Ready-Mix Volume, Weight & Cost Estimator — 2026 Specifications & Pricing Guide
C28/35 concrete is a mid-range structural concrete specification widely used across the United Kingdom for reinforced concrete elements, moderately aggressive foundation conditions, exposed external slabs, heavy-duty driveways, and a broad range of commercial and light industrial applications where the standard GEN3 / C20/25 grade is insufficient. Designated as RC28 or FND3 under the BS 8500 named mix system — depending on the specific application and cement type — C28/35 delivers a characteristic compressive cube strength of 35 N/mm² at 28 days, providing meaningfully greater structural capacity, durability, and resistance to aggressive environments than the lighter C20/25 / GEN3 grade commonly used in standard domestic foundations.
The designation C28/35 follows the Eurocode concrete strength class convention: C for concrete, 28 for the characteristic cylinder strength in N/mm², and 35 for the characteristic cube strength in N/mm² — both measured at 28 days after casting under standard curing conditions. The cylinder-to-cube strength relationship (28:35 = 0.80) reflects the standard geometric correction factor used in European structural design to align cylinder and cube test results. In day-to-day UK practice, the cube strength of 35 N/mm² is the value most commonly quoted when ordering from ready-mix suppliers and when checking against structural engineer specifications.
In 2026, the price of C28/35 concrete per cubic metre in the UK ranges from approximately £142 to £182 per m³ for standard ready-mix delivered by a full transit mixer, depending on region, order volume, and supplier. This represents a premium of approximately £15–£25 per m³ above the equivalent C20/25 / GEN3 price, reflecting the higher cement content and tighter quality control requirements of the stronger mix. Understanding when C28/35 is the correct specification — and when a lighter or heavier grade is more appropriate — is essential for cost-effective and compliant structural concrete design in the UK.
C28/35 concrete occupies an important middle ground in the UK concrete grade spectrum — stronger and more durable than GEN3 / C20/25 for standard foundations, but more economical than C30/37 or C32/40 for applications that do not require the highest strength class. The most common uses of C28/35 concrete in UK construction in 2026 are as follows:
Foundations in moderately aggressive ground (AC-3 sulfate class): Where a site investigation reveals ground aggressivity class AC-3 — typically found in soils with medium sulfate content or in sites adjacent to brownfield or industrial land — BS 8500 specifies a minimum concrete designation of FND3, which corresponds to C28/35 with a sulfate-resisting or blended cement. The higher cement content and lower water-cement ratio of C28/35 significantly improves resistance to sulfate attack compared to standard GEN3 concrete, protecting the foundation from long-term chemical degradation.
Reinforced concrete ground floor slabs and suspended slabs: For commercial, light industrial, and agricultural floor slabs where the imposed loading exceeds the capacity of standard GEN3, C28/35 is a common specification. The higher compressive strength directly improves the slab's flexural capacity and resistance to cracking under load, while the lower water-cement ratio reduces permeability — important for slabs exposed to moisture from below or liquid spills from above.
Exposed external concrete in freeze-thaw conditions: C28/35 with an air-entraining admixture is widely specified for external concrete exposed to repeated freezing and thawing in a wet condition — including external steps, ramps, balconies, exposed retaining wall faces, and concrete copings. The combination of higher strength and air entrainment provides significantly better frost resistance than standard C20/25 concrete, dramatically reducing the risk of surface scaling and spalling in cold, wet UK winters.
Reinforced structural elements: Columns, beams, retaining walls, and other reinforced concrete structural elements in residential and commercial construction are frequently specified in C28/35 or C30/37. Structural engineers often specify C28/35 for elements where the loads are moderate and the exposure conditions do not require the full durability provision of C30/37 or higher — achieving a cost-effective balance between structural performance and economy.
Heavy-duty driveways and car parks: For driveways subject to heavier vehicle loading, frequent turning movements, or potential de-icing salt application, C28/35 provides significantly better surface durability than C20/25. The higher strength resists abrasion, the lower permeability reduces water and chloride ingress, and the stronger matrix better withstands the concentrated tyre loads from delivery vehicles and larger domestic vehicles such as motorhomes and caravans.
The price of C28/35 concrete per m³ in the UK in 2026 varies by delivery method, order volume, regional location, and supplier. The following prices represent typical May 2026 pricing for trade customers at major UK ready-mix suppliers including Hanson, Aggregate Industries, Tarmac, and CEMEX:
Full ready-mix transit mixer (6m³ minimum): £142–£182 per m³ for standard RC28 / C28/35 concrete. The mid-point of approximately £158/m³ is a useful planning figure. As with all ready-mix grades, the per-m³ price typically includes delivery within a standard radius of the batching plant (usually 20–30km), with mileage surcharges applying beyond that distance. The premium over C20/25 / GEN3 reflects the higher cement content (320 kg/m³ versus 240 kg/m³) and the use of blended or specialist cements where required by the sulfate class designation.
Mini-mix (under 3m³, smaller truck): £195–£265 per m³. Mini-mix C28/35 is appropriate for small structural pours — reinforced column bases, retaining wall sections, exposed step repairs — where a full transit mixer would deliver an uneconomically large volume. The higher per-m³ cost is offset by the elimination of unused concrete waste and the smaller vehicle's better access to restricted domestic sites.
Volumetric / on-site mix: £162–£205 per m³. Volumetric trucks mix C28/35 on site from separate dry constituents, allowing precise volume control with no minimum order and no waste from over-ordering. The per-m³ price is higher than ready-mix for the same grade but the ability to use exactly the volume required — without paying for unused concrete — makes volumetric economically attractive for awkward volumes between 2m³ and 8m³. Volumetric concrete also allows the mix design to be adjusted on site within the approved parameters if conditions require it.
Regional price variation: As with all concrete grades, C28/35 prices vary by 15–25% across the UK. London and the South East consistently attract the highest prices — typically £165–£195 per m³ for C28/35 in Greater London. The North East of England and Central Scotland offer the lowest prices — approximately £135–£158 per m³. Rural Wales, the Scottish Highlands, and the Islands attract additional mileage surcharges that can push delivered prices to £180–£240 per m³ or higher.
Ready-Mix Suppliers — C28/35 UK 2026: Hanson Concrete UK | Aggregate Industries | Tarmac Ready Mix | CEMEX UK | Technical standards: BSI Group | Guidance: The Concrete Centre
A standard C28/35 / RC28 concrete mix design for UK structural applications contains higher cement content and a tighter water-cement ratio than the lighter GEN3 / C20/25 grade, reflecting the need for both greater strength and improved durability. A typical C28/35 mix per cubic metre contains approximately: 300–340 kg of Portland cement (CEM I 42.5N) or an equivalent blended cement (CEM II or CEM III with GGBS or PFA additions); 145–165 litres of free water; 680–720 kg of fine aggregate (sharp sand, zone 2–3); 1,100–1,180 kg of 20mm coarse aggregate; and a water-reducing plasticiser or superplasticiser admixture to achieve the required workability without compromising the water-cement ratio.
The key quality control parameter for C28/35 concrete is the maximum water-cement ratio of 0.55, compared to 0.65 for C20/25 / GEN3. This tighter limit is non-negotiable — adding extra water on site to improve workability reduces the strength and dramatically increases the permeability of the hardened concrete, invalidating the BS 8500 compliance and potentially causing structural and durability problems in service. If additional workability is required on site, it must be achieved through an approved plasticiser admixture added at the batching plant, not by adding water on site.
Where C28/35 is specified as FND3 for moderately aggressive ground conditions (AC-3), the cement type must be appropriate for the aggressivity class — typically a blended cement combining Portland cement with ground-granulated blast furnace slag (GGBS) or pulverised fuel ash (PFA), or a sulfate-resisting Portland cement (SRPC). The specific cement type is determined by the ACEC (Aggressive Chemical Environment for Concrete) class derived from the site investigation results and must match the requirements of BS 8500-1 Table A.2. Always provide your concrete supplier with the confirmed ACEC class so they can select the correct cement type for your application.
The choice between adjacent concrete grades — C25/30, C28/35, and C30/37 — is one that structural engineers and specifiers make frequently in UK construction. Understanding the differences helps ensure the right balance of structural performance, durability, and cost for each specific application.
C25/30 (RC25 / FND2) is appropriate for reinforced concrete in mildly aggressive conditions (AC-2 sulfate class), lightly reinforced slabs in covered internal environments, and applications where a modest increase over C20/25 is warranted but the full durability of C28/35 is not required. In 2026, C25/30 costs approximately £135–£175 per m³ — a saving of £5–£10 per m³ versus C28/35 that is meaningful on large volume pours.
C28/35 (RC28 / FND3) bridges the gap between C25/30 and C30/37, offering moderately aggressive ground compliance (AC-3), good freeze-thaw resistance with air entrainment, and adequate strength for most reinforced domestic and light commercial structural elements. The 35 N/mm² cube strength provides a useful margin above the structural demands of standard residential construction, and the tighter quality control provisions of the RC28 designation give confidence in consistent performance. C28/35 is the correct default choice where a project's ground conditions have been confirmed as AC-3, or where the structural engineer has specified RC28 without a specific application driver.
C30/37 (RC30) is appropriate for more demanding structural applications — exposed concrete subject to chloride from de-icing salts or marine spray (XD and XS exposure classes), slabs in abrasive environments, and structural elements designed to tight Eurocode 2 stress limits. The higher cement content and 37 N/mm² cube strength of C30/37 also improves bond to reinforcement, which can be advantageous in elements with closely spaced bars or where bond development lengths are critical. In 2026, C30/37 costs approximately £145–£185 per m³ — a modest premium over C28/35 that is justified whenever the exposure class or structural loading demands it.
The durability requirements for C28/35 concrete are defined by the exposure class system in BS EN 206 and BS 8500, which describes the specific chemical and physical environments to which the concrete will be exposed in service. The exposure class determines the minimum concrete strength class, minimum cement content, maximum water-cement ratio, and cover to reinforcement. C28/35 is commonly specified for the following BS EN 206 exposure classes:
XC3/XC4 (Carbonation-induced corrosion of reinforcement): Concrete subject to moderate or high humidity, or cyclically wet and dry — including external exposed concrete elements, retaining walls, and bridge piers. C28/35 satisfies the minimum concrete class requirement for XC4 (cyclically wet and dry) under BS 8500.
XF1/XF2 (Freeze-thaw attack): Concrete exposed to freezing and thawing — external stairs, ramps, horizontal surfaces exposed to rain. C28/35 with 3–5% entrained air satisfies XF1 and XF2 exposure class requirements. For more severe freeze-thaw with de-icing salt (XF3/XF4), C30/37 or higher with higher air content is required.
XA1 (Chemical attack — weak): Ground containing low concentrations of aggressive chemicals including weak sulfates (AC-2 to AC-3 class). C28/35 with appropriate cement type satisfies XA1 requirements — this is the FND3 application where the ground investigation has confirmed AC-3 sulfate aggressivity.
Successfully ordering and placing C28/35 ready-mix concrete requires careful planning across several key areas. Unlike standard GEN3 / C20/25 pours, the higher cement content and tighter water-cement ratio of C28/35 mean that the concrete stiffens more quickly and is less forgiving of delays — having sufficient labour and all preparations complete before the truck arrives is even more important than for lighter grades.
When contacting your ready-mix supplier to order C28/35, be prepared to provide: the BS 8500 designation (RC28 or FND3, as appropriate); the ACEC class from your site investigation if ordering FND3 for aggressive ground; the required slump class (S2 for foundations, S3 for pumped pours); the maximum aggregate size (typically 20mm); whether air entrainment is required (for freeze-thaw exposed applications — specify 3–5% entrained air); any admixture requirements; and the required delivery time, site access details, and vehicle weight restrictions. Providing all this information upfront avoids misunderstandings, ensures the correct mix is batched, and gives the supplier time to source any specialist cement or admixture required.
For structural reinforced concrete pours, your structural engineer may require compliance testing — the taking of concrete cube samples from the delivered mix for laboratory testing at 7 and 28 days to verify that the concrete meets the specified strength class. Cube moulds and a standard sampling procedure are defined in BS EN 12350-1. Arrange cube testing with an accredited testing laboratory before the pour and ensure that samples are taken and labelled correctly on site. Most building control surveyors accept the concrete supplier's plant testing data for standard domestic applications, but require site cube tests for commercial structural elements.
| Region | C28/35 / RC28 Price per m³ | C25/30 Price per m³ | C30/37 Price per m³ | Notes |
|---|---|---|---|---|
| London | £165–£195 | £158–£180 | £175–£210 | Highest in UK — ULEZ / access surcharges common |
| South East England | £158–£185 | £150–£175 | £168–£198 | Competitive market, good plant coverage |
| South West England | £150–£175 | £142–£168 | £160–£188 | Rural areas attract mileage surcharges |
| East Anglia | £146–£172 | £138–£165 | £155–£182 | Good plant coverage across most areas |
| Midlands (national avg.) | £142–£168 | £135–£162 | £152–£180 | Close to national average — well served |
| North West England | £138–£165 | £132–£158 | £148–£176 | Competitive — multiple major suppliers |
| Yorkshire & Humber | £136–£162 | £130–£156 | £145–£172 | Good availability and competitive pricing |
| North East England | £133–£158 | £128–£152 | £142–£168 | Lowest prices in England |
| Wales | £142–£172 | £136–£165 | £152–£182 | Rural areas significant surcharges |
| Scotland (Central Belt) | £138–£165 | £132–£160 | £148–£178 | Good supply in Glasgow / Edinburgh area |
| Scotland (Highlands / Islands) | £165–£220 | £158–£210 | £178–£238 | Remote surcharges — consider site-mix |
| Northern Ireland | £135–£162 | £130–£156 | £145–£172 | Competitive local market |
Prices are indicative May 2026 trade account estimates for ready-mix transit mixer delivery. Cash/retail prices typically 10–18% higher. Volume discounts apply on orders above 20m³. Always obtain at least two quotes from local suppliers before ordering.
| Method | Min. Order | Price per m³ (2026) | Delivery Charge | Short Load Fee | Best For |
|---|---|---|---|---|---|
| Ready-mix transit mixer | 6m³ (typical) | £142–£182/m³ | Included up to ~25km | £50–£130 if <6m³ | Foundations, slabs, pours >4m³ |
| Mini-mix (small drum truck) | 0.25m³ | £195–£265/m³ | £28–£60 fixed | None | Small structural pours 0.25–3m³ |
| Volumetric / on-site mix | None | £162–£205/m³ | £35–£80 mobilisation | None — pay per m³ used | Awkward volumes 1–8m³, no waste |
| Bagged dry-mix (25kg) | 1 bag | £260–£380/m³ equiv. | Free (from merchant) | None | Very small repairs / post holes <0.2m³ |
| Pump + ready-mix | 6m³ concrete | £142–£182/m³ + pump | Pump: £380–£1,200/day | As per transit mixer | Pours >5m³ with poor access |
| Grade | BS 8500 Name | Cube Strength | Max w/c | Min. Cement (kg/m³) | Price per m³ (2026) | Typical Use |
|---|---|---|---|---|---|---|
| C20/25 | GEN3 | 25 N/mm² | 0.65 | 240 | £125–£160 | Strip foundations, oversite, garage slabs |
| C25/30 | RC25 / FND2 | 30 N/mm² | 0.60 | 280 | £135–£175 | Reinforced slabs, mildly aggressive ground |
| C28/35 ★ | RC28 / FND3 | 35 N/mm² | 0.55 | 320 | £142–£182 | Mod. aggressive ground, exposed slabs, RC elements |
| C30/37 | RC30 | 37 N/mm² | 0.55 | 300 | £145–£185 | Exposed slabs, car parks, chloride environments |
| C32/40 | RC32 / FND4 | 40 N/mm² | 0.50 | 340 | £155–£200 | Highly aggressive ground, heavy loading |
| C35/45 | RC35 | 45 N/mm² | 0.45 | 360 | £160–£210 | Structural columns, bridge decks, precast |
| C40/50 | RC40 | 50 N/mm² | 0.40 | 380 | £175–£230 | High-rise, post-tensioned, marine |
★ C28/35 / RC28 / FND3 is the focus of this page. All prices are 2026 UK trade account ready-mix estimates. Confirm current pricing with your local supplier.
| Constituent | Quantity per m³ | Notes |
|---|---|---|
| Portland Cement (CEM I 42.5N) or blended | 300–340 kg | CEM II/B-V (PFA), CEM III (GGBS), or SRPC for sulfate exposure |
| Free water | 145–170 litres | Free water only — water in aggregate not included |
| Fine aggregate (sharp sand) | 620–700 kg | Zone 2 or 3 BS EN 12620 grading |
| Coarse aggregate (20mm) | 1,080–1,170 kg | Crushed granite, limestone or gravel — 20mm NMS |
| Plasticiser / superplasticiser | 1.0–3.0 litres | Required to achieve workability at w/c ≤ 0.55 |
| Air-entraining admixture | 0.05–0.15 litres | Required for XF1/XF2 freeze-thaw applications — target 3–5% air |
| Water-cement ratio (w/c) | ≤ 0.55 maximum | Key durability parameter — never add water on site |
| Fresh density | ~2,380–2,420 kg/m³ | Approximately 2.40 tonnes per m³ |
| 28-day cube strength | ≥ 35 N/mm² | Characteristic — 95% of cubes must exceed this value |
| Standard slump — foundation | S2: 50–90mm | S3 (100–150mm) for pumped concrete; specify when ordering |
The most common reason for specifying C28/35 / FND3 concrete in foundation applications is a ground aggressivity class of AC-3 confirmed by site investigation. The following table summarises the relationship between sulfate concentration in the ground, the ACEC class, the required concrete designation, and the cement type needed.
| SOâ‚„ in Ground (mg/l) | pH | ACEC Class | Required Designation | Concrete Grade | Cement Type Required |
|---|---|---|---|---|---|
| < 500 mg/l | > 6.5 | AC-1 | GEN3 | C20/25 | CEM I (standard Portland) |
| 500–1,500 mg/l | 5.5–6.5 | AC-2 | FND2 | C25/30 | SRPC or PC+GGBS blend |
| 1,500–3,000 mg/l | 4.5–5.5 | AC-3 | FND3 | C28/35 ★ | SRPC or PC+GGBS (>66%) |
| 3,000–6,000 mg/l | 4.0–4.5 | AC-4 | FND4 | C32/40 | PC+GGBS (>80%) or specialist |
| > 6,000 mg/l | < 4.0 | AC-5 | Special | Specialist design | Geotechnical engineer required |
Source: BS 8500-1:2023 and BRE Special Digest SD1 (2005). Ground aggressivity class must be confirmed by chemical testing of soil and groundwater samples collected during a site investigation. Never assume AC class without testing — sulfate concentrations vary enormously across UK sites and cannot be predicted from soil type alone.
C28/35 achieves a characteristic compressive cube strength of 35 N/mm² at 28 days — 40% stronger than standard GEN3 / C20/25 (25 N/mm²). The cylinder strength designation is 28 N/mm² per Eurocode convention.
In the BS 8500 designated mix system, C28/35 is ordered as RC28 (reinforced concrete applications) or FND3 (AC-3 aggressive ground foundation applications). Both designations produce C28/35 strength class concrete — the difference is in cement type specification for FND3.
Ready-mix C28/35 costs £142–£182 per m³ in 2026 — approximately £15–£25/m³ more than equivalent C20/25 / GEN3. London and South East prices reach £165–£195/m³. Always obtain at least two quotes.
The maximum water-cement ratio for C28/35 is 0.55 — tighter than C20/25's 0.65. Never add water on site to increase workability. Request a plasticiser admixture from the supplier instead — this maintains workability without weakening the mix.
C28/35 / RC28 requires a minimum cement content of approximately 320 kg/m³ — 33% more than GEN3 / C20/25 at 240 kg/m³. This higher cement content is the primary driver of the increased material cost per m³.
FND3 / C28/35 is the minimum required concrete designation for foundations in AC-3 aggressive chemical environment ground, confirmed by soil and groundwater sulfate analysis. SRPC or high-GGBS cement is required alongside the C28/35 strength class.
C28/35 with 3–5% entrained air satisfies XF1 and XF2 freeze-thaw exposure class requirements — suitable for external steps, ramps, retaining walls and exposed horizontal surfaces subject to repeated freezing in wet conditions in the UK climate.
Fresh C28/35 concrete weighs approximately 2,380–2,420 kg/m³. A standard 6m³ transit mixer load weighs approximately 14.4 tonnes. Check site access and ground bearing for the ~26–30 tonne gross vehicle weight of a loaded ready-mix truck.
C28/35 achieves approximately 75% of its 28-day cube strength at 7 days and over 90% at 14 days under normal curing conditions. Cold weather slows strength gain significantly — protect from frost for the first 48 hours minimum.
Structural reinforced concrete pours in C28/35 should be accompanied by cube sampling per BS EN 12350-1. Retain delivery tickets from every load. Your structural engineer or building control may require conformity test results before sign-off.
Specify S3 slump (100–150mm) when ordering C28/35 for pump placement. Standard S2 slump (50–90mm) suits direct chute placement into foundations. Do not request higher slump on site by adding water — always specify the correct slump class when ordering.
All C28/35 / RC28 / FND3 concrete supplied in the UK must comply with BS 8500-1:2023. Request a Declaration of Performance or conformity certificate from your supplier confirming mix designation, strength class, and exposure class compliance.
C28/35 is a mid-range structural concrete strength class with a characteristic compressive cube strength of 35 N/mm² at 28 days. It is used in the UK for: foundations in moderately aggressive ground (AC-3 sulfate class, designated FND3); reinforced concrete slabs, columns, beams, and retaining walls in domestic and commercial construction (designated RC28); exposed external concrete subject to freeze-thaw cycles; heavy-duty driveways; and any application where the lighter GEN3 / C20/25 grade is insufficient but the full durability of C30/37 or higher is not required. It is a versatile mid-grade concrete that covers a wide range of structural and durability applications efficiently.
In May 2026, C28/35 ready-mix concrete costs approximately £142–£182 per m³ delivered by a standard transit mixer truck across most of England, with the Midlands close to the national average of approximately £155–£158/m³. London and the South East are consistently the most expensive at £165–£195/m³. The North East of England is cheapest at approximately £133–£158/m³. Mini-mix delivery costs £195–£265/m³; volumetric trucks cost £162–£205/m³. Always obtain at least two local quotes as prices can vary by 15–20% between suppliers in the same area.
All three designations refer to C28/35 strength class concrete, but they indicate different applications and cement type requirements under BS 8500. RC28 (Reinforced Concrete 28) is specified for general reinforced concrete structural elements not subject to aggressive ground conditions — the cement type can be standard Portland (CEM I). FND3 is specified for foundation concrete in AC-3 aggressive chemical environment ground (moderately sulfate-bearing) — it requires the same C28/35 strength class but mandates a sulfate-resisting cement type (SRPC, or PC+GGBS with minimum 66% GGBS content). Always tell your ready-mix supplier which designation you need so they use the correct cement type for your application.
No — C28/35 and C30/37 are adjacent but distinct strength classes. C28/35 has a characteristic cube strength of 35 N/mm², while C30/37 has a cube strength of 37 N/mm². The difference in strength is modest (approximately 6%), but the exposure class coverage and structural design assumptions differ between them. C30/37 is the minimum required grade for XD (chloride from de-icing salts) and XS (chloride from sea water) exposure classes, and is often preferred by structural engineers for exposed above-ground reinforced concrete elements. In 2026, C30/37 costs approximately £3–£8 per m³ more than C28/35 — a modest premium that is frequently justified by the improved durability for exposed applications.
Fresh C28/35 concrete weighs approximately 2,380–2,420 kg/m³ — commonly rounded to 2.40 tonnes per m³ for structural dead load calculations. The higher cement content of C28/35 versus C20/25 adds marginally to the density, but the difference is negligible for most practical purposes. A standard 6m³ transit mixer load of C28/35 weighs approximately 14.4 tonnes of concrete. The loaded truck gross vehicle weight (concrete plus the truck itself) is typically 26–30 tonnes — always check that site access roads and any bridges, culverts, or soft ground can support this weight before the truck arrives.
Yes — C28/35 is structurally superior to C20/25 / GEN3 for foundation use and using it does not create any structural problem. Many structural engineers and self-builders choose to specify C28/35 or C30/37 for domestic foundations as a precautionary measure, particularly where: the ground investigation results are slightly uncertain; the site is adjacent to brownfield land that might have elevated sulfate content; the project is in an area with known ground chemistry issues; or the client wants additional confidence in the foundation durability. The cost premium is approximately £15–£25/m³ — on a standard house foundation requiring 10–15m³ of concrete, this adds £150–£375 to the total concrete cost — a modest insurance against potential durability issues.
Specify S2 slump (50–90mm) for C28/35 poured direct from the truck chute into strip foundations or trenches. Specify S3 slump (100–150mm) for pours placed by concrete pump or into congested reinforcement. For self-consolidating concrete in highly reinforced elements, S4 (160mm+) or a self-compacting concrete (SCC) designation may be appropriate — discuss with your structural engineer and concrete supplier. Never request higher slump by adding water on site — this increases the water-cement ratio above 0.55 and invalidates the C28/35 designation. If you need higher workability, request a plasticiser or superplasticiser admixture from the supplier when ordering.
Calculate your concrete volume using the formula: length (m) × width (m) × depth (m) = volume (m³). For irregular shapes, break the element into rectangles or regular shapes and sum the volumes. Add 10% wastage to the net volume to get the order quantity — for example, a retaining wall 6.0m long × 0.25m thick × 2.0m high = 3.0m³ net + 10% = 3.3m³ to order. Use the calculator at the top of this page to automate this calculation. Always round up to the nearest 0.5m³ when ordering. Running short of concrete during a pour risks a cold joint — a plane of weakness between old and new concrete that is difficult and expensive to remediate.
For standard domestic foundation pours using C28/35, most building control surveyors accept the ready-mix supplier's own plant quality control data (delivered on the concrete ticket with each load) as evidence of compliance without requiring site cube tests. For reinforced structural elements in commercial projects — columns, beams, slabs carrying significant loads — your structural engineer or building control may require conformity testing per BS EN 12350-1 (taking cube samples from the delivered concrete, curing them correctly, and testing at 7 and 28 days at an accredited laboratory). Arrange cube moulds and testing in advance. Always retain concrete delivery tickets — they form part of the quality record for the project and may be requested by building control or the client at any time.
Ready-mix concrete — including C28/35 — must be discharged within 90 minutes of leaving the batching plant (or within 300 drum revolutions, whichever comes first) per BS EN 206 and BS 8500. If the truck is delayed beyond this time, the concrete becomes unworkable and the pour must be stopped. Partial loads already placed may need to be treated as a construction joint. Never ask the driver to add water to re-plasticise stiffened concrete — this invalidates the C28/35 specification and dramatically weakens the concrete. To minimise delay risk: book deliveries for morning (before traffic builds); have all preparations complete before the truck arrives; have sufficient labour on site to spread and compact the concrete quickly; and discuss contingency plans with your supplier when booking. For large or complex pours, consider retarded concrete (with a set-retarding admixture) that extends the working time by 1–2 hours.
C28/35 / RC28 / FND3 ready-mix concrete is supplied by all major UK concrete producers including Hanson, Aggregate Industries, Tarmac, and CEMEX, as well as hundreds of independent regional batching plants across the UK. For small volumes (under 3m³), search for mini-mix or volumetric concrete suppliers in your local area — most operate within a 30km radius of UK towns and cities. For bagged dry-mix alternatives, Jewson, Travis Perkins, and Buildbase stock a range of dry-mix products suitable for very small repair and fixing pours, though these are not available in a true C28/35 designation and are unsuitable for structural or foundation applications.
Yes — C28/35 / RC28 is an appropriate and commonly used concrete grade for reinforced concrete retaining walls in domestic and commercial construction. For a retaining wall, the concrete specification must be appropriate for the exposure class — typically XC3/XC4 (carbonation risk on the retained face) and potentially XF1 (freeze-thaw on the exposed face). C28/35 satisfies both these exposure classes, provided the correct cover to reinforcement is maintained (typically 35–45mm for XC3/XC4) and air entrainment is added for XF1 freeze-thaw resistance. The structural design of the wall — base dimensions, stem thickness, reinforcement arrangement — must be carried out by a structural engineer using Eurocode 2 / BS EN 1992 and Eurocode 7 / BS EN 1997 for the retained soil pressure calculations.
Additional Resources 2026: Ready-mix at Hanson Concrete | Tarmac Ready Mix | CEMEX UK | Standards at BSI Group | Technical guidance at The Concrete Centre | Building control at LABC | Structural engineers at IStructE
© 2026 C28/35 Concrete Calculator UK. All prices are indicative May 2026 estimates. Concrete specification must be confirmed by your structural engineer and agreed with your building control authority. Ground aggressivity class must be determined by site investigation and chemical testing before selecting FND3 concrete.