This research paper delves into self-compacting concrete (SCC), a type of concrete that consolidates without the need for vibration. However, external loading and chemical reactions often lead to the development of microcracks. Addressing this issue, the study concentrates on CaCO3 precipitation in SCC as a method for self-healing microcrack repair. The research encompasses five different concrete mixes, incorporating two supplementary cementitious materials (SCMs), microsilica (MS), and metakaolin (MK), with and without the inclusion of the bacteria Sporosarcina pasteurii. Experimental findings indicate that mixes SCCMSSP and SCCMKSP increased compressive strength by 15.32% and 21.29%, tensile strength by 12.1% and 16.14%, and flexural strengths by 15.62% and 21.88%, respectively, at 28 days compared to the corresponding control mix. Moreover, these mixes improved compressive strength by 10.86% and 20.28%, tensile strength by 15.34% and 20.82%, and flexural strength by 17.65% and 26.47%, respectively, at 56 days compared to the corresponding control mix. The concrete's integrity concerning self-healing ratio, damage level, and strength regain ratio was evaluated through an ultrasonic pulse velocity test. Results showed that mix SCCMKSP exhibited optimal reduction of damage level by 27.36%, and mixes SCCMSSP and SCCMKSP demonstrated healing efficiencies of 14.06% and 12.52% at 28 days and 14.84% and 15.64% at 56 days, respectively, compared to the corresponding control mix. The research also employed scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to examine the mobility and elemental composition of bacterial concrete. These analyses further bolster the positive effects of bacteria in enhancing the self-healing capabilities of SCC mixes when combined with mineral admixture.

Over the last 20 years, the development of electrically conductive composites for removing snow and ice from transportation infrastructure has received exceptional traction. However, these composites need to exhibit stable electrical conductivity and high mechanical properties to be sustainable and cost-effective. Towards this goal, the article investigates the roles of ground granulated blast furnace slag (BFS) and copper slag (CS) content, in addition to hooked-end steel fiber length, on the electrical properties of eco-friendly ultra-high performance hybrid fiber-reinforced self-compacting concrete (HFR-SCC) for the first time in the literature. For this purpose, sixteen eco-friendly electrically conductive ultra-high-performance HFR-SCC were designed based on the variable parameters of four different BFS/total binder ratios (20, 40, 60, and 80 %), a CS/total fine aggregate ratio of 50 %, and two different hooked-end fiber lengths (30 and 60 mm), while all mixes used 1.75 % by volume fraction of steel fibers. After determining the workability properties (slump-flow and T500 values) of all mixes, compressive strength and electrical resistivity/conductivity tests of 90-day specimens were conducted. Additionally, environmental and economic evaluations of all mixes in terms of sustainability were performed in order to clarify the effects of the variable parameters. Taking into account the experimental results obtained, it was observed that all electrically conductive ultra-high performance HFR-SCC mixes demonstrated satisfactory workability properties, while the compressive strength values reached to impressive values of 127 MPa. The optimum BFS/total binder ratio was identified to be 40 % for higher compressive strength and conductivity of ultra-high performance HFR-SCC specimens. On the other hand, the addition of CS to the mixes resulted in an increase of almost 9 % in compressive strength compared to one without CS, while at the same time, a significant increase of approximately 363 % was observed in the electrical conductivity values of the specimens. As for the influence of different lengths of hooked steel fibers, the use of 30 mm length hooked-end steel fibers in HFR-SCC mixes performed better in terms of compressive strength, whereas 60 mm fibers performed better regarding electrical conductivity. In conclusion, this experimental work has evidenced that it is possible to develop an ecofriendly and sustainable electrically conductive ultra-high performance cementitious composite (the optimal mix compressive strength and electrical resistivity values were 127 MPa and 2242 Omega.cm, respectively) by using waste from different industries such as iron and copper. Thus, it will provide important insights for the design and application of future electrically conductive concretes, which can be an important alternative in efficient active deicing and snow-melting applications.

Stress Corrosion Cracking (SCC) poses a significant challenge in the oil and gas pipeline industry, jeopardizing pipeline integrity and posing risks to both the environment and human life. This research applies simulative finite element analysis (FEA), based on phase field modeling (PFM), and experimental methods to analyze the influence of applied potential on corrosion rate in simulated near neutral soil solution (NS4), utilizing Slow Strain Rate Testing to investigate the role of electrochemistry in SCC under NS4 solution conditions. Smooth round tension specimens were employed in the experiments, with data acquisition and logging facilitated through a condition-based monitoring system. The obtained results include stress-strain curves observed across various experimental conditions, along with detailed discussions on Tafel plots highlighting the effects of different applied potentials on time-to-failure, and the results showed that the time-to-failure of the material increased when the applied potential is decreased lower than the corrosion potential, which is noted to decrease the time-to-failure from roughly 7.25 days at normal conditions and no corrosive solution to roughly 5.12 days at -2000 mV. And it is noted that an increase of the applied potential to a certain value over the corrosion potential would increase the life of the material to 7.40 days at +400 mV, this increase requires further investigation. An FEA model was developed to predict the electrochemical behavior of the material and assess the impact of applied potential on material properties, aiding in the design of materials and structures resistant to stress corrosion cracking. The PFM model findings showed agreement with the experimental results, in terms of the stress-strain curves, the change in the corrosion rate, and the material time-to-failure. The findings have the potential to inform the development of preventive measures against SCC in pipeline systems, leading to lifesaving interventions and environmental damage prevention. Furthermore, the study emphasizes the reliability and importance of utilizing slow strain rate testing as an effective approach for investigating SCC in AISI 4340 steel alloys.