Background In order to cover the bare tree pits in our cities and look for an innovative and ecological approach of organic cover. The cover plate, which was added the environmentally friendly waterborne polyurethane adhesive into green waste (dead branches of Cupressus funebris) were used to cover the bare tree pits. Application performances were carried out to determine its capacity of water-holding, ability of pressure resistance and resistance to cigarette burning in the indoor simulation experiment.

Methods The size of dead branches of C. funebris was divided into 2 types:0~1 cm length(fine) and 1~3 cm length(coarse). The added amounts of waterborne polyurethane adhesive were in 5 levels (20%, 25%, 30%, 35% and 40%, respectively). Then the raw materials and the adhesive were mixed up thoroughly and was put into the size 10 cm×10 cm×5 cm cuboid opening mold and pressed with 20 kPa pressure, 10 different sizes of cover plates were obtained at last. Its capacity of water-holding, ability of pressure resistance and resistance to cigarette burning was determined.

Results 1) The cost of cover plate with area of 1 m² and thickness of 5 cm (the amount of adhesive was 25%) was RMB 87 Yuan, almost 1/5 cost of the same size cast iron cover plate.2) All cover plates had a certain density deviation and had a slight water absorption thickness expansion phenomenon. 3) There was a significant logarithmic function between water-holding capacity and soaking time, and there was a significant power function between water absorption rate and soaking time. The 5 fine branched cover plates had a higher water-holding capacity than that of 5 coarse branched cover plates, but its pressure resistance was slighter than the five fine branched cover plates. The water-holding capacity was highest, 2 209.25 g/kg and 999.15 g/kg respectively, when the amount of the adhesive of fine branched and coarse branched cover plates were at 25% and 30%, the effective interception capacity and effective rate of interception capacity were also maximum. 4) Compression strength of all cover plates were considerably higher than 0.52 MPa (Maximum pressure generated by a pedestrian weighing 100 kg during normal walking), all cover plates had not been burned by cigarettes.

Conclusions Among all cover plates, fine branched with the 25% amount of waterborne polyurethane adhesive, had the largest water-holding capacity, ability of pressure resistance and resistance to cigarette burning. Therefore, not only could it cover the bare tree pits in our cities replacing the traditional inorganic cover material such as the cast iron but also utilize garden waste adequately and environmentally friendly.