Comparison between Four-Probe and Two-Probe Electrical Resistivity Measurement to Monitor the Curing and Piezoresistivity Behavior of Smart Cement Paste Modified with Waste Steel Slag and Green Nano-magnetite

Abstract This study aims to examine the compressive strength, electrical resistivity, and piezoresistivity characteristics of ordinary Portland cement (OPC) with a constant water-to-cement ratio (w/c) of 0.38. The optimal value of steel slag (SS) was determined to be 5 % based on the compressive strength of six different mixes of cement paste modified with various SS from 0 % to 30 % weight of cement. Additionally, the investigation will include modified cement samples containing 1 % green synthesized material and commercially available nano-magnetite (NM). Because iron is the primary component of SS and NM, the electrical resistivity, which is the primary criterion for structural health monitoring of cementitious material, can be increased by adding SS and NM. Hence, a comparative analysis was conducted to assess the resistivity of cement paste throughout the early curing period up to 28 days using an alternative current (AC) and embedding wires into the specimen, employing both the two-probe (2P) and four-probe (4P) methodologies. The findings suggest that the 4P method is a more precise approach for determining electrical resistivity than the 2P method, as the wire probe is not considered in the 4P method. Hence, it is imperative to compute the correlation between the 2P and 4P methodologies in order to attain a precise resistivity measurement. The suggested model indicates that the expected 4P resistivity can be measured with high precision, a high coefficient of determination (R2) of .97, and a low root mean square error (RMSE) of 7.33 Ω·m, based on the 2P result. The piezoresistivity results demonstrated that the cement paste modified with green synthesis nano-magnetite (GSNM) had a higher electrical resistivity (ER) change, 10.85 % greater than cement paste only, 57 % higher than cement modified with SS, and 34.2 % higher than cement paste modified with commercial nano-magnetite (CNM) after 28 days of curing. In addition, the compressive strength of cement paste modified with GSNM was higher than that of cement paste, cement paste modified with SS, and cement paste modified with CNM by 15.96 %, 21 %, and 1.7 %, respectively, after 28 days of curing. A Vipulanandan p–q model was used to forecast the electrical resistivity of cement paste versus time at start hydration during 28 days of curing and the change of electrical resistivity versus compressive strength at 3, 7, and 28 days. The Vipulananda p–q model anticipated both electrical resistivity and piezoresistivity behavior well.