Test 35 - Strength and Strength Development of Hardened Concrete

Question 1 ప్రశ్న 1

Which current Indian Standard test-method provision directly covers compressive, flexural and split tensile strength testing of hardened concrete?

A IS 516 (Part 1/Sec 1):2021 B IS 1199 (Part 2):2018 C IS 2386 (Part 4):1963 D IS 4031 (Part 6):1988

Question 2 ప్రశ్న 2

Which statement best describes the relative strength characteristics of ordinary concrete?

A Concrete is generally strong in compression but considerably weaker in direct tension. B Concrete normally has greater tensile strength than compressive strength. C Concrete has identical compressive and tensile strengths. D Concrete possesses tensile strength but no measurable compressive strength.

Question 3 ప్రశ్న 3

A 150 mm concrete cube fails under a compressive load of 675 kN. What is its compressive strength?

A 20 N/mm² B 25 N/mm² C 30 N/mm² D 45 N/mm²

Question 4 ప్రశ్న 4

Approximately what failure load corresponds to a compressive strength of 40 N/mm² for a 150 mm concrete cube?

A 600 kN B 750 kN C 900 kN D 1200 kN

Question 5 ప్రశ్న 5

For concretes made with comparable materials, properly compacted and similarly cured, what is the general effect of substantially increasing the effective water-cement ratio?

A Compressive strength generally decreases because greater capillary porosity is created. B Compressive strength necessarily increases because more water is available. C Strength is unaffected by water-cement ratio. D The concrete automatically becomes high-strength concrete.

Question 6 ప్రశ్న 6

Two concrete batches have the same water-cement ratio and constituent materials. Batch X is fully compacted, while Batch Y contains significant entrapped air because of inadequate vibration. Which result is most likely?

A Batch Y will generally develop lower compressive strength because the entrapped voids reduce effective load-carrying material. B Batch Y must have higher strength because air is stronger than concrete. C Both must develop exactly the same strength because their water-cement ratios are equal. D Compaction affects only appearance and cannot influence strength.

Question 7 ప్రశ్న 7

A properly proportioned concrete is allowed to dry severely soon after finishing instead of receiving adequate curing. What is the most likely effect on strength development?

A Strength development may be reduced because hydration is restricted by loss of available moisture. B Strength must increase because drying accelerates all hydration reactions. C Curing has no influence once concrete has been compacted. D Only aggregate strength is affected by curing.

Question 8 ప్రశ్న 8

Why does the compressive strength of normally cured concrete generally increase with age during its early and intermediate life?

A Continued hydration forms additional cementitious products and develops a denser load-carrying microstructure. B Coarse aggregate particles continuously increase in mineral strength after casting. C Mixing water is converted directly into aggregate. D The concrete cube becomes physically larger with age.

Question 9 ప్రశ్న 9

A site engineer assumes that every concrete must attain exactly 70 percent of its 28-day strength at 7 days. Which response is technically correct?

A The assumption is unsafe because the 7-to-28-day strength relationship varies with cement type, supplementary cementitious materials, temperature, curing and mix proportions. B The assumption is universally correct for every cement and concrete. C Seven-day concrete strength is always exactly equal to 28-day strength. D Concrete strength cannot be measured before 28 days.

Question 10 ప్రశ్న 10

For two properly designed concretes having comparable later-age strength requirements, which cementitious system is generally more likely to show comparatively gradual early-age strength development?

A A concrete containing a substantial proportion of fly ash or slag, depending on binder reactivity, temperature and curing B A concrete using Rapid Hardening Portland Cement specifically for high early strength C A concrete whose cement has completely hydrated before mixing D A concrete containing no cementitious binder

Question 11 ప్రశ్న 11

Which statement best describes the effect of concrete age on strength when adequate curing is maintained?

A Strength gain is generally rapid at early ages and progressively slower at later ages. B Strength increases by exactly the same amount every day indefinitely. C Concrete reaches all possible strength immediately after final setting. D Strength necessarily begins decreasing after seven days.

Question 12 ప్రశ్న 12

Why is tensile-related strength particularly important even though concrete is primarily valued for compressive strength?

A Cracking commonly initiates when tensile stresses exceed the comparatively low tensile capacity of concrete. B Concrete can never crack under tensile stress. C Tensile strength is always higher than compressive strength. D Tensile strength determines aggregate grading.

Question 13 ప్రశ్న 13

What is the fundamental principle of the split tensile strength test on a concrete cylinder?

A A diametral compressive load is applied so that transverse tensile stresses develop and split the cylinder. B The cylinder is pulled directly from both ends using reinforcing bars. C The cylinder is subjected only to torsion. D The cylinder is submerged until it cracks from water absorption.

Question 14 ప్రశ్న 14

A concrete cylinder 150 mm in diameter and 300 mm long fails in a splitting test under a load of 200 kN. Using fct = 2P/(πLD), what is the approximate split tensile strength?

A 1.41 N/mm² B 2.83 N/mm² C 4.24 N/mm² D 8.89 N/mm²

Question 15 ప్రశ్న 15

Flexural strength of concrete is also commonly referred to as:

A Modulus of rupture B Bulk modulus of aggregate C Compacting factor D Fineness modulus

Question 16 ప్రశ్న 16

Using the IS 456 expression fcr = 0.7√fck, what is the estimated flexural tensile strength of M25 concrete?

A 2.5 N/mm² B 3.5 N/mm² C 5.0 N/mm² D 17.5 N/mm²

Question 17 ప్రశ్న 17

Using fcr = 0.7√fck, what is the approximate estimated flexural tensile strength for M40 concrete?

A 3.13 N/mm² B 3.50 N/mm² C 4.43 N/mm² D 7.00 N/mm²

Question 18 ప్రశ్న 18

Why can aggregate strength become particularly important when producing high-strength concrete?

A As the cementitious matrix becomes stronger, weak aggregate particles or weak aggregate-paste interfaces can become the controlling locations of failure. B Aggregate has no influence on concrete strength at any strength level. C High-strength concrete is made without aggregate. D Increasing paste strength automatically increases aggregate mineral strength.

Question 19 ప్రశ్న 19

How can well-proportioned aggregate grading indirectly assist concrete strength development?

A It can improve packing and compactability, reduce unnecessary voids and help achieve the required workability without excessive paste or water. B It chemically increases the cement grade. C It makes curing unnecessary. D It guarantees strength irrespective of water-cement ratio.

Question 20 ప్రశ్న 20

A site crew adds substantial extra water to a concrete mix immediately before placing because the concrete has lost slump. Assuming no compensating change in cementitious material, what is the likely strength consequence?

A The effective water-cementitious-material ratio rises and the hardened concrete strength will generally be reduced. B Strength necessarily rises because the concrete becomes easier to place. C The water-cementitious-material ratio remains unchanged. D The added water increases aggregate crushing strength.

Question 21 ప్రశ్న 21

A compatible superplasticizer permits a concrete mix to achieve the required workability with substantially less mixing water while cementitious content is unchanged. If compaction and curing remain satisfactory, which strength tendency is generally expected?

A Strength can increase because the effective water-cementitious-material ratio is reduced while workable placement is maintained. B Strength must decrease because less water always prevents all hydration. C Strength is necessarily unchanged because admixtures cannot affect water demand. D The concrete automatically becomes lightweight concrete.

Question 22 ప్రశ్న 22

Concrete placed in cold conditions remains at a low temperature during its early curing period but is protected from freezing and kept moist. What strength-development behaviour is generally expected compared with otherwise similar concrete cured at a suitable warmer temperature?

A Early strength development will generally be slower because hydration proceeds more slowly at low temperature. B Early strength must always be higher because low temperature accelerates hydration. C Temperature has no influence on cement hydration. D The concrete necessarily loses all ultimate strength immediately.

Question 23 ప్రశ్న 23

Why must concrete specimens intended for comparative strength testing be made, cured and tested under standardized conditions?

A Specimen size, preparation, compaction, curing, moisture condition and loading procedure can all influence the measured strength. B Only the colour of the specimen affects strength results. C Concrete strength is independent of specimen preparation and testing procedure. D Standardized testing is necessary only for aggregate and not for concrete.

Question 24 ప్రశ్న 24

A concrete is designed with a low water-cement ratio but is badly compacted and inadequately cured. Which conclusion is most appropriate?

A A low water-cement ratio alone does not guarantee high strength; inadequate compaction and curing can substantially reduce the strength actually achieved. B The concrete must achieve high strength because water-cement ratio is the only factor that matters. C Poor curing increases strength enough to compensate for entrapped air. D Compaction influences only fresh concrete and has no effect after hardening.

Question 25 ప్రశ్న 25

Consider the following statements about hardened-concrete strength:
1. Lower water-cement ratio generally favours higher strength when adequate workability, compaction and curing are maintained.
2. Continued curing supports strength development by allowing hydration to proceed.
3. Split tensile and flexural strength represent tensile-related behaviour and are much lower than concrete compressive strength in ordinary concrete.
4. Aggregate quality, compaction and curing may be ignored once the concrete has been assigned an M-grade.

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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