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.

Compared to external curing, internal curing enables the judicious use of available water to provide additional moisture in concrete for more effective hydration, and improvement in the performance of concrete structures. However, certain challenges with the incorporation of internal curing materials (ICMs) still need to be addressed as its effectiveness depends on several factors. Furthermore, sustainable construction demands the use of recycled materials, and this paper discusses the comparative evaluation of recycled aggregate (RA) as an ICM with two other types of ICMs on various properties of high-performance concrete in the hardened state under two curing conditions. Concrete mixes were prepared with pre-wetted recycled aggregates (RA), superabsorbent polymers (SAPs), and pre-wetted lightweight volcanic aggregates (LWVA) as ICMs. Concrete performance was compared through the investigation on the strength development, shrinkage, mass loss, and volumetric water absorption. In addition, the change in internal humidity of concrete with time at different stages of hardening was determined. The compressive strength results showed that RA and LWVA are more efficient in the early days, and the performance of SAP is better in the later age due to its slow water-releasing capabilities. Compared to the control mixture, the least reduction in strength of 4% and 8% at 28 days and 90 days, respectively could be observed for the mixes containing RA under both air and water curing.

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.

The focus of this study is to determine the optimum length of micro (average diameter less than 0.3 mm) and macro (average diameter greater than or equal to 0.3 mm) hemp fibers subjected to tensile loading in a cement paste mixture. Optimizing the length of the fibers to carry tensile loading for concrete members is important to minimize waste of hemp material and to provide the best performance. This study evaluated three water-cement ratios (w/c): 0.66, 0.49, and 0.42 (fc′ = 17.2, 24.1, and 27.6 MPa [2500, 3500, and 4000 psi], respectively). Because of the high cost of cement, replacement of cement with fly ash was also part of the program to determine if the addition of fly ash would have a negative impact on the performance of the hemp fibers. The results show that hemp micro- and macrofibers bonded to the cement matrix and carry higher tensile loads at higher w/c. Statistical analysis (regression modeling) shows that the optimum length for hemp macrofibers is 30 and 20 mm (1.18 and 0.79 in.) for microfibers.