Clay Strength With Polyester Resin Depends Strongly on Initial Moisture

Adding unsaturated polyester resin to low-plasticity clay can substantially increase its unconfined compressive strength, but the outcome depends strongly on the clay’s starting water content. In tests reported in Scientific Reports, specimens containing 20% resin achieved 9.88 megapascals after 14 days of curing when prepared at 0.5 times the liquid limit. By contrast, specimens prepared at the liquid limit reached their maximum strength of 5.52 megapascals with 10% resin, after which additional resin was associated with lower compressive strength.

The researchers prepared clay at two initial water contents, 0.5 LL and LL, and treated the samples with resin contents ranging from 0% to 20%. They then measured unconfined compressive strength after 14 days and used scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier-transform infrared spectroscopy to examine selected specimens. The results show that moisture did more than alter the amount of strength gained: it changed the dosage-response pattern and the organization of the material at the microscopic scale.

Scanning electron microscopy and elemental analysis indicated that the drier clay developed polymer-rich domains and a more integrated fabric. Samples prepared at the liquid limit had a more heterogeneous microstructure, which was consistent with their lower peak strength and the decline observed when resin content rose beyond 10%. The evidence therefore associates moisture-dependent differences in polymer distribution and binding with the mechanical performance of the tested clay–polymer system, rather than establishing a simple rule that more resin always produces stronger material.

Mineralogical and chemical analyses did not indicate a distinct new crystalline reaction product. X-ray diffraction patterns did not show evidence of such products, while infrared spectroscopy confirmed a polyester-related ester carbonyl response near 1,720 reciprocal centimeters. Taken together, the observations suggest that the strength changes were linked primarily to how effectively resin-associated binding formed within the clay, not to the creation of a new crystalline phase. The study was limited to one low-plasticity clay, two initial water contents, a 0–20% resin range and 14-day curing, so the results do not establish how the system would perform under other soils, moisture conditions, formulations or longer curing periods.

Subject of Research: Effects of initial moisture and polyester resin dosage on the strength and microstructure of stabilized low-plasticity clay

Article Title: Moisture-dependent strength and microstructural response of clay stabilized with unsaturated polyester resin

Article References: Yurtcan, U. E. (2026). Moisture-dependent strength and microstructural response of clay stabilized with unsaturated polyester resin. Scientific Reports. https://doi.org/10.1038/s41598-026-77420-w

Image Credits: AI Generated

DOI: 10.1038/s41598-026-77420-w

Keywords: clay stabilization, unsaturated polyester resin, unconfined compressive strength, soil moisture, microstructure, polymer binding, SEM–EDX, X-ray diffraction, FTIR spectroscopy, Moisture-dependent, strength, microstructural