NaHCO₃ / Na₂CO₃ 对熟石灰的碳化改性研究

Study on Properties of Hydrated Lime Modified by NaHCO ₃ / Na ₂ CO ₃

摘要

为了解决熟石灰早期碳化速率慢的问题,在熟石灰中分别掺入碳酸氢钠(NaHCO₃)和碳酸钠(Na₂CO₃)2种碳化促进剂,研究了碳化促进剂中CO^2-₃与熟石灰中Ca²⁺的物质的量比(n(CO^2-₃)∶n(Ca²⁺))对熟石灰物理性能、抗压强度及微观结构的影响。结果表明,在保持稠度相同的条件下,n(CO^2-₃)∶n(Ca²⁺)的增大可以缩短熟石灰净浆的初凝时间和终凝时间,但同时水灰比的增大不利于NaHCO₃和Na₂CO₃改性熟石灰的水分蒸发和后期碳化。当n(CO^2-₃)∶n(Ca²⁺)<0.18时,2种碳化促进剂均能有效降低熟石灰的毛细吸水率、吸水率及孔隙率,同时提升熟石灰的软化系数。碳化促进剂对石灰早期抗压强度的提升效果显著,当n(CO^2-₃)∶n(Ca²⁺)=0.18时,养护28 d的2种改性熟石灰的强度最高,相较于对照组L,强度分别提升了97.73%和39.77%,但n(CO^2-₃)∶n(Ca²⁺)>0.18则不利于熟石灰后期强度发展。由扫描电子显微镜(scanning electron microscope,SEM)图像可知,方解石型CaCO₃是熟石灰碳化的主要产物,且n(CO^2-₃)∶n(Ca²⁺)增大有助于促进熟石灰碳化反应。综合来说,由于碳化促进剂中的Na⁺会对熟石灰性能产生不利影响,只有当n(CO^2-₃)∶n(Ca²⁺)<0.18时,内掺碳化促进剂能明显改善熟石灰的性能。

Abstract

To address the slow early-stage carbonation rate of hydrated lime, two carbonation accelerators, NaHCO₃ or Na₂CO₃, were mixed into the hydrated lime, and the effects of the molar ratio of CO^2-₃ to Ca²⁺ (n(CO^2-₃)∶n(Ca²⁺)) on physical properties, compressive strength and microstructure of hydrated lime were investigated. Results show that increasing n(CO^2-₃)∶n(Ca²⁺) can shorten the initial and final setting time of the hydrated lime paste when the consistency is kept the same, however, the increasing water-lime ratio is not conducive to the water evaporation of hydrated lime moisture and later carbonation. When n(CO^2-₃)∶n(Ca²⁺) is less than 0.18, both carbonation accelerators can reduce capillary water absorption, water absorption and porosity of hydrated lime, while increasing the softening coefficient of hydrated lime. The carbonation accelerators can significantly increase the early compressive strength of hydrated lime, and the 28 d compressive strength of two hydrated lime pastes modified by carbonation accelerator is the highest at n(CO^2-₃)∶n(Ca²⁺) of 0.18, respectively, with increases of 97.73% and 39.77%, compared to the control group. However, n(CO^2-₃)∶n(Ca²⁺) more than 0.18 is not conducive to the later strength development of hydrated lime. According to SEM images, calcite-type CaCO₃ is the main product of hydrated lime carbonation, and the increased n(CO^2-₃)∶n(Ca²⁺) promotes to hydrated lime carbonation. In conclusion, carbonation accelerators containing Na⁺ adversly affect the hydrated lime property, and the internal mixing of carbonation accelerator has a significant upliftment on hydrated lime properties when n(CO^2-₃)∶n(Ca²⁺) is less than 0.18.

关键词

熟石灰 / 方解石 / 碳化 / 促进剂 / 物理性能 / 强度

Key words

hydrated lime / calcite / carbonation / accelerator / physical properties / strength

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基金资助

河南省科技攻关计划资助项目(222102320362)