| With the continuous development of economy and building technology,as well as people's increasing demand for green and functional buildings,the research and development of green,energy-saving,lowconsumption and environmentally friendly building materials is of great significance to achieve energy conservation and emission reduction and the development of circular economy.Compared with cement,gypsum-based cementing materials have the advantages of low energy consumption and simple processing technology.The application of gypsum-based cementing materials to wall materials can not only exert its resource advantages of abundant reserves,but also have green environmental protection characteristics.At the same time,the recycling of waste EPS in building materials meets the current development needs of circular economy.EPS/gypsum composite materials have the advantages of light weight and good thermal insulation performance,and have good development prospects in the application of lightweight thermal insulation enclosure walls.In view of this,this paper systematically studied the preparation and performance optimization of lightweight water-resistant EPS/gypsum composite wall materials.The main research contents and results are as follows:Firstly,the water-resistant modification of gypsum cementite was studied.Taking Portland cement,fly ash and quicklime as modifiers,based on the content range of the three modifiers determined by single factor test,a three-factor and three-level test was designed by response surface method according to the principle of Box-Behnken center combination design.By analyzing the test results with the design-Expert software,the optimal ratio of each material content was determined: gypsum powder content 69.98%,cement content 15.32%,fly ash content 9.17%,and quicklime content 5.53%.The compressive strength,softening coefficient and other indexes of the selected group were verified and analyzed.The results showed that the 1d compressive strength,28 d compressive strength and softening coefficient of the modified gypsum matrix were 5.50 mpa,20.30 mpa and 0.45 respectively,which were increased by 48.65%,54.96% and 21.62%,respectively,compared with the blank gypsum group.In order to further improve the construction property,water resistance and strength of gypsum based cementitious materials,the effects of water-binder ratio,water-reducing agent,retarder and grinding time on the properties of the modified cementitious materials were studied.The results show that the composite cementitious material has the best comprehensive performance such as workability,flexural strength and compressive strength when the water-binder ratio is 0.25.The experimental results of different water reducing agents showed that when the content of polycarboxylic acid water reducing agent was 0.28%,the 1d dry compressive strength,28 d compressive strength and softening coefficient of the composite cementing material were 32.10 mpa,53.70 mpa and 0.80 respectively,which were 492.59%,164.53% and 77.78% higher than that of the blank group.Compared with melamine superplasticizer,polycarboxylic acid superplasticizer has better compatibility.The retarder test results show that when the SC retarder content is 0.15% and the initial and final setting time of the composite slurry reaches 47 min and 56 min respectively,it meets the requirements of construction operation time and rapid demodulation.By grinding the powder,it was found that the fineness of gypsum,cement and quicklime increased by 39.02%,37.53% and 22.35% respectively when the powder was added with polycarboxylic acid water-reducing agent for 20 min.The compressive strength on 1d and 28 d was 33.50 mpa and 61.50 mpa respectively,which were 24.07% and 32.54% higher than before grinding.The results show that the parameters corresponding to the best comprehensive performance of gypsum based composite cementitious materials within the test range are: water-binder ratio 0.25,polycarboxylic acid water-reducing agent content 0.28%,retarder content 0.15%,grinding time 20 min.The recycled EPS particles were used as the aggregate and compounded with the gypsum based composite cementite material to prepare EPS/ gypsum composite material,and its performance was optimized.First,the influence of HPMC content on the performance of EPS/ gypsum composite was studied.Adobe Photoshop CC2018 and Image-Pro Plus graphics processing software were used to quantitatively characterize the uniformity of EPS particles in the composite cementitive material.The experimental results showed that when the EPS particle size was 3?5mm,compared with 3mm and 5mm,single-grain aggregate was more beneficial to the improvement of various properties of the composite.The effects of EPS volume dosage(40%,50%,60%,70% and 80%)on the strength and bulk density of EPS/ gypsum composites were studied,and the relationship between the mechanical properties of EPS/ gypsum composites and EPS volume fraction,as well as the effect of EPS volume fraction on the apparent density and thermal conductivity of EPS/ gypsum composites were investigated.In addition,the effect of PVA fiber on the properties of EPS/ gypsum composite and its modification mechanism were studied.The results showed that PVA fiber could improve the bending strength of composites,and the addition of fiber could also solve the floating problem of EPS particles to a certain extent.In this paper,the preparation and performance control methods of EPS/ gypsum composites were studied systematically.The green lightweight wall materials with apparent density of 855.20kg/m3,compressive strength of 6.40 MPa,thermal conductivity of 0.295W/(m ·K)and softening coefficient of 0.71 were prepared,and the thermal insulation properties were good.It provides a reference for the utilization of waste renewable resources and the application of EPS/ gypsum composites in new wall materials. |
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