Tamil Nadu HSE Second Year Basic Civil Engineering key terms

A paste made by mixing slaked lime with sand and water, used to bind masonry units or to finish plaster surfaces. It hardens slowly by absorbing carbon dioxide from air and is weaker than cement mortar.

A mixture of cement, fine aggregate and water used to join bricks or stones and to plaster walls. It sets by chemical hydration, gains strength quickly, and is stronger and more water-resistant than lime mortar.

The mass of loose cement occupying a unit volume, usually about 1440 kg per cubic metre. It is used to convert cement bags into volume for site measurement, since one bag of 50 kg occupies roughly 0.035 cubic metre.

The increase in volume of moist sand caused by films of water pushing the grains apart. Because damp sand bulks, more loose sand is needed to give a fixed solid volume, so bulking must be allowed for in volumetric batching.

An index describing the average coarseness of an aggregate, obtained by sieving a sample through standard sieves and summing the cumulative percentages retained, divided by 100. A higher value means a coarser aggregate.

The distribution of particle sizes within a sample of coarse or fine aggregate. Well-graded material contains a range of sizes so that voids are minimised, giving denser, stronger concrete with less cement paste.

A concrete mix specified by volume proportions, such as 1:2:4 for cement, fine aggregate and coarse aggregate. It is used for ordinary work where strength is assumed from the proportions rather than established by testing.

A concrete mix whose proportions are chosen by calculation and trial testing to achieve a specified strength, workability and durability for the given materials. It is used for important or high-strength work.

The mass of water divided by the mass of cement in a concrete mix. It governs strength and durability: more water increases workability but reduces strength and raises permeability, so the ratio is kept low.

A field test in which freshly mixed concrete is placed in a standard cone, the cone is lifted, and the drop in height of the concrete is measured. It indicates workability and consistency of the mix.

The process of keeping concrete moist and at a suitable temperature after placing so that cement continues to hydrate. Curing for the specified period develops strength, reduces shrinkage cracking and improves durability.

The maximum pressure a soil can safely carry at the base of a foundation without excessive settlement or shear failure. It decides the size and type of footing chosen for a structure.

A shallow foundation widened at the base so that the load from a column or wall is distributed over a larger soil area. The width is fixed so that soil pressure stays within the safe bearing capacity.

A deep foundation in which long columns of concrete, steel or timber are driven or cast into the ground to carry loads to firm strata below. It is used where soil near the surface is weak.

The internal turning effect at a section of a beam caused by loads acting at a distance from that section. It produces bending stresses, compressive on one face and tensile on the other.

The internal force acting across a section of a beam that tends to slide one part of the member past the adjacent part. It is found by summing vertical forces on one side of the section.

A geometric property of a cross-section equal to the moment of inertia divided by the distance to the extreme fibre. It relates bending moment to maximum bending stress in the member.

The ratio of direct stress to the corresponding strain within the elastic limit of a material. It measures stiffness, so a material with a high value deforms less under the same load.

The surveying operation of finding the relative heights of points on or below the ground surface. It uses a level instrument and staff to read backsights and foresights and so compute reduced levels.

The height of a survey point expressed with reference to a chosen datum, usually mean sea level. It is computed by adding backsight readings and subtracting foresight readings along a levelling run.

A fixed, permanent point of known reduced level, often marked on a building or pillar, from which levelling work starts and is checked. Temporary bench marks are set up for a single job.

A line on a map joining points of equal elevation above the datum. Contours show the shape and steepness of ground, and their spacing indicates whether a slope is gentle or steep.

A graphical method in which the plan is drawn directly in the field on a sheet fixed to a drawing board mounted on a tripod. Directions to objects are sighted and plotted without recording angles numerically.

The placing of a building on its site so that rooms receive suitable sunlight and breeze while avoiding harsh heat. In Tamil Nadu, longer walls are often aligned to reduce afternoon sun on the hot west face.

The open distance that must be left between the building line and the plot boundary under local planning rules. It provides light, ventilation, privacy and space for access and drainage.

The total floor area of all storeys of a building divided by the area of its plot. Planning authorities fix a maximum value to control the density of construction on a site.

An underground chamber in which sewage is retained long enough for solids to settle and be digested anaerobically. The clarified liquid flows out to a soak pit or drain field for further treatment.

A covered pit of loose stones or rings through which effluent from a septic tank seeps into the surrounding soil. It disposes of liquid waste where no public sewer is available.

The minimum flow velocity in a drain or sewer that keeps solid matter moving so that silt does not settle. It is balanced against the maximum velocity that would erode the pipe material or joints.

The average quantity of water used per person per day for domestic, industrial and public purposes in a town. It is multiplied by population to fix the capacity of supply and distribution works.

The slight transverse slope given to the surface of a road so that rain water drains quickly to the sides. It is expressed as a ratio such as 1 in 40 and depends on surface type and rainfall.

The raising of the outer edge of a road curve above the inner edge to balance the centrifugal force on moving vehicles. It is limited so that slow vehicles do not slide inward on the slope.

A small bridge-like structure built under a road or embankment to carry a stream or drain across it. It is generally of span less than about six metres and may be of pipe, slab or box form.

The covered area of a building measured at the plinth level, usually taken as the area between the outer faces of walls. In many schedules it forms the basis for computing estimated cost at a plinth area rate.

The cost of constructing one square metre of plinth area of a building of a given type and standard. Multiplying it by the total plinth area gives a quick approximate estimate.

The fall in the value of a property or structure due to age, wear, obsolescence or changes in surroundings. It is deducted from replacement cost when arriving at the present value of a building.

A locally made mortar material in Tamil Nadu, produced by grinding burnt clay bricks or tiles with lime. It is used in lime-surki mortar and plaster for traditional masonry work.