花岗岩废料再生混凝土路面砖抗冻融性能研究

Freeze-Thaw Resistance of Granite Waste Recycled Concrete Pavement Brick

采用慢冻法对花岗岩废料再生混凝土路面砖进行50次冻融循环试验,以质量损失与抗压强度作为依据研究影响再生混凝土路面砖抗冻融性变化规律。基于体积膨胀及渗透压理论并结合扫描电镜分析,对比冻融前后再生混凝土路面砖显微结构与水化产物组成,从细微裂缝积累与膨胀性应力作用角度揭示其冻融损伤机理,建立浆体孔隙结构变化模型和浆体浓度差所产生的渗透压模型。研究结果表明,微、细、粗集料分别以20%、30%、50%(质量分数)为最佳取代率的再生混凝土路面砖的质量损失率为1.5%,抗压强度损失率为10.0%,较基准组有所降低,但较大程度上提高了花岗石废料的利用率,且满足试验标准和路用性能的基本要求。微观分析结果表明,浆体水化产物中较高的钙矾石含量使混凝土微裂缝富集,最终形成宏观裂缝导致冻胀破坏,所建立的模型揭示了外界水的侵入引起体积膨胀、毛细孔与凝胶孔中浆体浓度差所产生渗透压引起的膨胀性应力是致使冻融损伤发生的真正原因。

50 freeze-thaw cycles of recycled concrete pavement brick with granite waste were carried out by the slow freezing method.Based on the mass loss and compressive strength,the change rule of freeze-thaw resistance of recycled concrete pavement brick was studied.Based on the theory of volume expansion and osmotic pressure and combined with scanning electron microscope analysis,the microstructure,and hydration product composition of recycled concrete pavement brick before and after freeze-thaw were compared.The freeze-thaw damage mechanism was revealed from the perspective of microcrack accumulation and expansive stress.The slurry pore structure change model and the osmotic pressure model caused by slurry concentration difference were established.The results show that the mass loss rate and compressive strength loss rate of recycled concrete pavement brick with the optimal replacement rate of micro,fine and coarse aggregates of 20%,30% and 50%(mass fraction)are 1.5% and 10.0% respectively,which is lower than reference group.But the utilization rate of granite waste is improved to a great extent and meets the basic requirements of experimental standards and road performance.The microscopic analysis results show that higher content of ettringite in the hydration products of slurry makes the microcracks of concrete enriched,and finally leads to the formation of macrocracks causing frost heave failure.The model reveals that the invasion of external water,resulting in volume expansion,and the expansive stress caused by osmotic pressure in the pores and gel pores are the real reasons for freeze-thaw damage.