International Concrete Abstracts Portal

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.

The paper describes part of the preliminary results of the of the MATERSOS project, funded by the Emilia Romagna Region, Italy. This research project aims at implementing circular economy processes in the constructions industry, through the usage of secondary raw materials. The present paper focuses on structural concrete. After an analysis of locally available waste materials, those with the highest potential as concrete components were identified. Normal and self-compacting concrete mixes containing powder from ceramic tile grinding, shell powder, and construction demolition waste aggregates, were then developed. Ceramic powders were used both as replacement for a fraction of cement and as filler while shell powders were used as filler only. The paper presents the results of various experimental tests that were carried out to evaluate the mechanical properties of these concretes. In particular, their compressive and flexural-tensile strengths, elastic moduli, shrinkage and creep deformations were evaluated and compared with traditional concretes. The results of the experimental tests indicated that the mechanical properties of some of the concretes containing secondary raw materials were comparable to those of traditional concretes suggesting that their adoption in real world applications is possible.

This paper presents a study into the shear behavior of reinforced concrete beams made with Recycled Concrete Aggregates (RCA). Three beams were cast. The first beam was made entirely with natural coarse aggregates to serve as control beam. The second beam was made with 50% replacement ratio of coarse aggregates and the third beam was made with 100% recycled concrete aggregates. The replacement was done by volume method. Replacement of sand was not considered. All beams had 150 x 300 mm cross section and were 3 m long. The reinforcement ratio was constant at ρ=1.04% with constant shear span a/d=3.5. The beams were subjected to four-point loading test. Twelve control specimens were cast with each beam to study the mechanical properties of the three concrete mixes designed. Beams’ deflection, crack patterns, yielding, ultimate shear capacity, and failure modes are all observed and analyzed. Results suggest no significant changes in the shear behavior as the replacement ratio of coarse aggregates increases. ACI Code provisions for predicting the concrete shear capacity are applicable to reinforced concrete beams made with recycled aggregates. This project is part of an ongoing research on the effect of the all parameters that affect the shear capacity of reinforced concrete beams.

This study presents the results of an experimental campaign aimed at investigating the influence of recycled aggregates, derived from concrete debris (i.e., recycled concrete aggregates, RCAs), on the mechanical performance of the resulting concrete (i.e., Recycled Aggregate Concrete, RAC) after the exposure at elevated temperatures. As a matter of principle, RCAs are, generally, more porous in comparison with natural aggregates, due to the presence of the Attached Mortar (AM) and, this, may affects the physical properties of the aggregates as well as the RAC performance produced with RCAs. For this reason, in order to promote the possible use of RCAs for structural concrete production there is a strong need of understanding the influence of RCAs on the concrete performance, especially when these mixtures are subjected under “extreme conditions”. In this aim, the present experimental campaign investigates the “residual” mechanical performance of both ordinary and high strength concrete class (i.e., C25 and C65) produced with coarse RCAs (up to 100 %) and subjected at elevated temperatures (up to 650°C). The results unveil the role of the AM on affecting the compressive and tensile strengths as well as the elastic modulus of RACs exposed to elevated temperatures.

The paper deals with the usage of slag waste from production of ferroalloys containing calcium and aluminum oxides, and also vanadium oxides as impurities. It is established that vanadium in small quantities at the synthesis of CA and CA₂ forms with them solid solutions and increases their hydration activity. The optimum amount of vanadium oxide introduced into the composition of the initial raw mix is 3% wt. The carried out study showed that properties of alumina cement with a small quantity of V2O5 is useful. Hydration activity of alumina cement increases especially at early period of its hydration. Exceeding this value (more than 3%wt in row mix) leads the formation of CaO∙V₂O₅ along with calcium aluminates. But this compound is characterized by very low hydration activity. Therefore cement strength reduces.