International Concrete Abstracts Portal

Recently, considerable attention has been given to the use of calcined clays in cementitious systems due to their availability and the enhancement of concrete durability properties they can generate thanks to the pozzolanic reaction. However, the interpretation of the macro-mechanical behavior of cementitious materials incorporating calcined clays is still challenging, especially when combined with other supplementary cementitious materials, and an investigation at the microscale is required. To this end, micro and nanoindentation are local mechanical techniques that can be used to assess the micromechanical properties of these heterogeneous and complex systems.

In this study, three ternary systems with 30%, 45%, and 60% substitution of cement with calcined clay and slag are compared to a CEM I-based reference mix at 28 days, in terms of mechanical performance, pore structure, and micromechanical properties. Results show that compressive strength is higher/equivalent to reference mix up to 45% of cement replacement. In addition, the elastic modulus of the pastes assessed by micro indentation was found to decrease with the substitution ratio, while the creep resistance was enhanced. Finally, mercury porosity and nanoindentation analysis showed that the higher the replacement ratio, the higher the amount of CSH in the tested ternary cement blends.

During an extreme event occurring on a reinforced concrete structure, characterized by the loss of a load-bearing element, the remaining resisting members may develop alternate load paths to resist gravity loads. However, it is recognized that reinforced concrete flat slabs are prone to punching shear failure. This issue is particularly relevant for existing reinforced concrete structures where creep, shrinkage, and corrosion effects due to environmental conditions play a fundamental role before the occurrence of the extreme event. In this paper, nonlinear pushdown and dynamic analyses were performed on an existing continuous reinforced concrete flat slab to investigate the structural response in the case of an interior column loss. Firstly, the flexural and membrane action resisting contributions were in-deeply analyzed. Secondly, the crucial effects of creep, shrinkage and corrosion on the dynamic response and punching shear resistance of the system were critically evaluated. Finally, useful insights for the structural robustness assessment of existing RC structures subjected to material deterioration were provided.

In May 1978, the Canada Centre for Mineral and Energy Technology (CANMET), in association with the American Concrete Institute (ACI) sponsored a 3-day conference in Ottawa, ON, Canada, on the use of superplasticizers in concrete. Selected papers from the conference were published as ACI SP-62. In 1981, CANMET, again in association with ACI, sponsored a second 3-day international conference in Ottawa on the use of the superplasticizers in concrete. Proceedings of the conference were published as ACI SP-68. The purpose of the third international conference in Ottawa in 1989 was to review the progress made since the meetings in 1978 and 1981, and to bring together representatives of the chemical admixtures, cement, and concrete industries to exchange information and delineate new areas of needed research. The scope of this conference was expanded to include chemical admixtures other than superplasticizers. Proceedings of the conference were published as ACI SP-119. In October 1994, CANMET in association with ACI and several other organizations sponsored the fourth conference in Montreal, QC, Canada. The objective of this conference was to bring attention to new developments in chemical admixture since the last conference in 1989. The proceedings of the conference were published as ACI SP-148. In October 1997, the Committee for the Organization of CANMET/ACI International Conference, (ACI Council), in association with ACI and several cement and concrete organizations in Italy, sponsored the fifth conference in Rome, Italy. The conference was aimed at transferring technology in the fast-moving field of chemical admixtures. The proceedings of the conference were published as ACI SP-173. In October 2000, Committee for the Organization of CANMET/ACI International Conferences, (ACI Council), in association with several organizations in Canada and France, sponsored the sixth conference in Nice, France. More than 50 papers from more than 20 countries were received and reviewed by an ACI review panel, and 37 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-195. In October 2003, the Committee for the Organization of CANMET/ACI International Conferences (ACI Council) in association with several organizations in Canada and Germany, sponsored the seventh conference in Berlin, Germany. The conference attracted more than 275 delegates and proceedings of the conference consisting of 39 papers, were published as ACI SP-217. In October 2006, the Committee for the Organization of CANMET/ACI International Conferences, (ACI Council), sponsored the eighth conference in Sorrento, Italy. More than 60 papers from more than 25 countries were received, and peer reviewed by the CANMET/ACI review panel in Budapest, and 36 were accepted for publication as ACI SP-239. In October 2009, the Committee for the Organization of International Conferences (COIC) (formerly CANMET/ACI International Conferences) sponsored the ninth ACI International Conference in Seville, Spain. More than 50 papers from more than 20 countries were received and peer reviewed, and 35 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-262. In October 2012, COIC sponsored the Tenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Prague, Czech Republic. More than 70 papers from all over the world were peer reviewed, and 33 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-288. In July, 2015, the COIC in association with ACI sponsored the Eleventh International Conference on Superplasticizers and Other Chemical Admixtures in concrete in Ottawa, ON, Canada. More than 60 papers from the world over were peer reviewed, and 28 were accepted for publication in the proceedings of the conference. Also, additional papers were presented at the conference that were published in the Supplementary Papers Volume. In October 2018, the Chinese Ceramic Society and the China Academy of Building Research (CABR), Beijing China, in association with ACI, sponsored the Twelfth International Conference on Superplasticizers and other Chemical Admixtures in Concrete in Beijing China. More than 80 papers from all over the world were received and peer reviewed. A total of 36 refereed papers were accepted for publication in the proceedings of the conference. The proceedings were published by as ACI SP-329. The proceedings were published as ACI SP-302. Also, 54 additional papers were presented at the conference, and were published in the Supplementary Papers Volume. In July, 2022, after a postponement for the COVID-19 pandemic, the ACI Italy Chapter and the University of Bergamo, Italy, sponsored the Thirteenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Milan, Italy. The proceedings of the conference consisting of 35 refereed papers were published by ACI as SP-354. In addition to the refereed papers, about 20 other papers were presented at the conference, and were published in a supplementary papers volume. The main topics of the papers presented at the conference are related to superplasticizers, accelerating admixtures, retarding admixtures, air-entraining agents, shrinkage-reducing agents, superabsorbent polymers, and self-healing admixtures, and their influence on the properties of the concrete in fresh and hardened state. These properties include: workability, slump-loss, time of setting, heat of hydration, strength, durability, shrinkage, and creep of the concrete mixtures. Thanks are extended to the reviewers for the valuable efforts in reviewing all the manuscripts published in the conference proceedings and in the supplementary volume. The guidance from Dr. V. M. Malhotra and Prof. M. Collepardi, the Honorary Chairpersons of the conference, is sincerely appreciated. Also, acknowledged is the support of ACI International for the publication of the proceedings (ACI SP-354). The Editors Dr. Denny Coffetti Prof. Luigi Coppola Dr. Terence Holland

Optimum thickness of a concrete flat plate is the best or the most favourable for an objective. The most common objective is often miuimum cost; however, it can also be noise insulation, least vibration or plane soffit, with or without beams or drop panels. The minimum cost is often achieved by the smallest thickness that avoid excessive deflection in service. With small thickness, reinforcement is commonly needed for safety against shear failure. Part I: Serviceability, presents a procedure to predict long-term deflection of floors and bridge decks considering the effects of cracking, creep and shrinkage of concrete and relaxation of prestressing reinforcement. The system consists of a solid slab with or without drop panels and/or beams. For analysis, the system is idealized as grid of rigidly connected short beam elements. Strain distributions at end sections are determined, assuming linear elasticity and that plane cross sections remain plane. The analysis is based on compatibility and equilibrium principles, combined with time-dependent parameters for concrete and prestressed reinforcement. The displacements – translations and rotations – are determined from strain parameters by virtual work. Part II is concerned with design of slabs for shear strength.

The paper presents a scheme of instrumentation setup for monitoring creep and shrinkage in a newly constructed reinforced concrete structure. The structure consists of in-situ concrete structural elements including beams, slabs, and columns. Some construction aspects are discussed in the paper, along with experimental tests and the scheme of installations for the monitoring of real-life creep and shrinkage behavior of the structure. A simple monitoring system using Demec gauges is employed. The installation consisted of gluing Demec targets onto surfaces of structural elements for long-term recording of measurements. The in-situ strain monitoring allows the compilation of long-term data for comparison with model predictions and with creep test results. Preliminary results of up to 90 days are discussed, giving a 3-way comparison of the early age creep and shrinkage observations. It is shown that the three methods comprising the creep test, model predictions, and in-situ measurements are in agreement.