Building Durability Surveys
Acquisition or pre-acquisition surveys are undertaken prior to the purchase of a property to determine the durability of the reinforced concrete frame and floors and the potential for reinforcement corrosion to occur.
The inspection comprises a concrete materials survey to determine the presence in the building structure of any deleterious materials.
This will include concrete dust sampling to determine the chloride content of the concrete and measurement of the depth of carbonation penetration and depth of concrete cover checks using a covermeter.
Also investigated is the presence of high alumina cement (HAC) concrete, woodwool slabs and visual evidence of potential problems, such as dampness or honeycombed concrete.
Moorhead Richardson is able to help building owners and prospective purchasers by planning and undertaking these surveys and providing an interpretative report assessing the investigation findings against current guidance.
Defects and Condition Surveys
A building custodian may have concerns over the durability and safety of the reinforced concrete elements in a building if there is visual evidence of deterioration, such as rust staining, cracking and spalling.
Various concrete investigation and testing techniques are employed to determine the cause and extent of such problems. These can include visual inspections, concrete sampling and testing, hammer tapping surveys to locate areas of delamination (hollow concrete) and cover meter surveys.
Moorhead Richardson is able to plan and carry out an investigation to determine the cause and extent of reinforced concrete deterioration. An interpretative report can be provided with recommendations for remedial action.
Reinforcement Corrosion Potential
Half cell surveys provide a method of estimating the reinforcement corrosion potential over larger areas of concrete and are often used on bridges, piers, jetties, etc. This method uses the electrochemical processes involved in corrosion to map out areas with the greatest corrosion potential. Incremental dust samples for chloride analysis are taken from the locations with highest corrosion potential. Moorhead Richardson has considerable experience of undertaking half cell surveys on structures throughout the UK and will plan the testing regime, undertake the site works and prepare an interpretative report on the investigation findings.
High Alumina Cement (HAC)
HAC concrete can be found in building elements, particularly precast units. The presence of HAC can usually be suggested by visual inspection and confirmed by sampling and laboratory testing (rapid chemical analysis). Once HAC is known to be present, further investigation can be undertaken to determine the degree of strength loss of the units affected.
Moorhead Richardson’s surveyors have inspected HAC structures many times over the years and are experienced in identifying, testing and reporting on these elements.
Alkali Aggregate Reaction (AAR)
AAR, commonly termed Alkali Silica Reaction (ASR) is often thought of as ‘concrete cancer'. It is caused by a swelling reaction between the alkaline cement paste and reactive aggregates.
Moorhead Richardson is able to investigate occurrences (or suspected occurrences) of AAR by extracting representative core samples of the affected concrete for laboratory analysis to assess its condition and serviceability.
Sulfate (or Sulphate) Attack
Sulfate attack is a form of concrete degradation and occurs when concrete comes in contact with water containing sulfate. Sulfate attack is normally associated with aggressive ground conditions surrounding concrete foundations, but can be found in other circumstances.
Moorhead Richardson investigates occurrences of sulfate attack by extracting representative concrete core samples and testing them in the laboratory to determine the sulfate content and extent of degradation.
Autoclaved Aerated Concrete (AAC)
Inspections of some pre-1980 installations of Reinforced AAC (RAAC) roof slabs have revealed serviceability problems, such as large deflections and cracking. It has been found that RAAC roofs have failed within 48 hours of cracks first appearing
Moorhead Richardson has experience in working with the client to implement a programme of inspection and testing of these units, along with a plan of maintenance activities to be undertaken to ensure that catastrophic sudden failure is avoided.
Filler Joist Floors
Filler joists were used widely from the late Victorian era to World War II and are encountered frequently in the alteration and remodelling of large office and institutional buildings. They are formed from iron or steel joists spaced up to about 1m apart and in-filled with (generally poor quality) concrete containing clinker and brick aggregate.
Corrosion of the joists, due mainly to the porosity of the concrete, is a common problem with these floors.
Moorhead Richardson is experienced in investigating these floor types to determine the condition of steel and the strength of the concrete. This provides useful information for the engineers to be able to assess the load carrying capacity of the floor.
Fire Damaged Concrete
Following a fire in a building, reinforced concrete elements in the vicinity need to be inspected to ascertain the damage sustained and their continuing durability. Concrete core samples are extracted from affected elements and assessed in the laboratory to determine the extent and severity of fire damage.
Moorhead Richardson has experience in managing and undertaking these investigations by extracting the samples and managing the testing regime of specialist laboratory analysis techniques.
The soundness of a sand and cement floor screed can be determined using the BRE Screed Tester. The device consists of a guide rod, along which an annular weight travels when released. At the bottom of the guide rod the weight strikes a steel anvil which transmits the impact to the surface of the screed. The depth of indentation is measured and evaluated against comparison values.
Moorhead Richardson’s experienced operatives can undertake this testing and provide a factual report showing the soundness of exposed floor screeds throughout a building.
Following the completion of siteworks, all retrieved samples are tested in a UKAS accredited laboratory, where applicable. On receipt of the test results, Moorhead Richardson will prepare a report. The report may be purely factual, if requested by the client, to allow the client’s engineers to make their own interpretation of the investigation findings. More usually, Moorhead Richardson will provide an interpretative report that assesses the investigation findings in relation to current British Standards, codes of practice and industry guidance.