8 research outputs found
Investigating the influence of parent concrete on mechanical properties of recycled concrete
No full textOne of the most significant concerns of recent years among scientists has been related to waste management actions and policies. Unfortunately, landfills are filled with various debris and demolition from old building including waste concrete, glass, brick, ceramic, and plastic. Waste concrete seems to occupy a large volume of these landfills; thus, they are potentially among the most appropriate choices for recycling process. However, different papers have focused on the impact of recycled concrete aggregates in concrete and in recent years, no specific model has been recommended to predict the behavior of parent concrete in recycled concrete. In this study, a central composite design along with response surface methodology was employed to prepare experimental designs and model the properties of concrete made of recycled aggregates. Effective factors included compressive strength of parent concrete, substitution rate of parent concrete, and value of cement, while the compressive strength, tensile strength, and water absorption of recycled concrete were introduced as goal responses. Based on the statistical analysis, all recommended models were adequate with acceptable coefficient of determination ( ). Response surface and perturbation plots revealed that compressive strength, tensile strength, and water absorption of recycled concretes depended heavily on the compressive strength of parent concrete. Moreover, in order to generate concretes with higher compressive strength than the compressive strength of parent concrete, the value of compressive strength for parent concrete should be above MPa. However, for low-strength parent concretes, substitution rate should be limited in order to reduce undesirable performance. As the compressive strength of recycled concrete aggregates increased from to MPa, the compressive strength of recycled concrete was enhanced by over percent. In this substitution, water absorption reduced over percent. Additionally, when the compressive strength of recycled aggregates was fixed at MPa, by changing substitution rate from % to %, the compressive strength of recycled concrete increased from to MPa. The tensile strength of recycled concrete also was enhanced from to MPa
SHORTFALLS OF GENERAL CONDITIONS OF CONSTRUCTION CONTRACT AT UNIVERSITIES AND RESEARCH INSTITUTES PROJECTS OF IRAN
No full textUniversities and research institutes typically consider short-term and long-term construction projects according to their strategic plan to expand their education and research programs. Iranian general conditions of construction contracts should be attached to such construction projects' contracts. Conflict of interests among contracting parties may arise in projects which may put success of the project on risk. The contractor may act on its own interest instead of the owner interest. General conditions of construction contracts are central in mitigating such conflicts and in improving the success of the project. However, there may exist some shortfalls in general conditions of construction contracts. This research explores and addresses shortfalls in general conditions of construction contracts of Iran focusing on construction projects conducted at universities and research
institutes. Two hypotheses are proposed to evaluate the importance of revising
different chapters of the general conditions of contracts and to consider their
possible shortfalls. A survey is made by the use of a questionnaire.Construction practitioners from seventy universities and research institutes are involved in the research. The practitioners are senior personnel coming from owners, consultants and contractors organizations. One way analysis of variance, non-parametric Kruskal Wallis and the least significant difference methods are adopted to analyze the survey data in SPSS. The results in most cases indicate no meaningful difference based on the importance of need for revising different chapters of general conditions of construction contracts. The results also in majority of cases show no meaningful difference among owners, consultants and contractors perceptions about the importance of need for revising different chapters of such general conditions of contracts. It can be concluded that the revision's committee should put the same priority in revising different chapters of general conditions of construction contracts. Based on the perception of the research participants recommendations for improvement of general conditions of construction contracts are provided. This research would be relevant to those interested in revising the general conditions of construction contracts by providing insights for further
improvement
A study of the physical properties and chemical reagents of epoxy mortar floor intermediate coating using recycled glass sand as filler
No full textExperimental Design and Response Surface Methodologies Use for the Treatment of Leachates by Electrocoagulation Process
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Concentrated Leachate Treatment by Electro-Fenton and Electro-Persulfate Processes Using Central Composite Design
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