Portland-Composite Cement Concrete Volume, Weight & Cost Estimator — 2026 Specifications & Pricing Guide
CEM II concrete is concrete manufactured using a Portland-composite cement — a blended cement that combines Portland cement clinker with one or more supplementary cementitious materials (SCMs) in proportions defined by the European standard BS EN 197-1. The designation CEM II covers a wide family of blended cements, each identified by a suffix indicating the type and proportion of the added material: CEM II/A-L (Portland-limestone), CEM II/B-V (Portland-fly ash), CEM II/B-S (Portland-slag), and several others. In 2026, CEM II cements — particularly CEM II/A-L and CEM II/A-M — are the most widely used cement types in the United Kingdom, having largely displaced pure Portland cement (CEM I) for the majority of ready-mix and bagged concrete applications due to their lower carbon footprint, competitive pricing, and technical equivalence for most standard construction uses.
The shift toward CEM II cements in the UK accelerated significantly between 2018 and 2026 as the UK construction sector responded to climate targets and as cement manufacturers invested in the grinding and blending infrastructure needed to produce composite cements at scale. The UK's readiness to adopt CEM II/A-L and CEM II/A-M as the standard cement type — replacing the CEM I 42.5N that dominated UK practice for decades — has been faster than in many European countries, driven by the combination of Government policy, client sustainability requirements, and the technical advocacy of organisations including the Mineral Products Association (MPA), the Concrete Centre, and major cement producers. In 2026, approximately 65–70% of all cement sold in the UK is a CEM II product.
For the construction professional, contractor, or self-builder, the practical significance of CEM II concrete is that it is almost certainly the cement type in the ready-mix concrete being delivered to your site today — whether you have specified it or not. Understanding what CEM II means, how it performs relative to CEM I, which sub-types are available, and how to specify it correctly is essential knowledge for anyone involved in concrete construction in the UK in 2026.
The CEM II family encompasses a broad range of blended cements, each with distinct performance characteristics driven by the type and proportion of the supplementary material added to Portland clinker. The naming convention under BS EN 197-1 is systematic: the letter after the slash (A or B) indicates the proportion of additions — A for 6–20%, B for 21–35%; the letter after the hyphen identifies the addition type (L for limestone, V for siliceous fly ash, S for granulated blast furnace slag, etc.). The most important CEM II sub-types in the UK in 2026 are:
CEM II/A-L and CEM II/B-L (Portland-Limestone Cement): The most widely used CEM II type in the UK. Limestone filler replaces 6–20% (A-type) or 21–35% (B-type) of the Portland clinker. Limestone is chemically inert in the cement — it acts primarily as a filler and nucleation site for early hydration products, giving CEM II/A-L performance very close to CEM I in most standard applications. The carbon footprint is reduced proportionally to the clinker substitution — CEM II/A-L with 15% limestone has approximately 15% lower embodied CO₂ per tonne than the equivalent CEM I. In 2026, CEM II/A-L and CEM II/A-M are the default cements used by all major UK ready-mix producers for GEN3 through RC30 concrete mixes.
CEM II/A-V and CEM II/B-V (Portland-Fly Ash Cement): Siliceous fly ash (PFA — pulverised fuel ash) from coal-fired power stations replaces 6–20% (A-type) or 21–35% (B-type) of the Portland clinker. PFA is a pozzolanic material — unlike limestone, it reacts chemically with the calcium hydroxide produced during cement hydration, forming additional cementitious compounds that improve long-term strength and reduce concrete permeability. CEM II/B-V concrete gains strength more slowly than CEM I or CEM II/A-L in the early days but typically exceeds CEM I performance in long-term strength and durability. It also generates less heat during hydration — making it valuable for mass concrete pours and hot weather concreting where temperature-induced cracking is a risk.
CEM II/A-S and CEM II/B-S (Portland-Slag Cement): Ground granulated blast furnace slag (GGBS) replaces 6–20% or 21–35% of the Portland clinker. Like PFA, GGBS is a latently hydraulic material that reacts with calcium hydroxide from Portland cement hydration. CEM II/B-S provides improved sulfate resistance compared to standard Portland cement — making it a useful specification for mildly to moderately aggressive ground conditions — and reduces the heat of hydration. Higher GGBS replacements (above 36%) take the cement into the CEM III category, providing the most pronounced sulfate resistance and the lowest heat of hydration.
CEM II/A-M (Portland-Composite Cement — multi-component): A blend of Portland clinker with two or more SCMs in combination, each in proportions between 6–20% total. CEM II/A-M cements allow cement manufacturers to combine the benefits of multiple additions — for example, the early strength contribution of limestone with the long-term durability of fly ash or GGBS — while remaining within the CEM II/A designation. CEM II/A-M cements have become increasingly common from UK producers in 2026 as they offer greater flexibility in cement chemistry and carbon footprint optimisation while maintaining the performance characteristics expected by the market.
The most common question about CEM II concrete is whether it performs as well as the CEM I concrete it has largely replaced. For the vast majority of UK construction applications — domestic foundations, floor slabs, driveways, retaining walls, and standard reinforced concrete elements — the answer is yes. CEM II/A-L and CEM II/A-M concretes designed to BS 8500 strength classes perform equivalently to CEM I mixes across all the parameters that matter in standard construction: 28-day compressive strength, workability, durability under normal UK exposure conditions, and compatibility with standard finishing and curing practices.
The key differences between CEM II and CEM I concrete that contractors and specifiers should be aware of in 2026 are: Early strength development — CEM II/B-V (fly ash) and CEM II/B-S (slag) concretes develop strength more slowly than CEM I in the first 3–7 days, which can affect formwork striking times and the timing of prestress or post-tension operations in structural construction. Heat of hydration — CEM II/B-V and CEM II/B-S generate less heat during curing, which is beneficial for thick pours and mass concrete but means additional frost protection may be needed in cold weather. Colour — CEM II/A-L concrete is typically slightly lighter in colour than CEM I, which can affect the appearance of architectural concrete finishes. Sulfate resistance — CEM II/B-S and CEM III concretes provide progressively better sulfate resistance as GGBS content increases; CEM II/A-L provides similar sulfate resistance to CEM I and should not be used for aggressive sulfate exposure (AC-3 and above) without additional guidance.
One of the primary drivers for the adoption of CEM II cements in the UK is the significant reduction in embodied carbon compared to pure Portland cement (CEM I). Cement manufacture is one of the most carbon-intensive industrial processes — globally responsible for approximately 8% of CO₂ emissions — and the Portland clinker component of cement is the primary source of that carbon, through both the calcination of limestone (which releases CO₂ as calcium carbonate converts to calcium oxide) and the combustion of fuel in the kiln.
Replacing clinker with SCMs that require no kiln firing reduces the carbon footprint of the cement in direct proportion to the clinker replacement level. Typical embodied CO₂ values for different cement types in 2026 (expressed as kg CO₂e per tonne of cement) are: CEM I 42.5N — approximately 820–880 kg CO₂e/t; CEM II/A-L (15% limestone) — approximately 700–760 kg CO₂e/t; CEM II/B-V (30% PFA) — approximately 560–620 kg CO₂e/t; CEM II/B-S (30% GGBS) — approximately 540–600 kg CO₂e/t. For a typical 6m³ domestic foundation pour using GEN3 concrete with approximately 240 kg/m³ cement content, switching from CEM I to CEM II/A-L saves approximately 90–120 kg of CO₂e — equivalent to the carbon cost of approximately 50–65 miles of average petrol car travel.
On larger commercial and infrastructure projects, the carbon savings from specifying CEM II or CEM III concrete are proportionally larger and form an important part of whole-life carbon assessments, BREEAM credits, and increasingly mandatory embodied carbon reporting under PAS 2080 and the RIBA 2030 Climate Challenge. Many UK clients — particularly public sector bodies, developers working to net zero targets, and projects seeking BREEAM Excellent or Outstanding ratings — now require embodied carbon assessments that specifically consider cement type as a key variable. Choosing CEM II/B-V or CEM II/B-S over CEM I for appropriate applications can reduce the concrete element of a building's embodied carbon by 20–40%, making cement type selection one of the most impactful single decisions in low-carbon structural design.
Professional Resources 2026: CEM II guidance at The Concrete Centre | Carbon data from Mineral Products Association | Standards at BSI Group | Sustainability at UK Green Building Council | Ready-mix at Hanson Concrete UK
The price of CEM II concrete in the UK in 2026 is broadly comparable to equivalent CEM I mixes — in many cases slightly lower, reflecting the lower clinker content and the lower raw material cost of the supplementary additions (particularly limestone and PFA). The price difference between CEM II and CEM I concrete depends on the specific sub-type and application:
CEM II/A-L concrete (the most common type used by UK ready-mix producers) is typically priced identically to CEM I concrete of the same strength class — the limestone addition is so standard that most producers' base prices already assume a CEM II/A-L or CEM II/A-M cement. In 2026, standard GEN3 / C20/25 using CEM II/A-L costs approximately £125–£158 per m³ ready-mix across most of England — essentially the same as the GEN3 CEM I price quoted in our other concrete guides.
CEM II/B-V (fly ash) and CEM II/B-S (slag) concrete are sometimes priced slightly below equivalent CEM I mixes — fly ash (PFA) and GGBS are by-products of industrial processes and their raw material cost can be lower than Portland clinker when supply is plentiful. In 2026, CEM II/B-V and CEM II/B-S concrete mixes from major UK suppliers are typically priced £3–£8/m³ below equivalent CEM I strength class mixes, reflecting the lower clinker content. However, price varies between suppliers — always request quotes specifying the cement type explicitly and compare on a like-for-like basis.
Specialist CEM II mixes for aggressive exposure conditions or sustainability-driven specifications may carry a small premium of £5–£12/m³ if they require specialist blended cements that are not standard production items at the local batching plant. Always check with your supplier whether the required CEM II sub-type is available from stock or needs to be specially sourced, and allow additional lead time if a non-standard blend is required.
Specifying CEM II concrete correctly under the BS 8500 designated mix system requires understanding how cement type interacts with the strength class and exposure class requirements. BS 8500 designations (GEN3, RC25, RC28 etc.) do not specify the cement type — they define the performance requirements that the concrete must meet. The cement type is a producer choice within those performance requirements, provided it is permitted under BS 8500 for the specific application and exposure class.
For standard domestic applications (GEN3 foundations, RC25 slabs, driveways), any CEM II sub-type is acceptable and the producer will typically default to CEM II/A-L or CEM II/A-M without needing to be asked. For applications requiring specific durability properties — sulfate resistance (AC-2 and above), chloride resistance (XD exposure), or freeze-thaw resistance (XF3/XF4) — the CEM II sub-type must be selected carefully against the BS 8500 exposure class tables. For example: CEM II/B-S (slag 21–35%) provides adequate sulfate resistance for AC-2 ground but not AC-3, which requires CEM III or higher GGBS content. CEM II/B-V (fly ash 21–35%) improves chloride resistance modestly but is insufficient for XD3 (de-icing salt) without additional w/c tightening. Always consult BS 8500-1 Table A.2 and your structural engineer or concrete technologist when specifying CEM II for aggressive exposure conditions.
For the majority of domestic construction projects in the UK in 2026, CEM II concrete — specifically CEM II/A-L or CEM II/A-M — can be used exactly as CEM I concrete with no change to site practice, finishing techniques, or curing requirements. The ready-mix driver will deliver concrete with a CEM II cement and the site team can proceed as normal. The following guidance applies to the cases where CEM II choice may require a change in site approach:
For CEM II/B-V (fly ash) concrete in cold weather: the lower heat of hydration and slower early strength development of high-fly ash mixes means that frost protection is more important than for CEM I. At temperatures below 5°C, protect CEM II/B-V concrete with insulated blankets for the first 48–72 hours — longer than the 24–48 hours that might be adequate for CEM I. Check with your concrete supplier for their specific cold weather guidance for the CEM II/B-V mix you are receiving.
For CEM II/B-V or CEM II/B-S concrete in hot or windy conditions: the slower early strength development of fly ash and slag blended concretes makes them slightly more vulnerable to plastic shrinkage cracking in hot, dry, or windy conditions before the concrete has gained sufficient strength. Apply curing compound promptly after finishing, or cover with damp hessian and polythene sheeting. Wind-breaks around the pour area help significantly on exposed sites.
For CEM II/B-V concrete and formwork striking: the lower 7-day strength of high-fly ash mixes means formwork striking times may need to be extended by 20–40% compared to CEM I. For simple slab formwork, this is rarely an issue — but for column or beam soffit shuttering carrying the weight of the concrete element, always check the required minimum stripping strength with the structural engineer and verify by cube testing rather than relying on age-based rules derived from CEM I experience.
| Designation | Addition Type | Addition % | Early Strength | Long-Term Strength | Heat of Hydration | Sulfate Resistance | COâ‚‚ vs CEM I | Price vs CEM I (2026) |
|---|---|---|---|---|---|---|---|---|
| CEM I 42.5N | None (pure Portland) | 0% | Very high | High | High | Standard | — | Baseline |
| CEM II/A-L ★ | Limestone | 6–20% | Very high | High | High | Standard | –10–20% | Same / –£1–3 |
| CEM II/B-L | Limestone | 21–35% | High | Good | Moderate–high | Standard | –20–35% | Same / –£2–4 |
| CEM II/A-V | Fly ash (PFA) | 6–20% | High | High–very high | Moderate | Slightly improved | –10–20% | –£2–5 |
| CEM II/B-V | Fly ash (PFA) | 21–35% | Moderate | Very high | Low–moderate | Improved | –25–38% | –£3–7 |
| CEM II/A-S | GGBS slag | 6–20% | High | High–very high | Moderate | Improved | –10–18% | –£2–5 |
| CEM II/B-S | GGBS slag | 21–35% | Moderate | Very high | Low–moderate | Good (AC-2/3) | –22–35% | –£3–8 |
| CEM II/A-M | Multi-component | 6–20% total | High | High | Moderate | Depends on blend | –10–20% | Same / –£1–4 |
★ CEM II/A-L is the most common cement type in UK ready-mix concrete in 2026. Price differences versus CEM I shown per m³ of finished concrete — not per tonne of cement. CO₂ reduction is approximate and based on MPA and ICE Database v3.0 figures.
| Cement Type | Clinker Content | SCM Addition | 28-Day Strength | Sulfate Resistance | COâ‚‚ vs CEM I | Typical UK Use | BS EN 197-1 Class |
|---|---|---|---|---|---|---|---|
| CEM I 42.5N | 95–100% | None | Highest early | Standard | — | Precast, PT, specialist | CEM I |
| CEM II/A-L | 80–94% | Limestone 6–20% | Near CEM I | Standard | –10–20% | General purpose — dominant in UK 2026 | CEM II |
| CEM II/B-V | 65–79% | PFA 21–35% | High long-term | Improved | –25–38% | Mass concrete, sustainable RC | CEM II |
| CEM II/B-S | 65–79% | GGBS 21–35% | High long-term | Good (AC-2) | –22–35% | RC foundations, moderate sulfate | CEM II |
| CEM III/A | 35–64% | GGBS 36–65% | Good long-term | Very good | –40–60% | FND3/FND4 foundations, marine | CEM III |
| CEM III/B | 20–34% | GGBS 66–80% | Slower early | Excellent | –60–75% | FND4 highly aggressive ground | CEM III |
| SRPC | ~95% | Low C₃A clinker | Near CEM I | Very good | Similar to CEM I | Sulfate-bearing ground (older spec) | Special |
In 2026 UK practice, CEM II (highlighted) is the default cement type for the vast majority of ready-mix concrete. CEM I is mainly reserved for precast and post-tensioned applications requiring rapid early strength. CEM III is specified for aggressive sulfate conditions and very high durability requirements.
| BS 8500 Designation | Strength Class | Typical Binder (kg/m³) | Max w/c | CEM II Suitable? | Best CEM II Sub-type | Price per m³ (2026) | Application |
|---|---|---|---|---|---|---|---|
| GEN2 | C16/20 | 220 | 0.70 | Yes — all sub-types | CEM II/A-L | £108–£132 | Blinding, oversite, fill |
| GEN3 | C20/25 | 240 | 0.65 | Yes — all sub-types | CEM II/A-L or CEM II/A-M | £122–£158 | Foundations, floor slabs, driveways |
| RC25 / FND2 | C25/30 | 280 | 0.60 | Yes — check sulfate class | CEM II/B-S for AC-2 ground | £132–£170 | RC slabs, mildly aggressive ground |
| RC28 / FND3 | C28/35 | 320 | 0.55 | Yes — CEM II/B-S or CEM III for AC-3 | CEM II/B-S (≥21% GGBS) | £140–£178 | Moderate aggressive ground, RC elements |
| RC30 | C30/37 | 300 | 0.55 | Yes — with care for XD/XF | CEM II/B-V or CEM II/B-S | £142–£182 | Exposed slabs, moderate chloride |
| RC32 / FND4 | C32/40 | 340 | 0.50 | CEM III preferred for FND4 | CEM III/B (≥66% GGBS) for AC-4 | £152–£198 | Highly aggressive ground — note: CEM III, not CEM II, for AC-4 |
For FND4 (AC-4 highly aggressive sulfate ground), CEM III/B (≥80% GGBS) is required under BS 8500 — this exceeds the CEM II range. CEM II/B-S (21–35% GGBS) is appropriate for AC-2 conditions but insufficient for AC-3 and above without additional measures. Always confirm cement type requirements with your structural engineer and geotechnical adviser.
CEM II cements — particularly CEM II/A-L and CEM II/A-M — account for approximately 65–70% of all cement sold in the UK in 2026, having displaced CEM I as the default cement type for ready-mix, bagged, and most precast applications over the past decade.
All CEM II cements in the UK are manufactured to BS EN 197-1 (Composition, specifications and conformity criteria for common cements). The standard defines the clinker content, addition types, and strength classes permitted for each CEM II sub-type.
CEM II cements reduce embodied CO₂ by 10–38% versus CEM I, depending on addition type and proportion. CEM II/B-V (35% PFA) and CEM II/B-S (35% GGBS) offer the greatest carbon reduction within the CEM II range — important for BREEAM, net zero, and PAS 2080 reporting.
For standard construction applications, CEM II/A-L (6–20% limestone) produces concrete with early strength development, workability, and durability essentially identical to CEM I — making it a direct substitute in most domestic and commercial applications without any site practice changes.
CEM II/B-V (21–35% fly ash) concrete develops strength more slowly in the first 7 days than CEM I or CEM II/A-L, but typically equals or exceeds CEM I performance at 28 days and beyond. Formwork striking times must be adjusted — extend 7-day rule-of-thumb estimates by 25–40%.
CEM II/B-V and CEM II/B-S concretes generate less heat during curing than CEM I — beneficial for thick pours and mass concrete where temperature rise risks thermal cracking. In cold weather, this means longer frost protection is needed compared to CEM I mixes.
CEM II concrete is typically priced the same as or marginally less than equivalent CEM I mixes of the same strength class. CEM II/A-L is often the base product at no premium; CEM II/B-V and CEM II/B-S mixes may save £3–£8/m³ depending on local PFA and GGBS availability.
CEM II/A-L and CEM II/A-M offer the same sulfate resistance as CEM I — suitable for AC-1 ground. CEM II/B-S (21–35% GGBS) is suitable for AC-2 conditions. For AC-3 and above, CEM III/A or CEM III/B is required — these are outside the CEM II range.
Post-tensioned construction requiring stressing at 3–5 days typically specifies CEM I 52.5N for rapid early strength development. CEM II/A-L is acceptable where 7-day stressing is feasible, but CEM II/B-V and CEM II/B-S are generally unsuitable for early PT stressing.
CEM II/B-V and CEM II/B-S concretes are more sensitive to inadequate curing than CEM I, as the pozzolanic and latent hydraulic reactions of fly ash and GGBS require moisture to progress. Apply curing compound or polythene covering immediately after finishing — minimum 7 days.
CEM II/A-L is the cement type in most bagged dry-mix concrete, post-mix concrete, and bagged Portland cement products sold through UK builders merchants in 2026. Bags labelled "Portland cement" or "Portland limestone cement" almost certainly contain a CEM II/A-L product.
All CEM II concrete from QSRMC-certified plants comes with a Declaration of Performance (DoP) confirming the cement type used. For structural applications, always request the DoP and retain it in the project quality file — the cement type is part of the concrete's structural compliance record.
CEM II is one of the five main cement families defined in BS EN 197-1 — the European standard for common cements. It covers Portland-composite cements containing Portland clinker combined with one or more supplementary cementitious materials (SCMs) in proportions of 6–35% by mass. The designation after the slash indicates the SCM proportion (A = 6–20%, B = 21–35%) and the letter after the hyphen identifies the SCM type: L = limestone, V = siliceous fly ash, S = granulated blast furnace slag (GGBS), M = multiple components. For example, CEM II/A-L is Portland cement with 6–20% limestone; CEM II/B-V is Portland cement with 21–35% fly ash. In the UK in 2026, CEM II is the most widely used cement family in construction, having largely displaced pure Portland cement (CEM I) for general-purpose applications.
For the most widely used sub-type — CEM II/A-L (Portland-limestone with 6–20% limestone) — the answer is yes for all practical purposes. CEM II/A-L concrete designed to the same BS 8500 strength class as CEM I achieves equivalent 28-day compressive strength and performs equivalently in standard construction applications. For CEM II/B-V (fly ash) and CEM II/B-S (GGBS) concretes, the 7-day strength development is slower than CEM I, but by 28 days — and especially at 56 and 90 days — CEM II/B-V and CEM II/B-S concretes often match or exceed CEM I strength due to the continued reaction of the pozzolanic and latently hydraulic SCMs. The key practical implication is that formwork striking decisions should not be based on age rules derived from CEM I experience when using CEM II/B-V or CEM II/B-S concrete.
CEM II/A-L and CEM II/B-V are both CEM II cements but with completely different additions. CEM II/A-L contains 6–20% limestone — an inert filler that dilutes the clinker without significantly changing the chemistry of hydration, giving performance very similar to CEM I with a modest CO₂ reduction of 10–20%. CEM II/B-V contains 21–35% siliceous fly ash (PFA) — a pozzolanic material that reacts chemically with calcium hydroxide from Portland cement hydration to form additional strength and durability-enhancing compounds. CEM II/B-V develops strength more slowly in the first 7 days but achieves higher long-term strength and better durability than CEM II/A-L; it also reduces embodied CO₂ by 25–38%. For most domestic foundations and slabs, either is suitable — CEM II/B-V is preferred for large pours, warm weather, or where sustainability credits are important.
In 2026, CEM II concrete is typically priced the same as or marginally less than equivalent CEM I mixes of the same strength class. CEM II/A-L is so standard in UK ready-mix production that most suppliers' base prices already assume it — there is no premium. CEM II/B-V and CEM II/B-S mixes may save £3–£8 per m³ compared to equivalent CEM I mixes, depending on local fly ash and GGBS availability. Requesting CEM II/B-V or CEM II/B-S specifically from your ready-mix supplier may require some advance notice and is subject to local plant capability — not all UK batching plants stock these cements as standard. Always confirm availability and pricing with your supplier when specifying a specific CEM II sub-type.
Yes — CEM II/A-L and CEM II/A-M concrete (GEN3 / C20/25 strength class) is the standard specification for domestic strip foundations in the UK in 2026. It is accepted by all building control bodies and satisfies the requirements of Approved Document A and BS 8103-1 for standard domestic strip foundation applications on normal, non-aggressive ground (AC-1 aggressivity class). For foundations on mildly aggressive ground (AC-2), CEM II/B-S (21–35% GGBS) can provide the necessary sulfate resistance and is accepted under BS 8500 for FND2 (C25/30) applications. For AC-3 and above, CEM III/A or CEM III/B is required — outside the CEM II range.
For CEM II/A-L concrete — the most common type — curing requirements are essentially the same as for CEM I: keep the surface moist and protected from wind and frost for a minimum of 3–7 days. For CEM II/B-V (fly ash) and CEM II/B-S (GGBS) concretes, curing is more critical because the secondary pozzolanic and latent hydraulic reactions of the SCMs require moisture to proceed — without adequate water, these reactions stop and the potential long-term strength and durability benefits of the CEM II blend are not realised. Apply curing compound immediately after surface finishing, or cover with wet hessian and polythene for a minimum of 7 days. In hot, dry, or windy conditions, consider pre-wetting the surface before applying curing compound and erecting wind-breaks around the pour.
CEM II/B-V (fly ash) concrete should be used with extra care in cold weather — below 5°C — because the pozzolanic reaction of fly ash is strongly temperature-dependent and effectively stops at near-freezing temperatures, leaving the concrete dependent entirely on the residual Portland clinker for early strength. In these conditions, CEM II/B-V concrete gains strength significantly more slowly than CEM I or CEM II/A-L. If using CEM II/B-V in cold weather: protect the concrete from frost for at least 48–72 hours with insulated blankets; use hot water in the mix if permitted by the supplier; consider heating the sub-base and formwork before pouring; and monitor cube strength development before applying any load or stripping formwork. In extreme cold, switching to a CEM I or CEM II/A-L mix may be more practical than attempting to manage the temperature sensitivity of high-PFA concrete.
CEM II/A-M is a Portland-composite cement containing a combination (mixture) of two or more supplementary cementitious materials — each individually and in total within the A-range of 6–20% additions. For example, a CEM II/A-M might contain 10% limestone combined with 8% fly ash. The M designation gives cement manufacturers greater flexibility in cement chemistry and allows them to optimise the blend for cost, carbon footprint, and performance without exceeding the total addition level permitted under the CEM II/A designation. In 2026, CEM II/A-M is increasingly common from UK cement producers as it allows them to respond to seasonal variation in SCM availability (particularly fly ash, whose supply has been affected by UK coal power station closures) while maintaining a consistent, certificated product. From the contractor's perspective, CEM II/A-M performs very similarly to CEM II/A-L for standard applications.
Yes — slightly, depending on the sub-type. CEM II/A-L concrete is typically a slightly lighter grey than equivalent CEM I concrete, because the pale limestone filler dilutes the grey clinker colour. CEM II/B-V (fly ash) concrete tends to have a slightly bluish-grey tint. CEM II/B-S (GGBS) concrete is initially very light — almost white or cream — when freshly demoulded, gradually greying as carbonation proceeds. For standard structural concrete where colour is not critical, these differences are irrelevant. For architectural concrete, off-form concrete finishes, or exposed aggregate work, specify the cement type carefully and request trial panels to confirm colour before proceeding with the main pour.
Yes — CEM II concrete is entirely suitable for reinforced concrete applications when designed to the appropriate BS 8500 strength class and exposure class. CEM II/A-L and CEM II/A-M provide fully adequate performance for most above-ground reinforced concrete in XC1–XC4 carbonation exposure. CEM II/B-V and CEM II/B-S provide improved resistance to chloride ingress compared to CEM I or CEM II/A-L, making them preferable for reinforced concrete in XD1 and XD2 chloride exposure classes. For the most demanding chloride environments (XD3, XS3), CEM III with higher GGBS content is typically required. Regardless of CEM II sub-type, reinforcement cover to the requirements of BS EN 1992-1-1 and BS 8500 for the specific exposure class must be maintained — cement type improves durability but does not substitute for adequate cover.
Using CEM II concrete — particularly CEM II/B-V (fly ash) or CEM II/B-S (GGBS) in place of CEM I — reduces the embodied carbon of the concrete element by 25–38% per m³. Under BREEAM 2018 and BREEAM UK New Construction 2023, embodied carbon reduction contributes to the Materials (Mat) and Innovation credits. Projects using the RICS Whole Life Carbon Assessment (WLCA) framework or reporting under PAS 2080 (Carbon management in infrastructure) will record the cement type as part of the A1 (manufacturing) stage embodied carbon calculation. For projects targeting BREEAM Excellent or Outstanding, net zero whole life carbon, or compliance with the RIBA 2030 Climate Challenge, specifying CEM II/B-V or CEM II/B-S where structurally appropriate — rather than defaulting to CEM I — is one of the single most impactful and cost-neutral decisions available to the design team. Carbon data for specific CEM II products should be sourced from manufacturer-specific EPDs (Environmental Product Declarations) for the most accurate project reporting.
In 2026, CEM II concrete is the default product from virtually every UK ready-mix supplier — you almost certainly receive CEM II/A-L or CEM II/A-M concrete when ordering standard GEN3 or RC-class mixes without specifying cement type. Major UK ready-mix producers including Hanson, Aggregate Industries, Tarmac, and CEMEX all produce CEM II/A-L and CEM II/A-M standard mixes. CEM II/B-V and CEM II/B-S may require advance notice or specialist ordering at some plants — contact your local supplier to confirm availability. For bagged cement, Portland limestone cement (CEM II/A-L) is widely available from all major builders merchants including Jewson and Travis Perkins.
Additional Resources 2026: CEM II guidance at The Concrete Centre | Carbon data from Mineral Products Association | Standards at BSI Group | Sustainability at UK Green Building Council | Ready-mix at Hanson | Tarmac | CEMEX UK | Structural engineers at IStructE
© 2026 CEM II Concrete Calculator UK. All prices are indicative May 2026 estimates. CEM II sub-type suitability for specific exposure classes must be confirmed against BS 8500-1 and with your structural engineer or concrete technologist before ordering.