In this study, smart cement with a water-to-cement ratio of 0.38 was modified with up to 1 % silica nanoparticles (NanoSiO2) to evaluate the effect not only on the sensing properties but also on the compressive stress-strain relationship and strength. The oil well cement (class H) and cement modified with NanoSiO2 were characterized using X-ray diffraction analysis and thermal gravimetric analysis. The smart cement was prepared by adding 0.1 % of the conductive filler based on the percolation theory concept to make the cement piezoresistive yet remain a nonconductive material. Testing evaluated the smart cement behavior with and without NanoSiO2 to verify the sensitivity of electrical resistivity changes with time and compressive loading. The addition of 0.5 and 1 % NanoSiO2 increased the initial electrical resistivity of the smart cement by 17 and 35 %, respectively. In one day, the maximum change in the electrical resistivity (RI24hr) for the smart cement without NanoSiO2 was 364 %. The RI24hr for the smart cement with NanoSiO2 decreased with the amount of NanoSiO2. The addition of 1 % NanoSiO2 increased the compressive strength of the smart cement by 14 and 42 % after 1 and 28 days of curing, respectively. The nonlinear Vipulanandan p-q curing model was used to predict the changes in electrical resistivity with curing time. The piezoresistivity of smart cement with NanoSiO2 was over 500 times higher than the regular cement, depending on the curing time and NanoSiO2 content. The Vipulanandan p-q stress strain and stress change in resistivity models also predicted the experimental results very well. For smart cement modified with NanoSiO2, the resistivity change at peak stress was over 1,250 times higher than the change in the compressive strain. A linear correlation was obtained between the RI24hr and the compressive strength of the modified smart cement based on the curing time.
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