The Test Study On Improved Phosphogypsum Used As The Roadway's Filling

Phosphogypsum is a waste materials produced in the course of ammonium phosphate producing. As a kind of waste materials, it occupied volumes of space, restricted enterprises from development and made a serious pollution on environment. Phosphogypsum was used to road construction, which can help enterprises solve the problem of ammonium phosphate waste materials regeneration and the need of filling stuff in the road construction. It is important to the development of enterprises, social and environment protecting. Phosphogypsum which taking from De yang, was meliorated by using solidified agent manufactured in Zhi-Yuan company. According to the general soil test and dynamic model testing in lab, the characteristics of improved phosphogypsum and the subgrade-pavement structural dynamic-fatigue were learned to the feasibility and reliability of solidfied phosphogypsum as highway subgrade fillings.The general soil test including compaction test, CBR test, unconfined compressive test, alternation of wetting and drying test and the simulataneous test of in two kinds solidified styles and eight different kinds of matching ratios were carried out. The test results showed that the pure phosphogypsum's hydrophilicity was strong and its water stability was low. When it meeted the water, the strength decreased a lot and would induce subgrade distortion. So, the pure phosphogypsum cann't be used as fillings without handling. The improved phosphogypsum modified by ZY1 solidified agent with 6% matching ratio had well water stability. The CBR and unconfined compressive strength of the improved phosphogypsum were achieved the design request of highway subgrade. The CBR and unconfined compressive strength of the improved phosphogypsum with 20% ZY2 solidified agent and 0.9% ZY3 liquid solidified agen satisfied the strength request of the standard of base layer stuffing in Highway's Base layer Design. So, the two kinds of improved phosphogypsum were reliable as fillings.The subgrade-pavement sturctural model with 4m length, 3.5m width and 1.4m high was constructed by the two kinds of improved phosphogypsum mentioned above. Thereinto the pavement sturcture was C30 concret. The model was loaded repeatedly by simulating the carload. The loading times exceed 10~6 times. The amplitude value of repeated loading was two times as the highway load design standard. The test results showed the subgrade dynamic stress was 1/30 of the unconfined strength, the distortion of structure was small, the settlement was steady. It proved that the bed layer and subgrade using the improved phosphogypsum as fillings had favorable load-bearing capacity. Even in the condition of no pavement, the bed layer surface didn't bring obvious track and affect the safety and comfortability...