Engineering Answers

Design a non-air-entrained concrete mix for a small job with a nominal maximum gravel size of 25

mm (1 in.). Show the results as follows:

a. masses of components to produce 2000 kg (4400 lb) of concrete

b. volumes of components to produce 1 m3

(36 ft3

) of concrete

The design of a concrete mix requires 1173 kg/m3

of gravel in dry condition, 582 kg/m3

of sand in

dry condition, and 157 kg/m3

of free water. The gravel available at the job site has a moisture

content of 0.8% and absorption of 1.5%, and the available sand has a moisture content of 1.1%

Design the concrete mix according to the following conditions:

Design Environment

 Pavement slab, Bozeman, Montana (cold climate)

 Required design strength = 3,000 psi

 Minimum dimension = 12 in

 Statistical data indicate a standard deviation of compressive strength of 250 psi is expected

(more than 30 samples).

 Only air entrainer is allowed.

Available Materials

 Air entrainer: Manufacture specification 0.15fl.oz/1% air/100 lb cement.

 Coarse aggregate: 2 in nominal maximum size, crushed stone

 Bulk oven-dry specific gravity = 2.573, Absorption = 0.1%

 Oven-dry rodded density = 120 pcf

 Moisture content = 1%

 Fine aggregate: Natural sand

 Bulk oven-dry specific gravity = 2.54, Absorption = 0.2%

 Moisture content = 3.67%

 Fineness modulus = 2.68

Design the concrete mix according to the following conditions:

Design Environment

 Building frame

 Required design strength = 27.6 MPa

 Minimum dimension = 150 mm

 Minimum space between rebar = 40 mm

 Minimum cover over rebar = 40 mm

 Statistical data indicate a standard deviation of compressive strength of 2.1 MPa is expected

(more than 30 samples).

 Only air entrainer is allowed.

Available Materials

 Air entrainer: Manufacture specification 6.3 ml/1% air/100 kg cement.

 Coarse aggregate: 19 mm nominal maximum size, river gravel (rounded)

 Bulk oven-dry specific gravity = 2.55, Absorption = 0.3%

 Oven-dry rodded density = 1761 kg/m3

 Moisture content = 2.5%

 Fine aggregate: Natural sand

 Bulk oven-dry specific gravity = 2.659, Absorption = 0.5%

 Moisture content = 2%

 Fineness modulus = 2.47

Using the following data for an unreinforced PCC Pavement slab, find the following:

 Design strength f’c = 4,000 psi

 Slab thickness = 12”

 Standard deviation f’c of obtained from 20 samples = 200 psi

 Ignore any exposure requirement

 Use air entrained concrete

 Fineness modulus of fine aggregate = 2.60

 Maximum aggregate size = 2” and nominal maximum aggregate size = 1.5”

 Bulk oven-dry specific gravity of coarse aggregate = 2.6

 Oven-dry rodded density of coarse aggregate = 125 pcf

a. required compressive strength

b. water-cement ratio

c. Coarse aggregate amount

d. If the w/c ratio is 10% reduced, will the quantity of coarse aggregate increase, decrease or remain

the same? Explain your answer.

A project specifies a concrete strength of at least 3000 psi. Materials engineers will design the mix for

a strength higher than that. Calculate the required average compressive strength of the mix design if

the standard deviation is s = 350 psi. Estimate the modulus of elasticity of the concrete at the required

average compressive strength (the calculated strength, not the given strength).

The design engineer specifies a concrete strength of 5500 psi. Determine the required average

compressive strength for

a. a new plant where s is unknown

b. a plant where s = 500 psi for 22 test results

c. a plant with extensive history of producing concrete with s = 400 psi

d. a plant with extensive history of producing concrete with s = 600 psi

You must provide a fully referenced, detailed log of researched evidence that you have extracted from component manufacturers’ catalogues, materials and design databases in relation to the development of your design work. 

Your work must include the information that you have used. 

2. Two parallel shafts connected by rolling cylinders turn in the same direction 150 rpm and 100 rpm respectively. The smaller cylinder is 16 in. in diameter. How far apart are the axes of the shafts? Please explain the answer.