جستجوی مقالات مرتبط با کلیدواژه "عمق نفوذ آب" در نشریات گروه "عمران"

Todays, use of concrete barriers has increased due to its advantages over the steel guardrails, including high impact resistance, greater safety and useful service life of about 50 years with minimal repair and maintenance costs. However, in our country, concrete barriers have a shorter service life, and therefore, more costs are imposed annually on highways for the production and replacement of old barriers In most cases, the destruction of concrete barriers is caused by changes in the volume of concrete at an early age. Improper method of execution, such as early opening of the molds, insufficient compaction and lack of wet processing of concrete are the reasons for the spread of damage. Damage caused to concrete barriers includes spalling, surface delamination, horizontal cracks, corrosion, salinization, vertical cracks, surface cracks, and concrete destruction.In this research, after experimental studies on used materials, a suitable mixture design of concrete containing zeolite pozzolan, air entraining additive and superplasticizer with a durability approach has been prepared to increase the service life of New Jersey concrete barriers; In addition to economic justification, it will also prevent the destruction of the environment. In experimental studies, the slump, temperature and air content of fresh concrete, and compressive strength, water penetration depth and resistance to freezing and thawing cycles of hardened concrete have been investigated and their results have been presented. Also, for cores of existing New Jersey concrete barrier, prepared from concrete mixture design containing zeolite, the compressive strength, deterioration of cores of New Jersey exposed to freezing and thawing cycles, and water penetration depth, have been measured.

In this study, to evaluate the effect of magnetic water along with the effect of smelting slag on concrete, electrical resistance tests, water permeation depth and frost and melting resistance tests were carried out. Three types of environmental conditions (sulfate, chlorate and ordinary water solutions) and conventional water ponds were used to perform the tests. The mixing design used in this study has two types of compressive strengths of 25, 40 MPa. The results showed that magnetic water has a great effect on the concrete and its application increases the specific electrical resistance of the concrete and reduces the chance of corrosion of buried steel in the concrete. Magnetic water also reduces the depth of water infiltration, increases the number of thawing and frost cycles, and increases the durability index. Increasing the percentage of smelting slag in concrete increases the specific electrical resistance of concrete, decreasing water penetration depth, increasing the number of frost and melting cycles, and concrete durability index. Increasing the compressive strength of the concrete from 25 to 40 MPa in addition to having a great effect on the mechanical properties, increased the specific electrical resistance of the concrete, decreased the water penetration depth, and also increased the number of frost and thaw cycles and the concrete durability index. It should be noted that the samples exposed to the sulfate medium performed better than the samples exposed to the chlorate medium and had lower electrical resistance and increased water penetration depth than the samples exposed to ordinary water.

Plastic concrete is usually used to build impermeable barriers (cut-off walls), contaminated sites, or leakage control of foundations with high penetration in dams. Effect of clay dosage, aggregate and cement were studied on compressive and tensile strength of bentonite plastic concrete. There was a tendency to reduce the compressive and tensile strength with increasing water to fine fraction and reducing cement and aggregate amounts. In addition, the plastic concrete showed a time-dependent behavior and changes in the mechanical properties of bentonite concrete will be improved by adding silt and clay adsorbents which could be used in water leakage with high contamination. The evaluation of water penetration depth in samples with ages of 28 and 90 days showed a decrease in penetration with increase in clay dosage and curing time. Also, the result of cadmium adsorption by bentonit clay showed that the clay can be effective in terms of water leakage with high pollution conditions.The most appropriate clay amount with respect to the economic issues, compressive and tensile strength would be 20% clay dosage and mix design containing silt and also 200 kg/m-3 cement. Also, in this study some equations have been developed to predicte the 28 and 90 days compressive strength of plastic concrete based on the 7 days compressive strength, and 90 days tensile strength based on the 28 days tensile strength. The R2 more than 0.95 for the developed equations confirms the accuracy of these relations.

Hot or cold weather condition affects the quality of the concrete in different ways, which one of them is increase or decrease in the initial temperature of the concrete. In this study, the impact of the initial temperature of the concrete on its quality in concrete kerbs made by dry pressing method with Portland cement is examined. Concretes with similar mix designs and initial temperatures of 17, 25, 29, and 39  C were made and cured in the standard laboratory condition. Then, in different ages some tests were carried out on them. The test results showed that the temperature of the concrete during placement is a parameter that affects the strength and durability properties of the concrete. For the initial temperature of 39  C, the quality of the concrete had a significant decrease. For the temperature range in this study, the initial temperature of 25 C resulted in the highest quality of the concrete. In the 7 and 42 days of age, the concrete with 25C initial temperature obtained the highest compressive strength and the lowest water absorption. The highest electrical resistivity in high ages was related to the concrete with 17C initial temperature.

Preservation of our environment، the need to a balanced consumption of the natural resources، particularly fossil fuels، and the need to reduce greenhouse gas emissions will all make us decrease our cement consumption especially clinker. As a result، in producing the concrete and the mortar، we must take a lower consumption of cement in to our account as much as possible without hurting the volume of construction in the country. In this article، we have shown that cement content is reduced with a constant w/c ratio and its impacts on the fresh and hardened concrete are studied. In continuation of the research، we reduced the w/c ratio (in 4 different ratios) and again the cement content was reduced in order to study the impacts of this reduction on lower ratios of w/c. It is clear that by reducing the cement mix (reducing cement content and w/c ratio)، the workability of the concrete will be highly reduced. To treat this problem، we can use plasticizers and superplasticizers which are explained thoroughly in the following sections. According to the obtained test results on fresh and hardened concrete، it can be concluded that reducing cement content (360kg to 450kg per m3) at the constant water / cement ratio will result in better strength and slump. On the other hand with reduction of w/c and adding super plasticizers for having better workability and flows more durability and higher strength could be gained.