###### Abstract  
This paper shows the scientific possibilities of computed tomography for the study of concrete porosity. The enormous technological advances in computed tomography equipment used in materials research, with increasingly higher energy, better resolution and smaller pixel size will allow, in the near future, viewing pore sizes that are currently unthinkable, competing in resolution with the traditional techniques of mercury porosimetry and nitrogen adsorption. The challenge at that time (and to a lesser extent today) will be how to extract as much information as possible from the large amount of data provided by computed tomography equipment. In this article, through the study of six cubic specimens of 40 mm sides, different techniques of extraction and presentation of the information are shown, which help us to better understand the characterization of the morphology and distribution of the pores inside the concrete matrix. This information is essential to understand some of the macroscopic responses of the concrete. CT-scan technology; porosity; circumferential test; neighborhood test; porosimetric curve; maximum pore size; pore orientation +
Footnote †: journal: Applied Sciences  
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Footnote 1: _Applied Sciences_  
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Footnote 1: _Applied Sciences_  
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: _Applied Sciences_  
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Footnote 1: No branch of engineering is alien to this technology, and almost any material has been studied using this technique, from metals or plastics to composites or rocks [5; 6; 7; 8; 9; 10]. A detailed review of the state of the art in this field can be found in [11; 12]. Concrete is also no stranger to this trend. In recent years there has been an increase in the use of computed tomography for the study of its microstructure in order to analyze how it affects its macroscopic response [13; 14; 15; 16; 17]. Within the microstructure of concrete there are two singular elements whose influence on its macroscopic response is well known: pores and fibers. Fibers can only be found in fiber-reinforced concretes. However, pores are present in all concretes. In most cases, this is an unintended \"component\"; nevertheless, there are other situations where concretes are designed with a certain level of porosity. This occurs, for example, in pervious concretes used mainly in concrete pavements [18; 19; 20] or in porous concretes to improve their response to freeze-thaw cycles [21; 22; 23]. Figure 1 shows the trend of scientific papers published between 2001 and 2021 in the most relevant fields applying CT. All data were obtained from WoS (Web of Science) [24], a widely used bibliographic database that collects the most influential international journals in all fields of science and technology. Figure 1 reveals how most of the research works on concrete microstructure using computed tomography focus on the study of fiber orientation and distribution, while only a small percentage of them focus on porosity. This is due to the fact that the resolution of the computed tomography equipment provided by the market so far shows insufficient resolutions. According to IUPAC, pores can be classified according to their size into micropores (smaller than 2 nm), mesopores (from 2 to 50 nm) and macropores (larger than 50 nm) [25; 26; 27; 28]. The pores that have the greatest influence on the macroscopic response of concrete are micropores and mesopores. Macropores have a minor influence. There is one exception: pervious concretes. In this case, the largest pores are the most important, although what is sought in this type of concrete is its hydraulic capacity and not so much its structural response. Figure 1: Evolution in the number of scientific publications related to computed tomography in concrete (2001–2021). The last ten years have seen an impressive development in computed tomography equipment. Resolution has improved significantly, from around 100 \(\upmu\)m a decade ago to 1 \(\upmu\)m today.