نشریه مهندسی و مدیریت ساخت
سال چهارم شماره 4 (پیاپی 16، زمستان 1398)

Under acid rain conditions, physical and chemical reactions occur in the concrete structure, which leads to a change in pH. As these reactions continue, the concrete begins to lose its mechanical strength, leading to cracking, weight loss, and eventual structural damage. Since the control of acid rain and its effects on the environment is inevitable in some cases, researchers have done many studies on this topic and have proposed 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 focused on silica nanoparticles, with the aim of using this material to further enhance the properties of concrete. The addition of nanosilica to concrete reduces the water permeability of the concrete as well as higher resistance to chemical attacks. In this paper, the mechanical properties and durability of nanosilica-containing concrete including weight loss, compressive strength, electrical resistance and water absorption under acidic conditions are investigated. By increasing nanosilica to concrete under normal conditions, the mechanical properties of concrete are improved, but according to the observed results, when the samples are placed in acidic conditions, the nanosilica in the samples reacts with acid and the performance of nanosilica improves the properties. The mechanical properties of the concrete deteriorate due to the mechanical replacement of the percentage of cement with nanosilica.

Today, according to the rapid development in construction industry in our country, safety issues in construction sites become a serious challenge. So, paying attention to the safety, indicating effective factors and safety evaluation in projects are essential in order to improving construction projects safety. This paper is conducted to assess the effectiveness of project management maturity model on safety standards in mass construction projects. A Researcher made questionnaire with approved reliability and validity was used in this paper and based on this questionnaire the effectiveness of project management knowledge maturity model on important safety indicators of projects such as performance, cost, time and safety quality has been evaluated. The mentioned questionnaires were distributed between mass production projects in District 1 in Tehran province and collected data were analyzed by SPSS software and regression techniques. The results of regression analysis indicate the strong and positive effects of the project management knowledge maturity model on the standard safety of projects. Therefore, it can be concluded that the application of project management knowledge maturity model in mass production projects has a significant impact on improving the standard safety indicators of projects and in addition to increasing safety performance, safety costs and the waste of time reduction will greatly increase the safety quality of projects.

AbstractFrom the past to today, for reasons such as high cost, long-term return on investment, poor financial and non-support of laws from the private sector, the establishment of infrastructure has been the responsibility of the public sector or the government and public and public organizations. Public participation Private is considered as a fundamental strategy for the development and infrastructure of countries using the expertise of the private sector in resource and time management. Consequently, in recent years, these contracts have been increasingly leaked by governments due to the lack of government resources and the need to develop metropolitan infrastructure. And municipalities have been used. One of the main objectives of PPP project is to reduce project risk and increase the financial value of the project. On the other hand, PPP projects face a high risk due to complexity and uncertainties. Therefore, risk should be tailored to individuals or groups based on the ability to tolerate risk. According to some studies, the lack of skills in identifying, assessing, valuing and transferring risk factors has led to lack of revenue and project success for governments. This article seeks to describe the structure of the risks and the success rates of each of them by studying and presenting the experiences of registered companies, and then seeking to reconcile the views of the domestic experts to identify and present the risks of the current state of the country to deal with the native infrastructure for risk management Of these projects in the country.

Private sector participation, especially in the urban economy and municipal projects, plays a vital role in the development of communities. Undoubtedly, the first step in developing private sector participation in urban management projects is to identify the reasons for reluctance and remove existing barriers to the sector's participation in urban projects. In this regard, the purpose of this study is to identify and evaluate the barriers affecting the non-participation of private companies in investment management projects in Alborz province. The present research is applied research in terms of purpose and descriptive-survey research in terms of method and nature. The method of data collection is based on library studies and field studies, including a researcher-made questionnaire and interviews. The findings of this study indicate that the effective barriers to non-participation of private companies in urban management projects in Alborz province are barriers related to economic, political, legal, social, technical and environmental factors, respectively. Economic factor by preventing fluctuations in inflation and interest rates and foreign exchange market, as the most effective and environmental factor by preventing natural risks including risks related to the climate and climate of the project site, internal and external environmental conditions of the project and force majeure, were identified as the least effective factors.

Most concrete cracks are due to incorrect designs and incorrect execution methods. One of the designs that should be done for concrete parts is the design for twisting. The amount of torsion is significant in edge beams or beams that are connected to the slab on one side, so if a crack occurs on the concrete parts due to torsion, it should be repaired using different methods. One of the existing methods is to use GFRP rebars inside concrete under the title of using NSM method to repair concrete. In this research, by making concrete parts with dimensions of 15 × 15 × 120 cm and creating cracks on them, they are repaired using The NSM method and the effect of using that method on the components of the final torsional anchor, the final torsional force and the final torsional angle have been investigated. The results showed that the use of this method increased the torsional strength of cracked concrete beams by 9.52 times.

Self-compacting concrete is one of the most important and significant achievements of concrete technology. In some countries, studies are being conducted on the use of magnetic water and its effect on concrete. According to the results of this research, by applying a magnetic field to ordinary water, the structure of its molecules changes so that it can be said that as water molecules pass through a magnetic field, there is a significant change in the arrangement of them in the liquid. In this paper, changes in the properties of hardened self-compacting mortars due to the use of magnetic water in the fabrication and processing stage have been investigated. It has been done for 5, 10, 15 and 20 minutes using ordinary water as well as processed water. The results of the experiments show that magnetic water improves the strength standards of hardened concrete. Therefore, in order to achieve a certain level of efficiency and strength, if the magnetic water is used, the ratio of water to concrete or superplasticizer can be reduced.