Study On The Solidification Rate Of Expansion Of The α-High-Strength Gypsum Plaster

In recent years,α-High-Strength gypsum plaster has been widely used in theprecision casting, automobile, aircraft and some new development of application field,the survey found that the emerging fields of gypsum are strict with solidificationexpansion properties, except for some special requirements of the high expansion rate,do not want too high expansion rate. It is urgent to solve the problem of extremely suchas to find the influence factor of high-strength gypsum solidification expansion rate andaccording to the influence rules to reduce gypsum expansion rate. This paper adopts anew experimental equipment to measure the solidification expansion rate ofα-High-Strength gypsum plaster, using Vicat tester test, strength test, the rate ofhydration analysis, SEM to reveal its beginning and final setting time, strengthdevelopment process, the size of water law and hardening the submicroscopic structure.Detailed study of three different sizes, four kinds of mixing rate and different additives(retarder and water reducer) to a high-strength gypsum material solidificationexpansion rate of law, as well as the setting expansion mechanism of high-strengthgypsum. The successful establishment of high-strength gypsum initial and final settingtime,2h bending strength,3h the rate of hydration, hardening properties andmorphology of solidification rate of expansion effect. Through the experimental studycan get the following conclusions:1、The grain of α-type high-strength gypsum is smaller, and the Particle size isdistributed relatively centralization; The hydration expansion is about0.4%; themorphology of the hydration products is relatively more complex, The vast majority ofthe hydration products appears irregular short columnar, its compressive strength ismore than60Mpa, other performance indicators are far more than the requirements inthe JC/T2038-2010《α-type high-strength gypsum》.2、As the particle size of gypsum decreases, and as the fine particles and porosityincreases, setting time of plaster declines sharply, but the flexural strength increasesgradually. Setting expansion rate of gypsum is reduced as the accretion of the particlesize. This is mainly because hydration is more sufficient, the link of crystal andcrystalline nature is in good condition, so the strength and solidification inflation rate of the plaster increases.3、In the range of the standard thick, the hydration of high-strength gypsum isfullest, the crystal lines is in good condition and cross-overlap between the crystal isalso very close, the setting expansion rate is the biggest. The standard thick as the basepoint, mixing with water rate decrease or increase the setting expansion rate will bereduced, but with the mixing water rate increasing, the beginning and final setting timeof gypsum increases,2h flexural strength plummets.4、Under the conditions of the same kind of retarder, as the dosage increase, thesetting expansion rate of high-strength gypsum decreases continuously, add retarder toreduce the number of gypsum nuclei, thereby reducing the hardening of the systemdensity, reducing the strength of the hardened body, thus affecting gypsum coagulationexpansion. Different mechanisms of the different role of gypsums, so the effect of theplaster setting expansion rate is different. The test uses of citric acid, sodiumpyrophosphate, tartaric acid, gypsum dedicated retarder and gypsum-dedicatedretarder five kinds of slow coagulant, tartaric acid on the rate of expansion is the mostobvious.5、In this paper，we study the influence on the performance of gypsum with the SMsuper plasticizer, and found that with the increasing of the dosage, the solidificationexpansion of gypsum first decreases and then increases. When the dosage is0.2%,thesolidification expansion is the minimum. When the content is greater than0.2%, withthe increasing of the content, the solidification expansion becomes greater. Due to theadsorption of a large number of acid molecules in the form of chemical adsorption onthe surface of the crystal, reducing the freedom of the crystal surface, leading to thecoarsening of the crystal, and the flexural strength of gypsum significantly reduced. Sothe plaster setting expansion rate of the gypsum will increase when the SM contentexceeds a certain.