(a) Briefly discuss why it is more advantageous to use high strength concrete for construction of high-rise buildings and large-span bridges as compared to normal strength concrete. (10 marks)

(b) Briefly discuss the advantages of using hollow concr

Question

(a) Briefly discuss why it is more advantageous to use high strength concrete for construction of high-rise buildings and large-span bridges as compared to normal strength concrete. (10 marks)

(b) Briefly discuss the advantages of using hollow concrete blocks for masonry works of a building as compared to stone or brick masonry works. (10 marks)

(c) Determine the total present worth of maintenance cost of a 4-lane highway using the capitalized equivalent approach.

The following costs are estimated for maintenance of the above highway :
(i) Periodic maintenance cost to be carried out at every five years = ₹ 2 crores
(ii) Annual maintenance cost = ₹ 0.06 crore

Assume the interest rate as 10% per year compounded annually. (10 marks)

(d) The laying temperature during the construction of plain cement concrete pavement of slab thickness 20 cm is 15 °C and the maximum slab temperature during the summer is used to be 45 °C. If the width of expansion joint gap is 2.5 cm, calculate the spacing between the expansion and contraction joints.

Assume the following data :
Coefficient of thermal expansion of concrete = 12×10⁻⁶ per °C
Unit weight of concrete = 2360 kg/m³
Allowable stress in cement concrete in tension = 0.8 kg/cm²
Coefficient of friction of the interface = 1.5 (10 marks)

(e) Explain the different types of resolutions in remote sensing with suitable examples. (10 marks)

UPSC Answer Check · Accepted Answer

The directive 'discuss' for parts (a), (b), (e) requires balanced exposition with merits and contextual application, while parts (c) and (d) demand rigorous numerical solution. Allocate approximately 15% time each to (a), (b), (e) for conceptual depth; 25% each to (c) and (d) for calculations. Structure: begin with theoretical foundations for concrete technology and masonry, proceed through step-by-step engineering economics and pavement thermal analysis, conclude with remote sensing applications in Indian infrastructure monitoring.
- Part (a): High strength concrete advantages—reduced column sizes increasing floor area, lower dead load enabling taller structures, enhanced durability, reduced creep and shrinkage for bridges; mention M60-M100 grades used in Burj Khalifa and Bandra-Worli Sea Link
- Part (b): Hollow concrete block advantages—thermal insulation, sound absorption, 50% material saving, faster construction, lighter dead load reducing foundation cost; comparison with traditional Kota stone or Flemish bond brickwork
- Part (c): Capitalized equivalent calculation—convert periodic maintenance to equivalent annual cost using capital recovery factor, add annual maintenance, divide by interest rate; correct application of (A/P,10%,5) and final present worth formula
- Part (d): Expansion joint spacing from thermal expansion formula L = δ/(α×ΔT), contraction joint spacing from friction-stress equilibrium L = 2×σ×h/(μ×γ×100); correct unit conversions and temperature differential handling
- Part (e): Four resolution types—spatial (Landsat 30m vs Cartosat 2.5m), spectral (hyperspectral vs multispectral), radiometric (11-bit vs 8-bit), temporal (revisit period); Indian examples from NRSC/ISRO missions

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	25%	12.5	Demonstrates precise understanding of HSC microstructure (dense C-S-H, low w/c ratio), hollow block cavity thermal resistance R-value, capitalized cost perpetuity concept, pavement joint stress-friction mechanics, and resolution trade-offs in Indian remote sensing programs	States general advantages without mechanistic explanation; confuses capitalized cost with simple present worth; mixes up expansion and contraction joint formulas; lists resolution types without distinguishing parameters	Fundamental errors like attributing HSC strength to aggregate alone, treating hollow blocks as solid in load calculation, using simple interest for part (c), ignoring temperature differential sign convention, omitting temporal resolution entirely
Numerical accuracy	25%	12.5	Part (c): Correctly computes A = ₹2 crore × 0.2638 = ₹0.5276 crore, total annual = ₹0.5876 crore, PW = ₹5.876 crore; Part (d): Expansion L = 2.5/(12×10⁻⁶×30) = 69.44m, Contraction L = 2×0.8×20/(1.5×2360×10⁻⁴) = 90.4m; all unit conversions flawless	Correct formulas but arithmetic errors; wrong interest factor interpolation; omits factor of 2 in contraction joint formula; temperature range errors (uses 45°C instead of 30°C differential)	Major calculation errors—uses simple interest, ignores periodic-to-annual conversion, confuses cm-m units producing order-of-magnitude errors, omits entire numerical working for one part
Diagram quality	15%	7.5	Clear labeled sketches: hollow block cross-section showing cavities and shell thickness; pavement joint detail with dowel bar, filler, sealant; remote sensing resolution cube showing pixel, band, radiometric depth; cash flow diagram for maintenance costs	Basic diagrams without labels or dimensions; generic pavement joint sketch without thermal movement indication; missing cash flow representation	No diagrams despite visual nature of topics; messy unlabelled sketches; diagrams contradicting described concepts
Step-by-step derivation	20%	10	Explicit derivation chain: for (c) shows i(1+i)ⁿ/((1+i)ⁿ-1) application, perpetuity 1/i division; for (d) shows δ = αLΔT rearrangement, then σ = μγL/2 equilibrium from free-body diagram of slab segment	States final formulas without derivation; skips intermediate steps in interest factor calculation; presents answers without showing thermal stress buildup logic	No derivation shown—only final answers; incorrect formula substitution without explanation; missing free-body diagram basis for friction-stress relationship
Practical interpretation	15%	7.5	Contextualizes HSC for Indian seismic zones (IS 13920 ductility), hollow blocks for cost-effective PMAY housing, maintenance costs for NHAI BOT projects, joint spacing for concrete roads in Rajasthan's 50°C extremes, ISRO's RISAT for all-weather agricultural monitoring	Generic applications without Indian context; mentions standard codes without specific project references; ignores economic implications of maintenance scheduling	No practical linkage—purely academic treatment; irrelevant examples from unrelated fields; misses that calculated joint spacing must be rounded down for construction feasibility

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