Influence of Formwork Surface Roughness on Appearance Quality of Concrete Products

doi:10.16552/j.cnki.issn1001-1625.2025.0766

Abstract

Abstract:

To systematically explore the influence mechanism of formwork surface roughness on the apparent quality of concrete， this study employed image analysis technology to investigate the influence of different formwork surface roughness on the concrete surface porosity， pore distribution， mirror reflection characteristic （gray value）， and color difference （gray level standard deviation value）. XRD and SEM analyses were employed to analyze the formation mechanism of the color difference. The results indicate that as formwork surface roughness increases， the concrete surface porosity shows an upward trend， and the proportion of large pores increases， while the proportion of small pores decreases accordingly. The gray value of the concrete surface decreased with the increase of the formwork surface roughness. Lower formwork surface roughness helps the surface structure of the specimens more compact and enhances the mirror reflection ability， thereby increases the gray value. However， surface color difference （gray level standard deviation value） of the concrete first increases and then decreases with the increase of the formwork surface roughness，and is most pronounced in concrete formed under the lowest formwork surface roughness.Microscopic test results show that when formwork surface roughness is low， the surface of formwork is smooth， the content of Ca（OH）₂ and the microstructure density in adjacent parts of the concrete surface are slightly increased， resulting in the formation of dark areas on the formed surface and causing color differences.

Key words: formwork surface roughness, porosity, pore distribution, mirror reflection characteristic, color difference, gray value

CLC Number:

TU528

LI Shunkai, DOU Huakang, SUN Fengpin, CHEN Ronghui, LI Jie. Influence of Formwork Surface Roughness on Appearance Quality of Concrete Products[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(1): 123-132.

Figures/Tables 13

Table 1 Chemical composition of cement

Chemical composition	CaO	SiO₂	Al₂O₃	Fe₂O₃	MgO	P₂O₅	K₂O	TiO₂	MnO	Other
Mass fraction/%	60.31	17.83	5.40	7.22	2.00	0.10	6.22	0.85	0.05	0.02

Table 2 Main parameters of aggregates

Material

Apparent density/ （kg·m^-3）

Loose bulk

density/（kg·m^-3）

Void ratio/%

Stone powder

（mass fraction）/ %

Crushing

index/%

MB value

Fineness

modulus

Table 3 Mix proportion of concrete

Strength grade	Mix proportion/（kg·m^-3）
Strength grade	Cement	Sand	Stone	Water	Water-reducing agent
C40	426	857	1 006	162	2.31

Fig.1 Distribution map of formwork surface survey area

Fig.2 Concrete surfaces with different formwork surface roughness

Table 4 Evaluation grade of gray level standard deviation value［18］

Evaluation grade	Excellent	Good	Poor
Evaluation index	S＜6	6≤S≤10	S＞10

Fig.3 Effect of formwork surface Ra value on porosity and pore dstribution of specimen surface

Fig.4 Mirror reflection characteristics of concrete surfaces formed by different formwork surface roughness

Table 5 Gray value statistical values of the specimen

Formwork surface roughness/ $μ$ m	Grayscale data	Average gray value
0.05	139.205 242 1	137.943 070 2
	136.017 833 7
	135.043 321 0
	141.505 884 0
0.91	124.424 191 3	125.806 956 5
	124.622 610 0
	126.607 392 0
	127.573 632 5
1.74	120.790 458 0	119.107 446 8
	114.312 963 9
	116.096 740 2
	125.229 625 4
2.60	116.547 569 5	117.007 462 9
	117.155 535 9
	118.517 495 1
	115.809 251 3
3.38	106.564 125 2	106.898 259 6
	107.308 069 0
	110.548 796 0
	103.172 048 0

Table 5 Gray value statistical values of the specimen

Formwork surface roughness/ $μ$ m	Grayscale data	Average gray value
0.05	139.205 242 1	137.943 070 2
	136.017 833 7
	135.043 321 0
	141.505 884 0
0.91	124.424 191 3	125.806 956 5
	124.622 610 0
	126.607 392 0
	127.573 632 5
1.74	120.790 458 0	119.107 446 8
	114.312 963 9
	116.096 740 2
	125.229 625 4
2.60	116.547 569 5	117.007 462 9
	117.155 535 9
	118.517 495 1
	115.809 251 3
3.38	106.564 125 2	106.898 259 6
	107.308 069 0
	110.548 796 0
	103.172 048 0

Fig.5 Linear fitting between formwork surface Ra value and gray value of specimen surface

Fig.6 Influence of formwork surface Ra value on gray level standard deviation value of specimen surface

Fig.7 XRD patterns of concrete

Fig.8 SEM images of A0 and A1 specimens

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