# Construction

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## Job Description

Part A: Section B (10 short answer Question) (40)

7- Distinguish between cement, mortar and concrete.

8- What are the major ingredients for concrete? List them provide their role.

9- What is meant by “ease of placement of concrete?”

10- What will happen to the concrete if it is not cured?

11- Suppose you were to be the chief designer in charge of building a 100 storey concrete skyscraper. How would you get the concrete to the required height? What properties would the concrete need to have?

12- Explain how can you measure the workability of concrete?

13- Breifly discuss the difference between a water/cement ratio of 0.3 and 0.7.How would the two major concrete properties differ?

14- Explain the purpose of a admixtures in marking concrete. List 2 of them.

15- You are the engineer on site and ordered a concrete of 25 MPa and slump of 50mm. What should you do when you notice the slump is only 5 mm and in another instance the slump is 100 mm?

16- Explain what is meant by the standard 28 days strength of concrete, and how is it determined? Draw the graph and list all key points.

Part A: Section C: (1 long Question) (44)

17- (concrete mix design)

You are the chief engineer of a Melbourne based firm who has just been awarded the construction of a major sports stadium in Dubai. The stadium is to be built mainly by concrete and steel construction. Your firm has been successful in securing the project as costs have been, minimized as it has been agreed upo0n that locally available materials will be used for the concrete construction. The exposure classification and strength requirement is class C concrete (use Table 1.1 in the appendix). Due to restrictions, the concrete will be pumped on site. The scope of the project required that one hundred laboratory test results on the controlling mix had to be carried out which resultant in a standard deviation of 5.0 MPa.

Assume that you will be using general purpose Portland cement (Type A) with the density 3100 kg/m^3. The density of crushed coarse aggregate is 2800 kg/m^3 and its maximum size is 20 mm. The dry rodded density of coarse aggregate is 1600 kg/m^3. The density of fine aggregate is 2700 kg/m^3 and its fineness modulus is 3.0. The approximate amount of accidentally-entrapped air in the fully-compacted concrete should be estimated as 3%. All calculations are based on the British mix design concept.

(a) Show and explain that the design compressive strength is 60 MPa assuming a bell shape distribution and there is only a 5% margin of error

(b) Using the tables provided, what is the recommended slump?

(c) Using the supplied figure and assuming that the locally available cement has a maximum 28 day curing strength under normal conditions of 80 MPa for a water/cement ratio of 0.3, what is the required water cement ratio for the required concrete design?

(d) What is the required water per kg/m^3 of concrete?

(e) What is the required cement per kg/m^3 of concrete?

(f) What is the wet density of the concrete per kg/m^3 ignoring the entrapped air.

(g) What is the wet density of the concrete per kg/m^3 taking into account 3% of entrapped air?

(h) Determine the amount of sand per kg/m^3 of air entrained concrete

(i) Determine the amount of aggregate per kg/m^3 of air entrained concrete.

(j) During your trail mixes you have discovered that the locally available material is completely dry and absorption tests have determined that both aggregate and sand are at a moisture content of 1%. It is expected that the sand will absorbed a total of 4% water and the aggregate 5% when in completely dried condition. Determine the additional amount of water per kg/m^3 of air entrained concrete to achieve SSD conditions.

(k) You are required to carry out testing on 3 Australian standard cylinders and 3 beams. Assume a safety volume factor of 20%. 6 marks (Hint the cylinder is 200 mm high × 100 mm diameter, the beam is 100 × 100 × 350 mm).

(l) Sketch the 28 compressive strength profile of your design compressive strength. Assume the design compressive strength at 28 days, 15% at 1 day, 25% at 3 days, 50% at 7 days, and 75% at 21 days. 4 marks

(m) Explain how the compression test, tensile test and flexural strength tests are carried out in the lab by the way of sketches and dot points. List the compressive strength formula determined by these tests. Do not list the formulas for the other tests. Explain the importance when conducting the beam tests why we use a 4 point test rather than a 3 point test. Why can results differ from identical concrete samples?