Concrete Terminology » L
lacing—horizontal bracing between shoring members.
lagging—heavy sheathing used as in underground work to withstand earth pressure. (See also sheathing.)
laitance—a weak layer of cement and aggregate fines either: (1) carried by bleeding to the surface or to internal cavities of freshly placed concrete; or (2) separated from the concrete and deposited on the concrete surface or internal cavities during placement of concrete underwater.
laminate—to bond layers of a material.
lance—equipment for shooting refractory shotcrete material into areas that have a high temperature; typically, a length of metal pipe with an extended nozzle with various configurations.
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 water emulsion of a high molecular-weight polymer, used especially in coatings, adhesives, leveling compounds, and patching compounds.
latex-modified concrete—see concrete, polymer-modified.
lath, expanded-metal—a metal network, often used as reinforcement in concrete or mortar construction, formed by suitably stamping or cutting sheet metal and stretching in to form open meshes, usually of diamond shape. (See also mesh, diamond.)
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).
leakage—the quantity of material that accidentally enters or escapes through an opening such as a hole or crack.
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, development—the embedment length required to develop the design strength of a reinforcement at a critical section; formerly called bond length.
length, embedment—the length of embedded reinforcement provided beyond a critical section.
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—in cement testing, an increase or decrease in linear dimension due to causes other than applied load, usually measured along the longitudinal axis of a test specimen and expressed as a percentage of a gage 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 professional engineer (“Engineer”)––person that is registered in the jurisdiction where the project is located and based upon licensure, professional experience, and academic education or training can apply scientific and mathematical principles toward the structure assessment and design of existing structures.
lift—individual layer of repair material where several layers or courses are required to achieve the total depth of a repair.
lift-off test—a procedure that uses a calibrated hydraulic ram system to assess the effective force in an unbonded post-tensioned tendon or to detension existing tendons.
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.
lifting—softening and raising or wrinkling of a pervious coat by the application of an additional coat; often caused by coatings containing strong solvents.
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-saturated water—for curing test specimens, water containing calcium hydroxide at saturation and in contact with solid calcium hydroxide so that saturation is maintained.
limestone—a sedimentary rock consisting primarily of calcium carbonate.
limit, elastic—the limit of stress beyond which the strain is not wholly recoverable.
limit, liquid—water content, expressed as a percentage of the dry weight of the soil at which the soil passes from the plastic to the liquid state under standard test conditions. (See also limits, Atterberg.)
limit, plastic—the water content at which a soil will just begin to crumble when rolled into a thread approximately 1/8 in. (3 mm) in diameter. (See also limits, Atterberg.)
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, shrinkage—the maximum water content at which a reduction in water content will not cause a decrease in volume of the soil mass. (See also limits, Atterberg.)
limit, vibration—the age at which fresh concrete has hardened sufficiently to prevent its becoming mobile when subjected to vibration.
limits, Atterberg—arbitrary water contents (shrinkage limit, plastic limit, liquid limit) determined by standard tests that define the boundaries between the different states of consistency of plastic soils.
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 polarization—a nondestructive testing method to estimate the instantaneous corrosion rate of the concrete reinforcement located below the test point by measuring the current required to change by a fixed amount the potential difference between the reinforcement and a standard reference electrode.
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 protective material applied to the interior surface of a conduit, pipe, or tunnel to provide watertightness, erosion resistance, chemical resistance, or reduced friction.
lintel—a horizontal supporting member above an opening, such as a window or a door.
liquid limit—see limit, liquid.
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, 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—a constant load that in structures is due to the mass of the members, the supported structure, and permanent attachments or accessories.
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.
load, live—any load that is not permanently applied to a structure; transitory load.
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—all loads, static or transitory, imposed on a structure, or element thereof, during operation of a facility.
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, 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, 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 binder—a device used to tighten chains holding loads in place on a truck bed.
load cell—device for measuring the magnitude of an applied load.
load factor—a factor by which a service load is multiplied to determine a factored load used in the strength-design method.
load test—procedure consisting of applying loads to verify the strength and behavior of a structure or structural member.
load-bearing wall—see wall, load-bearing.
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, 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.
lock-off—device that maintains tension on a monostrand tendon while the end anchorage is replaced.
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, 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).
lot—a definite quantity of a product or material accumulated under conditions that are considered
uniform for sampling purposes.
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 spray-applied mortar—the placement of a repair material by spraying using a low-velocity pump with air added at the nozzle.
low-pressure steam curing—see curing, atmospheric-pressure steam (preferred term).
low-strength materials—see controlled low-strength cementitious material (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.
lubricity—in grouting, the physico-chemical characteristic of a grout material flow through a soil or rock that is the inverse of the inherent friction of that material to the soil or rock; comparable to “wetness.”