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Showing 1-5 of 125 Abstracts search results

Document: 

SP326

Date: 

September 20, 2018

Author(s):

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

Publication:

Symposium Papers

Volume:

326

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.

DOI:

10.14359/51711167


Document: 

SP326-57

Date: 

August 10, 2018

Author(s):

Vladimir Kakusha, Oleg Kornev, Mikhail Kovalev, Andrey Lapshinov, and Egor Litvinov

Publication:

Symposium Papers

Volume:

326

Abstract:

This paper represents the summary of the design criteria and construction details for the GFRP (glass fiber-reinforced polymer) reinforced foundation slab. The idea was to improve the foundation slab durability by using GFRP bars. This included the use of GFRP bars as main longitudinal reinforcement for the foundation slabs which represents the world first application of this type. During the design procedures, several non-standard issues related to GFRP reinforcement have been solved. The method statement has been created for Construction Company with the consideration of the specific properties of GFRP bars in comparison to steel reinforcement. Before the casting of concrete, strain gauges were attached to GFRP bars and concrete surface to control the strains during the erection and the maintenance of building.

DOI:

10.14359/51711040


Document: 

SP326-116

Date: 

August 10, 2018

Author(s):

Ivan Sitnikov and Vasily Sitnikov

Publication:

Symposium Papers

Volume:

326

Abstract:

Concrete with w/c ratio of 0.2 and lower is indeed material of a new generation. Its properties significantly surpass such of regular concrete grades in large due to the absence of mixing water not actively involved in the physical-chemical processes of cement hydration. In a sense, w/c ratio of 0.2 signifies a threshold in the material science of concrete that no research did reach before 1990s. To move this realm even further, we have been aiming at producing UHPC that crosses this threshold we felt a necessity to define a basic phenomenology of such concrete hardening, especially on the early stages. Our analysis of the kinetics of the strength gain provides that this concrete gains its main physical-mechanical properties after 7 days, and its compressive strength exceeds 100 MPa (14 500 psi) already after 24 hours in normal conditions. At last, this type of UHPC is economically viable due to a relatively low content of cement (500kg/m3 (31.2 pcf)), the use of ordinary fine aggregate, and a possibility of using standard batching equipment in the production.

DOI:

10.14359/51711099


Document: 

SP326-28

Date: 

August 10, 2018

Author(s):

Alessandra Mobili, Alberto Belli, Antonio Telesca, Milena Marroccoli, and Francesca Tittarelli

Publication:

Symposium Papers

Volume:

326

Abstract:

This work presents calcium sulfoaluminate (CSA) cement and geopolymeric binder (GEO) as environment-friendly alternatives to ordinary Portland cement (OPC). Mortars based on these binders were tested and compared at the same non-structural strength class (R2 ≥ 15 MPa, according to EN 1504-3). Binder pastes were preliminarily prepared to study their hydration behaviour by means of differential thermal-thermogravimetric (DT-TG) and X-ray diffraction (XRD) analyses. Afterwards, the relative mortars were compared in terms of both fresh (workability) and hardened state properties (compressive strength, dynamic modulus of elasticity, adhesion to bricks, and water vapor permeability). Durability was also investigated in terms of capillary water absorption, drying and restrained shrinkage. Porosimetric analysis allowed to better correlate experimental results with microstructural features of the investigated mixtures. Results showed that GEO-based mortar exhibits the lowest modulus of elasticity, causing the lowest restrained shrinkage and the highest free drying shrinkage. Moreover, its highest porosity determines both the highest capillary water absorption and permeability to water vapor. On the contrary, the CSA-based mortar displays the lowest drying shrinkage, the greatest modulus of elasticity, and the lowest porosity which ensures the lowest capillary water absorption.

DOI:

10.14359/51711010


Document: 

SP326-15

Date: 

August 10, 2018

Author(s):

VadimV. Potapov, Yuriy V. Efimenko, Alexander A. Karabtsov, and Denis S. Gorev

Publication:

Symposium Papers

Volume:

326

Abstract:

Experiments were carried out to obtain sols and nanopowders of SiO2 on the basis of hydrothermal solutions. Processes of orthosilicic acid polycondensation, ultrafiltration membrane concentration and cryochemical vacuum sublimation were carried out to achieve the result. Physical and chemical properties of sols and nanopowders of SiO2 were determined with the help of the set of methods. Samples of silica sols and powders were characterized by Dynamic Light Scattering, Scanning and Tunneling Electron Microscope, X-Ray Diffraction, BET Surface Area. In particular, it was shown that diameters of SiO2 nanoparticles in sols and nanopowders were in the range of 5-100 nm. The possibility of obtained silica use as a modifying additive for concrete strength increase was substantiated. The test results on concrete compressive strength rise using nanosilica additive extracted from hydrothermal solution are presented. Experiments were made using nano-SiO2 in the coarse-grained concrete of the same mobility mixtures with the same water-cement ratio W/C=0.715 when SiO2 consumption was 2.0 wt. %, and the consumption of superplasticizer polycarboxilate (PCX) was 1.0 wt % with respect to cement consumption. The addition of sol in conjunction with the PCX significantly increases the strength of concrete in all periods and in all modes of hardening. The compressive strength after 28 days was 40% higher compared to reference sample without additives of nano-SiO2, while in the initial stages of hardening (1 day) this indicator reaches 90-128 %. It was obtained by X-Ray diffraction and thermogravimetry that SiO2 can increase the rate of calcium silicates hydrates formation in puzzolanic reaction through its great specific surface area and high density of surface silanolthat leads to increasing strength.

DOI:

10.14359/51710985


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