ISO 5091-2:2023

INTERNATIONAL ISO
STANDARD 5091‐2
First edition
2023-07
Structural intervention of
existing concrete structures using
cementitious materials —
Part 2:
Top‐surface overlaying
Intervention structurelle sur les structures en béton existantes
utilisant des matériaux cimentaires —
Partie 2: Recouvrement de la surface supérieure
Reference number
ISO 5091‐2:2023(E)
© 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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 5091‐2:2023(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 . 2
4.2.1 Investigation using documents, records . 2
4.2.2 On-site investigation . 3
5 Intervention design. 3
5.1 General . 3
5.2 Structural plan . 3
5.3 Structural details . 3
6 Materials . 4
6.1 General . 4
6.2 Materials in existing structure . 4
6.3 Materials used in repairing or strengthening parts . 5
6.3.1 Cementitious materials . 5
6.3.2 Reinforcing materials . 5
6.3.3 Bonding products . 5
6.3.4 Waterproof materials . 5
6.3.5 Pavement materials . 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 . 7
8.2.1 General . 7
8.2.2 Modelling of structure. 7
8.2.3 Structural analysis . 7
8.2.4 Calculation of response values . 7
8.3 Durability verification . 7
8.3.1 General . 7
8.3.2 Verification related to steel corrosion . 7
8.4 Safety verification . 7
8.4.1 General . 7
8.4.2 Verification related to failure . 7
8.4.3 Verification related to fatigue failure . 8
8.5 Serviceability verification . 9
8.5.1 General . 9
8.5.2 Stress level limit . 9
8.5.3 Verification related to appearance . 9
8.6 Restorability verification . 9
iii
ISO 5091‐2:2023(E)
8.6.1 General . 9
8.7 Structural details . 9
8.7.1 Thickness of top-surface overlaying parts . 9
8.7.2 Cover . 10
8.7.3 Placement of reinforcing materials. 10
8.7.4 Joints for reinforcing materials . 10
8.7.5 Structural details related to seismic performance . 10
9 Construction .11
9.1 General . 11
9.2 Prior investigation and construction plan. 11
9.3 Mix proportion of cementitious materials . 11
9.4 Preparation .12
9.5 Surface treatment . 12
9.6 Assembly of reinforcing materials . 13
9.7 Manufacture of cementitious materials . 13
9.8 Transportation, placement, compaction and finish . 13
9.9 Curing .13
9.10 Pavement . 13
9.11 Quality control . 14
9.12 Inspection . 14
10 Records . .14
11 Maintenance .14
Annex A (informative) Examples of design and execution .15
Bibliography .18
iv
ISO 5091‐2:2023(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.
v
ISO 5091‐2:2023(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.
ISO 5091-2 describes a specific method of verifying the performance of a structure repaired or
strengthened by means of top-surface overlaying based on the currently available latest technologies.
Note, however, that the verification method described herein does not cover all kinds of verification.
For necessary information, reference need to be made to the relevant standard specifications and other
documents.
Given that members subject to intervention are mostly decks, the standard methods described herein
are considered the latest information on design and construction of top-surface overlaying using
fibre-reinforced concrete on overlaying parts. As technology advances, new materials and design and
construction methods are developed and methods for evaluating the post-intervention structural
performance with sufficient accuracy are established, making it possible to apply top-surface overlaying
for intervention parts and members other than decks, use materials other than fibre-reinforced
concrete, employ interface treatment methods other than cutting, cleaning and adhesive, etc., it is not
necessarily required to adhere to what is set forth in ISO 5091.
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 ISO 5091 series,
needs to be provided in each application case with consideration of the provisions of ISO 5091 series.
vi
INTERNATIONAL STANDARD ISO 5091‐2:2023(E)
Structural intervention of existing concrete structures
using cementitious materials —
Part 2:
Top‐surface overlaying
1 Scope
This document specifies the standards for design and construction using the top-surface overlaying
method, which increases the thickness of existing concrete members by integrating cementitious
materials onto the top surface of the members so as to improve the safety, serviceability, durability and
other properties of a concrete structure.
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 16311-3, Maintenance and repair of concrete structures — Part 3: Design of repairs and prevention
ISO 16311-4, Maintenance and repair of concrete structures — Part 4: Execution of repairs and prevention
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/
ISO 5091‐2:2023(E)
3.1
top‐surface overlaying
method in which the thickness of the structural element associated with the top surface of the existing
concrete members 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, 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
very high early strength cement
type of cement with a typical mix proportion that develops a compressive strength as high as 20 N/
2 2
mm to 30 N/mm within 2 h to 3 h of placement
3.6
reinforcing material
steel or FRP material used to sustain, restore or improve the mechanical performance of a structure
3.7
polymer hydraulic cement mortar
hydraulic composition made cementitious materials and fine aggregate modified by the addition of a
polymer
3.8
overlaying material
cementitious material, potentially reinforced, added on the top surface of an existing concrete structure
for the purpose of making an intervention to enhance the performance of that structure
3.9
FRP grid
resin-impregnated FRP reinforcing materials formed into a grid shape
4 Investigation of existing structure
4.1 General
The investigation of the existing structure for intervention using the top-surface overlaying method
shall be as set forth in ISO 5091-1:2023, Clause 4.
4.2 Investigation
4.2.1 Investigation using documents, records
The investigation of the existing structure using documents, records, etc. for top-surface overlaying
shall be as set forth in ISO 5091-1:2023, Clause 4.
ISO 5091‐2:2023(E)
If the intervention has already been performed, maintenance records need to be inspected.
4.2.2 On‐site investigation
The on-site investigation for considering the application of top-surface overlaying shall be as set forth
in ISO 5091-1:2023, Clause 4.
To ensure smooth construction work with top-surface overlaying on the site, the storage space and
arrangement of construction machines and materials, traffic restrictions and so forth should be
checked in the prior investigation phase.
5 Intervention design
5.1 General
The intervention plan for considering the application of top-surface overlaying shall be as set forth in
ISO 5091-1:2023, Clause 5.
The structural plan for degraded part removal, patching repair, concrete replacement, etc. shall be
formulated based on the correct judgment of the degradation status to ensure that the performance
level and design service life of the structure required from the intervention are achieved.
In structural details, a bonding method shall be established that ensures the integrity between the
existing parts and overlaying parts so that the intervention effect of top-surface overlaying is obtained.
5.2 Structural plan
The structural plan for considering the application of top-surface overlaying shall be as set forth in
ISO 5091-1:2023, Clause 5.
In designing intervention work, appropriate decisions shall be made on the method to remove degraded
concrete, the materials and method for patching repair, whether partial concrete replacement is
necessary and the range of replacement, the construction method of top-surface overlaying, etc. before
starting construction with top-surface overlaying, considering these circumstances. Materials for
patching repair for the top surface of decks are required to shrink little, be excellent in crack resistance
and deformation-following capability and Young's modulus equal to or smaller than that of the existing
concrete.
The intrusion of water into the inside of decks needs to be completely prevented and it is important to
apply waterproofing and ensure water drainage on the waterproof top surface. In order to ensure that
the repaired or strengthened structure sustains its performance as mentioned above, it is necessary to
take measures to prevent re-degradation while taking into consideration the maintenance following
completion of intervention as well.
5.3 Structural details
The structural details for considering the application of top-surface overlaying shall be as set forth in
ISO 5091-1:2023, Clause 5. An increase in the self-weight due to the overlay shall also be considered
appropriately.
For a structure repaired or strengthened with top-surface overlaying to fulfil the required performance,
the existing parts and overlaying parts need to function together as a composite structure. Figure 1
shows examples of the cross-section of decks to which top-surface overlaying is applied.
If the stiffness of the existing part is vastly different from that of the overlaying part, the strength,
Young's modulus and other properties of the existing concrete and overlaying materials need to be
considered.
ISO 5091‐2:2023(E)
Key
1 existing asphalt pavement
2 existing RC deck
3 asphalt pavement
4 overlaying concrete
5 water resistant layer
6 reinforcing steel
7 reinforcing FRP grid
8 overlaying concrete (concrete pavement)
a
Before overlaying.
b
After overlaying.
c
Top-surface overlaying with asphalt pavement.
d
Steel-reinforced top-surface overlaying with asphalt pavement.
e
FRP grid reinforced top-surface overlaying with asphalt pavement.
f
Top surface overlaying.
Figure 1 — Examples of the cross‐section of decks to which top‐surface overlaying is applied
6 Materials
6.1 General
The materials used for top-surface overlaying 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 and design values of the materials in the existing structure shall be as set
forth in ISO 5091-1:2023, Clause 6.
ISO 5091‐2:2023(E)
When setting the material properties of the existing structure based on documents, records, etc.
according to ISO 16311-2, the partial safety factor for materials should be determined taking into
consideration the impact of degradation. On the other hand, when the functionality of the existing
structure is restored using patching repair materials or the like prior to top-surface overlaying, the
material properties of the repair materials should be considered appropriately according to their
impact.
6.3 Materials used in repairing or strengthening parts
6.3.1 Cementitious materials
The cementitious materials used for top-surface overlaying shall be as set forth in ISO 5091-1:2023,
4.3.2. Water, cement, aggregate, fibre, mineral admixture and chemical admixture, polymeric resins
mixed with cement and others used for the cementitious materials shall be those compliant with the
relevant standards or those proven to have the required levels of quality based on existing test results
or through confirmation tests.
If shrinkage cracking of cementitious materials presents a problem, an expansive additive, which
expands upon setting and hardening may be used as a mineral admixture. When very high early
strength cement is combined with an expansive additive, the skeleton of the cement hardened body
is formed early and, therefore, there are cases in which an expansive additive generates expansive
hydration early is used.
It is necessary to use an appropriate material according to the required performance.
6.3.2 Reinforcing materials
The reinforcing materials used for top-surface overlaying shall be as set forth in ISO 5091-1:2023,
Clause 6. In top-surface overlaying for decks, grid-shaped steel and FRP reinforcing materials may be
used as reinforcements in addition to reinforcing steel.
6.3.3 Bonding products
The bonding products used for top-surface overlaying shall be as set forth in ISO 5091-1:2023, Clause 6.
In top-surface overlaying for decks, adhesive may be used on the placement interface to achieve
integrity between cementitious materials and existing decks.
6.3.4 Waterproof materials
The waterproof material to be used for top-surface overlaying shall be selected so as to fulfil the
required performance, taking into consideration the construction conditions and environment,
variations in quality, etc.
6.3.5 Pavement materials
With regard to the pavement material to be placed after top-surface overlaying for highway bridge
decks, its performance of bonding with the waterproof material shall be taken into consideration.
If the bonding between the pavement material and waterproof material is insufficient, it is possible that
the required waterproof performance will not be obtained.
ISO 5091‐2:2023(E)
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 top-surface overlaying shall be as
set forth in ISO 5091-1:2023, Clause 6.
6.4.2 Cementitious materials
The characteristic values and design values of the cementitious materials used for top-surface
overlaying shall be as set forth in ISO 5091-1:2023, Clause 6.
6.4.3 Reinforcing materials
The characteristic values and design values of the reinforcing materials used for top-surface overlaying
shall be as set forth in ISO 5091-1:2023, Clause 6.
6.4.4 Bonding products
A bonding product that ensures the integrity between the existing and overlaying parts for a necessary
period shall be selected and used appropriately based on a full understanding of its properties.
The bonding product is required to have material properties that ensure the overlaying parts are
bonded throughout the design service life. It is therefore necessary to check through appropriate testing
that the integrity between the existing and overlaying parts can be achieved with the bonding product.
The placement interface of the actual structure is likely to be in a complex stress status because of
loads, surrounding environmental actions, condition of the existing structure, etc. Also, there can be
combined actions of degradation factors. In the evaluation, the performance of the bonding product
should be checked by means of a technique whereby the influence of these factors can be taken into
consideration appropriately.
7 Actions
7.1 General
The actions used for performance verification of the intervention method using top-surface overlaying
shall be as set forth in ISO 5091-1:2023, Clause 7.
7.2 Actions for intervention design
The actions for intervention design that are used for performance verification of the intervention
method using top-surface overlaying shall be as set forth in ISO 5091-1:2023, Clause 7.
8 Performance verification for repaired or strengthened structure
8.1 General
The performance of a structure repaired or strengthened with top-surface overlaying shall be verified
by means of the method specified in this clause.
ISO 5091‐2:2023(E)
8.2 Calculation of response
8.2.1 General
The response values of a structure repaired or strengthened with top-surface overlaying shall be
calculated as set forth in ISO 5091-1:2023, Clause 8.
8.2.2 Modelling of structure
A structure repaired or strengthened with top-surface overlaying shall be modelled as set forth in
ISO 5091-1:2023, Clause 8.
8.2.3 Structural analysis
The structural analysis of a structure repaired or strengthened with top-surface overlaying shall be
performed as set forth in ISO 5091-1:2023, Clause 8.
8.2.4 Calculation of response values
The response values of a structure repaired or strengthened with top-surface overlaying shall be
calculated as set forth in ISO 5091-1:2023, Clause 8.
8.3 Durability verification
8.3.1 General
The durability of a structure repaired or strengthened with top-surface overlaying shall be verified as
set forth in ISO 5091-1:2023, Clause 8.
8.3.2 Verification related to steel corrosion
When a structure repaired or strengthened with top-surface overlaying is verified to check for steel
corrosion due to salt attack, an appropriate value of chloride ion concentration on the concrete surface
shall be established if salt attack due to de-icing substance has an impact as an environmental action.
8.4 Safety verification
8.4.1 General
The safety of a structure repaired or strengthened with top-surface overlaying shall be verified as set
forth in ISO 5091-1:2023, Clause 8.
8.4.2 Verification related to failure
8.4.2.1 General
The verification of failure shall be performed in accordance with ISO 5091-1:2023, 6.4, while the
verification method specific to top-surface overlaying shall be as set forth in Clause 8.
8.4.2.2 Verification related to bending moment and axial force
The verification related to bending moment and axial force shall be performed as set forth in
ISO 5091-1:2023, Clause 8.
When the flexural load-carrying capacity of repaired or strengthened concrete members is calculated,
it is assumed that the existing members and overlaying members behave as one without peeling away
ISO 5091‐2:2023(E)
from each other. Therefore, when the overlaying parts to be bent are located in the tension zone, the
tension-side concrete shall be ignored.
When the existing parts are located in the compression zone, the flexural load-carrying capacity
needs to be calculated using the design strength of the existing concrete. When the overlaying parts
are located in the compression zone, the strength and Young’s modulus of the overlaying parts do not
match those of the existing concrete and, therefore, it is desirable to calculate the flexural load-carrying
capacity using the design strength of the cementitious materials of the overlaying parts obtained in
accordance with 6.4.
8.4.2.3 Verification related to shear force
The safety verification related to shear force shall be performed as set forth in ISO 5091-1:2023,
Clause 8. This verification assumes that the existing members and overlaying members are integrated.
The design shear capacity of beams shall be as set forth in ISO 16311-3, appropriately taking into
consideration the effect of reinforcing materials used in top-surface overlaying. When the loaded
surface is separated from the free end or the opening of the member and the eccentricity of the load
is small, the punching shear capacity shall be as set forth in ISO 16311-3, appropriately taking into
consideration the effect of reinforcing materials used in top-surface overlaying. Calculation example is
shown in Annex A.
When there is shear reinforcement in the existing members, the design shear capacity V should be
yd
expressed as the sum of the contribution of the shear reinforcement V and V in accordance with
sd cd
ISO 16311-3.
If the strength level considerably differs between the existing parts and overlaying parts, the
verification needs to be performed carefully by making checks through experiments or by other means.
8.4.2.4 Verification related to torsional moment
If the action of the torsional moment is not negligible, a safety verification shall be performed by means
of an appropriate method in accordance with ISO 16311-3. However, there is almost no research on
the behaviour of torsional moment of members repaired or strengthened with top-surface overlaying,
performance should be checked through appropriate experiments.
8.4.3 Verification related to fatigue failure
8.4.3.1 Verification related to flexural fatigue capacity
It shall be verified that the members repaired or strengthened with top-surface overlaying are safe
against flexural fatigue under load and environmental actions. The fatigue strength of concrete and
steel may be calculated in accordance with ISO 16311-3. It is desirable to perform a flexural fatigue
verification for the overlaying parts on an as-needed basis in such cases as when negative bending
moment acts on top-surface overlaying decks.
If no data is available about the fatigue strength of the cementitious materials used for top-surface
overlaying, the flexural fatigue capacity needs to be calculated by means of an appropriate method
such as experiments, an experiment-based evaluation method or non-linear finite element analysis.
Since a fatigue test generally takes time, it is allowed to perform the verification using an S-N curve
created from existing research data. In that case, however, care shall be taken by assuming a life with
a survival probability of 95 %, defining the point of time when the progress of cracking suddenly
accelerates as the service limit life.
8.4.3.2 Verification related to punching shear fatigue capacity of slabs
It shall be verified that the surface members repaired or strengthened with top-surface overlaying are
safe against punching shear fatigue under load and environmental actions.
ISO 5091‐2:2023(E)
When the punching shear fatigue capacity of repaired or strengthened surface members is calculated,
it is assumed that the existing members and overlaying members behave as one without peeling away
from each other.
When top-surface overlaying is applied to bridge decks, the punching shear fatigue capacity is reduced
significantly as the decks are subject to the repeated action of moving wheel loads, compared to
the case where the load point is fixed. Therefore, the capacity needs to be estimated by means of an
appropriate method such as experiments, an experiment-based evaluation method or non-linear finite
element analysis. The estimation of fatigue life in a dry condition or in a water-filled condition is shown
in Annex A.
8.5 Serviceability verification
8.5.1 General
The serviceability of a structure repaired or strengthened with top-surface overlaying shall be verified
as set forth in ISO 5091-1:2023, Clause 8.
8.5.2 Stress level limit
The stress level limit of a structure repaired or strengthened with top-surface overlaying shall be as set
forth in ISO 5091-1:2023, Clause 8.
8.5.3 Verification related to appearance
The appearance verification of a structure repaired or strengthened with top-surface overlaying shall
use the crack width as the verification and check that the calculated response values resulting from
load and environmental actions satisfy the designated limit values determined from serviceability in
accordance with ISO 5091-1:2023, Clause 8.
The flexural crack width of members repaired or strengthened with top-surface overlaying shall
be calculated, using the stress level calculated for the composite section formed as the existing and
overlaying parts are integrated, according to ISO 16311-3. Since there is little knowledge, the crack
width should be checked through appropriate experiments.
8.6 Restorability verification
8.6.1 General
The restorability of a structure repaired or strengthened with top-surface overlaying shall be verified
as set forth in ISO 5091-1:2023, 6.6.
When top-surface overlaying is applied to decks, it is necessary to ensure the functionality required
after an earthquake and check that the structure can prevent the falling of the superstructure.
8.7 Structural details
8.7.1 Thickness of top‐surface overlaying parts
The top-surface overlaying parts shall have a sufficient covering thickness to achieve the specified
durability within a range that ensures the necessary intervention effect and constructability.
The thickness of overlaying cementitious materials shall be determined, taking into consideration the
maximum size of coarse aggregate and construction accuracy, in order to ensure constructability and
integrity with the existing members. Also, the overlaying parts shall have a covering thickness that
takes into consideration drying shrinkage and intrusion of degradation factors such as chloride ions.
ISO 5091‐2:2023(E)
If the overlaying member thickness is thinner than 50 mm, concrete or mortar with coarse aggregate
whose maximum size is 13 mm can be used. In such a case, the use of admixture should be considered
to improve the bonding property and following-deformation capability of polymer and other materials.
When reinforcing steel is used for the overlaying parts, the design thickness of the overlaying parts
shall be 100 mm in principle, combining the space between the existing concrete and reinforcing st
...