22 questions and answers
What is hydration of cement ? Discuss the reactions that take place between cement compounds and water.
Anhydrous cement does not bind fine and coarse aggregate it acquires adhesive property only when mixed with water.
Give the physical characteristics of 53 grade OPC.
OPC means Ordinary Portland Cement. If the 28 days strength is not less than 53 N/mm2.
Write notes on Mixing and Mixer machines of concrete.
Mixing:- Thorough mixing of the materials is essential for the production of uniform concrete.
Explain Kelly Ball to measure the workability of concrete. Mention the limitation of the test.
This is a simple field test consisting of the measurement of the indentation made by 15 cm dia. metal hemisphere weighing 13.6 kg when freely placed on fresh concrete.
Differentiate between creep and shrinkage of concrete.
Creep can be defined as the time dependent part of the strain resulting from stress.
The Oxide composition of O.P.C. is as follows :
CaO (50%), SiO2 (15%), Al2O3 (5%), Fe2O3 (3%), SO3 (2%)
Find the percentage of C3S and C3A.
% of C3S = 4.07 (CaO) – 7.6 (SiO2) – 6.72 (Al2O3) – 1.43 (Fe2O3) – 2.85 (SO3)
What are the initial and final setting times of cement ? How are they experimentally determined ?
It is regarded as the time elapsed between the moment that the water is added to cement to the time that the paste starts losing its plasticity.
Describe about the Rebound Hammer test method and the ultrasonic pulse testing method for determining the strength of concrete.
It consist of a spring control hammer that slides on a plunger within a tubular housing. When the plunger is pressed against the surface of the concrete, the mass rebound from the plunger.
How do water-cement ratio and workability affect the strength of concrete? What are the factors promoting shrinkage?
w/c ratio is directly proportional to workability and inversely proportional to strength.
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