碱激发下粉煤灰-市政污泥固废基混凝土抗冻融性能

Freeze-thaw Resistance of Concrete Based on Fly Ash and Municipal Sludge Under Alkali Excitation

为改善市政污泥对混凝土抗冻融性能的劣化效果,在氢氧化钠及水玻璃的复合激发下,用经生石灰改性后的市政污泥取代10%细骨料,粉煤灰分别取代10%、20%与30%水泥,制备了混凝土;分析不同冻融循环次数下,混凝土的表观现象、相对质量、相对动弹性模量、相对抗压强度及微观结构随粉煤灰掺量与碱当量的变化规律;分别以相对动弹性模量与相对抗压强度为损伤变量建立不同的冻融损伤模型。研究结果表明:随冻融循环次数增加,混凝土表观损伤愈发严重,内部孔隙增多,相对动弹性模量及相对抗压强度逐渐降低;与对照组相比,粉煤灰及碱激发剂的加入可以改善市政污泥对混凝土冻融耐久性的劣化效果,降低混凝土在冻融循环作用下的质量损失、动弹性模量损失及抗压强度损失;当粉煤灰掺量10%、碱当量4%时,粉煤灰会在碱激发剂及改性污泥中残余碱的联合作用下被较充分地激发,消纳改性污泥中的残余碱,减弱市政污泥对混凝土抗冻融性能的劣化效果,此时,混凝土水化程度最高,在冻融循环作用下的质量损失、动弹性模量损失及抗压强度损失最小,且服役寿命最长,约为16 a以上;相对动弹性模量与相对抗压强度相关性良好,分别以两者为损伤变量的冻融损伤模型与试验结果均吻合良好。

In this study,municipal sludge modified with quicklime is employed to replace 10%of the fine aggregate,while fly ash replaced 10%,20%,and 30%of the cement to mitigate the adverse effects of municipal sludge on the freeze-thaw resistance of concrete.This is assessed under the combined excitation of sodium hydroxide and sodium silicate.The research investigates the changes in apparent phenomena,relative mass,re-lative dynamic elastic modulus,relative compressive strength,and concrete microstructure with varying fly ash content and alkali equivalent un-der different freeze-thaw cycles.Models of freeze-thaw damage are established,using relative dynamic elastic modulus and relative compressive strength as damage variables.The results indicated that with an increase in freeze-thaw cycles,the concrete sustains more severe damage,exhib-its enlargement in internal pores,and gradually reduces relative dynamic elastic modulus and compressive strength.Incorporating fly ash and an alkali activator mitigates the mass,dynamic elastic modulus,and compressive strength losses in concrete during the freeze-thaw cycles,reducing the deteriorative impact of municipal sludge on the concrete’s durability compared to the control group.Optimal results are shown when the fly ash content is 10%and the alkali equivalent is 4%;under these conditions,the fly ash is fully activated by the combined action of the alkali initiat-or and the residual alkali in the modified sludge.This combination absorbs the residual alkali,diminishing the negative effect of municipal sludge on the concrete’s freeze-thaw resistance.At this point,the concrete achieves its highest hydration degree,exhibits the lowest losses in mass,dy-namic elastic modulus,and compressive strength during freeze-thaw cycles,and achieves the longest service life,exceeding 16 years.A strong correlation is found between the relative dynamic elastic modulus and the relative compressive strength,and the freeze-thaw damage models based on these variables closely match the experimental findings.