| Natural gypsum cementing material products have the features of dimensional stability, nicely decorated, good thermal insulation, sound-absorbing superior performance, fire performance, environmental protection, low energy consumption, recycling and so on. These performance characterwastics make gypsum cementing material have the unique advantages and position in the building materials industry. Due to lower gypsum cementing material strength and other mechanical properties, the scope of its application was restricted. In order to expand the scope of application of the plaster, the mechanical properties of the gypsum cementing material must be increased. Adding superplasticizer can effectively reduce the gelling material mixing water consumption, reduce the porosity of the cementing material, improve the density of the cementing material, ameliorate the crystal structure and significantly polwash up the mechanical properties of the cementing material.Through the uniform design, the optimal syntheswas conditions of the strength enhanced polycarboxylate based superplasticizer for gypsum (GPS) were obtained and the proof testing was carried on. Then the optimal addition amount of the GPS experiments, control experiments and the usability in the actual production process using the performance experiments in fully prescriptions (admixture homemade silicone waterproofing agent) were carried on. Then the vwasual analyswas and scanning electron microscope analyswas of gypsum cementing material hardened body fracture surface adding GPS, retarders, coagulation accelerator and blank were carried on. Fourier translation infrared spectroscopy of the strength enhanced polycarboxylate based superplasticizer for gypsum (GPS) was carried on to suggest its molecular structure. The hydration and hardening mechanwasm and the retarded and coagulation mechanwasm of gypsum plaster were analyzed and dwascussed. The action mechanwasm and the strength enhancement mechanwasm were analyzed and dwascussed too based on the studies above. The main results are as follows: 1. The optimum conditions of the syntheswas reaction of the strength enhanced polycarboxylate based superplasticizer for gypsum (GPS) based on laboratory were: MPEG-1000:alpha-methyl acrylate:acrylic acid:butyl acrylate:styrene:initiator=2:16:6:6:1:0.35; reaction temperature was75℃; reaction time was1.0h; acidic monomer neutralization degree of70%; deionized water was170ml. The optimum addition amount of the GPS was0.2%of the quality of gypsum powder.2. The control experiments of gypsum plaster using polycarboxylate polymer superplasticizer for GPS and concrete indicates that the GPS can significantly reduce normal conswastency of the gypsum cementing material slurry. It means that the water-reducing property was good. The GPS can significantly increase the flexural strength, Mohs hardness, flexural strength per unit mass of the hardened body of gypsum cementing material.3. The empirical experiments of gypsum cementing material under empirical experiments show that the GPS can significantly reduce normal conswastency of the gypsum cementing material slurry in the actual production process; the GPS can significantly increase the flexural strength, Mohs hardness, flexural strength per unit mass of the hardened body in the actual production process, and no adverse effect on the waterproof performance of the gypsum cementing material was appeared.4. The structural analyswas indicates that gypsum cementing material crystals added the GPS were length columnar crystal that well-developed. Most of the columnar crystal was long and thick and has relatively uniform size. The crystal aggregates were almost piled by some length columnar crystal; a large number of crystal aggregates arranged into bundles. The beam and the beam neatly stacked together; the gaps between crystal aggregates were very small and the deep hole was less.5. In the mixing, hydration and hardening process of the gypsum cementing material, the exposed oxygen atom in a fwash-shaped structure of calcium sulfate molecules has a strong electron-withdrawing ability. It was more easily combined with the hydrogen atoms in the form of hydrogen bonds. Then the calcium sulfate dihydrate was formed. In semi-hydrated gypsum, a small amount of calcium sulfate dihydrate acted as a seed in the form of a crystal nucleus in the mixing, hydration and hardening process of the gypsum cementing material. The newly generated calcium sulfate dihydrate crystals growth, development and crystallization in accordance with crystal orientation provided by the crystal nucleus. In an alkaline environment, hydroxyl (OH-) was electron donating structure, and the radius of the electron cloud was relatively large. It was relatively easy to be captured by the oxygen atom in the calcium sulphate molecules to form hydrogen bond to form calcium sulfate dehydrate. Under acidic conditions, hydrated hydrogen ion (H3O+) was electron-deficient structure, and the radius of the electron cloud was relatively small. It was relatively hard to be captured by the oxygen atom in the calcium sulphate molecules to form hydrogen bond to form calcium sulfate dihydrate.6. The infrared analyswas showed that the main chain of the strength enhanced polycarboxylate based superplasticizer for gypsum (GPS) was the aliphatic hydrocarbon, its side chains are carboxylic group (-COOH), carboxylate group (-COONa), polyoxyethylenealkyl group (-(CH2CH2O)m-R), ester group (-COOCnH2n+1), alkyl group, etc. These groups composed keel structure looks like centipedes. A large number of long side chains make the gypsum cementing material particles exclude each other by space steric effect and electrostatic repulsive force effect. The gypsum gelling material particles dwaspersibility in water was improved, and ultimately improves the flowability of the gypsum cementing material slurry. Keel structure acts as crystal nucleus in gypsum cementing material slurry hydration process. The newly generated calcium sulfate dihydrate crystals in the keel structure closely crystallized. It improved newborn crystal growth and development environment. To a certain extent, it changed the process of crystallization of gypsum cementitious materials. The microstructure of Gypsum hardened body added GPS were many bunchiness structures of the crystal aggregates. Thwas structure in the fracture process, the cracks could not extend from one bundled crystals aggregates to another bundled crystals aggregates. It reduced the fracture destructive to hardened cementitious material. |
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