نشریه مهندسی و مدیریت ساخت
سال چهارم شماره 3 (پیاپی 15، پاییز 1398)

One of the main costs in construction projects is the cost of human resources, the correct management of which will increase productivity in construction projects. The most important issue in human resource management is to identify the time and points where projects face time wastage. Time management and increasing the work efficiency of projects requires the use of methods and tools. In this article, with a case study of a construction workshop, we will discuss how to use six sigma methodology and the role of RFID technology in identifying the points and people who have the most wasted time in the workshop, and then by presenting solutions to try to optimize and reduce time wastage in the project. After applying changes to reduce time in this workshop, we can see the results obtained in relation to optimization and time reduction. In this regard, by combining two different branches of six sigma, which is an optimization method, and six sigma technology, a practical method was presented to reduce wasted times and manage them, so that one of the issues and problems in construction workshops was optimized and In fact, time management should be addressed in human resources. In this way, it was observed that with the implementation of RFID technology, the wasted time of the workers was calculated and the people who have a lot of wasted time were identified, and its optimization was done using the solution of replacing people.

In the conditions of acid rain, chemical reactions occur in the concrete structure, which leads to a change in pH. When these reactions continue, concrete begins to lose its mechanical strength, which leads to cracking, weight loss, and finally the destruction of the structure. Since the control of acid rain and its effects on the surrounding environment is unavoidable in some cases, so far researchers have conducted many studies on this category and have provided solutions to eliminate or control its effects. One of the new solutions in this field is the use of nanoparticles. In recent years, studies have been focused on silica nanoparticles, with the aim of increasing the properties of concrete by using this material. Adding nano-silica to concrete in non-acidic (neutral) conditions reduces water permeability in concrete and also increases resistance against chemical attacks. In this article, the mechanical characteristics and durability of concrete containing nano-silica, including weight loss, compressive strength, electrical resistance, and water absorption rate under acidic conditions are investigated. According to the obtained results, with the increase of nano-silica in concrete, the mechanical properties and durability of concrete improve, but with the increase of water acidity, the durability and mechanical properties of concrete decrease.

Widespread concerns about energy conservation, global warming, and the depletion of the planet's non-renewable resources have led to the development and expansion of green buildings, not only as a luxury and well-being, but also as an undeniable necessity for Conserve the life of the planet. Due to the importance of the issue on a global scale, many countries are determined to develop these buildings, but unfortunately in our country, due to some obstacles, the pace of progress in this area is very slow. In this study, an attempt has been made to identify the most important obstacles and risks against the implementation and expansion of green buildings in the country, and then prioritize them through hierarchical analysis based on distributional questionnaires between experts and specialists. These obstacles can be overcome. According to the results of the questionnaires, in the main criteria section, economic, technological, social, legal, political and environmental criteria, respectively, took the first to last priorities. In the sub-criteria section, high initial cost, low energy cost and people's resistance to change and maintenance costs of green building systems were the most important priorities, respectively. In the end, we have tried to provide solutions and suggestions in order to reduce these obstacles.

Small cracks in concrete may turn into large cracks over time, reducing the useful life of concrete structures. Therefore, the rate of growth and expansion of cracks should be limited. Repairing cracks in concrete is one of the effective ways to prevent the spread of cracks. Therefore, from the past until now, different methods for repairing cracks created on concrete due to different factors have been studied and compared. This study presents a biological method to improve the self-healing effect of concrete beams by the microbial activity of Bacillus subtilis. In this study, self-healing begins with the injection of Bacillus bacteria through an insulin syringe into the crack. For this purpose, 6 concrete beams with dimensions of 15 × 15 × 120 cm were made and the self-healing property by creating cracks by applying static torsional load was evaluated. In the end, according to the final torsional anchor of the beams, this result was obtained. The beam repaired with this method has increased the torsional capacity of the original control sample by 93.13% and the torsional capacity of the cracked beam has increased 7.6 times.

In recent years, self-compacting mortar is widely used in various parts of construction projects due to its high efficiency. The efficiency of self-compacting mortars depends on the composition used in the mixing plan and the characteristics of its components, such as the type of aggregates, super-lubricating quality, additives, etc. Also, to improve the properties of cement mortars, the use of additives such as fly ash, nano particles, etc. has become popular. Considering the importance of examining the mechanical properties and efficiency of cement mortars, in this study, the effect of microsilica and super-lubricant on the efficiency and compressive strength of self-compacting mortars has been investigated. The research results show that the addition of microsilica increases the compressive strength and reduces the small slump flow in the mortar. Also, the ratio of water to cement is one of the important parameters in increasing the short-term compressive strength, which has a greater effect than other parameters, and by reducing the ratio of water to cement, more compressive strength was obtained.

Today, the construction industry has become one of the mother industries, which forms a wide range of related industries. Rapid changes in the construction environment require different efforts for a company or organization to survive and grow, and their life depends on how they manage their projects correctly. The success of construction projects is one of the main goals of project managers. One of the ways to evaluate and control project success is to apply project performance management. According to the existing conditions, companies and organizations recognize the importance of performance evaluation to improve their competitiveness. Therefore, in this research, by reviewing and reviewing the research literature related to project performance evaluation, the most key indicators of performance measurement have been identified and presented. According to the calculations and investigations, the most important key indicators are: safety, cost, quality, schedule, productivity, customer satisfaction, profitability, team satisfaction, environment and sustainability. Also, considering that construction projects are always progressing and becoming more complex and have many linear and non-linear relationships and structures, these projects can be considered a type of dynamic systems. Studies show that the correct use of the system dynamics method in this field have a great impact on the success and improvement of the performance of construction projects.