Possible usage of five percent chloride ion by cement weight (2.56 M NaCl) in mixing water with pozzolanic materials emerging as sustainable construction materials

Abstract

Using recycled waste brine or recycled seawater as mixing water in concrete manufacturing and the cement production have led to an increase in CO2 emission, and thus, another alternative needs to be sought. This work was the first in incorporating 5% by cement weight (2.56 M NaCl) into mixing water blended with four different pozzolanic materials, examining its effect on fresh, 28-day hardened properties and the embedded reinforcing-steel (RS) corrosion. Results indicated that, with 5%, the slump flows of Portland cement type I (CemI), 8% CemI replaced by fly ash (CemI + FA), 8% CemI by silica fume (CemI + SF), and Portland cement type III (CemIII(slag)) at water/binder 0.55 were 193–223 mm, the bending and the compressive strengths were 4.43–7.12 MPa and 33.47–42.66 MPa, respectively, the porosities were 11.44–17.86%, the pore diameters were 0.024–0.026 μm and the bulk densities were 2087–2151 kg/m3. The chloride binding capacity was higher in CemI + SF (0.75%) and CemIII(slag) (0.74%) than in CemI (0.62%) and CemI + FA (0.63%). 5% encouraged the presence of an expansive gel sodium oxide (Na2O) in CemI (0.51%), CemI + FA (0.59%), CemI + SF (1.02%) and CemIII(slag) (1.27%) after 28-day curing. Due to better chloride binding in CemIII(slag), the RS mass loss was sequenced as CemIII(slag) (14.30 mg) < CemI + SF (51.30 mg) < CemI + FA (66.10 mg) < CemI (78.33 mg) at 430 days and the RS corrosion rate was CemIII(slag) (5.92 μm/year) < CemI + SF (6.54 μm/year) < CemI + FA (14.89 μm/year) < CemI (21.05 μm/year). © The Author(s) 2025.