International Concrete Abstracts Portal

This study investigates corrosion-induced cracking in reinforced concrete subjected to accelerated chloride exposure, with emphasis on the applicability of Faraday’s law for predicting steel mass loss (ML). Voltage drop variation proved to be a reliable indicator of crack initiation, showing close agreement with observed surface cracking. Reduced porosity and higher electrical resistivity in low water-cement ratio (w/c) concretes restricted ionic transport, resulting in an actual corrosion level (CL) of nearly 40% of that predicted by Faraday’s law. Faraday’s law accurately estimated ML for specimens preconditioned for 28 days and cast with medium-to-high w/c, whereas shorter preconditioning durations and low w/c resulted in systematic overestimation. Concrete compressive strength, rebar diameter, w/c, concrete cover, and exposure conditions exhibited strong coupled effects on crack initiation and propagation, with crack growth rates ranging from 0.142 to 0.586 mm (0.006 to 0.023 in.) per 3% CL, highlighting the need for integrated consideration of material and geometric parameters in durability-based design and corrosion assessment. An analytical model for estimating CL at crack initiation is proposed that shows strong agreement with experimental observations.

This study investigates the development of eco-efficient self-healing concrete incorporating calcined clay as a sustainable supplementary cementitious material (SCM) and bacterial-based crack healing. Ordinary portland cement was substituted with calcined clay at 4, 8, and 12% by weight of cement. Bacillus sphaericus (optical density ≈ 1.0, cell concentration ≈ 10⁹ cells/ml) was introduced at dosages of 400, 800, and 1200 ml/m³ (10.3, 20.7, and 31.0 fl oz/yd³) of concrete to induce microbially mediated calcium carbonate precipitation. The optimum performance was observed at 8% calcined clay replacement with 800 ml/m³ (20.7 fl oz/yd³) bacterial addition (CC08B20), showing a compressive strength of 60.3 MPa (8740 psi) and a splitting tensile strength of 5.7 MPa (830 psi) at 28 days. Water absorption and sorptivity were reduced, demonstrating enhanced durability, and SEM and XRD showed denser microstructure and calcite formation for bacterial mixtures. The self-healing efficiency after 7 days was approximately 73%, which reduced the crack width from 0.45 mm (0.018 in) to 0.12 mm (0.005 in).

The pressing need to reduce CO2 emissions from construction materials has driven the development of sustainable alternatives to ordinary portland cement (OPC). This study investigates a low-carbon ternary binder system—OMF-0.75—composed of 50% OPC, 30% reactive MgO, and 20% fly ash, with 0.75 M magnesium acetate as a hydration agent. Concrete with OMF-0.75 was exposed to 5% Na2SO4 and 5% H2SO4 solutions for up to 9 months, and its performance was compared to OPC concrete. OMF-0.75 exhibited better chemical resistance, with lower mass loss (4.14% in sulfate, 23.75% in acid) and reduced strength degradation (22.23 and 67.65%) compared to OPC (5.68%, 34.22%; 31.22%, 85.58%). Ultrasonic pulse velocity (UPV) retention was higher in OMF-0.75 (3.32 km/s sulfate, 1.66 km/s acid) than in OPC. Microstructural analysis revealed stable magnesium silicate hydrate (M-S-H) formation in OMF-0.75, while calcium-silicate-hydrate (C-S-H) in OPC deteriorated, as evidenced by a Ca/Si ratio below unity. These findings confirm OMF-0.75 enhances durability and potential as a low-carbon binder for aggressive environments.

Geopolymer concrete offers a lower-carbon alternative to ordinary portland cement (OPC) concrete, but long-term durability under aggressive exposure remains critical for field adoption. This study evaluated low-calcium fly ash geopolymer concretes with 0%, 10%, and 20% OPC replacement (denoted GPC100C0, GPC90C10, and GPC80C20) after immersion in tap water, seawater (pH ≈ 7.25), an alkaline solution (pH ≈ 12.5), and an acidic solution (pH ≈ 2.5). Compressive strength and ultrasonic pulse velocity (UPV) were measured at 1, 3, 6, 9, and 12 months. Across all conditions, net mass change remained below 3%. In tap water, 12-month reference compressive strengths were approximately 22 MPa (GPC100C0), 40 MPa (GPC90C10), and 43 MPa (GPC80C20). After 12 months, compressive strength loss was clearly dependent on the exposure medium. In seawater, losses ranged from approximately 20% (GPC80C20) to 30% (GPC90C10). In alkaline solution, losses were approximately 5% (GPC100C0), 20% (GPC90C10), and 33% (GPC80C20). In acidic solution, GPC80C20 showed the lowest loss (approximately 8%), whereas GPC90C10 showed the highest loss (approximately 30%). UPV in tap water was approximately 3.2 to 3.9 km/s, and UPV-strength relationships were mixture- and exposure-specific (best-fit R2 ≈ 0.84). These results provide practical guidance for durability-oriented mixture selection and UPV-based in-service condition assessment.

Hydrostatic pressure has a significant impact on the transport of chloride ions in concrete, especially in underground structures and marine environments. This paper proposes a new seepage velocity model that considers the combined effects of hydrostatic pressure and the initial hydraulic gradient on chloride-ion transport. By combining saturated and unsaturated concrete seepage models and convection-diffusion-coupled chloride-ion transport analysis, the influence of hydrostatic pressure and seepage velocity on chloride-ion transport in concrete is studied. Experimental verification shows that the proposed model can accurately predict the concentration distribution of chloride ions. The analysis results indicate that the seepage velocity under hydrostatic pressure is not only positively correlated with the permeability coefficient of concrete and hydrostatic pressure, but also negatively correlated with the initial hydraulic gradient, and that it has a significant impact on the transient seepage characteristics of unsaturated concrete. The effect of seepage velocity on the chloride-ion transport process exhibits nonlinear characteristics. Before a critical value, seepage velocity promotes the transport of chloride ions, while after exceeding this critical value, the influence gradually decreases. Based on this conclusion, the durability design of underground concrete structures should adopt a chloride-ion transport model that considers the convection-diffusion coupled effect for a more accurate prediction of the service life of the structure.