Preparation And Characterization Of Persulfur Titanium Gypsum Slag Cement Straw Wall Material

As one of by-products of titanium dioxide industrial production in China,the emissions of titanium gypsum is not only large but also difficult to handle under the current situation,which leads to have to be stacked for a long time.However,the stacking of titanium gypsum for a long time causes a series of environmental problems inevitably.Therefore,accelerating the utilization of titanium gypsum has become more urgent in recent years.In order to promote the resource utilization of titanium gypsum utilization especially in the field of wall materials,this paper developed a green cementitious material with good performance called persulfur titanium gypsum-slag cement by using 35% titanium gypsum and 60% blast furnace slag as the main raw materials,supplementing 5 % 42.5 grade cement as alkali activator with an appropriate amount of agent.On the basis of the developed cementitious material,the straw-persulfur titanium gypsum-slag cement was prepared by adding straw that is one of agricultural waste by-products into the developed cementitious material.Finally,the lightweight straw-persulfur titanium gypsum-slag cement wall material was prepared by doping polystyrene particles for reducing the bulk density of mortar specimens.The mechanical properties,thermal conductivity,microstructure and hydration process of titanium gypsum-slag cementitious material,persulfur titanium gypsum-slag cement and the resultant lightweight straw-persulfur titanium gypsum-slag cement wall material were systematically characterized by means of universal material machine,thermal conductivity instrument,X-ray fluorescence(XRF),scanning electron microscopy(SEM),Energy Disperse Spectroscopy(EDS)techniques.The results for the preparation of persulfur titanium gypsum-slag cement show that the bulk density and drying shrinkage rate and 7 d compressive strength of the cementitious material specimens decrease with the increasing content of titanium gypsum when the cementitious material is only activated by original titanium gypsum.However,the 28 d compressive strength of the above specimens increases significantly,which is up to 25.8 MPa as the content of titanium gypsum is 30%.When the content of titanium gypsum further increases to 30~35%,the softening coefficient of the samples is high and the thermal conductivity is low.When using original titanium gypsum and 42.5 grade cement as the alkali activators of the system,the early compressive strength(3 d)is obviously improved.The 28 d compressive strength of titanium gypsum-slag cement first increases with the increasing content of 42.5 grade cement from 0% to 5% and then decreases.As 42.5 grade cement content is more than 10 %,the compressive strength of specimens declines slowly.The SEM results display that the AFT product is enwrapped by C-S-H gel,Ca(OH)2 and excess CaSO4?2H2O in the titanium gypsum-slag cement specimens with 20% and 35% original titanium gypsum.The early strength of the specimens is distinctly enhanced when 5% 42.5 grade cement replaces 5% blast furnace slag as the alkali activator.For example,the 28 d compressive strength is increased by 13%.Meanwhile,the thermal conductivity of the specimen increases.Nevertheless,the softening coefficient decreases.The straw-persulfur titanium gypsum-slag cement was prepared by using straw as fine aggregate in a composition of 35% titanium gypsum,60% slag,5% 42.5 grade cement and 5% admixture.The experimental results illustrate that the bulk density and 7 d flexural compressive strength of the samples decrease with the increase of the straw content.The 28 d compressive strength and flexural strength firstly increase with the increasing amount of straw from 0 % to 30% and then decrease.Clearly,when the amount of straw is 30%,the maximum of the 28 d compressive strength and flexural strength for the straw-persulfur titanium gypsum-slag cement is obtained,respectively.When the content of straw ranges from 20 % to 30 %,the corresponding sample exhibits higher softening coefficient.In addition,the drying shrinkage rate and thermal conductivity of the sample decrease with the increase of the straw amount.The bulk density of mortar specimen significantly decreases when introducing polystyrene particles to straw-persulpur titanium gypsum-slag cement with 30 % straw.However,the 7 d and 28 d compressive strength and flexural strength decrease with the increasing amount of polystyrene particles.For instance,the 7 d and 28 d compressive strength and flexural strength of the sample with a bulk density of 600 kg/m3 is 1.74 MPa,4.3MPa,0.84 MPa and 1.02 MPa,respectively.The dry shrinkage rate,water absorption rate and thermal conductivity of straw-persulpur titanium gypsum-slag cement increase with the increase of bulk density.All the results indicate that the developed straw-persulpur titanium gypsum-slag cement can find a potential application as a kind of lightweight thermal insulation material.