Optimization of self-compacting concrete fresh properties and compressive strength using response surface modelling of superplasticizer and viscosity modifying agent dosages

This research examines how the combined doses of Superplasticizer (SP) and Viscosity Modifying Agent (VMA) affect the fresh and hardened properties of Self-Compacting Concrete (SCC) by utilizing Response Surface Methodology (RSM) and a D-Optimal experimental design. A total of 16 different mixes were created by adjusting the amounts of SP (0.30-1.00% by mass of binder) and VMA (0-0.40%) to evaluate their effect on slump flow, V-Funnel time, L-Box ratio, sieve segregation and compressed strength at 28 days. Response surface (quadratic) models were generated for each performance metric and analyzed using an Analysis of Variance (ANOVA) for all of the indicators used to measure performance, resulting in very high coefficients of determination (R2 > 0.95 for fresh properties) and all models were statistically valid. Results revealed that SP primarily controls the flowability and passing ability while VMA plays a significant role in improving the stability and resistance to segregation of the concrete mixture. Using excessive amounts of either will have a detrimental effect on performance due to an increase in viscosity or segregation potential. Using a multi-response optimization technique based upon a desirability function approach, the optimum combination of SP ∼0.48% and VMA ∼ 0.04% was determined to provide an optimal slump flow ∼ 670 mm; V-Funnel time = 13.5 sec; L-box Ratio = 0.86; Segregation Index ∼13%; and 28 day Compressive Strength ∼69 MPa, with an overall desirability = 0.68 (All of these values were within the recommended limits set forth by EFNARC for SCC). Furthermore, the data shows that the RSM is a robust and efficient system that will quantify the combined effect of chemical admixtures on SCC mix designs based on numerous performance criteria.