The increasing environmental concerns associated with conventional soil stabilization materials, particularly cement, have driven the exploration of sustainable alternatives such as biopolymers. However, the practical application of biopolymer-treated soils remains questionable due to their susceptibility to biodegradation and hydrolysis under fluctuating environmental conditions. This study investigates the durability of clay soil treated with carboxyl methyl cellulose (CMC) biopolymer under cyclic wetting and drying conditions, aiming to evaluate the progressive strength degradation and potential serviceability of such treated soils for temporary or medium-term geotechnical applications. The experimental program employed soft silty clay obtained from southeast Baghdad, Iraq, treated with 5% CMC biopolymer by dry weight of soil. Specimens were prepared at optimum moisture content and subjected to up to five cycles of controlled wetting (submersion in water for 24 hours) and drying (oven drying at 45°C for 24 hours), with unconfined compressive strength (UCS) measurements taken at each drying and wetting phase. The results revealed a progressive reduction in UCS from an initial dry strength of 2050 kN/m² after the first drying cycle to 460 kN/m² after the fifth drying cycle, while wet strengths decreased from 270 kN/m² to 49.5 kN/m² over the same period. Despite this substantial strength loss, partial strength recovery was observed during each re-drying phase, attributed to the re-establishment of polymer-soil bonds upon moisture removal. The study demonstrates that while biopolymer-treated clay exhibits significant vulnerability to cyclic moisture fluctuations due to the hydrophilic nature of CMC and irreversible polymer dissociation, the gradual rather than catastrophic strength degradation suggests potential viability for temporary geotechnical applications where long-term durability is not critical.
The conventional open sun drying is not efficient, it is slow and contaminated and there is a necessity to develop highly advanced technologies in solar drying. The review looks critically at solar dryers that are improved with concentrator, optical, thermal energy storage (TES) or phase-change materials (PCM). The incorporation of parabolic trough or compound parabolic concentrators leads to a high temperature of over 100-115 oC and a thermal efficiency of up to 88 %. Reflective walls are also made to enhance optical capturing by up to 37.6 %, and shorten drying time by 15-20 %. TES/PCM systems increase the operation of TES systems beyond the sunset, nano-enhanced PCMs reduce drying time by 40% and enhance thermal efficiency by more than 48%. These systems demonstrate short payback periods (0.43-5.14 years) with regard to economics. They minimise the emission of CO2 by 2-44 tons/ lifetime of systems. These combined technologies have addressed intermittency and low efficiency and enabled solar drying to be a reliable and cost-effective and sustainable solution, as the UN Sustainable Development Goals of clean energy and climate action suggest.