Test 32 - Concrete Constituents and Grades

Question 1 ప్రశ్న 1

Which combination correctly matches important concrete-related Indian Standards with their principal functions?

A IS 456 – plain and reinforced concrete practice; IS 10262 – concrete mix proportioning; IS 383 – aggregates for concrete; IS 9103 – concrete admixtures B IS 456 – aggregate abrasion only; IS 10262 – cement setting time; IS 383 – reinforcement; IS 9103 – brick testing C IS 456 – cement manufacture only; IS 10262 – steel design; IS 383 – water testing; IS 9103 – soil classification D All four standards deal exclusively with cement compressive strength

Question 2 ప్రశ్న 2

What is the principal role of the cementitious binder in normal concrete?

A To form, after reaction with water, the binding matrix that bonds aggregate particles together B To act only as an inert filler having no chemical reaction with water C To replace all coarse aggregate and provide the entire concrete volume D To prevent any contact between water and aggregate

Question 3 ప్రశ్న 3

Which statement best describes the main engineering role of fine aggregate in concrete?

A It fills part of the space between coarse aggregate particles and contributes to workability, cohesiveness and packing. B It functions only as reinforcement resisting tensile stress. C It completely replaces mixing water. D Its only purpose is to increase the colour intensity of concrete.

Question 4 ప్రశ్న 4

What is an important function of coarse aggregate in normal-weight concrete?

A To provide a major part of the granular skeleton and volume of concrete while contributing to strength and dimensional stability B To initiate cement hydration chemically C To function only as a colouring agent D To replace all cementitious material in structural concrete

Question 5 ప్రశ్న 5

Which statement about mixing water in concrete is most accurate?

A Water is required for cementitious reactions and workability, but excessive free water can increase porosity and reduce strength and durability. B Any quantity of water may be added because strength is independent of water content. C Water is required only to wet coarse aggregate and has no role in hydration. D More water always increases both workability and hardened strength without adverse effects.

Question 6 ప్రశ్న 6

What is the most appropriate description of a chemical admixture used in concrete?

A A material added before or during mixing to modify one or more properties of fresh or hardened concrete B A coarse aggregate particle larger than 20 mm C A mandatory substitute for all mixing water D A material used only after concrete has completely hardened

Question 7 ప్రశ్న 7

Before adopting a chemical admixture in a concrete mix, why is compatibility with the cementitious system important?

A Because admixture performance can depend strongly on the particular cement, supplementary material, dosage and concrete proportions B Because every admixture gives identical behaviour with every cement C Because compatibility affects only concrete colour and not performance D Because an admixture eliminates the need for trial mixes

Question 8 ప్రశ్న 8

What does the designation M30 principally mean under IS 456?

A Specified characteristic compressive strength of 30 N/mm² for a 150 mm concrete cube at 28 days B Average cement mortar strength of exactly 30 N/mm² at 3 days C Concrete containing exactly 30 percent cement by mass D Concrete having an initial setting time of 30 minutes

Question 9 ప్రశ్న 9

Which statement correctly defines characteristic compressive strength of concrete under IS 456?

A The strength below which not more than 5 percent of test results are expected to fall B The lowest strength ever recorded from any individual concrete cube C The arithmetic average of all concrete test results with no statistical interpretation D The cement strength below which exactly 50 percent of results must fall

Question 10 ప్రశ్న 10

Which classification correctly represents the concrete grade groups in IS 456 after the applicable amendments?

A M10–M20 ordinary concrete; M25–M60 standard concrete; M65–M100 high-strength concrete B M10–M20 ordinary concrete; M25–M55 standard concrete; M60–M100 high-strength concrete C M10–M30 ordinary concrete; M35–M60 standard concrete; M65–M100 high-strength concrete D M10–M25 ordinary concrete; M30–M65 standard concrete; M70–M100 high-strength concrete

Question 11 ప్రశ్న 11

Which pair is correctly classified according to the amended IS 456 grade table?

A M60 – standard concrete; M65 – high-strength concrete B M60 – high-strength concrete; M65 – standard concrete C M20 – standard concrete; M25 – ordinary concrete D M100 – standard concrete; M55 – high-strength concrete

Question 12 ప్రశ్న 12

Which statement correctly reflects the IS 456 approach to design mix and nominal mix concrete?

A Design mix concrete is preferred; if it cannot be used, nominal mix may be permitted for M20 or lower with permission of the engineer-in-charge. B Nominal mix is compulsory for every grade up to M100. C Design mix is permitted only for M20 and lower. D There is no distinction between nominal and design mix concrete.

Question 13 ప్రశ్న 13

A structural element requires M25 concrete. Which mix-selection statement is correct under IS 456?

A A design mix should be used because nominal mix provisions apply only to M20 or lower. B A nominal mix is mandatory because M25 is an ordinary concrete grade. C Either an arbitrary 1:2:4 mix or 1:3:6 mix may automatically be called M25. D No mix proportioning is required when the cement is OPC 53.

Question 14 ప్రశ్న 14

What most accurately distinguishes design mix concrete from nominal mix concrete?

A Design mix proportions are established from material properties, performance requirements and trials, whereas nominal mix uses prescribed conventional proportioning provisions for limited lower grades. B Design mix means that only cement is measured, while nominal mix means only water is measured. C Nominal mix always produces higher strength than design mix. D Design mix and nominal mix are differentiated only by aggregate colour.

Question 15 ప్రశ్న 15

Which statement correctly describes the nominal-mix provisions in Table 9 of IS 456?

A They specify maximum total dry aggregate mass per 50 kg cement, a fine-to-coarse aggregate mass relationship and maximum water quantity rather than prescribing one universal fixed volumetric ratio. B They specify only a universal 1:2:4 volume ratio for every grade. C They apply only to M25 and higher grades. D They allow unlimited water to be added without changing cement content.

Question 16 ప్రశ్న 16

For M20 nominal mix concrete, IS 456 Table 9 permits a maximum total dry aggregate mass of 250 kg per 50 kg cement. What is the corresponding maximum total aggregate-to-cement mass ratio?

A 2:1 B 3:1 C 5:1 D 10:1

Question 17 ప్రశ్న 17

For a nominal mix using Zone II fine aggregate and 20 mm maximum-size coarse aggregate, which fine-aggregate-to-coarse-aggregate mass proportion is given as the IS 456 example?

A 1:1 B 1:1.5 C 1:2 D 1:3

Question 18 ప్రశ్న 18

For an M40 design mix, IS 10262:2019 gives assumed standard deviation S = 5 N/mm² and factor X = 6.5 N/mm². Using target mean strength = fck + 1.65S or fck + X, whichever is higher, what target mean compressive strength should be adopted?

A 40.0 N/mm² B 46.5 N/mm² C 48.25 N/mm² D 55.0 N/mm²

Question 19 ప్రశ్న 19

Why is a design concrete mix proportioned for a target mean strength greater than its characteristic strength?

A To provide a statistical margin for normal production variability so that the required characteristic strength is achieved with the intended reliability B Because characteristic strength is always greater than every individual test result C Because target mean strength is the same as cement grade D To ensure that exactly 50 percent of test results fall below the grade strength

Question 20 ప్రశ్న 20

A contractor argues that using OPC 53 automatically produces M53 concrete. Which response is correct?

A The statement is incorrect because cement grade refers to standard cement-mortar strength, while concrete grade depends on the complete concrete mix and its characteristic cube strength. B The statement is correct because cement and concrete grades are numerically identical by definition. C OPC 53 automatically produces concrete no stronger than M20. D Concrete grade is determined only by cement setting time.

Question 21 ప్రశ్న 21

Two concrete mixes contain the same cementitious material and aggregates, but Mix X has a substantially higher effective water-cementitious-material ratio than Mix Y. If both are properly compacted and cured, which tendency is generally expected?

A Mix X will generally have higher capillary porosity and lower strength than Mix Y. B Mix X must always have greater strength because it contains more water. C The water-cementitious-material ratio cannot influence hardened concrete. D Mix Y cannot hydrate because it contains less water.

Question 22 ప్రశ్న 22

Which statement correctly describes the use of supplementary cementitious materials such as fly ash or ground granulated blast-furnace slag in concrete?

A They can form part of the cementitious binder system and influence strength development, heat evolution, workability and durability. B They are always treated as coarse aggregate and have no cementitious role. C They eliminate the need for Portland cement in every concrete application. D Their presence cannot affect curing requirements or durability.

Question 23 ప్రశ్న 23

Which statement about water and admixtures in concrete is most appropriate under IS 456 practice?

A Mixing water should be of suitable quality, and chemical admixtures should conform to the applicable specification and be checked for satisfactory concrete performance. B Any industrial wastewater can be used without testing if a superplasticizer is added. C An admixture automatically makes poor-quality mixing water harmless. D Concrete admixtures are prohibited in all reinforced concrete.

Question 24 ప్రశ్న 24

A concrete specification states only 'M30' but gives no information about workability, maximum aggregate size, exposure or method of placing. Why is the specification incomplete for practical concrete production?

A Because grade designation defines characteristic strength but does not by itself define all the fresh-concrete, durability and material requirements needed for proportioning and construction. B Because M30 gives every material quantity and construction procedure automatically. C Because concrete grade is unrelated to compressive strength. D Because maximum aggregate size and exposure have no influence on a concrete mix.

Question 25 ప్రశ్న 25

Consider the following statements about concrete constituents and grades:
1. M40 denotes a characteristic 28-day cube compressive strength of 40 N/mm².
2. Design mix concrete is preferred to nominal mix concrete under IS 456.
3. Nominal mix concrete may be permitted for M20 or lower under the stated IS 456 conditions.
4. Concrete grade is determined solely by the grade of cement used.

Which statements are correct?

A 1 and 2 only B 1, 2 and 3 only C 2, 3 and 4 only D 1, 2, 3 and 4

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