Utilizing recycled aggregates (RAs) in concrete production represents a promising path toward sustainability; however, it often results in reduced physical and durability properties. The weak interfacial transition zone (ITZ) and the adhered mortar in recycled aggregate concrete (RAC) contribute to lower mechanical strength and limit its application in demanding environments. This study investigates an accelerated carbonation technique to enhance the mechanical and durability properties of RA and RAC. Recycled aggregates, with a particle size of 10–20 mm, were subjected to carbonation at 1 bar for 2 h in a controlled carbonation chamber. Results demonstrate substantial improvements in the compressive and split tensile strengths of the carbonated recycled aggregate concrete (CRAC), with increases of 30% and 42% compared to conventional RAC, respectively. The CRAC mix also exhibited a 1.5% increase in dry density and reduced water absorption (6%) compared to RAC (7.58%). After 90 days of acid exposure, compressive strength reductions of 48.85% and 37.9% were observed for RAC and CRAC mixes, respectively, from their 28-day strength, while weight loss in CRAC was limited to 5.4%, compared to 10.92% in RAC. In sulfate exposure tests over 150 days, RAC and CRAC showed compressive strength reductions of 31.4% and 19.7% and weight losses of 3.6% and 2.2%, respectively, indicating enhanced resistance of CRAC to harsh environments. However, CRAC blended with supplementary cementitious materials (SCMs) showed diminished mechanical properties, likely due to a reduced alkaline environment caused by rapid calcium hydroxide absorption in RA pores during carbonation. Overall, the findings highlight the practical potential of accelerated carbonation to improve the performance of RAC, offering a viable pathway for sustainable construction applications.

The engineering and construction of super-tall buildings represent one of the most complex frontiers of civil engineering, requiring innovative approaches to materials, structural design, and risk management. Concrete, as the most widely used construction material in skyscraper projects, faces unique technical challenges when employed at extreme heights, where issues of compressive load resistance, pumpability, durability, thermal behavior, and long-term sustainability become critical. The Burj Khalifa, currently the tallest structure in the world, provides a benchmark case study for understanding how advanced concrete innovations, combined with rigorous civil engineering frameworks for risk management, enable the safe realization of such mega-structures. This paper investigates the integration of advanced high-strength concrete (HSC) and self-consolidating concrete (SCC) in the design and execution of super-tall buildings, emphasizing their role in mitigating structural, environmental, and construction-related risks. High-strength concrete allows engineers to achieve compressive strengths exceeding 60–100 MPa, reducing column sizes and thereby maximizing usable floor space, while simultaneously ensuring that the vertical gravity system can withstand extraordinary loading conditions. Self-consolidating concrete, on the other hand, offers exceptional workability and flow, facilitating placement in congested reinforcement zones without mechanical vibration, which is particularly critical at high elevations where uniformity and defect prevention are essential. Together, these material innovations address critical construction challenges, such as pumping concrete to unprecedented heights, minimizing segregation, preventing honeycombing, and ensuring structural integrity under continuous vertical and lateral stresses. The paper further examines the risk management dimension, proposing a comprehensive framework that links material selection, structural design strategies, and construction logistics into a unified approach. Key risk categories include: (i) structural risks, such as creep, shrinkage, and lateral instability due to wind and seismic forces; (ii) construction risks, including concrete pumping pressure, placement uniformity, and temperature control to prevent early-age cracking; (iii) durability risks, covering fire resistance, carbonation, chloride penetration, and long-term sustainability of reinforced concrete elements; and (iv) operational risks, ensuring long-term performance monitoring through structural health systems and predictive maintenance. The framework integrates advanced simulation tools, real-time thermal and stress monitoring, and redundancy in structural systems, ensuring resilience against both predictable and uncertain conditions. Using the Burj Khalifa as a reference, the study highlights how the buttressed core structural system, combined with advanced HSC and SCC mixes, enabled engineers to balance efficiency, stability, and constructability while meeting the demands of both safety and sustainability. The lessons from this case study underscore the importance of linking concrete material science with risk engineering practices to deliver future-ready skyscrapers. The findings argue that the future of super-tall buildings will increasingly rely on advanced material innovations integrated with holistic risk management strategies. By positioning high-strength and self-consolidating concrete at the center of structural innovation, civil engineering is not only pushing the boundaries of height and design but also advancing sustainability imperatives, reducing environmental impact, and ensuring long-term resilience of vertical cities. This research contributes a multidisciplinary perspective to civil engineering by demonstrating how material innovations, when embedded within structured risk management frameworks, can reshape the possibilities for safe, sustainable, and efficient super-tall construction in the 21st century. Keywords: High-Strength Concrete (HSC), Self-Consolidating Concrete (SCC), Super-Tall Structures, Skyscraper Engineering, Burj Khalifa Case Study, Structural Risk Management, Wind and Seismic Risk in Tall Buildings, Structural Health Monitoring.