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IJSTR >> Volume 2- Issue 12, December 2013 Edition

International Journal of Scientific & Technology Research  
International Journal of Scientific & Technology Research

Website: http://www.ijstr.org

ISSN 2277-8616

"Investigation of the Hardening and Strength Characteristics of Gypsum in Mould Casting for POLY-CRETE™"

[Full Text]



J.N. Lambi, C.W. Adegoke



Keywords: (polyethylene fibers, poly-crete, asbestos-free, building materials, gypsum-pop; composite materials, mould casting, mix ratio)



Abstract: Poly-crete™ is an engineered asbestos-free alternative building material product recently innovated from polyethylene waste materials. Mould design and fabrication is an important step in the final production of prototype 600 mm x 600 mm ceiling boards of Poly-crete. Hardness, strength, durability and weight of moulds have been found to be directly related to the mix ratio of Portland cement, sand aggregate and gypsum (plaster of paris- pop) used in the production of moulds. It is established in this study, through the measurement of hardness (on the Mohs' Scale) and final weight of production trials, that a mix ratio of 1 1/2 sand + 3/4 cement + 3/4 pop (by volume) produces the best durable mould with a setting time of less than 30 minutes and a hardness of about 3.25. Even though the mix ratio of 2 sand + 1 cement + 0 pop demonstrated the highest hardness/strength characteristics, with a hardness of about 3.75, it was considered to be too heavy and bulky for routine use. Its setting time of about 24 hours was also considered to be too long (cf. 30 minutes for product with 3/4 pop) for its mass production to be economical and profitable. A third mix ratio of 1 1/2 sand + 1/2 cement + 1 gypsum (pop) also gave a product with a fairly good setting time of about 30 minutes and a hardness of about 3.25. On the other hand, a mix ratio of 1 1/2 sand + 1 cement + 1/2 pop took more than 4 hours to set/harden and with a hardness of about 3.5. The studies, therefore, indicate that the addition of pop to a normal sand-cement mix serves to reduce the setting time - that is, the mix hardens more quickly, though with a corresponding decrease in strength/hardness. Unacceptably long setting time results are obtained with products containing cement in higher proportion than that of pop. In other words, the ration of pop in the mixture must be either equal to or greater than that of cement to obtain a short setting time. On the whole, however, it was found that the mould mix with equal proportion of cement and pop gave the best and optimum mould production in terms of both short setting time and hardness/strength considerations. This was the case with the mould cast at a mix ratio of 1 1/2 sand + 3/4 cement + 3/4 pop and is therefore recommended for future poly-crete mould production. It is estimated that a typical SME - (Small Medium Enterprise) polycrete production factory based on Franchise Business Model would require about 300 moulds for optimal operation.



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