| Gypsum is a kind of high quality wall material, with energy-saving environmental protection, safety and comfort, and excellent construction performance. But the defect of water resistance in gypsum restricted the application and development of gypsum in the field of building wall, seriously, especially building facades and load-bearing wall areas.In order to overcome the shortcoming of gypsum, preparation of water resistant gypsum-based materials was prepared by inorganic modification of gypsum. Using the building gypsum powder as main material, cement, lime, fly ash and other inorganic modifier as auxiliary materials; Water resistant admixture was developed independently, on the basis of a number of experiments and theoretical analysis, At the same time, the affection on the materials after the admixture added was researched and discussed, following conclusions were got:(1) The principle of gypsum and cement hydration reaction of C-S-H gel, Ettringite and other components of the insoluble in water was used, Portland cement and aluminate cement were single doped into gypsum as inorganic modification. The results showed that Portland cement and aluminate cement all could improved the gypsum water resistance and mechanical properties, and composite Portland cement of gypsum modified effect was better than that of aluminate cement on the gypsum modified effect. When the composite Portland cement content was 20%, compressive strength of gypsum in the dry state was 22.82 MPa, increased 18.85%, the flexural strength in the dry state was 6.95 MPa, increased 14.12%, compressive strength of water saturation was 10.73 MPa, increased 46.79%, flexural strength of water saturation was 4.22 MPa, increased 31.06%, compressive softening coefficient was 0.47, increased 23.68%, flexural softening coefficient was 0.61, increased 15.09%; 5% dosage of aluminate cement could make compressive strength of gypsum in the dry state increase 8.03%, compressive strength of water saturation increase 12.11%, flexural strength of water saturation increase 4.10%, the compressive softening coefficient increase 2.7%, flexural softening coefficient increase 11.90%.(2) The principle which would rapidly condensation when aluminate cement and Portland cement mixed meet water was used to prepare compound inorganic modifier, in order to matching gypsum setting time, reducing destruction of crystal compound structure by hydration of cement after the initial setting of gypsum. The results showed that the compound inorganic modifier was more obvious than cement by single doped on the effect of the water resistance of gypsum. 15% dosage of the compound inorganic modified agent could make absorption rate of water saturation decrease 1.38%, the compressive strength in the dry state increase 9.26%, the compressive strength of water saturation increase 42.95%, flexural strength of water saturation increase 18.77%, compressive softening coefficient increase 31.51%, the flexural softening coefficient increase 56.10%.(3) 30% fly ash was incorporated in gypsum, and lime was used as early activator of fly ash, to inspiring early activity of fly ash, to improving the waterproof performance of gypsum. The results showed that the lime as alkali activator of fly ash was an effective way to improving water resistance of fly ash-gypsum based materials. 24% dosage of quicklime could make water absorption rate of gypsum decrease 4.3%, the compressive strength in the dry state increase 21.78%, the compressive strength of water saturation increase 34.32%, flexural strength of water saturation increase 12.37%; compressive softening coefficient increased 10.50%, the flexural softening coefficient increase 62.36%.(4) Based on the conclusion of the study on single doped of modified inorganic agent, compound inorganic modification and inspiring the activity of fly ash, by the test by, a water resistant admixture of gypsum which is convenient and practical was prepare by a variety of inorganic modified agent as a certain proportion of group assignment, and study of the effect of the admixture on the modification of gypsum. The results showed that the additive could improve the waterproof performance of gypsum greatly. When the admixture content was 30%, compressive strength in dry state of gypsum, compressive strength of water saturation, flexural strength of water saturation, compressive softening coefficient and flexural softening coefficient was increased by 23.44%, 115.23%, 14.00% and 73.00% and 300% respectively, water absorption rate of water saturated was reduced by 16.12%。(5) Compared and analyzed on the modification effects of different modifiers, admixture was the best and the optimal dosage of water resistant additive is 30%, applied admixture to the plaster wall material to proved the modification effect of the gypsum wall material. Showed that after modification of admixture, softening coefficient of hollow gypsum lath and plaster block had been greatly improved, was 0.65 and 1.23 respectively, reached the requirements of the current standard, other indicators also fully satisfied the current state and industry standards, the use of admixtures to modify the way very feasibility and practicality of gypsum. |
