Concrete Exposure and Cover to Eurocodes and BS 8500

Tables for exposure class, bond cover and duability cover for different concrete grades are given below.

Bond Cover

Reinforcement Type and Arrangement	Minimum cover for bond \( c_{min,b}\)
Individual Bars	Diamater of the bar
Bundled Bars	Equivilant diameter of thebars
Post-tensioned Circular Ducts	Smaller of diameter of duct or 80mm
Post-tensioned Rectangular Ducts	Minimum of smallest duct dimension, half the largest duct dimension or 80mm
Pre-tensioned strand or wire	1.5 times strand or wire diameter
Pre-tensioned indented wire	2.5 times wire diameter

Exposure Classes

Class designation	Class description	Informative examples applicable in the United Kingdom
No risk of corrosion or attack (X0 class)
X0	For concrete without reinforcement or embedded metal: all exposures except where there is freeze-thaw, abrasion or chemical attack. For concrete with reinforcement or embedded metal: very dry	Unreinforced concrete surfaces inside structures. Unreinforced concrete completely buried in soil classed as AC-1 and with a hydraulic gradient not greater than 5. Unreinforced concrete permanently submerged in non-aggressive water. Unreinforced concrete surfaces in cyclic wet and dry conditions not subject to abrasion, freezing or chemical attack. Reinforced concrete surfaces exposed to very dry conditions.
Corrosion induced by carbonation (XC classes)
(where concrete containing reinforcement or other embedded metal is exposed to air and moisture)
XC1	Dry or permanently wet	Reinforced and prestressed concrete surfaces inside enclosed structures except voided superstructures and areas of structures with high humidity. Reinforced and prestressed concrete surfaces permanently submerged in non-aggressive water.
XC2	Wet, rarely dry	Reinforced and prestressed concrete surfaces permanently in contact with soil not containing chlorides.
XC3 and XC4 (XC3/4)	Moderate humidity or cyclic wet and dry	External reinforced and prestressed concrete surfaces sheltered from, or exposed to, direct rain. Reinforced and prestressed concrete surfaces subject to high humidity (e.g. poorly ventilated bathrooms, kitchens). Reinforced and prestressed concrete surfaces exposed to alternate wetting and drying. Interior concrete surfaces of pedestrian subways not subject to de-icing salts, voided superstructures or cellular abutments. Reinforced or prestressed concrete surfaces protected by waterproofing.
Corrosion induced by chlorides other than from sea water (XD classes)
(where concrete containing reinforcement or other embedded metal is subject to contact with water containing chlorides, including de-icing salts, from sources other than from seawater)
XD1	Moderate humidity	Concrete surfaces exposed to airborne chlorides Reinforced and prestressed concrete wall and structure supports more than 10 m horizontally from a carriageway. Bridge deck soffits more than 5 m vertically above the carriageway. Parts of structures exposed to occasional or slight chloride conditions.
XD2	Wet, rarely dry	Reinforced and prestressed concrete surfaces totally immersed in water containing chlorides. Buried highway structures more than 1 m below adjacent carriageway.
XD3	Cyclic wet and dry	Reinforced and prestressed concrete walls and structure supports within 10 m of a carriageway. Bridge parapet edge beams. Buried highway structures less than 1 m below carriageway level. Reinforced pavements and car park slabs.
Corrosion induced by chlorides from sea water (XS classes)
(where concrete containing reinforcement or other embedded metal is subject to contact with sea water or airborne salt originating from sea water)
XS1	Exposed to airborne salt but not in direct contact with sea water	External reinforced and prestressed concrete surfaces in coastal areas.
XS2	Permanently submerged	Reinforced and prestressed concrete surfaces completely submerged or remaining saturated, e.g. concrete below mid-tide level.
XS3	Tidal, splash and spray zones	Reinforced and prestressed concrete surfaces in the upper tidal zones and the splash and spray zones, including exposed soffits above sea water.
Freeze-thaw attack (XF classes)
(where concrete is exposed to significant attack from freeze-thaw cycles whilst wet)
XF1	Moderate water saturation without de-icing agent	Vertical concrete surfaces such as façades and columns exposed to rain and freezing. Non-vertical concrete surfaces not highly saturated, but exposed to freezing and to rain or water.
XF2	Moderate water saturation with de-icing agent	Concrete surfaces such as parts of bridges, which would otherwise be classified as XF1, but which are exposed to de-icing salts either directly or as spray or run-off.
XF3	High water saturation without de-icing agent	Horizontal or near horizontal concrete surfaces, which are exposed to freezing whilst wet. Concrete surfaces subjected to frequent splashing with water and exposed to freezing.
XF4	High water saturation with de-icing agent or sea water	Horizontal concrete surfaces, such as roads and pavements, exposed to freezing and to de-icing salts either directly or as spray or run-off. Concrete surfaces subjected to frequent splashing with water containing de-icing agents and exposed to freezing.
Chemical attack (XA classes)
(where concrete is exposed to chemical attack). Chemical attack by aggressive ground (ACEC classes)
XA1	Slightly aggressive chemical environment	Concrete exposed to natural soil and ground water according to BS EN 206. These European exposure classes are not used in the UK where Table A.2 shall be used to determine the ACEC-class. See BRE Special Digest 1 [1] for guidance on site investigation.
XA2	Moderately aggressive chemical environment
XA3	Highly aggressive chemical environment
Chemical attack from seawater (XAS class)
Chemical attack from seawater (XAS class)
XAS	Exposed to sea water	Concrete surfaces in contact with sea water

Durability Cover

Table A4 of BS 8500-1:2015 + A1:2016 - 50 year service life

**Table Key**
A) Where appropriate, account should be taken of the recommendations to resist freeze‑thaw damage, aggressive chemicals and abrasion.
B) Expressed as the minimum cover to reinforcement plus an allowance in design for deviation, Δc, e.g. to allow for workmanship. Check the appropriate design code to see whether it is recommended that the minimum cover to prestressing steel is adjusted.
C) Resistance to chloride ingress (XD and XS exposure classes) is mainly dependent upon the cement or combination type and the w/c ratio, with aggregate quality being a secondary factor. Compressive strength is included as an indirect control on these parameters.
D) Also applies to heavyweight concrete. For lightweight concrete the maximum w/c ratio and minimum cement or combination content applies, but the compressive strength class needs to be changed to a lightweight compressive strength class on the basis of equal cylinder strength if designing to BS EN 1992-1-1 and BS EN 1992-1-2.
E) For adjustments to cement or combination content for different maximum size of aggregate, see BS 8500-1.
F) If the concrete is specified as being air entrained in accordance with the XF2 or XF4 recommendations in BS 8500-1, the minimum compressive strength class for corrosion induced by chlorides may be reduced to C28/35.
G) In some parts of the UK it is not possible to produce a practical concrete with a maximum w/c ratio of 0.35.
H) For IVB-P, IVB-Q and IVB‑V increase the strength class to C28/35.
	Compressive strength class ^C), maximum w/c ratio and minimum cement or combination content for normal-weight concrete ^D) with 20 mm maximum aggregate size ^E)														Cement/combination types
Nominal cover ^B) mm	15+Δc	20+Δc	25+Δc	30+Δc	35+Δc	40+Δc	45+Δc	50+Δc	55+Δc	60+Δc	65+Δc	70+Δc	75+Δc	80+Δc
Corrosion induced by carbonation (XC exposure classes)
XC1	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	All
XC2	-	-	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	All
XC3/4	-	C40/50 0.45 340	C32/40 0.55 300	C28/35 0.60 280	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	All except IVB-V
XC3/4	-	-	C40/50 0.45 340	C32/40 0.55 300	C28/35 0.60 280	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	IVB-V
Corrosion induced by chlorides other than sea water (XD exposure classes) adequate for any associated carbonation induced corrosion (XC)
XD1	-	-	C40/50 0.45 360	C32/40 0.55 320	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	All
XD2	-	-	-	C40/50F) 0.40 380	C32/40F) 0.50 340	C28/35 0.55 320	C28/35 0.55 321	C28/35 0.55 322	C28/35 0.55 323	C28/35 0.55 324	C28/35 0.55 325	C28/35 0.55 326	C28/35 0.55 327	C28/35 0.55 328	CEM I, IIA, IIB-S, CEM I-SR0, CEM I-SR3
XD2	-	-	-	C35/45F) 0.40 380	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XD2	-	-	-	C32/40F) 0.40 380	C25/30 0.50 340	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	IIIB, IVB-V
XD3	-	-	-	-	-	C45/55F) 0.35 G) 380	C40/50F) 0.40 380	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	CEM I, IIA, IIB-S, CEM I-SR0, CEM I-SR3
XD3	-	-	-	-	-	C35/45F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 321	C25/30 0.55 322	C25/30 0.55 323	C25/30 0.55 324	IIB-V, IIIA
XD3	-	-	-	-	-	C32/40F) 0.40 380	C28/35 0.45 360	C25/30 0.50 340	C25/30 0.50 341	C25/30 0.50 342	C25/30 0.50 343	C25/30 0.50 344	C25/30 0.50 345	C25/30 0.50 346	IIIB, IVB-V
Corrosion induced by chlorides from sea water (XS exposure classes) adequate for any associated carbonation induced corrosion (XC)
XS1	-	-	-	-	-	-	C45/55F) 0.35 G) 380	C40/50F) 0.40 380	C35/45F) 0.45 360	C32/40F) 0.50 340	C28/35 0.55 320	C28/35 0.55 321	C28/35 0.55 322	C28/35 0.55 323	CEM I, IIA, IIB-S
XS1	-	-	-	C40/50F) 0.35 G) 380	C32/40F) 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XS1	-	-	-	C35/45 F) 0.40 380	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS1	-	-	-	C32/40 F) 0.40 380	C25/30H) 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IV-B, IIIB
XS2	-	-	-	-	-	-	-	-	-	C45/55F) 0.35 G) 380	C40/50F) 0.40 380	C40/50F) 0.40 380	C35/45F) 0.45 360	C32/40F) 0.50 340	CEM I, IIA, IIB-S
XS2	-	-	-	-	-	C35/45F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XS2	-	-	-	-	C40/50F) 0.35 G) 380	C32/40F) 0.45 G) 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS2	-	-	-	-	C35/45F) 0.35 G) 380	C28/35 0.45 360	C25/30 0.50 340	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	IV-B, IIIB
XS3	-	-	-	-	-	-	-	-	-	-	-	-	-	C45/55 0.35 G) 380	CEM I, IIA, IIB-S
XS3	-	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C35/45 F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XS3	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C32/40F) 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS3	-	-	-	-	-	-	C35/45F) 0.35 G) 380	C28/35 0.45 360	C25/30 0.50 340	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	IV-B, IIIB

Table A5 of BS 8500-1:2015 + A1:2016 - 100 year service life

**Table Key**
A) Where appropriate, account should be taken of the recommendations to resist freeze‑thaw damage, aggressive chemicals and abrasion.
B) Expressed as the minimum cover to reinforcement plus an allowance in design for deviation, Δc, e.g. to allow for workmanship. Check the appropriate design code to see whether it is recommended that the minimum cover to prestressing steel is adjusted.
C) Resistance to chloride ingress (XD and XS exposure classes) is mainly dependent upon the cement or combination type and the w/c ratio, with aggregate quality being a secondary factor. Compressive strength is included as an indirect control on these parameters.
D) Also applies to heavyweight concrete. For lightweight concrete the maximum w/c ratio and minimum cement or combination content applies, but the compressive strength class needs to be changed to a lightweight compressive strength class on the basis of equal cylinder strength if designing to BS EN 1992-1-1 and BS EN 1992-1-2.
E) For adjustments to cement or combination content for different maximum size of aggregate, see BS 8500-1.
F) If the concrete is specified as being air entrained in accordance with the XF2 or XF4 recommendations in BS 8500-1, the minimum compressive strength class for corrosion induced by chlorides may be reduced to C28/35.
G) In some parts of the UK it is not possible to produce a practical concrete with a maximum w/c ratio of 0.35.
H) For pre-cast, pre-tensioned concrete only
	Compressive strength class ^C), maximum w/c ratio and minimum cement or combination content for normal-weight concrete ^D)with 20 mm maximum aggregate size ^E)														Cement/combination types
Nominal cover ^B) mm	15+Δc	20+Δc	25+Δc	30+Δc	35+Δc	40+Δc	45+Δc	50+Δc	55+Δc	60+Δc	65+Δc	70+Δc	75+Δc	80+Δc
Corrosion induced by carbonation (XC exposure classes)
XC1	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	C20/25 0.70 240	All
XC2	-	-	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	All
XC3/4	-	-	-	C40/50 0.45 340	C35/45 0.50 320	C32/40 0.55 300	C28/35 0.60 280	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	All except IVB-V
XC3/4	-	-	-	-	C40/50 0.45 340	C35/45 0.50 320	C32/40 0.55 300	C28/35 0.60 280	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	C25/30 0.65 260	IVB-V
Corrosion induced by chlorides other than sea water (XD exposure classes) adequate for any associated carbonation induced corrosion (XC)
XD1	-	-	-	C45/55 0.40 380	C40/50 0.45 360	C35/45 0.50 340	C32/40 0.55 320	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	C28/35 0.60 300	All
XD2	-	-	-	-	-	C35/45 0.45 360	C32/40 0.50 340	C28/35 0.55 320	C28/35 0.55 320	C28/35 0.55 320	C28/35 0.55 320	C28/35 0.55 320	C28/35 0.55 320	C28/35 0.55 320	CEM I, IIA, IIB-S, CEM I-SR0, CEM I-SR3
XD2	-	-	-	-	-	C32/40 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XD2	-	-	-	-	-	C28/35 0.45 360	C25/30 0.50 340	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	IIIB, IVB-V
XD3	-	-	-	-	-	-	-	-	C45/55F) 0.35 G) 380	C40/50F) 0.40 380	C40/50F) 0.40 380	C35/45F) 0.45 360	C35/45F) 0.45 360	C35/45F) 0.45 360	CEM I, IIA, IIB-S, CEM I-SR0, CEM I-SR3
XD3	-	-	-	-	-	-	C40/50F) 0.35G) 380	C35/45F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XD3	-	-	-	-		-	C32/40F) 0.40 380	C28/35 0.45 360	C25/30 0.50 340	C25/30 0.50 340	C25/30 0.50 340	C25/30 0.50 340	C25/30 0.50 340	C25/30 0.50 340	IIIB, IVB-V
Corrosion induced by chlorides from sea water (XS exposure classes) adequate for any associated carbonation induced corrosion (XC)
XS1	-	-	-	-	-	-	-	-	-	-	C45/55F) 0.35 G) 380	C40/50F) 0.40 380	C35/45F) 0.45 360	C32/40F) 0.50 340	CEM I, IIA, IIB-S
XS1	-	-	-	-	C40/50F) 0.35 G) 380	C40/50F) 0.35 G) 380	C35/45 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XS1	-	-	-	-	-	C35/45 F) 0.40 380	C32/40 0.45 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS1	-	-	-	-	-	C32/40 0.45 380	C28/35 0.45 360	C25/30 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IV-B, IIIB
XS2	-	-	-	-	-	-	-	-	-	-	-	-	-	-	CEM I, IIA, IIB-S
XS2	-	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C35/45F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	IIB-V, IIIA
XS2	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C35/45 0.40 380	C32/40F) 0.45 G) 360	C28/35 0.50 340	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS2	-	-	-	-	-	-	C35/45F) 0.35 G) 380	C32/40 0.40 380	C28/35 0.45 360	C25/30 0.50 340	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	C20/25 0.55 320	IV-B, IIIB
XS3	-	-	-	-	-	-	-	-	-	-	-	-	-	-	CEM I, IIA, IIB-S
XS3	-	-	-	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C40/50F) 0.35 G) 380	C35/45 F) 0.40 380	C32/40F) 0.45 360	C28/35 0.50 340	IIB-V, IIIA
XS3	-	-	-	-	-	-	-	-	-	C40/50F) 0.35 G) 380	C40/50F) 0.35 G) 380	C32/40F) 0.45 360	C25/30 0.55 320	C25/30 0.55 320	IIB-V ≥25% fly ash, IIIA ≥46% ggbs
XS3	-	-	-	-	-	-	-	-	-	C35/45F) 0.35 G) 380	C32/40 0.40 380	C28/35 0.45 360	C25/30 0.55 320	C25/30 0.55 320	IV-B, IIIB

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