Durability Analysis of Load-Bearing Recycled Concrete Blocks in Severe Cold Regions of Qinghai-Tibet

doi:10.12141/j.issn.1000-565X.250120

Abstract

Abstract:

To realize resource utilization of solid waste and improve the performance of recycled concrete blocks in severe cold regions of the Qinghai-Tibet Plateau, this study investigates the effects of recycled fine aggregates and active supplementary cementitious materials on the impermeability, water resistance and frost resistance of load-bearing concrete blocks, based on 100% replacement of coarse aggregates with recycled aggregates. The microstructure of recycled concrete was analyzed by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). A life cycle assessment (LCA) approach was employed to quantitatively evaluate material performance, costs and carbon emissions. The results show that the permeability and water absorption of load-bearing recycled concrete blocks increase with the increase of the proportion of recycled fine aggregates, while they decrease first and then increase with a reduction in the fly ash-to-slag blend ratio. Conversely, frost resistance and the softening coefficient exhibit the opposite trend. Under the condition of 100% recycled coarse aggregate replacement and a fly ash-to-slag blend ratio of 3∶1, the compressive strength of the blocks reached 11.77 MPa, flexural strength was 3.89 MPa, softening coefficient was 0.99, water absorption was 0.7%, mass loss after 50 freeze-thaw cycles was 2.2%, and the loss rates of compressive and flexural strength were 10.2% and 13.9%, respectively. These properties meet the load-bearing and durability requirements for severe cold regions, making this mix ratio the recommended formulation. Microscopic analysis shows that alkali activation promotes secondary hydration in the composite cementitious materials, generating additional hydration products that fill internal pores, thereby enhancing the densification of the recycled concrete. However, with the increasing freeze-thaw cycles, the number of internal pores gradually increases, with micropores and mesopores envolving into macropores and cracks, leading to performance degradation. Based on the performance-cost-carbon emission analysis, using 100% recycled coarse aggregates alone is unfavorable for carbon reduction. In contrast, the recommended mix proportion incorporating both recycled aggregates and active SCMs demonstrates the optimal comprehensive benefits, achieving a carbon reduction rate of 31.03%.

Key words: solid waste, load-bearing recycled concrete block, severe cold region, durability, microstructure

CLC Number:

TU522.3

QI Yunpeng, WANG Qiusheng, LI Zhiyi, XIONG Yijun. Durability Analysis of Load-Bearing Recycled Concrete Blocks in Severe Cold Regions of Qinghai-Tibet[J]. Journal of South China University of Technology(Natural Science Edition), 2026, 54(3): 160-171.

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骨料	表观密度/（kg·m^-3）	堆积密度/（kg·m^-3）	空隙率/%	含泥量/%	吸水率/%	压碎指标/%
天然碎石	2 630	1 564	41	0.3	0.47	10.4
再生粗骨料	2 594	1 410	46	0.5	5.19	20.6
天然河砂	2 600	1 801	31	0.5	2.30
再生细骨料	2 468	1 693	33	1.6	19.60

材料	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	SO₃	Na₂O	K₂O
水泥	20.45	4.99	4.10	59.76	2.13	2.93	0.17	0.71
粉煤灰	46.72	31.16	8.35	4.07	2.83	1.27	0.63	0.59
矿渣	30.19	15.01	2.14	36.35	8.78	1.68	0.49	0.45

试样	水玻璃	水	水泥	再生粗骨料	碎石	河砂	再生细骨料	活性掺合料		F/S复掺比
试样	水玻璃	水	水泥	再生粗骨料	碎石	河砂	再生细骨料	粉煤灰（F）	矿渣（S）	F/S复掺比
A1	50	100	500	1 172		578
A2	50	100	500	1 172		520	58
A3	50	100	500	1 172		405	173
A4	50	100	500	1 172		289	289
B1	50	100	300	1 172		578		200		4∶0
B2	50	100	300	1 172		578		150	50	3∶1
B3	50	100	300	1 172		578		100	100	2∶2
B4	50	100	300	1 172		578		50	150	1∶3
B5	50	100	300	1 172		578			200	0∶4
C	50	100	500		1 172	578

试样	块体密度/（kg·m^-3）	抗压强度/MPa	抗折强度/MPa	折压比	成本/（元·m^-3）
A1	1 162±0.88	10.42±0.89	3.46±0.83	0.33	359.74
A2	1 138±0.78	9.26±0.50	3.14±0.06	0.34	355.99
A3	1 122±0.94	8.27±0.99	2.88±0.22	0.35	348.55
A4	1 119±0.06	7.11±0.84	2.17±0.97	0.31	341.05
B1	1 182±0.94	10.73±0.58	3.73±0.39	0.35	329.23
B2	1 174±0.30	11.77±0.35	3.89±0.80	0.33	330.93
B3	1 161±0.15	9.67±0.16	3.33±0.79	0.34	332.63
B4	1 147±0.60	8.57±0.11	2.93±0.08	0.34	334.33
B5	1 126±0.49	7.41±0.94	2.57±0.93	0.35	336.03
C	1 211±0.58	10.49±0.95	3.81±0.66	0.36	429.43