Specification - Concrete Mix Design, Quality Control and Specification - page 122

code) provides guidance for a service life of 40 to 60 years. In AS
3600-2009 exposure to the tidal and splash zone would be classified
as C2 exposure and require a minimum 50 MPa compressive strength
and 65 mm cover.
ACI 318-11 deems exposure to moisture and an external source of
chlorides as severe and requires a maximum w/cm of 0.40 and a mini-
mum characteristic strength of 5000 psi (34.5 MPa cylinder strength).
British Standard (BS) 8110: Part 1: 1997 provides no explicit reference to
the intended design life. Regarding durability requirements, concrete
in seawater tidal zone down to 1 m below the lowest water level
would be classified as “most severe”. The minimum requirements are
C50, maximum w/cm ratio = 0.45, minimum cementitious content of
400 kg/m 3 , and minimum cover of 50 mm.
BS 6349: Part 1: 2000 classifies concrete structures in the upper tidal
and “dry” internal faces of submerged structures as XS3. Limiting
values for composition and properties of concrete for a required
design working life of 100 years in UK seawater conditions are 37
MPa (cube strength), maximum w/cm ratio = 0.45, minimum cementi-
tious content of 370 kg/m 3 (based on 50% < ground granulated
blast-furnace slag (GGBS) < 80% or 35% < fly ash (FA) < 55%) and
minimum cover of 50 mm.
BS 8500-1:2002 also classifies concrete in tidal zone to be classified as
XS3. Limiting values for composition and properties of concrete for
a required design working life of 50 years in UK seawater conditions
are C45, maximum w/cm ratio = 0.40, minimum cementitious content
of 360 kg/m 3 (based on 36% < GGBS < 65% or 21% < FA < 35%),
and minimum cover of 40 mm. Interestingly, the requirements for
100-year design life are not given.
Building Research Establishment Special Digest No. 1 (SD1) was written
primarily in response to the growing recognition of the occurrence of
thaumasite form of sulfate attack (TSA) in UK buildings and structures
since the 1990s. Thaumasite is a form of sulfate attack that only occurs
at cold temperature. While not related to marine environments, SD1
provides useful guidance on the specification of concrete for instal-
lation in aggressive ground conditions. The guidelines for concrete
specification include recommendation for 100-year design life. Based
on a hydraulic gradient less than 5, Table E1 recommends DC-4 and
an additional protective measure (APM) for an intended working
life of at least 100 years. This equates to a concrete mix containing
minimum 380 kg/m 3 cementitious incorporating 36%-65% GGBS or
21%-35% FA, maximum water/cement ratio of 0.40. A waterprooing
membrane, controlled permeability formliner or others would be
considered the additional protective measure.