creep and shrinkage may tend to distribute the Vn-load to more connectors than when normal weight composite beams are tested.
The other property is the better performance of lightweight concrete in fire tests, because of its improved insulation characteristics.
Segregation:- Segregation can be defined as the separation of the constituent materials of concrete. If a sample of concrete exhibits a tendency for separation of say, coarse aggregate from the rest of the ingredients then that sample is said to be showing the tendency for segregation.
Bleeding:- Bleeding is sometimes referred as water gain. It is a particular form of segregation in which some of the water from the concrete comes out to the surface of the concrete.
Due to bleeding water comes up and accumulates at the surface. Sometimes along with this water certain quantity of cement also comes to the surface and reduces the wearing quality of the top surface of slabs and pavements.
White Cement:- For manufacturing various white cement or grey Portland cement is used as a base. The use of white cement as a base is costly. White cement consists of Portland cement with 5-10% of pigment. The raw material used are high purity limestone. The other raw material are china clay with iron content of about 0.72 to 0.8%, silica sand, fluorspar, as flux and selenite as retarder.
Abrasion Value:- This test helps to determine the abrasion value of coarse aggregates as per IS: 2386 (Part IV) – 1963.
The apparatus used in this test are Los Angles abrasion testing machine, IS Sieve of size – 1.7mm, Abrasive charge – 12 nos. cast iron or steel spheres approximately 48mm dia. and each weighing between 390 and 445g ensuring that the total weight of charge is 5000 +25g and Oven.
Procedure to determine Aggregate Abrasion Value:
The test sample and the abrasive charge should be placed in the Los Angles abrasion testing machine and the machine rotated at a speed of 20 to 33 revolutions/minute for 1000 revolutions. At the completion of the test, the material should be discharged and sieved through 1.70mm IS Sieve.
Short notes on :
What are the initial and final setting times of cement ? How are they experimentally determined ?
