LIU Qing¹， XU Fei^1，2， RAN Fengling¹， TANG Xiaolin¹， CHEN Zhenfu⁵， YANG Rui⁴， WANG Dongxing^1，3

1. School of Civil Engineering， University of South China， Hengyang 421001， China； 

2. Henan Zhonggong Design and Research Institute Group Co. ， Ltd. ， Zhengzhou 450009， China；

3. School of Civil Engineering，Wuhan University，Wuhan 430072， China； 

4. College of Civil and Construction Engineering， Hunan Institute of Technology， Hengyang 421001， China；

5. Hunan YiHui Construction Co. Ltd. ， Hengyang 421001， China

Abstract

Objective China is a major global producer and consumer of lead and zinc， but the mining of these resources generates large quantities of lead-zinc tailings. Due to the differences in mining technologies and mineral processing techniques， the comprehensive utilization rate of these tailings remains low， resulting in significant accumulation. This not only poses serious environmental risks， such as heavy metal pollution， but also threatens public safety as dams of tailings reservoirs may breach due to earthquakes or floods. Although tailings have certain applications in building materials， such as cement clinker， unburned bricks， and wall panels， their overall resource utilization rate remains low. Geopolymer concrete， a green alternative to traditional cement， uses activated aluminosilicate precursors to replace conventional cementitious materials. This concrete has excellent mechanical properties and durability， with lower energy consumption and CO₂ emissions compared to ordinary concrete. Using lead-zinc tailings powder， rich in silicon and aluminum， as a precursor for geopolymer concrete can help reduce the environmental impact of tailings accumulation， while reducing the amount of cement used， saving costs， and reducing CO₂ emissions.

Methods In this study， the modulus of sodium water glass composite alkali activator was set to 1. 20. To avoid the influence of aggregates on experimental results， the mass ratio of aggregate to cementitious material was fixed to 2. 8， the sand ratio at 0. 30， and the concrete density at 2 500 kg/m³， according to the ordinary concrete mix design specifications. Experimental variables included： water-binder ratio（ k₁）（ 0. 30， 0. 33， 0. 35， 0. 38， 0. 41， 0. 47， and 0. 5）， lead-zinc tailings powder content（k₂） （30%， 40%， and 50%）， and alkali equivalent （k₃） （Na₂O content in sodium silicate relative to total cementitious material weight being 10. 5%， 11. 5%， and 12. 5%）. By adjusting these variables， the workability， cube failure morphologies， and mechanical properties of the concrete were tested， and a nonlinear fitting analysis of compressive and splitting tensile strengths was carried out based on the test results.

Results and Discussion 　k₁ had a significant effect on the slump and expansion of geopolymer concrete. With the increase in k₁， both slump and expansion increased， but its effects on cohesiveness and water retention were more complex. When k₁ was less than 0. 35， the mixture became too viscous， requiring extensive vibration. When k₁ was between 0. 35 and 0. 44， the mixture showed optimal cohesiveness and water retention， with no bleeding observed. However， when k₁ was greater than 0. 44， segregation and bleeding occurred， adversely affecting mold formation. The choice of water-binder ratio was critical for concrete workability. Too low or too high ratios impaired the performance of geopolymer concrete. With the increase in cubic compressive strength， the failure mode changed from interfacial zone failure to a interfacial zone-aggregate joint failure. The compressive strength and splitting tensile strength increased first and then decreased significantly with the increase in k₁. A power function was used to fit the relationship between splitting tensile strength and compressive strength， which was in good agreement with the experimental results. The tensile-compressive ratio for lead-zinc tailings geopolymer concrete was ranged from 1/12 to 1/15， comparable to that of ordinary concrete and high-performance concrete.

Conclusion　Considering workability， compressive strength， and splitting tensile strength， the optimal mix for lead-zinc tailings geopolymer concrete is： water-binder ratio of 0. 35， lead-zinc tailings powder content of 40%， alkali equivalent of 11. 5%. Under these conditions， the compressive strength and splitting tensile strength are 55. 87 MPa and 4. 01 MPa， respectively. In general， geopolymer concrete prepared by lead-zinc tailings powder exhibits excellent workability and mechanical properties.

Keywords：lead-zinc tailings powder； geopolymer concrete； workability； failure morphology； mechanical property