- Slump
- A measure of how stiff or fluid fresh concrete is, taken by filling a cone, lifting it away and measuring how far the pile sags. Adding water raises slump but lowers strength, so reading slump results correctly matters for placement and acceptance decisions.
- Air entrainment
- Microscopic bubbles deliberately created in the paste by an admixture so the concrete can absorb freezing and thawing and deicing stress without scaling. Exposure conditions determine whether it is required, and too much air costs strength, so it is checked at delivery.
- Water-cementitious materials ratio
- The weight of mix water divided by the weight of cement plus any fly ash or slag. A lower ratio gives denser, stronger, more durable concrete, which is why extra water at the truck is a mistake even when it makes the pour easier.
- Specified compressive strength
- The minimum strength, in pounds per square inch at a stated age, that the plans demand for a concrete element. The mix is designed above it, the cylinders are tested against it, and the code sets floors that vary with exposure and structural use.
- Test cylinders
- Samples of fresh concrete cast into molds, cured under controlled conditions and later crushed in a testing machine to confirm strength. How they are filled, rodded, protected and transported affects the result, so careless handling can make good concrete appear weak.
- Vapor retarder
- A sheet of polyethylene laid under an interior slab to slow ground moisture from rising into floor finishes and the room. Lap the seams, patch punctures and keep it intact through steel placement; its location relative to the base course is a frequent exam point.
- Capillary break
- A layer of clean, coarse, free-draining stone beneath a slab that stops water from wicking upward through fine soil. When a vapor retarder is used, this layer works beside it, and the two together keep moisture away from the concrete and flooring.
- Curing compound
- A liquid membrane sprayed over finished concrete to hold in mixing water so cement keeps hydrating. It must go on evenly at the right moment and rate, and some types interfere with later coatings, so the compound must suit the finish planned for the slab.
- Plastic shrinkage cracking
- Short, random surface cracks that appear within hours when evaporation outruns bleed water, typical on hot, windy or dry days. Fog misting, windbreaks, evaporation retardants and polypropylene fibers reduce them, and recognizing the cause separates them from later structural cracks.
- Control joint
- A groove cut or tooled into a slab to create a weakened line where shrinkage cracking is meant to happen, hidden in the pattern instead of wandering across the surface. Spacing depends on thickness, and cutting too late lets random cracks form first.
- Bleed water
- The thin film of water that rises to a slab's surface after consolidation as heavier solids settle. Finishing while it is still present traps water and weakens the top, so troweling waits until the sheen disappears, a timing judgment that appears in finishing questions.
- Cold joint
- A plane of weakness left where fresh concrete is placed against concrete that has already begun to set, so the two layers do not blend. Planning delivery intervals, using retarders and vibrating into the previous lift help prevent it in walls and deep placements.
- Bar chairs
- Small plastic or wire supports that hold reinforcing bars at the right height within a slab so they end up inside the concrete, not lying on the base. Spacing, stability under foot traffic and moisture-barrier protection all matter for their use.
- Drum revolution limit
- A cap on how many turns a truck mixer drum may make, along with a time limit, between batching and discharge. Concrete that is mixed too long or sits too long stiffens and loses quality, so late loads can be rejected.
- Special inspection
- Independent verification by a qualified inspector, required by the building code for certain structural concrete work such as strength sampling, reinforcement placement and tendon stressing. Knowing which operations need someone watching continuously versus periodically avoids stalled pours.
- Honeycombing
- Voids and exposed stone left in a wall or column where mortar failed to fill the spaces between coarse aggregate, usually from poor consolidation, congested steel or leaking forms. It exposes reinforcement and demands evaluation and repair.
- Respirable crystalline silica
- Extremely fine dust released when concrete is cut, ground, drilled or chipped, which can lodge deep in the lungs. Wet methods, dust collection and respiratory protection are the controls; the hazard is a recurring topic for saw, grinder and demolition tasks.
- Form stripping
- Removing the molds from hardened concrete once it has gained enough strength to carry its own weight and construction loads. Stripping early risks sagging and damaged edges, so strength evidence, element type and any required reshoring decide the timing.
- Presumptive bearing value
- A conservative soil pressure, in pounds per square foot, that the residential code assigns by soil type when no engineering soil report exists. It sets how wide a footing must be so the load spreads out enough for the ground to carry it.
- Polypropylene fiber
- Short synthetic strands blended into the mix to hold fresh concrete together while it is most vulnerable. Their main role is limiting early shrinkage cracks; they do not replace structural reinforcement or the need for joints and proper curing.
