Experimental Study of Concrete Mixes with Nano Silica and Silica Fume

Abstract

During the manufacturing of cement, when limestone and clay are crushed and heated at high temperature, there is emission of global warming gasses including carbon dioxide (CO2) into the atmosphere. As the current atmospheric concentration of CO2 has reached an alarming high value to the tune of 410 ppm (April, 2017), it has become obligatory to develop Green concretes in order to decrease the CO2 emission from cement industry. The aim of the study undertaken herein is to highlight the utilization of nano silica in high performance concrete in order to reduce the environmental pollution and to also see if the strength as well as the durability properties of the concrete can be altered positively. In the experimental work undertaken, cement was partially replaced by nano silica at 2%, 3% and 4% replacement levels and replacement level of silica fume was kept constant at 8% for four different water binder ratios (w/b) of 0.30, 0.34, 0.38 and 0.42. The concrete samples were casted and tested for strength (compressive and split tensile) and durability properties (abrasion resistance and rapid chloride ion penetration resistance) after 7, 28 and 56 days of curing ages. Scanning Electron Microscopy, X-Ray diffraction and Energy Dispersive Spectroscopy tests were also conducted to analyze changes in the concrete microstructure. The results were statistically analyzed as well. The test results after 56 days curing period show 34.54 % and 36.52 % increase in compressive and split tensile strength for w/b ratios 0.38 and 0.30, respectively whereas a 56.31% reduction in average loss of thickness and 38% increase in resistance of chloride ions penetration was observed for w/b ratio of 0.30. Although, the experimental results also show that the maximum increase in compressive and split tensile strength, maximum reduction in abrasion and maximum decrease in rapid chloride ion penetration value were found at 0.30 w/b ratios at the replacement level of 4% of nano silica and 8% silica fume for 56 days of curing.