DEVELOPMENT OF HIGH STRENGTH MULTI-FUNCTIONAL CONCRETE WITH INCORPORATION OF CARBON BASED NANO MATERIALS

Abstract

In the present study, cost-effective carbonaceous nano-inerts were synthesized via pyrolysis of agricultural wastes in the form of wheat straw, cotton stalk and scrap tires at a temperature of 500C in an inert environment. Carbon rich solid residue obtained from pyrolysis was milled to nano size and characterized through energy dispersive x-ray spectroscopy, x-ray diffraction analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. Synthesized carbonaceous nano-inerts from wheat straw, cotton stalk and scrap tires have been intruded in to cementitious matrix for the first time in the best knowledge of author, to enhance its fracture characteristics, electromagnetic interference shielding effectiveness and self-sensing properties. Cement mortar specimens were prepared with the intrusions of carbonaceous inert particles by 0.025, 0.05, 0.08, 0.2, 0.5 and 1 wt. % of cement in addition mode, after being effectively dispersed in water. Three point bending tests were performed on notched prisms at a very sensitive strain rate of 0.003/min in strain controlled mode with the broken halves analyzed for resistance in compression. Substantial increase of 59.8, 48.9 and 47% in fracture toughness was attained with the addition of 1% pyrolyzed cotton stalk, 1% pyrolyzed scrap tire and 0.5% pyrolyzed wheat straw respectively. While in compression, a maximum increment of 48.95% was achieved with 0.08% addition of PST. Investigations through scanning electron microscopy of broken specimens have verified the involved strengthening mechanisms encompassing crack branching, pinning and crack contouring via intruded inert particles. Furthermore, shielding against electromagnetic radiations was tested in X-band frequency range of 8-12GHz and maximum improvement of 24.97db, 23.5db and 22.9db was achieved with intrusion of pyrolyzed scrap tire, pyrolyzed wheat straw and pyrolyzed cotton stalk inert particles respectively. Lastly, a notable decrease in the electrical resistivity was observed with 3% addition of pyrolyzed scrap tire that reached to the lowest resistivity of 3.55 KOhm-cm giving the highest damage sensing potential among all. Pyrolyzed scrap tire engineered composites also proved to be the most sensitive to the variation of the stress applied giving the highest gauge factor of 216 owing to the highest content of carbon. Furthermore, these synthesized carbonaceous inert particles were used as additive in concrete for the first time to impart superior mechanical characteristics to conventional concrete. The mechanical performance of concrete incorporated with synthesized inert particles by 1% of cement weight was evaluated and compared with the reference formulation of concrete having no amount of synthesized inert particles. A significant improvement of 51.42% in terms of flexural resistance was achieved by using pyrolyzed cotton stalk. Fracture toughness index and fracture energy were also improved with the inclusion of these inert particles. To rationalize the improved performance of specimens engineered with synthesized inert xvi particles, fracture path analysis was conducted. In comparison to the reference formulation, composites reinforced with pyrolyzed scrap tires rendered maximum improvement in compressive strength by 43.1%. In terms of piezoresistive response, a gauge factor of 45 was achieved with pyrolyzed scrap tire concrete that was highest among other materials used in this study. Durability of concrete was also investigated in terms of sorpitivity, chloride ion migration coefficient and corrosion resistance. Pyrolyzed wheat straw endowed maximum durability to concrete giving lowest water absorption of 0.67, 38.3% lower coefficient of Cl- migration and 58.6% corrosion inhibiting efficiency. Large scale reinforced concrete beams were also tested for their mechanical performance as well as for damage monitoring capability. Two different approaches i.e embedded sensors and attached sensors were employed. Experimental findings seem to suggest that the embedded approach for mortar sensors is capable of accomplishing higher monitoring efficiency and lower construction costs because it only needs to be positioned at key locations within the concrete component and a high precision and repeatability can be achieved with less effort involved. The environmental impact assessment was also carried out to gauge the impact of pyrolysis process on char production and the global warming potential for engineered concrete. Waste from agriculture and industrial sources, transformed into valuable bio-char also reduced the environmental threats associated with the open burning of this waste. Based on the analysis, pyrolysis of scrap tires manifested the lowest net global warming potential of -1.285 kgCO2-eq. From the analysis of the emissions to strength ratio of concrete, specimens containing pyrolyzed scrap tires ensued the maximum reduction of 31.31% relative to the reference formulation