Optimising Controlled Low-Strength Material: Unravelling the Impact of Key Mixture Parameters

Abstract

Controlled Low-Strength Material (CLSM) is increasingly utilised in construction for its advantageous properties such as self-compaction and cost-effectiveness. However, well-established models are lacking in predicting its fresh and hardened properties, particularly when incorporating Waste Paper Sludge Ash (WPSA) as a supplementary cementitious material (SCM). Statistical models have been carried out to model the influence of key mixture parameters (water-to-cementitious material ratio, WPSA percentage, and total cementitious material) on fresh and hardened properties affecting the performance of CLSM through the application of Central Composite Design (CCD). Such responses included flowability, bleeding, segregation, initial stiffening time, and unconfined compressive strength at 7 and 28 days. Twenty mixtures were prepared to derive the numerical models and evaluate the accuracy. The models were valid for a wide range of mixture proportioning. The research presented derived numerical models that can be useful in reducing the test procedures and trials needed to proportion CLSM. The qualities of these models were evaluated based on several factors, such as level prediction, residual error, residual mean square, and correlation coefficients. Full quadratic models in all the responses (flowability, bleeding, segregation, initial stiffening time, and unconfined compressive strength at 7 and 28 days) showed a high correlation coefficient (R2), adjusted correlation coefficient, less level of significance, and the sum of square errors (SSE) from the two predictions models (linear and full quadratic) were developed.