A new approach for proportioning self-consolidating earth paste (SCEP) using the Taguchi method

Abstract

Rammed earth (RE) construction is an ancient sustainable construction method, which offers various economic and environmental advantages such as the availability of local materials. However, RE construction is a very time-consuming and labor-intensive process due to the consolidation required to achieve the targeted performance. The use of self-consolidating earth concrete (SCEC) can facilitate casting and speed the construction process. However, developing SCEC is challenging due to the presence of clay in earth, which can significantly hinder flowability. Optimizing the paste matrix of SCEC, namely self-consolidating earth paste (SCEP), is essential for achieving targeted workability performance of SCEC. In this study, the Taguchi method was employed to evaluate the effect of various mixture parameters, including clay and admixture type, cement content, and water-to-powder (W/P) and cement-to-clay (Ce/Cl) ratios to proportion SCEP mixtures. These parameters form different binder compositions with various Atterberg limits and water contents to investigate the compatibility and efficiency of different admixture types on the workability and compressive strength of their corresponding SCEP mixtures. Adequate clay dispersion was achieved using sodium hexametaphosphate (NaHMP) whereas polycarboxylate ether (PCE) was only efficient on cement particles. Sodium silicate (NaSil) did not contribute to dispersion of single-powder systems, while sodium polynaphtalene (PNS) and non-esterified polycarboxylate (NE-PC) showed compatibility with both clay and cement particles. Signal-to-noise ratio (S/N) analyses revealed that lower cement content and higher W/P and Ce/Cl resulted in lower admixture demand for targeted workability and marsh cone test (MCT) values. Regarding 1-day compressive strength, to facilitate the demolding process, PNS, PCE and NaSil showed the highest efficiency. As concluded from the analysis of variance (ANOVA), clay and admixture type had the highest contribution on workability, while cement content and W/P were significant on compressive strength. Several theoretical models were also established to predict the workability of SCEP mixtures from Atterberg limits of the corresponding soil. Finally, a new SCEP proportioning approach was proposed based on the established models and compressive strength contours to be used for different earth types.