(a) Briefly discuss why it is more advantageous to use high strength concrete for construction of high-rise buildings and…

(a) High-strength concrete

High-strength concrete is more advantageous for high-rise buildings and large-span bridges because it allows larger loads to be carried by smaller sections. In tall buildings, smaller columns, beams, and cores increase usable floor area, improve architectural flexibility, and reduce the self-weight of upper floors. The lower dead load also reduces foundation demand and makes taller structures more economical. In urban high-rises, the increase in leasable area can be significant. For bridges, high-strength concrete improves prestressing efficiency, reduces long-term creep (and hence prestress loss), and limits deflection over long spans; thinner decks also improve clearance and reduce material volume. Its dense matrix gives lower permeability and enhanced durability against carbonation, chloride attack, sulphate action, and abrasion, which is important for marine and heavily trafficked structures. This also lowers long-term maintenance. Grades of M60 and above are used where compact sections, long spans and long service life are critical; Burj Khalifa, for example, used about 80 MPa concrete in its lower vertical elements. HSC does need stricter quality control, and it is more brittle and prone to explosive spalling in fire, which is managed through confinement reinforcement and polypropylene fibres. Thus HSC is not merely a stronger material; it changes the structural, economic, and durability performance of the project.

(b) Hollow concrete blocks

Hollow concrete blocks offer several advantages over stone or brick masonry. The voids in the blocks reduce heat flow and provide thermal insulation, making interiors more comfortable and reducing cooling or heating demand. They also improve sound absorption and insulation compared with solid stone or brick walls. Because the blocks are hollow, the voids (typically 25–50% of the gross volume, IS 2185 Part 1) save material compared with solid masonry, and the units are lighter, which reduces dead load, foundation cost, and transport cost. The lighter wall is also useful on soft ground. In Indian climates, thermal insulation can reduce cooling demand, and sound insulation is valuable near traffic. Construction is faster because the blocks are larger, require less mortar, and can be laid with simpler alignment. Compared with random rubble stone masonry or English/Flemish-bond brickwork, hollow block masonry can reduce labour time, material handling, and wall weight while giving a reasonably smooth finish. The main design consideration is that load-bearing hollow block walls still require proper reinforcement, lintels, and bonding, but for ordinary building masonry the benefits are substantial.

(c) Capitalized equivalent

For a highway with indefinite service life, the capitalized present worth is the equivalent annual cost divided by the interest rate. The method is appropriate because highway maintenance is a perpetual recurring cost; the five-year cost is spread over each cycle and then capitalized. The periodic maintenance of ₹2 crore every five years is not simply divided by five, because money has time value. With i = 10% and n = 5, the equivalent annual amount is found using the five-year factor i/[(1+i)^n - 1]. Thus A = 2 × 0.10/(1.10⁵ - 1) = 0.20/0.61051 = ₹0.3276 crore per year. Adding the annual maintenance of ₹0.06 crore gives a total equivalent annual maintenance cost of ₹0.3876 crore per year. The total present worth is therefore A/i = 0.3876/0.10 = ₹3.876 crore, approximately ₹3,87,60,000. This is the capitalized equivalent of the recurring five-year and annual maintenance obligations at 10% per year.

(d) Pavement joint spacing

The temperature rise from laying to summer is ΔT = 45 °C - 15 °C = 30 °C. The expansion joint gap must accommodate thermal expansion, so the expansion joint spacing is L_e = (δ/2)/(α ΔT) = 1.25 cm/(12×10⁻⁶ × 30) = 3472 cm, or about 34.7 m. Only half the gap (δ/2) is allowed for expansion, because the joint filler compresses by only about 50%. For contraction joints, the friction-stress equilibrium is used. Convert unit weight to kg/cm³: γ = 2360 kg/m³ = 0.00236 kg/cm³. With slab thickness h = 20 cm, allowable tensile stress σ = 0.8 kg/cm², and friction coefficient μ = 1.5, the spacing is L_c = 2σh/(μγh) = 2σ/(μγ) = (2×0.8)/(1.5×0.00236) = 452 cm ≈ 4.5 m; the slab thickness cancels. The unit conversion is essential because the stress, thickness, and unit weight are given in mixed units. Equivalently, using γ in kg/m³, L_c = (2σ×10⁴)/(μγ) = 4.52 m. Thus the thermal calculation gives an expansion joint spacing of about 34.7 m, while the friction-tension calculation gives a contraction joint spacing of about 4.5 m; in actual layout the smaller or code-specified spacing would govern.

(e) Remote sensing resolutions

Remote sensing data are characterized by four main types of resolution. Spatial resolution is the ground size of one pixel. A 2.5 m Cartosat-1 image can resolve buildings, roads, and small infrastructure, while a 30 m Landsat image is more suitable for land-cover mapping. Spectral resolution is the number and width of wavelength bands. Multispectral sensors, such as those on Resourcesat, record a limited set of broad bands for vegetation, water, and soil; hyperspectral sensors record many narrow bands and can distinguish minerals, crop stress, or water quality more precisely. Radiometric resolution is the sensor’s ability to distinguish small differences in brightness. An 8-bit sensor records 256 levels, while an 11-bit sensor records 2048 levels, giving better discrimination of subtle surface reflectance in urban, coastal, or agricultural mapping. Temporal resolution is the frequency of repeat observation. Indian missions such as Cartosat, Resourcesat, Oceansat, and RISAT provide repeat coverage for monitoring infrastructure, floods, coastal change, and land use; radar-based RISAT is especially useful for all-weather temporal monitoring. Cartosat supports cadastral and urban planning, Resourcesat supports agriculture and water resources, Oceansat supports coastal monitoring, and RISAT supports flood and disaster monitoring. The choice depends on scale: national mapping may use coarser spatial but frequent temporal data, while site-level engineering needs finer detail. Together, these resolutions determine whether a mission is best suited for mapping, monitoring, or detailed engineering assessment.