BRE Digest 1 Concrete in aggressive ground. 3rd Edition, 2005

70 Pages·2016·14.71 MB·English

by  BRE Construction Division

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

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.