ISO 5091-3:2023

Structural intervention of existing concrete structures using cementitious materials — Part 3: Bottom-surface (soffit) underlaying

This document specifies the standards for design and construction using the bottom-surface (soffit) underlaying method. Bottom-surface (soffit) underlaying is a method whereby reinforcing materials are placed on the bottom surface of the slabs or beams whose performance is lower than required and the improvement of durability, serviceability, safety and other performance of the members is achieved by the integrity between the reinforcing materials and existing members. This document specifies structural intervention of existing concrete structures using cementitious materials design and execution principles, and strategies for defects and on-going deterioration including, but not limited to: a) mechanical actions, e.g. fatigue, impact, overloading, movement caused by settlement, blast, vibration, and seismic actions; b) chemical and biological actions from environments, e.g. sulfate attack, alkali-aggregate reaction; c) physical actions, e.g. freeze–thaw, thermal cracking, moisture movement, salt crystallization, fire, and erosion; d) reinforcement corrosion; e) original construction defects that remained unaddressed from the time of construction.

Intervention structurelle sur les structures en béton existantes utilisant des matériaux cimentaires — Partie 3: Recouvrement de la surface inférieure (soffite)

General Information

• Status: Published
• Publication Date: 20-Jul-2023
• ICS: 91.080.40 - Concrete structures
• Technical Committee: ISO/TC 71/SC 7 - Maintenance and repair of concrete structures
• Drafting Committee: ISO/TC 71/SC 7 - Maintenance and repair of concrete structures
• Current Stage: 6060 - International Standard published
• Start Date: 21-Jul-2023
• Due Date: 18-Jun-2023
• Completion Date: 21-Jul-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 5091-3
First edition
2023-07
Structural intervention of
existing concrete structures using
cementitious materials —
Part 3:
Bottom-surface (soffit) underlaying
Intervention structurelle sur les structures en béton existantes
utilisant des matériaux cimentaires —
Partie 3: Recouvrement de la surface inférieure (soffite)
Reference number
ISO 5091-3:2023(E)
© ISO 2023

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ISO 5091-3:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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ISO 5091-3:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Investigation of existing structure.2
4.1 General . 2
4.2 Investigation . 3
4.2.1 Investigation using documents, records . 3
4.2.2 On-site investigation . 3
5 Intervention design. 3
5.1 General . 3
5.2 Structural plan . 4
5.3 Structural details . 4
6 Materials . 4
6.1 General . 4
6.2 Materials in existing structure . 4
6.3 Materials used in repairing or strengthening parts . 4
6.3.1 General . 4
6.3.2 Cementitious materials . 4
6.3.3 Reinforcing materials . 5
6.3.4 Bonding products . 5
6.4 Characteristic values and design values of materials for repaired or strengthened
parts . 5
6.4.1 General . 5
6.4.2 Cementitious materials . 5
6.4.3 Reinforcing materials . 5
6.4.4 Bonding products . 5
7 Actions . 5
7.1 General . 5
7.2 Actions for intervention design . 5
8 Performance verification for repaired or strengthened structure .6
8.1 General . 6
8.2 Calculation of response values . 6
8.2.1 General . 6
8.2.2 Modelling of structure. 6
8.2.3 Structural analysis . 6
8.2.4 Calculation of design response values . 6
8.3 Durability verification . 8
8.4 Safety verification . 8
8.4.1 General . 8
8.4.2 Verification related to failure . 8
8.4.3 Verification related to fatigue failure . 8
8.5 Serviceability verification . 9
8.5.1 General . 9
8.5.2 Verification related to appearance . 9
8.5.3 Verification related to displacement and deformation . 9
8.6 Restorability verification . 9
8.7 Structural details . 9
8.7.1 Thickness of bottom-surface (soffit) underlaying parts. 9
8.7.2 Cover . 10
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ISO 5091-3:2023(E)
8.7.3 Space between reinforcing materials . 10
8.7.4 Joints for reinforcing materials . 10
8.7.5 Anchoring and securing methods of reinforcing materials . 10
9 Construction .10
9.1 General . 10
9.2 Prior investigation and construction plan. 10
9.3 Surface treatment . 11
9.4 Assembly of reinforcing materials .12
9.5 Surface preparation . 12
9.6 Storage, mixing and transportation of underlaying materials .12
9.7 Execution of underlaying .13
9.8 Curing .13
9.9 Quality control . 13
9.10 Inspection . 13
10 Records . .14
11 Maintenance .14
Annex A (informative) Examples of design and execution procedure .15
Bibliography .28
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ISO 5091-3:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-
stressed concrete, Subcommittee SC 7, Maintenance and repair of concrete structures.
A list of all parts in the ISO 5091 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 5091-3:2023(E)
Introduction
As a repairing and strengthening method, attaching of cementitious material layer to surface of existing
concrete structures has been widely accepted. Since the cementitious layer does not have enough tensile
strength, tension reinforcement is generally placed in the cementitious layer. There are two types of
attaching way. For the first way, the cementitious layer is attached either on top surface or bottom
surface of horizontal concrete members, especially slabs, while, for the second way, the cementitious
layer is attached to jacket vertical concrete members, especially columns. There has not been any ISO
standard on design, execution, and maintenance for this method with attaching cementitious layer. The
ISO 5091 series serves as the first ISO standard for the intervention by attaching cementitious material
layer with tension reinforcement inside.
At the same time, the ISO 5091 series is the first ISO standard developed for a specific intervention
method, which conforms to the umbrella code, ISO 16311, especially ISO 16311-3 and ISO 16311-4.
The ISO 5091 series consists of four parts. ISO 5091-1 provides the issues common to all three parts,
while ISO 5091-2, 3 and 4 provide the issues specific to each attaching way of cementitious material
layers.
Generally, polymer hydraulic cement mortar (PCM) is used as the underlaying material. This is because
PCM bonds well with the existing members and has large tensile strain at cracking, and makes the
penetration of degradation factors less likely. As reinforcing materials, reinforcing steel, welded wire
mesh, FRP grid are used.
Bottom-surface (soffit) underlaying has evolved as a strengthening method for fatigue of RC decks.
drawing attention because of examples of applications like the one shown in Figure 1. The members that
are currently repaired or strengthened using this method include RC decks, tunnel linings, box culverts,
waterways and beams. In this document, the latest information about the design and construction of
the bottom-surface (soffit) underlaying method using underlaying materials has been collected and the
best possible standards are presented.
The ISO 5091 series can serve as a practical standard for construction industry, such as client, design
consultant and general contractor, to apply the structural intervention with externally attached
cementitious layer. Additional technical information, which is not provided explicitly in the ISO 5091
series, needs to be provided in each application case with consideration of the provisions of the ISO 5091
series.
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INTERNATIONAL STANDARD ISO 5091-3:2023(E)
Structural intervention of existing concrete structures
using cementitious materials —
Part 3:
Bottom-surface (soffit) underlaying
1 Scope
This document specifies the standards for design and construction using the bottom-surface (soffit)
underlaying method. Bottom-surface (soffit) underlaying is a method whereby reinforcing materials
are placed on the bottom surface of the slabs or beams whose performance is lower than required and
the improvement of durability, serviceability, safety and other performance of the members is achieved
by the integrity between the reinforcing materials and existing members.
This document specifies structural intervention of existing concrete structures using cementitious
materials design and execution principles, and strategies for defects and on-going deterioration
including, but not limited to:
a) mechanical actions, e.g. fatigue, impact, overloading, movement caused by settlement, blast,
vibration, and seismic actions;
b) chemical and biological actions from environments, e.g. sulfate attack, alkali-aggregate reaction;
c) physical actions, e.g. freeze–thaw, thermal cracking, moisture movement, salt crystallization, fire,
and erosion;
d) reinforcement corrosion;
e) original construction defects that remained unaddressed from the time of construction.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5091-1:2023, Structural intervention of existing concrete structures using cementitious materials —
Part 1: General principles
ISO 22966, Execution of concrete structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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ISO 5091-3:2023(E)
3.1
bottom-surface (soffit) underlaying
method in which the thickness of the structural element associated with the bottom surface of the
existing concrete is increased using cementitious materials, which will generally be reinforced
Note 1 to entry: The technique enhances the performance (e.g. strength, stiffness) of the existing concrete
structure and is applicable to highway bridge decks, tunnel linings, box culverts/waterway structures, beams,
etc.
3.2
bonding product
material, such as a primer or adhesive, that is applied to bond concrete and mortar
Note 1 to entry: The grouting material for bonding concrete and reinforcing material is also included in this term.
3.3
filling material
material injected to fill the gap between a reinforcing material, such as intermediate penetrating tie,
and concrete
3.4
filling property
degree of filling of cracks and adhesion of crack filling material to substrate
3.5
reinforcing material
steel or FRP material used to sustain, restore or improve the mechanical performance of a structure
3.6
polymer hydraulic cement mortar
hydraulic composition made cementitious materials and fine aggregate modified by the addition of a
polymer
3.7
FRP grid
resin-impregnated FRP reinforcing materials formed into a grid shape
3.8
design response value
value of structural response obtained by numerical analysis on design process, such as sectional force
and deformation
3.9
design limit value
design value for quantified limit state on design process, such as strength of element, allowable crack
width
3.10
maintainability
ability of a structure to meet service objectives with a minimum expenditure of maintenance effort
under service conditions in which maintenance and repair are performed
4 Investigation of existing structure
4.1 General
The study of the existing structure for which to consider intervention using the bottom-surface (soffit)
underlaying method shall be as set forth in ISO 5091-1:2023, Clause 4.
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ISO 5091-3:2023(E)
4.2 Investigation
4.2.1 Investigation using documents, records
When the climatic conditions, environmental conditions and geographical conditions of the local
site are studied using documents, records, etc., the study shall be conducted in accordance with
ISO 5091-1:2023, 4.2.1.
4.2.2 On-site investigation
The on-site study on degradation, damage and initial defects of the existing concrete structure shall be
conducted in accordance with ISO 5091-1:2023, 4.2.2.
The work environment and other relevant conditions of the site shall be checked in advance.
5 Intervention design
5.1 General
When repairing or strengthening a concrete structure using bottom-surface (soffit) underlaying as
shown in Figure 1, it shall be verified by means of an appropriate method that the structure fulfils the
required performance for the required period. Also, the environment for the intervention construction,
constructability, post-intervention maintainability and economy shall be taken into consideration.
Key
1 pavement
2 RC deck
3 main girder
4 underlaying
5 distribution reinforcement
6 main reinforcement
7 bottom-surface (soffit) underlaying
Figure 1 — Example of application of bottom-surface (soffit) underlaying for deck
strengthening
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ISO 5091-3:2023(E)
5.2 Structural plan
The structural plan for a structure repaired or strengthened with bottom-surface (soffit) underlaying
shall be as set forth in ISO 5091-1:2023, 5.2. The repaired or strengthened structure shall fulfil the
required levels of durability, safety, serviceability and restorability throughout the design service life.
Also, the intervention shall be planned taking into consideration the causes of degradation and damage
of the existing members subject to bottom-surface (soffit) underlaying.
In flexural strengthening of existing members, the verification is mainly intended for serviceability,
safety, etc. In fatigue strengthening of bridge decks, the punching shear capacity of the decks is required
to be improved. In seismic strengthening of box culverts and tunnels, the verification is intended for
restorability.
5.3 Structural details
The structure of bottom-surface (soffit) underlaying shall ensure the integrity between the existing
and underlaying parts in the repaired or strengthened members to avoid brittle failure.
The structure of bottom-surface (soffit) underlaying shall ensure that reinforcing materials are
securely anchored to the existing parts to reduce the risk of peeling.
The structure of bottom-surface (soffit) underlaying shall prevent retention of water in the interface
between the existing and underlaying parts to avoid degradation of the interface or a decrease in
adhesion.
The reinforcing materials used for bottom-surface (soffit) underlaying shall have a certain level of
tensile stiffness that allows the reinforcing materials to behave with the existing parts as one. The
reinforcing materials used for bottom-surface (soffit) underlaying shall not have excessive tensile
stiffness against the existing parts.
If the tensile stiffness of the reinforcing materials is excessive, care shall be taken because the forces
transferred through the interface between the existing and underlaying parts as well as the anchoring
parts of the reinforcing materials become great, potentially leading to peeling or some other problem.
6 Materials
6.1 General
The materials used for bottom-surface (soffit) underlaying shall be of proven quality to ensure that the
required performance is fulfilled for a necessary period.
6.2 Materials in existing structure
The characteristic values of material strength, partial safety factor for materials and design values of
the materials in the existing structure that are used for the design shall be determined in accordance
with ISO 5091-1:2023, 6.2.
6.3 Materials used in repairing or strengthening parts
6.3.1 General
The quality of the materials used in the parts repaired or strengthened with bottom-surface (soffit)
underlaying shall be as set forth in ISO 5091-1:2023, 6.3.
6.3.2 Cementitious materials
The underlaying materials used for bottom-surface (soffit) underlaying shall have a bonding property
and durability sufficient to integrate the existing parts with added reinforcing materials.
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ISO 5091-3:2023(E)
Materials having Young's modulus and compressive strength that are the same as or similar to those of
the existing members are suitable.
The underlaying materials shall have performance equal to or greater than the resistance against
permeation of the existing members against environmental factors.
6.3.3 Reinforcing materials
Considering the performance requirements, reinforcing materials having appropriate tensile stiffness,
design tensile strength and durability shall be selected.
6.3.4 Bonding products
The bonding products used in the interface between the existing and underlaying parts shall ensure
the specified bonding property.
The bonding products shall prevent the degradation in the bonding property of the underlaying and
existing parts. The bonding products shall be those proven to be compatible with the materials used in
both the underlaying and existing parts and have sufficient durability.
6.4 Characteristic values and design values of materials for repaired or strengthened
parts
6.4.1 General
The characteristic values and design values of the materials used for bottom-surface (soffit) underlaying
shall be as set forth in ISO 5091-1:
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 5091-3
ISO/TC 71/SC 7 Secretariat: KATS
Voting begins on: Voting terminates on:
2022-07-19 2022-10-11
Structural intervention of existing concrete structures
using cementitious materials —
Part 3:
Bottom-surface (soffit) underlaying
ICS: 91.080.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 5091-3:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

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ISO/DIS 5091-3:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 5091-3
ISO/TC 71/SC 7 Secretariat: KATS
Voting begins on: Voting terminates on:

Structural intervention of existing concrete structures
using cementitious materials —
Part 3:
Bottom-surface (soffit) underlaying
ICS: 91.080.40
COPYRIGHT PROTECTED DOCUMENT
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2022
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
NOT BE REFERRED TO AS AN INTERNATIONAL
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on STANDARD UNTIL PUBLISHED AS SUCH.
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
IN ADDITION TO THEIR EVALUATION AS
or ISO’s member body in the country of the requester. BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
ISO copyright office
USER PURPOSES, DRAFT INTERNATIONAL
CP 401 • Ch. de Blandonnet 8
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
CH-1214 Vernier, Geneva
POTENTIAL TO BECOME STANDARDS TO
Phone: [phone]
WHICH REFERENCE MAY BE MADE IN
Reference number
Email: [e-mail]
NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 5091-3:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
Published in Switzerland
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
ii
  © ISO 2022 – All rights reserved
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

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ISO/DIS 5091-3:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
3.1 General . 2
4 Investigation of existing structure.2
4.1 General . 2
4.2 Investigation . 2
4.2.1 Investigation using documents, records, etc. . 2
4.2.2 On-site investigation . 3
5 Intervention design. 3
5.1 General . 3
5.2 Structural plan . 4
5.3 Structural details . 4
6 Materials . 4
6.1 General . 4
6.2 Materials in existing structure . 5
6.3 Materials used in repairing or strengthening parts . 5
6.3.1 General . 5
6.3.2 Cementitious materials . 5
6.3.3 Reinforcing materials . 5
6.3.4 Bonding products . 5
6.4 Characteristic values and design values of materials for repaired or strengthened
parts . 6
6.4.1 General . 6
6.4.2 Cementitious materials . 6
6.4.3 Reinforcing materials . 6
6.4.4 Bonding products . 6
7 Actions . 6
7.1 General . 6
7.2 Actions for intervention design . 6
8 Performance verification for repaired or strengthened structure .6
8.1 General . 6
8.2 Calculation of response values . 7
8.2.1 General . 7
8.2.2 Modeling of structure . 7
8.2.3 Structural analysis . 7
8.2.4 Calculation of design response values . 7
8.3 Durability verification . 11
8.4 Safety verification . 11
8.4.1 General . 11
8.4.2 Verification related to failure . 11
8.4.3 Verification related to fatigue failure . 18
8.5 Serviceability verification . 20
8.5.1 General .20
8.5.2 Verification related to appearance . 20
8.5.3 Verification related to displacement and deformation . 21
8.6 Restorability verification . 21
8.7 Structural details . 21
8.7.1 Thickness of bottom-surface (soffit) underlaying parts. 21
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ISO/DIS 5091-3:2022(E)
8.7.2 Cover . 21
8.7.3 Space between reinforcing materials . 22
8.7.4 Joints for reinforcing materials . 22
8.7.5 Anchoring and securing methods of reinforcing materials .22
9 Construction .22
9.1 General .22
9.2 Prior investigation and construction plan. 23
9.3 Surface treatment . 24
9.4 Assembly of reinforcing materials . 24
9.5 Surface preparation . 25
9.6 Storage, mixing and transportation of underlaying materials . 25
9.7 Execution of underlaying .25
9.8 Curing . 26
9.9 Quality control . 26
9.10 Inspection . 27
10 Records . .27
11 Maintenance .27
Annex A (informative) Examples of execution procedure .28
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ISO/DIS 5091-3:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organisation (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-
stressed concrete, Subcommittee SC 7, Maintenance and repair of concrete structures.
A list of all parts in the ISO 5091 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
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ISO/DIS 5091-3:2022(E)
Introduction
As a repairing and strengthening method, attaching of cementitious material layer to surface of
existing concrete structures has been widely accepted. Since the cementitious layer does not have
enough tensile strength, tension reinforcement is generally placed in the cementitious layer. There are
two types of attaching way. For the first way, the cementitious layer is attached either on top surface
or bottom surface of horizontal concrete members, especially slabs, while, for the second way, the
cementitious layer is attached to jacket vertical concrete members, especially columns. There has not
been ISO standard on design, execution and maintenance for this method with attaching cementitious
layer. This ISO 5091 serves as the first ISO standard for the intervention by attaching cementitious
material layer with tension reinforcement inside.
At the same time, this ISO 5091 is the first ISO standard developed for a specific intervention method,
which conforms to the umbrella code, ISO 16311 Maintenance and repair of concrete structures,
especially ISO 16311-3 – Part 3: Design of repairs and prevention and ISO 16311-4 – Part 4: Execution of
repairs and prevention.
ISO 5091 Structural intervention of existing concrete structures using cementitious materials consists
of four parts; ISO 5091-1 – Part 1: General principles, ISO 5091-2 – Part 2: Top-surface overlaying,
ISO 5091-3 – Part 3: Bottom-surface (soffit) underlaying, and ISO 5091-4 – Part 4: Jacketing. ISO 5091-1
provides the issues common to all three parts, while ISO 5091-2, 3 and 4 provide the issues specific to
each attaching way of cementitious material layers.
It is expected that this ISO 5091 could serve as a practical standard for construction industry, such as
client, design consultant and general contractor, to apply the structural intervention with externally
attached cementitious layer. Additional technical information, which is not provided explicitly in
ISO 5091, needs to be provided in each application case with consideration of the provisions of ISO 5091.
vi
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DRAFT INTERNATIONAL STANDARD ISO/DIS 5091-3:2022(E)
Structural intervention of existing concrete structures
using cementitious materials —
Part 3:
Bottom-surface (soffit) underlaying
1 Scope
These guidelines specify the standards for design and construction using the bottom-surface (soffit)
underlaying method. Bottom-surface (soffit) underlaying is a method whereby reinforcing materials
are placed on the bottom surface of the slabs or beams whose performance is lower than required and
the improvement of durability, serviceability, safety and other performance of the members is achieved
by the integrity between the reinforcing materials and existing members.
Generally, polymer hydraulic cement mortar (hereinafter PCM) is used as the underlaying material.
This is because PCM bonds well with the existing members and has large tensile strain at cracking, and
making the penetration of degradation factors less likely. As reinforcing materials, reinforcing steel,
welded wire mesh, FRP grid are used.
Bottom-surface (soffit) underlaying has evolved as a strengthening method for fatigue of RC decks,
drawing attention because of examples of applications like the one shown in Figure 1. The members
that are currently repaired or strengthened using this method include RC decks, tunnel linings, box
culverts, waterways and beams. In these guidelines, the latest information about the design and
construction of the bottom-surface (soffit) underlaying method using underlaying materials has been
collected and the best possible standards are presented. Matters not mentioned herein shall be as set
forth in ISO /NP 5091-1.
Figure 1 — Example of application of bottom-surface (soffit) underlaying for deck
strengthening
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ISO/DIS 5091-3:2022(E)
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 16311-1:2014, Maintenance and repair of concrete structures — Part 1: General principles
ISO 16311-2:2014, Maintenance and repair of concrete structures — Part 2: Assessment of existing concrete
structures
ISO 16311-3:2014, Maintenance and repair of concrete structures — Part 3: Design of repairs and
prevention
ISO 16311-4:2014, Maintenance and repair of concrete structures — Part 4: Execution of repairs and
prevention
ISO 22966:2009, Execution of concrete structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General
The definitions of the terms used in the Bottom-surface (soffit) underlaying section shall be as defined
in Clause 3 of ISO / NP 5091-1.
4 Investigation of existing structure
4.1 General
The study of the existing structure for which to consider intervention using the bottom-surface (soffit)
underlaying method shall be as set forth in Clause 4 of ISO /NP 5091-1.
4.2 Investigation
4.2.1 Investigation using documents, records, etc.
When the climatic conditions, environmental conditions and geographical conditions of the local site
are studied using documents, records, etc., the study shall be conducted in accordance with 4.2.1 of ISO
/NP 5091-1.
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4.2.2 On-site investigation
The on-site study on degradation, damage and initial defects of the existing concrete structure shall be
conducted in accordance with 4.2.2 of ISO /NP 5091-1.
NOTE It is necessary to check that the shape, size and other characteristics of the existing members subject
to bottom-surface (soffit) underlaying are consistent with the documents and records. In the investigation,
the steel materials of the existing members need to be checked in terms of size, arrangement, etc. through a
non-destructive inspection, chipping inspection or the like as necessary. Also, the degree of degradation and
the progress of damage of the existing members subject to bottom-surface (soffit) underlaying shall be grasped
through checking for changes in appearance (cracks, water leaks, efflorescence, rust staining flaking and peeling
of cover concrete, and exposed reinforcing bar, etc.), measurement of chloride-ion concentration, checking of the
carbonation depth, covering depth and degree of steel corrosion, etc. At the same time, the causes of degradation
and damage shall be presumed based on the surrounding environment (coastal lines, traffic conditions, climatic
conditions, etc.), the characteristics of damage, the flow of rainwater, water leaks, vibration generated when
heavy vehicles pass and so forth.
The work environment and other relevant conditions of the site shall be checked in advance.
NOTE It is necessary to check the status of the approach route for work vehicles, work machines, etc. as well
as whether the storage space and temporary structures such as scaffoldings can be set up.
5 Intervention design
5.1 General
When repairing or strengthening a concrete structure using bottom-surface (soffit) underlaying, it shall
be verified by means of an appropriate method that the structure fulfills the required performance
for the required period. Also, the environment for the intervention construction, constructability, post-
intervention maintainability and economy shall be taken into consideration.
NOTE Bottom-surface (soffit) underlaying is applied for purposes such as flexural strengthening and shear
strengthening of structural members by providing thin reinforcing underlaying layers. One feature of this method
is that the increase in weight due to intervention is small. When it is used for box culverts, tunnels, waterways,
etc., there is only a small reduction in the inner section. When structural members such as bridge decks are
repaired or strengthened using bottom-surface (soffit) underlaying, a verification related to the punching
shear failure of the decks needs to be performed. In the case of waterways or box culverts, it is necessary to
verify ordinary design loads such as earth pressure and water pressure. Even for tunnels and water channels,
a verification related to level 2 ground motions may be required. While the verification methods described in
these guidelines do not cover all kinds of verification, the currently available latest technologies are presented
herein.
NOTE An example of the construction section observed when bottom-surface (soffit) underlaying is applied
to bridge decks is shown in Annex.
NOTE Bottom-surface (soffit) underlaying requires that underlaying materials protect reinforcing materials
from corrosion as well. With the bottom-surface (soffit) underlaying method using PCM, the thickness of
underlaying parts is 30 mm or so in many cases. Therefore, underlaying materials can be applied to underlaying
parts by either spraying or trowelling. A rational method should be selected taking into consideration the
application environment and quantity.
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ISO/DIS 5091-3:2022(E)
5.2 Structural plan
The structural plan for a structure repaired or strengthened with bottom-surface (soffit) underlaying
shall be as set forth in 5.2 of ISO /NP 5091-1.
NOTE The repaired or strengthened structure shall fulfill the required levels of durability, safety,
serviceability and restorability throughout the design service life. The performance requirements differ
depending on the structure repaired or strengthened with bottom-surface (soffit) underlaying. In flexural
strengthening of existing members, the verification is mainly intended for serviceability, safety, etc. In fatigue
strengthening of bridge decks, the punching shear capacity of the decks is required to be improved. In seismic
strengthening of box culverts and tunnels, the verification is intended for restorability. Also, the intervention
shall be planned taking into consideration the causes of degradation and damage of the existing members subject
to bottom-surface (soffit) underlaying.
NOTE Since thin members are used as underlaying materials in bottom-surface (soffit) underlaying, the
covering of reinforcing materials becomes relatively thin. This makes it possible for degradation factors to
intrude more quickly in a severe corrosion environment. Therefore, durability verification is a key point in
maintenance and necessary measures shall be considered.
5.3 Structural details
The structure of bottom-surface (soffit) underlaying shall ensure the integrity between the existing
and underlaying parts in
...