Preparation and properties of polyurethane grouting materials modified by waterglass
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Abstract:
During the construction of the headrace tunnel, water inrush and rock instability often occur when facing unfavorable geological bodies, causing project delays and equipment damage. Grouting has been used as a traditional and effective solution to water blocking and reinforcement to effectively avoid the occurrence of accidents. The grouting material is one of the important factors influencing the grouting effect. To realize the high-performance grouting treatment, a variety of grouting materials such as cement, ultrafine cement, sol-gel, waterglass, epoxy resin, polyurethane, and acrylate have been developed. Among grouting materials, polyurethane has been attracting tremendous attention in terms of its extraordinary properties. More specifically, the isocyanate group (—NCO) in polyurethane reacts with water rapidly, the secondary filling ability for micro-fractures due to carbon dioxide exerted from the reaction between —NCO and water, which is especially suitable for the treatment of water inrush. However, there are some drawbacks of polyurethane such as expensive and low compressive strength, which limits its practical applications. Given the problems such as high cost and low compressive strength of polyurethane grouting materials when it is used in water blocking and reinforcement of unfavorable geological bodies, the composite strategy is an important consideration in the performance improvement of grouting materials, such as PU/cement, and epoxy/cement.Some previous studies have shown that polyurethane/waterglass is an organic-inorganic hybrid material that integrates the advantages of both polyurethane and waterglass but avoid their drawbacks. To date, the highly efficient consolidation of polyurethane and waterglass grouting materials has been achieved. Oil-soluble polyurethane was modified by waterglass and the modified polyurethane was prepared successfully. However, the content of raw materials such as polyphenyl polymethylene polyisocyanate (PAPI), waterglass, and catalyst has an impact on the compressive strength of the modified polyurethane. Therefore, to explore the influence of the content of PAPI, waterglass, and catalyst on the compressive strength of materials, the orthogonal experiment design was used to analyze the influence of different PAPI, waterglass, and catalyst content on the compressive strength of the modified polyurethane, and the significant factors affecting the compressive strength were determined. The structures and properties of the materials were characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) to understand the influence of microstructure on macro strength. Results showed that the strength of materials was most affected by the content of waterglass, less by the catalyst, and least by the PAPI. When m(PAPI):m(waterglass):m(catalyst)=20∶20∶1, the strength of the curing body and stone body reached 49.5 and 16.5 MPa, respectively, which is superior to other similar products. Further microstructure analysis demonstrated that the surface of the modified polyurethane was uniform without obvious fine crevices, and the phases in grouting materials were interconnected with each other. The characteristic absorption peak near 1050cm?1 gradually increased with the increase of waterglass content, indicating that —NCO reacted with the activated silanol generated from the hydrolysis of waterglass. Inorganic Si—O bond was introduced into the polymer chain segment and formed a stable inorganic-organic interpenetrating network structure, which further improved the compressive strength of the material.In this research, polyurethane was modified by cheap waterglass. This not only reduce the cost but also improve the compressive strength of materials, which is expected to expand the application scale of polyurethane in the water plugging and reinforcement engineering of broken surrounding rock during the construction of the headrace tunnel.
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