Simulation of Concrete Batch Plant Production

The decision-making process is a very essential part of any construction operation. Simulation can be used as a tool to assist construction managers in making informed decisions. In this paper, simulation is applied to concrete batching operations to analyze alternative solutions and resource management. Data are collected to define activity durations for the plant. A simulation model is constructed for the plant using the MicroCYCLONE simulation system. Based on sensitivity analysis, management tools are constructed to help the decision maker. These tools are a time-cost-quantity chart, a feasible region analysis, and a contour lines chart. Time-cost-quantity and contour lines charts are used for determining production time, production cost, and resources for a required distance from the plant. The feasible region chart is used for determining the range of alternative solutions that can be taken to minimize production time and cost of the available plant resources, according to the required transportation distance.     

HKCONSIM: A Practical Simulation Solution to Planning Concrete Plant Operations in Hong Kong

Newly developed approaches for construction simulation have been used to model the one-plant-multisite ready mixed concrete (RMC) production system, validated by real-life operations data in Hong Kong. HKCONSIM—a computer system for simulation modeling and analysis of Hong Kong’s RMC production operations was developed in-house. The system is suitable for the resource provision planning and the production planning of a RMC plant, so as to meet given demands at a number of sites for concrete over a working day. The emphasis of the simulation modeling is on the interactions of multiple sites with the plant, and the objective is to improve the supply service levels and the utilization of plant resources. One significant improvement achieved via the research is that to simulate the RMC production operations with HKCONSIM does not require familiarity by the user with any software-specific terminology and modeling schematics, in contrast with existing simulation methods; the process of constructing a simulation model is reduced to specifying the attributes for each pour and site and providing the plant and truckmixer resources available on self-explanatory on-screen forms. Therefore, by experimenting on a HKCONSIM produced model the user, being a practitioner in the concreting industry, can readily study complicated relationships between the pattern of demand for concrete, the resources available to the system, and the service levels achieved together with the utilization levels achieved for the resources involved. Conclusions are given on the research and recommendations for future work made.     

高效均化库的优化设计及应用

分析认为石灰石是影响熟料生产中质量状况的主要因素。通过对目前水泥生产中原料预均化设施进行分析及比较。优化设计实施了以矩形均化库和配套闭路筛分破碎设施等组成的高效均化库。使石灰石中CaO标准偏差由进厂时的5％降至磨成的0．8％，石灰石粒径由原25mm降至9mm，出磨生料三率值KH、n、p合格率分别提高12．1％、10．0％、8．4％，熟料标号提高，降低了生产成本，年效益可达310余万元。     

Torsional Design of Hybrid Concrete Box Girders

Hybrid concrete box-girder bridges that include prestressed slabs and corrugated steel webs provide a major improvement over traditional prestressed concrete box-girder bridges. To reduce the self-weight, high strength concrete is used for the top and bottom slabs and corrugated steel webs are employed for the webs. Because the weight of the girders has been reduced, the span length can be increased for more cost-effective design. A series of systematic tests on hybrid concrete box girders subjected to torsion has been performed. According to the test results, an analytical model was developed. Using the developed analytical model, a step-by-step procedure for torsional design of such bridges is presented in this article. Based on the design procedure proposed, a girder is designed by the analytical model and checked to satisfy structural codes.     

Structure transformation of alpha-brass subjected to cold work

X-ray evidence has been observed which indicates that a change from cubic to a hexagonal structure can occur in plastically deformed alpha-brasses. This transformation occurs only in the bulk of the material and not at the surface. The amount of deformation required to produce the transformation decreases for alloys containing lead. A model for the transformation is proposed. Calculated X-ray reflections of the proposed new hexagonal structure are consistent with the observed reflections.     

Nonlinear Analytical Solution for Cable Truss

In this technical note the nonlinear closed-form static solution of the suspended biconvex and biconcave cable trusses with unmovable, movable, or elastic yielding supports subjected to vertical distributed load applied over the entire span is presented. Irvine’s linearized forms of the deflection and the cable equations are modified because the effects of the nonlinear truss behavior needed to be incorporated in them. The concrete form of the system of two nonlinear cubic cable equations is derived and presented. From a solution of a nonlinear vertical equilibrium equation for a loaded cable truss, the additional vertical deflection is determined. The transformation analytical model serves to determine the response, i.e., horizontal components of cable forces and deflection of the geometrically nonlinear truss, due to the applied loading, considering effects of elastic deformations, temperature changes, and elastic supports. The deflection of asymmetric prestressed cable trusses has been compared with Irvine’s linear solution as well as the nonlinear finite element model results.     

Increasing the efficiency of the process of the alumina production by the Bayer method with the aid of a computer model

The object of studies was an alumina plant operating according to the Bayer process; the basic tool of these studies was a computer model of alumina production which allows optimization. Methods have been developed, which make it possible to reveal the degree of the influence of the properties of raw materials and technological characteristics of production on the economic efficiency of the production. The greatest attention was given to the technological processes which form the Bayer cycle, i.e., to leaching, decomposition, thinning, and evaporation. The process of the passage of material flows through the entire Bayer cycle and the obtaining of qualitative and quantitative characteristics of these flows has been simulated. A model of phase diagrams which makes it possible to approximately determine the shape and position of the solubility isotherms of gibbsite depending on temperature has been constructed. The main result of this work is the development of an efficient tool which ensures conducting the optimization of the most important technological characteristics of alumina production on the basis of its complex technical and economic estimation.     

The Perun-S Computer-Aided Detonation Plant

A commercial variant of a computer-aided detonation plant for application of protective coatings has been designed and manufactured. Because of the technological capabilities of the equipment it may be used to solve problems of scientific research as well as production problems.     

Design and Application of Risk Adjusted Cumulative Sum for Strength Monitoring of Ready Mixed Concrete

The cumulative sum procedure is an effective statistical process control tool that can be used to monitor the quality of ready mixed concrete during its production process. In this paper, an attempt has been made to design and apply a new cumulative sum procedure for the ready mixed concrete industry, which takes care of the risks involved in and associated with the production of concrete. This new procedure can be termed as risk adjusted cumulative sum. The 28-day characteristic cube compressive strengths of the various grades of concrete and detailed information regarding the production process and the risks associated with production were collected from the operational ready mixed concrete plants in and around Ahmedabad and Delhi, two important cities in India. The risks were quantified using a likelihood-based scoring method. Finally, a risk adjusted cumulative sum model was developed by imposing the weighted score of the estimated risks on the conventional cumulative sum plot. This model is a more effective and realistic tool for monitoring the strength of ready mixed concrete.     

Constitutive Model for Time-Dependent Behavior of FRP–Concrete Interface

A fundamental understanding of fiber-reinforced polymer (FRP) laminate bonding behavior, including bond strength and effective bonding length, is of primary importance for the development of design guidelines and codes for concrete structures strengthened with externally bonded FRP reinforcement as a bond-critical application. However, the long-term serviceability of such FRP-strengthened structures is still a concern due to a lack of both long-term performance data and a suitable model to represent these performances. This study aims at presenting a viscoelastic model describing the time-dependent behavior of the FRP–concrete interface. The proposed model has been calibrated using strain measurements of the designed specimen for the experimental investigation of the time-dependent behavior of the FRP–concrete interface, including the development of the effective bonding length. Afterward, the proposed model satisfactorily predicts the time-dependent bonding length of the FRP sheet in comparison with the experimental results. The effects, both of creep of the adhesive layer and of creep and shrinkage of the concrete, on the changes in the effective bonding length of the PFRP sheet are also discussed.     

Optimal Distribution and Control of Storage Tank to Mitigate the Impact of New Developments on Receiving Water Quality

Storage tanks are commonly installed in a combined sewer system to control the discharge of combined sewer overflows that have been identified as a leading source for receiving water pollution. The traditional approach to determine the distribution of storage tank volume in the sewer system is confined to the use of objectives within the system itself due to the limits of separate modeling of urban wastewater systems, consisting of the sewer system, wastewater-treatment plant, and receiving water. The aim of this study is to investigate the optimal distribution and control of storage tanks with an objective to mitigate the impact of new residential development on receiving water quality from an integrated modeling perspective. An integrated urban wastewater model has been used to test three optimization scenarios: optimal flow rate control, storage distribution, and a combination of these two. In addition to the cost of storage tank construction, two receiving water quality indicators, dissolved oxygen and ammonium concentration, are used as optimization objectives. Results show the benefits of direct evaluation of receiving water quality impact in the context of storage distribution optimization. Results indicate that storage allocation should be considered in conjunction with optimal flow rate control to achieve the maximum effectiveness in water pollution mitigation.     

Plasmachrome process for ferrochrome production – thermochemical modelling and application to process data

Plasmachrome is a new process for the production of ferrochrome and chargechrome using a variety of chromium bearing materials. In this paper a thermochemical model has been developed for the Plasmachrome process. The model is based on the equilibrium approach and considers mass and heat balances for the shaft and smelting zone of the reactor. A review of available literature has been made and gaps in thermodynamic data of relevance to the process have been identified. The model has been applied to available plant data for the process. Calculations show a good agreement between model predictions and plant data. It has been shown that the equilibrium approach can be effectively used for process analysis. The model has been used to study the possible effect of different types of material additions on process performance. The results indicate the process to be flexible, permitting many process variations to enable optimal use of different raw materials.     

Fundamental Principles of Site Material Management

This paper was written to fill a void created by the absence of fundamental principles of site construction management. Efficient material management is essential to managing a productive and cost efficient site. For more than 25?years, the senior author has been observing and writing about inefficient labor productivity practices resulting from poor site material management. Using deductive reasoning, fundamental principles were developed to avoid poor practices. A construction site should be portioned into three areas or zones: semipermanent (exterior) storage, staging areas, and workface (interior) storage. Each has a unique function relative to site material management. Using these areas as a framework, fundamental principles are stated and illustrated using a case study project accompanied by numerous photographs and narratives.     

Externally Prestressed High Strength Concrete Viaduct

This paper presents an externally prestressed high strength concrete viaduct designed and erected in Spain. This viaduct, a three-span (41 + 50 + 41 m) continuous beam, has been designed and built with a 60-MPa strength concrete and a fully external replaceable prestressing. The paper describes the bridge, the erection procedure, the ultimate analysis performed with a nonlinear finite-element numerical model, and the thermal stresses measured and calculated at the anchorage diaphragms due to the hydration heat of the concrete. The results of the static tests carried out on the bridge also are commented upon.     

Improving Air-Cooled Condenser Performance in Combined Cycle Power Plants

It has been recognized in recent times that air-cooled condensers (ACCs) are environmentally preferable to the traditional water-cooled condensers for rejecting heat in combined-cycle power plants (CCPPs). However, a drawback of ACCs is that their performance can decline with increasing ambient air temperature. A new approach is proposed in this paper that has the potential to alleviate this drawback of ACCs. In this approach, a chilled-water thermal energy storage system (TES) is used to precool the inflow air to the ACC whenever the ambient air temperature increases above the design air inlet temperature. The temperature of the TES system is maintained by an absorption refrigeration system (ARS) driven by low-quality waste heat from the CCPP. A process model integrating the CCPP with the ARS and the TES has been developed to optimize the volume of the TES. A 500?MW CCPP with steam turbine net output of 170.9?MW was chosen to evaluate the application of this approach for a power plant to be located in southern New Mexico. This analysis showed that a tank volume of 4,500?m3 will be required to maintain the air temperature at the inlet to the ACC at the design value of 20°C throughout the year. Simulations under ambient air temperatures up to 40°C indicated that the proposed system is capable of maintaining the rated net power output of the plant with minimal fluctuations. Simulations also showed that TES tank volume is most sensitive to the design air inlet temperature to the ACC—an increase of this temperature by 1°C can result in at least 25% reduction in the volume.     

Generic Debonding Resistance of EB and NSM Plate-to-Concrete Joints

It is well established that adhesively bonding plates to the surfaces of reinforced concrete members is an efficient retrofitting approach. Specifically, two techniques have emerged: Using thin externally bonded (EB) sheets/plates and near-surface mounted (NSM) strips/bars. A good amount of research has been undertaken worldwide to understand the fundamental behavior describing such adhesively bonded plate-to-concrete joints. Unfortunately, until now, no generic model exists to determine the debonding resistance of both retrofitting techniques. In this paper, a generic analytical model is derived to determine the debonding resistance of any adhesively bonded plate-to-concrete joint using an idealized linear-softening local interface bond-slip relationship. The model is derived using a unique definition of the debonding failure plane and confinement ratio such that it is suitable for both the externally bonded and near-surface mounted techniques. The model is validated by comparison with existing push-pull data as well as 14 new push-pull tests with varying plate cross-section aspect ratios. Comparison with an existing well-known model demonstrates the suitability of the proposed generic model. The model can be used to predict the intermediate crack debonding resistance of strengthened reinforced concrete members.     

Time-Dependent Behavior of RC Beams Retrofitted with CFRP Straps

A retrofitting technique that uses prestressed unbonded carbon-fiber-reinforced polymer (CFRP) straps to provide additional shear capacity has previously been shown to be successful under short-term static loading conditions. The current study explores the longer-term behavior of this retrofitting technique through two experiments (a sustained load and a cyclic load experiment) and the development of a model based on the modified compression field theory. The experiments indicated that the strain in the CFRP straps changes with time due to changes in the load sharing with the concrete (caused by creep) and the steel stirrups (caused by yield of these elements). The predictive model was initially validated against static experimental results before being applied to the longer-term experiments. The model predicts the trends in behavior well although it is conservative in its estimates of strap strain. The model was then used to determine the influence of stirrup yielding, the load level before and after retrofitting, and the duration of loading on the CFRP strap strains. The initial results suggest that the largest increases in long-term strap strain will occur when the straps are installed early in the structure’s service life although further experimental validation is required.     

Cloning and biochemical characterisation of Aspergillus niger hexokinase--the enzyme is strongly inhibited by physiological concentrations of trehalose 6-phosphate

Three crystal forms of Naja naja naja phospholipase A2 were discovered through random crystallization screening, including two heretofore uncharacterized forms. The crystallization conditions for both of these novel crystal forms are Ca(2+)-free whereas previously reported conditions include Ca2+. One of the new crystal forms has a cubic lattice in the space group P2(1)3 (a = b = c = 69.24 A), the other has an orthorhombic lattice in the space group P2(1)2(1)2(1) (a = 67.22 A, b = 73.48 A, c = 87.52 A) and a previously characterized crystal belong to the tetragonal space group P4(3)2(1)2 (a = b = 88.6 A, c = 107.4 A). The structure from the cubic crystal form has been determined to 1.8 A and refined to an R-factor of 17% while the structure from the orthorhombic form has been determined to 2.65 A and has been refined to an R-factor of 21%. The determination of the cubic structure extends the resolution to which structures of this molecule have been determined from 2.3 A to 1.8 A. The two newly determined structures, in combination with the previously determined structure, generate an informative structural ensemble from which structural changes due to Ca2+, which is required for catalysis, and the effect of crystal contacts on side-chain conformations and oligomeric association can be inferred. Both of the newly determined structures reveal a trimeric oligomer as observed in the tetragonal structure; this appears to be a unique feature of the Naja naja naja enzyme.     

Reuse of Industrial Sludge as Pelletized Aggregate for Concrete

Industrial sludge is generated at a rate of 100 metric tons∕day, from a copper slag recycling plant. The industrial sludge is currently being landfilled. However, limited availbility of landfill sites has raised the need of an alternative disposal. A renewed interest in converting the industrial sludge into construction materials has been prompted to achieve a viable disposal option in saving the depleting natural resources of raw materials as well as the environment. This study describes the use of sintered sludge pellets as a complete replacement for regular granite aggregates in concrete. The pelletized sludge was fired to a temperature of 1,135°C at which the sintering process occurs, producing a hard fused basalt-like mass. In comparison with normal granite aggregates, the sintered sludge pellets display a higher aggregate strength, a higher porosity, and a lower aggregate density that manifests attributes better than that required of construction aggregates. The concrete cast with the pelletized aggregtes achieved a compressive strength of 38.5 N∕mm2 after 28 days and was comparable to the control specimen. Leaching tests conducted on the sludge pellets and concrete showed that all leachate contamination levels determined using the column leaching test are within acceptable ranges after 130 days of stabilization. The experimental results indicated that a complete replacement of conventional aggregates with sintered sludge pellets for structural concrete is both technically and environmentally feasible.