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International Concrete Abstracts Portal

Showing 1-5 of 1000 Abstracts search results

Document: 

SP-349_24

Date: 

April 22, 2021

Author(s):

Marta Roig-Flores, Eduardo J. Mezquida-Alcaraz, Ariel A. Bretón-Rodríguez, Juan Navarro-Gregori and Pedro Serna

Publication:

Symposium Papers

Volume:

349

Abstract:

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) is a type of concrete with superior mechanical and durability properties, which might be improved even further with the addition of nano-materials. This work studies the influence of adding nano-additions to two UHPFRCs with compressive strength around 150MPa (21755 psi), with and without crystalline admixtures. Two nano-materials were considered: cellulose nano-crystals (4-5 nm diameter, 50–500 nm length, 0.157-0.197 μin diameter, 1.97-19.7 μin length); in a dosage up to 0.15% by the cement weight; and aluminum oxide nanofibers (diameter 4-11nm, length 100-900nm, 0.157-0.433 μin diameter, 3.94-35.4 μin length) in a dosage of 0.25% by the cement weight. Water content of the mixes with nanomaterials was modified to maintain workability in a similar range aiming to maintain the self-compacting behavior. The following properties were analyzed: workability, compressive strength, modulus of elasticity and tensile properties calculated through a simplified inverse analysis after performing four-point bending tests. The study considered the effect of using three levels of mixing energy to ensure a proper dispersion of all the components, and its effect in the aforementioned properties. The results show a potential effect of these nanomaterials as nanoreinforcement, with slightly better ultimate strength and strain values for the higher energy level.


Document: 

SP347

Date: 

March 15, 2021

Publication:

Symposium Papers

Volume:

347

Abstract:

Sponsors: Sponsored by ACI 370 Committee Editors: Eric Jacques and Mi G. Chorzepa This Symposium Volume reports on the latest developments in the field of high strain rate mechanics and behavior of concrete subject to impact loads. This effort supports the mission of ACI Committee 370 “Blast and Impact Load Effects” to develop and disseminate information on the design of concrete structures subjected to impact, as well as blast and other short-duration dynamic loads. Concrete structures can potentially be exposed to accidental and malicious impact loads during their lifetimes, including those caused by ballistic projectiles, vehicular collision, impact of debris set in motion after an explosion, falling objects during construction and floating objects during tsunamis and storm surges. Assessing the performance of concrete structures to implement cost-effective and structurally-efficient protective measures against these extreme impacting loads necessitates a fundamental understanding of the high strain rate behavior of the constituent materials and of the characteristics of the local response modes activated during the event. This volume presents fourteen papers which provide the reader with deep insight into the state-of-the-art experimental research and cutting-edge computational approaches for concrete materials and structures subject to impact loading. Invited contributions were received from international experts from Australia, Canada, China, Czech Republic, Germany, South Korea, Switzerland, and the United States. The technical papers cover a range of cementitious materials, including high strength and ultra-high strength materials, reactive powder concrete, fiber-reinforced concrete, and externally bonded cementitious layers and other coatings. The papers were to be presented during two technical sessions scheduled for the ACI Spring 2020 Convention in Rosemont, Illinois, but the worldwide COVID-19 pandemic disrupted those plans. The editors thank the authors for their outstanding efforts to showcase their most current research work with the concrete community, and for their assistance, cooperation, and valuable contributions throughout the entire publication process. The editors also thank the members of ACI Committee 370, the reviewers, and the ACI staff for their generous support and encouragement throughout the preparation of this volume.


Document: 

SP346

Date: 

March 9, 2021

Author(s):

Sponsored by ACI Committee 345

Publication:

Symposium Papers

Volume:

346

Abstract:

A Sustainable built-environment requires a comprehensive process from material selection through to reliable management. Although traditional materials and methods still dominate the design and construction of our civil infrastructure, nonconventional reinforcing and strengthening methods for concrete bridges and structures can address the functional and economic challenges facing modern society. The use of advanced materials, such as fiber reinforced polymer (FRP) and ultra-high performance concrete (UHPC), alleviates the unfavorable aspects of every-day practices, offers many new opportunities, and promotes strategies that will be cost-effective, durable, and readily maintainable. Field demonstration is imperative to validate the innovative concepts and findings of laboratory research. Furthermore, documented case studies add value to the evaluation of emerging and maturing technologies, identify successful applications or aspects needing refinement, and ultimately inspire future endeavors. This Special Publication (SP) contains nine papers selected from three technical sessions held during the virtual ACI Fall Convention of October 2020. The first and second series of papers discuss retrofit and strengthening of super- and substructure members with a variety of techniques; and the remaining papers address new construction of bridges with internal FRP reinforcing and prestressing in beam, slabs, decks and retaining walls. All manuscripts were reviewed by at least two experts in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and anonymous reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance.


Document: 

SP-347_10

Date: 

March 1, 2021

Author(s):

Grace Darling, Stephan A. Durham, and Mi G. Chorzepa

Publication:

Symposium Papers

Volume:

347

Abstract:

Concrete median barriers (CMB) are installed to decrease the overall severity of traffic accidents by producing higher vehicle decelerations. In 2016, an update to the AASHTO Manual for Assessing Safety Hardware (MASH) saw a 58% increase in impact severity of test level 4 (TL-4) impact conditions when compared to the NCHRP Report 350 testing criteria. This study investigates the use of fiber-reinforced rubberized CMBs in dissipating the impact energy to improve driver safety involved in crashed vehicles. Two full-scale barrier prototypes with shear keys were constructed and tested under impact conditions in a laboratory setting. Compared to the Georgia Department of Transportation specified single-slope barrier, the fiber-reinforced rubberized concrete mixture, a design with 20% replacement of the coarse aggregate by volume with recycled rubber tire chips and a 1.0% steel fiber addition, was evaluated based on its performance in toughness, energy absorption capacity, and its recoverable deformation. It is concluded that the TC20ST1 barrier performed as well as the control barrier at the impact load of 150.0 kips (667.2 kN), with neither barrier experiencing any visible damage.


Document: 

SP-347_07

Date: 

March 1, 2021

Author(s):

Andrew D. Sorensen, Robert J. Thomas, Ryan Langford and Abdullah Al-Sarfin

Publication:

Symposium Papers

Volume:

347

Abstract:

The impact resistance of concrete is becoming an increasingly important component of insuring the durability and resilience of critical civil engineering infrastructure. Design engineers are not currently able to use impact resistance as a performance-based specification in concrete due to a lack of a reliable standardized impact test for concrete. An improved method of the ACI standard, ACI 544.2R-89 Measurement of Properties of Fiber Reinforced Concrete, is developed that provides a resistance curve as a function of impact energy and number of blows (N) to failure. The curve provides information about the life cycle (N) under repeated sub-critical impact events and an estimate of the critical impact energy (where N=1), whereas the previous method provided only a relative value. The generated impact-fatigue curve provides useful information about damage accumulation under repeated impact events and the effectiveness of the fiber-reinforcement. In this paper, the improved method is demonstrated for three fiber types: steel, copolymer polypropylene, and a monofilament polypropylene. Additionally, the analytical solution for the specimen geometry is given as well as the theoretical considerations behind the development of the impact-life curve. The use of a specimen geometry provides a path to generalize the test results to full-scale structures.


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