Effects of high volume dolomite sludge on the properties of eco-efficient lightweight concrete: Microstructure, statistical modeling, multi-attribute optimization through Derringer's desirability function, and life cycle assessment

Abstract

Micro fines stone sludge (μSS) as dolomite, is a hazardous waste and creates many health problems along with air, water and land pollution. The research paper presents the statistical models with the help of response surface methodology, aiming to develop μSS incorporated structural grade lightweight cellular concrete (SG- LCC) using novel mix design (with 15 design steps). The three level-three factorial (33) Box Behnken Design was employed to investigate the effects of three input parameters i.e. temperature of water to be diluted with surfactant (Tw), flowability value (FV) and percentage replacement of μSS (%RμSS) on all the dependent responses i.e. oven dry density (ρOD), uniaxial compressive strength (fc.28d), performance factor for uniaxial compressive strength (PFc.28d) and thermal conductivity (λ-value). The regression analysis and Derringer's desired function methodology was applied to find out an optimum condition for developing SG-LCC (as replacement of masonry brick) containing maximum volume of wet μSS. It was finally concluded that by optimizing above sensitive input parameters, eco-efficient SG-LCC can be produced at Tw of 31°C, %RμSS of 51.50% and FV of 135.50%.The developed SG-LCC have ρOD of 1243 kg/m3, fc.28d of 8.23 MPa, PFc.28 of 6621 Pa/(kg/m3) and λ-value of 0.456 W/mK. Microstructure studies indicated that μSS filers does not participate chemically in cement hydration reactions. However, these filers imparted physical effect by acting as nucleation sites for the cement hydration products. The economic index was 18.42% higher for the final optimized mix, than that of the control mix. Use of wet μSS (up to 51%) to produce optimized SG-LCC mix, will not only reduce the production cost up to 17.54%, but also it will conserve natural RS and tap water by 26.28% and 100%, respectively. Life cycle assessment also showed that production of SG-LCC containing higher amount of μSS; consumes lower energy, and emits lesser amount of greenhouse gases that are the key parameters requirements for sustainable development goals.