كليدواژه :
پودر نانو كربنات كلسيم , مهندسي نانو , بتن غلتكي , مقاومت مكانيكي
چكيده فارسي :
يكي از پارامترهاي تأثيرگذار در ميزان عمر مفيد روسازي‌هاي بتن غلتكي، مقاومت آن‌ها در برابر تنش‌هاي ناشي از نشست زمين وابسته به زمان است كه در اين رابطه اعمال تنش ناشي از نشست‌هاي زمين به علل زمين‌شناختي باعث خرابي شريان‌هاي حياتي مي‌شود كه از جمله مي‌توان به ايجاد شكست‌هايي در سطح روسازي راه‌ها مي‌شود. در اين راستا به بررسي تأثير فناوري نانو در بتن غلتكي و تحمل تنش‌هاي ناشي از اين گونه نشست‌ها مي‌پردازيم. در اين پژوهش سعي شده است كه با استفاده از مهندسي نانو، درصدهاي مختلف نانو كربنات كلسيم، جاي‌گزين سيمان در بتن غلتكي شده و آزمايش‌هاي مقاومت فشاري و كششي بتن غلتكي در سنين مختلف انجام شود. نتايج حاصل از اين پژوهش نشان مي‌دهد كه با افزايش بهينه ميزان پودر نانو كربنات كلسيم حرارت اوليه بتن غلتكي و مقاومت مكانيكي نمونه‌ها در سنين بالا به‌علت ريزدانه بودن و خاصيت پركنندگي و سطح ويژه بالا افزايش چشم‌گيري مي‌يابد. نتايج اين تحقيق نشان مي‌دهد استفاده بهينه از اين مواد باعث بهبود برخي خواص بتن غلتكي از جمله مقاومت كششي و فشاري مي‌شود كه در برابر تنش‌هاي ناشي از پديده فرو نشست مقاومت چشم‌گيري از خود نشان مي‌دهد.
چكيده لاتين :
Nanostructured materials have gained increasing attention of industry and the academia in recent decades, due to their prominent behaviors. In this regard, the building industry is considered to be the major consumer of nanostructured materials in terms of its needs, including strength, resistance, durability and high performance. Studies on nanoscale behavior of cement and concrete to develop new building materials and their applications are of high importance. A typical method for the development of high performance concrete (HPC) often contains various parameters, including the mix of conventional concrete with different types of additives. Nano-Calcium carbonate (Nano-Precipitated Calcium Carbonate) is a nano-sized filler which is used in this research. The results indicate that the higher the optimal content of nano-precipitated calcium carbonate powder, the higher the initial heat of the roller-compacted concrete; also, the resistance of the samples significantly increases over time. However, the level of permeability of roller-compacted concrete decreases by optimal increase of nano-calcium carbonate powder due to its fine grains, filling properties, and high specific level. The results of this study show that the adequate use of this material improves some properties of roller-compacted concrete.
Material and methods
In this study, the content of Nano-calcium carbonate used was selected at 0, 1, 2, 3 and 4 percent replacing a volume of cement consumed in concrete. Type II Portland cement, crushed fluvial sand, and crushed coarse aggregates with a maximum size of 19 mm were used. The aggregates’ grading range in the mix has been selected according to the ACI325-10R. The chemical formula of Nano-calcium carbonate powder is CaCo3 and the average particle size is between 15-40 nm
According to the roller-compacted concrete specifications, 5 mix designs have been used with different proportions of stone materials in preparing of concrete. The samples were made on a vibrating table and in the cylindrical molds of 15 × 30 cm according to ASTM C1176 standard.
By increasing the cement grade, the slope of the Vebe curve increases, which means an increase in speed and reduction in efficiency over time in higher grades. Increasing the cement grade from 275 to 300 kg/m3 leads to increased Vebe time. In other words, it can be said that the efficiency is reduced at a lower rate in lower grades of new roller-compacted concrete mix. The Vebe time of the roller-compacted concrete pavement should be between 30-40 s to achieve optimal efficiency. According to the results of Vebe time, the efficiency of the roller-compacted concrete with the grade of 300 kg/m3 has a better functionality than other mixtures and lasted more than others in the 30 to 40 second range. Accordingly, concrete with a grade of 300 kg/m3, is the compressive strength according to this design.
