Ali Akbarnezhad

Effects of the Parent Concrete Properties and Crushing Procedure on the Properties of Coarse Recycled Concrete Aggregates

AbstractFine tuning of concrete recycling processes requires a comprehensive understanding of the overlapping interactions and effects of the various influencing parameters. The most important parameters associated with recycled concrete aggregate (RCA) production that may affect quality and yield include such properties of the parent concrete as the composition, strength and aggregate grading, type of crushers used, number of crushing stages, the size of the RCA particles, and the size reduction sequence. The effects of such parameters overlap and interact with one another and render it impossible for firm conclusions to be drawn on the effects of one parameter in isolation as evidenced by results reported in available literature. The present paper reports on the findings of an experimental study on the concomitant effects of the strength of the parent concrete, size of the natural aggregates used in the parent concrete, and the number of crushing stages on the properties of coarse recycled concrete aggr...

Acid Treatment Technique for Determining the Mortar Content of Recycled Concrete Aggregates

The presence of old cementitious mortar in recycled concrete aggregates (RCA) has been reported to be one of the main factors contributing to a lowering of the performance of concrete made with RCA relative to those made with natural aggregates (NA). This difference in performance has been attributed to the proportion of mortar present in the RCA vis-a-vis the NA used to cast the original parent concrete. Therefore, determining the mortar content might provide an effective means of assessing the overall quality of RCA. Also, as reported in the available literature, it is essential to take into account the amount of mortar present in RCA as part of the total mortar present when designing concrete mixes cast with RCA. However, an easy-to-use standard method for accurately determining the cementitious mortar content of RCA is not available at present. In this study, an acid treatment testing method is proposed to determine the mortar content of RCA. The method is able to remove most, if not all, of the cementitious mortar and takes approximately 24 h to carry out. In addition, the effects of mortar content on properties of RCA including 24-hour water absorption, bulk density, and Los Angeles abrasion resistance were investigated. The effects of the original parent concrete strength on the relationships between mortar content and RCA properties were also investigated. The study was confined to only granitic coarse aggregates.

A Computational Method for Estimating Travel Frequencies in Site Layout Planning

Optimizing the layout of facilities on a construction site to minimize the material handling costs has been widely investigated in the literature. An integral part of the objective function utilized in the previously proposed optimization models is the frequency parameter, which generally provides a rough estimate of the frequency of travel between each pair of facilities at a specific stage of the project. The majority of travel frequencies deduced in prior studies have been estimated merely based on past experience and may not be an actual representation of movements within the project studied. There is currently a lack of a systematic approach for estimating travel frequencies, required in site layout planning, based on the information available at early stages of the project. Obtaining a reasonable estimate of the travel frequency matrix requires a realistic evaluation of the material transportation quantities at each construction stage. This necessitates the utilization of information on the progress of different activities and their corresponding material needs during the various stages. This paper presents a framework for obtaining travel frequencies at different construction project phases by taking advantage of the information made available by building information models and project schedules. The estimated frequencies are later embedded as parameters in an optimization model to improve site layout planning. The results of a case study are presented to highlight the capabilities of the proposed framework.

Incorporating Multiskilling and Learning in the Optimization of Crew Composition

AbstractThe presence of multiskilled workers in a crew can increase the crew’s productivity through reducing inefficiencies and supervision requirements, while also providing on-the-job learning opportunities for single-skilled workers. The effect of the presence of multiskilled workers on the learning rate of workers, which is also a function of skill level and experience, and thus on the crew’s productivity, is especially significant in repetitive construction projects. This paper presents a mathematical model for identifying the optimal combination of single-skilled and multiskilled workers with different levels of experience in the crew to minimize the duration of construction projects by accounting for the overlapping effects of multiskilling, skill level, and learning on the crew’s productivity. The model is applied to an illustrative case project to demonstrate the practicality of the model. The optimum crew compositions for different activities involved in the case project are identified using a s...

BIM-enabled sustainability assessment of material supply decisions

Purpose Enhancing sustainability of the supply process of construction materials is challenging and requires accounting for a variety of environmental and social impacts on top of the traditional, mostly economic, impacts associated with a particular decision involved in the management of the supply chain. The economic, environmental, and social impacts associated with various components of a typical supply chain are highly sensitive to project and market specific conditions. The purpose of this paper is to provide decision makers with a methodology to account for the systematic trade-offs between economic, environmental, and social impacts of supply decisions. Design/methodology/approach This paper proposes a novel framework for sustainability assessment of construction material supply chain decisions by taking advantage of the information made available by customized building information models (BIM) and a number of different databases required for assessment of life cycle impacts. Findings The framework addresses the hierarchy of decisions in the material supply process, which consists of four levels including material type, source of supply, supply chain structure, and mode of transport. The application is illustrated using a case study. Practical implications The proposed framework provides users with a decision-making method to select the most sustainable material alternative available for a building component and, thus, may be of great value to different parties involved in design and construction of a building. The multi-dimensional approach in selection process based on various economic, environmental, and social indicators as well as the life cycle perspective implemented through the proposed methodology advocates the life cycle thinking and the triple bottom line approach in sustainability. The familiarity of the new generation of engineers, architects, and contractors with this approach and its applications is essential to achieve sustainability in construction. Originality/value A decision-making model for supply of materials is proposed by integrating the BIM-enabled life cycle assessment into supply chain and project constraints management. The integration is achieved through addition of a series of attributes to typical BIM. The framework is supplemented by a multi-attribute decision-making module based on the technique for order preference by similarity to ideal solution to account for the trade-offs between different economic and environmental impacts associated with the supply decisions.

Location Optimization of Tower Crane and Allocation of Material Supply Points in a Construction Site Considering Operating and Rental Costs

AbstractThe choice of a suitable tower crane along with its location may considerably affect the costs and duration of the construction process. The location of the tower crane determines the travel time of transporting material between the supply and demand points and thus the operation costs. On the other hand, the distance between the tower crane and supply points as well as the distance between the tower crane and demand points considerably affects the minimum required load moment capacity of the cranes and thus the cranes’ rental and operating costs. Previous studies on optimizing the location of tower cranes on a construction site have focused mainly on minimizing the crane operation costs through minimizing their operation time, overlooking the effect of tower crane location on its required capacity and thus rental and operation costs. This paper presents a modified crane location optimization model that also accounts for the effects of crane location on its required capacity, on top of operating t...

A cutting plane algorithm for the site layout planning problem with travel barriers

A novel discrete Construction Site layout planning model (SLP) is proposed, where multiple coverage of locations by facilities is permitted.We contrast the proposed model with the approach commonly adopted in the literature to solve the SLP problem to exact optimality.We quantify the impact of space discretisation on discrete SLP models.We propose a novel cutting plane algorithm to solve large instances of the discrete SLP problem.We provide a comprehensive analysis on the computational effectiveness of the proposed models. Site layout planning is an imperative procedure that may significantly impact the productivity and the efficiency of logistical operations undertaken on a construction site. This paper considers the site layout planning problem (SLPP) which entails the allocation of temporary facilities on a construction site in the presence of travel barriers such that the total transportation cost between facilities is minimised. In order to account for travel barriers, the SLPP is typically solved under the assumption that the available region for facility layout can be discretised. In this paper, we propose a general Mixed Integer Programming (MIP) model to represent the SLPP, accounting for the presence of barriers, and we show how space-discretised formulations can be derived from this model. In particular, we propose a novel MIP model, which permits facilities to cover multiple locations. This is then benchmarked against a commonly adopted MIP model in the literature. We also highlight a systematic procedure to convert the continuous feasible space in SLPP to a set of discretised locations based on the concept of d-visibility, enabling us to approximate the barrier distance function embedded in the objective function. In particular, we focus on presenting a simple space discretisation approach for converting the continuous SLP into a discrete problem for which the discrete SLP models would be applicable. Space-discretised MIP formulations are highly combinatorial and we introduce a cutting plane algorithm to improve their tractability. Specifically, we propose a novel exact location-decomposition algorithm which works from a relaxed MIP formulation and iteratively generates feasibility cuts to converge to an optimal solution. Both space-discretised MIP models and the decomposition algorithm are tested on a large group of instances to analyse their effectiveness in solving the SLPP. Computational results indicate that the proposed location-decomposition algorithm improves on the pure MIP approach and provides a competitive framework to solve realistic SLPP instances.

Accounting for Transport Times in Planning Off-Site Shipment of Construction Materials

AbstractOff-site transportation of construction materials is planned commonly by considering the transportation costs as the dominant decision variable. Despite the significant impact of delays in the delivery of materials on the progress of projects, there is a lack of a systematic approach to estimating the off-site transport time of materials by considering the material characteristics and logistics options. This paper uses the results of a case study to highlight the importance of accounting for off-site material transport time in the planning of an industrial megaproject where small delays in activities requiring diverse materials could significantly delay the progress of the project, leading to considerable financial loss in some cases. In addition, a framework is proposed for estimating the duration of off-site transportation in industrial megaprojects by categorizing construction materials based on their supply chain structure and accounting for the effects of the transport mode, size, and weight ...

Separation processes to improve the quality of recycled concrete aggregates (RCAs)

After undergoing a number of conventional cycles of crushing and sieving, coarse recycled concrete aggregates (RCA) particles generally comprise one or more particles of natural coarse aggregates surrounded fully or partially by a layer of mortar and/or cement paste. Some of the RCA particles may even be just lumps of mortar embedded with smaller sized natural aggregates (NA). It is this presence of mortar that has been reported as the main factor contributing to quality issues relating to RCA. This chapter begins by discussing how reducing mortar content can improve the properties of RCA and recycled aggregate concrete (RAC). It makes references to available international standards and reviews and compares various state-of-art, effective and innovative beneficiation processes available.

Importance of Planning for the Transport Stage in Procurement of Construction Materials

The use of logistics milestones, as predecessors for construction works, is gaining popularity to improve the control over the material procurement stage and minimize the risks of delay in the project completion resulting from late material deliveries. Transportation is an important phase in the procurement process which can account for up to 20% of the total project expenditure in some industrial construction projects. However, despite its importance, transportation is usually overlooked when planning the material procurement stage and evaluating the potential risks of delay. This study evaluates the current practices in managing transportation stage of the construction material procurement process and the perception of the industry practitioners about the importance of considering material transportation in project planning using the results of a limited systematic survey. In addition, the importance of transportation in the procurement of construction materials is studied by considering the actual data on shipment of construction materials/components in two industrial projects. Results indicate that material handling procedures adopted in industry are highly disorganized and transportation variables are ineffectively articulated. The results highlight the need for methods to plan, monitor and control the transportation stage as an independent activity in the material’s life cycle. Besides the travelling distance, weight, dimension, mode of transportation, and terms of delivery were identified as the main factors affecting the transportation of the construction materials.