International Concrete Abstracts Portal

There are large numbers of existing buildings around the world and in North America especially in California have been constructed with reinforced masonry since 1930s. These old reinforced masonry walls have not been improved to meet the current standards. Current ACI 440.7R reported as Guide for Design & Construction of externally bonded FRP System for Strengthening Unreinforced Masonry Structures. This document does not address strengthening of existing reinforced masonry structures (i.e. with steel reinforcement). The principle objective of this study was to determine and discuss the failure mechanism as well as to investigate the flexural behavior of reinforced masonry walls strengthened with externally bonded system and subjected to out-of-plane cyclic loading. This will be evaluated by comparing the flexural capacity and ability to sustain large deflection of specimens strengthened with different strengthening systems. In addition, the effect of specific parameters on the flexural response of reinforced masonry wall was investigated including: type and amount of fiber and masonry bond pattern. This study aimed to develop a database of experimental test results to validate the design model presented in next version of ACI 440.7R document. The performance of twelve strengthened masonry specimens was investigated. The strengthening systems that used in this study are fiber reinforced cementitious matrix (FRCM) and fiber reinforced polymer (FRP) technique. These simply supported walls were tested in four-point bending with an effective span of 1.12 m (44-in.) between the supports under an out-of-plane cyclic load at a rate 1.27 mm/min (0.05-in./min). The test results indicated that the flexural behavior of reinforced masonry walls strengthened externally by FRP may be controlled by either FRP rupture or debonding (intermediate crack or plate end debonding failure). The flexural behavior of reinforced masonry walls strengthened externally by FRCM may be controlled by either fiber slippage or debonding.

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.

Current structural concrete design standards require that post-tensioned slab systems be provided with mild steel or post-tensioning tendons to control potential transverse cracking due to shrinkage and temperature effects that may occur soon after concrete is cast and over the life of the structure. For the case of prestressed concrete structures, the ACI 318 Building Code requires that the tendons should be designed such that they provide a minimum average compressive stress of 100 psi (0.7 MPa) on a gross concrete area as an effective prestress. This level of prestress is expected to be sufficient to control cracking caused by shrinkage and temperature effects. The Code further requires that the effects of restraint be considered. Field evidence suggests that this minimum value may not be adequate for some post-tensioned one-way slab systems. Relevant case studies are presented and discussed. In these cases, the structural design included the minimum prestress as required, yet significant transverse cracking was observed on some areas of the slab despite the presence of the shrinkage and temperature tendons. This paper presents a design procedure for controlling shrinkage and temperature cracking in post-tensioned one-way slab systems consistent with current code requirements. A method is proposed by which an equivalent shrinkage stress is calculated. This stress is then used to design the shrinkage and temperature tendons. The equivalent shrinkage stress is calculated considering the restraint on the slab provided by elements such as columns and shear walls. It is shown that this restraint, which is a function of the respective stiffness of the restraining elements, is very significant and its effects should be considered if shrinkage and temperature cracking is to be effectively controlled by either tendons or mild steel reinforcement.

Important and often overlooked parts of any building or structure are the systems located behind the walls, under the floors, and in the ceilings of these structures. Installed when the framework of a building is just taking shape, these systems provide the occupants of the building with potable water and remove the waste water safely, quietly, and efficiently. Because these systems are installed within walls, floors, and ceilings, the reliability and longevity of the systems must be equal to the expected life of the building. Two such systems are the sanitary and stormwater piping systems found in all buildings. The wastewater system removes wastewater from the bathrooms, kitchens, and restrooms located inside these structures. The stormwater or rainwater systems drain the exposed roofs, patios, and terraces of rainwater, melted snow, and ice. Both systems use cast iron soil pipe, which is joined with varying types of fittings, within the building's structure. Both systems operate in nonpressure applications, using gravity to remove the rainwater and wastewater from the building. A necessary part of these piping systems is a reliable, cost efficient method of joining the pipe and fittings. This paper traces the history of cast iron soil pipe and discusses design changes in pipe and fittings and the development of applicable standards.

The quality and cost effectiveness of concrete construction is strongly influenced by the choice of the construction method. In the slipforming method, the stripped walls typically exhibit rough faces and often are deeply cracked. The advantages of working with the highly productive vertical conveyor such as the slipform may be lost, and the appearance of the concrete structure may not meet today's standards. With this disruption of quality, the volume of finishing labor and delivery materials increases, and so do other construction costs. These are some of the reasons that slip forming is not widely used, and is limited to special projects only. The idea behind the roller form system is to avoid the shortcomings of the slipforming method, and to offer the quality and precise geometry made possible by construction systems with immovable forms sheathing and the efficiency of working with the highly productive vertical conveyor of slipforms. The rollerform system can be applied to structures for which the conventional Slipforms method has been used, such as grain elevators, silos, flour mills, bridge piers, nuclear containment vessels, and multistory residential buildings.