General Concrete Questions 2026

Cement is a powder ingredient (typically Portland cement) that acts as the binding agent in concrete. Concrete is the finished product—a composite material made by mixing cement, water, sand, and aggregate (gravel or crushed stone).

Think of cement as flour in a cake recipe—it's one crucial ingredient, but not the final product. When cement reacts with water through a chemical process called hydration, it binds the aggregates together to form the solid, rock-like material we call concrete. Cement typically comprises only 10-15% of the concrete mixture by volume.

Concrete consists of four basic components in these approximate proportions:

• Cement (10-15%): Portland cement powder that binds everything together
• Water (15-20%): Clean water that activates cement hydration
• Fine aggregate (25-30%): Sand particles passing through 4.75mm sieve
• Coarse aggregate (40-50%): Gravel or crushed stone ranging from 4.75mm to 40mm

Modern concrete often includes admixtures (chemical additives) to modify properties like workability, setting time, strength development, or freeze-thaw resistance. Common admixtures include water reducers, air-entraining agents, accelerators, and retarders.

Portland cement is the most common type of cement used in concrete worldwide. It was named in 1824 by English inventor Joseph Aspdin because the hardened concrete resembled Portland stone, a type of limestone quarried on the Isle of Portland in Dorset, England.

The name has nothing to do with the city of Portland, Oregon or any other Portland location. Modern Portland cement is produced by heating limestone and clay to about 1450°C (2640°F) in a kiln, then grinding the resulting clinker into a fine powder. It's manufactured to strict standards defined in BS EN 197-1 (Europe/UK) or ASTM C150 (USA).

Concrete hardens through a chemical reaction called hydration, not by "drying out." When water is mixed with cement, chemical compounds in the cement react with water molecules to form calcium silicate hydrate (C-S-H) gel and calcium hydroxide crystals. These products bind aggregate particles together and fill the spaces between them.

Hydration generates heat and continues for months or even years, though most strength gain occurs in the first 28 days. This is why keeping concrete moist during curing is crucial—the hydration reaction requires water. If concrete dries out too quickly, hydration stops prematurely and the concrete never reaches its design strength.

All three are cement-based materials but designed for different applications:

• Concrete: Contains cement, water, sand, and coarse aggregate (gravel/crushed stone). Used for structural elements like foundations, slabs, beams, and columns. Typical compressive strength: 20-50 MPa.
• Mortar: Contains cement, water, and sand only (no coarse aggregate). Used as a binding agent between bricks, blocks, or stones in masonry construction. More workable but weaker than concrete. Typical strength: 5-20 MPa.
• Grout: Similar to mortar but with a more fluid consistency. Used to fill voids, seal joints, or fill hollow masonry units. May contain fine aggregates or be pure cement paste depending on application.

No, they are not the same, though the terms are often confused. Cement is a fine powder ingredient—the active binding agent. Concrete is the composite material made by combining cement with water, sand, and gravel.

Using the terms interchangeably is like saying "flour" and "bread" are the same thing. You can have cement without concrete (bags of cement powder), but you cannot have concrete without cement. When someone says "cement mixer" or "cement truck," they technically mean a "concrete mixer" or "concrete truck" because these vehicles mix and deliver the finished concrete product, not just cement powder.

Reinforced concrete (RC) is concrete that contains steel reinforcement bars (rebar), mesh, or fibers to improve its tensile strength. Plain concrete is strong in compression but weak in tension. Steel reinforcement provides the tensile strength that concrete lacks, creating a composite material that resists both compression and tension.

The most common form uses deformed steel bars (rebar) placed in areas where tensile stresses occur—typically the bottom of beams and slabs. The concrete and steel work together because they have similar thermal expansion coefficients and the concrete protects the steel from corrosion. Almost all structural concrete in buildings, bridges, and infrastructure is reinforced concrete.

Ancient forms of concrete date back over 8,000 years. The earliest known use was around 6500 BCE in the Middle East, where builders used lime and clay-based mortars. The Romans perfected concrete technology around 300 BCE, creating a material called opus caementicium using volcanic ash, lime, and aggregate. Roman concrete structures like the Pantheon (built 126 CE) still stand today, demonstrating remarkable durability.

Modern Portland cement was invented in 1824 by Joseph Aspdin in England, revolutionizing construction. The first reinforced concrete structure was built in 1849 by Joseph-Louis Lambot in France. Today's concrete technology continues to advance with self-healing concrete, ultra-high-performance concrete (UHPC), and carbon-neutral formulations being developed in 2026.

The water-to-cement (w/c) ratio is the mass of water divided by the mass of cement in a concrete mix. This ratio fundamentally controls concrete strength, durability, and permeability. Lower w/c ratios produce stronger, more durable concrete.

• High strength (0.35-0.40): For structural applications requiring 40+ MPa strength
• Standard strength (0.45-0.55): For typical residential and commercial construction (25-35 MPa)
• Moderate strength (0.55-0.65): For non-structural applications like blinding or fills (15-25 MPa)

The theoretical minimum w/c ratio for complete cement hydration is 0.23, but this produces unworkable concrete. Practical mixes require w/c ratios of 0.35-0.65 depending on desired strength, workability requirements, and admixture use. Never exceed 0.65 for durable concrete exposed to weather or aggressive conditions.

No, never add extra water to concrete. This is one of the most damaging mistakes in concrete placement. Adding water beyond the designed mix reduces concrete strength, increases permeability, promotes cracking, and compromises long-term durability.

Every 5% increase in water content (beyond design) can reduce compressive strength by 20-30% and significantly increase drying shrinkage. If concrete is too stiff to place, use proper consolidation techniques (vibration), or specify water-reducing admixtures (plasticizers) in the mix design. Ready-mix drivers should never add water on-site without approval from the engineer or structural designer, as this violates design specifications and may void warranties.

Admixtures are chemicals added to concrete in small quantities (typically less than 5% by cement weight) to modify specific properties. Common types include:

• Water reducers/Plasticizers: Improve workability without adding water, or allow lower w/c ratios for higher strength
• Air-entraining agents: Create microscopic air bubbles for freeze-thaw resistance
• Accelerators: Speed up setting and early strength gain (useful in cold weather)
• Retarders: Slow down setting time (useful in hot weather or long transport distances)
• Superplasticizers: Dramatically increase workability for self-compacting concrete or very low w/c ratios
• Corrosion inhibitors: Protect reinforcement in chloride environments

Modern concrete rarely uses no admixtures. Water reducers are standard in most ready-mix concrete in 2026, allowing better workability at lower water contents for improved strength and durability.

The slump test (ASTM C143 / BS EN 12350-2) measures concrete workability—how easily concrete flows and consolidates. It's performed by filling a cone-shaped mold with concrete, removing the mold, and measuring how much the concrete slumps (settles) under its own weight.

• 0-25mm (very low slump): Very stiff concrete for immediate unmolding (precast, paving)
• 50-75mm (low slump): Stiff but workable for slabs and foundations
• 75-100mm (medium slump): Standard for most construction applications
• 100-150mm (high slump): Flowing concrete for complex forms or heavy reinforcement
• 150mm+ (very high slump): Self-compacting concrete (SCC) or pumped concrete

Slump should match project specifications. Higher slump doesn't mean better concrete—it often indicates excess water that will reduce strength. Use plasticizers to achieve required slump without increasing water content.

Maximum aggregate size affects concrete strength, workability, and economy. The general rule is to use the largest aggregate size practical for the application, as larger aggregates reduce cement requirements and shrinkage. However, maximum size is limited by:

• Spacing of reinforcement: Maximum size should not exceed 3/4 of the clear spacing between bars
• Section thickness: Maximum size should not exceed 1/3 to 1/5 of the thinnest section dimension
• Concrete cover: Maximum size should not exceed the concrete cover over reinforcement

Common maximum aggregate sizes: 10mm for thin sections or dense reinforcement, 20mm for standard structural concrete (most common in UK), 40mm for mass concrete or lightly reinforced sections. For pumped concrete, maximum size is typically limited to 20mm or less.

Calculate concrete volume by multiplying Length × Width × Depth (all in the same units). Always order 5-10% extra to account for spillage, uneven subgrade, and variations in formwork.

Example calculation for a rectangular slab:

• Slab dimensions: 6m long × 4m wide × 0.15m thick
• Volume = 6 × 4 × 0.15 = 3.6 m³
• Add 10% for waste: 3.6 × 1.10 = 3.96 m³
• Order 4.0 m³ of concrete

Use our concrete volume calculator for automatic calculations including cylindrical columns, irregular shapes, and material cost estimates. Ready-mix concrete is sold by the cubic meter (m³) in the UK or cubic yard (yd³) in the USA.

Concrete grades indicate the minimum compressive strength at 28 days. The UK uses designation like C25/30 where C = Concrete, 25 = cylinder strength (N/mm²), and 30 = cube strength (N/mm²). Common grades in 2026:

• C15/20: Blinding concrete, mass fill, non-structural applications
• C20/25: Domestic foundations, internal floor slabs (non-structural)
• C25/30: Residential foundations, light-duty floors, kerbs
• C30/37: General structural use, commercial floors, suspended slabs
• C35/45: Heavy-duty commercial floors, bridge decks, structural beams
• C40/50: High-strength applications, prestressed concrete, marine structures

Always use the concrete grade specified by your structural engineer. Using lower grade concrete to save money compromises structural safety and building regulations compliance.

Concrete reaches different strength milestones at various ages. The standard testing age is 28 days, but hydration continues for months or years:

• 24 hours: Initial set complete, formwork can be carefully removed (for vertical surfaces)
• 7 days: Approximately 70% of 28-day strength achieved
• 28 days: Design strength reached (100% by definition)
• 90 days: 105-110% of 28-day strength (continuing hydration)
• 1 year+: 110-120% of 28-day strength with proper curing

Light foot traffic is typically safe after 24-48 hours, but full loading should wait until design strength is achieved. For driveways, wait at least 7 days before vehicle traffic. The curing period (keeping concrete moist) should be minimum 7 days in normal conditions, or longer in cold weather or for high-performance concrete.

Concrete compressive strength varies widely depending on mix design, ranging from 15 MPa to over 150 MPa for ultra-high-performance concrete (UHPC). Standard structural concrete ranges from 25-50 MPa (approximately 3,600-7,250 psi).

However, concrete is much weaker in tension—typically only 8-12% of its compressive strength. This is why reinforcement (steel rebar) is essential for structural applications. A typical C30/37 concrete has:

• Compressive strength: 30 MPa (cylinder) or 37 MPa (cube)
• Tensile strength: 2-3 MPa (about 8-10% of compressive strength)
• Flexural strength: 3-5 MPa (modulus of rupture)
• Modulus of elasticity: 30-35 GPa

Strength continues to increase with age beyond 28 days, especially with supplementary cementitious materials like fly ash or slag cement.

Concrete cracks are common and occur for several reasons. Understanding the cause helps with prevention:

• Plastic shrinkage cracks: Rapid surface drying before concrete sets (hot weather, wind, low humidity). Prevented by proper curing and wind protection.
• Settlement cracks: Concrete settles around reinforcement or when forms deflect. Prevented by proper vibration and rigid formwork.
• Drying shrinkage cracks: Concrete shrinks as excess water evaporates over months. Controlled by control joints, lower w/c ratio, and proper joint spacing.
• Thermal cracks: Temperature changes cause expansion/contraction. Controlled by expansion joints and avoiding rapid temperature changes.
• Structural cracks: Overloading or inadequate reinforcement. Requires structural assessment and possible repair/strengthening.

Some cracking is normal and acceptable if crack widths remain below 0.3mm for aesthetic concerns or 0.2mm for water-tightness. Control joints should be placed to control where cracks form, with spacing typically 4-6m or 2-3 times the slab thickness in meters.

Yes, using unnecessarily high-strength concrete can be problematic and wasteful. Issues with over-strength concrete include:

• Higher cost: Higher grade concrete costs more due to increased cement content
• Increased brittleness: Very high-strength concrete can be more brittle with less ductility
• Higher shrinkage: More cement means more shrinkage, increasing crack risk
• Greater heat generation: More cement produces more heat during hydration, increasing thermal crack risk in mass concrete
• Unnecessary environmental impact: Cement production is carbon-intensive; using more than needed increases the project's carbon footprint

Always use the concrete grade specified by the structural engineer—no more, no less. If the specification calls for C25/30, using C40/50 doesn't make the structure "better" and may actually cause problems while wasting money and resources.

Concrete strength is influenced by numerous factors during both design and construction:

Mix Design Factors:

• Water-cement ratio (most important—lower is stronger)
• Cement type and content
• Aggregate quality, size, and grading
• Use of supplementary cementitious materials (fly ash, slag, silica fume)
• Admixtures and their dosages

Construction Factors:

• Mixing thoroughness and duration
• Placement techniques and consolidation (vibration)
• Curing conditions (temperature and moisture)
• Age at testing (strength increases with time)
• Ambient temperature during placing and curing

Quality control in both design and construction is essential for achieving specified strengths reliably.

Yes, concrete continues gaining strength for years after placement, provided moisture is available for ongoing hydration. The rate of strength gain depends on cement type and curing conditions:

• Portland cement (CEM I): Rapid early strength gain, reaches 70% by 7 days, 100% by 28 days, 110-115% by 1 year
• Slag cement (CEM III): Slower early strength, 50-60% by 7 days, 100% by 28 days, 120-130% by 1 year
• Fly ash blends (CEM II): Moderate early strength, 60-70% by 7 days, 100% by 28 days, 115-125% by 1 year

Properly cured concrete in structures can reach 120-140% of 28-day strength after several years. Ancient Roman concrete structures have continued gaining strength over 2,000 years due to ongoing pozzolanic reactions. However, this long-term strength gain can't be relied upon for structural design—28-day strength remains the standard design criterion.

Curing is the process of maintaining adequate moisture, temperature, and time to allow concrete to achieve its design properties. Proper curing is critical because cement hydration requires water—if concrete dries out too quickly, hydration stops and strength development ceases permanently.

Curing Methods:

• Water curing: Ponding, spraying, or wet burlap/hessian kept continuously wet (most effective)
• Plastic sheeting: Covering concrete with polyethylene to prevent moisture loss
• Curing compounds: Sprayed liquid membranes that seal the surface (convenient but less effective)
• Wet blankets: Absorbent materials kept moist and covering the concrete surface

Minimum curing duration: 7 days in normal conditions (20°C), 10-14 days in cold weather (<5°C), or 3 days with accelerators in warm conditions. Inadequate curing can reduce final strength by 30-50% and severely compromise durability.

Formwork removal timing (striking time) depends on concrete strength development and the structural element's loading condition. Premature removal risks surface damage, sagging, or collapse:

• Vertical surfaces (walls, columns): 12-24 hours in normal conditions (no loading)
• Slab soffits (props left in place): 3-4 days minimum
• Beam soffits (props left in place): 7 days minimum
• Props under slabs: 7-14 days depending on span and loading
• Props under beams: 14-21 days depending on span and loading

In cold weather (<5°C), double these periods. For early formwork removal, cube tests should confirm adequate strength (typically 5-10 MPa for vertical surfaces, 70% of design strength for soffit removal). Always follow the structural engineer's specifications for formwork striking times on critical structural elements.

Light rain during concrete placement is manageable with precautions, but heavy rain should stop concreting operations. Key considerations:

Light rain (before finishing):

• Continue placement if rain isn't washing surface cement or creating puddles
• Have plastic sheeting ready to cover concrete immediately if rain intensifies
• Account for rainwater when checking slump—don't let excess water collect on surface

Heavy rain (before or during finishing):

• Stop concreting operations—heavy rain will wash cement from the surface, reducing strength and durability
• Cover fresh concrete immediately with plastic sheeting weighted down
• Remove any water pooled on surface before resuming finishing operations

Rain after finishing: Generally not a problem and can actually aid curing. Cover surface with plastic to prevent erosion if concrete hasn't gained sufficient strength. Never let standing water accumulate on fresh concrete surfaces.

Cold weather concreting presents challenges when air temperature falls below 5°C (41°F). Below this threshold, hydration slows significantly and frost damage risk increases. Special precautions required:

Temperature Guidelines:

• Above 5°C: Normal procedures, standard curing
• 0-5°C: Cold weather concrete recommended (accelerators), extended curing, insulated blankets
• Below 0°C: Special measures mandatory—heated enclosures, heating of aggregates/water, rapid hardening cement
• Below -5°C: Generally not recommended without heated enclosures and specialist cold-weather concrete systems

Concrete that freezes before reaching 5 MPa (approximately 2 days) can suffer permanent strength loss of 40-50%. Use heated enclosures, insulating blankets, concrete accelerators, and ensure minimum concrete temperature of 5°C at placement. Extend curing time to 2-3 times normal duration in cold conditions.

Hot weather concreting challenges begin when ambient temperature exceeds 30°C (86°F) or when rapid evaporation occurs. High temperatures accelerate setting, increase water demand, reduce workable time, and increase plastic shrinkage cracking risk:

Hot Weather Precautions:

• Schedule pours early morning or evening to avoid peak temperatures
• Use retarding admixtures to extend workability time
• Use chilled mixing water or ice to reduce concrete temperature
• Shade aggregates and mixing equipment from direct sunlight
• Have extra workers available for rapid placement and finishing
• Use fog spray or evaporation retarders to prevent rapid surface drying
• Begin curing immediately after finishing—within 30 minutes in hot conditions
• Avoid placing concrete when wind speed exceeds 15 mph combined with high temperature

Maximum recommended fresh concrete temperature is 32°C (90°F) at placement. Above 35°C ambient temperature, specialist hot-weather concrete techniques and experienced contractors are essential.

Vibration (consolidation) is essential for properly placed concrete, especially in heavily reinforced sections. Vibration removes entrapped air voids (not desired air-entrained bubbles), ensures concrete flows around reinforcement, and eliminates honeycombing.

When vibration is essential:

• Structural elements with dense reinforcement
• Deep sections (walls, columns, footings)
• Low slump concrete (< 75mm)
• Narrow forms or congested areas

When vibration may not be needed:

• Self-compacting concrete (SCC) specially designed to flow without vibration
• Shallow, unreinforced slabs with high slump
• Very thin sections where vibrators don't fit

Use immersion (poker) vibrators inserted vertically at 300-600mm spacing, vibrating each spot for 5-15 seconds until surface appears glossy and air bubbles stop emerging. Never vibrate too long (over 20 seconds per spot) as this can cause segregation with heavier aggregates sinking.

Surface scaling (spalling or flaking) is the loss of the concrete surface layer, typically 3-15mm deep. Common causes include:

• Freeze-thaw damage: Water in surface pores freezes, expands, and breaks the surface. Prevention: Use air-entrained concrete (4% air content) for freeze-thaw exposure.
• Deicing salt damage: Salts create osmotic pressure causing surface deterioration. Prevention: Use low w/c ratio (< 0.45), air entrainment, and adequate curing. Apply penetrating sealer.
• Finishing too early: Working the surface while bleed water is present brings excess water and cement paste to surface, creating weak layer. Prevention: Wait until bleed water evaporates before finishing.
• Inadequate curing: Rapid drying creates weak surface layer. Prevention: Proper curing for minimum 7 days.

Repair scaled surfaces by removing loose material, cleaning thoroughly, and applying polymer-modified overlay or resurfacing compound. For extensive scaling, complete surface replacement may be necessary.

Efflorescence is a white, chalky deposit that appears on concrete surfaces. It occurs when water moves through concrete, dissolves soluble salts (mainly calcium hydroxide), and deposits them on the surface as water evaporates.

Prevention strategies:

• Use low w/c ratio (< 0.50) to minimize permeability
• Ensure proper curing to develop dense surface
• Apply quality penetrating sealer after concrete has cured
• Provide adequate drainage to keep concrete dry
• Use low-alkali cement when available
• Avoid adding calcium chloride accelerators

Removal: Efflorescence is primarily aesthetic and doesn't harm concrete strength. Remove by dry brushing for light deposits, or dilute muriatic acid (5-10% solution) for stubborn staining—rinse thoroughly after treatment. Efflorescence often diminishes naturally over time as soluble salts are depleted.

A dusty, powdery surface (dusting) indicates weak surface concrete that hasn't developed proper strength. This occurs for several reasons:

• Bleed water during finishing: Working wet concrete brings excess water to surface, creating weak, dusty layer. Solution: Wait for bleed water to evaporate before troweling.
• Rapid drying/inadequate curing: Surface dries before gaining adequate strength. Solution: Proper curing immediately after finishing.
• Over-troweling: Excessive finishing brings too much paste to surface with insufficient aggregate support. Solution: Minimal troweling, use proper finishing sequence.
• Carbonation of fresh concrete: Heaters producing CO₂ cause surface carbonation before hardening. Solution: Properly vented heaters, avoid combustion products near fresh concrete.
• Frost damage: Freezing before adequate strength gained. Solution: Protect from freezing for minimum 48 hours.

Treatment: Apply penetrating silicate-based hardener/densifier which reacts with concrete to densify and harden the surface. For severe dusting, mechanical surface removal and overlay may be necessary.

Honeycombing is the presence of voids and pockets in concrete where aggregate particles are visible but cement paste is absent. It creates a honeycomb-like appearance and represents incomplete consolidation—a serious defect affecting structural integrity and durability.

Causes:

• Inadequate vibration or lack of vibration entirely
• Harsh mix with insufficient cement paste or sand
• Overly congested reinforcement preventing concrete flow
• Formwork leakage allowing paste loss
• Excessive drop height during placement causing segregation

Repair: Minor surface honeycombing: Remove loose aggregate, wet surface, pack with cement paste or fine mortar. Structural honeycombing: Consult structural engineer—may require complete section removal/replacement, epoxy injection, or external reinforcement. Prevent by proper vibration, appropriate mix design, and careful placement techniques.

Many concrete problems can be successfully repaired without complete replacement, depending on the extent and type of damage:

Repairable conditions:

• Surface cracks < 0.5mm wide: Epoxy or polyurethane injection
• Surface scaling/spalling: Remove loose material, apply polymer-modified overlay
• Minor honeycombing: Fill with repair mortar after cleaning
• Isolated reinforcement corrosion: Remove deteriorated concrete, treat steel, patch
• Cosmetic imperfections: Grinding, overlays, decorative treatments

Replacement usually required:

• Widespread structural cracking > 1mm
• Extensive reinforcement corrosion
• Freeze-thaw damage exceeding 30% of surface area
• Alkali-silica reaction (ASR) causing widespread cracking
• Sulfate attack causing severe deterioration
• Concrete not achieving design strength due to mix errors

Consult a structural engineer for assessment of any significant concrete damage before deciding repair vs. replacement approach.

Ready-mix concrete costs in the UK vary significantly by location, specification, and order size. Typical 2026 prices per cubic meter (m³):

• Standard C20/25 concrete: £90-£115 per m³
• Standard C30/37 concrete: £100-£125 per m³
• High-strength C40/50: £115-£140 per m³
• Fiber-reinforced concrete: Add £10-£20 per m³
• Colored concrete: Add £15-£30 per m³
• Self-compacting concrete (SCC): Add £25-£40 per m³

Additional costs:

• Delivery charges: £50-£100+ depending on distance
• Small load surcharge: £15-£40 per m³ for orders < 3-4m³
• Pump hire: £200-£400 for typical residential job
• Waiting time: £2-£5 per minute after free time (typically 20-30 min)

Use our concrete cost calculator for detailed project estimates based on your location and specifications.

Most ready-mix concrete suppliers have minimum order quantities and impose small-load surcharges for orders below their minimum. Typical UK requirements in 2026:

• Standard minimum: 3-4 m³ (depends on supplier and location)
• Small load minimum: 1 m³ with significant surcharge (£15-£40 per m³ extra)
• Mini-mix trucks: Some suppliers offer 1-3 m³ loads with volumetric mixing on-site

For very small quantities (< 1 m³), consider:

• Bagged dry-mix concrete: Mix on-site for quantities < 0.25 m³ (£8-£15 per 25kg bag making 12-13 liters)
• Mini-mix/volumetric trucks: Mix concrete on-site, pay only for exact quantity used (premium price per m³)
• Combine with neighbor: Share a delivery to meet minimum order requirements

Always order 5-10% more than calculated volume to account for spillage and subgrade irregularities.

Provide complete information to ensure correct concrete specification and smooth delivery:

Essential information:

• Concrete grade: E.g., C25/30, C30/37 (check structural drawings or building control requirements)
• Volume required: Cubic meters (m³) including 5-10% allowance for waste
• Slump: Typically 75-100mm for most applications, 100-150mm if pumping
• Maximum aggregate size: Usually 20mm for standard work, 10mm for dense reinforcement
• Delivery date and time: Confirm you'll be ready—concrete can't wait
• Delivery address and access: Describe site access, parking, obstacles

Special requirements:

• Air entrainment if required for freeze-thaw resistance
• Rapid hardening for early loading or cold weather
• Retarder for hot weather or long transport
• Sulfate-resisting cement for aggressive ground conditions
• Fibers for crack control or impact resistance
• Pumping requirements (affects mix design)

Ready-mix concrete has limited workable life from the time water is added at the batching plant. Time limits depend on ambient temperature, concrete specification, and admixtures used:

Standard guidelines (from batching):

• Normal conditions (15-25°C): 90-120 minutes maximum
• Hot weather (> 30°C): 60-90 minutes with retarder
• Cold weather (< 10°C): 120-180 minutes
• With retarders: Can extend to 3-5 hours depending on dosage and temperature

Most suppliers allow 20-30 minutes free time on-site for discharge. Waiting time charges apply after this period (typically £2-£5 per minute). Plan to discharge concrete immediately upon arrival—don't order until formwork, reinforcement, and crew are ready. If concrete becomes too stiff before placement is complete, it must be rejected—never add water to "freshen" it as this severely compromises strength.

Concrete pumps significantly improve placement efficiency and access but add cost. Consider pumping when:

Pumping is beneficial:

• Pour location not accessible to concrete truck chute (> 3-4m from truck)
• Elevated placements (upper floors, roof slabs)
• Obstructions between truck and pour location
• Large volumes requiring rapid placement (> 10 m³)
• Complex access requiring long hose runs
• Rear or side garden projects where truck can't reach

Direct discharge adequate when:

• Pour location within 3-4m of truck position
• Ground-level slabs with good truck access
• Small volumes (< 4 m³)
• Budget constraints—save £200-£400 pump hire cost

Pump hire typically costs £200-£400 for residential jobs (2-4 hours). Pumping requires slightly higher slump (100-150mm) and maximum aggregate size usually limited to 20mm. Some suppliers include pump in ready-mix price for larger orders (> 15-20 m³).