Effect of Low Air Pressure on Performance and Pore Structure of Foamed Concrete in Pouring Period

doi:10.12141/j.issn.1000-565X.220621

Abstract

Abstract:

Due to its advantages of light weight, adjustable strength, self-supporting after curing, good heat insulation and durability, etc., foamed concrete has been successfully used in soft foundation replacement, underground cavity and cavity filling, heat insulation and some other projects, especially in highway embankment filling projects, such as road reconstruction and expansion, bridge backfilling, subway space overlay’s load reduction, etc. If the foamed concrete is affected by such adverse environmental factor as low air pressure in the period from pouring to curing, performance degradation and deterioration of the cured foamed concrete may occur. However, there is a lack of research on the macroscopic properties and pore structure of foamed concrete after being affected by low air pressure in the pouring period. In order to investigate the service performance of foamed concrete after being affected by low air pressure in the pouring period, a simulation box of low air pressure environment was designed, and the evolution of macroscopic performance and pore structure of the foamed concrete at low air pressure (50, 60 and 80 kPa) were comparatively explored. The results show that the dry density and compressive strength of the foamed concrete decrease continuously, while the water absorption increases continuously as the air pressure decreases in the pouring period. Concretely, the dry density of the foamed concrete at 50 kPa is 63.9% of that at atmospheric pressure (101 kPa), the compressive strength is 15.8% of that at atmospheric pressure, and the water absorption of the foamed concrete reaches the maximum of 38.7% at 60 kPa. As the air pressure decreases, the equivalent pore size and the fractal dimension of pore distribution of foamed concrete both increase continuously. The number of large pores (more than 500 μm in diameter) at 50 kPa increases by 24% as comparing with that at atmospheric pressure, the number of irregular large pores and connected pores increases, and the distribution of small pores becomes more and more uneven. Moreover, in the range of pore roundness from 1.0 to 1.1, the percentage of pore number of the foamed concrete decreases gradually with the decrease of air pressure.

Key words: foamed concrete, pouring period, low air pressure, macroscopic performance, pore structure

CLC Number:

TU528.2

LIU Xin, YAO Yunlong, YAO Zirui, et al. Effect of Low Air Pressure on Performance and Pore Structure of Foamed Concrete in Pouring Period[J]. Journal of South China University of Technology(Natural Science Edition), 2023, 51(7): 72-80.

Figures/Tables 13

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指标	取值		取值
80 μm细度/%	1.20	终凝时间/min	232
标准稠度用水量/%	25.48	3 d抗压强度/MPa	28.7
初凝时间/min	165	28 d抗压强度/MPa	45.4

成分	含量/%		含量/%
SiO₂	20.31	Al₂O₃	4.80
K₂O	0.39	Fe₂O₃	4.93
SO₃	2.12	MgO	1.35
CaO	65.55	Na₂O	0.12

气压/kPa	抗压强度/MPa	孔隙分布分维
50	0.35	1.763 76
60	0.50	1.752 75
80	0.76	1.723 72
101	2.21	1.624 62

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