摘要
We analyzed the influence of sodium polyphosphate（STPP） on the performances of recycled gypsum（RG）. This analysis was performed with two different ways of STPP addition： One was that the STPP was added into Plaster of Paris（POP）, then recycled plaster（R-SP） was obtained after a series of processes and the other was that the STPP was directly put into recycled plaster（R-PS）. The conclusions confirmed that STPP increased the water demand and delayed the hydration of R-PS. With regard to its hardened performance, STPP provided hardened recycled gypsum with a loose structure which led to the lower strength and higher water absorption than recycled plaster（R-P） without STPP. On the contrary, the water requirement and the setting time were decreased and shortened by STPP in R-SP, respectively. A dense structure was also possessed by R-SP which contributed to the high strength and low water absorption. The analysis shows that STPP is selectively chemisorbed on the（111） face of R-PS crystals, it inhibits the growth in c axis direction, resulting in the extending of setting time and the transformation of morphology, making the hardened R-PS crystals coarsened, which results in high W/P and low strength. Whereas the low W/P is made by both the rod-like crystals of low length-radius possessed by R-SP and the relatively high ζ-potential absolute value caused by –（PO_3Ca） on the surface of R-SP, leading to the complete development of crystals and their close overlapping, thus bringing about the increase of strength.
We analyzed the influence of sodium polyphosphate（STPP） on the performances of recycled gypsum（RG）. This analysis was performed with two different ways of STPP addition： One was that the STPP was added into Plaster of Paris（POP）, then recycled plaster（R-SP） was obtained after a series of processes and the other was that the STPP was directly put into recycled plaster（R-PS）. The conclusions confirmed that STPP increased the water demand and delayed the hydration of R-PS. With regard to its hardened performance, STPP provided hardened recycled gypsum with a loose structure which led to the lower strength and higher water absorption than recycled plaster（R-P） without STPP. On the contrary, the water requirement and the setting time were decreased and shortened by STPP in R-SP, respectively. A dense structure was also possessed by R-SP which contributed to the high strength and low water absorption. The analysis shows that STPP is selectively chemisorbed on the（111） face of R-PS crystals, it inhibits the growth in c axis direction, resulting in the extending of setting time and the transformation of morphology, making the hardened R-PS crystals coarsened, which results in high W/P and low strength. Whereas the low W/P is made by both the rod-like crystals of low length-radius possessed by R-SP and the relatively high ζ-potential absolute value caused by –（PO_3Ca） on the surface of R-SP, leading to the complete development of crystals and their close overlapping, thus bringing about the increase of strength.
基金
Funded by the National Natural Science Foundation of China(No.50872160)
