Case study Questions

Question 1

talk me through the process of estimating the date of a building

Answer 1

check maps online and bomb map in our office
look for key features, construction materials used such as cast iron rainwater goods, brick types, lintel types and types of damp proof course, check whether the soil and vent pipe are located externally.
ask for construction documents and deeds.

Question 2

how did you establish the client brief

Answer 2

i held a meeting with the client and stakeholders to

Question 3

who was the client

Answer 3

the client was the residents management company

Question 4

what did you produce in terms of PCI documentation

Answer 4

2.0 Description of Project
2.1 Brief Details of Property
2.2 Proposed Works
2.3 Project and Programme Details
2.4 Details of Project Team
2.5 Extent and Location of Existing Records and Plans
3.0 Clients Considerations and Management Requirements
3.1 Structure and Organisation
3.2 Safety Goals for the Project
3.3 Permits and Authorisation Requirements
3.4 Emergency Procedures
3.5 Location map
3.6 First Aid
3.7 Welfare Facilities and Contractor’s Area
3.8 Traffic Management
3.9 Site Rules
3.10 Arrangements for Liaison Between Parties
3.11 Security Arrangements for the Site
3.12 Fire Precautions
3.13 Site Tidiness
3.14 Access to the Site
3.16 Car Parking
3.17 Noisy work

4.1 Site Safety Hazards
4.2 Adjacent Land Uses
5.0 Significant Design and Construction Hazards

5.3 Anticipated Temporary Works for the Project.
6.0 Health and Safety File
7.0 Construction Phase Plan 18
7.1 Description of Project 18
7.2 Management of the Work 18
7.3 Arrangements for: 18
7.4 Arrangements for Controlling Significant Site Risks Specific Risks, Including:
7.5 The Health and Safety File 19
7.6 Implementing and Monitoring the Construction Phase Plan

Question 5

explain the process of carbonation of concrete

Answer 5

Carbonation is the reaction of carbon dioxide in the environment with the calcium hydroxide in the cement paste. This reaction produces calcium carbonate and lowers the pH to around 9. At this value the protective oxide layer surrounding the reinforcing steel breaks down and corrosion becomes possible

Question 6

Talk me through the checks for potential conflicts of interest

Question 7

how does the coastal location make carbonation more susceptible

Answer 7

coastal locations have high exposure to prevailing winds and rain, the coast is also milder and studies by the concrete society suggest that carbonation occurs more rapidly in steady temperature

Question 8

rebar depths 1960s v now

Answer 8

1960s: Rebar cover was typically thinner, often much closer to the surface, i have seen many examples of only 10mm making them more susceptible to corrosion as .
Today: Modern codes require greater cover depths, often around 30-50 mm or more depending on exposure conditions. For coastal or highly corrosive environments, covers of 50-75 mm may be required to provide additional protection.

Answer 9

Rebar depth, or cover depth, varies in structures depending on factors like the type of structure, environmental exposure, load requirements, and design codes.

Question 10

how does concrete crack and spall

Answer 10

Shrinkage Cracks: As concrete cures, it loses moisture, leading to shrinkage. If the shrinkage is restricted by factors like embedded rebar or adjacent concrete sections, it can cause tensile stresses that lead to cracking. Shrinkage cracks are often seen as small surface cracks that develop shortly after pouring.

Thermal Cracks: Temperature changes, especially rapid cooling or heating, cause concrete to expand or contract. These movements create internal stresses that can lead to cracking if the concrete cannot move freely. In massive concrete pours, like foundations and dams, heat generated during hydration can cause thermal gradients that lead to cracking as the exterior cools faster than the interior.

Loading and Structural Stress Cracks: Concrete is strong in compression but weak in tension. Under load, especially if it’s not evenly distributed, tensile stresses develop that can exceed the concrete’s capacity and cause cracking. Cracks from loading can appear in beams, columns, or slabs due to bending, shear, or excessive deflection.

Corrosion of Reinforcement: When steel rebar in concrete corrodes (often due to carbonation or chloride penetration), it expands, putting pressure on the surrounding concrete. This pressure leads to internal tensile forces that cause the concrete to crack.

Chemical Reactions: Some chemical reactions, like alkali-silica reaction (ASR), cause concrete to swell and crack. ASR occurs when certain reactive aggregates in the concrete react with alkalis in the cement paste, creating an expansive gel that generates internal stress and leads to cracking.

2. Spalling in Concrete
   Freeze-Thaw Cycles: When water infiltrates cracks or pores in concrete and then freezes, it expands by approximately 9%, creating internal pressure. Over repeated freeze-thaw cycles, this pressure causes pieces of the concrete to break away, leading to surface deterioration known as spalling.

Corrosion of Rebar: When steel reinforcement in concrete corrodes, the rust formed (iron oxide) occupies a much larger volume than the original steel, generating expansive forces that push against the concrete. This expansion causes the concrete cover to crack and eventually break away, creating spalling. Coastal structures, where chloride intrusion accelerates corrosion, are especially susceptible.

Poor Construction Practices: Low-quality concrete, inadequate curing, insufficient cover depth over rebar, or improper placement of rebar can lead to spalling. If the concrete mix has high water content, it can be more porous and vulnerable to cracking and spalling.

Question 11

what were you initial thoughts on the stepped cracking through the mortar

Question 12

How did you ensure that your client understood the nature of the risk and the likelihood of occurrence, along with the potential impact?

Question 13

You mention Phenolphthalein testing of concrete to fully establish the extent of works required; talk me through the process of testing concrete using this method - how is it done, what do the results mean?

Answer 13

Phenolphthalein testing is a straightforward and widely used method for assessing carbonation in concrete. Carbonation is a process where carbon dioxide (CO₂) reacts with the calcium hydroxide in concrete, forming calcium carbonate. This reaction lowers the concrete’s pH, which in turn reduces its ability to protect embedded steel reinforcement from corrosion. Here’s a step-by-step overview of how phenolphthalein testing is conducted, along with an explanation of what the results mean:

1. Purpose of Phenolphthalein Testing
   
   • The primary purpose of this test is to determine the depth of carbonation within concrete. It provides a visual indication of the areas where carbonation has occurred, which is crucial for planning repair and maintenance work.
2. Materials Needed
   
   • Phenolphthalein Solution: A pH indicator prepared by dissolving phenolphthalein powder in ethanol or isopropyl alcohol. When applied to concrete, phenolphthalein changes color depending on the pH level of the concrete.
   • Concrete Core Samples or Broken Surface: Concrete samples taken from the structure (core samples) or broken/exposed surfaces of concrete to expose a fresh surface.
   • Protective Equipment: Gloves, eye protection, and sometimes a mask, since the phenolphthalein solution contains alcohol and can be mildly irritating.
3. Procedure for Phenolphthalein Testing
   
   1. Expose a Fresh Concrete Surface: Ideally, this is done by drilling or coring to reveal an unweathered section of the concrete. For an accurate test, it’s essential to have a fresh, clean surface where carbonation depth hasn’t been altered by exposure to air.
   2. Apply the Phenolphthalein Solution: The phenolphthalein solution is sprayed or brushed onto the freshly exposed surface of the concrete. The solution will start to react with the concrete almost immediately, revealing the depth of carbonation.
   3. Observe Color Changes:
      • The phenolphthalein solution turns pink or purple in areas where the pH is high (above about 9.5), which indicates uncarbonated concrete. This high pH is typical of healthy concrete, where the alkalinity protects embedded steel from corrosion.
      • Areas that remain colorless indicate carbonation, as the pH of the concrete has dropped below around 9.0 due to carbonation. This colorless region marks where CO₂ has penetrated the concrete, reacting with calcium hydroxide and lowering the pH.
4. Interpreting the Results
   
   • Depth of Carbonation: The boundary between the pink (or purple) area and the colorless area represents the depth of carbonation. By measuring this depth, you can assess how far carbonation has penetrated into the concrete.
   • Implications for Reinforcement:
     
     • If carbonation has reached or is close to the rebar, it’s a warning sign that the pH has dropped in the rebar’s vicinity, which could make the steel vulnerable to corrosion.
     • If the concrete around the rebar remains pink or purple, the alkalinity is still intact, indicating that carbonation hasn’t yet reached the reinforcement.
5. Next Steps Based on Test Results
   
   • Minor Carbonation (Shallow Depth): If the carbonation depth is relatively shallow and far from the reinforcement, only minor surface treatments or sealants may be needed to slow down further carbonation.
   • Moderate to Deep Carbonation: If carbonation has penetrated close to or has reached the rebar, repair measures are typically necessary. These can include removing and replacing the carbonated concrete, applying corrosion inhibitors, or using cathodic protection to safeguard the rebar.
   • Monitoring and Maintenance: If carbonation is found but hasn’t reached critical depth, periodic phenolphthalein testing can help track its progression over time, aiding in proactive maintenance.

Summary
Phenolphthalein testing is a simple, rapid method for determining carbonation depth in concrete. It provides critical information on the structural integrity of concrete by visually identifying low-pH areas vulnerable to rebar corrosion. The test is valuable for assessing the extent of required repairs and guiding preventive maintenance, especially in structures at high risk for carbonation, like those in coastal or urban environments.

Question 14

In your recommendation for the use of helifix bars, who did the design detail work for this?

Answer 14

I am not competent to design the application of helifix bars so a structural engineer provided the calculations for this part of the repair

Question 15

Talk me through the requirements of BS EN 1504.

Answer 15

BS EN 1504, titled “Products and systems for the protection and repair of concrete structures,” is a comprehensive European standard that outlines requirements and guidelines for repairing, protecting, and maintaining concrete structures. It serves as a key framework for ensuring quality, durability, and safety in concrete repairs across a wide range of environments. BS EN 1504 is divided into 10 parts, each addressing specific aspects of concrete repair and protection. Here’s a breakdown of the standard’s main requirements and how it is structured:

1. BS EN 1504-1: Definitions
   This part provides definitions for terms used throughout the BS EN 1504 series. It covers basic concepts and terms related to concrete repair, like types of damage, protection methods, and repair techniques. Clear definitions ensure a shared understanding and consistency across the industry.
2. BS EN 1504-2: Surface Protection Systems for Concrete
   This part focuses on protective coatings and systems that prevent deterioration from external factors like moisture, chlorides, carbonation, and other aggressive chemicals. It specifies requirements for surface protection methods such as:
   Hydrophobic Impregnation: Repels water but allows the concrete to breathe.
   Impregnation and Coatings: Penetrate the concrete or coat the surface to prevent pollutant ingress.
   Surface Coatings: Provide physical barriers against environmental exposure.
   It outlines performance requirements, including resistance to weather, abrasion, and environmental exposure, to ensure durability and efficacy.
3. BS EN 1504-3: Structural and Non-Structural Repair
   This part addresses materials and methods for both structural and non-structural repairs to restore concrete’s load-bearing capacity and appearance. It covers:
   Classification of Repair Mortars: Mortars are classified based on their strength, modulus of elasticity, and shrinkage.
   Performance Requirements: Includes compressive strength, bond strength, shrinkage, and compatibility with existing concrete.
   Types of Repairs: Defines structural repair, non-structural repair, and requirements for selecting materials based on the type of damage and intended use.
4. BS EN 1504-4: Structural Bonding
   Focuses on materials used for bonding structural elements, like concrete sections, steel plates, or reinforcement. It specifies requirements for adhesives and bonding agents that join structural elements or reinforce existing structures. The performance criteria include:
   Shear Strength: Ensures the bonded area can handle structural loads.
   Durability: Covers resistance to chemicals, moisture, and environmental exposure.
5. BS EN 1504-5: Concrete Injection
   Outlines requirements for injection materials used to fill cracks, voids, or cavities to restore structural integrity and prevent further degradation. It includes:
   Material Types: Includes resins, grouts, and hydraulic binders.
   Performance Criteria: Adhesion, compressive strength, flexibility, and resistance to environmental factors.
   Application Guidance: How to ensure the correct application of injection materials to achieve proper penetration and bonding.
6. BS EN 1504-6: Anchoring of Reinforcing Steel
   Specifies requirements for materials used to anchor reinforcing steel in concrete, commonly used in structural strengthening or repair of rebar. Key criteria include:
   Adhesion and Pull-Out Strength: Ensures that the anchoring system can withstand applied loads.
   Compatibility with Concrete: Prevents interaction issues between the anchor and concrete.
   Durability: Resistance to chemicals, corrosion, and environmental factors.
7. BS EN 1504-7: Reinforcement Corrosion Protection
   This part addresses methods and materials used to protect reinforcing steel from corrosion, a major cause of concrete deterioration. It includes:
   Corrosion Inhibitors and Protective Coatings: Applied to reinforce steel before embedding in concrete.
   Cathodic Protection: Electrical systems to control corrosion on embedded steel.
   Performance Requirements: Resistance to environmental exposure, bond strength with concrete, and effectiveness in preventing rust.
8. BS EN 1504-8: Quality Control and Conformity Assessment
   Outlines requirements for quality control and conformity assessment to ensure that materials and methods meet the specifications of BS EN 1504. Key areas include:
   Inspection and Testing: Regular checks on materials and application methods.
   Documentation: Ensuring all repairs are documented with details of materials, methods, and testing.
   Certification and Compliance: Requirements for certifications to verify that products and systems meet the standard.
9. BS EN 1504-9: General Principles for the Use of Products and Systems
   Defines the fundamental principles for selecting and applying repair and protection systems. It provides guidance on assessing damage, selecting suitable repair techniques, and ensuring durability, including:
   Principles of Repair and Protection: Concepts like limiting damage, structural stability, and durability.
   Methods: Defines acceptable repair methods for various damage types and deterioration mechanisms.
   Application Criteria: Provides guidance on selecting appropriate products based on environmental exposure and intended use.
10. BS EN 1504-10: Site Application of Products and Quality Control of the Works
    Focuses on best practices for applying products on-site and ensuring quality control during repair and protection work. It includes:
    Application Guidelines: Requirements for surface preparation, mixing, application, curing, and protection during and after repair.
    Quality Control Procedures: Regular testing and inspections to ensure work meets specifications.
    Health and Safety: Includes guidelines for safe handling and application of repair materials.
    Summary
    BS EN 1504 provides a comprehensive framework for assessing, protecting, and repairing concrete structures, with each part dedicated to specific aspects of the process. It emphasizes choosing the right repair and protection systems based on a structure’s needs, environmental exposure, and expected lifespan. By following BS EN 1504, contractors and engineers can improve the durability, safety, and performance of repaired concrete structures

Question 16

Which BRE documentation did you use?

Question 17

What is TG20?

Answer 17

TG20 is a comprehensive set of guidelines developed by the National Access & Scaffolding Confederation (NASC) in the UK, providing standards and best practices for the safe erection, use, and dismantling of tube-and-fitting scaffolding. Officially known as “TG20: Guide to Good Practice for Scaffolding with Tube and Fittings”, it aims to ensure compliance with relevant safety regulations and industry standards, particularly the Work at Height Regulations and British Standards (BS EN 12811).

Here’s a breakdown of what TG20 covers and why it’s essential in the construction industry:

1. Purpose of TG20
   
   • TG20 establishes a standard for safe scaffolding using tube-and-fitting (traditional) scaffolding, as opposed to modular or system scaffolding.
   • It provides engineered designs and calculations that meet British safety standards, meaning that scaffolders do not need to obtain bespoke engineering designs for most standard scaffolding configurations, which helps save time and cost.
   • TG20 enables compliance with regulations, making sure that scaffolding practices meet the Work at Height Regulations 2005 and BS EN 12811, which is the European standard for temporary structures on construction sites.
2. Key Components of TG20
   TG20 consists of several main components that guide scaffold design and use:
   • TG20 eGuide: A software tool that helps users create compliant scaffolding designs by selecting configurations, dimensions, and loadings. The eGuide produces printable “TG20 Compliance Sheets” that confirm a design’s compliance without requiring an engineer’s involvement, provided the scaffolding setup is standard.
   • TG20 Compliance Sheets: These are customized, project-specific sheets generated by the eGuide. They detail configurations like dimensions, bay lengths, and other parameters and confirm that the scaffolding complies with TG20 safety standards. These sheets are often required on-site to show evidence of compliance.
   • TG20 Design Guide: For more complex scaffolding structures that fall outside standard configurations, the TG20 Design Guide provides criteria for seeking bespoke engineering designs, ensuring unique structures are properly assessed and designed.
   • TG20 Operational Guide: This guide provides practical advice for scaffolders on how to erect, modify, and dismantle scaffolding safely and effectively. It covers day-to-day operations, including recommendations for different types of scaffolds, such as independent scaffolds, birdcages, and loading bays.
3. Types of Scaffolding Covered by TG20
   TG20 provides standards for a range of scaffolding structures commonly used on construction sites, including:
   
   • Independent Scaffolds: Single and double scaffolds with varying bay lengths and heights.
   • Facade Scaffolding: Typical scaffolds used for work on building exteriors.
   • Loading Bays and Bridging Structures: Scaffold structures designed to support materials and allow access for workers.
   • Cantilevered and Free-Standing Scaffolds: Special configurations for work that requires more flexibility.
4. Safety and Compliance Benefits of TG20
   
   • Standardized Safety: TG20 improves safety by providing clear standards, helping reduce accidents and ensuring structures can support loads and withstand environmental factors like wind.
   • Regulatory Compliance: It helps companies comply with health and safety regulations, such as the Work at Height Regulations 2005 and BS EN 12811, and avoids costly non-compliance penalties.
   • Efficiency in Scaffolding Design: With the TG20 eGuide, common scaffold configurations can be quickly verified as compliant, eliminating the need for engineering input for each standard scaffold design.
   • On-Site Verification: TG20 Compliance Sheets provide an easily verifiable record that the scaffold structure has been built to meet safety standards, which is useful for inspections and audits.
5. Updates in TG20:21
   The most recent edition, TG20:21, introduced updates to further enhance scaffolding safety and efficiency:
   
   • Enhanced eGuide: The TG20:21 eGuide includes more configurations and improved tools for creating compliance sheets for more complex scaffolding setups.
   • Wind Loading Guidance: TG20:21 includes updated guidance for assessing wind loads, helping scaffolders assess and mitigate wind risk in specific locations.
   • Expanded Scaffold Configurations: TG20:21 includes more scaffold configurations and loading options, making it more adaptable to modern site needs.

Summary
TG20 is an essential guide that helps scaffolders and contractors safely and efficiently erect tube-and-fitting scaffolding on construction sites. By following TG20 standards, companies can ensure regulatory compliance, reduce the need for engineering approval on standard configurations, and create a safer working environment for workers at height.

Question 18

If a scaffold cannot be erected to TG20, what must then happen?

Answer 18

it must be designed by a temporary works engineer

Question 19

How does BS 5975 apply to scaffolding?

Answer 19

BS 5975, titled “Code of practice for temporary works procedures and the permissible stress design of falsework,” is a British Standard that provides guidance on managing, designing, and implementing temporary works, including scaffolding. While it primarily addresses falsework, which is temporary support for structures during construction, BS 5975 also includes essential procedures and safety management practices that apply to scaffolding and other temporary works on construction sites. Here’s how BS 5975 is relevant to scaffolding:

1. Temporary Works Management and Procedures
   
   • Temporary Works Coordinator (TWC): BS 5975 establishes the role of a Temporary Works Coordinator (TWC), responsible for coordinating temporary works like scaffolding. The TWC oversees the design, implementation, inspection, and dismantling of scaffolding to ensure it’s done safely and according to specifications.
   • Temporary Works Supervisor (TWS): The TWS supports the TWC by supervising the scaffolding erection, modification, and dismantling on-site to maintain safety and compliance.
   • Temporary Works Register: BS 5975 recommends keeping a register of all temporary works on a construction site, including scaffolding. This register ensures proper tracking, inspection schedules, and status updates on scaffolding structures.
2. Design and Approval Processes
   
   • Design Checks and Approval: For complex scaffolding structures or non-standard configurations (such as cantilevered or high-rise scaffolds), BS 5975 mandates a formal design check and approval process. Designs may need to be reviewed by a competent engineer to ensure they meet safety standards.
   • Categories of Design Check: BS 5975 specifies different categories for temporary works design checks (from Category 0 to Category 3), depending on complexity and risk level. Scaffolding that falls outside standard configurations might require a Category 2 (independent check by another qualified engineer) or even Category 3 check (for high-risk structures needing a third-party review).
   • Design Brief: BS 5975 emphasizes the importance of creating a detailed design brief for temporary works. In scaffolding, this design brief specifies the load requirements, height, environmental conditions, and safety requirements to guide the scaffold design.
3. Risk Management and Safety Requirements
   
   • Risk Assessment: BS 5975 requires a thorough risk assessment for all temporary works, including scaffolding. This assessment identifies hazards, such as collapse, instability, or environmental loads (like wind), and helps determine the necessary precautions.
   • Load Management: The standard sets out requirements for ensuring scaffolding can handle intended loads (e.g., workers, equipment, materials) without risk of overload or collapse. Load capacity must be factored into the design, with considerations for potential additional loads from wind or impact.
   • Inspection and Maintenance: BS 5975 requires regular inspection and maintenance of temporary works. For scaffolding, this includes:
     
     • Inspections after erection, before use, and at regular intervals.
     • Checks after adverse weather, impact, or modifications.
     • Documentation of all inspections in the temporary works register, ensuring that scaffolding remains compliant throughout its use.
4. Permissible Stress Design
   
   • BS 5975 includes guidance on permissible stress design, an approach where temporary works (like falsework or scaffolding) are designed based on allowable stress limits rather than more conservative ultimate load capacities. This method can be applied to scaffolding designs, particularly for cases where scaffold loads are known and controlled.
   • Material Strength and Stability Calculations: When permissible stress design is used, BS 5975 requires precise calculations to ensure that scaffolding can withstand applied forces without exceeding safe stress levels. These calculations account for the structural properties of scaffold tubes, joints, and bracing.
5. Communication and Collaboration
   
   • BS 5975 emphasizes the importance of clear communication among all parties involved in temporary works, including scaffolders, site managers, and engineers. This is especially crucial for complex scaffolding designs where collaboration between the TWC, designers, and contractors ensures that the scaffold structure meets safety standards and project requirements.
   • Documentation and Record-Keeping: Detailed documentation is required for all stages of scaffolding work, including design briefs, calculations, inspection reports, and modifications. This record-keeping allows for accountability and traceability, which is critical for managing risks and ensuring compliance with health and safety regulations.

Summary
BS 5975 provides a framework for managing temporary works, including scaffolding, by setting standards for planning, design, risk assessment, and inspection. Although BS 5975 does not replace scaffolding-specific guidelines (like TG20), it complements them by ensuring that scaffolding work is coordinated, designed, inspected, and documented in line with best practices for temporary works management. This holistic approach helps to enhance site safety, reduce risks, and ensure that all scaffolding work meets regulatory requirements.

Question 20

How did you communicate the planned use of MEWPs with the residents?

Answer 20

I held a meeting with the client and managing agent - a meeting was held with all residents and notices were located in each entrance . the carpark was securely excluded during the works each day

Question 21

How, if there were any, were changes to the programme conveyed, for example, when planned sections weren’t completed and needed additional time?

Question 22

What information did you obtain through the pre-qualification process for the contractors?

Answer 22

health and saftey information ,

Question 23

As well as the weather delays you mentioned, were there any other concerns with carrying out the work in winter?

Question 24

How did you explain the risk to the client?

Question 25

How were risks identified, tracked and mitigated?

Answer 25

via a project risk register

Question 26

Did you consider the ‘drying time’ for the concrete repairs in the programme, particularly as the programme had moved from the warmer months into mid-winter?

Answer 26

yes i checked the data sheets for the specified product and checked with the contractor

Question 27

How were you checking the moisture content of the concrete repair work prior to applying the coating?

Answer 27

i did not test the moisture content of the concrete between applications, this was undertaken by the contractor as they are approved contractors

Question 28

The coating will have specified a maximum moisture content; what consideration was given to this prior to instructing the works?

Question 29

Was any consideration given to an interim final account, or was the work separated into two separate contracts?

Question 30

What was the rectification period in this contract?

Question 31

What elements of the scheme did you design?

Question 32

How did you make your reports to the client easy to understand?

Question 33

You stated that the client’s main driver was quality, yet the client opted to carry out the work by use of an MEWP. What discussions did you have to try and influence the use of a scaffold?

Question 34

With the driver being quality, how did you formulate a decision on the original coating system?