Traditional methods for evaluating the quality of the Deep Mixing Method (DMM) in Japan, such as the phenol
phthalein tracer method, present limitations in ensuring strength improvement. This study explores handheld X-ray
f
luorescence (XRF) as a sustainable alternative for quality assessment. The elemental composition of cement-treated
soil was investigated, focusing on Calcium (Ca), Silicate (Si), and Sulfate (S), which play crucial roles in the formation
of hydrated products, aiming to accurately determine their influence on the strength development of the improved
soil. A controlled protocol was employed using commercial Kaolin clay and the needle penetration test for strength
assessment. Our laboratory experiments, conducted with a cement-based binder (C) dosage of 110 kg/m3
and a water-cement (W/C) ratio of 1, furthered our understanding of the hydration process. Results indicate an appar
ent increase in Ca amount over time, correlating with improved strength, while the apparent amount of Si decreases,
suggesting its integration into hydration products such as C-S–H gel. Strength assessment rose significantly
between day 1 and 28, aligning with variations observed in Si, Ca, and S, underlining their role in strength evolu
tion. This research underscores the potential of handheld XRF as a sustainable substitute for conventional methods
in field-quality assurance, offering real-time data on the formation of possible hydrated products during the hydration
process for improved soil in geotechnical engineering.

Quality assurance, Handheld XRF, Phenolphthalein tracer, Cement hydrated products, Cement-improved soil