CARBONATION DEPTH MEASUREMENT SYSTEM FOR BUILDING MATERIALS

As concerns carbonation, the EN13295 standard suggests spraying a phenolphthalein solution on the target to highlight the presence of carbonated/non-carbonated areas. The phenolphthalein solution changes its colour in relation to the pH of the material: in the non-carbonated part of the specimen, where concrete has still a highly alkaline behaviour (pH > 9), a purple-red coloration is obtained, whereas in the carbonated area of the specimen (pH < 9) no colour change is observed [9]. The standard describes a procedure in which the operator is asked to manually measure the carbonation depth (dk), i.e. “the average distance, measured in mm, from the surface of the concrete or mortar where the CO2 has reduced the alkalinity of the hydrated cement to an extent such that an indicator solution based on phenolphthalein remains colourless”, by using rulers, callipers, etc.

Even if this measurement method is relatively easy to perform, it suffers from subjectivity, due to operator’s experience, colours perception, and manual ability. Hence, the measurement will be characterized by low repeatability and low reproducibility, leading to non-optimal results.

The proposed method aims at developing an automated and objective approach, based on machine vision, for measuring penetration depth of contaminants in concrete (not limiting to carbonation). Artificial intelligence is used to automatically discard aggregates that would lead to misleading results.

The proposed measurement system (hardware and software) is targeted to the automated detection of carbonation depth in cement-based specimens, previously treated on an exposed surface with a colorimetric solution. The system includes:

• An image acquisition device, to frame the whole exposed surface;
• A first illuminating device projecting a diffused light to the exposed surface, from the same direction of observation as the imaging device;
• A data processing device for image digitalisation and exposed surface selection. Hence, the perimeter and area of the exposed surface are computed, as well as the area coloured by the colorimetric indicator, then subtracted from the total one to derive the uncoloured portion area. Then, the contaminants penetration is obtained as the ratio between area and perimeter, at first in pixels and then converted into millimeters.

Such a measurement system results to be objective (not operator-dependent), precise and accurate (expanded uncertainty with coverage factor k = 2: 0.08 mm). Both average and maximum penetration depth values are provided, as indicated in the EN 13295 standard for carbonation depth measurement. Moreover, the correlation with the method suggested by the EN 13295 standard is very strong (R2 = 0.96). This technology is suitable for a stand-alone system, which can be deployed in different forms depending on the target application, which can be in laboratory or in field.

In order to commercialise the proposed system in the form of a portable cabinet or as integrated in a mobile device (e.g. smartphone, PDA – Portable Data Assistant), possible directions of work could be the following ones:

• Contracts with customers of the service;
• Creation of a spin-off;
• Search of EU fundings within Fast Track to Innovation actions.

Potential customers could be engineering firms, consulting companies and measuring systems developers.

Further research is necessary to develop the innovation as a stand-alone system (both portable cabinet or mobile device with specific application installed).