جستجوی مقالات مرتبط با کلیدواژه "میکروسکوپ الکترونی روبشی (sem)" در نشریات گروه "عمران"

One of the disadvantages of using conventional concrete in road paving is its low resistance to traffic loads. But today, scientists have been able to improve the strength of concrete by using new materials such as slag in the composition of concrete. These materials contain adhesives and fillers such as aluminate and silicate, which ensure the improvement of strength in concrete after the process of chemical reaction with alkaline solutions. The purpose of this laboratory research is to make concrete with higher strength than ordinary concrete used in road pavement. In this regard, a mixing plan was made of ordinary concrete with a cement grade of 450 kg/m3. A mixing design was also made of fermented concrete based on composite kiln slag to compare and evaluate the ultrasonic pulse (UPV) rate of concrete under ambient temperature and temperature of 500 °C, at a 90-day curing age. Continuation of X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM) imaging tests to further evaluate and verify the UPV test results at 90 days of processing at ambient temperature and 500 °C on the sample Concrete works were carried out. Based on the results, the amount of UPV at ambient temperature was 5930 m/s for ordinary concrete and 4920 m/s for alkaline concrete, which had a difference of 17.03%. By applying heat to concrete samples, the rate of UPV drop in ordinary concrete was 37.26% and in quilted concrete was 45.93%. The results of XRD and SEM tests were in agreement with each other and overlapped with the results of UPV test.

The purpose of this research is to reduce cement consumption by replacing nano fly ash (NFA) in the concrete mixture and increase the compressive strength of concrete by strengthening the interfacial transition zone (ITZ). Thus, four proportions of NFA with values of 0.1, 0.5, 1 and 5% by weight were selected in the concrete mixture and the compressive strength of concrete was evaluated within 7 and 28 days. A scanning electron microscope (SEM) equipped with an X-ray energy diffraction spectrometer (EDS) was used to detect the compounds resulting from the reaction between particles. Based on the results, in the sample containing 1% NFA (optimal sample), compared to the samples without NFA, the 7-day compressive strength of concrete increases by 97% and the 28-day compressive strength increases by 61%; which shows the NFA has a better performance in increasing the strength of concrete at early ages. Also, the amount of water absorption in the sample containing 1% NFA decreased to 33%, therefore, the permeability of concrete against destructive agents is improved. These results show that the interfacial transition zone (ITZ), which is the weakest link in the concrete chain and the limiting factor of concrete strength, is strengthened in the presence of NFA, and leads to an increase in durability and compressive strength of concrete.

Contamination of soils with petroleum products, in addition to being an environmental problem, also makes it difficult from the point of view of geotechnical engineering and doubts the use of this soil following structures, road pavements, and other constructed structures. Sridharan et al. (1981) reported an increase in soil settlement due to contamination of the region's soil with hydrocarbons, resulting in damage to industrial buildings. In recent decades, due to the importance of studying the geotechnical behavior of contaminated soils with petroleum products, many studies have been conducted on the physical and chemical properties of these soils. Much research has been done on the geotechnical properties of fine-grained and coarse-grained soils contaminated with petroleum products (Shin and Das, 2001; Ratnaweera and Meegoda, 2006; Rahman et al., 2010; Al-Aghbari, 2011; Kermani and Ebadi, 2012; Karpuzcu et al., 2018). In this study, the emphasis is on the evaluation of the polluting effect of gas oil as a pollutant with a specific gravity less than water on the fine-grained and coarse-grained behavior of soil. For this aim, a set of geochemical (including XRD and XRF analyzes), geotechnical tests (including grain size distribution, gas evaporation, Atterberg limits, and unconfined compression strength), as well as observation by scanning electron microscopy on contaminated Clayey Sand by gas oil was done.

Saturated deposits of sands and silty sands are liquefiable during earthquakes. One of the new methods proposed for non-disruptive mitigation of liquefaction risk at developed sites is passive site stabilization. It involves slow injection of colloidal silica at the edge of a site and delivery of the stabilizer to the target location using natural groundwater flow [1]. Colloidal silica is an aqueous suspension of microscopic silica (SiO2) particles produced from saturated solutions of silicic acid [2]. The particles size can range in size from 2 to 100 nm, although the particle size is fairly constant in a given suspension. During manufacturing, colloidal silica solutions are stabilized against gelation so they can have long induction periods during which the viscosity remains fairly low up to a few months. A few studies have investigated the behavior of sands stabilized with colloidal silica. Persoff et al. measured short term strength of about 430 kPa at concentration of 20 wt% colloidal silica [3]. Gallagher and Mitchell found the baseline unconfined compressive strength ranged from 32 to 222 kPa in period of 7-30 days at sands samples treated with 5-20 wt% colloidal silica. They also did a series of cyclic triaxial tests and found that for passive site remediation, a 5 wt% concentration of colloidal silica is expected to be able to adequately mitigate the liquefaction risk of loose sands [4]. The stabilization of loose silty sand with colloidal silica has not been studied comprehensively so the present study was undertaken to investigate the unconfined compressive strength and microstructure analysis of silty sands stabilized with colloidal silica.