Research On Waterproof Properties Of Gypsum And Gypsum-based Composite Materials

Due to the simple molding technological, extensive raw material, and low energy consumption, gypsum and gypsum-based products are widely used in construction industry. Gypsum is gelled material whose water-proof is poor. And after being damped, gypsum-based products are easily bended and soften, the performance is decreased. Therefore, these disadvantages prevent the development and application of Gypsum's.In order to improve the poor water-proof property of gypsum-based composites, combined to water-proof methods are used, the methods include: hydrophobic latex became coating to proof water, organics matter became coating to prevent water, and hydration mineral expansion closed pores and so on. The hydrophobic latex used in gypsum-based product was prepared, and the water-proof mechanisms of hydrophobic latex, organics matter, hydration mineral expansion, and combined water-proof method were discussed. The above research results played an important role in guiding gypsum-based composites production, provided the theory basis for gypsum application, and promoted gypsum wall materials development.In this paper, the raw materials of paraffin emulsion were wax and Vaseline, and studied the effects of emulsifying agent kind, ratio of wax to Vaseline, emulsification temperature, emulsification time and stirring rate on the performance of paraffin emulsion. Emulsifying compound used for emulsifying paraffin was made out. Both the influence of paraffin emulsion dosage on gypsum performance and the waterproof mechanism of paraffin emulsion were explored. Results show that: when the ratio of paraffin to water was 1 to 3, emulsifying compound dosage was 10%, the ratio of paraffin to Vaseline was 85 to 15, emulsification temperature was 85-90℃, emulsification time was 70-80min, stirring rate was 1000r/min, paraffin emulsion performance was better, and the optimum dosage of gypsum was 5%.The influence of organics matter on gypsum property was studied, organics matter included VAE emulsion, styrene-acrylic emulsion and polyving akohol solution. Results show that the optimum dosage of VAE emulsion, styrene-acrylic emulsion and polyving akohol solution was 6%, 3% and 4% respectively, and the property of sample adding VAE emulsion was best. The gypsum morphology adding organics matter was observed, and the mechanism of organics matter waterproof agent was discussed.The influences of naphthalene series water-reducer, polycarboxylate series water-reduce and amino sulfonic acid series water-reduce and calcium lignin sulfonate water-reduce on gypsum water reducing ratio, absorption capacity, softening coefficient and absolutely dry strength were studied respectively, the optimum dosage of water-reducer was made sure, and the mechanism of polycarboxylate series water-reduce was discussed. Research results showed that polycarboxylate series water-reduce function was better, and the optimum dosage was 0.7%.In this experiment, expansion agent was developed to enhance gypsum water-proof property, expansion agent optimum dosage was made sure, and the influence of curing condition on samples property was researched. The mechanism of expansion agent was also analysed, and the compound waterproof synergy mechanism among paraffin emulsion, VAE emulsion, HC water-reducer and expansion agent was discussed. Compared to blank sample, the 2h and 24h absorption capacity of sample adding compound water proof agent decreased by 95.7% and 95.0% respectively, flexural softening coefficient and compressive softening coefficient enhanced by 120.9% and 174.3% respectively, and flexural strength and compressive strength enhanced by 44.3% and 71.3% respectively.Corn straw fiber was chosen as reinforcement material to produce gypsum-based composites, and the optimum dosage of corn straw fiber was made sure. In order to improve composites water-proof property, the surface of straw fiber was modified by polyving akohol coating, and compound water proof agentwas added. The mechanism of polyving akohol coating modification was discussed. Results show that: when fiber dosage was 3%, fiber was modified by polyving akohol, and compound water proof agent was added, composites 2h and 24h absorption capacity decreased by 96.0% and 94.6% respectively, flexural softening coefficient and compressive softening coefficient enhanced by 200.0% and 225.0% respectively, and flexural strength and compressive strength enhanced by 47.1% and 42.1% respectively.