Mechanical and Deformation Properties of Calcium Carbonate Whisker Biphasic Reinforced Recycled Concrete

doi:10.16552/j.cnki.issn1001-1625.2026.0345

Abstract

Abstract:

In order to improve the mechanical and deformation properties of recycled concrete， two methods of using calcium carbonate whisker （CCW） to enhance recycled aggregate （RCA） and cement matrix were proposed in this paper. The effects of two strengthening methods on the compressive strength， stress-strain relationship， shrinkage resistance and creep properties of recycled concrete were systematically studied. The results show that the better treatment schemes of the two reinforcement methods are as follows： RCA enhancement method is soaked in CCW suspension with a concentration of 3% for 2 d， and the better volume content of CCW in cement matrix reinforcement method is 2%. Under the optimal treatment scheme， compared with the unreinforced specimens， the RCA reinforcement method and the cement matrix reinforcement method increase the peak stress of the specimens by 8.6% and 6.3%， respectively. The RCA reinforcement method can significantly improve the stiffness and strength of the recycled concrete， while the cement matrix reinforcement method is more conducive to improving the post-peak ductility. The 7 d shrinkage strain decreases by 35.7% and 13.5%， respectively， and the 90 d shrinkage strain decreases by 13.2 % and 8.1 %， respectively. At 90% and 95% stress levels， the creep failure time is extended by 22.5%， 9.9% and 78.6%， 35.7%， respectively. The creep deformation is reduced by 23.5 % and 19.8 % respectively at 85 % stress level for 80 d. Microscopic analysis shows that CCW can not only fill pores and bridge cracks， but also induce the nucleation of free Ca²⁺ and accelerate the formation of hydration products through surface adsorption， thereby strengthening the old mortar and interfacial transition zone attached to the RCA surface.

Key words: recycled concrete, calcium carbonate whisker, recycled aggregate reinforcement, cement matrix reinforcement, stress-strain, shrinkage resistance, creep performance

CLC Number:

TU528

KANG Tianbei, GAO Mingrui, DING Xiangqun, LI Yanfeng, WANG Fengchi. Mechanical and Deformation Properties of Calcium Carbonate Whisker Biphasic Reinforced Recycled Concrete[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(9): 3233-3244.

Figures/Tables 16

Table 1 Physical and mechanical properties of coarse aggregates

Type	Apparent density/（kg·m^-3）	Gradation/mm	Water content/%	Water absorption rate/%	Crushing index/%
NCA	2 750	5~25	0.26	0.97	8.8
RCA	2 660	5~25	3.93	7.64	17.7

Table 2 Physical performance of CCW

Density/（g·cm^-3）	Length/mm	Diameter/μm	L/D	Elasticity modulus/GPa	Tensile strength/MPa	pH value
2.86	0.01~0.02	0.5~1.0	10~40	410~710	3 000~6 000	9.0~9.5

Fig.1 Macroscopic morphology and SEM images of CCW

Table 3 Mix proportion of concrete

Sample No.	CCW content%	Mix proportion/（kg·m^-3）
Sample No.	CCW content%	Cement	Sand	RCA	NCA	Water
NC	0	500	660	0	990	250.00
RC50	0	500	660	495	495	264.85
RC100	0	500	660	990	0	279.70
RC50C1	1	500	660	495	495	264.85
RC50C2	2	500	660	495	495	264.85
RC50C3	3	500	660	495	495	264.85

Fig.2 Crushing index and water absorption rate of RCA

Fig.3 Range analysis of various influencing factors

Table 4 Variance analysis

Age/d	Factor	Quadratic sum	Degree of freedom	MSE	F	P
7	A	12.759	3	4.253	0.746	0.563
	B	13.760	3	4.587	0.805	0.535
	C	11.315	3	3.772	0.662	0.605
	Error	34.196	6	5.699
	Total	72.030	15
28	A	192.172	3	64.057	7.761	0.017
	B	7.497	3	2.499	0.303	0.823
	C	59.978	3	19.993	2.422	0.164
	Error	49.524	6	8.253
	Total	309.168	15

Fig.4 Influences of replacement rate of RCA and CCW reinforcement methods on compressive strength

Fig.5 Stress-strain curves of recycled concrete

Fig.6 Environmental condition and shrinkage resistance of recycled concrete

Fig.7 Creep damage under different influencing factors

Fig.8 Creep deformation at 85% stress level

Fig.9 Comparison of predicted values from various models

Fig.10 Comparison of corrected ACI-209R model calculated values with experimental values

Fig.11 CCW reinforcement mechanism for RCA

Fig.12 CCW reinforcement mechanism for cement matrix

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