International Concrete Abstracts Portal

This study reviewed, synthesized, and extended the service life prediction models for conventional reinforced concrete (RC) structures to those with advanced concrete materials (that is, high-performance- concrete [HPC] and ultra-high-performance concrete [UHPC]), and corrosion-resistant steel reinforcements (that is, epoxy-coated [EC] steel, high chromium [HC] steel, and stainless- steel [SS]) subjected to chloride attack. The developed corrosion initiation and propagation models were validated using field and experimental data from literature. A case study was performed to compare the corrosion initiation and propagation times, and service life of RC structures with different concretes and reinforcements in various environments. It was found that UHPC structures surpassed 100 years of service life in all studied environments. HPC enhanced the service life of conventional normal-strength concrete (NC) structures by over three times. In addition, the use of corrosion-resistant reinforcement prolonged the service life of RC structures. The use of HC steel or epoxy-coated steel doubled the service life in both NC and HPC. SS reinforcement yielded service lives exceeding 100 years in all concrete types, except for NC structures in marine tidal zones, which showed an 88-year service life.

Reinforcing seawater sea-sand concrete (SSC) with basalt fiber reinforced polymer (BFRP) bars can adequately resolve chloride corrosion issues. However, the multiple-element ions in seawater and sea sand can increase the concrete alkalinity and accelerate the degradation of BFRP bars. This study aims to enhance the durability performance of BFRP-SSC beams by regulating concrete alkalinity. A low-alkalinity SSC (L-SSC) is designed by incorporating a high-volume content of fly ash and silica fume. A total of 16 BFRP-SSC beams were designed based on the current standards and prepared using normal SSC (N-SSC) and L-SSC. The beam flexural performances before and after long-term exposure are characterized through the four-point bending test. The test results indicate that exposure in the simulated marine environment can reduce the load-bearing capacity and change the failure mode of BFRP beams with N-SSC. After exposure at 55°C for 4 months, the load-bearing capacity of the BFRP-SSC beams was reduced by 70.0%. Moreover, a slight enhancement of load-bearing capacity and ductility of the BFRP-L-SSC beams was observed due to the enhanced interface performance with further concrete curing. Furthermore, the long-term performance of the sand-coated BFRP bars is better than that of the BFRP bars with deep thread. The load-bearing capacity of the BFRP-L-SSC beams increased by approximately 20% after 4 months of accelerated aging due to concrete strength growth, and the BFRP-L-SSC beams maintained the concrete crushing failure mode after exposure. Finally, a loadbearing capacity calculation model for the BFRP-SSC beams is proposed based on the experimental investigation, and its prediction accuracy is higher than that of the current standards. This study can serve as a valuable reference for applying BFRP-SSC structures in the marine environment.

In marine structures, concrete requires adequate resistance against chloride-ion penetration. As a result, numerous studies have been conducted to enhance the mechanical properties and durability of concrete by incorporating various pozzolans. This research investigated the curing conditions of samples including zeolite and metakaolin mixed with micro-/nanobubble water in artificial seawater and standard conditions. The results indicated that incorporating zeolite and metakaolin mixed with micro-/nanobubble water, cured in artificial seawater conditions, compared to similar samples that were cured in standard conditions, improved the mechanical properties and durability of concrete samples. The 28-day compressive strength of the concrete samples containing 10% metakaolin mixed with 100% micro-/nanobubble water and 10% zeolite blended with 100% micro-/nanobubble water cured in seawater increased by 25.06% and 20.9%, respectively, compared to the control sample cured in standard conditions. The most significant results were obtained with a compound of 10% metakaolin and 10% zeolite with 100% micro-/nanobubble water cured in seawater (MK10Z10NB100CS), which significantly increased the compressive, tensile, and flexural strengths by 11.13, 14, and 9.1%, respectively, compared with the MK10Z10NB100 sample cured in standard conditions. Furthermore, it considerably decreased the 24-hour water absorption and chloride penetration at 90 days— by 27.70 and 82.89%, respectively—compared with the control sample cured in standard conditions.

The early-age material parameters of three-dimensional (3-D)-printable concrete defined under the umbrella of printability, namely, pumpability, extrudability, buildability, and the “printability window/open time,” are subjective measures. The need to correlate and successively substitute these subjective measures with objective and accepted material properties, such as tensile strength, shear strength, and compressive strength, is paramount. This study validates new testing methodologies to quantify the tensile and shear strengths of printable fiber-reinforced concretes still in their fresh state. A tailored mixture with high sulfoaluminate cement and nonstructural basalt fibers has been assumed as a reference. The relation between the previously mentioned parameters and rheological parameters, such as yield strength obtained through International Center for Aggregates Research (ICAR) rheometer tests, is also explored. Furthermore, in an attempt to pave the way and contribute toward a better understanding of the mechanical properties of 3-D-printed concrete, to be further transferred into design procedures, a comparative study analyzing the work of fracture per unit crack width in three-point bending has been performed on printed and companion nominally identical monolithically cast specimens, investigating the effects of printing directions, position in the printed circuit, and specimen slenderness (length to depth) ratio.

The penetration of chloride ions causes degradation of reinforcing bars, which directly affects the service life of the element. In this study, four different alternatives for the construction of a reinforced concrete (RC) caisson parapet beam are investigated: conventional RC, the addition of a corrosion inhibitor to concrete, and the use of glass fiber-reinforced bars (GFRP) and galvanized steel instead of steel bars. The durability of the RC element under marine environment was studied based on measurements performed both in-place and in well-controlled laboratory conditions on specimens prepared in the laboratory, as well as specimens taken from the actual structural element. It was concluded that the exposure of fresh concrete to seawater splash has no effect on mechanical properties. In addition, galvanized rods were found to be a less effective protection strategy compared to the other alternatives studied. GFRP bars, however, provide better protection than the other tested alternatives, although chloride ion penetration in these bars was found to be more accelerated in an alkaline environment compared to a chloride environment. In contrast to the prevailing approach, which considers plain concrete and according to which the electrical resistance of the concrete decreases because of chloride penetration, this study found that electrical resistance in the reinforced element is increased due to an increase in the amount of corrosion products formed between steel and concrete if no cracks occur. Furthermore, it was found that the potential measured using the half-cell method in all the alternatives slowly increased with time, as well as the corrosion risk in the three alternatives with reinforcing steel. The remaining question is whether this change of potential is a direct characteristic of the corrosion risk. Therefore, more research in this direction is needed.