Chapter 15: Civil and Construction Technology

Construction materials

Cement (usually Portland cement) sets by hydration. Concrete is cement, fine aggregate (sand), coarse aggregate (gravel or crushed stone), and water. A common nominal mix is 1:2:4 (cement:sand:coarse aggregate by volume). Strength depends strongly on the water–cement ratio (lower is stronger but harder to place), compaction, and curing (keeping it moist for several days). The slump test measures workability, and the 28-day cube compressive strength is used for grading (Neville, 2011).

Reinforced concrete adds steel bars: concrete resists compression; steel resists tension.

Bricks and blocks, timber, structural steel, glass, roofing materials, and paints.

Surveying and setting out

Levelling finds heights. With a level, a backsight (BS) on a point of known level gives the height of instrument, , and a foresight (FS) gives . Example: a backsight of 1.525 m on a benchmark of reduced level 100.000 m gives m; a foresight of 0.875 m gives m. Distances are measured by tape or electronic distance measurement; angles by theodolite or total station; positions by GPS/GNSS (Schofield & Breach, 2007). Surveyors carry out site surveys, contour surveys, and setting out (marking building lines on the ground).

Structures and loads

Structures carry dead loads (self-weight), live loads (people, furniture), wind loads, and, in some places, seismic and flood loads. A simply supported beam of span with a uniformly distributed load has reactions at each support and a maximum bending moment at mid-span. Example: m and kN/m give reactions of 30 kN and a maximum moment of kN m. Structural elements: beams, columns, slabs, walls, footings, trusses, and frames. Foundations spread loads to the soil; their type depends on soil bearing capacity. Sri Lanka’s heavy monsoon rains and hill-country slopes make drainage, retaining structures, and landslide hazards important in design.

Building construction

Stages: site investigation and clearing; setting out; excavation and foundations; substructure (plinth, damp-proof course); superstructure (walls, columns, beams, slabs); roofing; services (plumbing, electrical); plastering, flooring, and finishes; painting and completion (Chudley & Greeno, 2016). Quantity estimation: a slab of 5 m × 4 m with thickness 0.15 m needs of concrete (plus an allowance for wastage). A bill of quantities lists items, units, quantities, rates, and cost.

Roads, water supply, and sanitation

Road pavements have layers: subgrade, sub-base, base course, and surfacing (asphalt or concrete). Good drainage keeps water out of the pavement. Water supply involves intake, treatment (Chapter 8), storage, and distribution. Flow in a pipe: ; for a 0.10 m diameter pipe with water at , and L/s. Sanitation includes septic tanks and soak pits (where there is no sewer), sewerage, and wastewater treatment (Chapter 20). Rainwater harvesting and stormwater management reduce flooding and water stress.

Building services and sustainable construction

Building services include electrical installations, plumbing, ventilation, lighting, fire protection, and lifts. Green building practice uses natural ventilation and daylight, shading, insulation, energy-efficient appliances, rainwater harvesting, solar water heating, locally sourced and recycled materials, and designs that reduce heat gain in tropical climates.

Safety and quality on site

Construction is one of the most dangerous industries. Key measures: helmets, boots, high-visibility clothing, gloves, eye and ear protection; scaffolding and ladders checked and used correctly; fall protection at height; trench support in excavations; safe lifting; electrical safety and machinery guards; dust control; and site rules for visitors. Quality needs correct materials, supervision, testing of concrete cubes and soil, and record keeping.

Common mistakes

Adding too much water to concrete to make it easier to place.

Ignoring curing.

Forgetting wastage allowances in quantity estimates.

Practice questions

A backsight of 2.340 m is taken on a benchmark of RL 50.000 m. A foresight on a point is 1.785 m. Find its RL. [50.555 m]

Find the maximum bending moment of a simply supported beam of span 8 m carrying 5 kN/m. [40 kN m]

Find the concrete volume of a 3.0 m × 3.0 m × 0.12 m slab. [1.08 m³]

Part Four: Bio-Systems Technology

Bio-Systems Technology (BST) applies science and technology to biological production and processing: growing crops, raising animals and fish, processing food, protecting the environment, and managing agricultural enterprises. The A/L subject combines theory with practical skills and leads to the Bachelor of Biosystems Technology degrees at the Faculties of Technology (University of Sri Jayewardenepura, n.d.-b). The chapters here follow the chain from soil and water to the farm, to the processing plant, and to the market. Standard references include Brady and Weil (2016), Taiz et al. (2015), Allen et al. (1998), Boyd (2015), Tchobanoglous et al. (2014), and the Codex Alimentarius Commission (2020). The NIE syllabus defines the exact units and order.