Concrete Condition Surveys

Carbonation depth is generally assessed on-site using a solution of phenolphthalein indicator that appears pink in contact with alkaline concrete with pH values in excess of 9 and colourless at lower levels of pH.

Carbonation testing provides a means with which the inspector can determine the extent of carbon dioxide infiltration into the concrete. The process is similar to chloride ion testing where a sample is either removed, either by coring or drilling and the sample is tested by the application of a revealer.

The Concrete Test Hammer is a measuring tool for testing the strength of concrete. The Concrete Test Hammer measures strength according to the Schmidt principle. According to this measurement method, the quality of concrete can be measured with the Concrete Test Hammer.

Hammer Sounding can aid in detecting impending spalls and existing delaminations, which when struck with a hammer, give off a dull sound or loud pop as opposed to the sharp ring of hard concrete without any internal discontinuities. This sound is easily noted when progressing from solid areas to delaminated areas.

The optimum carbonation depth was 9.7 mm, which was determined at conditions; 1300 kg/m3, 40 ◦C, and 20% of CO2 concentration after 28 d.

The main factors affecting concrete carbonation are: Pore system of Hardened Concrete which in turn depends upon w/c ratio, type of binder, and degree of hydration, Relative humidity (for dissolution of Ca(OH)2), The concentration of CO₂.

Chlorides cause corrosion of reinforcement present in the concrete decreasing its load-bearing capacity. Rusting of corrosion may lead to cracks or failure of the structure. Thus, chlorides decrease the durability of concrete and negatively affect the concrete.

Chlorides have little effect on hardened concrete but they increase the risk of reinforcement corrosion. Corrosion of the reinforcement will be initiated when the chloride ion concentration at the steel reaches the so called ‘threshold level’.

The test involves crushing a sample of the concrete to a fine dust, extracting the chloride with hot dilute nitric acid and then adding silver nitrate solution to precipitate any chloride present.

Covermeter surveys form part of most concrete condition surveys of buildings or structures. Covermeter surveys can also locate main and secondary reinforcement to determine bar sizes, and bar spacing, to determine minimum cover and cover variability across an element.

Half-cell potential refers to the potential developed at the electrode of each half cell in an electrochemical cell. In an electrochemical cell, the overall potential is the total potential calculated from the potentials of two half cells. The measurement of half-cell potential is used to evaluate:

• Presence of corrosion
• Potential vulnerability of element surface area to corrosion

The half-cell potential measurement can only indicate the corrosion probability at a given location and time, but long-term monitoring of the half-cell potential reading is necessary to correctly assess and predict the corrosion severity.