Use Calcium Carbide Slag To Produce Light And High-strength Study Of Autoclaved Aerated Concrete Blocks

As industrial waste,fly ash and calcium carbide slag have the potential of gel materials,and the use of these solid wastes to produce green building materials has the characteristics of energy saving,waste recycling,environmental protection and low carbon.Because calcium carbide slag is a by-product produced by calcium carbide in the production of acetylene,it contains a large amount of calcium hydroxide and is a solid waste.To this end,calcium carbide slag is used as a calcium material,all replace quicklime,and autoclaved aerated concrete blocks are produced to reduce production costs and realize waste recycling.When calcium carbide slag replaces quicklime to produce aerated concrete blocks,there are the following shortcomings:First,calcium carbide slag has no hydrated heat release,which will lead to too low slurry temperature and affect the slurry gas process.Second,due to the long-term stacking and extrusion of calcium carbide slag,the calcium carbide slag particles are coarse,which is difficult to disperse uniformly,which affects the slurry flow of aerated concrete,thereby affecting the slurry aeration process.Therefore,when using calcium carbide slag to produce aerated blocks,this thesis considers increasing the temperature of the mixing water to fill the heat released during quicklime hydrolysis and make the slurry gassing normally.After experiments,it can be seen that when the temperature of the mixing water is 60°C,the slurry is normally gassed,and at this time,the slurry temperature reaches about 32°C;Considering that the original calcium carbide slag particles are coarse and difficult to distribute evenly,the calcium carbide slag is ball-milled by ball-milling.Through experiments,it can be seen that when the ball grinding time is 55 min,the mechanical properties of the aerated block prepared by calcium carbide slag are better.According to the following formula:unused fly ash 67%,cement 10%,calcium carbide slag(55min)20%,desulfurization gypsum 3%,the aluminum powder content was 0.08%,the mixing water temperature was 6 0°C,the water-to-material ratio was adjusted between 0.48-0.50,and the dry density of the prepared calcium carbide slag aeration block was 690 kg/m~3,compressive strength 4.1 MPa.Compared with the aeration block prepared by quicklime,the compressive strength meets the B06 grade qualification requirements in GB/T11969-2020.However,the dry density of the aerated block prepared by calcium carbide slag is high,which does not meet the density requirements of B06.Due to the high dry density,large pore size and uneven distribution of calcium carbide slag aerated block,the effects of the doped surfactants sodium hexametaphosphate,sodium stearate,sodium hydroxymethylcellulose,sodium dodecyl benzene sulfonate and sodium lauryl sulfate on the performance of calcium carbide slag gas block were studied.Through experiments,it was concluded that the dry density of the block was 640 kg/m 3,the strength was 3.8 MPa,and the distribution of block pores was relatively uniform.In order to stimulate the activity of fly ash volcanic ash and improve the effect of slurry aeration,the excitants sodium hydroxide and sodium silicate were mixed to study the effect of the provocator on the performance of calcium carbide slag gas block.Through experiments,it can be seen that with the addition of0.3%sodium hydroxide,the dry density of calcium carbide slag aerated block is 645 kg/m~3,and the compressive strength is 4.5 MPa.In order to improve the early strength of calcium carbide slag aerated block and thus affect the final strength of the aerated block,the influence of early strength agent on the performance of calcium formate,calcium chloride and triethanolamine was studied by adding early strength agents to the performance of calcium carbide slag gas block.Through experiments,it can be seen that calcium formate was selected as an early strength agent,0.8%calcium formate was added,the dry density of the block was654 kg/m~3,and the compressive strength was 4.1 MPa.Through orthogonal experiments,the optimal formula for preparing grade B06 calcium carbide slag aerated block was determined as follows:fly ash 67%,cement10%,calcium carbide slag 30%.,desulfurization gypsum 3%,0.1%high-efficiency polycarboxylic acid water reducing agent,water ratio 0.46(doped with sodium dodecyl benzene sulfonate 0.06%,sodium hydroxide0.4%,calcium formate 0.8%),calcium carbide slag aerated block dry density 654 kg/m~3,Compressive strength 5.4 MPa.Then calcium carbide slag is further used to replace cement to prepare B06 grade autoclaved gas block,add external admixture 0.5%triethanolamine,and the adjusted formula is according to fly ash 63%,calcium carbide slag 30%,desulfurization gypsum 7%and 0.1%polycarboxylic acid water reducing agent,water-to-material ratio 0.46,prepared the dry density of the aerated block 697 kg/m~3,compressive strength of 5.7 MPa.By observing the micromorphology of XRD and SEM in the hydration reaction between calcium hydroxide and silica and free water in the calcium hydration block prepared by the optimal formula,the test results show that most of the hydration products of the optimal formula autoclaved gas block are water garnet and tobemorite.Optimally formulated blocks,tobemolite is in the form of willow leaves and cards.