Distribution of High pH

About

Background: Concrete typically begins its life at a highly basic pH of about 13.5. The pH level soon falls as reactions occur between the aggregates and the surrounding alkaline matrix - a process known as Alkali-Silica Reactions (ASR). This internal process is deleterious and ultimately results in the cracking of concrete. Furthermore the exposed surfaces soon react to carbon dioxide from the atmosphere and it in turn causes carbonation in the vicinity of embedded reinforcing steel bars, leading to the onset of steel corrosion. With all this in mind, mapping of the pH levels in concrete is vital for early detection of degradation in concrete & corrosion in the embedded steel bars. Researchers at New York University have developed a new highly robust diagnostics method for mapping of pH levels in concrete. During the past decades, there are a few diagnostics methods that have been tested for high pH sensing but none offer the resolution demonstrated by NYU’s novel technique. Mapping pH levels with high spectral & spatial resolution is crucial for understanding the pH dependent degradation of concrete. Through extensive research & studies our team developed a Porphyrinoid-based high-pH indicator. The Porpholactone Platinum(II) complex TFPLPt used in the method, is shown to possess a rare dynamic sensing range from pH 11 to 13, furthermore it is chemically robust and highly specific for OH− and alkoxide ions, even in high-salinity conditions. To map the pH distribution in concrete materials, the technique uses a sensor compound containing Porpholactone Platinum(II) complex which is calibrated using a classic spectrophotometer. Subsequently, the sensor molecule is dissolved in a hydrophilic polymer and applied onto newly fractured surfaces of the mortar and hardened concrete samples of different pH values using a digital camera. The intensity ratio of the two diagnostic absorption bands identified in the solution state experiments is used for the calculation of pH at each pixel. Thus, this ratio-metric imaging procedure provides spatially well-resolved maps of the pH level of the surfaces of the complex and heterogeneous solid materials.   Applications: Its main applications lie in the building & construction industry: pH Mapping of both wet & hardened cement and mortar Infrastructure monitoring Advantages: Provides superior resolution compared to existing techniques. Very low volume of sampling solutions are required. The process is transient & offers ease of operation. Can be used to map early stages of concrete carbonation. Low cost of operation involving minimal equipment.