Review+Exam+-+Concrete copy l

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252

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Feb 20, 2024

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Fall 2021 CNST 252 Name: ______________________ Review Aggregate/Concrete Exam This exam is open calculator but closed cell phone and closed neighbor. 1) (2 points) Calculate the moisture content of the following aggregate sample: Weight of the moist aggregate and dish: 170 grams Weight of the dry aggregate and dish: 159 grams Weight of the dish: 96 grams Aggregate moisture content: __________ Note: You must supply correct units for full credit. (one decimal place please) 2) (18 points) You created a trial batch of concrete with the following quantities of materials: Water: 6.5 pounds Cement: 14.5 pounds Coarse Aggregate: 33.1 pounds Fine Aggregate: 26.9 pounds Total weight of batch: 81.0 pounds total What water/cement ratio are you using in the initial mix design? ( two decimal places please ) ________ When performing the unit weight test, you filled a container with water and found the container full of water weighed 35.8 pounds. When you filled the container with concrete, the container and concrete weighed 51.7 pounds. Empty, the container weighed 24.2 pounds. The unit weight of water is 62.4 lbs/ft 3 . Find the unit weight of your concrete mix. ( one decimal place please ) concrete = _______________ Based upon the batch weights above and assuming the unit weight of your concrete mix is 150 lbs/ft 3 , how many pounds of the each of the following constituents do you need to make one cubic yard of concrete? ( Round weights to nearest whole number. ) Water __________ lbs Cement __________ lbs Coarse Aggregate __________ lbs Fine Aggregate ___________ lbs 3) (15 points) You have two stockpiles of aggregate, one coarse and the other fine. The coarse aggregate has a moisture content of 2.4% measured in the stockpile while the fine 1
aggregate has a moisture content of 1.9% measured in the stockpile. The SSD moisture content of the coarse aggregate is 0.9% while the SSD moisture content of the fine aggregate is 2.5%. Using the unadjusted mix design shown below, what quantity of each of the following constituents is needed for one cubic yard of concrete if you adjust for moisture on CA and FA? (Round weights to the nearest whole pound.) Unadjusted Mix Design (for 1 CY) Adjusted Mix Design 325 lbs Water _________ lbs 700 lbs Cement __________ lbs 1700 lbs Coarse Aggregate __________ lbs 1350 lbs Fine Aggregate __________ lbs What is the water/cement ratio of the adjusted mix? _________ ( two decimal places, please ) 4) (2 points) From the chart below, what is the target air content for a concrete mixture composed of one-inch nominal size aggregate under mild exposure conditions? ( You must supply correct units for full credit. ) _____________ 2
Name ________________________ 5) (3 points) What is the fineness modulus of the aggregate shown in the table below? Sieve Cum % Number Passing 3/8" 97.0 No. 4 88.8 No. 8 67.2 No. 16 54.3 No. 30 44.2 No. 50 33.5 No. 100 22.7 Pan 0 ( one decimal place please ) _________ 6) (3 points) From the table below, if the specified compressive strength @ 28 days is 5,600 psi, what is the appropriate water to cement ratio for non-air- entrained concrete? (two decimal places please) ________ 7) (2 points) Self-compacting concrete has what primary advantage over other types of concrete: A. It has higher long-term strength and cures in less time. B. It has lower hydraulic conductivity and lower heat of hydration. C. It is much more durable in highway applications when used as a slab-on-grade. D. It flows and consolidates under its own weight so vibration is unnecessary. E. It is lighter in weight and therefore easier to transport. 3
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8) (2 points) Which of the following statements about curing concrete is TRUE? A. Proper curing decreases concrete’s durability, strength, water-tightness, abrasion resistance and resistance to freezing/thawing and deicers. B. Higher curing temperature provides early strength gain but decreases the long- term strength of concrete. C. The type of cement used to make concrete does not affect the period of time that concrete needs to be protected from freezing temperatures. 9) (3 points) Using interpolation and the table above, what weight of CA per CY of concrete is needed if the CA’s dry-rodded unit weight is 96 lbs/ft 3 , nominal size of CA is 3/4” and the fineness modulus of the FA is 2.50? ( Round to the nearest pound.) ______________ lbs 4
Name ______________________ 10) (3 points) A sieve stack is being used to determine the distribution of aggregate particle sizes. The air dry sample (before it was transferred to the stack) weighed 492.71 grams. The cumulative weight of material recorded retained by all sieves plus the pan was 496.18 grams. A. Was material lost or gained through the sieving process? ____________ B. What was the percentage of loss or a gain during the sieving process? ( two decimal places please ) ____________ 11) (20 points) Specifications called for 4,200 psi concrete to be delivered to your construction site for a road repair project. Compression testing of samples from fresh concrete indicated that original specifications were not met, so each pavement section was cored in three places and the cored samples compression tested. Results of the compression tests are shown below. Pavement Cylinder 1 Cylinder 2 Cylinder 3 Section __(psi)__ (psi) (psi) __ A 3760 3910 3190 B 4210 4220 4100 C 3760 3780 3650 D 3910 3140 4290 E 4030 3340 3960 F 4080 3070 3870 G 4180 3510 4040 H 3990 3120 3870 I 3640 3990 3420 J 3870 3770 3760 5
Test specifications for cored samples include: (1) each cylinder has to test > 75% f’c, and (2) the average for each pavement section has to test > 90% f’c. Which sections, if any, meet both specifications? ______________ Which sections, if any, meet specifications for all individual samples but fail to meet specifications for the pavement section average? ______________ Which sections, if any, fail specifications for one or more individual samples but meet specifications for the pavement section average? ______________ Which sections, if any, fail both specifications? ______________ (Answers should reflect letters of pavement section(s), if any, meeting each criterion.) 6
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Name __________________ 12) (2 points) Curing affects all of the following properties of concrete EXCEPT: A. Durability B. Strength C. Hydraulic conductivity (water-tightness) D. Resistance to freeze-thaw action E. Water/cement ratio A. No loss of entrained air is expected during transportation and placement of air-entrained concrete. 13) (6 points) The absolute volume of the ingredients of a concrete mix are listed below: Water 5.20 ft 3 Cement 3.80 ft 3 Air 1.35 ft 3 Admixture 0.45 ft 3 CA 9.25 ft 3 Using the absolute volume mix design method and the volumes of the constituents above, what volume of FA is needed in this mix? (Y ou must supply correct units for full credit ) ____________ If the FA has a relative density of 2.55, how many pounds of FA are needed in each CY of mix? (R ound your answer to nearest whole number ) __________ 7