Concrete / Protective Coatings / Water Ingress
Concrete is not the all-enduring material it is often thought to be and many poorly designed or constructed structures require considerable maintenance to prolong service life. Structural investigations can include tests to identify poor materials, environmental contamination from road salts, sulphates and carbon dioxide to offer valuable information for the engineer to determine refurbishment cost and project the safe lifespan of the structure.
Highline Rope Access carry out many inspections of high-rise office and residential structures. These often consist of concrete framed structures with either brick infill or precast concrete panels, sometimes with a render finish. Outlined below are some of the building inspection services we can carry out. This is not an exhaustive list, for further detail you can contact us directly and discuss your specific requirements. In all cases the locations at which the testing is carried out are recorded as location markers on elevation drawings within the final inspection report.
VISUAL INSPECTION AND TAP TESTING
All areas of the building exterior are visually examined at close quarters and details recorded of the general condition and the type, dimensions and location of more specific defects. All areas of the building exterior are hammer sounded by light tapping or broad sweeps of an inspection hammer across the surface of brick, render or concrete. Particular attention is paid to column edges, beam edges, cracked material, previously repaired areas and areas displaying signs of bulging or displacement. Changes in pitch indicate the presence of spelling material or badly adhered render/slip bricks. Spalling in concrete typically occurs as a result of moisture reaching the underlying reinforcing bar via minor cracking and porosity, subsequent corrosion then forcing off the surface material. Another cause may be salt spalling, this is a specific type of weathering which occurs in porous building materials. Dissolved salt is carried through the material in water and crystallises near the surface as the water evaporates. As the salt crystals expand this builds up shear stresses which break away spall from the surface. Hammer sounding can detect spalling at an early stage allowing the building owner to act in time to prevent material falling from height. Details of the visual inspection and hammer testing are presented in a schedule of defects within the final inspection report.
Carbonation is an important form of deterioration. On the one hand carbonation gives concrete the immediate positive effects of increased; compressive strength, modulus of elasticity, surface hardness, and resistance to frost and sulphate attack. However, more importantly, it reduces the alkalinity of the concrete which leads to the corrosion of the reinforcing steel. The increased volume of the resulting corrosion spalling, delamination and the ultimate reduction of the structure's capacity. Calcium hydroxide, Ca(OH)2 , is formed during cement hydration, and because of the high alkalinity of calcium hydroxide, the presence of calcium hydroxide will ensure a high pH-value in the concrete. The pH-value is roughly constant, as long as calcium hydroxide is present, regardless of the specific content. During the carbonation process, calcium hydroxide reacts with carbon dioxide, CO2, from the atmosphere. When all calcium hydroxide in an area has reacted, the pH-value in the area drops. Testing is undertaken by applying a phenolphthalein solution to a freshly exposed surface of concrete, noncarbonated areas turn red or purple while carbonated areas remain colourless. The phenolphthalein indicator changes colour at a pH of 9.0 to 9.5. The pH of good quality noncarbonated concrete is usually greater than 12.5.
Carbonation is time-dependent generally tends to be greatest on the north side and least on the south side. The presence of carbon dioxide from vehicle exhaust corresponded to levels of carbonation, thus carbonation rates are often found to be higher at the bottom of high-rise structures than at higher elevations. Sometimes exceptions to this may occur at higher levels were carbonation can be caused by the presence of a rooftop exhaust outlets.
Our NACE trained technicians can assist with rope access coatings inspections ensuring that the quality assurance is running in accordance with the product specifications and work procedure documents. We will assess dry film thickness, surface profiles, soluble salts and environmental conditions are adhering to the project requirements and provide a clear reporting service which will enable you to make informed decisions about your project.