Study On The Preparation And Properties Of High Strength And Low Water Absorption Foamed Concrete

As a new energy-saving building material, foamed concrete possesses many excellent properties such as light weight, thermal insulation, fireproof performance and other characteristics. However, the application of foamed concrete is restricted due to the low compressive strength and poor water resistance. It is important to take measures to enhance the compressive strength and the waterproof performance of foamed concrete. In this paper, the effects of different reinforcing methods on the compressive strength of foamed concrete were studied by means of fiber addition, CMC addition and chemical additives. The effects of different types of water repellent and water reducing agent were also investigated.The results of fiber reinforced experiments showed that the optimum contents of polypropylene fiber, glass fiber and carbon fiber were 0.4%, 0.4% and 0.2% respectively in the same length. The polypropylene fiber addition samples gave the best properties at the optimum dosage. The foamed concrete with short fiber had the better performance. Compared with the blank sample, the 28d compressive strength of foamed concrete was increased by 94% under the addition of 0.4% polypropylene fiber with a length of 6mm. The experimental results of CMC experiments showed that the compressive strength of foamed concrete improved in some extent with CMC solution at different temperature. The 25 ? CMC solution addition sample gave the optimum compressive strength of 1.06 MPa, while that of the sample with 50 ? CMC solution addition sample reached 1.26 MPa. Meanwhile,the optimum dosage of CMC was 0.085 ‰ and 0.069 ‰, respectively.The compressive strength was 71% and 103% higher .than that of the blank sample, respectively. In the foamed concrete, CMC could not only promote the cement hydration and volcanic ash effect of fly ash, but change the microstructure of foamed concrete which increase the compactness of pore wall structure. The results of the chemical admixture enhancement experiments showed that the effect of sodium bisulfate on the compressive strength of foamed concrete was the greatest, the effect of thiourea was second, while sodium sulfide had little effect on the compressive strength. When the content of sodium bisulfate was 0.1%, the 28d compressive strength of the sample reached 1.13MPa, which was 30% higher than that of the blank sample. Sodium bisulfate was beneficial to the hydration of cement and the reduction of Ca(OH)2 content. The hydration products crossed each other to form a network structure, so that the skeleton of the foamed concrete was dense.Test results showed that the addition of waterproofing agent did not reduce the water absorption of foamed concrete obviously. Compared to the blank sample, the water absorption of the sample with waterproofing agent decreased from 38% to 34%. However, waterproofing agent reduced the compressive strength of foamed concrete. Thus, it is not suitable for the chemical foamed concrete. Water reducing agent could effectively reduce the water absorption of foamed concrete. The water absorption of foamed concrete reduced from 38.4% to 22% when the content of naphthalene water reducer increased from 0.1% to 0.9%. At the optimal content of 0.9%, compared with the blank sample, the water absorption was reduced by 43%, and the compressive strength did not change significantly. However, when the content of polycarboxylate superplasticizer changed in the same range, the water absorption ranged from 38.4% to 35%. The effect of polycarboxylate superplasticizer was not as good as naphthalene water reducer.According to the study mentioned above, the mixing proportion of foamed concrete with high strength and low water absorption was: the main materials were 70% cement + 30% fly ash, the water cement ratio was 0.4, other additives such as hydrogen peroxide, 6mm polypropylene fiber, calcium stearate, lithium carbonate, sodium bisulfate, CMC, and naphthalene water reducer, their proportions were 5%, 0.4%, 0.8%0.08%, 0.1 %,0.069 ‰, 0.9%, respectively, and the temperature of CMC solution was 50 ? . The dry density, compressive strength, water absorption and thermal conductivity of the foamed concrete prepared by this mixing proportion were 286 kg/m3, 1.26 MPa, 22%, and 0.045 W/(m·K). Compared with JC/T 266, the advantages of the foamed concrete were high strength and low water absorption.In order to expand the source of raw materials and reduced the production cost of foamed concrete. On the basis of this mixing proportion, slag was used for instead of part of the cement, and tailings were used for part replacement of fly ash. The effect of slag and tailings on the foamed concrete were studied. Test results showed that the slag had a negative effect on the compressive strength of foamed concrete.However, the part replacement of fly ash with ground siliceous tailings increased the compressive strength of foamed concrete in a certain extent.With the increase of tailings fineness, the compressive strength enhanced gradually. The compressive strength of the foamed concrete consisting of 50% cement, 20% fly ash, 20% slag and 10% tailings (specific surface area, 1161.7 m2/kg) reached 1.19MPa. The dry density, water absorption and thermal conductivity were 272kg/m3, 27%, and 0.049W/ (m·K),respectively, which are superior than those required in JC/T 266.