| According to statistics, the energy consumption of the existing buildings in China is high,which accounts for one third of total energy consumption and energy consumption of heating inChina is three times as much as developed countries. Adding external heat insulation layer isvery beneficial to building energy efficiency. Because of lightweight, incombustible, the sameduration as buildings, foamed cement has been recognized universally. At present, the productquality is difficult to control based on only practical experience. In order to generalize it, it isnecessary to propose theoretical basis. In this research, foamed cement was prepared usingsulphoaluminate cement as cementitious materials, hydrogen peroxide as foaming agent andadditives for complements, and the optimal ratio was obtained. The principle of foamed cementwas analyze and different materials and preparation process were studied. The researchconsequences may offer a theoretical and experimental reference to foamed cement. The mainconclusions could be drawn as follows:(1) Decomposition reaction of hydrogen peroxide was affected by temperature andbasicity alkalinity. In the alkaline environment of cement, decomposition reaction of hydrogenperoxide was high, hydrogen peroxide as foaming agent was entirely feasible in cement. Theprinciple of foamed cement was proposed and had four stages: forming heterogeneous cementpastes, nucleation, expanding, stability and shaping. Bubble stability related to viscosity of thecement paste. With cement ratio decreasing, hydration time prolonged and EVA dosageincreasing, the slurry viscosity increased.(2) Three themes of preparation process were particularly relevant for foamed cement.Stirring rate affected the dispersion of the foaming agent. If the stirring rate was too fast, thebubbles combined easily and a large hole formed. If the stirring rate was too fast, bubblesformed were heavy losses. The reasonable stirring rate was1000r/min. Stirring homogeneityand flowability were influenced by water-cement ratio. EVA affected slurry viscosity andplayed its key role in collapsing.(3) Foamed cement was made up of several kinds of materials, such as water-cement ratio,EVA, coagulant, foaming agent, etc. Foaming agent affected bubble amount and controlled drydensity. Its addition was4-5%. When it was too high, water-cement ratio would change the pore structure, which damaged to the mechanical properties, durability and insulation. The optimumvalue was0.46. EVA prolonged cement setting time. When its dosage was0-2%, flexuralstrength increased with the addition increasing. To ensure the stability of the foamed cement,coagulant agent accelerated the rate of the cement hydration and matched it with the foamingrate. And appropriate addition was0.04%.(4) Performance of foamed cement was excellent and pore structure was good by adjustingthe ratio at different temperature. Dry density was around250kg/m~3and28d compressivestrength reached to0.55MPa, thermal conductivity was0.077W/(m.k), the porosity was85%,pore size was2mm to3mm, water absorption was36%.(5) Sulphoaluminate cement mixed with ordinary Portland cement caused setting timeshortened, so it could reduce the amount of coagulant agent. But alkalinity increasing wasbeneficial to foaming reaction and pore became bigger. When slurry temperature was28℃,stirring rate6min, water-cement ratio0.46, mixing ordinary Portland cement was20%,performance was best. In this ratio, dry density was around248kg/m~3and28d compressivestrength reached to0.45MPa, thermal conductivity was0.078W/(m.k), the porosity was86%and water absorption was38%.(6) Mixed with polypropylene fibers, mechanical property was obviously increased andpore structure was more homogeneous. When dosage of polypropylene fibers was0.04%, drydensity was253kg/m~3and28d compressive strength reached to0.65MPa,28d flexural strengthwas0.23MPa and flexibility factor was2.82. |
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