Study on effect of pore structure on the permeability of concrete after a century natural carbonation

Figures & data

Figure 1. Zhejiang library in Hangzhou, China.

Figure 2. Illustration of sampling preparation (a) coring process (b) sampling locations.

Table 1. Physical characteristics of concrete samples.

Parameter	Value
Concrete density (kg/m^3)	2160
Finesse modulus of fine aggregate	2.3–3.0
Coarse aggregate density (kg/m^3)	2220
Particle size of coarse aggregate (mm)	14–30

Figure 3. Cross section of sampling (a) macro morphology of concrete sample surface and (b) micro morphology of mortar.

Figure 4. Specimens used for carbonation depth analysis.

Figure 5. Experimental apparatus of oxygen diffusion measurement (Zhou, Jin, and Fu 2018). Legend: 1 = Concrete specimen; 2 = Epoxy resin; 3 = Rubber sealing gasket; 4 = Chamber tube wall; 5 = Intake valve; 6 = Move the piston; 7 = Piston seals; 8 = Stud bolts; 9 = Oxygen sensor; 10 = Oxygen concentration tester; 11 = Data logger; 12 = Gas catheter; 13 = Gas cylinders.

Figure 6. XRD patterns of five specimens (a) S1-S3 (b) S4-S5.

Table 2. Cement mortar compositions determined by XRD.

	S1	S2	S3	S4	S5
SiO2	66.5	65.4	61.4	59.2	66
CaCO3	33.5	34.6	38.6	40.8	34

Table 3. Oxygen concentration gradient versus time fitting functions.

S1-1	Linear	$\mathrm{y}=-1.09175\mathrm{x}+9657.52384$	R^2 = 0.99500
	Exponential	$\mathrm{y}=9348.14055{\mathrm{e}}^{-\frac{\mathrm{x}}{6555.25881}}+499.26507$	R^2 = 0.99998
	Logistic	y =$\frac{16480.35331}{1+{\left(\frac{\mathrm{x}}{11373.83993}\right)}^{1.00075}}$-6628.05999	R^2 = 0.99999
S1-2	Linear	$\mathrm{y}=-0.45777\mathrm{x}+7440.39533$	R^2 = 0.99797
	Exponential	$\mathrm{y}=5676.68774{\mathrm{e}}^{-\frac{\mathrm{x}}{10472.90629}}+1812.57357$	R^2 = 0.99992
	Logistic	y =$\frac{14149.63346}{1+{\left(\frac{\mathrm{x}}{29155.32664}\right)}^{0.96347}}$-6650.8377	R^2 = 0.99994

Table 4. Oxygen diffusion coefficients.

Specimen	Oxygen diffusion (x 10^−8 m^2/s)
S1-1	3.71
S1-2	4.11
S2-1	7.99
S2-2	13.28
S3-1	4.00
S3-2	8.35
S4-1	3.86
S4-2	8.35
S5-1	6.19
S5-2	4.36

Table 5. Porosity values and pore size distributions of samples.

Specimen	Porosity [%]	Aperture distribution ratio [%]
		0–20 nm	20–50 nm	Harmless and less harmless
S1-1	16.70	5.03	9.61	14.64
S1-2	18.58	5.54	12.58	18.12
S2-1	18.62	0	3.39	3.39
S2-2	19.30	3.72	8.07	11.79
S3-1	24.25	7.65	13.31	20.96
S3-2	22.26	2.13	7.13	9.26
S4-1	19.85	10.26	5.45	15.71
S4-2	21.08	4.63	4.89	9.52
S5-1	19.57	1.14	6.73	7.87
S5-2	17.98	8.18	18.80	26.98

Figure 7. Plots used to determine the fractal dimensions of pore structures for two representative specimens (a) S1-1 (b) S1-2.

Table 6. Fractal dimensions of the pore structures.

Specimen	${\mathrm{D}}_{\mathrm{s}}$	${\mathrm{R}}^2$
S1-1	2.6941	0.9986
S1-2	2.7136	0.9978
S2-1	2.5851	0.9968
S2-2	2.6600	0.9981
S3-1	2.6837	0.9990
S3-2	2.6565	0.9971
S4-1	2.7165	0.9991
S4-2	2.6438	0.9969
S5-1	2.6632	0.9968
S5-2	2.7970	0.9989

Figure 8. Relationship between fractal dimension and oxygen diffusion coefficient.

Figure 9. Relationship between the fractal dimension for the pore structure and the combined proportion of harmless and less harmless pores.

Zhou, L. Q., N. G. Jin, and C. Q. Fu. 2018. “Determination Method and Testing Device of Oxygen Diffusion Coefficient of cement-based Material.” Experimental Technology and Management 35 (7): 117–120.

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