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Example: The Penguin Dictionary of Civil Engineering

Penguin Dictionary of Civil Engineering

concrete roofs Concrete can be used for building many sorts of roof. The simplest roofs, solid reinforced-concrete slabs, are suitable for spans up to about 6 m. For spans from 4.5 to 10 m, hollow-tile floor construction is lighter, cheaper and sometimes also thinner. Precast beams can be laid dry very rapidly to form a roof, and precast, prestressed beams can be used for large spans and low construction depths. The main difficulty with prestressed floor beams is that it is difficult to obtain them bent upwards by an equal amount and the ceiling may therefore be uneven. For large spans of about 30 m the concrete dome or shell is completely smooth underneath. The flat Diagrid floor is popular now though expensive, and spans 15 m without difficulty. Prestressed or reinforced concrete girders often cover large spans.

concrete spreader, asphalts. A roadbuilding machine which may be part of a slipform or fixed form paving train. It uniformly spreads concrete or asphalt poured into it or dumped in front of it. Apart from the roller, the mixer and the trucks, it is the main unit needed for rolled concrete.

concrete technology Designing, testing and analysing concretes and their components, the aggregates, cements, pozzolans, admixtures, release agents, etc. A knowledge of concrete mixers, formwork and the production equipment for the components is essential, as well as of concrete defects and the chemical reactions between cements, water and aggregates. Most concrete technologists are civil engineers or chemists, not necessarily fully qualified. Leading concrete technologists are members of the Institution of Concrete Technology.

concrete tensile strength The tensile strength of concrete is usually between 20% and 5% of its compressive strength. For strong concretes it is nearer 5% and for weak ones nearer 20%.

concrete testing The commonest tests for concrete are of two types: for the workability of wet concrete and for the strength of set concrete. Testing is used both for mix design (see trial mix) and for site control. The strength of a concrete in any structure is usually less than that of a standard cube or cylinder taken from the mix during casting and cured for 28 days, but see Seattle. Curing conditions for the cube or cylinder are better. Destructive tests can rarely be used on a structure and when possible they are expensive and slow. Semi-destructive tests may help, for example the internal fracture test of the BRE.

The main non-destructive testing (ND T) methods for investigating concrete strength are the rebound hammer and pulse velocity determination by ultrasonic testing. For other properties of concrete, many NDT methods exist. Magnetic devices (cover meters) can find reinforcement or show if it has not enough cover. Gamma radiography discovers steel bars as well as voids or their opposite dense, usually strong concrete. Simple electrical probes can measure the content of chloride or moisture, or whether steel is corroding, or the thickness of a concrete slab on the ground. Acoustic methods find cracks. The cement content of hard concrete can be found by the RAM test. Chemical testing also can find the chloride and aggregate contents and the presence of some admixtures, See core test.

concrete-vibrating machine A machine which travels like the concrete-finishing machine or spreader and vibrates up to 30 m3 of concrete per hour. See vibrated concrete, vibrator, slip-form paver.

concreting boom A light metal truss supported at one end on a frame near a concrete mixer and at the other end on another frame on wheels. On its underside is a rail along which a concreting bucket can travel, carried by a pair of overhead wheels. A 200 litre capacity bucket can be carried on a 12 m long boom weighing 180 kg. A placing boom is much more elaborate.

condensate Water which condenses from air, flue gas, etc. cooled below the dewpoint.

condensed silica fume (CSF) See microsilica.

condition monitoring Checking the condition of a machine by such techniques as vibration analysis and oil debris analysis.

conditions of contract, general c. of c. Conditions of contract are published by many bodies, including the Joint Contracts Tribunal, FIDIC, the ICE and the Department of the Environment. They describe in detail how contractors should view the contract and do the work. In addition to the conditions themselves, books exist to explain them, such as the ICE's Guide to the Fifth of 120 pages, A4 size. The first edition of the 'ICE conditions' was published in 1945. Most contractors are familiar with the ICE conditions and they are drawn up and periodically revised by agreement between consulting engineers and contractors (ACE, FCEC).

conditions of engagement The agreement between a consulting engineer and his or her client.

conductor pipe The outermost casing section of an offshore oil or gas well. It extends from a short distance below the seabed, up to the deck of the offshore platform. Its diameter is from 700 to 910 mm (2.3-3 ft).

conductor rail [rly] A rail carried on electrical insulators and parallel to running rails. It provides the power for an electric train through the locomotive's metal shoes pressing against it.

conduit [hyd.] Any open channel, pipe, etc. for flowing fluid. See also (B).

cone of depression The cone shape of the water table around a well being pumped. A similar cone or crater is formed around a structure built on clay or other compressible soil as the soil slowly squeezes under the load of the structure. See subsidence.

cone penetration test, deep p.t. [s.m.] The testing of soils by pressing a standard cone into the ground under a known load and measuring the penetration. These methods are used in Scandinavia and the Netherlands. In the Dutch deep-sounding test, which is used in the Netherlands to deeper than 30 m, an inner mandrel is driven separately- from the outer casing. This enables the toe resistance to be measured separately from the skin friction of the casing. This method is used for forecasting the resistance to driving of bearing piles, and can supply rapidly and cheaply the information for a preliminary site exploration. The cone diameter is 36 mm, so the force required to push it in is not very great. The method is not suitable for clays, for which the vane test is preferred, nor for stony soils. Cf. dynamic penetration test.  

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