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1、 Concrete in aggressive ground Special Digest 1:2005 Third edition BRE Construction Division Acknowledgements The principal funding for the preparation of this Special Digest was provided by The Concrete Centre. A list of sponsors and members of the steering group who advised on its preparation is s
2、hown on page vi. BRE Contact details For technical enquiries or comment on the use of this Special Digest please email: constructionbre.co.uk BRE is committed to providing impartial and authoritative information on all aspects of the built environment for clients, designers, contractors, engineers,
3、manufacturers and owners. We make every effort to ensure the accuracy and quality of information and guidance when it is published. However, we can take no responsibility for the subsequent use of this information, nor for any errors or omissions it may contain. BRE is the UKs leading centre of expe
4、rtise 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 enquiriesbre.co.uk www.bre.co.uk BRE publications are available from or IH
5、S Rapidoc (BRE Bookshop) Willoughby Road Bracknell RG12 8DW Tel: 01344 404407 Fax: 01344 714440 Requests to copy any part of this publication should be made to the publisher: BRE Bookshop Garston, Watford WD25 9XX Tel: 01923 664761 Cover photo by Graham Gaunt, courtesy of Arup SD1 BRE 2005 First p
6、ublished 2001 Second edition 2003 Third edition 2005 ISBN 1 86081 754 8 iii Contents Sponsors and members of steering groupvi Part A: Introduction A1Problem of chemical attack1 A2Scope and structure of the guidance1 A2.1Types of site and chemical agents covered1 A2.2Readership2 A2.3Structure of the
7、guidance2 A2.4Diagrammatic overview of ground assessment and concrete specification2 A3Background to guidance on sulfate attack4 A4Key changes since SD1:20035 A5Relationship between SD1:2005 and British and European Standards for concrete5 Appendix A1Glossary of terms6 References: Part A8 Part B: Ch
8、emical attack on concrete B1General9 B2Principal types of chemical attack on concrete9 B2.1Sulfate attack9 B2.2Acid attack11 B3Other types of chemical attack on concrete12 B3.1Magnesium ions12 B3.2Ammonium ions12 B3.3Chloride ions13 B3.4Organic compounds13 B4Attack from aggressive carbon dioxide14 B
9、5Attack from pure water14 B6Damage to concrete from crystallisation of salts14 B7Microbial contribution to chemical attack on concrete15 References: Part B15 ivContents Part C: Assessing the aggressive chemical environment C1General16 C2Principal constituents of aggressive ground and groundwater17 C
10、2.1Sulfates and sulfides17 C2.2Acids20 C2.3Magnesium, calcium, sodium and potassium ions20 C2.4Ammonium ions20 C2.5Chloride ions20 C3Presence and mobility of groundwater21 C3.1Static groundwater21 C3.2Mobile groundwater22 C3.3Flowing groundwater22 C4Site investigation for aggressive ground condition
11、s23 C4.1Introduction23 C4.2Desk study23 C4.3Site inspection (walk-over survey)24 C4.4Visual description of the ground24 C4.5Sampling and testing soils25 C4.6Sampling and testing groundwater25 C5Classification of site locations for chemicals aggressive to concrete29 C5.1Groundwater and soil analyses2
12、9 C5.2Aggressive Chemical Environment for Concrete (ACEC) classification34 Appendix C1Recommended test procedures for ground aggressive to concrete36 Appendix C2Guidance on comprehensive site investigation of sulfate ground36 References: Part C37 Part D: Specifying concrete for general cast-in-situ
13、use D1Introduction38 D2Changes since SD1: 200338 D3Design process39 D4Selection of the DC Class and APMs40 D4.1Background40 D4.2Key factors40 D5Composition of concrete to resist chemical attack41 D5.1Background41 D5.2Using Table D242 D5.3Cement and combination types42 D5.4Aggregate type44 D6Addition
14、al protective measures (APMs)44 D6.1General44 D6.2Enhance concrete quality (APM1)45 D6.3Use controlled permeability formwork (APM2)45 D6.4Provide surface protection (APM 3)45 D6.5Provide a sacrificial layer (APM4)46 D6.6Address drainage of site (APM5)46 D7Intended working life47 D8Contract documenta
15、tion48 References: Part D48 Contentsv Part E: Specifying surface-carbonated precast concrete for general use in the ground E1Introduction49 E2Changes since SD1:200350 E3Design process50 E3.1Selection of the DC Class and APMs50 E3.2Specifying composition of concrete50 E3.3Additional protective measur
16、es50 References: Part E51 Part F: Design guides for specific precast concrete products F1Introduction52 F2Procedure for using design guides53 F3Design guides for precast concrete pipeline systems55 F3.1General considerations55 F3.2Using Design Guide F1a for specifying concrete for pipes and associat
17、ed units56 F3.3Using Design Guide F1b for specifying internal linings to pipes and associated units57 F4Precast box culverts and precast segmental linings for tunnels and shafts58 F4.1General considerations58 F4.2Using Design Guide F2a for specifying concrete for precast box culverts and segmental l
18、inings59 F4.3Using Design Guide F2b for specifying internal linings to precast box culverts and segmental linings60 F5Design guides for precast concrete masonry units61 References: Part F62 vi Sponsors The Concrete Centre Quarry Products Association (QPA) Cementitious Slag Makers Association (CSMA)
19、UK Quality Ash Association (UKQAA) Members of Steering Group Professor L A ClarkChairman, Thaumasite Expert Group Department of Civil Engineering, University of Birmingham Dr C A ClearBritish Cement Association (BCA) Dr N J CrammondCentre for Concrete Construction, BRE Mr I HainingCostain Professor
20、T HarrisonQuarry Products Association (QPA) and BSI Committee B/517/1 Mr J C Haynes National House-Building Council (NHBC) Dr D D HigginsCementitious Slag Makers Association (CSMA) Mr I Holton British Precast Concrete Federation / Loughborough University Mr P LiveseyCastle Cement Mr T I LongworthAss
21、ociate, BRE Mr N Loudon The Highways Agency Dr B K MarshArup Dr J D Matthews,Associate, BRE Mr A MortonHepworth Concrete / Concrete Pipeline Systems Association (CPSA) Dr P J Nixon Associate, BRE Ms L ParkerTarmac Ltd Ms A ScothernThe Concrete Centre Dr L K A SearUK Quality Ash Association (UKQAA) D
22、r J F Troy Tarmac Ltd Principal Consultees Mr D Appleton Hanson Building Products Dr J C CrippsDepartment of Civil and Structural Engineering, University of Sheffield Mr A J ElliottMilton Precast / Box Culvert Association Dr T GroundsTarmac Topblock Dr A HaimoniKeller Ltd / Federation of Piling Spec
23、ialists (FPS) Mr R M Raymond Hughes Concrete Ltd / Concrete Pipeline Systems Association (CPSA) Mr P RhodesRMC Mr S WadeStent / Federation of Piling Specialists (FPS) Sponsors and members of steering group A1 Problem of chemical attack Chemical agents that are destructive to concrete may be found in
24、 the ground. In the UK, sulfates and acids, naturally occurring in soil and groundwater, are the agents most likely to attack concrete. The effects can be serious (Figure A1) resulting in expansion and softening of the concrete to a mush. A substantial number of other substances are known to be aggr
25、essive, most resulting from human activity, but collectively these are a lesser problem as they are encountered only rarely by concrete in the ground. It has been standard practice in the UK for at least six decades to design concrete for installation in the ground to be resistant to attack from com
26、monly 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 pe
27、rformed 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 cove
28、red 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 d
29、ecade1. 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 compre
30、hensive 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. A2 Scope and structure of the guidance A2.1 Types of site and chemical agents covered SD
31、1 provides guidance on the specification of concrete for installation in natural ground and in brownfield locations. The definition of a brownfield location adopted here is one that has been subject to industrial development, storage of chemicals, or deposition of waste, and which may contain aggres
32、sive chemicals in residual surface materials or in ground penetrated by leachates. The procedures given for ground assessment and concrete specification cover the fairly common occurrence of sulfates, sulfides and acids. They also cover the more rarely occurring aggressive carbon dioxide found in so
33、me ground and surface waters. 1 Figure A1 Extreme example of sulfate attack in a 30-year-old highway bridge sub-structure exposed to wet, pyritic clay fill Part A Introduction While SD1 discusses several aggressive agents (eg ammonium salts and phenols) occasionally found in heavily contaminated gro
34、und, no specific procedures are included for dealing with these. Specialist advice should be sought if they are encountered. A2.2 Readership SD1 provides practical guidance to ground specialists on the assessment of ground in respect of aggressiveness to concrete, and to concrete designers, contract
35、ors, specifiers and producers on the specification of concrete to resist chemical attack. A2.3 Structure of the guidance Guidance is given in Parts B to F as follows. Part B describes modes of chemical attack and discusses the mechanisms of the principal types, including sulfate and acid attack, and
36、 the action of aggressive carbon dioxide. Part C deals with assessment of the chemical aggressiveness of the ground. It gives procedures for the determination of Design Sulfate Class (DS Class) from soluble sulfate and magnesium, and from the potential sulfate (eg from oxidation of pyrite). It shows
37、 how the DS Class together with pH and mobility of groundwater may be collectively taken into account for natural ground and brownfield sites to classify a location in terms of Aggressive Chemical Environment for Concrete Class (ACEC Class). Part D gives recommendations for the specification of conc
38、rete for general cast-in-situ use in the ground. It explains how to derive an appropriate quality of concrete, termed the Design Chemical Class (DC Class), from a consideration of the ACEC Class together with the hydraulic gradient due to groundwater, the type and thickness of the concrete element,
39、and its intended working life. In some cases, where conditions are highly aggressive, additional protective measures (APMs) are recommended. Part D follows this with guidance on the constituents of concrete required to achieve the identified DC Class. Specification is shown as maximum free-water/cem
40、ent ratio, minimum cement content and type of cement. Part E gives recommendations for specifying surface- carbonated precast concrete for general use in the ground. An essential requirement for compliance with this part is that surface carbonation is assured by exposure of the precast concrete to a
41、ir for a minimum of 10 days after curing. Since such carbonation provides a degree of resistance to sulfate attack, the recommendations for the derivation of DC Class in respect of sulfates is relaxed by one level. Other than this, the recommendations of Part D are followed for concrete specificatio
42、n. Part F includes design guides for specification of specific precast concrete products, including pipeline systems, box culverts, and segmental linings for tunnels and shafts. These products are manufactured under rigorous quality control to ensure appropriate mix composition and achieve relativel
43、y low concrete permeability. Together these provide an inherently high quality in respect of chemical resistance. Consequently, a further relaxation (beyond that allowed for surface carbonation) is permitted in respect of specification of DC Class for aggressive sulfate conditions. In practice this
44、relaxation is used to offset the general-use recommendation that a higher DC Class should be specified where concrete is of thin cross-section, or will encounter a relatively high hydraulic gradient. Part F also covers specification of precast concrete masonry units (concrete blocks) for aggressive
45、ground conditions. The guidance is based on Design Sulfate Class rather than ACEC Class as there is currently no correlation of block performance with the latter, though work on this is ongoing. A glossary of terms is included as Appendix A1 on page 6. A2.4 Diagrammatic overview of ground assessment
46、 and concrete specification An overview of the various procedures for ground assessment and specification of concrete is given in Figure A2. This is arranged in four stages according to the construction sector that has key responsibility. Within each of these stages, the principal tasks are shown in
47、 boxes with references to the relevant sections of SD1. While most steps are equally applicable to all uses of concrete, there is a 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. 2Part A Introducti
48、on3 Consider design options for building or structure and prepare specification for site investigation. Inform geotechnical specialist of design concept and site investigation requirements Carry out site investigation to determine chemical conditions for concrete, including water mobility. See Part
49、C Determine DS Class and ACEC Class for site locations using Tables C1 and C2. See Section C5 Determine the intended working life of proposed building or structure, and the form and use of specific concrete elements. See Section D7 General use of cast-in-situ concrete Find specification of concrete and APM using procedure in Part D: determine the DC Class and any APM from Table D1 adjust DC Class / APM for section thickness and hydraulic gradient determine options for APM from Table D4 General use of surface- carbon