TIME PROVEN PERFORMANCE SPECIFICATION FOR MARIINE CONCRETE
Ultra-Low Absorption Spec Time-Proven Successful Over 40 Years (Nov 2001)
The Concrete Institute of Australia introduced the new guideline document “Performance Criteria for Concrete in Marine Environments” at a well-attended seminar in Sydney recently.
Industry interest in a viable performance-based specification for design-life durability is obviously very strong, however the document does not provide an actual specification.
Drafting Committee member Mr. Daksh Bawega cited two major challenges as;
1) The divergence of views on which criteria are most appropriate (e.g. absorption, diffusion, resistivity, strength, etc.).
2) The difficulty of correlating results from “early-age” or accelerated tests, with long-term durability under real conditions.
Formal agreement on the criteria & test method that satisfy all views may well be some time away. Adam Fitzhenry of Standards Australia suggested that an Australian Standard for marine concrete might be produced within two years at best, calling for industry-wide input.
In the meantime, important marine project specifications are limiting the absorptiveness or Absorption of air-exposed concrete elements.
Researchers from authorities like the CSIRO, Transport Research Laboratory (UK), the NSW RTA and VicRoads confirm that capillary absorption is the primary mechanism by which water & chlorides infiltrate the air-exposed elements of marine concrete. This means that here diffusion is a secondary “symptom” of absorption, & that if concrete did not absorb water or get “wet” inside, corrosion would not occur.
In air-exposed marine concrete, all corrosion processes require the presence of absorbed water, so this makes logical sense too.
Work by international concrete technologies group Cementaid has validated this research. Non-Absorptive concrete structures exposed in salt pans over 40 years, remain corrosion-free.
This has given Cementaid the unique ability to correlate results from simple to perform “early-age” tests, with successful long-term performance under varied conditions, over periods of up to 40 years.
Absorption testing & chloride analysis of samples from these corrosion-free, ultra-low absorption concretes, allowed the development of a “time-proven” Performance Specification, based closely on the BS Absorption test.
For all air-exposed elements, a maximum 7-Day BS Absorption value of 1% (one percent) is specified. This is based on the proven corrosion-free durability of ultra-low absorption concretes over periods of up to 40 years. If required, compliance testing of production concrete and non-compliance remediation procedures are also provided.
The BS Absorption test does not directly “measure” durability – No test does. However it is directly related to the primary water & chloride transport mechanism, and has a long history of use elsewhere in the (British) Standards for durability of concrete paving (BS368:1956). It also has the important advantages of being accurate & repeatable, as well as quick and low cost to perform.
The Specification further requires that any admixtures or ingredient used to achieve the absorption limit should have a successful history of use under severe marine conditions, without any diminution of performance, or adverse effect on other concrete properties. This protects the owner, specifier & builder against unproven, “short-lived” and / or unsafe materials.
Commenting on the need for low absorption at early-age (7 days), concrete consultant Dr. Adam Neville (UK) said; “While PFA or ggbfs mixes show good behavior at 28 days, they are very vulnerable at the age of a few days. Testing at an early age is useful both because the quality is assessed when there is still time to manoeuvre and also because it is important that the concrete is satisfactory at the time of its first exposure to an aggressive environment.” Noting cases of past admixtures where their effect did not persist over the years, Dr. Neville said “It is clear that a material with a long history of successful behavior justifiably inspires confidence”.
The Absorption-based Performance Specification has been in successful use for over 15 years now. “CALTITE” concretes are compliant with this Specification, and continue in-service now over 40 years under extremely severe chloride and sulphate conditions – without any incidence of corrosion, or maintenance down-time.
A copy of the Specification follows, and more information can be reviewed / downloaded HERE
PERFORMANCE SPECIFICATION (Absorption) FOR MARIINE CONCRETE
GUIDANCE NOTE: The performance and the effective life of integral waterproofing compounds can vary greatly within the industry. Therefore, an ingredient with an established, long-term history of successful use, such as that stated in clause (d) below, is ane ssential component in aperformance-based specification of this type. This specification is based on the long-term performance of one such ingredient, Everdure Caltite, continuously performing in acutal field structures up to 40 years old.
Ultra-Low Absorption concrete;
“All concrete (specify sections) shall conform with all specified requirements and also the following;
The minimum contents of Ordinary Portland Cement (OPC) and / or blended cementitious materials (in Kg / m3) shall be:
|OPC / slag||400||160|
|OPC / PFA||380||300|
1) The concrete shall contain an approved High Range Water Reducing admixture such that the free water:cement ratio shall not exceed 0.40 and the concrete will be of adequate workability for placement.
2) The concrete shall contain a time-proven effective Hydrophobic Pore-blocking Ingredient (HPI) system (such as “Everdure Caltite”, or proven equal and approved in writing), used strictly in accordance with manufacturers’ instructions and providing a hydrophobic / non-absorptive cement matrix throughout and dispersed polymer particles suitable for use as a pore-blocking agent.
3) The HPI system must produce concrete conforming with all specified requirements and shall further be shown to produce concrete with a corrected 30 minute absorption of not greater than 1% as measured by BS 1881: Part 122: 1983, except that the age at test shall be 7 days.
3.1) Absorption testing is to be conducted on cores taken from cubes or cylinders as specified in the standard, unless the use of cast specimens is approved by the Engineer.
3.2) Where an existing or pre-approved mix design shown to comply with the above absorption requirement is not available then, prior to construction and at least 30 days before the actual Ultra-Low Absorption concrete is to be cast, the Main Contractor shall arrange for trial mixes to be conducted, under the supervision of the Engineer or his representative, and with the supplier of the Hydrophobic Pore-blocking Ingredient present, to confirm that the proposed mix conforms with the absorption limit and other specified requirements.
4) Any admixture or ingredient, other than cement, aggregate or approved water-reducing admixture, used by the Contractor to comply with the absorption requirement must be shown by an independent authority to have been successfully used in concrete structures, including those exposed to a severe marine environment, for a minimum of 15 years without significant deterioration of the cement matrix, embedded reinforcing steel, or measurable reduction in performance of the product on absorption.
5) Admixtures must not contain chlorides. The Supplier shall satisfy the Engineer that any admixture or ingredient used, or their combination, does not detrimentally affect the strength or other properties of the concrete.
Production, Testing and Quality Assurance
6) During construction, two absorption test samples shall be taken at the same time as samples for compressive strength testing. These samples shall be tested as above and shall conform with the specified absorption requirement. In the event of non-compliance, the Main Contractor will follow the procedures set out in Section II.
7) The concrete as placed and cured in the actual structure is required to comply with the water absorption limit within 7 days of placement. The Engineer reserves the right to take cores to confirm compliance.