Working Mechanisms and Design Principles of Comb-like Polycarboxylate Ether Superplasticizers in Cement Hydration: Quantitative Insights for a Series of Well-Defined Copolymers
Working Mechanisms and Design Principles of Comb-like Polycarboxylate Ether Superplasticizers in Cement Hydration: Quantitative Insights for a Series of Well-Defined Copolymers
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DOI：
10.1021/acssuschemeng.0c08566
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发表时间：
2021-05-29
影响因子：
8.4
通讯作者：
Heinz, Hendrik
中科院分区：
文献类型：
--
作者：
Javadi, Ali;Jamil, Tariq;Heinz, Hendrik
水泥和混凝土是最广泛使用的建筑材料，并且含有梳形共聚物如聚羧酸酯醚（PCE）作为水合和凝固改性剂。这些添加剂在水泥水化过程中的作用机理仍不确定，这限制了添加剂和具有较低CO2足迹的新型水泥材料的合理设计。我们确定了PCE共聚物结构，吸附和水泥固化性能之间的定量相关性，一系列的共聚物结构和浓度，结合原子模拟的构象和吸附机制的见解。与早期研究相比，PCE共聚物仅具有一小部分多分散性，并且分子动力学模拟利用C-S-H相的界面力场模型，与早期模型相比，该模型能够更准确地了解纳米级聚合物界面的动态。发现了两组不同的属性相关性。(1)PCE的羧酸盐含量，即，每单位质量的离子侧基的摩尔密度与聚羧酸酯醚在水泥浆上的吸附量、水泥浆的电导率和水泥水化加速期的延迟相关。(2)聚合物主链的离子特性和非离子聚乙二醇（PEG）侧链的长度的组合与加工所需的水-水泥比、zeta电位和水泥浆在小型坍落度测试中的流动性相关。模拟表明，PCE吸附到水泥颗粒上涉及丙烯酸酯骨架中的钙离子迁移到硅酸钙水合物表面或氢氧化钙表面上，然后是阴离子聚合物骨架与带正电的矿物表面的离子配对。PEG侧链对矿物表面没有亲和力。使用PEG侧链的体积与阴离子主链的体积的最佳比率，平衡通过离子主链的足够表面键合和通过非离子PEG侧链的颗粒间力的最小化，实现最佳流动性和水减少。电荷密度太低会妨碍有效吸附，而电荷密度太高会导致多层沉积和涂覆颗粒之间的离子附聚力，这会降低流动性并增加必要的水-水泥比。所提出的机制取代先前的模型，并提供定量指标的合理设计的聚合物添加剂的水泥和相关的颗粒分散体。
Cement and concrete are the most widely used building materials and contain comb copolymers such as polycarboxylate ethers (PCEs) as hydration and setting modifiers. The working mechanisms of these additives in cement hydration have remained uncertain, which limits the rational design of additives and of new cement materials with lower CO2 footprint. We identified quantitative correlations between PCE copolymer structure, adsorption, and cement setting properties for a series of copolymer structures and concentrations, combined with insights into conformations and adsorption mechanisms by atomistic simulations. The PCE copolymers have only a small fraction of polydispersity compared to earlier studies, and molecular dynamics simulations utilize Interface force field models for C-S-H phases that enable order-of-magnitude more accurate insights into the dynamics of the nanoscale polymer interfaces compared to earlier models. Two distinct sets of property correlations were discovered. (1) The carboxylate content of the PCEs, i.e., the molar density of ionic side groups per unit mass, correlates with the adsorbed amount of polycarboxylate ethers onto cement pastes, the conductivity of the cement paste, and the retardation of the acceleration period of cement hydration. (2) The combination of the ionic character of the polymer backbone and the length of non-ionic polyethylene glycol (PEG) side chains correlates with the water-to-cement ratio necessary for processing, zeta potentials, and fluidity of the cement pastes in mini slump tests. Simulations indicate that PCE adsorption onto cement particles involves migration of calcium ions in the acrylate backbone onto the calcium silicate hydrate surface, or calcium hydroxide surfaces, followed by ion pairing of the anionic polymer backbone with the positively charged mineral surface. PEG side chains exhibit no affinity to the mineral surface. The best fluidity and water reduction are achieved using an optimum ratio of the volume of PEG side chains to the volume of the anionic backbone, balancing sufficient surface bonding through the ionic backbone and minimization of interparticle forces by the non-ionic PEG side chains. A charge density too low prevents effective adsorption, and a charge density too high leads to multilayer deposition and ionic agglomeration forces between coated particles that reduce the fluidity and increase the necessary water-to-cement ratio. The proposed mechanism supersedes prior models and provides quantitative metrics for the rational design of polymer additives for cement and related particle dispersions.