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These criteria can also be used to organize a "lessons learned" database that future efforts could access to enhance their chance of success. Does it offer the potential to be cost-effective?
This factor examines, from basic considerations, the ability of a process to provide the required quality level at minimum input cost per unit of output. This would include, for example, the minimization of such factors as energy use, scrap generation, and labor costs. Thus, a single precisely controlled process that combines in essentially one operation what had previously required multiple operations could be highly rated by this criterion.
Does it provide a unique way to cost-effectively exploit the physical properties of an advanced material? Too often, advanced materials with outstanding properties have languished in the laboratory because little, if any, consideration had been given to the methods required to produce them in usable shapes and quantities.
Processes that are fundamentally simple, requiring low capital investment, would be highly rated by this criterion. Can it shorten the time to transform a product technology from the research stage to commercialization? This factor includes the capability of providing rapid response to customer needs. Unit processes that are relatively easy to scale-up from the laboratory to the factory due to their inherent flexibility, as well as efforts to develop process technology concurrently with the product technology, would be highly rated.
Does it provide a method of processing that is fundamentally environmentally friendly? Since it is often difficult to attach a firm cost to environmental transgressions a priori, processes that avoid the difficulty in the first place, or that produce environmental effects that can be readily mitigated, would be highly rated.
Is it applicable to a diverse range of materials? This criterion would rate higher those processes that are adaptable to a range of materials, and those that are more specialized would rate lower. However, it should be noted that nearly every unit process requires some amount of adjustment to accommodate different types of materials. For example, processes in the consolidation family are used in the production of metals powder compaction , ceramics hot pressing , and polymer composites autoclaving.
In addition, each combination of process and material requires consideration of the five process components for successful production.
Figure illustrates this interaction of process families, materials, and process components. The committee examined the many research opportunities that were identified within each family of unit processes in Part II to determine which were the most important to the advancement of unit process technology. The committee concluded that the efficacy of a new unit process, or process improvement, could only be assessed in the context of a specific application, although criteria could be developed to identify promising research opportunities.
This led the committee to synthesize the various research opportunities identified for each family of unit processes. In doing so, it became apparent that a thorough understanding of any unit process with its five process components is dependent on six critical or key technologies that enable the correct design and operation of all processes. The committee determined that the six enabling technologies are workpiece material behavior, process simulation and modeling, process sensors, process control, process precision and metrology, and equipment design.
Materials behavior involves an understanding of materials properties and microstructure of the workpiece at the start of the process and during the process as the material is modified. A large database for properties for the extremes of processing conditions e.
The evolution of microstructure, the conditions under which fracture occurs, and an understanding of interface conditions such as friction are among the factors that must be understood in the context of specific unit processes.
To achieve this goal, they should have a sound knowledge of the basic underlying principles and interactions. From their many years of experience gained in close collaboration with industrial partners, the authors concluded that this was exactly where a real gap existed in the literature on precast technology, which is why they decided to write this book. Chapter 1 outlines the basic principles required to understand the interactions referred to above. The process for manufacturing concrete products is first described on the basis of the process elements, process layout and process flow.
The processing behaviour of concrete is described with particular attention paid to moulding and compaction of the concrete mix. The associated processing parameters are defined. This chapter also describes the raw materials used to produce the concrete mix whilst also looking at the concrete mix design in greater detail.
The evolution from a ternary mixture to the current quinary system is also discussed. The empirical solutions commonly applied in the past will be increasingly replaced by process optimisation and simulation exercises that take account of the properties of the concrete mix, fresh and hardened concrete as well as their testing.
The fundamentals of the products are outlined starting with a clear definition of the concrete products and product groups whose manufacture is described in subsequent chapters. This is followed by a discussion of the requirements for the product properties and a description of the associated testing methods. In the chapter describing the basic aspects of the equipment, reference is first made to the various types of vibration equipment, which is crucial for the manufacture of concrete products.
The current situation with regard to modelling and simulation of the workability behaviour of mixes is then described. This option to evaluate processing work steps in conjunction with laboratory-, pilot- and industrial-scale testing is becoming increasingly popular. The development of the associated hardware and software will strengthen this trend.
The application of these principles is demonstrated in Chapter 2: The same applies to the dynamic modelling and simulation of production equipment. Modelling of equipment using. The application of these simulation methods is then described along with the individual equipment components. The processes and equipment to manufacture precast concrete products are then discussed for the individual product groups:. The characteristics of the final product are of crucial importance, which is why in-process quality control is becoming increasingly popular.
Implementation of a quality control system requires state-of-the-art measuring and automation technology, which is also discussed in this book. Also addressed are issues associated with appropriate measures for reducing noise and vibration during the manufacture of precast products.
The production process to manufacture concrete products can also be considered a system, just like any other process. The schematic representation shown in Fig. As is the case with any system, the basic characteristics of this production process are its function and structure. The function of the production process is the conversion of certain input parameters e. The structure of the production process serves to fulfil the function and includes a set of elements that are interlinked by particular relationships.
The production process is subject to certain conditions that must be considered during the planning, preparation and execution stages. These are:. The process to manufacture concrete products is a complex, dynamic system made up of technical and organisational elements.
Process elements are basic processes or workflows that can no longer be sub-divided from a macro-technological perspective. These process elements are linked by temporal, spatial and quantitative relationships that are determined by the process function. Therefore, the following parameters need to be determined to describe the production process fully:. Like any other process, the basic operation, as a process element, has both a function and a structure.
The function of the basic operation is a fundamental change in the state of the target object towards the final product and aims to achieve a certain intermediate state. They are modified by basic operations of the various types of change, all of which can be assigned to the following categories:.
Depending on the relevant type of change, the basic operations are elements that determine the production process and can most generally be described, from a functional point of view, as:. With regard to the overall production process, the characteristics of its elements also form the basis for its constituents:.
In the basic operation, a human being uses a technical means to affect the object of change directly or indirectly, thus modifying it with a certain aim or purpose. The technological method governs the basic way in which this proceeds. Technological methods thus represent the approach usually applied in practice to implement scientific effects and to thus modify the object in accordance with the intended purpose.
The technological method is not an object itself, it is inherent to the technical means that fulfils its function within the technological process. The technical means represents a technical object that can be considered a system, i. The function of the technical means is to implement one or several technological methods within the technological process. In accordance with this function, it is useful to classify these means analogously to the functional relationships between the basic operations i.
The set of material-related means comprises all technical means that serve to change the state of materials in the most general sense. These include all pieces of equipment such as machines, apparatus, devices and systems that are used to manufacture products from the materials. Energy-related means comprises all technical means that convert or transform energy, such as drive motors, steam generators, transformers or energy distribution systems. Information-related means comprise all technical means that serve to process information.
These include, for instance, IT systems, signalling installations, measuring equipment as well as weighing and batching units. The coupled set of technical means used in the production process represents the production line, which is an overall entity technological line and is also a prerequisite to carry out the production process Fig. The technical means are thus at the very heart of the various processes. Within the technological process, certain relationships exist between the process elements that are determined in space and time.
As a result, the set of relationships between the process elements represents the spatial and temporal organisation of the technological process, i. Both sides of the structure are governed by the following underlying conditions that must be met by an appropriately designed structure:. The spatial arrangement is thus defined by the allocation of the process elements to the required functional sequence and the associated flow of materials, as well as by the options that exist with respect to the set-up and positioning of the technical means.
The temporal arrangement of the process elements is determined by the required functional sequence and by factors associated with the output parameters and work scheduling. Couplings are the links that permit transfer of the object of change material, energy, information between process elements.
Certain compatibility conditions must be met in order to fulfil the coupling function. To achieve compatibility, the output variables of the preceding operation must correspond to the input variables of the subsequent operation with respect to space, time and quantity.
If this condition is not met, the operations cannot be coupled. In such a case, either a modification of the elements to be coupled or the integration of additional elements is required.
In this model, a spatial coupling refers to a spatial-geometrical relationship between process elements. This requires geometrical compatibility at the spatial points where objects of change are transferred. For this purpose, the three-dimensional coordinates of the boundaries of the process elements the technical means are aligned with each other in such a way that the objects of change can be transferred. A spatial coupling must fulfil the following conditions:.
A temporal coupling refers to the alignment of process times of the various process elements. Two process categories can be distinguished with respect to their temporal characteristics:.
Serial processes require that a process element must have been completed before the following element can commence. Parallel processes require that all parallel processes involved must have been completed at the lateral nodes so that they can be merged into a common process. In this model, the co-determinative processes must be adjusted to the determinative process Fig.
The following compatibility condition applies to the quantitative coupling of two consecutive process elements:. Process elements to be integrated as intermediate elements mainly include storage elements that are introduced for compensation purposes and which put a certain number of objects of change on hold for a defined period Fig.
A parallel arrangement is required if there are process elements with varying flow increments. In this case, a single, larger-flow element is coupled to several elements with smaller flows in such a way that an alignment is achieved. The spatial structure refers to the three-dimensional arrangement and coupling of the process elements. It represents the spatial organisation of the technological process and thus of the production line as the entity that comprises all technical means [1.
Its configuration can be varied according to the following types of spatial organisation:. Basic types of arrangement are distinguished according to the process- or product-driven nature of the spatial arrangement. Technical means that implement identical processes are grouped together in a spatial arrangement and treat various types of objects of change Fig.
Technical means that implement different processes are grouped together in a spatial arrangement according to the work sequence required for a certain type of object of change Fig. Types of motion can be distinguished according to the state of motion between objects of change and technical means:.
The objects of change OC remain at the same manufacturing station during the determinative basic operations. The technical means Mt are mobile.
They are moved towards the object of change, where they act on it, and are then moved to the next manufacturing station Fig.
The principle of stationary production is used by a number of different systems, of which the following are of particular relevance to the production of wall and structural framework elements:.
The objects of change OC move from one manufacturing station to the next. The technical means Mt are stationary Fig. One or more work steps are carried out at each of the stations manufacturing units , which is why these work steps run parallel to each other [1.
Block machines used to manufacture concrete products are another example of this manufacturing principle. Concrete products include durable goods made of concrete, reinforced concrete and prestressed concrete [1.
In accordance with these stages, concrete products are manufactured in the following sequence Fig. In this workflow, the production of concrete elements is the main process to shape and manufacture the concrete products.
The steps of mix production as well as fabrication of reinforcements, moulds and formwork may be allocated to one or several element production processes. They may also be located outside the boundaries of the factory; however, this would increase outlay for organisation and transportation.
The manufacture of concrete products requires a number of changes in the state of the material to achieve a defined manufactured state at each of these stages. During these changes in the state or condition, which are brought about by the intentional action of the technical means, the respective object i. In other words, this constitutes the reaction of the material to the action of the technical means. The processing behaviour is thus process-driven.
In accordance with the main classes defined for the types of change, main processing behaviour classes can also be established Table 1. Just like finished concrete, the initial concrete mix is a very versatile material. With respect to its mechanical properties, it takes an intermediate status between a bulk material and a suspension.
These mechanical characteristics undergo substantial changes during the compaction process, which thus alters the compaction behaviour. Compaction is closely related to the moulding behaviour of the concrete mix to produce the concrete product.
Moulding and compaction serve to transform the concrete mix into a quasi-solid geometric body of fresh concrete [1. This process creates an artificial stone that has a low initial strength, the so-called green strength.
The aim of the moulding process is to produce an accurately shaped concrete product. The concrete mix is poured into the mould so that it completely fills all the corners and edges. The placement behaviour of the concrete is crucial to achieve this goal and depends on the flow properties of the concrete mix. For most types of concrete mixes used to manufacture concrete products, natural compaction effects are also utilised to support the placement process.
Highly flowable mixes, such as self-compacting concretes SCCs , show a very good pouring behaviour because any remaining pores are removed by the gravity effect and the motion of the mix during the placement process. As these concretes are already self-compacted, additional compaction is neither necessary nor possible.
Compaction serves to largely eliminate the external porosity of the concrete mix. The reduction in the void volume should lead to higher densities and thus improve the strength and dimensional stability. Concrete can be considered strong if an almost homogeneous body held together by adhesive and cohesive forces was created due to the high packing density of the concrete constituents.
Concrete can be considered dimensionally stable if no significant dimensional changes occur under ambient conditions in both the loaded and the unloaded states. Despite numerous attempts to find alternative methods, vibration — alone or in combination with other processes — continues to be the most popular method for moulding and compacting concrete mixes in order to manufacture both concrete products and precast elements [1.
The type of action on the concrete mix is a crucial factor that determines the moulding and compaction behaviour. As shown in Fig. With respect to the location of the action, and thus its direction, a fundamental distinction can be made between horizontal, vertical and three-dimensional actions.
As regards the function of the vibration action, harmonic and anharmonic modes of excitation can be distinguished. Both directional counter-acting and non-directional circular exciters can be used to introduce vibration into the concrete. Anharmonic exciter functions can be sub-divided further into periodic and pulsed actions. For instance, a periodic exciter function can be a multi-frequency action that consists of several harmonic components.
Pulsed excitation, also known as shock vibration, is generated by shock-like processes. This triggers the inherent oscillation of all system elements capable of vibration, i. Parameters that characterise the intensity of the action on the concrete mix are discussed in Section 1. The type of exciter function, the mode of action and number of exciters and, in particular, their phase position in relation to each other have a major influence on the moulding and compaction behaviour of the concrete mix.
For example, a phase coincidence of the harmonic vibration components of the vibrating table and tamper head would hardly achieve a good compaction effect. The crucial factor is the generation of a dynamic pressure gradient between the layers of the mix that enables relative motion of these layers and mutual rotation of the mineral aggregate particles.
These requirements must be met by state-of-the-art processes. When producing large-scale precast elements, for example, the low-frequency action on the fresh concrete is complemented by a higher-frequency vertical excitation.