Aiming at the problems such as weak electromagnetic protection ability of ordinary concrete, insufficient mechanical properties and poor durability of traditional cement-based wave absorbing materials, a new concrete design method was proposed by combining electromagnetic wave absorbing ceramsite and functional fiber components. Carbon fiber (CF), basalt fiber (BF) and polypropylene fiber (PF) were used to toughen and optimize the electromagnetic parameters of the concrete. The electromagnetic wave absorption and the mechanical properties such as compressive strength, splitting tensile strength, flexural strength and frost resistance of electromagnetic wave absorbing aggregate concrete under different fiber types and volume contents were studied through experiments. Experimental results showed that the wave absorption of electromagnetic wave absorbing aggregate concrete was improved by adding these three fibers, especially in the higher frequency Ku band (12?18 GHz), where the bandwidth broadened greatly when the reflectivity is less than ?7 dB, and the peak reflectivity decreased significantly. The compressive and splitting tensile strength of the electromagnetic wave absorbing aggregate concrete was increased distinctly by BF and PF, BF improved the early mechanical strength greatly, and PF optimized the mechanical strength at every age. All three fibers increased the flexural strength of electromagnetic wave absorbing aggregate concrete by more than 50% with the base group, and the frost resistance of the concrete was optimized by the fibers also. After 150 freeze-thaw cycles, the specimens were reduced by more than 50% compared with the base group, and the relative dynamic elastic moduli were increased by 8%?24%.
Fig.1Preparation of electromagnetic wave absorbing ceramsite
纤维
ρ/(g·cm?3)
L/mm
D/μm
σt/MPa
E/GPa
ε/%
CF
1.75
9
7
4900.0
230.0
2.1
BF
2.65
9
17
4100.0
100.0
2.6
PF
0.91
9
18
556.9
4.1
19.0
Tab.1Physical properties of different fibers
Fig.2Test specimens for different experiments
粗集料
水泥基中复掺吸波剂
R/dB
BW7/GHz
碎石[7]
无
?6.2~?4.0
0
10%铁氧体陶粒[3]
无
?9.1~?8.1
10
30%TiO2陶粒[4]
无
?8.0~?4.0
3.9
30%TiO2陶粒[4]
wB(TiO2)=3%
?9.0~?5.8
4.8
15%铁氧体陶粒[7]
无
?10.0~?4.8
6.5
15%铁氧体陶粒[7]
φB(CF)=0.2%
?13.6~?4.6
6.5
Tab.2Wave absorbing properties of common electromagnetic wave absorbing aggregate concrete
Fig.3Reflectivity curves of different electromagnetic wave absorbing aggregate concrete specimens
组别
Rm/dB
BW7/GHz
BW10/GHz
无纤维
?10.00
6.5
0.50
NBV0.4
?14.14
9.8
1.70
NPV0.6
?20.10
7.8
1.45
NCV0.2
?13.64
6.0
3.10
Tab.3Comparison of wave absorbing properties of different electromagnetic wave absorbing aggregate concrete specimens
Fig.4Relative compressive strength of different electromagnetic wave absorbing aggregate concrete specimens
Fig.5Splitting tensile strength of different electromagnetic wave absorbing aggregate concrete specimens
组别
ff/MPa
$\overline f_{\mathrm{f}} $/MPa
试件1
试件2
试件3
无纤维
4.60
4.78
4.80
4.73
NCV0.4Tb
6.80
7.00
7.70
7.17
NCV0.8Tb
7.34
7.50
8.15
7.66
NBV0.4Tb
7.72
7.93
8.20
7.95
NBV0.8Tb
8.42
8.55
9.08
8.68
NPV0.4Tb
6.80
8.08
8.38
8.13
NPV0.8Tb
7.34
8.68
9.30
8.83
Tab.4Flexural strength of different electromagnetic wave absorbing aggregate concrete specimens
Fig.6Typical failure form of test specimen
Fig.7Microstructure of electromagnetic wave absorbing aggregate concrete with fiber component
Fig.8Variation of freezing index of electromagnetic wave absorbing aggregate concrete with freeze-thaw cycles
Fig.9Appearance morphology of electromagnetic wave absorbing aggregate concrete after 150 freeze-thaw cycles
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