1. General
This specification sets out the minimum technical requirements for the investigation, preparation, repair, protection and quality control of reinforced concrete car park slabs. The works shall be undertaken by a competent concrete repair contractor using appropriately trained personnel and proprietary repair materials suitable for the intended exposure and service conditions.
Concrete repair works shall be designed and executed in accordance with the principles and requirements of the BS EN 1504 series, Products and systems for the protection and repair of concrete structures. BS EN 1504 is a ten-part standard covering definitions, surface protection, structural and non-structural repair, bonding, injection, anchoring, reinforcement corrosion protection, conformity, repair principles and site application.
Particular attention shall be given to BS EN 1504-3 for structural and non-structural repair materials, BS EN 1504-7 for reinforcement corrosion protection, BS EN 1504-2 for surface protection systems and BS EN 1504-10 for site application and quality control.
2. Assessment and Investigation
Prior to repair, the car park slabs shall be subject to a detailed condition survey to establish the cause, extent and severity of deterioration. The investigation shall identify areas of cracking, spalling, delamination, exposed reinforcement, corrosion staining, water penetration and surface deterioration.
Where appropriate, additional investigation shall include:
- Hammer sounding to identify delaminated concrete.
- Concrete cover surveys.
- Carbonation-depth testing.
- Chloride contamination testing.
- Concrete strength assessment.
- Reinforcement condition and corrosion assessment.
- Crack-width and crack-movement monitoring.
- Moisture and water-ingress assessment.
The repair strategy shall address the cause of deterioration, rather than simply replacing visibly defective concrete. BS EN 1504-9 establishes general principles for selecting appropriate protection and repair methods based on the identified deterioration mechanisms.
Where deterioration may affect the structural capacity of the slab, a structural engineer shall assess the condition and determine whether temporary propping, strengthening or reinforcement replacement is required.
3. Concrete Removal
Defective, loose, contaminated or delaminated concrete shall be removed until sound and adequately bonded concrete is exposed. Breakout shall be undertaken using controlled methods that minimise damage to the remaining concrete and reinforcement.
Mechanical breakers, hydro-demolition, scabbling or other suitable methods may be used, subject to the condition of the structure and the repair design.
The perimeter of each repair shall be clearly defined and shall generally have a suitable square-cut edge. Feather edges shall not be permitted where they could result in inadequate repair thickness or premature debonding.
Following breakout, the substrate shall be thoroughly cleaned to remove dust, laitance, loose aggregate, oil, grease and other contaminants.
4. Reinforcement Preparation
Where reinforcement is exposed, all corrosion products shall be removed by mechanical cleaning, abrasive blasting or another approved method. The reinforcement shall be cleaned sufficiently to provide a sound surface for corrosion protection and reinstatement.
The exposed reinforcement shall be inspected for loss of cross-sectional area. Where significant corrosion has occurred, the structural engineer shall determine whether additional or replacement reinforcement is necessary.
Where specified, reinforcement shall receive an approved corrosion-protection system complying with BS EN 1504-7. The coating shall be applied strictly in accordance with the manufacturer's instructions and the requirements of the repair system.
Adequate clearance shall be maintained around reinforcement to allow complete encapsulation by the repair material.
5. Repair Materials
Repair mortars and concrete shall be selected according to the type of repair, structural requirements and environmental exposure. Materials used for structural and non-structural repairs shall comply with the applicable performance requirements of BS EN 1504-3. The standard covers identification, performance, durability and safety requirements for repair concretes and mortars.
Repair materials shall be compatible with the existing concrete in terms of strength, stiffness, shrinkage, permeability, thermal movement and durability.
Where structural repairs are required, materials shall provide the specified structural performance. BS EN 1504-3 classifies repair products according to their performance characteristics and intended use.
Materials shall be stored, mixed and applied in accordance with the manufacturer's technical data. Water addition, mixing times, application thicknesses and working times shall not be exceeded.
6. Application of Repair Concrete
Prior to application, the substrate shall be prepared to the moisture condition required by the selected repair system. Where a bonding primer or bonding coat is required, it shall be applied in accordance with the manufacturer's requirements.
Repair mortar shall be firmly compacted against the prepared substrate and around reinforcement to eliminate voids and ensure full encapsulation.
Deep repairs shall be undertaken in suitable layers where required. Each layer shall be properly compacted and prepared before subsequent application. The maximum permissible thickness for each application shall comply with the manufacturer's requirements.
The finished repair shall be brought to the required profile and surface texture to match the surrounding concrete and accommodate any specified waterproofing or protective coating.
7. Crack Repair
All cracks shall be assessed before treatment to determine whether they are structural, non-structural, static or moving.
Static cracks may be repaired using suitable resin or cementitious injection systems. Where structural crack injection is required, the selected system shall be suitable for the intended application and comply with the relevant requirements of BS EN 1504-5.
Moving cracks shall not be treated with a rigid repair system unless the repair design specifically permits it. Flexible sealing systems or other appropriate movement-accommodating solutions shall be used where required.
8. Surface Protection and Waterproofing
Car park slabs are subject to water, chlorides, de-icing salts, vehicle traffic, abrasion and potentially aggressive environmental conditions. Following concrete repair, an appropriate surface protection system should therefore be considered.
Where specified, protective coatings shall comply with the relevant requirements of BS EN 1504-2, which addresses surface protection systems for concrete and their performance and durability characteristics.
The selected system may provide protection against water ingress, carbonation, chloride penetration and other deterioration mechanisms. Particular attention shall be given to movement joints, cracks, drainage outlets, upstands and areas susceptible to standing water.
The substrate shall be inspected for moisture content, surface profile and cleanliness before application. Coatings shall be applied at the manufacturer's specified thickness and environmental conditions.
9. Curing and Protection
Freshly repaired concrete shall be protected from premature drying, rain, frost, excessive temperatures, vibration and traffic.
Curing shall be undertaken in accordance with the repair-material manufacturer's requirements. Repaired areas shall remain protected until the specified curing period has elapsed, and the material has achieved the required performance.
Vehicular and pedestrian traffic shall not be permitted over repaired areas until the repair material and any protective coating have achieved adequate strength and durability.
10. Quality Control and Inspection
Quality control shall form an integral part of the repair process. BS EN 1504-10 provides requirements concerning substrate condition, structural stability, preparation, application, quality control and maintenance of repaired concrete structures.
Inspection records shall include:
- Location and extent of each repair.
- Breakout depth and substrate condition.
- Reinforcement condition.
- Repair-material manufacturer and product reference.
- Batch numbers and shelf life.
- Environmental conditions during application.
- Mixing and application records.
- Curing arrangements.
- Photographic records.
- Test and inspection results.
Where specified, testing may include pull-off/bond testing, compressive-strength testing, coating-thickness measurement and visual inspection.
11. Completion and Acceptance
On completion, repaired areas shall be fully bonded, sound, properly cured and free from cracking, debonding, voids or other visible defects attributable to defective workmanship.
The finished repair shall provide a durable and compatible solution appropriate to the car park environment. Particular consideration shall be given to reinforcement corrosion, chloride exposure, water penetration, traffic loading and long-term durability.
All repair materials and systems shall be supported by appropriate technical documentation and evidence of conformity with the relevant requirements of BS EN 1504.
The completed works shall only be accepted following satisfactory inspection and confirmation that the specified repair system, workmanship and quality-control requirements have been achieved.