Preparation And Characterization Of Lightweight Aggregate Concrete With Foaming In Situ

Lightweight concrete(LC) has the outstanding significance in the construction field involving of dead load decreasing, energy saving, and earth-quake protection of building. It is an effective measure to prepare LC by foaming method. In this paper,the LC specimens were prepared using sludge expanded ceramsite(SEC) and expanded perlite(EP) as lightweight aggregate(LA) and using H2O2 solution(with30% solubility) as chemical foaming agent to further lighten the specimens. The LC specimens were made by ordinary chemical foaming method(abbr. OCFM, namely the H2O2 being put into cement paste directly to product bubbles) and by in-situ foaming method(IFM) which can make the process of chemical foaming controllably.The properties of resulting LC specimens were characterized systematically. In the properties characterization of LC specimens made by OCFM, it was found that the apparent density(AD), mechanical properties(MP), and the thermal conducting coefficient(TCC) of resulting LC specimens were decreased with the increase of the foaming agent content. When 2% and 4% H2O2 solution of total amount binding material(TABM) were used, the AD of resulting specimens were 950 kg/m3 and 600kg/m3 respectively. Their TCC were 0.22 W·m-1·K-1 and 0.18 W·m-1·K-1 respectively,and which were decreased by 25% and 40% respectively as compared with the LC specimens without foaming. The resulting LC specimen made by OCFM had the compressive strength of 13 MPa as using 2% foaming agent content of TABM. The dry shrinkage of specimens made by OCFM were increased with the increase of the foaming agent content, and as the content of foaming agent being ￡2% of TABM, the dry shrinkage of resulting LC specimens were ￡460×10-6.As compared with OCFM, The IFM is put H2O2 into the carrier of EP firstly, and then H2O2 was carried into the cement paste between LA to further relax from its carrier for foaming indirectly. In this method, the process of foaming and bubble’s distribution could be controlled, and the fine LC structure could be obtained based on it. The LC specimens were firstly made by IFM using EP as LA and using gelatin as foam stabilizer. It was found that the properties of resulting LC specimens made by IFM, such as the AD, the MP and the TCC were decreased with the increase of thecontent of foaming agent and increased with the increase of the content of foam stabilizer respectively. The 28 d compressive strengths of resulting specimens were 21 MPa and 15 MPa when they had the foaming agent content of 1.4% and 2.8% of TABM respectively, and they both had the same the foam stabilizer content of 1.5%.The resulting specimen made by IFM had the AD of 800 kg/m3 as the foaming agent content of 2.8% of TABM and foam stabilizer content of 1.5% were used. The water absorption of the resulting LC specimens made by IFM was increased with the increase of the content of foaming agent, and it was decreased with the increase of the foam stabilizer content. At the foaming agent content of 2.8% of TABM, the water absorption of the resulting specimens made by IFM were decreased from 26% to 13%as the content of foam stabilizer increased from 1% to 1.5%.In addition, the LC specimens made by IFM were prepared using SEC as LA and HPMC as thickening agent at the foaming agent content of 2.8% of TABM. It was found that the thickening agent had the apparent influence on the properties of resulting LC specimens. As the content of thickening agent was increased from 0.05%to 0.125%, the properties of resulting LC specimens were increased with the increase of the content of thickening agent. The properties included the AD, the MP and TCC.On the other hand, the dry shrinkage and water absorption of the specimens were decreased with increase of the content of thickening agent in the above mentioned range. In the case of the resulting LC specimens with the content of thickening agent being 0.125%, its 28 d compressive strength, AD and water absorption were 31 MPa,1245 kg/m3, and 6.1% respectively. As compared with the LC specimens with thickening agent content of 0.05%, the water absorption and dry shrinkage were decreased by 21% and 42% respectively for the specimens with thickening agent content of 0.125%, and former(with thickening agent content of 0.05%) had the TCC of 0.27 W·m-1·K-1.