Essential Steps in the IMPLEMENTATION AND MEASUREMENT OF CONCRETE - - PowerPoint PPT Presentation

Essential Steps in the IMPLEMENTATION AND MEASUREMENT OF CONCRETE REPAIR PROJECTS

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All structures built by man-kind age and degrade, as does the environment where the structures are built. Change is one of the constants that can be applied to the life of any structure.

High capital costs

• f demolition and reconstruction,

it makes sound economic sense to upgrade buildings and structures, rather than to knock them down.

Essential steps required to complete a concrete repair project. Importance of skill set, correct specification, measurement and itemization during the pre-tender documentation stage.

In recent decades; 60’s, 70’s, 80’s and 90’s; all around the world, concrete structures were built with inadequate attention to:

 Make it Safe  Restore Structural Competence  Extend The Service Life  Change of Use  Improve The Appearance

Corrosion of reinforcement The Main Culprits:

 Chloride Attack  Carbonation

 Chloride induced corrosion

 Corrosion Causing Substances

The high alkalinity of the pore solution (pH > 12.5) forms a protective layer. Quality of cover limits the ingress

• f corrosion causing substances

i.e. O2, H2O, CO2 and Cl-

Thickness of cover – protective layer between the air and the embedded steel. Density or permeability

Increased CO2 concentrations (exceeded 400ppm in 2013 for the first time!)

As the pH reduces, corrosion sites appear on the steel reinforcement. The steel expands under the influence of corrosion firstly cracking then spalling

• Concrete structures are failing to meet

their service life expectations.

• Unscheduled and costly maintenance is

required.

• Structures start to pose a threat of injury
• r even death.

“If no maintenance is carried out, the later repair costs will be five times the money saved on maintenance costs.” AND “If no repair is carried out, the cost of renovation or reconstruction will be five times the money saved by not repairing.”

MAINTAIN – REPAIR – RENOVATE ? Maintenance Cost

e.g. R100,000

Repair Cost

R500,000 Time

Renovation Cost

R2,500,000 !!!

Time

Essential steps before embarking on a concrete repair project.

• 1. Health, Safety & Environment
• 2. Definition of the client's objectives
• 3. Assessment of damage or deterioration and diagnosis
• 4. Specification of the repair work and estimation of costs
• 5. Preparation of contract documents including a full

specification and bill of quantities

Health, Safety and the Environment is the number one step. Even if nothing is done - safety for the

• ccupants or pedestrians is of paramount

importance. Loose spalls are at least safely restrained

• r collected.

As Local Authorities become more environmentally aware, following the publication of ISO 14000, the conditions that sites enforce on their surrounding areas must be properly managed.

An understanding and consideration of the client's

• bjectives both financial, and technical before work

commences. Includes life expectancy, prevention or reduction of further deterioration, strengthening, and possibly reconstruction.

A proper assessment will include analysis of the current condition of the visible and latent deterioration. Typically 2 types of problems;

‘Degradation of the concrete matrix’, and /or ‘Defects caused by reinforcement corrosion’.

Mechanical Chemical Physical

• Impact/

Concussion

• Overload
• Movement (e.g.

Settlement)

• Explosion/ seismic
• ASR
• Aggressive agent

(e.g. sulphates, demin water)

• Thermal
• Freeze/thaw
• Erosion
• Wear
• Shrinkage
• Fire
• Carbonation
• Ingress of Chlorides

A medical term defined as: “The art of identifying illnesses or disorders in patients through…”

 Visual assessment  Analytical investigation  Symptomatic presentation

In a similar way, we conduct an evaluation of cracking, spalling and other defects which have occurred in a concrete structure.

Diagnostic survey:

 You cannot prescribe the medicine if you

do not know what is making you sick!

 Find:

• The cause
• The severity
• The extent
• The likely cost

What should it include?

1.

A review of the available design and construction documentation

2.

A review of the operational and maintenance records

3.

A visual examination of the structure

4.

Testing of specimens of concrete recovered from the structure and ND testing on site

5.

An assessment of the scale and severity of the defects

6.

Detailed stability and stress analysis together with forensics would be undertaken by professional engineering bodies.

Specified by experienced people

1.

Effects of repair work on the environment (e.g. noise, dust, etc.)

2.

Health and safety considerations.

3.

Structural considerations (e.g. do any of the repaired components require strengthening and propping during the repair process).

4.

Preventing or slowing continued deterioration.

5.

Appearance of repaired concrete.

6.

Durability of chosen repair method.

The specification and the correct calibre of a specialist contractor who also understands the intricacies of each repair option, will ensure the success of a repair project. Manufacturer to comply with BS EN 1504 and should, therefore, possess CE grading for the product.

Repair of concrete structures is not a standard process! Problems occur in preparing an accurate schedule of quantities. Measurement and re-measurement.

Schedule of Rates are estimates only. Contractors and consultants alike are recommended to ensure that the Principal is aware that actual quantities will vary from those scheduled.

Define Objectives Assess the Structure (diagnostics) Specify Strategy (Do nothing, repair, demolish, etc.) Compile a schedule of likely quantities Consider The Environment

Does not exist in RSA !

Bills of quantities which bear little resemblance to the work we are expected to carry out…! There is no doubt that we need to formalise the method of measurement. Financial consequences.

LM m³ m² Deci m³ It lump sum No. kg rate only PC sum each as required If required?-!!!

Access Scaffolding and Propping

45%

Add the cost of traffic management in the case of bridge works Labour

25%

Specialised Materials

15%

Professional Services

5%

Contractors P&G

10 %

Contentious issue is quantity. Diagnostics - very accurate for finding causes but we cannot determine quantities with anything like the same accuracy! Three approaches:

• 1. Contractor to make his own assessment
• 2. Survey of each m2 of the structure
• 3. Interpolate quantity from partial survey

Limitations:

• 1. An incorrect estimate is likely to result in the
• wner paying too much or the contractor being

tempted to take short cuts.

• 2. Ostensibly a better option but in reality this falls short.
• 3. Realistic option - limit of accuracy i.e upper and lower

limit, dependent on the quality of the survey information.

Access Scaffolding and Propping –Not part of P&G Access Scaffolding and propping Fixed Cost Initial supply and erection of access scaffolding De-establishment of access scaffolding Time Related Maintain, move, adjust and re-erect scaffolding as required Temporary propping of structural members

Access Options

Surface Preparation

Description Unit Surface Preparation Cleaning Surfaces by Water Blasting m2 Specify bar pressure Cleaning surfaces by water blasting m2 Entrained with grit Cleaning surfaces by dry grit blasting m2 Prepare surfaces by grinding m2 Prepare surfaces by scabbling m2 Chemical neutralisation of surfaces m2

Surface Preparation

Survey and Testing After Cleaning !

Description Unit Cover meter survey m2 ( detect areas of low cover) Hammer sounding survey m2 (hollow sound = de-bonding) Depth of Carbonation testing No. Other tests specified by engineer PC

Depth of Carbonation testing with phenolphthalein pH indicator Hammer Testing

Crack Repairs

Description Unit Surface Preparation

Identify, rout out and prepare cracks - front surface LM Fix injection nozzles along the crack length No. Spacing to be specified Seal back surface of crack with thixotropic epoxy LM Apply crack filling medium by mechanical Lt

• r hand pumping. Specify crack injection medium

Crack Repairs

Crack Repairs Gravity Filling Low viscosity epoxies can gravity fill cracks. ideal for areas with multiple surface cracks that are dormant.

REPAIRS TO REINFORCED CONCRETE - Preamble

Description

The work includes but is not limited to: Locating and marking out of the repair area Breaking out of concrete to expose reinforcing bars Ensuring breaking out continues 20 mm behind rebars Incising perimeter of the repair area to a depth of 10-15 mm Removal of corrosion from exposed reinforcing bars. Application of an epoxy based primer to reinforcing steel Application of a bonding agent to the concrete substrate Application of approved concrete repair mortars or other selected repair medium in multiple layers Finishing and curing. Removal of rubble to dumps off site

Various Repair Techniques Patch Repair

• Partial depth repair
• Full depth repair

Shutter and cast method of repairing structural members Consider propping requirements ? Various Repair Techniques

Gunite/Shotcrete Advantages:

 Good consolidation  Speed of application  High build

Limitations:

 High set up costs  Uneven finish  Messy

Various Repair Techniques

Concrete Repair

Concrete Patch Repairs Specify location Vertical and Horizontal surfaces Measure soffits separately Depth range - not exceeding 25 mm Area not exceeding 0.01m² No. Area exceeding 0.01 m² but not 0.05m² No. Area exceeding 0.05m² but not 0.1m² No. Area exceeding 0.1 m² but not 0.25 m² No. Area exceeding 0.25 m² but not 0.5 m2 No. Area exceeding 0.5 m² but not 1.0 m2 No. Area Exceeding 1.0 m2 m²

Concrete Repair

Concrete Patch Repairs Vertical and Horizontal surfaces Depth range - exceeding 25mm but not 50mm Measure soffits separately Area not exceeding 0.01 m² No. Area exceeding 0.01 m² but not 0.05 m² No. Area exceeding 0.05 m² but not 0.1 m² No. Area exceeding 0.1 m² but not 0.25 m² No. Area exceeding 0.25 m² but not 0.5 m2 No. Area exceeding 0.5 m² but not 1.0 m2 No. Area Exceeding 1.0 m2 m²

Reinforcing

Supply, fix cut and splice onto existing bars Cut out and remove existing damaged reinforcing bars where the bars have reduced by more than 10% of their original diameter. Replace with new high tensile steel bars. Splice length to existing sound main reinforcing steel to be 40 times diameter. Lap length important Y10 m Y12 m Y16 m Y20 m

 Edges Cut  Concrete Excavated  Steel Cleaned  Lap length checked  Steel Coated  Concrete Primed

FINAL ACCURATE MEASUREMENT ONLY POSSIBLE AT THIS STAGE !

Pore/Blow Hole Fillers Description Unit Pore/Blow Hole Filler Specify product: Apply pore/blow hole filler to prepared surfaces of concrete (preparation measured elsewhere) Surfaces not exceeding 150 mm wide LM Surface over 150 mm but not exceeding 300 mm wide LM Surfaces over 300 mm wide m2

Pore/Blow Hole Fillers

Levelling Mortars/ Fairing Coats

Description Unit Specify product thickness and required surface finish: Apply levelling mortars or fairing coats to prepared surfaces of concrete (preparation measured elsewhere) Surfaces not exceeding 150 mm wide LM Surface over 150 mm but not exceeding 300 mm LM Surfaces over 300 mm wide m2

Levelling Mortars/ Fairing Coats Level surfaces for later application

• f protective coatings

Reduces coating consumption

Protective Coatings Description Unit Specify product thickness and required application rate, colour: Surfaces not exceeding 150 mm wide LM Surface over 150 mm but not exceeding 300 mm wide LM Surfaces over 300 mm wide m2

Migrating Corrosion inhibitors

Migrating Corrosion inhibitors

 Effective cover  Crack bridging  Uniform appearance and colour  Molecular structure allows structure to “breath” yet prevents

water ingress

Anti Carbonation Coatings

SUMMARY

SCHEDULE Description 1 PRELIMINARY AND GENERAL 2 ACCESS SCAFFOLDING AND PROPPING 3 SURFACE PREPARATION 4 TRIALS AND TESTING 5 CRACK REPAIRS 6 REPAIRS TO REINFORCED CONCRETE 7 REINFORCEMENT 8 BLOW HOLE FILLER & SKIM COAT 9 APPLICATION OF PROTECTIVE COATINGS CONTINGENCY!!!

• 1. Health, Safety & Environment
• 2. Definition of the client's objectives
• 3. Assessment of damage or deterioration and

diagnosis of its cause

• 4. Specification of the repair work
• 5. Preparation of contract documents including a

full specification and bill of quantities

The UK Concrete Repair Association’s Standard Method of Measurement for Concrete Repair The US US-base ased d Intern rnati ational al Concre crete Repair air Institute’s Guideline #03735 Guide for Methods of measurement and Contract Types for Concrete Repair Work. AIQS’s Australian ralian Stan andard dard Method of Measu sure rement of Building Work