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International Concrete Abstracts Portal

Showing 1-5 of 923 Abstracts search results

Document: 

SP-349_06

Date: 

April 22, 2021

Author(s):

Damien Gaudrel, Annabelle Phelipot-Mardelé, Christophe Lanos and Marie Glorennec

Publication:

Symposium Papers

Volume:

349

Abstract:

Nowadays, recycling and recovery of construction waste are major environmental issues. Gypsum, which is widely used in construction industry, generates around 400 000 tons of waste per year in France. Thermal activation of gypsum is well known and controlled, especially for the implementation of plaster or anhydrite. This study focuses on the recovery by flash calcination of a recycled gypsum from a gypsum recycling factory, using a flash furnace prototype allowing adjustment of multiple calcination parameters. In order to compare the thermal activation behaviour of recycled gypsum, a “noble” gypsum, derived from a hydrated industrial gypsum plaster is also used. Different calcination temperatures allow to obtain multiphase products with different degrees of reactivity. The raw gypsums (recycled and noble) as well as calcined materials are characterized by XRD, TGA, and Helium pycnometry. The hydration reactivity and setting time of calcined products and mechanical performances are also evaluated. The results highlight a similar behaviour regarding the thermal activation by flash calcination between a noble gypsum and a recycled one. They also emphasize a high reactivity of some of the calcined products. This study leads to identify the calcination conditions usable to reach the different hydrated or anhydrous calcium sulphate phases. Carefully tailored calcium sulphate binder is then accessible from recycled material.


Document: 

SP-349_01

Date: 

April 22, 2021

Author(s):

Carol Namnoum, Benoît Hilloulin,Maxime Robira, Frédéric Grondin, Ahmed Loukili

Publication:

Symposium Papers

Volume:

349

Abstract:

The production of cement by calcination of limestone releases large amounts of carbon dioxide. Development of concrete quality lead to optimize the sustainability and maintenance phases of concrete structures, so, using supplementary cementitious materials (SCM) is one of the methods adapted to reduce the environmental impact of cement production. In addition, self-healing of concrete appears as a process to considerably improve the durability of a damaged structure [1]. As revealed by most analyses, mineral additions can be used to improve the autogenous healing ability of cementitious materials [2].

In this study, the influence of using a combination of SCMs, such as ground granulated blast furnace slag and metakaolin, on the mechanism of autogenous crack healing was assessed in ternary formula. Self-healing evolution was characterised by means of mechanical tests carried out on notched mortar samples with different substitution ratios. The mechanical recovery was investigated after the healing period. Moreover, the micro-chemical structure of the healing products was determined using various techniques (TGA, SEM/EDS and XRD). The primary results showed that using metakaolin and ground granulated blast furnace slag together greatly improve the healing efficiency.


Document: 

SP-349_43

Date: 

April 22, 2021

Author(s):

Yassine El Khessaimi, Youssef El Hafiane, and Agnès Smith

Publication:

Symposium Papers

Volume:

349

Abstract:

Ye’elimite-rich cements or calcium sulfoaluminate cements (CSA) are commercialized to prepare shrinkage compensation and self-stressing concretes. Moreover, CSA cements show environmentally friendly characteristics associated to their production, which include reduced CO2 footprint. The expansive behavior of CSA cements is mainly controlled by ettringite amount, produced upon hydration of the key-phase, ye’elimite [Ca4(Al6O12)SO4]. This paper presents, on one hand, the optimal conditions for the synthesis of highly pure ye’elimite by solid state reactions, and on the other hand, it shows a fundamental description of ye’elimite formation mechanisms. Another aspect of the study encompasses the influence of fineness and citric acid addition on ye’elimite phase dissolution, then on hydrates composition of lab made ye’elimite-rich cement. For the fineness effect study, a highly fine and pure ye’elimite was originally synthetized by sol-gel methods. Various experimental techniques were performed to conduct the different aspects of the present study, namely XRD-Quantitative Rietveld analysis, Thermal analysis (TGA, DTA and Dilatometry), SEM (BSE imaging and EDS mapping), BET analysis, PSD by laser diffraction, and Image analysis (2D porosity and 2D PSD).


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: 

SP-347_14

Date: 

March 1, 2021

Author(s):

Seong Ryong Ahn and Thomas H.-K. Kang

Publication:

Symposium Papers

Volume:

347

Abstract:

Impact resistance of concrete panels has been researched since the 19th century. Studies therein primarily focused on conventionally reinforced concrete and steel fiber-reinforced concrete. Little research on the impact resistance of prestressed concrete exists. This paper investigated the impact resistance of prestressed concrete panels subject to hard and soft/hollow projectiles and under an assortment of prestressing levels. Damage mode, velocity change, impact force, and internal energy were measured and analyzed. A total of twelve finite element analyses, which considered high strain rate effects, were performed, as well as preliminary analyses with different mesh sizes. It is observed that level of prestressing tends to improve perforation resistance of concrete panels. Additionally, large deformation at soft projectiles occurred during impact, consuming the greater internal energy of the projectiles, unlike hard projectiles. As a result, soft projectiles caused a smaller degree of local failure on the concrete panels than hard projectiles with the same mass and velocity.


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