Regulation And Evaluation Of Foamed Concrete’s Hole Structure

With the world’s energy-resource situation increasingly serious, saving energy, reducing emission and developing low-carbon economy has become a basic national policy of China, which is also the new strategic direction of China’economy. Foam concrete, due to its excellent properties, such as thermal insulation, high strength, non-combustible, plays an important role in building energy efficiency. The porosity of foam concrete is generally above50%, which makes the pore structure have a decisive impact on the thermal conductivity, sound absorption, mechanical properties, durability, etc.This study comes from the "12th Five-Year" national support program:The Application Technology of Multifunctional Composite Wall Panels (2011BAJ04B02). The method of measuring the pore structrue of foam concrete based on image analysis was studied in this paper. The content of vesicant (SDS), thickener (MC), early strength accelerator (CaCl2) on the strength, pore structure, and water absortion of foam concrete was also studied. The main results obtained are listed as follows:1. The method to measure pore structure of foam concrete based on image analysis.(1) Used the reflection optical microscope as image acquisition system: Polishing, polishing+epoxy impregnated, these two sample handling methods cann’t help to obtain better pictures with strong contrast ratio, and in the pictures obtained it’s difficult to divide between the pores and the matrix, so pore structure test can not be carried out by these two methods. In the pictures taken by the sample after polishing+CaCO3powder filled approach, there was a good gray-scale differences between the pores and the matrix, and it’s very easy to conduct image segmentation and tests of pore structure.(2) Uesd SEM’s secondary electron imaging system as the image acquisition system:Without any treatment and shooting directly into the fresh section, the pore structure in the pictures was clearer, but due to the presence of some shallow pores, it was difficult to determine the appropriate segmentation valve value; sobel edge detection can better identify pore, but it shrinked the boundary of pores, and the measurement result was lower. There were a lot of power residues on the surface of specimen after polishing, it was difficult to clean them, seriously affecting the image quality, and dual-threshold segmentation method and sobel edge detection method can not extract the stomatal boundary on the pictures.(3) When the magnification was greater, the resolution of the picture was higher, and the test results was more accurate, but the large pores can not be detected which beyond the picture boundaries, at the same time in order to ensure the statistical significance of the measurement results, more pictures must be tested, if the magnification was too big. Taking the testing object of this paper (pore size range between10-1000μm) into account,100times was decided as the magnification to measure the pore structure of foam concrete.(4) In this paper, IPP was used as image analysis software, and in order to reduce the workload, the batch script CHM was programed to automatically analyze the images and collect measure data.2. The content of SDS, MC and CaCl2on the strength, the pore structure parameters, and water absorption of the foam concrete.(1) With the SDS content increasing, the strength of foam concrete decreased, but the porosity, the content of large pores and the degree of deformation of pore increased. In addition, the bulk density and oven dry bulk density decreased, while the total porosity increased. At the same time, the connectivity of pore improved, so the ratio of water absorption increased.(2) MC can significantly improve the pore structure. With the MC content increasing, the strength of the foam concrete increased first, but then decreased when the content of MC higher than0.15%, yet still greater than the non-doped MC sample. In addition, the bulk density and total porosity increased, while the oven dry bulk density decreased. After adding MC, the porosity slightly increased, the pore shape was more close to sphere, the content of large pores reduced, while small pores increased. The ratio of water absorption decreased, which showed the degree of connectivity of pore decreased.(3) With the CaCl2content increasing, the porosity, stomatal deformation decreased. In addition, the bulk density and oven dry bulk density increased, while the total porosity decreased. The strength of foam concrete of each age significantly increased, while the ratio of water absorption decreased, which showed the degree of connectivity of pore decreased.