RRB JE Civil Engineering — Complete CBT-2 Study Guide

• Cement: Ordinary Portland Cement (OPC) setting has two stages — initial setting time (min 30 min) and final setting time (max 600 min, i.e. 10 hrs), tested via Vicat apparatus. • Compressive strength of OPC (28-day) for grade 43 ≈ 43 MPa, grade 53 ≈ 53 MPa — the grade number IS the guaranteed 28-day compressive strength in N/mm². • Bricks: standard modular brick size in India is 190mm × 90mm × 90mm (with mortar joint, nominal size 200×100×100mm); water absorption for first-class bricks should not exceed 20% of dry weight. • Steel (TMT bars): Thermo-Mechanically Treated bars have a tough outer rim (quenched) and a soft ductile core, giving both strength and earthquake ductility — Fe415/Fe500/Fe500D/Fe550 grades denote minimum yield strength in N/mm². • Aggregates: fineness modulus (FM) is obtained by summing cumulative % retained on standard sieves and dividing by 100; higher FM = coarser aggregate. Water-cement ratio directly controls concrete strength and workability (lower w/c = higher strength, per Abrams' law).

• Chain surveying is suited for small, flat, open areas with few obstacles; compass surveying uses magnetic bearings but is affected by local attraction (magnetic materials nearby); plane table surveying combines field observation and plotting simultaneously. • Levelling terms: Back Sight (BS) — first reading after setting up instrument at a new station; Fore Sight (FS) — last reading before shifting the instrument; Intermediate Sight (IS) — any reading between BS and FS at the same setup. • Reduced Level (RL) by Height of Instrument (HI) method: HI = RL of BM + BS; RL of point = HI − FS/IS. By Rise & Fall method: compare consecutive staff readings — a decrease in reading is a Rise, an increase is a Fall. • Contour lines: closer spacing indicates steeper slope; contour lines never cross each other (except at an overhanging cliff, shown as dashed); a contour line always closes on itself (may be outside the map area). • Total Station combines EDM (Electronic Distance Measurement) and theodolite angle measurement in one instrument, giving 3D coordinates directly — has largely replaced the traditional chain-and-compass method on major projects.

• RCC works on the principle that concrete is strong in compression but weak in tension, while steel is strong in tension — reinforcement bars are placed in the tension zone to compensate. • Nominal mix ratios (by volume) for common grades: M15 = 1:2:4 (cement:sand:aggregate), M20 = 1:1.5:3 — "M" denotes the characteristic compressive strength in N/mm² at 28 days. • Effective cover = clear cover + half the bar diameter; clear cover protects reinforcement from corrosion and provides fire resistance — minimum clear cover for a slab is typically 15-20mm, for a beam/column 25-40mm depending on exposure condition. • Development length (Ld) is the embedment length required to transfer bar force to surrounding concrete by bond — insufficient development length causes bond-slip failure even if the bar itself doesn't yield. • Limit State Method (current IS 456 approach) checks two limit states: Limit State of Collapse (strength/safety) and Limit State of Serviceability (deflection, cracking) — replacing the older Working Stress Method for most new designs.

• Bernoulli's equation (for ideal, incompressible, steady flow): P/ρg + v²/2g + z = constant along a streamline — represents conservation of pressure, kinetic, and potential energy heads. • Flow measurement devices: Venturimeter (converging-diverging tube, measures discharge via pressure difference, low head loss); Orifice meter (simpler, cheaper, but higher head loss than venturimeter for the same accuracy). • Types of flow: laminar (Reynolds number Re < 2000, smooth parallel layers) vs turbulent (Re > 4000, chaotic mixing); Re = ρvD/μ (density × velocity × diameter / viscosity) — dimensionless. • Open channel flow: Manning's equation V = (1/n)R^(2/3)S^(1/2), where n = roughness coefficient, R = hydraulic radius, S = bed slope — used for canal/drain discharge calculations. • Pumps: Centrifugal pumps convert kinetic energy (impeller rotation) to pressure energy, suited for high discharge/low head; Reciprocating pumps use piston displacement, suited for low discharge/high head applications.