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.

Over the last few decades, ever-increasing demands of society to the built environment have continually increased consumption of energy and materials for the construction and maintenance of structures. Meanwhile, Strain Hardening Ultra High-Performance Fiber Reinforced Concrete (SH-UHPFRC) have the potential to be one of the solutions to contain the explosion of maintenance costs (Economy and Environment), considering their extremely low permeability associated to outstanding mechanical properties and load bearing efficiency compared to deadweight.

The objective of this research is to further improve the already established concept of UHPFRC application for rehabilitation. This paper reports firstly on the development and validation of new low Embodied Energy (EE) SH-UHPFRC mixes with 50 % clinker replacement by Supplementary Cementitious Materials and replacement of steel fibers by ultra-high molecular weight polyethylene (UHMW-PE) ones. In a second step, the mechanical and protective properties of the mixes are investigated with a special emphasis on their quasi-static tensile response, and transport properties. Finally, the dramatic improvement in terms of reduction of EE and deadweight of the proposed mixes is demonstrated.

To investigate the flexural behavior of fiber-reinforced concrete beams, even in the presence of traditional steel rebar, an experimental campaign has been carried out performing three-point bending tests. Conventional raw materials have been used to cast the concretes, which contain different amounts of steel fibers combined, in some cases, with a fixed amount of rebar. In addition, the use of a patented high performance self-compacting fiber-reinforced concrete mixture has been analyzed. In all these cases, the ductility index, measured on the experimental load-deflection curves and used to assess the brittle/ductile behavior of the beams, can also be correlated with some durability parameters. Specifically, better fresh properties of concrete and the increment of flexural ductility improve the resistance to water penetration. In other words, the higher the ductility index the longer the beam durability measured in accordance with major standards.

This work studied the possibility of reusing waste from demolished concrete as aggregate for bedding mortars as well as biomass ash coming from paper mill sludge as partial cement replacement.

During incineration of paper mill sludge, paper and organic compounds are burned out, whereas mineral fillers and inorganic salts are trans-formed into the corresponding oxides at higher temperatures. The obtained paper mill sludge ash is classified as waste, and at present it is mainly conferred to landfill at high costs.

In order to evaluate the quality of joining mortars made of recycled aggregate and biomass ash, both mechanical behavior of mortars and the bond strength developed at the interface mortar–brick were studied. The experimental results show that mortars containing recycled aggregates develop lower mechanical strength with respect to the reference cementitious mortar, particularly when recycled aggregates and biomass ash are used together. Nevertheless, the bond strength at the interface between the mortar and the brick resulted higher if an inorganic primer is used. However, concerning bedding mortars, the mechanical performance of the overall mortar–brick system, strictly related to the mortar–brick adhesion, makes the mortar bond strength certainly more important than its mechanical strength.

Textile-reinforced concrete (TRC) has great potential for application in structures exposed to severe mechanical or environmental loading. This article presents an overview of the current knowledge available on the durability of this composite and its components. An additional focus is centered on the protection of steel reinforcement, such as in the case of the strengthening or repair of RC structures using TRC. In doing this, the transport properties of TRC in the cracked state, its long-term tensile strength and strain capacity, and resistance to aggressive environments have been identified as critical parameters. Current knowledge indicates that TRC can exhibit over the long term high mechanical performance and favorable transport properties when cracked. While the superior resistance of TRC to aggressive environments is to be expected when compared to ordinary concrete, there is little information available on the effects of aggressive environments on the mechanical properties of the material. Since TRC is still a relatively new material, there is no information available on its long-term performance in the field. To be able to utilize the superior qualities of TRC fully, it will be necessary to develop a realistic and reliable performance-based durability design concept for structures made of or strengthened by TRC. This paper is an attempt to provide elements for such a framework.