低温环境下硅灰改性煤矸石混凝土孔隙结构演变

Evolution of Pore Structure in Silica Fume Modified Coal Gangue Concrete under Low Temperature Environment

针对低温环境下煤矸石混凝土服役寿命短的问题,本文采用内掺硅灰(SF)的改性方法,对不同水胶比(0.45、0.35、0.25)和SF掺量(0%、5%、10%、15%,质量分数)的煤矸石混凝土试件进行冻融循环试验和核磁共振试验,测试各组试件质量损失率、相对动弹性模量和孔隙结构分布,并分析冻融循环作用下孔隙结构演变对煤矸石混凝土抗冻耐久性的影响。结果表明:经50次冻融循环后,煤矸石混凝土的质量损失率由负转正,水胶比为0.25的试件逐渐发生碱-骨料反应,经75次冻融循环后,SF使相对动弹性模量提高了13.60%~62.98%,掺入SF可以改善煤矸石混凝土的质量损失率、相对动弹性模量及抑制碱-骨料破坏;在冻融过程中胶凝孔(r≤0.01μm)和细毛细孔(0.01μm<r≤0.05μm)逐渐转变为粗毛细孔(0.1μm<r≤10μm),粗毛细孔数量是决定冻融破坏是否发生的主要因素,SF掺入后延缓了粗毛细孔增加速率,提高了煤矸石混凝土的抗冻耐久性;建立了基于宏观尺度(相对动弹性模量)与细观尺度(不同孔径积分面积)的冻融损伤模型,考虑不同孔径的细观尺度冻融损伤模型同样适用于煤矸石混凝土,并且当水胶比为0.35、SF掺量为10%时,煤矸石混凝土可在西北地区低温环境下服役4 714 d。

To solve the problem of short service life of coal gangue concrete at low temperature,the freeze-thaw cycle test,and nuclear magnetic resonance test were carried out on the coal gangue concrete specimens with different water-binder ratios(0.45,0.35,0.25),and silica fume(SF) content(0%,5%,10%,15%,mass fraction) by adding SF.The mass loss rate,relative dynamic elastic modulus,and pore structure distribution of each group of specimens were tested,and the influence of pore structure evolution on the frost resistance durability of coal gangue concrete under freeze-thaw cycle was analyzed.The results show that after 50 times freeze-thaw cycles,the mass loss rate of coal gangue concrete changes from negative to positive,and the specimen with water-binder ratio of 0.25 gradually produces alkali-aggregate reaction.After 75 times freeze-thaw cycles,SF increases the relative dynamic elastic modulus by 13.60%~62.98%.The addition of SF can improve the mass loss rate and relative dynamic elastic modulus,and inhibit alkali-aggregate failure of coal gangue concrete.During the freeze-thaw process,gel pores(r≤0.01 μm) and fine capillary pores(0.01 μm<r≤0.05 μm) are gradually transformed into large capillary pores(0.1 μm<r≤10 μm).The number of large capillary pores is the main factor that determines the occurrence of freeze-thaw damage.The addition of SF slows down the increase rate of large capillary pores and improves the anti-freezing durability of coal gangue coarse aggregate.The freeze-thaw damage model based on macro-scale(relative dynamic elastic modulus) and micro-scale(different pore size integral area) is established.The micro-scale freeze-thaw damage model considering different pore size is also suitable for coal gangue concrete.When the water cement ratio is 0.35 and the SF content is 10%,the coal gangue concrete can serve for 4 714 d in low temperature environment in the northwest region.