Essential Steps in the IMPLEMENTATION AND MEASUREMENT OF CONCRETE REPAIR PROJECTS Presented by:
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 of 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: Carbonation Chloride Attack
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 of 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 CO 2 concentrations (exceeded 400ppm in 2013 for the first time!)
As the pH reduces, The steel expands under corrosion sites appear on the influence of the steel reinforcement. 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 or even death.
MAINTAIN – REPAIR – RENOVATE ? “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.” Repair Cost Maintenance Cost Time Time R500,000 e.g. R100,000 Renovation Cost R2,500,000 !!!
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 occupants or pedestrians is of paramount importance. Loose spalls are at least safely restrained or 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 objectives 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/ ASR Thermal Concussion Aggressive agent Freeze/thaw Overload (e.g. sulphates, Erosion Movement (e.g. demin water) Wear Settlement) Shrinkage Explosion/ seismic 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? A review of the available design and construction 1. documentation A review of the operational and maintenance records 2. A visual examination of the structure 3. Testing of specimens of concrete recovered from the 4. structure and ND testing on site An assessment of the scale and severity of the defects 5. Detailed stability and stress analysis together with 6. forensics would be undertaken by professional engineering bodies.
Specified by experienced people Effects of repair work on the environment (e.g. noise, dust, etc.) 1. Health and safety considerations. 2. Structural considerations (e.g. do any of the repaired components require 3. strengthening and propping during the repair process). Preventing or slowing continued deterioration. 4. Appearance of repaired concrete. 5. Durability of chosen repair method. 6.
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.
Consider The Environment Define Objectives Assess the Structure (diagnostics) Specify Strategy (Do nothing, repair, demolish, etc.) Compile a schedule of likely quantities
Does not exist in RSA ! Bills of quantities which bear little resemblance to the work we are expected to carry out…! LM m³ m² No. Deci m³ It lump sum PC sum each as required If required?-!!! kg rate only There is no doubt that we need to formalise the method of measurement. Financial consequences.
Professional Specialised Contractors Services Materials P&G 5% 15% 10 % Access Scaffolding and Propping Labour 45% 25% Add the cost of traffic management in the case of bridge works
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 owner 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
Hammer Testing Depth of Carbonation testing with phenolphthalein pH indicator
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 or 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
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