# Ultrasonic Non-Destructive Testing of Accelerated Carbonation Cured-Eco-Bricks
###### Abstract  
This study aimed to investigate the behavior of accelerated carbonation-cured laboratory specimens using the ultrasonic non-destructive testing (UNDT) method and compare the results with the destructive testing (DT) method. The materials used in the study included a blend of lime kiln dust and ground granulated blast furnace slag (LKD-GBFS) wastes, natural fine aggregate (sand), and alternative fine aggregates from waste tires. The chemical analysis of the LKD and GBFS samples highlighted them as suitable alternatives to OPC, hence their utilization in the study. A 60:40 (LKD-GBFS) blending ratio and a 1.2 mix design (one part LKD-GBFS blend and two part sand) was considered. The natural fine aggregate was partially replaced with fine waste tire rubber crums (TRCs) in stepped increments of 0, 5, and 10% by the volume of the sand. The samples produced were cured using three curing regimens: humid curing (HC), accelerated carbonation curing (ACC) with no water curing (NWC) afterwards, and water curing after carbonation (WC). From the results, an exponential model was developed, which showed a direct correlation between the UNDT and DT results. The developed model is a useful tool that can predict the CS of carbonated samples when cast samples are unavailable. Lastly, a total CO\({}_{2}\) uptake of 15,912 g (15.9 kg) was recorded, which underscores ACC as a promising curing technique that can be utilized in the construction industry. This technique will bring about savings in terms of the time required to produce masonry units while promoting a change in the basic assumptions of a safer and cleaner environment. accelerated carbonation curing; ultrasonic pulse velocity; compression strength; CO\({}_{2}\) uptake; scanning electron microscope; chemical analysis +
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industrial activities, contributing to about 5-8% of anthropogenic global warming [10; 14]. By 2050, the demand for cement globally is projected to increase by 12-23% over the 2020 level, driven by spiraling urbanization, industrialization, and global population patterns, on top of infrastructure development needs [15]. To realign the cement sector with the Paris Agreement on global climate change, the annual emissions of CO2 gas should drop by a minimum of 16% by 2030 [16]. The goal of the Paris Agreement is to mitigate global warming to below 2 \({}^{\circ}\)C, preferably to about 1.5 \({}^{\circ}\)C by the end of the current century [17; 18], although records of global temperature show increments of 0.07 \({}^{\circ}\)C per decade from 1880 and over twice this increment since 1981 [19]. Hence, it is of utmost importance to lower the emissions linked to the manufacturing of cement. Furthermore, to plummet the global temperature increase, fast carbon dioxide sequestration (CO2S) technologies involving the capture, utilization, and storage of (CUS) carbon are essential [20; 21]. Due to this alarming rate of carbon emissions associated with OPC, research is constantly being carried out on the utilization of wastes (agricultural and industrial) as alternative cementitious material (ACMs) for developing cementless construction materials, units [22; 23; 24; 25; 26; 27], and the utilization of captured CO2 gas as a curing regimen [28; 29; 30] to enhance CUS. Additionally, quicker testing methods of these cementless construction units at the production stage are essential, emphasizing the importance of adequate quality control [26]. Quicker testing methods include the UNDT [26], ground-penetrating radar [31], and rebound hammer tests [32], which are all non-destructive. In line with CUS, recent studies investigating the effect of CO2S technologies on ACMs have been successfully performed [33; 34]. [PERSON] et al. [33] investigated the outcome of accelerated carbonation curing (ACC) on masonry units produced from alkali-activated slag. The study was carried out to assess masonry units' carbon sequestration performance, potentials, and microstructure.