Special Digest 1:2005 Third edition Concrete in aggressive ground BRE Construction Division BREis committed to providing impartial and authoritative Acknowledgements information on all aspects of the The principal funding for the preparation of this built environment for clients, Special Digest was provided by The Concrete designers, contractors, engineers, Centre. A list of sponsors and members of the manufacturers and owners. We steering group who advised on its preparation is make every effort to ensure the shown on page vi. accuracy and quality of information and guidance when it is published. BRE Contact details However, we can take no For technical enquiries or comment on the use of responsibility for the subsequent this Special Digest please email: use of this information, nor for any [email protected] errors or omissions it may contain. BRE is the UK’s leading centre of expertise on the built environment, construction, sustainability, energy, fire and many associated issues. Contact BRE for information about its services, or for technical advice: BRE, Garston, Watford WD25 9XX Tel:01923 664000 [email protected] www.bre.co.uk BREpublications are available from www.brebookshop.com or IHS Rapidoc (BREBookshop) Willoughby Road Bracknell RG12 8DW Tel:01344 404407 Fax: 01344 714440 [email protected] Requests to copy any part of this publication should be made to the publisher: BREBookshop Garston, Watford WD25 9XX Tel:01923 664761 [email protected] Cover photo by Graham Gaunt, courtesy of Arup© SD1 © BRE 2005 First published 2001 Second edition 2003 Third edition 2005 ISBN 1 86081 754 8 iii Contents Sponsors and members of steering group vi Part A: Introduction A1 Problem of chemical attack 1 A2 Scope and structure of the guidance 1 A2.1 Types of site and chemical agents covered 1 A2.2 Readership 2 A2.3 Structure of the guidance 2 A2.4 Diagrammatic overview of ground assessment and concrete specification 2 A3 Background to guidance on sulfate attack 4 A4 Key changes since SD1:2003 5 A5 Relationship between SD1:2005 and British and European Standards for concrete 5 Appendix A1 Glossary of terms 6 References: Part A 8 Part B: Chemical attack on concrete B1 General 9 B2 Principal types of chemical attack on concrete 9 B2.1 Sulfate attack 9 B2.2 Acid attack 11 B3 Other types of chemical attack on concrete 12 B3.1 Magnesium ions 12 B3.2 Ammonium ions 12 B3.3 Chloride ions 13 B3.4 Organic compounds 13 B4 Attack from aggressive carbon dioxide 14 B5 Attack from pure water 14 B6 Damage to concrete from crystallisation of salts 14 B7 Microbial contribution to chemical attack on concrete 15 References: Part B 15 iv Contents Part C: Assessing the aggressive chemical environment C1 General 16 C2 Principal constituents of aggressive ground and groundwater 17 C2.1 Sulfates and sulfides 17 C2.2 Acids 20 C2.3 Magnesium, calcium, sodium and potassium ions 20 C2.4 Ammonium ions 20 C2.5 Chloride ions 20 C3 Presence and mobility of groundwater 21 C3.1 Static groundwater 21 C3.2 Mobile groundwater 22 C3.3 Flowing groundwater 22 C4 Site investigation for aggressive ground conditions 23 C4.1 Introduction 23 C4.2 Desk study 23 C4.3 Site inspection (walk-over survey) 24 C4.4 Visual description of the ground 24 C4.5 Sampling and testing soils 25 C4.6 Sampling and testing groundwater 25 C5 Classification of site locations for chemicals aggressive to concrete 29 C5.1 Groundwater and soil analyses 29 C5.2 Aggressive Chemical Environment for Concrete (ACEC) classification 34 Appendix C1 Recommended test procedures for ground aggressive to concrete 36 Appendix C2 Guidance on comprehensive site investigation of sulfate ground 36 References: Part C 37 Part D: Specifying concrete for general cast-in-situ use D1 Introduction 38 D2 Changes since SD1: 2003 38 D3 Design process 39 D4 Selection of the DC Class and APMs 40 D4.1 Background 40 D4.2 Key factors 40 D5 Composition of concrete to resist chemical attack 41 D5.1 Background 41 D5.2 Using Table D2 42 D5.3 Cement and combination types 42 D5.4 Aggregate type 44 D6 Additional protective measures (APMs) 44 D6.1 General 44 D6.2 Enhance concrete quality (APM1) 45 D6.3 Use controlled permeability formwork (APM2) 45 D6.4 Provide surface protection (APM 3) 45 D6.5 Provide a sacrificial layer (APM4) 46 D6.6 Address drainage of site (APM5) 46 D7 Intended working life 47 D8 Contract documentation 48 References: Part D 48 Contents v Part E: Specifying surface-carbonated precast concrete for general use in the ground E1 Introduction 49 E2 Changes since SD1:2003 50 E3 Design process 50 E3.1 Selection of the DC Class and APMs 50 E3.2 Specifying composition of concrete 50 E3.3 Additional protective measures 50 References: Part E 51 Part F: Design guides for specific precast concrete products F1 Introduction 52 F2 Procedure for using design guides 53 F3 Design guides for precast concrete pipeline systems 55 F3.1 General considerations 55 F3.2 Using Design Guide F1a for specifying concrete for pipes and associated units 56 F3.3 Using Design Guide F1b for specifying internal linings to pipes and associated units 57 F4 Precast box culverts and precast segmental linings for tunnels and shafts 58 F4.1 General considerations 58 F4.2 Using Design Guide F2a for specifying concrete for precast box culverts and segmental linings 59 F4.3 Using Design Guide F2b for specifying internal linings to precast box culverts and segmental linings 60 F5 Design guides for precast concrete masonry units 61 References: Part F 62 vi Sponsors and members of steering group Sponsors The Concrete Centre Quarry Products Association (QPA) Cementitious Slag Makers Association (CSMA) UK Quality Ash Association (UKQAA) Members of Steering Group Professor L A Clark Chairman, Thaumasite Expert Group Department of Civil Engineering, University of Birmingham Dr C A Clear British Cement Association (BCA) Dr N J Crammond Centre for Concrete Construction, BRE Mr I Haining Costain Professor T Harrison Quarry Products Association (QPA) and BSI Committee B/517/1 Mr J C Haynes National House-Building Council (NHBC) Dr D D Higgins Cementitious Slag Makers Association (CSMA) Mr I Holton British Precast Concrete Federation / Loughborough University Mr P Livesey Castle Cement Mr T I Longworth Associate, BRE Mr N Loudon The Highways Agency Dr B K Marsh Arup Dr J D Matthews, Associate, BRE Mr A Morton Hepworth Concrete / Concrete Pipeline Systems Association (CPSA) Dr P J Nixon Associate, BRE Ms L Parker Tarmac Ltd Ms A Scothern The Concrete Centre Dr L K A Sear UK Quality Ash Association (UKQAA) Dr J F Troy Tarmac Ltd Principal Consultees Mr D Appleton Hanson Building Products Dr J C Cripps Department of Civil and Structural Engineering, University of Sheffield Mr A J Elliott Milton Precast / Box Culvert Association Dr T Grounds Tarmac Topblock Dr A Haimoni Keller Ltd / Federation of Piling Specialists (FPS) Mr R M Raymond Hughes Concrete Ltd / Concrete Pipeline Systems Association (CPSA) Mr P Rhodes RMC Mr S Wade Stent / Federation of Piling Specialists (FPS) 1 Part A Introduction A1 Problem of chemical attack A2 Scope and structure of the guidance Chemical agents that are destructive to concrete may be A2.1 Types of site and chemical agents covered found in the ground. In the UK, sulfates and acids, naturally SD1 provides guidance on the specification of concrete for occurring in soil and groundwater, are the agents most installation in natural ground and in brownfield locations. likely to attack concrete. The effects can be serious (Figure The definition of a brownfield location adopted here is one A1) resulting in expansion and softening of the concrete to a that has been subject to industrial development, storage of mush. A substantial number of other substances are known chemicals, or deposition of waste, and which may contain to be aggressive, most resulting from human activity, but aggressive chemicals in residual surface materials or in collectively these are a lesser problem as they are ground penetrated by leachates. The procedures given for encountered only rarely by concrete in the ground. ground assessment and concrete specification cover the fairly common occurrence of sulfates, sulfides and acids. It has been standard practice in the UK for at least six They also cover the more rarely occurring aggressive decades to design concrete for installation in the ground to carbon dioxide found in some ground and surface waters. be resistant to attack from commonly found chemicals, including sulfates and acids. BRE has underpinned this approach by issuing a series of guidance notes and Digests, dating back to 1939, on the causes of chemical attack and how to specify chemically resistant concrete. Consequently, most concrete installed in the ground has performed entirely satisfactorily and is expected to do so for its required working life. Occasionally, however, cases of chemical attack have come to light and have been subject to research by BRE and others. Some of these cases have been attributed to rarely occurring chemicals not specifically covered by BRE Digests: some to natural ground conditions for which there was insufficient guidance, such as occurrence of pyrite; and some to the emergence of previously unrecognised attack mechanisms, such as the thaumasite form of sulfate attack (TSA) which has been extensively reported in the last decade[1]. Guidance in BRE Digests has necessarily evolved to cater for successive adverse field findings; to take advantage of the emergence of new concrete constituents and construction methods; and to maintain harmony with newly published standards, latterly European ones. In order to be both comprehensive and flexible, Digests have tended to become longer and more complex. One objective of this third edition of Special Digest 1 (SD1) is to simplify the guidance. Other aims and changes are discussed later. Figure A1 Extreme example of sulfate attack in a 30-year-old highway bridge sub-structure exposed to wet, pyritic clay fill 2 Part A While SD1 discusses several aggressive agents (eg Part E gives recommendations for specifying surface- ammonium salts and phenols) occasionally found in heavily carbonated precast concrete for general use in the contaminated ground, no specific procedures are included ground. An essential requirement for compliance with for dealing with these. Specialist advice should be sought if this part is that surface carbonation is assured by they are encountered. exposure of the precast concrete to air for a minimum of 10 days after curing. Since such carbonation provides a A2.2 Readership degree of resistance to sulfate attack, the SD1 provides practical guidance to ground specialists on recommendations for the derivation of DC Class in the assessment of ground in respect of aggressiveness to respect of sulfates is relaxed by one level. Other than this, concrete, and to concrete designers, contractors, specifiers the recommendations of Part D are followed for concrete and producers on the specification of concrete to resist specification. chemical attack. Part F includes design guides for specification of specific A2.3 Structure of the guidance precast concrete products, including pipeline systems, Guidance is given in Parts B to F as follows. box culverts, and segmental linings for tunnels and shafts. These products are manufactured under rigorous Part B describes modes of chemical attack and discusses quality control to ensure appropriate mix composition the mechanisms of the principal types, including sulfate and achieve relatively low concrete permeability. and acid attack, and the action of aggressive carbon Together these provide an inherently high quality in dioxide. respect of chemical resistance. Consequently, a further relaxation (beyond that allowed for surface carbonation) Part C deals with assessment of the chemical is permitted in respect of specification of DC Class for aggressiveness of the ground. It gives procedures for the aggressive sulfate conditions. In practice this relaxation determination of Design Sulfate Class (DS Class) from is used to offset the general-use recommendation that a soluble sulfate and magnesium, and from the potential higher DC Class should be specified where concrete is of sulfate (eg from oxidation of pyrite). It shows how the thin cross-section, or will encounter a relatively high DS Class together with pH and mobility of groundwater hydraulic gradient. may be collectively taken into account for natural ground and brownfield sites to classify a location in terms of Part F also covers specification of precast concrete Aggressive Chemical Environment for Concrete Class masonry units (concrete blocks) for aggressive ground (ACEC Class). conditions. The guidance is based on Design Sulfate Class rather than ACEC Class as there is currently no Part D gives recommendations for the specification of correlation of block performance with the latter, though concrete for general cast-in-situ use in the ground. It work on this is ongoing. explains how to derive an appropriate quality of concrete, termed the Design Chemical Class (DC Class), A glossary of terms is included as Appendix A1 on page 6. from a consideration of the ACEC Class together with the hydraulic gradient due to groundwater, the type and A2.4 Diagrammatic overview of ground assessment thickness of the concrete element, and its intended and concrete specification working life. In some cases, where conditions are highly An overview of the various procedures for ground aggressive, additional protective measures (APMs) are assessment and specification of concrete is given in Figure recommended. A2. This is arranged in four stages according to the construction sector that has key responsibility. Within each Part D follows this with guidance on the constituents of of these stages, the principal tasks are shown in boxes with concrete required to achieve the identified DC Class. references to the relevant sections of SD1. While most steps Specification is shown as maximum free-water/cement are equally applicable to all uses of concrete, there is a ratio, minimum cement content and type of cement. differentiation in Stage 3 for the determination of DC Class and APM between the three categories of concrete element dealt with in Parts D, E and F. Introduction 3 Stage 1 Consider design options for building or structure and Part C Designer of building or prepare specification for site investigation. structure Inform geotechnical specialist of design concept and site investigation requirements Stage 2 Carry out site investigation to determine chemical Geotechnical specialist conditions for concrete, including water mobility. See Part C Determine DS Class and ACEC Class for site locations using Tables C1 and C2. See Section C5 Parts D, E Stage 3 Determine the intended working life of proposed building or and F Designer of building or structure, and the form and use of specific concrete elements. structure See Section D7 General use of cast-in-situ General use of surface- Specific precast concrete concrete carbonated precast concrete products Find specification of concrete and Find specification of concrete and ● Use Part F APM using procedure in Part D: APM using procedure in Part E: ● Determine the DC Class and ● determine the DC Class and any ● determine the DC Class and any APM for the concrete using APM from Table D1 APM from Table E1 Design Guides F1a, F1b, F2a, ● adjust DC Class / APM for section ● adjust DC Class / APM for section F2b, F3a, F3b thickness and hydraulic gradient thickness and hydraulic gradient ● determine options for APM from ● determine options for APM from Table D4 Table D4 State in contract documents the DS Class and ACEC Class of the ground and the method of deriving the concrete specification (eg use of Tables C1, D1 and D2, or Table C2 and Design Guide F1a). State requirements and options for concrete specification, including: ● specified DC Class of concrete after any enhancement ● specified number and type of APM and compressive strength class of concrete ● any other requirements Stage 4 Obtain from contract documents the specified DC Class, Contractor for building number and type of APM, and any other design or structure in liaison requirements for each concrete element with any third party concrete producer Formulate concrete mix design and consistence for structural element taking into account specified DC Class, strength class, availability, and cost of materials and contract requirements Where concrete is being supplied ready-mixed, check the proposed mix for conformity to the DC Class specification Are all requirements of design guides and No contract documents met? Yes Accept concrete mix design for specific use. Implement any APM specified for DC Class or in contract documents Figure A2 Procedure for design of buried concrete for use in an aggressive chemical environment