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Concordia University *

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BLDG 6831

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Industrial Engineering

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Feb 20, 2024

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26

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The Group Assignment of the Course: CONSTRUCTION PROCESSES (BLDG492-6831 – UU) G ROUP F IRST N AME F AMILY N AME S TUDENT ID MARIO CESAR CASTRO LA BARRERA 40270431 TASHWINI MANJUNATH 40264245 SEYED ILIA MOUSAVI 40204305 JENIL RANA 40263428 SHIVA DARIHAKI 40221999 MD FAZLE RABBI 40239821 H ADI HATAMI RASTGOO BAJGIRAN 40277000 MARIA SHENODA 40270571 SAI KARTHIK VAKKANTHULA 40260589 Instructor: SHAHIN KARIMIDORABATI Concordia University Department of Building, Civil, & Environmental Engineering Fall 2023 Comments and Feedback (FOR TUTORS/MARKERS ONLY) Mark:
1) EARTHMOVING MATERIALS AND OPERATIONS A. C ALCULATIVE Q UESTION An earthwork excavation includes filling of a basement of dimensions 25m x 50m x 3m. The material to be excavated is common earth. On a sample of 120 grams taken from the borrow pit laboratory tests were conducted and it has been determined that the weight of the sample when oven dried is 100 grams. Independently, a modified proctor test has also been conducted and it has been determined that the required density is obtained at a moisture content of 22%. Given this, which of the following is correct? A. 6250 LCY and 260 kg/ m 3 of water to be added. B. 6945 BCY and 260 kg/ m 3 of water to be added. C. 6250 LCY and 260,254 kg of water to be added. D. 6945 BCY and 260,254 kg of water to be added. Sol. The Correct answer is D. Volume of fill = 25m x 50m x 5m = 6250 m 3 = 6250 CCY To convert bank volume to compacted volume, we use shrinkage factor. From Table 2 –5, shrinkage factor is 0.90 Volume of earthwork required = 6250 CCY / 0.75 = 6944.44 BCY say 6945 BCY The % moisture content = sample weight – dry weight / dry weight = 120 –100/ 100 = 20% As the moisture content in bank measure is less than that optimum moisture i.e., 20% < 22%, additional water is required to be added to excavated material. Weight of water in bank measure per cubic metre of soil = 1839 kg/ m 3 x 0.2 = 367.80 kg Weight of water in 8334 = 367.80 kg x 6945 m 3 = 2,554,371 kg Weight of water in compacted measure per cubic metre = 2047 kg/ m 3 x 0.22 = 450.34 kg Weight of water in 6250 = 450.34 kg x 6250 m 3 = 2,814,625 kg Difference = 2,814,625 – 2,554,371 = 260,254 kg (or) 260 m 3 B. N ON -C ALCULATIVE Q UESTION 2
Which of the following is the correct earthmoving process? A. Excavating, loading, hauling, placing, compacting, grading and finishing. B. Hauling, Loading, excavating, placing, compacting, grading and finishing. C. Excavating, Loading, placing, hauling, compacting, grading and finishing. D. Excavating, Placing, hauling, loading, compacting, grading and finishing. Sol. The correct answer is A. In the earthmoving process, first the required quantity is excavated then loaded into haul units which haul the material to the required location. At the location the material is placed in required shape and depth, and then compacted using appropriate machinery. At last, the compacted material is brought to required grading and finishing. 2) EXCAVATION EQUIPMENT C. C ALCULATIVE Q UESTION An excavator is tasked with digging a trench which is 2000 meters long, 2 meters width and 2.5 meters depth. Consider the job conditions are poor, but the management has enough skills and experience to perfectly coordinate the project. The project manager (P.M.) is contemplating whether to use a medium-sized excavator priced at $210 per hour or a small- sized excavator priced at $120 per hour. The materials are mostly including common earth. For a small sized excavator, the maximum depth of cut is 6 meters and for the medium sized is 8.3 meters. Which one of the excavators do you suggest for this job for the best-case scenario. A. More information needed to compare the two scenarios. B. The medium sized excavator with the total amount of $8279. C. The medium sized excavator with the total amount of $8715. D. The small sized excavator with the total amount of $9224. Sol. The correct answer is C. 3
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Total volume of the trench= 2000 (m)* 2 (m)* 2.5 (m)= 10000 m 3 Productivity for a small sized excavator: V= 0.76 m 3 for best case scenario (according to table) C= 200 c/h (according to table) Depth of cut (% of maximum) = (2.5 m / 6 m) *100 = 41.67 % Angle of swing = 45 degree, for best case scenario Interpolation: S= 1.33 + ((1.28-1.33)/ (50-30)) *(41.67-30) = 1.30 (according to table) B= 1.10 for best case scenario (according to table) E= 0.63 (according to table) Adjustment factor for trench= 0.95 for best case scenario (according to table) Productivity = V*C*S*B*E*adjustment factor for trench = 0.76 (m 3 ) * 200 (c/h) * 1.3* 1.1* 0.63* 0.95 Productivity= 130.09 (m 3 /h) for small sized excavator Total amount of time needed to excavate the trench= 10000 (m 3 )/ 130.09 (m3/h) = 76.87 h Total to be paid for the small excavator= 76.87 (h)* 120 ($) = 9,224.4 $ Productivity for a medium sized excavator: V= 1.72 m 3 for best case scenario (according to table) C= 160 c/h (according to table) Depth of cut (% of maximum) = (2.5 m / 8.3 m) *100 = 30.12 % Angle of swing = 45 degree, for best case scenario S≈ 1.33 (according to table) (according to table) B= 1.10 for best case scenario (according to table) E= 0.63 (according to table) Adjustment factor for trench= 0.95 for best case scenario Productivity = V*C*S*B*E*adjustment factor for trench = 1.72 (m 3 ) * 160 (c/h) * 1.33* 1.1* 0.63* 0.95 Productivity= 240.97 (m 3 /h) for medium sized excavator 4
Total amount of time needed to excavate the trench= 10000 (m 3 )/ 240.97 (m 3 /h) = 41.50 h Total to be paid for the small excavator= 41.50 (h)* 210 ($) = 8,715 $ $ 8,715 < $ 9,224.4, So the medium sized excavator is better for these circumstances. D. N ON -C ALCULATIVE Q UESTION Which of the following statements is NOT correct regarding earthwork excavating equipment? A. The three criteria to select the proper shovel: Maximum depth needed, working radius, and dumping height. B. Heaped volume is the maximum volume that can be placed in the bucket without spillage based on the material’s angle of repose. C. Maximum productivity of a dragline is obtained with a minimum swing angle. D. Shovels are good for above track level conditions and cannot operate and dig below track level. Solution: The correct answer is A. The three selection criteria indicated in the option A are applicable to a hydraulic excavator but not to a shovel. 3) LIFTING EQUIPMENT E. C ALCULATIVE Q UESTION The maximum lifting capacity of a tower crane rigged with two-part line is 27,600 lb and the maximum hoist speed is 100 fpm, within the structural capacity constraints of the tower and jib configuration. For the same tower crane and jib configuration, what is the maximum lifting capacity and speed for a four-part line. A. 55,200 lb and 50 fpm B. 55,200 lb and 100 fpm C. 27,600 lb and 100 fpm. D. Unknown, more information required. 5
Sol. The correct answer is A. The maximum lifting capacity of the crane is increased by 100% with four-part-line configuration and the increased lifting capacity is accompanied by loss of 50% in vertical hoist speed. [Peurifoy, R.L. “Chapter-17: Cranes, p. 565” in Construction Planning, Equipment, and Methods, 7th Edition, McGraw-Hill Publications, Montreal, 2018.] As such, 27,600 lb x 2 = 55,200 lb 100 / 2 = 50 fpm. The maximum lifting capacity of tower crane with four-part line is 55,200 lb and the maximum hoist speed is 50 fpm. F. N ON -C ALCULATIVE Q UESTION Which of the following is true about two-part-line and four-part-line configurations of a tower crane? A. When operating radius is less than 90 feet, the crane has a greater lifting capacity with a two-part-line than the four-part-line arrangement. B. When operating radius is greater than 90 feet, the capacity of hoisting system controls the load-lifting capacity C. When operating radius is less than 90 feet, the structural capacity of crane controls the load-lifting capacity. D. When operating radius is greater than 90 feet, the crane has a greater lifting capacity with a two-part-line than the four-part-line arrangement. 6
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Solution: The correct answer is D. When the operating radius of a tower crane is less than 90 feet, a four-part line has more lifting capacity than a two-part line. When the operating radius is greater than 90 feet, the converse is true. When the operating radius is greater than 90 feet, the structural capacity of the tower crane controls the load-lifting ability, and when operating radius is less than 90 feet the hoisting system controls the load-lifting ability. 4) LOADING AND HAULING – PART 1 G. C ALCULATIVE Q UESTION Calculate the Max. Usable Pull for a vehicle with a weight of 12 tons, moving on a road with a grade of 5%, a penetration of 3 cm, and at an altitude of 1000 meters. Assume a coefficient of traction of 0.85. A. 11.5 tons B. 10.2 tons C. 6.5 tons D. 17.9 tons Solution: The correct answer is B. 1. Calculate Rolling Resistance Factor: Rolling resistance factor (Kg/t)=20+(6×penetration) Rolling resistance factor (Kg/t)=20+(6×3)=38 Kg/t 2. Calculate Grade Resistance Factor: Grade Resistance factor (kg/t)=10×grade (%) Grade Resistance factor (kg/t)=10×5=50 kg/t 3. Calculate Grade Resistance: Grade resistance (Kg)=Vehicle weight (t)×Grade Resistance factor (Kg/t) Grade resistance (Kg)=12×50=600 Kg 4. Calculate Effective Grade: Effective Grade(%)=Grade (%)+Rolling Resistance factor (Kg/t)10 Effective Grade (%)=5+3810=8.8% 5. Calculate Derating Factor: 7
Derating Factor (%)=Altitude (m) - 915×10−2 Derating Factor (%)=(1000−915)×10−2=8.5% 6. Calculate Max. Usable Pull: Max. Usable Pull=Coefficient of traction×Weight on driving wheels Max. Usable Pull=0.85×12=10.2 tons Therefore, the Max. Usable Pull for the given conditions is 10.2 tons. H. N ON -C ALCULATIVE Q UESTION What is the significance of the "Coefficient of Traction" in determining a vehicle's maximum usable pull? A. It represents the vehicle's total weight B. It indicates the force exerted at the rim of each driving wheel C. It influences the vehicle's pulling capability on different surfaces D. It measures the vehicle's horsepower Sol. The correct answer is C. The coefficient of traction is crucial because it influences how well a vehicle can grip different surfaces. A higher coefficient means better traction, allowing the vehicle to exert more force and pull heavier loads, especially on surfaces with lower friction. This directly impacts the vehicle's pulling capability on various terrains. 8
5) LOADING AND HAULING – PART 2 I. C ALCULATIVE Q UESTION Determine how many dozers are needed to spread a stockpile of 15.50 m3 into a ditch with a distance of 75 m. The crawler Dozer has a 5.40 LCM rated blade capacity and the highest reverse speed of 6 kilometres per hour. Consider the management condition and the job condition on the construction site are good and fair respectively. The bucket fill factor is 1. A. 4 B. 8 C. 11 D. 9 Sol. The correct answer is B. With regards to a stockpile, we concluded that it is in loose condition and consider it as loose material. With regard to the highest reverse speed, we consider the crawler loader as a direct drive transmission. Then the fixed time is 0.10. (Typical Dozer Cycle Times Table) The total C is the sum of C variable and the C fix. The C variable is the sum of doze and return. Formula for this is DISTANCE over SPEED. C variable doze is equal to 75 / 4*16.67 = 1.124 C variable return is equal to 75/ 6*16.67 = 0.749 C total is equal to 0.10 + 1.124 + 0.749 = 1.973 This is for one cycle, so 60 / 1.973 = 30.41 cycle/hr The productivity formula is equal to: P = V * C * E 5.40 * 30.41* 0.69 = 113.30 lcm/min 113.30 / 60 =1.88 LCM/ hr. The number of Dozer = total volume / productivity Total volume = bucket fill factor * 15.50 = 1 * 15.50 = 15.50 The number of Dozer = 15.50 / 1.88 = 8.24 = 8 Dozer 9
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J. N ON -C ALCULATIVE Q UESTION A construction operation involves spreading of clean granular gravel for creation of subgrade of 6 metres width for a road. The subgrade has a camber of 1-in-50 (camber is the cross-slope of the road for effective drainage of rainwater). The following dozer configurations are available for selection and as a project manager what will be your recommendation? A. A dozer with a cushion blade with tilting adjustment B. A dozer with a universal blade with pitching adjustment C. A dozer with an angular blade with angling adjustment D. A dozer with a straight blade with tilting adjustment Sol. The correct answer is D A dozer can be used to both excavate and spread soils. Tilting is the adjustment operation for a dozer blade to achieve cross-slope when spreading or cutting soils. Of all the blades that are available for a dozer, cushion blade cannot be tilted. Hence, the only choice for the operation is a dozer with a straight blade with tilting adjustment. 6) LOADING AND HAULING – PART 3 K. C ALCULATIVE Q UESTION Estimate the total turnaround distance for a single-engine two-axle tractor based on the following information: Haul Route (single Pusher) Down a 5% grade, 500 m Up a 5% grade, 500 m Rolling resistance factor= 50 Kg/t Cycle time per hour= 4.41 min A. 250 m B. 300 m C. 350 m D.400 m 10
Sol: The correct answer is B 1. Calculate the fixed time from the table for single pusher: Spot time= 0.3 min Loading time= 0.6 min Maneuvering & Dump time= 0.7 min Fixed total time= 1.6 min 2. Total cycle time= variable time + fixed time 4.41 min= variable time + 1.6 Therefore, variable time= 2.81 min 3. Calculate the effective grade. Haul: -5 + 50/10 = 0% Return: 5+ 50/10= 10% Turnover: 0+ 50/10= 5% 4. Calculate the variable travel time for haul and return. Haul: 0.8 min (from the loaded graph) Return: 1.40 min (from the empty graph) Since 4.41= 0.8 + 1.40 + turnaround time + 1.6 Therefore, turnaround time = 4.41- (0.8+1.4+1.6) = 0.61 min 5. From the empty graph find the turnaround distance using 0.61 min and 5% effective grade. Therefore, turnaround distance = 300 m 11
L. N ON -C ALCULATIVE Q UESTION What type of scrapers are capable of achieving the highest efficiency in loading without the assistance of a pusher tractor or another scraper? A. Elevating scarpers B. Single powered axle scrapers C. Crawler tractor scrapers D. None of the previous answers Solution: The correct answer is A Of all the different types of scrappers available, “only the elevating scraper and the pull- scraper are capable of achieving high efficiency in loading without the assistance of a pusher 12
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tractor or another scraper”. [ S.W. Nunnally, “Loading & Hauling: Scrappers Operation and Employment” in Construction Methods & Management, Prentice-Hall Pearson, 8 th Edition, 2011, P. 64] 7) COMPACTING, GRADING, FINISHING, RIPPING M.C ALCULATIVE Q UESTION A contractor is faced with the decision of selecting between 2 compaction machinery (wheel tractor towed with tamping foot and a heavy pneumatic). It is known that the sandy soil weighs 1931.8 kg/BCM. The compacted lift has a thickness of 5 in. One machine has an effective roller width of 8m, while the other is equipped with a foot roller drum width of 4.5m. The cost per unit for the equipment with foot roller is $490/h, while the other is $460/h. What is the least cost-effective equipment (unit cost in $/CCM) considering optimal production? A. Wheel tractor towed with tamping foot, $0.48/CCM B. Wheel tractor towed with tamping foot, $0.70/CCM C. Heavy pneumatic with tamping foot, $0.37/CCM D. Heavy pneumatic with tamping foot, $1.30/CCM Solution: The correct answer is B The answer is the Wheel tractor towed with tamping foot will be the most economic to choose as the price would be $ 0.70 per m3 compacted. Step 1: Calculate the density. = 1.7 gr/cm3 13
Step 2: Number of passes required for the compactor. Number of passes = 11 Step 3: Estimate the Compactor Production Wheel tractor towed with tamping foot: = 698.27 CCM /h Heavy pneumatic: = 620.68 CCM /h 14
- 16 km/h and 8 km/h obtained from Table: Typical operating speed of compaction equipment. - 16 km/h and 8 km/h are chosen because in the statement it mentions optimal production. Step 4: Calculate Cost per Unit Wheel tractor towed with tamping foot: = $ 0.70 / CCM 15
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Heavy pneumatic: = $ 0.74 / CCM N. N ON -C ALCULATIVE Q UESTION Which compaction equipment is recommended for a wide range of materials, except for sand, clean, or silty materials? E. Pneumatic F. Steel wheel G. Tamping Foot H. Vibratory Solution: The correct answer is C Tamping Foot is the only machine that can be used in varied materials such as rock, gravel, clean or silty, gravel, clayey, sand, clayey silt, clay, sandy or silty and clay heavy; however, this equipment is least effective on sand, clean or silty materials. [ S.W. Nunnally, “Compaction and Finishing” in Construction Methods & Management, Prentice-Hall Pearson, 8th Edition, 2014, P.85, Figure 10] 16
8) AGGREGATE PRODUCTION O. C ALCULATIVE Q UESTION Concrete is to be produced at 200 cum per hour with a mix design of 1:2:4 (cement: fine aggregate: coarse aggregate) by weight with a minimum cement content of 400 kg per cum. The gradation of coarse aggregate is 25mm to 19mm - 70%, 19 to 13mm – 15%, 13 to 10mm – 15%. Considering open circuit, which of the following crusher closed side setting requires lowest total feed and yields the above gradation, so that the concrete production is continuous. A. 38mm B. 25mm C. 32mm D. 19mm Sol. The correct answer is B. Step – 1: Calculate the aggregate required to produce 200 cum of concrete per hour. Mix design is 1:2:4 by weight and minimum cement quantity is 400 kg per cum Total quantity of cement = 200 cum x 400 kg per cum => 80000 kg => 80 tonnes per hour Quantity of coarse aggregate = 4 x Total quantity of cement => 4 x 80 tonnes => 320 tonnes per hour 320 tonnes per hour of coarse aggregate is required to produce 200 cum of concrete per hour. Step – 2: Calculate the quantity of different aggregate sizes required. 25 – 19mm = 70% x 320 tonnes per hour => 224 tonnes per hour 19 – 13mm = 15% x 320 tonnes per hour => 48 tonnes per hour 13 – 10mm = 15% x 320 tonnes per hour => 48 tonnes per hour Step – 3: Select screen sizes required based on aggregate sizes required. The screen sizes required to yield the gradation in step-2 in the order of their placement in screen deck are 25mm, 19mm, 13mm, and 10mm. Step – 4: Select the crusher closed side setting with maximum retainage. 17
The total feed required is lowest when the percentage retained is highest for 25mm to 19mm. Based on the above table, the crusher closed side setting of 25mm yields highest percent retained as follows: Screen Size % passing 25mm 79% 19mm 61% 13mm 41% 10mm 29% Screen Size Gradation % retained 25mm > 25mm 100 – 79 = 21% 19mm 25mm to 19mm 79 - 61% = 18% 13mm 19mm to 13mm 61 - 41% = 20% 10mm 13mm to 10mm 41% - 29% = 12% Step – 5: check whether the total feed based on the percentage retained on each screen is yielding the required output. 25 mm – 19mm: The percentage of aggregate passing 25mm screen and retained on 19mm screen gives this grading; the percentage retained on 19mm screen from step – 5 is 18% Output = Total feed x percentage retained. 224 tonnes per hour = total feed x 18% Total feed = 224 tonnes per hour / 18% => 1244.45 tonnes per hour 19mm - 13mm: The percentage of aggregate passing 19mm screen and retained on 13mm screen gives this grading; the percentage retained on 13mm screen from step – 5 is 20% Output = Total feed x percentage retained. 48 tonnes per hour = total feed x 20% Total feed = 48 tonnes per hour / 20% => 240 tonnes per hour 18
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13mm -10mm: The percentage of aggregate passing 13mm screen and retained on 10mm screen gives this grading; the percentage retained on 10mm screen from step – 5 is 12% Output = Total feed x percentage retained. 48 tonnes per hour = total feed x 12% Total feed = 48 tonnes per hour / 12% => 400 tonnes per hour Every other crusher closed side setting requires total feed more than 1244.45 tonnes per hour, as the percentage of 25mm to 19mm retained is lower than 18%. P. N ON -C ALCULATIVE Q UESTION Which of the following is the correct sequence of producing aggregate? A. Excavation, loading, hauling, crushing, screening, washing, storage. B. Excavation, crushing, screening, loading, hauling, washing, storage. C. Excavation, crushing, screening, washing, loading, hauling, storage. D. Excavation, screening, crushing, washing, loading, storage. Sol. The correct answer is A. To produce aggregate, rock or gravel is excavated, loaded into haul trucks, and transported to the aggregate processing plant. Then the rock or gravel is crushed using rock crushers, screened, washed using log washers, scrubber drums, etc. and then stored. 9) CONCRETE FORM DESIGN Q. C ALCULATIVE Q UESTION You are the project engineer of a multiple story building project. while preparing the casting of the first typical floor slab designed for 200 lb/sq. ft, you have decided to lay out the joists at minimum 30 inches spacing due to the limited formwork material available at site. You have the choice between actual 1-inch plyform class 1 or actual 1-inch Eastern spruce for the decking material spanning a single span, which will be satisfactory for the 30-inch joist spacing? (Assume grains across the supports for the plyform calculations and l/360 for deflection limit). 19
A. Plyform class 1 B. Eastern Spruce C. Both of them D. None of them Sol: The correct answer is B Step-1: Calculate the design load for joist spacing We design joist for 1ft X 1ft sheathing. So, W (lb/ft)= 200 (lb/sq. ft)x 1ft = 200 lb/ft Step-2: Calculate joist spacing for plyform class 1 Considering the plyform 1” , from table 13-6: d=1” EI = 0.641 × 10 6 F b KS = 1.422 × 10 3 F s lb Q = 0.675 × 10 3 From table 13-5: choosing the plywood equations for 1 span condition: Bending: l = 9.8 ( F b KS W ) 1 2 = 9.8 ( 1.422 × 10 3 200 ) 1 2 = 26.13 in Shear: l = 24 ( F s lb Q W ) + 2 d = 24 ( 0.675 × 10 3 200 ) + 2 × 1 = 83 in Deflection (l/360): l = 1.37 ( EI W ) 1 3 = 1.37 ( 0.641 × 10 6 200 ) 1 3 = 20.19 in From these three values we can choose minimum value 20.19 in but it less than our minimum requirement 30 in. So, we cannot use plyform class 1 for above conditions. Step-3: Calculate joist spacing for Eastern spruce Considering the Eastern spruce 1 in From table 13-8: d=1 in, b=12 in (As we assume 1ft x 1ft strip) E = 1.2 × 10 6 × 0.97 × 1 = 1.164 × 10 6 F b = 1050 × 0.86 × 1.25 = 1128.75 F v = 140 × 0.97 × 1.25 = 169.75 and from cross section, A = 12 × 1 = 12 i n 2 20
I = bd 3 12 = 12 × 1 3 12 = 1 in 3 From table 13-5: choosing the wood equations for 1 span condition: Bending: l = 4 d ( F b b W ) 1 2 = 4 × 1 × ( 1128.75 × 12 200 ) 1 2 = 32.92 in Shear: l = 16 F v A W + 2 d = 16 × 169.75 × 12 200 + 2 × 1 = 164.96 in Deflection (l/360) : l = 1.37 ( EI W ) 1 3 = 1.37 × ( 1.164 × 10 6 × 1 200 ) 1 3 = 53.09 in From these three spacing we can choose minimum value 32.92 in that is greater than our minimum requirement 30 in. So, we use Eastern spruce for above conditions. R. N ON -C ALCULATIVE Q UESTION Based on the following statements select the correct option. I. Initial cost is high for conventional formwork and low for industrialized formwork. II. Only wood used for conventional formwork and steel used for industrialized formwork. III. Conventional and Industrialized formwork both can be handle by manually or mechanically. IV. Conventional and Industrialized formwork both can be reuse. A. I & III B. II & IV C. II D. None of them Sol: The correct answer is D I. False because Initial cost is high for industrialized formwork and low for conventional formwork. II. False because traditionally wood is used for conventional formwork, also steel may be used for that. Similarly, mainly steel is used for industrialized formwork, also plywood and wood may be used. III. False because conventional formwork can be handled by manually and Industrialized formwork handle by mechanically. 21
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IV. False because conventional formwork is non repetitive concrete elements and industrialized formwork is repetitive concrete formwork. 22
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10) CONCRETE PRODUCTION S. C ALCULATIVE Q UESTION Concreting of an element in a location exposed to freezing & thawing in a moist condition is to be done based on the mix design 1:2:4 by weight (Cement: Fine Aggregate: Coarse Aggregate). Which of the options is the correct quantity of water required (in kgs) for producing 1 cum of concrete based on the following information: Specific gravity of water – 1 Minimum quantity of cement – 350 kg per cum of concrete Specific gravity of cement – 3.15 Specific gravity of fine aggregate in saturated surface dry condition – 2.65 Specific gravity of coarse aggregate in saturated surface dry condition – 2.65 Moisture content of fine aggregate – 5% Excess Weight of representative sample of coarse aggregate in oven dry condition - 40 Kg Weight of representative sample of coarse aggregate in saturated surface dry condition – 48 Kg Weight of representative sample of coarse aggregate in field – 45 Kg. A. 157.50 kg B. 227.50 kg C. 297.50 kg D.17.50 kg Sol. The correct answer is B The questions require us to calculate the quantities of concrete component required to produce 1 cubic metre of concrete. Step – 1: calculate the quantity of cement. The quantity of cement required = 350 kg Step – 2: Calculate the quantity of fine aggregate required . As the mix design specifies 1:2:4 ratio by weight, Quantity of fine aggregate required = 2 x weight of cement quantity => 2 x 350 kg => 700 kg 23
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Step – 3: Calculate the quantity of coarse aggregate required . As the mix design specifies 1:2:4 ratio by weight, Quantity of coarse aggregate required = 4 x weight of cement quantity => 4 x 350 kg => 1400 kg Step – 4: Calculate the quantity of water required . As the concrete element is exposed to freezing & thawing in a moist condition, the water- cement ratio from Table 7-4 is 0.45, Quantity of water required = 0.45 X cement quantity => 0.45 x 350 kg => 157.50 kg Step – 5: Calculate excess water based on fine aggregate moisture content . Excess moisture content of fine aggregate is 5%. Excess water in sand = 700 kg x 0.05 => 35 kg Step – 6: Calculate excess/ less water based on coarse aggregate moisture content . Weight of coarse aggregate sample in oven dry condition = 40 kg Weight of coarse aggregate sample in saturated surface dry condition – 48 kg Weight of coarse aggregate sample in field condition – 45 kg Moisture content (%) for SSD = weight SSD condition weight ovendry condition weight ovendry condition 24
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=> 48 40 40 => 20% Moisture content (%) in field = weight field condition weight ovendry condition weight ovendry condition => 45 40 40 => 12.50 % Water absorption of coarse aggregate to achieve SSD conditions = 20% - 12.50% => 7.50% In other terms, the pores of coarse aggregate in field condition are not in surface dry condition, and water equal to 7.50% by weight of coarse aggregate will not be available for hydration. Water required to achieve SSD conditions for coarse aggregate = 7.50% x 1400 kg => 105 kg Step – 7: calculate field mix quantities of water. Adjusted water quantity = Original water quantity – excess water from fine aggregate + water required to achieve SSD condition of coarse aggregate => 157.50 kg – 35 kg + 105 kg => 227.50 kg T. N ON -C ALCULATIVE Q UESTION Which of the following types of cement is recommended for using in production of concrete that is planned to be used in cold-weather conditions? A. Type – I B. Type – III C. Type – IV D. Type - II Sol. The correct answer is B Of the 5 types of cement, type-III cement also known as high early strength cement is recommended for usage in cold-weather conditions or when early formwork removal is required, as this cement develops 190% of type – I strength after 1 day of curing. 25
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