动水作用下水下不分散混凝土高效抗分散剂的研制及其抗分散多尺度调控机制

Non-Dispersive Underwater Concrete has been known as epoch-making concrete or new generation of underwater construction materials at home and abroad scholars. But Non-Dispersive Underwater Concrete made in China is still far behind developed countries in terms of the scour resistance, slump loss and low strength, etc. The main reason is that the research and development of anti-dispersing agent under the action of moving water is relatively backward, and there is a big encumbrance in theory and technology about the adaptability between the concrete and its composition of materials. Firstly, the project focuses on the preparation of a new type of grafted acrylic polymer through modifying of polyacrylamide from the point of synthetic, in order to solve the contradictory between underwater non-dispersion fluidity and strength of concrete. Secondly, after the confirmation of the main agent, high efficiency water reducing agent, early strength agent, expansive agent, retarder and mineral admixture is used for developing highly active dispersants working under high pressure, high velocity of underwater construction environment, and its influence on the ordinary Portland cement, sulfate aluminate cement hydration process and hydration products and of hardened cement paste microstructure is also be systematically studied.. Thirdly, it is regulated the composition and structure of anti dispersion agent by test method such as infrared spectroscopy, zeta potential, comprehensive thermal analysis, etc, and it reveal and multi-scale controlingme chanism of anti-washout and the nature of concrete slump loss . Fourthly, the new theory and the key technology of the design on concrete under the action of flowing water are proved.

水下不分散混凝土被国内外学者称之为“划时代的混凝土或新一代的水下施工材料”，然而我国水下不分散混凝土在抗水流冲刷、坍损大以及强度低等方面与国外相比有较大的差距，主因是动水作用下抗分散剂的研发相对滞后，与混凝土组成材料之间的适应性以及调控机制存在较大的技术和理论瓶颈。项目首先从合成角度对聚丙烯酰胺进行改性，制备出新型的接枝丙烯系聚合物，从结构上解决水下不分散混凝土流动性与强度的矛盾；其次在主剂确定后，辅以高效减水剂、早强剂、膨胀剂、缓凝剂、矿物掺和料等，研制出针对高压以及高流速下水下施工用的高效抗分散剂，并系统研究其对普通硅酸盐水泥、快硬硫铝酸盐水泥的水化历程、水化产物以及硬化体微结构的影响规律；第三通过红外光谱、Zeta电位、综合热等微观测试手段，进一步调控抗分散剂的组份和结构，并揭示其复合抗分散剂的多尺度调控机理和混凝土坍损的本质；第四提出动水作用下混凝土配合设计的新理论和施工关键技术。

针对我国当前抗分散剂中主剂大多选用聚丙烯酰胺，其产品性能参差不齐，在抗分散性、适应性等方面与国外同类产品有较大的差距，具体表现在用于水下不分散混凝土存在的吸水量较大、混凝土工作性差、硬化后强度倒缩、耐久性差等问题。项目首先尝试从合成角度对聚丙烯酰胺进行改性，制备出新型的满足混凝土材料使用性能的接枝丙烯系聚合物；开发出相应的抗泥型减水剂，最终针对不同的水下施工环境，选用普通硅酸盐水泥和硫铝酸盐水泥作为胶凝材制备出高工作性、高抗分散性的高耐久混凝土。重要成果如下：. 以丙烯酰胺（AM）丙烯酸（AA）为主要单体，在氧化还原-偶氮复合引发体系作用下合成了接枝有减水功能基团（-COOH）的阴离子型聚丙烯酰胺（APAM），可显著降低混凝土在拌合时吸水量，其最适宜调控工艺参数为：温度35 ℃，pH值8，单体浓度27 %，引发剂用量0.6 %，单体配比(n(AM):n(AA))3；相应掺量为水泥质量的1.0 %时，水下浆体的浊度值仅为9.75 NTU，抗分散效果较好。以丙烯酸、异戊烯醇聚氧乙烯醚为主要反应原料，通过正交试验方法合成一种低吸附抗泥型聚羧酸减水剂（KN-PC），其最适宜调控工艺参数为：温度43℃，酸醚比4.2，链转移剂用量为0.45％，引发剂用量为1.6%，丙烯酰胺的用量0.7 mol，磷酸酯类抗泥单体用量1.0 mol，A溶液的滴加时间为2 h，B溶液的滴加时间为2.5 h的试验条件时，抗泥效果最佳。当减水剂为KN-PC，掺量为1.4%，絮凝剂掺量为0.8%，ZC缓凝剂掺量为0.07%，硫铝酸盐水泥的抗分散性能最优，在现有絮凝剂作用机理研究基础上，并根据宏微观试验结果，提出动水作用下抗分散剂的作用机理，可分为吸附-桥键-分散作用和表面活性-桥架-分散作用；采用因子设计方法建立了水下不分散混凝土的流动性、抗冲刷性和水陆抗压强度比预测模型，通过该模型可直接优化水下不分散混凝土性能的设计；应用分形理论和骨料堆积密实方法，提出了高流速下水下不分散混凝土的配合比设计方法，并结合施工工艺的优化，解决了水流速在1.0m/s左右时冲刷下的混凝土水下施工难题。