Study On Preparation And Properties Of Modified Flue Gas Desulfurization Building Gypsum Composite Walling Materials

Nowadays the national energy policies and carbon emission reduction policies become increasingly stringent,which bring the increase of the power station by-product the flue gas desulfurization(FGD)gypsum.The disposal and utilization of these huge quantities of FGD gypsum are focused.One of important way to consume FGD gypsum is changing them into building gypsum by calcining treatment to prepare the wall materials.However,FGD building gypsum has some shortcomings such as poor mechanical properties and water-resistance property,which is the main factor of restricting its application and development.In this paper,the FGD building gypsum-based wall materials with higher strength and better water-resistance property are prepared by modifying the FGD building gypsum.At meaning time,the moisture release ability of gypsum block are tested to realize the utilization of gypsum composite wall material.The FGD building gypsum as the main gel material,to ensure the content of not less than 75%.Firstly,the effect of single doped or mixing addition of inorganic materials including cement,fly ash,slag and silicon fume on the properties of FGD building gypsum are explored The mechanism are analyzed by XRD,SEM,DTA or TG and the optimal formula are confirmed.In order to improve the property of water resistance,the organosilicone waterproofing agent are added into the optimal modified FGD building gypsum.The effect of the organosilicone waterproofing agent amount on the properties of modified FGD building gypsum are discussed.The waterproofing effect of modified FGD building gypsum with organosilicone waterproofing is tested by contact angle test and submerging test.In order to improve the flexural strength and apparent density of FGD building gypsum products,the glass fiber and sorghum straw are added into the optimal modified FGD building gypsum.The effects of fiber length to diameter ratio,dosage and surface treatment on the performance of FGD gypsum composite system are studied.The reason of the performance change is analyzed by SEM.Finally,the modified and unmodified FGD building gypsum is made into a block,which is installed as a filling wall into a wooden frame to form a closed room where the moisture release ability of the two blocks is tested.The experimental results show that the partial performance can be improved by adding one inorganic modified materials.But the flexural strength is not effectively improved by this way.In terms of water resistance,only the addition of cement makes the softening coefficient of the system reach 0.6.The orthogonal experiments of complex mixing inorganic modified material and composite activator show that the sample block,with dry flexural strength of 6.70 MPa,the dry compressive strength of 25.45 MPa,the flexural softening coefficient of 0.683 and the compressive softening coefficient of 0.635,can be obtained when mixing desulfurization gypsum,cement,slag,silica fume and composite activator of 82: 5: 6.4: 5: 1.6.XRD test results show that the C-S-H gel and AFt crystal phase are generated in mixed system generates.And the SEM results show that except short briquette dihydrate gypsum there are more flocculent C-S-H gel and needle-like AFt crystals formed in the hydration products of the mixing system,which is the result of inspiration of the activity of slag and ordinary silica fume by the composite activator.DTA-TG analysis confirmed that the C-S-H gel phase and the AFt phase in the complex system lost part of the crystal water between 87° and 120°,resulting in endothermic and weight loss.The presence of the C-S-H gel phase and the AFt crystal phase is the intrinsic reason for the compact structure,the strength and the water resistance of the hydration hardening body of composite system.Organosilicone waterproofing agent is added into the modified FGD building gypsum composite system.When the content of the waterproofing agent is 0.8%,the performance of the sample block is at the inflection point,at which the flexural strength and compressive strength is the lowest while the flexural and compressive softening coefficients reach the highest.Meanwhile water absorption rate reduced to below 4% at this inflection point,reflecting the water resistance of the FGD building gypsum composite system are improved significantly.The air entraining effect of this kind of waterproof agent is the reason of inflection point of property.After adding different amount of silicone waterproofing agent,the contact angle of the sample block increased from 0° of pure FGD building gypsum to 36.29° of gypsum composite system and the immersion experiment show that samples are almost devoid of water intrusion,which indicates that the polysiloxane hydrophobic agent effectively change the pore properties of gypsum and block the micro crack.The glass fiber with length of 20 are sequencely treated by boiling,lactic acid and coupling agent.Then they are added into the modified FGD gypsum composite system.When their content is 0.8%,the dry flexural strength of sample block reach to 9.23 MPa.This is due to the increase of the surface roughness of the glass fiber,which can enhance the bonding force between the glass fiber and the gypsum.The sorghum straw with length of 7.5 are sequencely treated by NaOH and alkaline protease.Then they are added into the modified FGD gypsum composite system.When their content is 3%,the dry flexural strength of sample block reach to 8.01 MPa and the apparent density is 1100kg/m3.This is due to the increase of the surface roughness of the sorghum straw corroded by NaOH and the alkaline protease removes the heavy protein components and makes the fiber skeleton appear the hydrophobic action of organosilicone water proofing agent.The moisture releasing ability of the modified and unmodified FGD building gypsum block are studied in the process of air dehumidification treatment of 40 h.The inner humidity of the unmodified FGD building gypsum block decrease from 59.48% to 43.95% and average moisture releasing rate is 0.38% per hour.While the inner humidity of the modified FGD building gypsum block decrease from 59.48% to 50.92% and average moisture releasing rate is 0.21% per hour.