concrete repair

CONCRETE REPAIR ANDPROTECTION

J. Endawati

Intended Learning Outcomes

Bagaimanamemperbaiki beton?

Apakah metodeperbaikan beton yang umum dilakukan?

Bagaimanamenentukan metodeperbaikan yang akandipergunakan?

Concrete Repair

Proses ini lebih sophisticated dibandingkan membuatstruktur baru dan memerlukan keterlibatanspecialized Engineer untuk menentukan prosedurperbaikan yang sesuai.

Concrete Repair

Untuk dapat melakukan perbaikan yang tepat, mekanisme kerusakan perlu diselidiki sertadimengerti.

Engineer kemudian merencanakan strategiperbaikan yang tepat.

Tujuan Perbaikan Beton

A) Memperbaiki komponen beton yang rusaksehingga mempunyai kemampuan seperti awalrencana

B) Penyesuaian komponen beton yang sudah lama dengan kondisi peruntukan/layan yang baru = perubahan disain

Diagram AlirPerencanaan Retrofitting

Mulai

Penyelidikanawal

Analisis,evaluasi

Tidak CukupAmanatautidakperludiretrofitRetrofitting

Analisis

Mulai

MenentukanPemilihanMetodeKonstruksi

PersyaratanPemilik,Pemberitugas

StudiKelayakanKonstruksi

KembangkankembaliPenyelidikanawal

EksperimenPenyelidikan

PerhitunganPerencanaan

DetailKonstruksi

UjiLaboratrium,PenyelidikanLapangan

Ya

Tidak

TujuanTercapaiTidak

YaGambar,spesifikasi

Selesai

PelaksanaanPerbaikan

evaluasi

PerencanaanRetrofit

AnatomiPerbaikanBeton

IswantoNotemengelupas sampai tulangan

IswantoNotemempersiapkan elemen tersebutseblum diperbaikidikelupas sampaidibawah tulangan,dibersihkan dengan kompresor, atau blasting

Strategi Perbaikan

Pemilihan material Pemilihan metode

perbaikan Support Design Safety Precaution Costs / biaya Logistik

Proses

Tulangan Pemotongan Pembersihan Perbaikan Proteksi

Persiapan PermukaanBeton Bonding Apply new material

Ketentuan Performansi HasilPerbaikan Beton

Perlindungan terhadap tulangan Estetika Integritas dan kompatibilitas Beban yang dapat didukung Kedap air

Kriteria Pemilihan Sistem Perbaikan

Stabilitas elemen Biaya Gangguan terhadap pengguna Kondisi beton existing Kondisi sekitar Kesesuaian antara material yang diperbaiki dengan

substrate

Tahapan Perbaikan Beton

1) Persiapan permukaan beton2) Aplikasi sistem perbaikan yang sesuai3) After-Treatment

Persiapan Sebelum PekerjaanPerbaikan

Persiapan permukaan beton

Cleaning of reinforcement Coating reinforcement Bond Coat

Persiapan Permukaan Beton

Tujuan : Menyediakan permukaan beton yang kuat, bebas

dari bahan-bahan yang membahayakan


Permukaan beton yang akan diperbaiki harusbebas dari beton yang terlepas, lemah, retak atauyang rusak. Permukaan baja dengan deposit karat harus dibersihkan. Permukaan karat dalam batasnormal tidak memerlukan pembersihan lebihdahulu.


Techniques for surface treatment of concrete:- Mechanical- Thermal- Other methods (chemical, ...)


Cara Mekanis- Chipping: Jackhammer, hammer and chisel- Hammering: Needle gun, hammering machine- Milling: Miller- Grinding: Grinder- Brushing: Wire brushing, brushing machine- Shotblasting: Shotblasting machine- Free blasting: Gritblasting, sandblasting- Vacu-blasting: Gritblasting with suction unit attached


Mechanical Techniques for surface treatment of concrete:- Water-abrasive blasting: Water-grit/sand

blasting- Pressure water blasting: < 40 MPa- High pressure water blasting: 40 120 MPa- Ultra high pressure water blast.: 150 300 MPa- Water-vacu blasting: Water blasting with suction

unit attached usually for ultra high pressure units


Grinding


Shotblasting


Ultra high pressure water blasting


Cara Thermal :- Flame Treatment: Hand torch, Machine

driven torch- Cold blasting: Dry ice blasting, Liquid CO2-

blasting

Preparation of Concrete Surface

Marking out, Hack back to 10-20mm behind re-bars, ensure concrete cover

Saw cut the edge, Brush/grind the re-bar Prime coat for re-bar, bond coat for substrate Batching of repair mortar and apply.Dowel bars: Holes drilled with rotary-percussive drills to provide keys Air blown by pneumatic device Required length of insertion Give it a 1/2 turn and then turn back to original position Give 2 hrs initial set off time

Repair Systems/Treatment

Sistem perbaikan yang dipilih tergantung padapenutup beton yang dapat dicapai dan ketentuanperbaikan beton yang akan diperbaiki.

Concrete Repair Methods

Buildings Department (1998) lists the following common repair techniques for concrete:

Patch Repair Recasting/Partial Recasting Sprayed Concrete Micro-concrete Pre-packed concrete Non-shrinkage grout Sealing system Protective Coating

Traditional Repair Methods

Patch Repair Cementitious mortars Resin-based mortars

Recasting/Partial Recasting Sprayed Concrete

Dry process spray Wet process spray

1. Patch Repair

Sesuai untuk perbaikan beton dengan volume kecil. Bagian yang rusak harus dihilangkan dandiperbaiki dengan mortar untuk perbaikan yang sesuaiPada umumnya, terdapat dua macam repair mortar yang dapat dipakai untuk memperbaiki beton :

Cementitious mortars Resin-based mortars

1. Patch Repair

1. Patch Repair (Contd)

Mailvaganam and Taylor (1994) prefers resin based mortars. It isone-tenth of concrete.

The coefficient of thermal expansion is five times more than that of concrete. It has the strongest compressive strength than the other type of cementitious based mortars. Recently, polymer is added into the mortar in order to increase their strength. However, there are some limitations in polymer repair materials e.g. it may cause delamination or blistering when applied on the dampedareas; and It is not recommended to be applied in areas where fire resistance is required. It has poor fire resisting property and it has thermal incompatibility with substrate concrete

Properties of typical concrete repairmaterials (Mays, G. and Wilkinson, W., 1987)

Types of Mortar

Types of Mortar (Contd)

Tests on Repair Mortar:

Compressive strength (28 days) 30-60 MPa Tensile strength (7 days) 2 MPa Mod of Elasticity (28 days) 15-25 kN/mm2 Bond Strength (7days) 2.0 MPa Shrinkage Cracking (7 days) Coutinho ring test Permeability Workability Chemical Analysis Open-up inspection: 1 / 25sm patch repair Pull-off test (bond coat adhesion strength): 1/ 50sm patch repair

Pass if 1/2 fracture in substrate or pull-off stress > 1/4 of the 7-daybond str Core a 75mm dia. Full thick of the repair with 7days age.

Bond Strength of Patch Repair tested by pull-off test Pull-off test on the

adhesion strength of thebond between the repairmortar and the substrateconcrete, aided by any bond coat

identify re-bar position Repair area shall have a

minimum age of 7 days Re-bar sensor to identify the

location of reinforcement bars

Core

A 75mm dia. Core containing the full thickness of the repair was produced

Detail of the core

Dummy

A suitable metal plate was glued to the cored hole and let it dry for one hour;

this attachment was pulled with increasing tensile force using a calibrated device until failure occurs.

Result 1

Criteria: fracture shall be at least half in the substrate concrete, unless the pull-off stress is not less than 1/4 (i.e. 0.5 MPa) of the minimum 7 days

bond strength of the repairmortar (2.0 MPa).

Result 1 Fracture at bond surface,bond strength = 27psi (0.9MPa) - PASS

Result 2

Half of the fracture at substrate, bond strength = 18psi (0.6 MPa) - PASS

Results 3 & 4

Result 3: less than half of the fracture at substrate, bond strength = 12psi (0.4MPa) FAIL

Result 4: fracture at surface material, bond strength = 9psi (0.3 MPa) - FAIL

2. Recasting

In this method, the damaged part of the structural element will be demolished, replace corroded reinforcement and recast it with same or even better grade concrete in order to restore its structural strength.

Considerations for practical uses

Pay attention to the discontinuity which causes any instability to the linked structural elements due to demolition.

Dowel bars and/or replacement steel bars should be placed on the cleaned reinforcement bars.

For recasting of slabs, evacuation may be required for flats above or below the element.

The joint between old and new concrete should be paid with special attention. Poor joints will result easy seepage of water and causes of

corrosion.

Shear key is required for large areas of recasting.

Pre-soaking of substrate is necessary

Avoid air trapping by thorough compaction of repair mortar.

Recasting by form and pump

Application ranges

When defective depth is ranges from 75mm to 100mm.

Also for vertical members e.g. wall and column.

When structural restoration is required.

Full Depth Recast

3. Sprayed Concrete

Sprayed concrete is a technique which is widelyused in high-volume concrete repair work.

The concrete mix will be sprayed with or without admixture or polymers to the defected areas under high air pressure. This process can be done by means of nozzle gun.

Dry Spray Concrete There are two different methods of spraying:

Dry process spraying Wet process spraying

Dry process spraying is the process which the mixture of damp sand and cement is passed through the delivery hose to the nozzle and the water is mixed at that time.

This process is often used for repair work. It is because of its fast application process and restoration of structural strength at an early stage. The performance characteristics of dry sprayed concrete are they have good density and high strength. It has very good bond to a suitable substrate. These advantages make it more variable than conventional concrete and wet process sprayed concrete.

(SCA, 1999)

Wet Spray Concrete

Wet process spraying means all the ingredients including water are mixed together before transporting to the site for repairing works.

It is not normally applied for building repairs since the size of equipment is much larger than that of dry process spraying.

Cracks prevention

Concrete surface must be reinforced with small-mesh small diameter reinforcement before carrying out sprayed concrete. This can prevent developments of cracks when the concrete shrinks.

Spray Concrete Considerations for practical uses The process should be in a continuous process. Concrete mixed should be complied with acceptable standard and quality. The operation should be carried by experienced nozzleman. Acceptance test should be carried out to test the skill of the nozzleman. The process should be held at right angle to and at one meter from the surface of

the repair areas. Min. spray concrete thickness should be considered before spraying process. Reference should be made to Code of Practice for Structural Use of Concrete. Good surface preparation should be done. Sufficient safety precautions must be taken.

Application ranges Large areas of repairs with thickness > 50mm In vacant flats and/or public areas, this can minimize the nuisance to peoples. Partial strength is to be restored.

Spray Concrete

Other Repair Methods

Micro-concrete

Pre-packed concrete Non-Shrinkage Grout Joint Sealing System

1. Micro-concrete By applying this method, the contaminated or damaged concrete are removed and

replaced by fluid micro-concrete. It is used to re-form desired concrete profiles. Usually, prescribed mixes are available in the market with shrinkage compensators to

control shrinkage in plastic and hardened states.

Considerations for practical uses It needs special design by the supplier and specialist advice is required. Formwork with leakproof is required. Pre-soaking of the formwork and substrate is required. Aggregates used should not be greater than 10mm. In order to improve workability, aggregates should be rounded in size. Good curing of the repair is essential.

Application ranges For use in area with limited working space or congested reinforcement For use in thin sections where the use of normal concrete is impractical

1. Micro-concrete

After Treatment

All cement based repair systems require after treatment by means of keeping the surface moist for a certain time after application.

If after treatment is not carried out properly this can jeopardise the success of the repair.

Crack repairs

Structural crack repair

Sealing crack repair Re-bonding of delaminated concrete

Crack repairs (structural)

Structural crack repair

Injection with Epoxy Systems (EP) or

Injection with Microcement (CEM)

Crack repairs (sealing)

Sealing crack repair Injection with

Polyurethane Systems (PUR) or

Injection with Acrylic Systems (AY)

Crack repairs (sealing)

Crack repairs (re-bonding)

Re-bonding of delaminated concrete

Stitch pinning with Epoxy Systems (EP)

Structural Strengthening

A) Repair Insufficient reinforcement Corrosion of reinforcement Structural/fire damage

B) Adjustment to changing service conditions Excessive deflections Change in use Seismic upgrade Design mistakes


Composite strengthening systems Carbon fiber reinforced polymers (CFRP)

Plates Fabrics

Glass fiber reinforced polymers (GFRP) Fabrics

Pre-stressed systems


Provides secondary reinforcement Ensures failure mode remains ductile Enhance ductility, axial, flexural and shear strength Limit crack width


Sika CarboDur System


Pre-stressed systems

Cathodic Protection

Special method to repair concrete structureswith chlorid contamination

Cathodic Protection

Cathodic Protection

Maxit CarboCathSystem

concrete repair

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