Effect of different ways of STPP retarder addition on properties of recycled gypsum

Abstract

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 — (PO₃Ca) on the surface of R-SP, leading to the complete development of crystals and their close overlapping, thus bringing about the increase of strength.

Keywords

recycled gypsum / sodium polyphosphate / adding ways / properties

References

[1] Ramezanianpour A A. Cement Replacement Materials: Properties, Durability and Sustainablity[M]. 2012 German: Springer Geochemistry/Mineralogy.

[2] Zhao W, Leeftink R B, Rotter V S. Evaluation of the Economic Feasibility for the Recycling of Construction and Demolition Waste in China-The case of Chongqing[J]. Resour. Conserv. Recy., 2010, 54(6): 377-389.

[3] Femanda P T. Handbook of Recycled Concrete and Demolition Waste[M]. 2003 Cambridge: Woodhead Publishing Ltd.

[4] Xu B S. Use of Waste Gypsum in Ceramic Production as Set Retarders in Portland Cement[J]. Sichuan. Cem., 1998, 01: 4-5.

[5] Zhu X L. Research on the Use of Waste Modal-Gypsum to Replace Natural Gypsum to Produce Cement[J]. Resour. Compr. Util. China, 2001, 08: 15-17.

[6] Chea C, Khairun A M A, Zainal A A, et al. Use of Waste Gypsum to Replace Natural Gypsum as Set Retarders in Portland Cement[J]. Waste Manage., 2009, 29(5): 1675-1679.

[7] Sun J Y. The Performance of Waste Gypsum Backfill Material for Pavement Course and Its Savety Assessment[J]. Coal Ash China, 2006, 1: 37-38.

[8] Aly A, Keizo U, Takeshi K. Investigation of Recycled Gypsum in Conjunction with Waste Plastic Trays for Ground Improvement[J]. Constr. Build. Mater., 2011, 25(1): 208-217.

[9] Aly A, Keizo U. Environmental Influences on Durability of Soil Stabilized with Recycled Gypsum[J]. Cold. Reg. Sci. Technol., 2011, 66(2-3): 84-92.

[10] Takeshi K, Aly A, Toshihide S. Effect of Freeze-Thaw Cycles on Durability and Strength of Very Soft Clay Soil Stabilized with Recycled Bassanite[J]. Cold. Reg. Sci. Technol., 2012, 82: 124-129.

[11] Takeshi K, Aly A, Toshihide S. The Use of Recycled Bassanite and Coal Ash to Enhance the Strength of Very Soft Clay in Dry and Wet Environmental Conditions[J]. Constr. Build. Mater., 2013, 38: 224-235.

[12] Zhang Y Q. On Improves the Soft Soil Strength and Durability by Applying Renewable Gypsum and Fly Ash[J]. Shanxi Arct., 2013, 13: 108-109.

[13] Godinhocastro A P, Testolin R C, Janke L, et al. Incorporation of Gypsum Waste in Ceramic Block Production: Proposal for a Minimal Battery of Tests to Evaluate Technical and Environmental Viability of This Recycling Process[J]. Waste Manage., 2012, 32(1): 153-157.

[14] Yoshiyuki K, Tamotsu Y. Synthesis of Large Plate-Like Gypsum Dehydrate from Waste Gypsum Board[J]. J. Eur. Ceram. Soc., 2006, 26(4-5): 777-783.

[15] Chen B Y, Chen C L, Lu S D, et al. On Preparation of α-Hemihydrated Gypsum by Used Pottery Model[J]. J. Fuzhou Univ. (Nat. Sci.)., 1996, 24(6): 96-99.

[16] Xie E L. Research on the Recycled Gypsum from Used Model Gypsum[J]. Pet. Ind. Appl., 2008, 27(1): 21-22.

[17] Yang X Y, Mu S B, Ji L X. Research on the Property and Development Laws of Reproductive Gypsum[J]. Non-Metallic Mining Industry China, 2000, 06: 16-18.

[18] Yang X Y, Mu S B, Pan J. The Method and Mechanism Investigation of Improving Performance of Reproductive Gypsum[J]. J. Wuhan Univ. Sci. Technol., 2004, 04: 36-38.

[19] Paulo S B, Gladis C. Recycled Plaster: Physical and Mechanical Properties[J]. Adv. Mater. Res., 2011, 374–377: 1307-1310.

[20] Gladis C, Sayonara M M P, Katia T. Thermal Analysis of Recycled Gypsum from Construction and Demolition Waste[J]. Appl. Mech. Mater., 2013, 260–261: 977-980.

[21] Li Z X, Peng J H, Zhao H X, et al. Research on the Changes of Phase Composition, Pyrolysis Characteristics and Microstructure of Recycled Gypsum[J]. J. Sichuan Univ. (Eng. Sci. ed.), 2014, 46(2): 187-192.

[22] Magallanes-Rivera R X, Escalante-García J I, Gorokhovsky A. Hydration Reactions and Microstructural Characteristics of Hemihydrate with Citric and Malic Acid[J]. Constr. Build. Mater., 2013, 23(3): 1298-1305.

[23] Nilles V, Plank J. Study of the Retarding Mechanism of Linear Sodium Polyphosphates on α-calcium Sulfate Hemihydrate[J]. Cem. Con. Res., 2012, 42(5): 736-744.

[24] Khalil A A, Tawfik A, Hegazy A A, et al. Effect of Some Waste Additives on the Physical and Mechanical Properties of Gypsum Plaster Composites[J]. Constr. Build. Mater., 2014, 68: 580-586.

[25] Yu Q L, Brouwers H J H. Microstructure and Mechanical Properties of β-hemihydrate Produced Gypsum: An Insight from Its Hydration Process[J]. Constr. Build. Mater., 2011, 25(7): 3149-3157.

[26] Peng J H. Study on Action Mechanism of Water Reducers and Retarders for Building Gypsum[D]. 2004 Chongqing: Chongqing University.

[27] Singh N B, Middendorf B. Calcium Sulphate Hemihydrate Hydration Leading to Gypsum Crystallization[J]. Prog. Cryst. Growth. Ch., 2007, 53(1): 57-77.