水泥基材料中SAP的吸水、释水和再膨胀行为综述

Absorption,Desorption and Re-swelling Behavior of Superabsorbent Polymers in Cementitious Materials:a Review

裂缝及开裂后水密性的下降是导致水泥基材料耐久性能降低的重要因素。高吸水性树脂(SAP)可降低水泥基材料的自收缩并提高其抗冻性、开裂后抗渗性能和裂缝自愈合能力,进而增强水泥基材料的耐久性能。SAP的上述功能均与其在水泥基材料中的吸水、释水和再膨胀行为相关。本文首先总结了SAP吸水和释水的机理及在溶液和水泥基材料中的关键影响因素,然后综述了裂缝中SAP再膨胀行为的演化机制。在溶液中,凝胶体与溶液之间的渗透压是SAP膨胀的驱动力。作为关键离子,Ca^(2+)可与聚合物链上的羧基络合并导致SAP的离子交联密度增加,较高的离子交联密度可能诱发逆向渗透压并导致SAP释水。在硬化水泥基材料中,影响SAP释水的关键因素是渗透压和毛细力,抑制渗透压作用下的释水并促进毛细力作用下的释水有助于提升SAP的内养护效率。与AA型SAP相比,AA-co-AM型SAP具有更强的水约束能力,因而具有更加优异的内养护效果。水泥基材料裂缝中SAP的再膨胀能力低于溶液环境,这源于裂缝的约束作用和裂缝中较高的离子浓度。基于水泥基材料的配合比、水化进程和裂缝特征研发新型SAP有助于进一步增强SAP的作用效果。

Cracks and the reduction of water tightness after cracking are the important factors leading to the decrease of durability of cementitious mate-rials.Superabsorbent polymers(SAP)can relieve the self-shrinkage and improve the freeze-thaw resistance,impermeability after cracking,and self-healing ability of cementitious materials.The above functions of SAP rely on its absorption,desorption and re-swelling behavior in cementitious materials.In this paper,the mechanism of the absorption and desorption of SAP and its key influencing factors were first summarized.Then,the evolution mechanism of the re-swelling behavior of SAP in cracks was reviewed.In solutions,the osmotic pressure between the gel and solutions is the driving force for SAP swelling.Ca^(2+),as the key ion,can complex with the carboxyl group on the polymer chains and increase the ionic crosslinking density of SAP.A high ionic crosslinking density will produce a reverse osmotic pressure and induce the desorption of SAP.In cementitious materials,the key factors influencing the desorption rate of SAP are osmotic pressure and capillary force.Reducing the desorption under osmotic pressure and improving the desorption under capillary force can enhance the internal curing efficiency of SAP.Compared with AA SAP,AA-co-AM SAP has a more excellent internal curing effect due to its stronger water restraint ability.The re-swelling capacity of SAP in cracks of cementitious materials is lower than that in solutions,because the restraint effect of cracks and the high ion concentration in cracks inhibit the re-swelling of SAP.Designing new SAP based on the crack characteristics,mix designs and hydration process of cementitious materials may help to enhance the application effect of SAP.