Study On The Preparation And Properties Of Low-density Foamed Concrete

At present, the main building insulation materials in China are organic insulation materials.They are highly flammable, leading to lots of major fire accidents. Nowadays the fireproofperformance of building insulation materials becomes increasing stringent in China. In thiscase, the development of new inorganic building insulation materials to replace the organicbuilding insulation materials is quickly got the favor of people. Foamed concrete insulationmaterial is a new comparatively ideal inorganic building insulation material. It has manyadvantages, such as non-combustion, ageing resistance, high strength, good thermal insulationperformance, etc. However, the density of foamed concrete insulation material that has alreadylarge-scale applicated is generally greater than200kg/m3. Compared to the organic buildinginsulation materials, its density is too high and its thermal insulation performance is poor, thusit cannot effectively replace the organic building insulation. Against the above problems, thispaper is studied the foamed concrete insulation material with density about200kg/m3(referredto as low-density foamed concrete insulation material, the same below). Its optimum mixtureratio is determined and its weakness of easy cracking and poor toughness is overcome by theaddition of polypropylene (PP) fibers. The main contents and results are as follows.(1) The low-density foamed concrete insulation material is prepared by chemicalfoaming method with42.5R ordinary Portland cement, chemical foaming agent, coagulant,water-reducing agent, foam stabilizer and waterproof agent as raw materials. The type anddosage of coagulant, water-reducing agent and waterproof agent, the dosage of chemicalfoaming agent and foam stabilizer and the water-cement ratio are determined respectively bysingle factor experiment. The results show that the optimum mixture ratio are as follows:42.5R ordinary portland cement is100g, water-cement ratio0.44, chemical foaming agent7.0%(mass fraction with cement, the same below), compound coagulant (inorganic salt NC2.5%+triethanolamine0.05%), polycarboxylates water-reducing agent0.9%, foam stabilizer3.0%and sodium stearate2.0%. Under this condition, the sample’s density is188kg/m3; The3d flexural and compressive strength are0.12MPa and0.25MPa respectively; The28dflexural and compressive strength are0.28MPa and0.60MPa; The thermal conductivity is 0.054W/(m k) and the volumetric water absorption is5.2%.(2) With benzoyl peroxide (BPO) as initiator, the surface of PP fibers is modified withacrylic acid (AA) by two step-chemical grafting methods. The effects of initiation temperature,concentration of BPO, grafting temperature, grafting time and concentration of AA on thegrafting degree of PP fibers are studied with orthogonal analysis method. The results showthat the optimum reaction conditions are as follows: initiation temperature is90℃,concentration of BPO4.50×10-2mol/L, grafting time60min, grafting temperature75℃andconcentration of AA1.4mol/L. Under this condition, the grafting degree of PP fibers is13.12%. The interfacial bonding between cement matrix and PP fibers before and aftermodification is studied. The results show that after two step-chemical grafting modifications,the surface hydrophilicity of PP fibers is increased as the introduction of–COOH polar groupand the roughness of PP fibers is also increased, which make the chemical bonding force andmechanical engagement force between PP fibers and cement matrix improved, so that theinterfacial bonding between PP fibers and cement matrix is significantly enhanced.(3) The effects of modified PP fibers on plastic shrinkage cracking resistance,mechanical strength, flexural toughness and bubbles structure of low-density foamed concreteinsulation material are studied. The results show that modified PP fibers can improve bubblesstructure, plastic shrinkage cracking resistance, mechanical strength and flexural toughness ofsample. Its optimum dosage is0.7%(mass fraction with cement). Under this condition,compared with blank sample, the size of bubble holes in sample become smaller anduniformer and the spherical degree of bubble holes is increased and the degree of bubble holesinterconnection is decreased; The plastic shrinkage cracking value is decreased by82.1%, inthe meantime the plastic shrinkage cracks above two grade of crack level is disappeared andthe plastic shrinkage with one grade of crack level is as high as70.1%; The3d flexural andcompressive strength is increased by41.7%and16.0%respectively, and the28d flexural andcompressive strength is increased by25.0%and10.0%respectively; After the first cracksappeared, the sample can also maintain a certain extent carrying capacity and good ductilityfor a time, which indicate that the flexural toughness is increased significantly.