International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-5 of 911 Abstracts search results

Document:

SP326

Author(s):

Vyatcheslav Falikman, Roberto Realfonzo, Luigi Coppola, Petr Hàjek, Paolo Riva

Publication:

Special Publication

Volume:

326

Issue:

  

Abstract:

Modern construction is unthinkable without concrete, the world production and consumption of which is about 10 billion m3 per year. Given the steady growth of the world’s population by 2050, it is expected to double this volume, which will undoubtedly be significantly affected on energy consumption and increase global CO2 emissions. Concrete is perhaps the most universal building material since the beginning and development of civilization. It is sufficient to recall the Great Wall of China, the palaces and temples of Ancient India, the pyramids of Ancient Egypt, the unique buildings of Romans, made with the use of lime-pozzolanic binders. Universality of concrete is defined by simplicity and convenience of its production, rather low cost, structural integrity and homogeneity, durability and a long service life under various aggressive environments. However, the concrete image is sometimes not favorable. It is associated with greater labor intensity of construction works and dismantlement, massive structures, a large impact on the environment in connection with the s consumption of not renewable natural resources. The same perception is greatly facilitated by the fact that, according to Gigaton Throwdown Initiative, “the cement industry is responsible for about 5 to 7% of total CO2 emissions, or 2.1 Gt per year.” Indeed, when producing cement clinker about 0.9 t CO2 / t clinker are produced. Taking into account the annual increase in the production and use of Portland-based cement (more than 4.1 million tons per year) that is the main binder used in the production of concrete, this fact poses a significant threat to humanity as a whole. According to the Intergovernmental Panel on Climate Change (IPCC), actions are necessary to reduce carbon dioxide emissions because in about 30 years CO2 concentrations is expected to reach 450 ppm – a dangerous point above which irreversible climate change will occur on our planet. Since concrete will remain the main building material in the future, it is expected that if new ways and mechanisms to reduce the environmental burden by at least 50% will be not found, it is not possible to maintain the existing level of impact. This problem is so deep and serious that there is hardly a single way to solve it. There is a need for an integrated approach, several complementary activities that provide some synergy. Until recently, the main efforts were aimed at improving technological processes and reducing the consumption of clinker through the production of blended cements, as well as the creation of new types of binders. Active search for alternative binders has led to the development of sulfoaluminate-based cements; alkali-activated materials and geopolymers (slag, fly ash, metakaolin, etc.), efficient and fairly water-resistant magnesia cements; phosphate cements (ammonium phosphate, silicate phosphate, magnesium phosphate etc.), cements with calcium halogen-aluminate and the so called low water demand binders. With the advent of high-performance concretes and new technologies, the possibility of a radical increase of the cement factor in conventional concrete due to the use of high-performance superplasticizers and other chemical admixtures, dramatically reducing the water consumption of the concrete mixture; active mineral additives such as micro silica, metakaolin, fly ash, finely ground granulated slag, etc., as well as a variety of inert fillers that can improve the functionality of concrete mixtures, such as fine limestone. Strictly speaking, “pozzolanic effect” and “filler effect” are easily combined and provide a certain synergy. The potential for reducing cement consumption in concrete production is still undervalued. This is due to certain fears of decreasing the corrosion resistance of concrete and durability of reinforced concrete structures, since the great bulk of the existing standards is prescriptive and sets the minimum cement content in concrete under specific operating conditions. Reinforced concrete structures of buildings and constructions, as a rule, initially, shall have the design strength and sufficiently long service life because their construction often requires a significant investment. The durability of these structures, however, is determined by different ageing processes and the influence of external actions, so their life will be limited. As a result, many structures need to be repaired or even replaced in fairly short time periods, resulting in additional costs and environmental impacts. Therefore, there is a need to improve the design principles of structures taking into account the parameters of durability and thus achieving a sufficiently long service life. Development of the concept of design of structures based on their life cycle, “environmental design”, including a holistic approach that optimizes material and energy resources in the context of operating costs, allow us to completely revise our ideas about structural concrete construction. It should be noted that many recent developments in the field of life cycle analysis (LCA) are aimed at expanding and deepening traditional approaches and creating a more complete description of the processes with the analysis of sustainable development (LCSA) to cover not only the problems associated mainly with the product (product level), but also complex problems related to the construction sector of the economy (at the sector level) or even the general economic level (economy level). The approach to “environmental design” is based on such models and methods of design, which takes into account a set of factors of their impact on the environment, based on the concept of “full life cycle” or models of accounting for total energy consumption and integrated CO2 emission. All of this could become a basis for the solution of the global problem – to contain the growing burden on the environment, providing a 50% reduction in CO2 emissions and energy consumption in the construction industry. Hence a special sharpness P. K. Mehta’s phrase acquires: “...the future of the cement and concrete industry will largely depend on our ability to link their growth for sustainable development...” The above-mentioned acute and urgent problems form the basis of the agenda of the Second edition of International Workshop on “Durability and Sustainability of Concrete Structures – DSCS-2018,” held in Moscow on 6 – 7 June 2018 under the auspices of the American Concrete Institute, the International Federation on structural concrete and the International Union of experts and laboratories in the field of building materials, systems and structures. The selected papers of this major forum, which brought together more than 150 experts from almost 40 countries of the world, are collected in this ACI SP.

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Date:

September 20, 2018

  


Document:

SP328-03

Author(s):

Vahid Sadeghian and Frank Vecchio

Publication:

Special Publication

Volume:

328

Issue:

  

Abstract:

The Modified Compression Field Theory (MCFT) was introduced almost 40 years ago as a simple and effective model for calculating the response of reinforced concrete elements under general loading conditions with particular focus on shear. The model was based on a smeared rotating crack concept, and treated cracked reinforced concrete as a new orthotropic material with unique constitutive relationships. An extension of MCFT, known as the Disturbed Stress Field Model (DSFM), was later developed which removed some restrictions and increased the accuracy of the method. The MCFT has been adapted to various types of finite element analysis programs as well as structural design codes. In recent years, the application of the method has been extended to more advanced research areas including extreme loading conditions, stochastic analysis, fiber-reinforced concrete, repaired structures, multi-scale analysis, and hybrid simulation. This paper presents a brief overview of the original formulation and its evolvement over the last three decades. In addition, the adaptation of the method to advanced research areas are discussed. It is concluded that the MCFT remains a viable and effective model, whose value lies in its simple yet versatile formulation which enables it to serve as a foundation for accurately solving many diverse and complex problems pertaining to reinforced concrete structures.

Date:

September 12, 2018

  


Document:

SP326-96

Author(s):

Reinhard Martin

Publication:

Special Publication

Volume:

326

Issue:

  

Abstract:

This paper reviews the background, inspection and refurbishment of a hyperbolic cooling tower located at the Opole Power Station in Poland. The cooling tower is 132 m high with a base diameter 100,00 m. It was erected in 1977-1982. On the inner surface of the RC shell serious damage to the concrete and protective coating occurred as a result of an unexpected shut-down of the unit at low ambient temperature in winter 2010. It manifested itself by spalling, loss of the concrete, corrosion of the reinforcement and deterioration of the protective coating. For this reason, the tower was subjected to the detailed inspection and technical assessment in 2013 which resulted in required repair and protection of the RC shell of the cooling tower. General view of the concrete shell and columns of the cooling tower is displayed in Fig.1.

Date:

August 10, 2018

  


Document:

SP326-73

Author(s):

Hideo Araki

Publication:

Special Publication

Volume:

326

Issue:

  

Abstract:

Experiments were performed on two RC columns taken from a school building that was originally constructed in 1963. The columns were subjected to reverse loading with displacement control under constant axial load. Both columns were designed with a common shear span length of 1200 mm for the validation of shear capacity equations currently used for seismic evaluation. The concrete of both columns exhibited honeycombs. Thus, one column was repaired with epoxy resin injection, and the effect of retrofitting was investigated. The columns did not exhibit significantly different crack patterns. The collapse mechanism of the two columns were shear failure, and the shear force drift angle response was considerably brittle. The observed values of the original column could be predicted by the recommended standard equations for the strength of shear crack and shear capacity. The maximum strength and the initial stiffness of the retrofitted column were 1.18 times and 1.40 times, respectively, of those of the original column. Results indicated that epoxy resin injection improves the seismic performance of columns of the existing buildings.

Date:

August 10, 2018

  


Document:

SP326-67

Author(s):

Adriano Reggia, Alessandro Morbi, and Giovanni A. Plizzari

Publication:

Special Publication

Volume:

326

Issue:

  

Abstract:

The increasing age of Reinforcing Concrete (RC) road transport infrastructures, built mainly between the 60s and the 70s, is quickly becoming a key theme for the future development of constructions in many industrialized countries. It is believed that, given the age of the RC constructions, the increased traffic loads, and the growing awareness of seismic risk, there is a significant need for intervention in our country. The vertical elements, such as abutments and piers, are the parts of these structures more susceptible to seismic loading and the more exposed to the environment. During the last few years, new structural materials were developed and proposed to the market so that they are now ready for the national and international structural codes. Repairing, strengthening or seismic retrofitting RC structures with Ultra High Performance Fiber Reinforced Concrete (UHPFRC) offers a valuable opportunity to increase both seismic response and durability of these elements. This study demonstrates experimentally the possibility to enhance the seismic response of a RC bridge pier by means of the application of a thin layer of UHPFRC around the element.

Date:

August 10, 2018

  


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