CONSTRUCTION Flashcards
To compress 2.8 m3 of free air per minute from atmospheric (0.101 N/mm2) to (0.7 N/mm2 indicated on the gauge (i.e. 8.01 bar absolute) requires a compressor with a theoretical power value
Theoretical power = 103 Γ 0.101 Γ v1 log
A. 9.7 kW or 11.3 hp
B. 7.9 kW or 11.3 hp
C. 9.7 kW or 13.1 hp
D. 7.9 kW or 13.1 hp
9.7 KW /13.1 HP
The density of air decreases with increasing altitude and thus for a compressor operated above sea level, k should be reduced. For example, to compress 2.8 m3 of air per minute from 0.05 N/mm2 (atmospheric pressure) to 0.801 N/mm2 (absolute pressure) requires a compressor with a power value of
A. 7.46 kW B. 6.47 kW C. 7.64 kW D. 6.74 kW
6.47 KW
Calculate the pressure loss for a 200 m length of 50 mm diameter pipe, resulting from delivering 10 m3/min (free air) compressed to 7 bar, i.e. 8 bar absolute. Use π = 82 Γ 103 for steel pipes.
A. 0.64 bars
B. 0.44 bars
C. 0.46 bars
D. 0.66 bars
0.46 bars
A drill hole of diameter d (mm), with the bottom charge extending 1.3B from the base, contains explosive of unit weight P kg/m3, thus
π Γππ2 Γ1.3π΅=πβ²β² 1064π
πβ²β² =πΓ0.8Γπ(1.4π π΅2 +1.4π π΅3)+(π +π )π΅4 ππ€π΅2344
When f = 1, S/B = 1, w = 1, P = 1000, a2 = 0.07, a3 = 0.4, and terms with B4 are ignored. When d = 50 mm, then B is
A. 1.0 m B. 1.5 m C. 2.0 m D. 2.5 m
1.5 m
Wells are founded in a circular pattern around an excavation 30 m long and 25 m wide. The height of the water table above an impermeable stratum is 9 m. The depth of the excavation is 5 m and the water table lies 1 m below ground level. The coefficient of permeability of the soil k = 0.002 m/s. Determine the required number of wells.
A. 25 wells B. 15 wells C. 35 wells D. 45 wells
15 wells or 20 wells
Determine the hourly production of 0.57 m3 capacity backhoe, excavating a foundation 3 m deep in common earth.
A. 33 m3/h B. 44 m3/h C. 55 m3/h D. 66 m3/h
44 m^3/hr
Trucks are loaded by a 1 m3 capacity tracked loader machine at the rate of 30 m3/h bulked material. The truck transports the material to a tip 3 km away. Select the size and number of trucks required.
Select truck size, say, loader bucket capacity x 5 = 5 m3 capacity truck.
Minutes Load time = 60/30 x 5 β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.. 10 Cycle time to tip and back (average speed, 20 kph) .. 18
Dumping, turning and accelerating β¦β¦β¦β¦β¦β¦β¦β¦. 3 β-
31
A. Four 4 m3 capacity
B. Three 5 m3 capacity
C. Five 2 m3 capacity
D. Two 3 m3 capacity
Three 5 m^3 capacity
Trucks arrive at an excavator from distribution points on a large earthmoving project. The arrival time intervals of the trucks are observed and yield the following results.
Arrival time interval (min) Frequency (%)
2 10
3 15
4 30
5 25
6 20
The time taken to load the trucks, which are either 6 or 12 m3 capacity, are fairly constant at 3 and 5 min, respectively, and
both types are equally represented in the fleet.
If the excavator loads each of the trucks immediately it arrives, in the order that it arrives, calculate the total time that the excavator and trucks will be waiting in any one period of two hours selected at random.
A. Waiting time of excavator = 12 min; of trucks = 12 min
B. Waiting time of excavator = 16 min; of trucks = 16 min
C. Waiting time of excavator = 12 min; of trucks = 16 min
D. Waiting time of excavator = 16 min; of trucks = 12 min
Waiting time of excavator: 12 mins.
Waiting time of trucks: 16 mins.
Quarry rocks of 350 mm size are delivered to a crushing plant at a rate of 50 t/h. The sizes required are
38 mm to 19 mm
19 mm to fines
Select appropriate crushers and screens.
Hint: Maximum allowable size of material = 0.8 x feed opening
A. 438 mm
B. 348 mm
C. 384 mm
D. 483 mm
Size = 438 mm
A large number of test results produce a standard deviation (s) a 1.5 N/mm2, and average strength 10 N/mm2. If 5% of results are permitted to fail, what should be the minimum design strength of the mix?
Hint: π₯ = πΜ
β ππ
A. 6.70 B. 7.06 C. 7.60 D. 6.07
7.06
Calculatethemaximumpressureproducedwhen placing 75 mm slump concrete at a rate of 2m/h, shuttering 2.5 m high and 250 mm wide. Assume the temperature of the concrete in the formwork is initially 15Β°C and vibration is continuous.
46 kpa
55 kpa
56 kpa (arching)
62.5 kpa (height)
80 kpa (Stiffness)
Although paving machines are capable of travelling at 20 m/min or more, the logistical problems of supplying large quantities of concrete commonly result in no more than about 1000 m of pavement being laid during a typical day of production. Thus for a 9 m wide road 200 mm deep and a 50% efficiency factor, what is the production output in m3/h?
A. 115.2
B. 215.1
C. 112.5
D. 251.1
112.5 m^3/h
βββ occupy about βββ of the volume of concrete and are obtained either from naturally occurring deposits of sands and gravels, including sea-dredged material, or are produced by crushing quarried rock.
75%
While the quality and grading of the aggregate are important, the strength of concrete depends mainly on the
WATER CEMENT RATIO
the degree of stiffness of the mix and can be directly altered by changing the water/cement ratio.
Workability
a conical mould is filled in three equal layers and rodded 25 times per layer.
Slump Test
concrete is dropped from vessel to
vessel and finally into cylinder.
Compaction factor test
is used for very stiff concrete mixes and consists of vibrating a standard slump test specimen placed in a specified vessel.
Vabe Test
is designed for a very high workability mixes, i.e. those almost of flowing consistency.
DIN Test
Strength continues to improve provided sufficient water is supplied to the set concrete to ensure that drying out during the heat of hydration stage is prevented, otherwise the chemical reactions which allow strength to be developed, will cease. The process is known as
Curing
occurs as concrete hardens, being greater in wet mixes. Curing helps to limit its effect and therefore concrete in the actual structure should be thoroughly and continuously moistened for some considerable period after placing.
Shrinkage
The time between mixing and placing should not exceed ββminutes.
45 minutes
Good practice would normally require the transport distance from batching plant to paving unit to lie within β km.
3 km
Matchlist
DIFFERENCE BETWEEN TOTAL AND FREE FLOAT
Activity E
10 weeks
Project Logic MNOP
17 days
