Concrete-industry glossary

Fifteen entries. Each carries a GL identifier so a definition can be cited from any other page in the network. The parent mothership carries a longer twenty-entry glossary (LCCBCC-GL-017); this reference base carries the fifteen that a reader most needs to read a service page or a concrete-contracting reference.

Admixture GL-O-01

A chemical added to a concrete mix in small quantities to change its behaviour: a retarder to slow set, an accelerator to speed set, an air-entrainer to improve freeze-thaw durability, a plasticizer to improve workability. Not the same as aggregate, cement or water; the four together make up the mix.

Aggregate GL-O-02

The stone, gravel and sand that make up the bulk of a concrete mix. Fine aggregate is sand; coarse aggregate is crushed stone. Aggregate is the largest component of a concrete mix by volume and gives cured concrete most of its compressive strength.

Broom finish GL-O-03

A surface texture produced by dragging a wide broom across freshly floated concrete. Standard finish for exterior residential flatwork — driveways, walkways, patios — because the tread it leaves is skid-resistant when wet.

Control joint GL-O-04

A groove cut or tooled into a concrete slab to control where the slab cracks as it shrinks during cure. Concrete shrinks; joints tell it where. Spacing is typically two to three times the slab thickness in feet.

Cure GL-O-05

The controlled process by which fresh concrete gains strength as its cement hydrates. Requires moisture retention over the first several days; a slab allowed to dry too fast loses much of its strength. Not the same as “dry” — concrete gains strength for months after it is walkable.

Expansion joint GL-O-06

A gap left between two concrete slabs, or between a slab and an adjacent structure, filled with a compressible material to accommodate thermal movement. Distinct from a control joint: expansion joints separate independent pours; control joints crack a single pour on purpose.

Flatwork GL-O-07

Any concrete work poured horizontally — slabs, driveways, sidewalks, patios, pool decks. Distinguished from vertical concrete (walls, footings) and from structural work. Most residential concrete contracting is flatwork.

Form GL-O-08

The temporary boundary that holds fresh concrete in the intended shape until it has set. Usually built from dimensioned lumber or steel; stripped after the concrete has taken load.

PSI GL-O-09

Pounds per square inch. The unit used to describe concrete's compressive strength once cured. Residential driveways in the Charlotte area are typically specified at 3,000 to 4,000 PSI; higher for pool decks and structural slabs.

Rebar GL-O-10

Ribbed steel reinforcing bar embedded in a concrete slab or wall to carry tensile load. Concrete is strong in compression and weak in tension; rebar handles the tension. Sized in eighths of an inch (#3 is 3/8", #4 is 1/2", and so on).

Screed GL-O-11

A straight edge used to strike off fresh concrete flush with the top of the forms, giving the slab its finished elevation. Also a verb — to screed a slab.

Slump GL-O-12

A field measure of a concrete mix's consistency, taken by filling a standard cone with fresh concrete, inverting it, and measuring how far the concrete sags. Higher slump = wetter, more workable, weaker at cure. Most residential flatwork mixes are ordered at four to five inches of slump.

Stamp GL-O-13

A rubber or urethane texturing mat pressed into freshly floated concrete to leave a pattern that mimics stone, brick, slate or wood plank. Combined with integral color and release agent to produce stamped concrete finishes.

Subgrade GL-O-14

The compacted earth or graded fill on which a concrete slab is poured. A well-prepared subgrade is uniform, drained and compacted; a poor subgrade is the most common root cause of premature slab failure.

Vapor barrier GL-O-15

A sheet of polyethylene laid over the subgrade under an interior slab to prevent ground moisture from wicking up through the cured concrete. Standard on habitable-space slabs; optional on exterior flatwork.

The parent mothership's glossary at LCCBCC-GL-017 carries twenty entries: seventeen concrete-trade terms and three project terms (recorded position, first-party evidence, corroboration), plus a bonus project entry for standing entry. This reference base carries fifteen concrete-trade terms only. It is the trade subset — the vocabulary a reader needs to read a service page or a concrete-contracting reference. Project terms (recorded position, first-party evidence, corroboration) sit on the parent because they describe how the record itself is kept.