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 (i.e., high-performance and ultra-high-performance concrete (HPC and UHPC)), and corrosion-resistant steel reinforcements (i.e., epoxy coated steel, high chromium steel, and stainless-steel reinforcement) subjected to chloride attack. The developed corrosion initiation and propagation models were validated using field and experimental data from the 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 high chromium steel or epoxy-coated steel doubled the service life in both NC and HPC. Stainless steel 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.

This paper investigates the mechanical characteristics (encompassing compressive strength, flexural strength, toughness, and impact resistance) of ultra-high performance fiber-reinforced concrete (UHPFRC) incorporating polypropylene (PP) and polyvinyl alcohol (PVA) fibers. An experimental program was conducted, based on which the polymer and metallic fibers were utilized at the same fiber content, and different sets of single and hybrid fiber-reinforced composites were fabricated and tested. Despite the fact it has been exhibited through previous research that the hybridized PVA-PP fibers do not result in the development of the mechanical characteristics of engineered cementitious composites (ECC), the UHPC composites incorporating such hybrid fibers show augmented levels of toughness, flexural strength, and resistance to impact loads. A comparison was also made to assess the potentiality of the used fibers in terms of environmental impact and cost. Based on the results, hybridization with PVA and PP fibers leads to remarkable improvement in technical performance and mitigation of the economic and environmental impact of UHPFRC composites.

Although ultra-high-performance concrete (UHPC) is one of the promising materials for precast bridge girder applications due to its advanced properties and durability, its implementation in the precast industry is subject to several potential concerns. To support implementation, this paper presents the development of nonproprietary UHPC mixtures for precast, pretensioned UHPC bridge girder applications. The nonproprietary UHPC mixtures were developed using materials commonly available in the Texas precast industry, with the additional requirement of obtaining a compressive strength of 12 to 14 ksi (83 to 97 MPa) within 24 hours without any heat treatment while maintaining the current precast, pretensioned bridge girder fabrication practices. The fresh, hardened, and durability properties of both laboratory- and plant-made UHPC mixtures were investigated. The research results show that the selected nonproprietary UHPC mixture developed in a laboratory setting can be successfully produced in a precast plant setting with comparable properties.

In this study, low-carbon ultra-high-performance concrete (UHPC) was designed by adding fly ash-based mineral admixtures (SD-FA). The improved Andreasen & Andersen model was used to obtain SD-FA, which was then used to replace part of UHPC cement, to achieve the effect of low-carbon emission reduction. The effects of the composition and dosage of cement-based materials, the water-cement ratio, the composition of sand, the steel fiber content, and the lime-sand ratio on the properties of UHPC were studied, and the design of the batches was optimized. On this basis, the performance changes were analyzed at the micro level. The results show that when the 1~3 grade fly ash content after screening treatment is quantitative, the densest stacking is theoretically reached. The SD-FA optimized design improves the bulk density of UHPC and realizes the dense microstructure of UHPC. Under the optimal mixing ratio, its processability is guaranteed and the mechanical properties are enhanced.

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 με and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.