جستجوی مقالات مرتبط با کلیدواژه « additive » در نشریات گروه « عمران »

The purpose of this research is to conduct a laboratory study to investigate the effect of using microsilica additive on the compressive strength of concrete under different durations of accelerated steam curing. For this aim, four mix designs have been considered, in which in two of them microsilica additive is used in the amount of 10% and 15% by weight of cement. 48 cubic samples were cured by immersion in water and their compressive strength was measured at the ages of 3, 7, 14, and 28 days. Also, 84 cubic samples were subjected to accelerated steam curing under the maximum temperature of 66±2 ºC and their compressive strength was measured after 4, 8, 16, 24, 32, 40, and 48 hours of treatment. The research results show that by adding microsilica to concrete, the ultimate compressive strength increases in both types of curing. Calculating the ratio of the strength of the samples under steam curing to the corresponding value in water curing indicates that the designs with microsilica have weaker performance than the designs without microsilica in terms of gain rate in compressive strength. Also, the results show that with the reduction of the water-cement ratio, concrete strength setting in steam curing occurs faster. Finally, it is suggested that if microsilica powder is used in concrete as an additive, in order to provide 70% of the 28-day strength of concrete, which is necessary for producing prefabricated and prestressed concrete, microsilica powder must be used in the amount of 15% by weight of cement and concrete must be subjected to steam treatment for 24 hours.

The performance properties of bitumen can be improved by using several modifiers, including: polyphosphoric acid (PPA), semi-hot asphalt mixers (WMA) and styrene butadiene rubber (SBR). The present study evaluated the effect of PPA and WMA additives on the rheological behavior of SBR modified bitumen. Modified SBR / PPA and SBR / PPA / WMA bitumen were subjected to rotational viscosity, dynamic shear rheometer, multiple stress and creep recovery (MSCR) and linear slope sweep (LAS) tests. Based on the results of MSCR test at both stress levels, modification of the base bitumen by SBR, PPA and WMA additives improves the permanent deformation performance of the main bitumen. The results of LAS test showed that the use of SBR and WMA additives improves the fatigue life of bitumen. Also, by adding PPA, the fatigue life of SBR modified bitumen is increased. While the fatigue life is longer than the original bitumen. Among warm additives, Sasobit has a better effect on increasing the performance of bitumen.

Nowadays, access to safe drinking water is a major challenge in most arid and semi-arid regions of the world. Due to the low cost of raw materials for construction of concrete tanks, these types of structures are common in many areas where water problems are encountered. This study explores the use of porous concrete by utilizing the idea of old water storage tanks (Ab-Anbars), which played an important role in water storage for remote areas, rural and small towns until three to four decades ago, and their effect on reducing or increasing water temperatures. At the wall of the water storage tanks, effect of air passage through the porous concrete on the water inside the tanks is studied. For further investigation, LECA (5% by weight of aggregates) was used as an additive to porous concrete and 3 replicates of this treatment and control treatment were made. Daily ambient temperature and humidity were measured by the respective sensors, and inside temperature of the tanks was measured with two sensors, one in the middle of the stored water and one in the middle of the open space of the tanks, in the warmest hour of the day (14:30 pm) in spring and summer of 2019. Results showed that mean water temperature of LECA treatment was lower than mean water temperature of control and mean air temperature of control treatment was higher than mean air temperature of LECA treatment. Mean air and water temperatures were always less than mean ambient temperature. Also, the physical parameters of porous concrete (i.e., porosity, permeability and compressive strength) were investigated in this study. Results showed that the compressive strength and porosity of LECA treatment were higher than the control and its permeability was lower than the control.

As a new way of modifying asphalt or asphalt mixture, composite modification has obvious effects. In order to improve the perfor- mance of asphalt pavement in a simple, fast and efficient way, a new kind of composite reinforcing material (CRM) is used in this study. The Marshall Immersion test, the freeze–thaw splitting test and low-temperature bending test were conducted to evaluate the pavement performance of the asphalt mixture with different CRM contents. Test results show that the pavement performance of modified asphalt mixtures is better than unmodified asphalt mixture. When the CRM content increases, resistance to rutting at a high temperature increases significantly, low temperature cracking resistance and moisture damage resistance first rise and then fall. In consideration of other pavement performance, such as dynamic stability (DS), indirect tensile strength ratio (TSR) and maximum tensile strain, the sug- gested optimal CRM dosage is 5.9‰ to 7.9‰.

Environmental issues of production of reclaimed asphalt pavement (RAP) and efforts to preserve natural mines are among the main factors for the use of RAP. Besides, the characteristics of RAP can improve some of the properties of asphalt mixtures. Since these materials are produced during the maintenance and rehabilitation projects, it is better to be consumed in the same operation. One of the best methods of pavement maintenance is the use of micro surfacing operation as a surface treatment. Therefore, the use of RAP in the micro surfacing mixture can enhance the application of this method. In this study, first, the feasibility of using almost 100% (95%) RAP instead of virgin aggregate, according to micro surfacing preliminary mix design tests was studied. Then, the values of 69% and 43% RAP content were also evaluated to determine the preferred RAP content and to better analysis of the results. The results showed successful preliminary design of micro surfacing mixture with RAP aggregate and met the criteria of the regulations.
RAP containing samples needed a little more bitumen than those containing virgin aggregates, to obtain sufficient cohesion within the specified time. Nevertheless, samples containing more RAP values would require lower amounts of additive to increase the mixing time and workability, which could reduce the cost of material preparation. Also, RAP aggregate coating prevented the stripping of these materials in the vicinity of water. Among the RAP containing samples, those containing 69% RAP exhibited a better performance.