聚羧酸盐在高 pH、高离子强度环境下对硅灰的可逆吸附以控制混凝土流动性,Langmuir

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聚羧酸盐在高 pH、高离子强度环境下对硅灰的可逆吸附以控制混凝土流动性
Langmuir ( IF 3.7 ) Pub Date : 2022-01-28 , DOI: 10.1021/acs.langmuir.1c02419
Brant Walkley _{1,

2} , Daniel A Geddes ₁ , Taku Matsuda ₃ , John L Provis ₁

Affiliation

基于聚羧酸盐的减水剂对于生产超高性能混凝土 (UHPC) 至关重要，通过静电排斥和空间位阻促进颗粒分散。本研究首次检验了 pH、离子强度和电荷的变化对低 CO ₂ UHPC 中常见的水性化学物质中基于聚羧酸盐的减水剂对硅粉的吸附/解吸行为的影响。来自总有机碳测量、傅里叶变换红外和核磁共振光谱以及 zeta 电位测量的数据揭示了模拟 UHPC 中的二氧化硅表面化学和电动特性。添加二价阳离子 (Ca ²⁺ ) 通过 (i) Ca 的吸附导致聚羧酸盐吸附在硅粉上^{二氧化硅表面上的2+}离子和二氧化硅表面上较低量级的负 zeta 电势，以及 (ii) 由于与 Ca ²⁺离子的络合和反离子缩合，聚羧酸盐阴离子电荷密度降低。添加 OH ^–离子会导致聚羧酸盐通过硅醇基的去质子化解吸，并在二氧化硅表面产生更大的负 zeta 电位。同时添加 Ca ²⁺和 OH ^–^{通过 (i) 在二氧化硅表面形成双电层和负 zeta 电位，以及 (ii) 由于聚合物主链中的羧酸根基团去质子化，与 Ca 2}络合，聚羧酸根阴离子电荷密度增加，从而导致聚羧酸根快速解吸⁺离子和反离子冷凝。_{这解释了在向新鲜、低 CO 2}的 UHPC中添加少量（1.0 wt%）固体粉状 Ca 源后观察到的显着流化效果，UHPC 的新鲜状态 pH 值（>13）明显高于那些基于波特兰水泥 (pH 11)。

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Reversible Adsorption of Polycarboxylates on Silica Fume in High pH, High Ionic Strength Environments for Control of Concrete Fluidity

Polycarboxylate-based superplasticizers are essential for production of ultrahigh-performance concrete (UHPC), facilitating particle dispersion through electrostatic repulsion and steric hindrance. This study examines for the first time the effect of changes in pH, ionic strength, and charge on the adsorption/desorption behavior of a polycarboxylate-based superplasticizer on silica fume in aqueous chemistries common in low-CO₂ UHPC. Data from total organic carbon measurements, Fourier transform infrared and nuclear magnetic resonance spectroscopy, and zeta potential measurements reveal the silica surface chemistry and electrokinetic properties in simulated UHPC. Addition of divalent cations (Ca²⁺) results in polycarboxylate adsorption on silica fume via (i) adsorption of Ca²⁺ ions on the silica surface and a negative zeta potential of lower magnitude on the silica surface and (ii) reduction of polycarboxylate anionic charge density due to complexation with Ca²⁺ ions and counter-ion condensation. Addition of OH^– ions results in polycarboxylate desorption via deprotonation of silanol groups and a negative zeta potential of greater magnitude on the silica surface. Simultaneous addition of both Ca²⁺ and OH^– results in rapid polycarboxylate desorption via (i) formation of an electric double layer and negative zeta potential on the silica surface and (ii) an increase in polycarboxylate anionic charge density due to deprotonation of the carboxylate groups in the polymer backbone, complexation with Ca²⁺ ions, and counter-ion condensation. This provides an explanation for the remarkable fluidizing effect observed upon addition of small amounts (1.0 wt %) of a solid, powdered Ca source to fresh, low-CO₂, UHPC, which exhibits significantly higher fresh state pH (>13) than those based on Portland cement (pH 11).

更新日期：2022-02-09

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