Complete Construction & Concrete Dictionary
Essential Industry Terminology for UK Construction
Welcome to the comprehensive UK Concrete Terms Glossary - your complete reference for concrete and construction terminology used throughout the British construction industry. This glossary covers essential terms from BS EN 206, BS 8500, and industry best practices updated for 2026.
Whether you're a construction professional, architect, engineer, or DIY enthusiast, this glossary provides clear definitions of concrete-related terms, from basic materials and mixing processes to advanced structural concepts and British Standards terminology.
✅ How to Use This Glossary:
A chemical admixture added to concrete to speed up the setting and hardening process. Calcium chloride is the most common accelerator, particularly useful in cold weather concreting. Modern accelerators are often chloride-free to prevent corrosion of steel reinforcement. Accelerators reduce setting time by 25-75% depending on dosage and conditions.
A material other than cement, aggregate, or water that is added to concrete to modify its properties. Common types include plasticizers, superplasticizers, retarders, accelerators, air-entraining agents, and waterproofing compounds. Admixtures are typically added in small quantities (0.1-5% by weight of cement) and must comply with BS EN 934-2 standards.
Granular material such as sand, gravel, crushed stone, or recycled concrete used as a major component in concrete. Aggregates make up 60-80% of concrete volume and are classified as fine aggregate (sand, 0-4mm) or coarse aggregate (gravel/stone, 4-20mm or larger). Must meet BS EN 12620 standards for grading, strength, and durability.
The deliberate introduction of microscopic air bubbles (typically 0.05-1.2mm diameter) into concrete using air-entraining admixtures. These bubbles improve freeze-thaw resistance by providing expansion space for freezing water. Air-entrained concrete typically contains 4-7% air by volume and is essential for exposed concrete in cold climates per BS 8500 requirements.
The sharp edge formed at the junction of two concrete surfaces, such as where a wall meets a corner. Arrises are often chamfered (beveled) or rounded during formwork installation to prevent chipping and spalling of the vulnerable edge. Common UK practice is to provide 10-20mm chamfers on external corners.
The process of measuring and proportioning concrete ingredients (cement, aggregates, water, admixtures) before mixing. Can be done by weight (preferred for accuracy) or volume. Modern batching plants use computerized systems ensuring accuracy within ±2% for aggregates and ±1% for cement and water, meeting BS EN 206 production control requirements.
The appearance of water on the surface of freshly placed concrete, caused by settlement of solid particles and upward migration of mixing water. Some bleeding is normal, but excessive bleeding (>0.5 liters/m²/hr) can cause weak surface layers, reduced durability, and poor finish quality. Controlled by proper mix design and water-cement ratio.
A thin layer (typically 50-75mm) of weak concrete (C8/10 or C10/12) laid on prepared ground before constructing foundations or floor slabs. Provides a clean, level working surface for fixing reinforcement and installing damp-proof membranes. Also prevents ground water from diluting fresh concrete and protects the subgrade.
The adhesion between concrete and reinforcing steel, or between concrete and formwork, or between old and new concrete. Good bond is essential for composite action in reinforced concrete. Factors affecting bond include surface cleanliness, roughness, reinforcement bar profile (ribbed bars provide better bond than smooth), and concrete cover depth.
The complementary British Standard to BS EN 206, specifying concrete requirements for UK construction. Provides guidance on designated mixes (GEN, RC, PAV, FND), exposure classes, durability requirements, and concrete specification. Essential reference for all concrete work in the UK, updated regularly to reflect current best practice and building regulations.
Concrete that is mixed and poured directly into its final position on site, as opposed to precast concrete. Also called site-cast or in-situ concrete. Allows for custom shapes and sizes but requires formwork, longer construction time, and weather-dependent curing. Most residential foundations, slabs, and structural frames use cast in-situ methods.
A fine powder that acts as the binding agent in concrete when mixed with water. Portland cement (CEM I) is most common in UK, but blended cements (CEM II, CEM III) containing ground granulated blast furnace slag (GGBS) or pulverized fuel ash (PFA) are increasingly used for improved sustainability and durability. Must comply with BS EN 197-1 standards.
The process of removing air voids from freshly placed concrete to increase density, strength, and durability. Achieved through poker vibrators (internal vibration), vibrating screeds, or external formwork vibration. Proper compaction is critical - under-compaction reduces strength by up to 30%, while over-vibration can cause segregation and bleeding.
The ability of concrete to resist crushing loads, measured in N/mm² or MPa. The fundamental property defining concrete strength classes (C20/25, C30/37, etc.). Tested on 150mm cubes or 150mm × 300mm cylinders after 28 days standard curing. Typical structural concrete ranges from 20-50 MPa, with specialist applications exceeding 100 MPa.
The thickness of concrete between the outer surface and the nearest reinforcing steel. Critical for protecting steel from corrosion and fire. Minimum cover depends on exposure class, strength class, and fire resistance requirements - typically 25-50mm for most UK applications. Must be specified on structural drawings and verified during construction per BS EN 1992.
The process of maintaining adequate moisture, temperature, and time conditions for concrete after placement to allow proper cement hydration and strength development. Minimum 7 days curing recommended, ideally 28 days. Methods include wet hessian, curing membranes, polythene sheeting, or ponding. Poor curing can reduce final strength by 30-50% and cause surface cracking.
A waterproof barrier (typically polyethylene sheet, minimum 300 microns thick) placed under or within concrete floor slabs to prevent moisture rising from the ground. Essential in UK construction for meeting Building Regulations Part C (Site preparation and resistance to contaminants and moisture). Usually sandwiched between blinding layer and structural slab.
A concrete specification using a simple designation code (e.g., GEN1, RC30, PAV1) defined in BS 8500, rather than prescribing detailed mix proportions. The producer selects appropriate materials to meet the designated performance requirements. Simplifies specification and transfers responsibility for mix design to the concrete supplier. Most common system for UK residential work.
The ability of concrete to resist weathering, chemical attack, abrasion, and other degradation processes while maintaining desired engineering properties. Durability depends on strength class, cement type, water-cement ratio, cover depth, and curing quality. BS 8500 defines exposure classes (XC, XD, XF, XS, XA) specifying minimum concrete properties for different environmental conditions.
The compressive strength developed by concrete in the first few days after placement, typically measured at 1, 3, or 7 days. Important for construction programming, formwork removal, and post-tensioning timing. Rapid hardening cements or accelerating admixtures can increase early strength. Typical 7-day strength is 65-75% of 28-day characteristic strength.
A classification system in BS EN 206 and BS 8500 defining environmental conditions concrete will experience during its service life. Classes include XC (carbonation), XD (chloride non-seawater), XS (chloride seawater), XF (freeze-thaw), and XA (chemical attack). Each class has specific minimum requirements for strength, cement content, water-cement ratio, and cover depth to ensure adequate durability.
Temporary supporting structure used to hold formwork in position until concrete gains sufficient strength. Includes props, scaffolding, trusses, and bracing. Must be designed by competent persons to support all construction loads safely. Removal sequence and timing critical - premature stripping can cause structural failure. Governed by BS 5975 code of practice.
The final surface treatment applied to concrete after placement and initial levelling. Types include troweled (smooth), floated (textured), brushed, or exposed aggregate finishes. Timing is critical - finishing too early causes bleeding and weakness, too late makes working difficult. Power floating common for industrial floors, manual techniques for smaller domestic work.
The temporary mould or shuttering into which concrete is poured and held until it sets and gains sufficient strength. Can be timber, steel, aluminum, or plastic. Must be strong, rigid, watertight, and easily removable. Design must consider concrete pressure, construction loads, and safety. Face finish quality depends on formwork material and workmanship.
The ability of concrete to withstand repeated cycles of freezing and thawing without significant deterioration. Water in concrete pores expands approximately 9% when frozen, causing internal stresses. Air-entrainment provides expansion space, dramatically improving resistance. Essential for external UK concrete exposed to winter conditions. Specified through XF exposure classes in BS 8500.
A by-product from steel manufacturing used as a partial cement replacement (typically 30-70%) in concrete. Improves long-term strength, reduces permeability, enhances chemical resistance, and lowers carbon footprint. Slower strength gain than Portland cement requires extended curing. Common in UK for durable structures, foundations, and marine environments. Designated as CEM III in BS EN 197-1.
General purpose designated concrete mixes in BS 8500 for non-structural applications. GEN0 (C8/10) for blinding, GEN1 (C10/12) for mass fill, GEN2 (C16/20) for oversite, GEN3 (C20/25) for unreinforced foundations and domestic floors. Simple specification system avoiding detailed mix design requirements. Most economical option where structural performance not critical.
A fluid mixture of cement, sand, and water (sometimes with admixtures) used to fill voids, anchor bolts, or fill reinforcement ducts in post-tensioned concrete. More fluid than mortar with finer particles. Must be sufficiently flowable to penetrate restricted spaces but not segregate. Used for grouting reinforcement cages, filling gaps, and bedding structural components.
The process by which concrete gains strength after initial setting, caused by continuing cement hydration. Hardening continues for months or years, though design strength is based on 28-day values. Rate depends on temperature, moisture, cement type, and mix proportions. Long-term strength typically 110-125% of 28-day strength under good curing conditions.
The chemical reaction between cement and water that causes concrete to set and harden. An exothermic process releasing heat (heat of hydration) that can exceed 70°C in massive pours. Requires adequate water and favorable temperature (5-35°C optimal). Incomplete hydration reduces strength - proper curing essential to maintain moisture for continued reaction. Approximately 50% complete at 28 days.
Concrete cast in its permanent position on the construction site, as distinct from precast elements manufactured elsewhere. Requires formwork, temporary support, and weather protection. Advantages include design flexibility, monolithic construction, and elimination of joints. Disadvantages include longer construction time, weather dependency, and quality variability. Most UK residential construction uses in-situ methods.
A deliberate discontinuity in concrete to control cracking, accommodate movement, or divide work into manageable pours. Types include construction joints (between successive pours), expansion joints (allow thermal movement), contraction joints (control shrinkage cracking), and isolation joints (separate concrete from other structures). Proper joint design and installation crucial for durability and appearance.
A small upstand of concrete (typically 75-150mm high) cast at the base of walls or columns to provide accurate positioning for subsequent concrete pours. Acts as a stop-end for formwork and helps prevent grout loss. Surfaces must be clean and roughened before placing main concrete to ensure good bond. Common in UK reinforced concrete construction.
Concrete with relatively low cement content and high water-cement ratio, producing lower strength (typically C8/10 or C10/12). Economical for non-structural uses like mass fill, trench fill foundations, and sub-bases. Less durable than richer mixes but adequate where loads are light and exposure mild. Term increasingly replaced by GEN0 or GEN1 designated mixes in BS 8500.
The process of selecting and proportioning concrete ingredients to achieve specified properties (strength, workability, durability) at minimum cost. Considers aggregate grading, water-cement ratio, cement type and content, admixtures, and exposure conditions. Can be prescribed (exact proportions specified) or designed (performance specified, producer designs mix). BS EN 206 and BS 8500 provide design guidance.
The metric unit of pressure or stress equal to 1 Newton per square millimetre (N/mm²), used to measure concrete compressive strength. Replaced imperial units (psi) in UK construction. Typical UK structural concrete ranges from 20-50 MPa. C25/30 concrete has 25 MPa cylinder strength and 30 MPa cube strength. Higher numbers indicate stronger concrete.
A simple concrete specification using volumetric ratios (e.g., 1:2:4 means 1 part cement, 2 parts sand, 4 parts coarse aggregate). Historically common but now largely superseded by designated or designed mixes per BS 8500. Offers less control over strength and consistency than modern methods. Still occasionally used for minor non-critical works where precise strength unnecessary.
A concrete slab laid over prepared ground beneath ground floor constructions, typically 100-150mm thick. In suspended floor construction, provides working surface and ground sealing. May be structural (supporting loads) or non-structural (ground cover only). Usually specified as GEN2 (C16/20) or GEN3 (C20/25) depending on application and building control requirements.
Designated concrete mixes in BS 8500 specifically for heavy-duty external paving and roads. PAV1 (C32/40) for commercial/industrial paving with surface water drainage, PAV2 (C40/50) for very heavy-duty applications. Higher strength and durability than general purpose mixes. Must include air-entrainment for freeze-thaw resistance in UK climate.
Fine ash particles from coal-fired power stations used as partial cement replacement (typically 15-35%) in concrete. Also called fly ash. Improves workability, reduces permeability, enhances long-term strength, and lowers carbon footprint. Slower early strength gain than Portland cement. Increasingly scarce in UK due to coal power phase-out. Similar benefits now achieved with GGBS or manufactured alternatives.
An admixture that improves concrete workability without adding extra water, or allows water reduction while maintaining workability. Reduces water-cement ratio, increasing strength and durability. Standard plasticizers reduce water by 5-10%, superplasticizers by 15-30%. Essential for achieving high-strength, low-permeability concrete. Must comply with BS EN 934-2.
The most common type of cement, invented in the UK and named after Portland stone. Made by heating limestone and clay to form clinker, then grinding with gypsum. Designated CEM I in BS EN 197-1. Provides reliable strength development and widely available. Now often partially replaced with GGBS or PFA for improved sustainability and performance in UK construction.
Concrete elements (beams, columns, slabs, panels, stairs) manufactured in a factory or casting yard under controlled conditions, then transported and erected on site. Advantages include better quality control, weather independence, faster construction, and reduced site labor. Disadvantages include transportation costs, lifting equipment needs, and less design flexibility. Common for UK commercial and infrastructure projects.
Designated concrete mixes in BS 8500 for reinforced concrete work. RC25 (C25/30) for low/moderate exposure, RC30 (C28/35) for moderate exposure, RC32 (C32/40) for aggressive exposure, RC40 (C35/45) for very aggressive exposure. Specify based on exposure class and required durability. Most common structural specification in UK residential and commercial construction.
Concrete manufactured in a batching plant and delivered to site in rotating drum trucks (mixers). Also called RMC or ready-mixed concrete. Offers consistent quality, eliminates on-site batching, reduces site space requirements, and provides technical support. Standard UK delivery in 6-8m³ trucks. Must be placed within 2 hours of mixing (or longer with retarders). Accounts for >90% of UK concrete use.
Steel reinforcing bars embedded in concrete to resist tensile stresses. Available in various diameters (8-40mm typical) and grades (500 MPa characteristic yield strength most common in UK). Surface ribs provide mechanical bond with concrete. Requires minimum cover for corrosion protection. Essential component of reinforced concrete structures. Must comply with BS 4449 standards.
Composite structural material combining concrete (strong in compression) with steel reinforcement (strong in tension) to resist all types of loads. Steel bars, mesh, or fibers provide tensile capacity concrete lacks. Requires adequate cover for corrosion protection and fire resistance. Most versatile structural material, used for foundations, frames, slabs, walls, bridges. Design governed by Eurocode 2 (BS EN 1992).
A chemical admixture that delays concrete setting time, useful in hot weather, long hauls, or complex pours requiring extended workability. Typical delay 2-4 hours depending on dosage. Does not affect final strength. Allows better finishing and reduces cold joints in large pours. Must comply with BS EN 934-2. Common in UK summer concreting and major infrastructure projects.
A thin layer of sand-cement mortar (typically 25-75mm) applied over concrete slabs to provide a smooth, level surface for floor finishes. Can be bonded (to structural slab), unbonded (on membrane), or floating (on insulation). Mixed approximately 1:3-4 cement:sharp sand. Takes 1 day per mm to dry (50mm screed = 50 days). Critical for achieving level floors in UK construction.
Undesirable separation of concrete constituents, with coarse aggregate settling and cement paste/water rising. Causes weak, porous, non-uniform concrete. Caused by over-vibration, excessive handling, high slump, or poor mix design. Prevented by proper mix proportioning, careful placement, appropriate workability, and controlled compaction. Significantly reduces strength and durability.
The stiffening of concrete from a fluid to a rigid state, caused by early cement hydration. Initial set occurs when concrete can no longer be remoulded (typically 2-4 hours); final set when it has hardened significantly (typically 4-8 hours). Setting time distinct from hardening (strength gain). Varies with temperature, cement type, admixtures, and water content.
Volume reduction in concrete as it dries and ages. Plastic shrinkage occurs before setting due to surface water evaporation, causing surface cracking. Drying shrinkage occurs over months/years as internal moisture equilibrates with environment (typically 0.03-0.06% strain). Controlled by low water-cement ratio, proper curing, adequate reinforcement, and movement joints. Main cause of cracking in UK construction.
A measure of concrete workability and consistency, tested using a slump cone per BS EN 12350-2. Fresh concrete placed in 300mm high cone, compacted, cone lifted, and vertical settlement measured. Results classified: S1 (10-40mm), S2 (50-90mm), S3 (100-150mm), S4 (160-210mm), S5 (≥220mm). Higher slump = more fluid. Typical UK: S2-S3 for normal work, S4-S5 for congested reinforcement.
Breaking away or flaking of concrete surface, exposing aggregate beneath. Causes include freeze-thaw damage, corrosion of reinforcement (rust expansion), fire damage, impact, or inadequate cover. Prevention requires proper concrete specification, adequate cover, air-entrainment for freeze-thaw resistance, and quality construction. Common UK problem on exposed concrete with insufficient durability specification.
The designation of concrete based on characteristic compressive strength, using format C[cylinder]/[cube]. For example, C25/30 means 25 MPa cylinder strength and 30 MPa cube strength. Defined in BS EN 206. Standard UK classes range C8/10 to C50/60 for normal construction, with higher classes for specialist applications. Fundamental specification parameter for structural design.
High-range water-reducing admixture that dramatically improves concrete workability or allows major water reduction (15-30%) without reducing workability. Enables production of high-strength, self-compacting, or flowing concrete. Effects temporary (30-60 minutes typically). Essential for modern high-performance concrete. More effective than standard plasticizers. Must comply with BS EN 934-2.
The ability of concrete to resist pulling or stretching forces. Typically only 8-15% of compressive strength - concrete's primary weakness. Reinforcement (steel bars/mesh) added to resist tensile stresses. Measured by splitting cylinder test or flexural (bending) test. Important for pavement design, water-retaining structures, and crack control. Not normally specified except for specialist applications.
A flat-bladed hand tool used for spreading, leveling, and finishing concrete surfaces. Steel trowels create smooth, dense finishes suitable for internal floors. Wooden or magnesium floats produce slightly textured surface. Power trowels (helicopters) used for large industrial floors. Timing critical - troweling too early brings water to surface, too late is difficult and ineffective.
The mechanical process of consolidating fresh concrete by removing air voids and ensuring complete filling of formwork. Internal vibration (poker/immersion vibrators) most common, also external (formwork-mounted) or surface (screeds/plates) methods. Frequency typically 10,000-15,000 vibrations per minute. Essential for achieving design strength and durability. Over-vibration causes segregation; under-vibration leaves voids.
The ratio of water mass to cement mass in concrete, typically 0.40-0.65 for structural work. Most critical factor affecting concrete strength and durability. Lower ratios produce stronger, more durable concrete but require plasticizers for workability. BS 8500 specifies maximum ratios for each exposure class. Rule: each 0.05 increase in w/c ratio reduces strength by approximately 5-10%.
Methods and materials used to make concrete impermeable to water penetration. Includes integral waterproofing admixtures, surface coatings, membranes, or crystalline systems. Critical for basements, water tanks, tunnels, and retaining walls. BS 8102 provides guidance for below-ground waterproofing. Common UK requirement for habitable basements and water-retaining structures.
The ease with which concrete can be mixed, placed, compacted, and finished without segregation. Measured by slump test (most common), flow table, or Vebe test. Depends on water content, aggregate characteristics, cement type, and admixtures. Adequate workability essential for proper placement and compaction. Too low = incomplete compaction, too high = segregation and bleeding.
Exposure class system in BS EN 206 defining environmental aggressiveness: XC (carbonation-induced corrosion), XD (chloride-induced corrosion from non-seawater), XF (freeze-thaw with/without de-icing salts), XS (chloride from seawater), XA (chemical attack). Each has sub-classes (e.g., XC1-4) with specific minimum concrete requirements. Foundation of durability specification in UK construction.
The stress at which steel reinforcement begins to deform permanently without increase in load. Characteristic yield strength (fyk) for UK reinforcement typically 500 N/mm² per BS 4449. Used in structural design calculations per Eurocode 2. Higher than concrete compressive strength (20-50 MPa), enabling reinforcement to carry tensile forces concrete cannot resist.
📚 Related British Standards for Concrete: