CIV2235—STRUCTURAL MATERIALS
Week 4 Practice Class
Properties of Hardened Concrete
QUESTION 1: Select the appropriate option as answer and write down in the answer sheet (5 marks each)
1. The ability of the structure to provide a comfortable environment is called
a) Durability
b) Sustainability
c) Serviceability
d) Structural integrity
2. Strength of concrete increases with
a) increase in water-cement ratio
b) increase in fineness of cement
c) decrease in curing time
d) decrease in size of aggregate
3. Which of the following statements is true regarding the effect of crushed aggregates on the strength of concrete?
a) For a concrete member made of OPC and crushed aggregates, strength is less than that of a concrete member made of OPC and gravel aggregates.
b) For a concrete member made of RHPC and crushed aggregates, strength is less than that of a concrete member made of OPC and gravel aggregates.
c) The effect of crushed aggregates on strength is more in a concrete member made of RHPC compared to that made of OPC.
d) None of the above
4. When is the drying shrinkage measured by the certified laboratory?
a) After 7 days
b) After 28 days
c) After 1 year
d) None of the above
5. The drying shrinkage in concrete can be reduced by ---
a) Decreasing the aggregate’s elasticity modulus
b) Increasing the w/c ratio
c) Increasing the aggregate content
d) None of the above
6. Maximum allowed shrinkage strain in normal concrete as per AS1379, is
a) 1 µε
b) 10 µε
c) 100 µε
d) 1000 µε
7. Which of the following statements is wrong about the concrete mixer?
a) It distributes the concrete uniformly during mixing, discharging and agitating
b) It uses one specific speed during mixing, discharging and agitating
c) The mixed concrete inside the mixer is normally less than 65% of the mixer’s volume
d) None of the above
8. The design shrinkage in AS3600 standard is the sum of
a) Autogenous shrinkage strain and the drying shrinkage
b) Plastic shrinkage strain and the drying shrinkage
c) Plastic shrinkage strain and the thermal shrinkage
d) Autogenous shrinkage strain and the plastic shrinkage strain
QUESTION 2: Write BRIEF answers for the following questions.
1. List the three of the most important structural engineering properties of hardened concrete. For each of the 3 properties, outline the major factors affecting each of these mechanical properties. (12 marks)
2. Discuss which hardened property the most common concrete test measures and why it is important. (10 marks)
3. Describe two types of time-dependent deformation that occur in concrete and their mechanism. (8 marks)
4. A cylinder concrete sample with a diameter of 150 mm and the height is 300 mm.
(i) In splitting tensile test, the sample failed at a load of 300 kN and displacement of 0.3 mm. Calculate the tensile strength of concrete. (4 marks)
(ii) In compressive strength test, the sample failed at a load of 468 kN and displacement of 0.58 mm. Calculate the failure strength and failure strain. (4 marks)
(iii) Why an aspect ratio of 2 is adopted here to conduct the compressive strength test? (2 marks)
5. A concrete sample with a theoretical thickness of 37.5 mm. The characteristic compressive strength at 28 days is 50 MPa. The final basic drying shrinkage is 800×10-6.
(i) Calculate the dry shrinkage at 1000 days if we assume the sample is in interior environment. (8 marks)
(ii) Calculate the autogenous shrinkage at 1000 days. (8 marks)
(iii) Calculate the total design shrinkage strain at 1000 days. (4 marks)