ASSESSMENT & REPAIR OF CONCRETE STRUCTURES


Condition Evaluation, Service Life Prediction & Structural Assessment

Before implementing the repair works to a structure, it is essential to conduct a detailed investigation to evaluate the causes of the deterioration, design appropriate repair scheme, quantify the work for budgeting and to prepare repair scope of work. Detailed investigation also allows assessing the structural integrity and remaining service life of the structure.

Our services form a logical approach to the detailed investigation as follows:

  • Preliminary inspection to assess overall condition of the structure
  • Detailed survey involving deterioration mapping, field and laboratory tests, such as corrosion potential mapping, in-situ corrosion rates, chloride profile, alkalinity, resistivity, carbonation, pulse velocity, rebound hammer, compressive strength, cover to reinforcement, petrographic analysis, etc.
  • Service life prediction using reinforcement corrosion modeling.
  • Structural assessment to find residual strength of the structural members and identify any structural hazards.
  • Preparation of a condition evaluation report which will detail the condition of the structure and make recommendations regarding necessary repair work.
Repair Design and Durability

The main objective of the repair design is to reinstate the lost structural capacity and prolong the service life to the required length of time. Different techniques of structural repairs are available. The best repair system is the one which is durable and cost effective. Commonly used repair schemes include patch repairs, re- skinning, partial or complete replacement, strengthening, structural capacity upgrade, electro-chemical removal of chlorides and/or re-passivation and cathodic protection.

Our services form a logical approach to the detailed investigation as follows:

  • Developing detailed repair and durability procedures including strengthening and structural capacity upgrade (scope of work, bill of quantities, specifications & drawings)
  • Preparing complete repair contract (RFP) packages and cost estimates including scope of work, bill of quantities, specifications and drawings.
Supervision of Repair Works

Durable and cost-effective repairs can only be achieved under supervision of qualified engineers who are well versed with durability problems and repair of reinforced concrete structures. Supervision by qualified personnel ensures strict adherence to the material specifications, procedures and quality control.

We will provide assistance to the clients from the start to the end of a repair project i.e. from selection of prospective bidders to completion of repairs.

Our services form a logical approach to the detailed investigation as follows:

  • Pre-qualification of prospective bidders
  • Assistance in technical and commercial evaluation of bids
  • Review of designs and technical submittals
  • Supervision of repair works
  • Inspection and commissioning.
Review of Designs and Specifications

Implementation of corrosion control measures at the design stage itself ensures long term durability of new structures. Although sufficient data is available from laboratory research and field experience, it is seldom applied in the design of new structures due to non-availability of expertise with the design consultants in specialized fields of concrete technology, corrosion, cathodic protection and coatings. A small effort to incorporate corrosion control measures at the design stage goes a long way and in substantially reducing the life cycle cost.

Our services form a logical approach to the detailed investigation as follows:

  • Review of general construction specifications related to reinforced concrete, coatings and cathodic protection
  • Developing specifications for reinforced concrete, coatings and cathodic protection.
  • Review of contract specifications and drawings for corrosion protection.

REPRESENTATIVE PROJECTS IN ASSESSMENT & REPAIR OF CONCRETE STRUCTURES


Project # 1: Condition Assessment of reinforced Concrete Cooling Tower

Concrete delamination was observed on the external surface of the reinforced concrete cooling tower after a service life of about 10 years. CONTEC was commissioned to study the causes and extent of the concrete deterioration and to provide detailed procedures for repair and protection in the future.

The project scope required to assess condition of reinforced concrete cooling tower, 70 m diameter and 50 m high. The cooling tower was used to cool hot seawater for reuse for cooling. It was also required to provide procedures for repair and protection against corrosion and to extend the service of the cooling tower. The condition survey included quantifying concrete affected by reinforcement corrosion, determine compressive strength, cover to reinforcement, in-situ ultrasound testing of concrete, chloride and sulfate contents in concrete and corrosion potential mapping.

The survey indicated that the top portions of the cooling tower suffered concrete deterioration due to reinforcement corrosion and salt weathering. Procedures were provided for repairing distressed concrete. It was recommended to apply protective coating on the internal surfaces of the tower to protect reinforcing steel and concrete against corrosion and to install an impressed current cathodic protection system to protect the reinforcing steel on the external surfaces to prolong the service life of the structure.


Project # 2: Condition Assessment of Buried Seawater Concrete Cylinder Pipelines

The project involved assessing the condition of 27-year old AWWA 303 concrete cylinder pipes carrying seawater, assess risk of corrosion to the pipes and provide recommendations for repair and protection to extend the service life of the pipes. The condition survey included exposing the pipes at representative locations and conducting delamination mapping of the external cement mortar cover, corrosion potential mapping, measuring chloride and sulfate content profiles in concrete and measuring corrosion rate of reinforcing steel.

The survey showed that one of the pipes was undergoing corrosion of the helical reinforcing bars and steel cylinder due to ingress of chloride salt into concrete and depassivating the steel. It was recommended to repair the corroded segments of the pipes and install an impressed current cathodic protection system for protection of the pipe against corrosion and to extend the service life of the pipes.


Project # 3: Investigation of Cracks in Walls of a Three Story Building

Cracks were observed in walls of a 3-story building. The objective of the study included assessing the causes of the cracking and to provide procedures for repairing and arresting them. The scope of work included geometric survey to assess differential settlement of the foundations, mapping of the cracks, making bore logs to measure bearing capacity and settlement characteristics of the soil, exposing foundations for visual inspection, retrieving and testing concrete samples for compressive strength and chloride content, structural assessment and providing repair procedures.The study indicated that there was differential settlement of the foundations and that the observed cracks were located at the joints between the concrete elements and the block-work due to separation between them caused by differential thermal settlement frequent and due to wetting and drying of the block-work caused by spray and fogging by the irrigation water on the walls as well as due to drain water from the toilets due to apparently inefficient waterproofing on the floor. Structural analysis of the building showed that the footings, columns, beams and slabs are structurally safe and the pressure under the footings is less than the safe bearing capacity of the soil.

It was recommended to repair the cracks, reinstall the waterproofing system in all the toilets, relocate the landscaping at least 3 meters away from the walls of the buildings and to conduct visual inspection of the building after 3 years.


Project # 4: Condition Assessment and Repair Design for Buildings

The project scope of work included preparing as-built structural drawings, conducting detailed survey to assess the condition of a reinforced concrete, to provide detailed procedures for repair and protection and to prepare tender document for repair works. The condition survey included quantifying distressed concrete, determine compressive strength, cover to reinforcement, chloride and sulfate contents in concrete and corrosion potential mapping.

The survey indicated that some of the columns, beams and slabs were severely affected and were beyond repair. Detailed procedures were provided for rehabilitating distressed columns, beams and slabs by jacketing without removing the affected concrete in order to minimize disturbance to the operations. Tender document was also prepared including scope of work, bill of quantities, drawings, specifications and cost estimate.


Project # 5: Prepare Tender

Document for Repair & Protection and Supervision of Repair Contracts The project scope included preparing tender documents for repair and protection of various reinforced concrete facilities, including pipe supports in industry pipeline corridor, bridges, culverts, community parks and light pole foundations. The work included preparing scope of work, drawings, bill of quantities, specifications, form of proposal, special conditions, cost estimate and schedule.

The work also included technical evaluation of bids, review of technical submittals, design change notices, change orders, inspection and release of hold points and project close-out.