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 concrete is the ultimate building materials today and answers all the requirements of the modern architecture. The emulsion or the release agents are used to facilitate the concrete demoulding and to protect the formwork surfaces against corrosion. The final quality of the facings depends on the physicochemical characteristics of the demoulding products used. They must be selected according to the nature of the formwork and their compatibility with the casing skins. They must be consistently applied to the unit of the formwork, to a clean surface, in thin layers, uniform thickness. This agent must allow a placement of the more effective concrete while adhering perfectly to the formwork. The adherence of oil with the support is thus very important. It is studied by the determination of the adhesion energy Solid/Liquid on a formwork surface. This study is interested more particularly in the emulsions. Two forms are distinguished: Mineral reverses emulsion with the dispersed phase is water and Vegetable direct emulsion with the dispersed phase is oil. The first physicochemical results show an influence of the temperature on the adhesion energy. The quality of the concrete facings demoulded with emulsions appears better qualities that those carried out with oils demoulding.

It is a well-known fact that cement can react with carbon dioxide in the moisture environment. This paper deals with the effects of several factors, such as CO₂ pressure, CO₂ concentration, curing time, water- cement ratio and continued curing after CO₂ mixing or CO₂ curing of cement concrete in the above parameters. Finally, the compressive strength, CO₂ reaction, and carbonation degree of concretes were tested after the specific curing time. The performance of the CO₂ cured mortars was found through the measurement of pressure drop, temperature rise, strength development, mass gain, and carbonation. Results indicated that CO₂-mixed concrete could be more efficient to absorb carbon dioxide by using this pressure method. The results found that the mixing concrete react with carbon dioxide in a short time, and shorten the initial setting time of concrete. The phenolphthalein tests indicated that under most curing conditions the CO₂ penetrated through whole specimens, however, the reactions between CO₂ and cement matrix occurred mainly on the surface of cement particles. The results of CO₂-cured concrete show that the lower water-cement ratio or longer CO₂ curing time produced higher early strength. However, the concrete specimens mixed with CO₂ under 0.2~0.6 MPa pressure produced lower compressive strength.

The quality of hardened concrete is severely degraded if the concrete is frozen at its setting or hardening stage. To prevent the degradation of materials, heating of the materials, equipment and facilities is widely utilized in ready-mixed concrete plants in cold regions of Japan. The heating is widely mentioned and conditionally recommended in specifications and recommendations. While these documents refer to material types to be heated and maximum temperature that will affect the quality of concrete, they do not refer to the energy sources or heating method for equipment and facilities. These factors, however, do have influences on the environmental performances at production stage of concrete. The difference in energy sources, types of heating and operation design of heating make significant difference in the emission of carbon dioxide and other global warming substances. Considering these importance, this paper surveys the types of energy sources and its system for concrete production at ready-mixed concrete plants in cold regions of Japan. The comparison of plants by the difference in seasonal temperature and the location is analyzed through monthly use of energy and on-site observation in various plants.

The paper presents research on sulfur concrete designed with the following combustion products: fly ash, slag and phospho-gypsum. The purpose of this investigation was to evaluate characteristics of sulfur concrete, including its mechanical and durability properties. It was established that mechanical characteristics of sulfur concrete will correspond with those of cement concrete used in the production of small precast members used in civil engineering, hydraulic engineering, road constructions, structures exposed to aggressive environments especially chemical industry, petroleum industry, food industry and farming. The test results confirmed low water absorption, high resistance to wear abrasion, high freeze-thaw scaling resistance (surface weathering) in a salty environment and high compressive and tensile strength of individual compositions. However, the tests results did not confirm the freeze-thaw resistance of the sulfur concrete specimens due to low freeze-thaw resistance of sulfur binders. Further research is needed to increase the freeze-thaw attack resistance of the sulfur polymer to provide the proper resistance of the final sulfur concrete products.