Impact of Wetting and Drying Cycles on the Mechanical Properties and Microstructure of Vegetation-growing Concrete

Vegetation-growing Concrete (VC), as a new type of cemented soil, is usually used for plants growing on the surface of high and steep rocky slopes. With the widespread application of VC substrate, a pressing problem arises to ensure its durability under wetting and drying conditions. To explore the greatest possible impact on the mechanical properties and microstructure features of VC substrate, an experimental program including triaxial test, SEM analysis, and ultrasonic testing was implemented. The results showed that wetting and drying cycles can significantly decrease more than 40-percent of peak strength, 60-percent of residual strength, and 50-percent of cohesion for VC substrate under ultimate conditions. The fundamental cause of reduction in mechanical performance was found to be the weakening of the bond between soil particles. And it was discovered that structural damage increased as the number of wetting and drying cycles increased but at a slower rate. Based on the tested results, linear functions between the loss extent parameters of mechanical performance and the structural damage variable were established for the VC substrate. Finally, the action mechanisms of wetting and drying cycles for VC substrate were discussed, and the main influential factors were proposed.

WETTING AND DRYING CYCLES EFFECT ON DURABILITY OF GYPSUM SOILS TREATED WITH CALCIUM CHLORIDE OR CEMENT ADDITIVES

The study consists of two stages: the first one is to improve the gypsum soil with cement or calcium chloride and the second stage is to expose these soil specimens to series of wetting and drying cycles .Three soil specimens were taken and marked as (A,B and C) with gypsum content (47, 32 and 23)% respectively .The results show that cement additive increases the cohesion of soil specimens to 50% and collapse potential decreases with 65% and soil specimens improved with calcium chloride increase the cohesion up to more than 70% and collapse potential decreased about 70%. In the first cycle for wetting and drying cycles for soil specimens improved with cement the cohesion decreases about 25% and stays with the same ratio of the decreasing along the other cycle up to twelfth cycle. Collapse potential remains with the same value and is not affected by cycling of wetting and drying. In the first cycle for soil specimens treated with calcium chloride there is no effect in the first cycle whereas in the fourth cycle the cohesion increased by 60% and in the eighth cycle the cohesion decreased 8% and remains stable until the twelfth cycle. Collapse potential increases from one cycle to another by (30-50) % for all soil specimens.