Published at : 30 Oct 2019
Volume : IJtech Vol 10, No 5 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i5.2590
|Kolimi Shaiksha Vali||Research Scholar, School of Civil Engineering, Vellore Institute of Technology, Vellore, 632014, India|
|Bala Murugan||Assistant Professor Sr, School of Civil Engineering, Vellore Institute of Technology, Vellore, 632014, India|
The impact of nano SiO2 particles on the physical and mechanical properties of cold-bonded artificial lightweight aggregates by the pelletization process is investigated in this study. Twelve(12) varying cold-bonded artificial lightweight aggregates were manufactured from fly ash, cement, hydrated lime, metakaolin and steel slag (GGBFS) binder, with the addition of 0%, 0.5%, 1% and 1.5%nano SiO2, at a standard 17 min pelletization time, with 28% water content on a weight basis. The aggregates were air-dried for 24hrs, followed by hardening of the pellets by cold-bonding (water curing) for 28 days and then testing. The study found the highest individual aggregate compressive strength of 49.3Mpa for 12mm aggregate and lowest water absorption of 12.5%with a 0.5FHG combination. Moreover, the lowest impact strength of 13.6% for the 0.5FCH aggregate combination was observed. The results, obtained from different binders and the influence of nano SiO2 particles, could be very useful in the enhancement of both the physical and mechanical properties of artificial lightweight aggregates.
Cold-bonded artificial lightweight aggregates; Nano SiO2; Pelletization process; Physical and mechanical properties; Scanning electron microscope
Artificial lightweight aggregates (LWA) are produced from either conventional materials or industrial by-products (Cheeseman&Virdi, 2005; Turu’allo, 2015; Han et al., 2016). The manufacture of LWA from industrial by-products is by means of the pelletization process, which involves cohesive as well as tumbling forces, which bond the moisture particles. The fresh pellets are removed from the pelletizer and air-dried for 24hrs to attain strength for handling, but not to the level of utilization in concrete. Therefore, hardening techniques need to be subsequently used to produce stronger pellets (aggregates)and some of the materials used to enhance the properties of artificial lightweight aggregates which are utilized in concrete (Ramadhansyah et al., 2011; Vali& Abdul, 2016). The hardening of artificial aggregates involves different methods, such as sintering, cold-bonding and autoclaving. Among these, sintering has high power demand but leads to high strength aggregates (Wainwright &Cresswell, 2001; Cheeseman&Virdi, 2005; Ramamurthy&Harikrishnan, 2006; Tsai et al., 2006;Vali&Murugan, 2017).
Cold-bonding is an alternative and more economical method of sintering (Bijen, 1986).Cold-bonded artificial lightweight aggregates have been manufactured both with Class-C and Class-Ffly ash (Chi et al., 2003;Gesoglu et al., 2004; Manikandan&Ramamurthy, 2007), the addition of binder for Class-F fly ash which has a calcium hydroxide origin in order to enhance theproperties of theaggregates, such as production efficiency, density, specific gravity, water absorption and strength (Yang & Huang, 1998; Baykal &Doven, 2000;Gesoglu et al., 2004;Vali&Murugan, 2019).In general, cold-bonded artificial lightweightaggregates are heavier than sintered artificial aggregates. C-S-H gel forms during the reaction, which results in the strengthening of the aggregate (Bijen., 1986). LWA properties and their related effect on concrete depend on their microstructure. For the manufacture of artificial lightweightaggregates, the binder type hardening method has an impact on their microstructure.
The use of nanotechnology in the manufacture of cement mortar and concrete is an area of vital interest at present. The majority of nanoscale structure materials have been shown to offer an effective approach to the development of advanced sources of cement-based materials due to their superior properties (Sanchez &Soboley, 2010; Park et al., 2016). Different types of nanoparticles, such as nano-SiO2, nano-Al2O3, nano-TiO2, nano-ZnO2, nano-CaCO3, carbon nanotubes and carbon nanofibers, are utilized in concrete to modify its properties. Among these, nano-SiO2 has attracted interest and has been observed to be efficient because of its pozzolanic reaction with cement-based materials, in addition to the dense microstructure of aggregatedue to its fine particle size (Sanchez &Soboley, 2010). Therefore, this studyaims to determine the physical and mechanical properties of artificial lightweight aggregates without nano SiO2 in order to examine the influence of the addition of different percentages of nano SiO2 with binder materials and to make a comparison with natural gravel aggregate properties.
Based on the experimental results, the following conclusions are drawn.
1. The addition of nano SiO2 with different binders during pelletization provides a more stable production and excellent bonding efficiency of the artificial lightweight aggregates, with improved properties.
2. In the case of the fresh pellets and those air-dried for 24hrs, the highest efficiency was for the 0.5FHM aggregate and the lowest for the 0FHG aggregate.
3. The highest specific gravity value of 2.64 was observed for 0.5FHG artificial aggregate which is 1.9% lower than the natural gravel aggregate value. The lowest specific gravity of 1.49 for the 1.5FHC artificial aggregate.
4. It was found that the lowest water absorption value as 12.5% for the 0.5FHG aggregate, and similarly the highest absorption value of 30.1% for the1.5FHC aggregate.
5. Highest Bulk density was found to be 928 kg/m3 for the 0.5FHG aggregate and lowest to be 814.8 kg/m3 for the 1.5FHM aggregate. The bulk density of the 0.5FHG artificial aggregate was 37% lower than the natural gravel aggregate.
6. The highest impact value of 20.2% was observed for the 0FHG aggregate and the lowest of 13.6% for the 0.5FHC aggregate. The natural aggregate impact value was lower than the 0.5FHG type artificial lightweight aggregate but is still comparable.
7. The highest individual 12mm aggregate crushing strength of 49.3Mpa was noted for the 0.5FHG aggregate and the lowest value of 21.2Mpa for the 0FHM aggregate. Irrespective of nano SiO2 dosage and binder type, as the size of the aggregate decreases, pellet crushing strength increases because of its smaller specific surface area for the smaller aggregate.
8. However, due to the fineness of the binder and the addition of nano SiO2, the packing of the particles helps to decrease porosity which lead to greater efficiency in the form of lower impact strength, lower water absorption, higher specific gravity and higher compressive strength of the pellets at 0.5% nano SiO2, which are comparable values to the natural gravel aggregate.
9. In summary, for artificial lightweight aggregates with different binders, the addition of nano SiO2 at 0.5% is the optimum level. From the different investigations conducted, the 0.5FHG aggregate combination exhibited the most satisfactory results.
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