# Ultrasonic Non-Destructive Testing of Accelerated Carbonation Cured-Eco-Bricks
###### Abstract
Factors such as the initial curing duration, carbonation pressure, and carbonation curing duration were varied for comparison purposes. The water absorption capacity and the compressive strength improved with higher pressure and extended initial curing and carbonation durations. Furthermore, going by the global warming potential index, the carbon footprint of the carbonated samples was up to 46%, which was lower when compared to the non-carbonated counterparts, as is necessary to mitigate CO2 emission. [PERSON] et al. [34] subjected a mix of electric arc furnace (EAF) slag and Wollastonite to CO2 curing. It was reported that replacing cement with EAF slag at a higher volume resulted in volumetric expansion. To prevent this, the samples were carbonated with a CO2 gas of high purity. This resulted in the development of non-expansive products that included aragonite, calcite, and remains of tobermorite within the matrix microstructure. The EAF slag was added to the Wollastonite at 0%, 20%, 40%, and 60% increments. The sample with 40% slag had the maximum compressive strength (CS), whereas the sample produced with 60% slag had the least CS. It was concluded from the study that utilizing EAF slag in the perspective of the investigation would advance CO2 sequestration and avert the dumping of industrial waste into landfills. In line with performing rapid NDTs, which are tests that do not set off structural damage or destruction to the units, the use of ultrasonic pulse velocity (UPV) is receiving attention. However, there is limited current research on its application in ACC units. UPV involves using longitudinal (P) or shear (S) waves to estimate the strength of these units. The P waves are preferred over the S waves due to their higher velocity, easy generation, and measurement [35; 36]. In a study on the evaluation of rubbercrete samples, [PERSON] et al. [35] considered the use of non-destructive tests (UPV and rebound hammer) and destructive tests (compression) to establish a relationship between the non-destructive and destructive test results. After the experiments, an exponential model was selected as the most preferred, which could be used to show a correlation between the non-destructive test (NDT) and the destructive test (DT). Furthermore, they concluded that between the UPV and rebound hammer tests, the UPV utilizing P waves was more reliable for evaluating rubberized samples. In another study, [PERSON] et al. [37] investigated the strength properties of rubberized concretes to show a correlation between the NDT and DT using P waves and compression tests, respectively. The exponential model was selected as the most preferred model with an acceptable trendline, which could be used to validate experimental data to relate the NDT to the DT. In their conclusion, the P wave was recommended for estimating the CS of rubberized concretes as a quicker testing option. In summary, the highlighted challenges include the prominent levels of pollution caused by industrial activities, the production and use of OPC, and the disposal of wastes through landfills, which all imply a scaled-up emphasis on the need for sustainability in construction industries. From one perspective, ensuring that the products from the construction industry do not cause a high degree of carbonation is necessary. On the other hand, it is vital to ensure that the waste generated is reused in the construction industry while conserving energy [38; 39; 40; 41; 42]. It is also important to engage with technologies that will guarantee a reduction in the extraction of raw materials for construction purposes, such as utilizing alternative aggregates, so that these natural resources in the form of aggregates are not depleted [26; 27; 43; 44]. Furthermore, it is essential to test units produced with wastes non-destructively as a quick test to ascertain their strength properties, utilizing the P wave as recommended by research [35; 36; 37].