— L —

 

lacing — horizontal bracing between shoring members.

 

lagging — heavy sheathing used as in underground work to withstand earth pressure.  (See also sheathing.)

 

laitance — a layer of weak material derived from cementitious material and aggregate fines either: carried by bleeding to the surface or to internal cavities of freshly placed mixture; or  separated from the mixture and deposited on the surface or internal cavities during placement of the mixture. History

 

lap — the length by which one bar or sheet of fabric reinforcement overlaps another.

 

lap splice — see splice, lap.

 

lapping (reinforcing steel) — the overlapping of reinforcing steel bars, welded-wire fabric, or expanded metal so that there may be continuity of stress in the reinforcing when the concrete member is subjected to loading.

 

larnite — a mineral; beta dicalcium silicate (Ca₂SiO₄); occurs naturally at Scawt Hill, Northern Ireland, and artificially in slags and as a major constituent of portland cement.

 

lateral reinforcement — see reinforcement, lateral.

 

latex — a dispersion of organic polymer particles in water. History

 

lath, diamond mesh or expanded-metal — a metal network, often used as reinforcement in construction, formed by suitably stamping or cutting sheet metal and stretching it to form open meshes, either of diamond-shaped or rhomboidal-shaped openings.  (See also mesh, diamond.) History

 

law, Abrams’ — a rule stating that, with given concrete materials and conditions of test, the ratio of the amount of water to the amount of the cement in the mixture determines the strength of the concrete provided the mixture is of a workable consistency.  (See also water-cement ratio.)

 

law, Hooke’s — the law, which holds practically for strains within the elastic limit, that the strain is proportional to the stress producing it.  (See also limit, proportional and modulus of elasticity.)

 

layer — see course and lift.

 

layer, bonding — a layer of mortar, usually 1/8 to 1/2 in. (3 to 13 mm) thick, which is spread on a moist and prepared, hardened concrete surface before placing fresh concrete.

 

L-beam — a beam having a cross section in the shape of an L; a beam having a ledge on one side only.

 

L-column — the portion of a precast-concrete frame, comprising the column, the haunch, and part of the girder.

 

leaf — see wythe (leaf).

 

lean concrete — see concrete, lean.

 

lean mixture — see concrete, lean.

 

lean mortar — see mortar, lean.

 

ledger — any member with a protrusion or protrusions that support other structural members.  (See also L-beam and inverted T-beam.)

 

length —

 

length, development — the bonded length required to achieve the design strength of a reinforcement at a critical section. History

 

length, embedment — the length of embedded reinforcement provided beyond a critical section. History

 

length, transfer — the length from the end of the member where the tendon stress is zero to the point along the tendon where the prestress is fully effective; also called transmission length.

 

length, transmission — see length, transfer.

 

length change — increase or decrease in length.  (See also volume change and deformation.)

 

length change, autogenous — length change caused by autogenous volume change.  (See volume change, autogenous.)

 

lever arm — in a structural member, the distance from the center of the tensile reinforcement to the center of action of the compression zone; also the perpendicular distance of a transverse force from a point about which moment is taken.

 

L-head — the top of a shore formed with a braced horizontal member projecting from one side, producing an inverted L-shaped assembly.

 

licensed design professional — an engineer or architect who is licensed to practice structural design as defined by the statutory requirements of the professional licensing laws of a state or jurisdiction; or the architect or engineer, licensed as described, who is responsible for the structural design of a particular project (also historically referred to as the "engineer of record"). History

 

lift — the concrete placed between two consecutive horizontal construction joints, usually consisting of several layers or courses.

 

lift joint — see joint, lift.

 

lift slab — a method of concrete construction in which floor and roof slabs are cast on or at ground level and hoisted into position by jacking; also a slab that is a component of such construction.

 

lifts (or tiers) — the number of frames of scaffolding erected one above the other.

 

lightweight aggregate — see aggregate, lightweight.

 

lightweight concrete — see concrete, lightweight.

 

lime — specifically, calcium oxide (CaO); loosely, a general term for the various chemical and physical forms of quicklime, hydrated lime, and hydraulic hydrated lime.  (See also lime, hydrated; lime, hydraulic hydrated; and quicklime.)

 

lime, free — calcium oxide (CaO), as in clinker and cement, which has not combined with SiO₂, Al₂O₃, or Fe₂O₃ during the burning process usually because of underburning, insufficient grinding of the raw mixture, or the presence of traces of inhibitors.

 

lime, hard-burned — the product of heating limestone to temperatures sufficient to change the calcium carbonate to calcium oxide, which can undergo expansion when it slowly reacts with water.

 

lime, hydrated — calcium hydroxide, a dry powder obtained by treating quicklime with water.

 

lime, hydraulic hydrated — the hydrated dry cementitious product obtained by calcining a limestone containing silica and alumina to a temperature short of incipient fusion so as to form sufficient free calcium oxide to permit hydration and at the same time leaving unhydrated sufficient calcium silicates to give the dry powder its hydraulic properties.

 

lime, spray — a hydrated lime of such fineness that at least 95% of the particles pass a 45 m (No. 325) sieve.

 

limestone — a sedimentary rock consisting primarily of calcium carbonate.

 

limit —

 

limit, elastic — the limit of stress beyond which the strain is not wholly recoverable.

 

limit, proportional — the greatest stress that a material is capable of developing without any deviation from proportionality of stress to strain.  (See also law, Hooke’s.)

 

limit, vibration — the age at which fresh concrete has hardened sufficiently to prevent its becoming mobile when subjected to vibration.

 

limit design — a method of proportioning reinforced-concrete members based on calculation of their strength.  (See also strength-design method.)

 

limonite — an iron ore composed of a mixture of hydrated ferric oxides; occasionally used in heavyweight concrete because of its high density and combined-water content, which contribute to its effectiveness in radiation shielding; a mineral occurring commonly as a constituent of particles of natural aggregate.  (See also oxide, brown).

 

linear prestressing — prestressing applied to linear members, such as beams and columns.

 

linear transformation — the method of altering the path of the prestressing tendon in any statically indeterminate prestressed structure by changing the location of the tendon at one or more interior supports without altering its position at the end supports and without changing the basic shape of the path between any supports; linear transformation does not change the location of the path of the pressure line.

 

linear-traverse method — determination of the volumetric composition of a solid by integrating the distance traversed across areas of each component along a line or along regularly spaced lines in one or more planes intersecting a sample of the solid; frequently employed to determine characteristics of the air-void system in hardened concrete by microscopical examination along a series of traverse lines on finely ground sections of the concrete; sometimes called the Rosiwal method.  [See also point count method and point count method (modified).]

 

lining — any sheet, plate, or layer of material attached directly to the inside face of formwork to improve or alter the surface texture and quality of the finished concrete.  (See also form lining, tunnel lining, and sheathing.)

 

lintel — a horizontal supporting member above an opening, such as a window or a door.

 

liquid-volume measurement — measurement of grout on the basis of the total volume of solid and liquid constituents.

 

lithology — the study of rocks.  (See also petrography and petrology.)

 

live load — see load, live.

 

load —       

 

load, allowable — see load, service dead and load, service live.

 

load, axle — the portion of the gross weight of a vehicle transmitted to a structure or a roadway through wheels supporting a given axle.

 

load, balanced — load capacity at simultaneous compressive failure of concrete and yielding of tension steel. (See also load balancing.)

 

load, cracking — the load that causes tensile stress in a member to exceed the tensile strength of the concrete.

 

load, dead —

 

(1) the weights of the structural members, supported structure, and permanent attachments or accessories that are likely to be present on a structure in service; or

 

(2) loads meeting specific criteria found in the governing building code (without load factors). History

 

load, design — obsolete term for factored load.

 

load, dynamic — a load that is variable, that is, not static, such as a moving live load, earthquake, or wind.

 

load, factored — load, multiplied by appropriate load factors, used to proportion members by the strength-design method. History

 

load, live —

 

(1) load that is not permanently applied to a structure but is likely to occur during the service life of the structure (excluding environmental loads); or

 

(2) loads meeting specific criteria found in the governing building code (without load factors). History

 

load, point — a load whose area of contact with the resisting body is negligible in comparison with the area of the resting body.

 

load, safe leg — the load that can safely be directly imposed on the frame leg of a scaffold.  (See also load, service.)

 

load, service — unfactored loads, permanent or transient, imposed on a structure during operation. History

 

load, service dead — the dead weight supported by a member.

 

load, service live — the live load specified by the general building code or other bridge specification, or the actual nonpermanent load applied in service.

 

load, shock — impact of material, such as aggregate or concrete, as it is released or dumped during placement.

 

load, snow — the force considered in the design of a flat or pitched surface, usually a roof, for the possible amount of snow, ice, or both, lying on it.

 

load, static — the mass of a single stationary body or the combined masses of stationary bodies in a structure (such as the load of a stationary vehicle on a roadway); or, during construction, the combined mass of forms, stringers, joists, reinforcing bars, and the actual concrete to be placed.  (See also load, dead.)

 

load, superimposed — the load, other than its own weight, that is resisted by a structural member or system.

 

load, ultimate — the maximum load that may be placed on a structure or structural element before its failure.

 

load, wheel — the portion of the gross mass of a loaded vehicle transferred to the supporting structure under a given wheel of the vehicle.

 

load, wind — pressure of suction due to wind on part or all of a surface of a structure.

 

load, working — forces normally imposed on a member in service (obsolete term).

 

load balancing — a technique used in the design of prestressed-concrete members in which the amount and path of the prestressing is selected so that the forces imposed upon the member or structure by the prestressing counteract or balance a portion of the dead and live loads for which the member or structure must be designed.

 

load factor — a factor by which a service load is multiplied to determine a factored load used in the strength-design method.

 

load-bearing wall — see wall, load-bearing.

 

load test, structural — procedure consisting of applying loads to verify the strength of a structure or structural member.

 

load-transfer assembly — the unit (basket or plate) designed to support or link dowel bars during concreting operations so as to hold them in place while in the desired alignment.

 

loading —

 

loading, bulk — loading of unbagged cement in containers, specially designed trucks, railroad cars, or ships.

 

loading, dynamic — loading from units (particularly machinery) that, by virtue of their movement or vibration, impose stresses in excess of those imposed by their dead load.

 

loading, ribbon — method of batching concrete in which the solid ingredients, and sometimes also the water, enter the mixer simultaneously.

 

loading hopper — a hopper in which concrete or other free-flowing material is deposited for discharge into buggies or other conveyances used for delivery to the forms or to other place of processing, use, or storage.

 

locking device — a device used to secure a cross brace in scaffolding to the frame or panel.

 

long column — see column, long.

 

longitudinal bar — see reinforcement, longitudinal (preferred term).

 

longitudinal crack — see crack, longitudinal.

 

longitudinal joint — see joint, longitudinal.

 

longitudinal reinforcement — see reinforcement, longitudinal.

 

Los Angeles abrasion test — see test, Los Angeles abrasion.

 

loss —

 

loss, anchorage — see deformation, anchorage  or slip.

 

loss, elastic — in prestressed concrete, the reduction in prestressing load resulting from the elastic shortening of the member.

 

loss, friction — the stress loss in a prestressing tendon resulting from friction between the tendon and duct or other device during stressing.

 

loss, ignition — see loss on ignition (preferred term).

 

loss, plastic — see creep.

 

loss, shrinkage — reduction of stress in prestressing steel resulting from shrinkage of concrete.

 

loss, slump — the amount by which the slump of freshly mixed concrete changes during a period of time after an initial slump test was made on a sample or samples thereof.

 

loss of prestress — the reduction in the prestressing force which results from the combined effects of slip at anchorage, relaxation of steel stress, frictional loss due to curvature in the tendons, and the effects of elastic shortening, creep, and shrinkage of the concrete.

 

loss on ignition — the percentage loss in mass of a sample ignited to constant weight at a specified temperature, usually 1650 to 1830 °F (900 to 1000 °C).

 

low-alkali cement — see cement, low-alkali.

 

low-density concrete — see concrete, low-density and concrete, lightweight.

 

low-heat cement — see cement, low heat.

 

low-lift grouting — see grouting, low-lift.

 

low-pressure steam curing — see curing, atmospheric-pressure steam (preferred term).

 

low-strength materials — see controlled low-strength material (CLSM) (preferred term).

 

L-shore — a shore with an L-head.  (See also L-head.)

 

lubricant, dowel — a material applied to part of the surface of a dowel to reduce bond with the concrete and permit axial movement.