Mechanical and interface bonding properties of epoxy resin reinforced Portland cement repairing mortar
Introduction
Currently, deterioration and corrosion of concrete-made structures are faced with extremely great challenges due to ingress of various ions from surrounding environments such as seawater, sewage pipes and contaminated soil or waters [1], [2], [3]. As a result, significantly high financial cost associated with repair, maintenance and replacement of these concrete structures is spent annually [4], [5]. Compared to reconstruction of concrete structures, it is much cheaper and more convenient to employ repairing materials by simply attaching them on the corresponding deteriorated areas of concrete structures [6], [7]. Therefore, it is imperative and urgent to find a suitable and cost-effective repairing material in order to lengthen the service life of current-in-service concrete structures.
Polymer modified cementitious materials have been drawing a lot attention in academia and engineering industries because polymers are able to alleviate the drawbacks of cementitious materials such as poor toughness and drying shrinkage, leading to improvements in porous structures, related mechanical properties and durability [8], [9]. Moreover, these polymer modified cementitious materials are usually equipped with good adhesion to a concrete substrate [10], [11], [12]. As a result, polymer modified cementitious materials are often used as a type of repairing material for cementitious binders, which is known as polymer-cement repairing materials (PCRMs). Among different types of polymers, epoxy resin (EP) is widely used as a reinforcement in PCRMs due to its satisfactory mechanical properties, excellent adhesion behaviour, good resistance towards chemical and alkaline attacks as well as close expansion coefficient compared to normal concrete [13]. For instance, epoxy resin was used to modify a type of cement-based mortar by Zheng et al. [14] and it is found that the epoxy resin emulsion improved the bonding strength of this type of cement-based mortar. Another study conducted by Aggarwal et al. [15] investigated the improving effects of epoxy resin latex and polyacrylic emulsion on plain cement mortars. They found that the epoxy resin latex was more superior in improving the properties of cement mortars compared to the polyacrylic emulsion. In comparison with normal epoxy resins displaying an intrinsic incompatibility between its hydrophobic thermosetting behaviour and hydraulic cement-based materials, aqueous epoxy resin in the form of resin latex has attracted an increasing attention in recent years. As reported by Wang et al. [16], it is dispersion of latex of non re-emulsifiable epoxy resin particles with the size ranging between 0.05 and 5.00 μm in water. Compared to normal epoxy resin polymers, water-based aqueous epoxy resin could improve its dispersibility in water owing to emulsification and dispersion techniques, leading to an improved surface integrity of PCRMs [17].
For PCRMs, the interface between themselves and degraded concrete is considered as one of the weakest structure part compared to other parts because of many microcracks, viscous internal voids, gaps or other defects in the interface areas [17]. Besides, the interface bonding performance serves as the basic premise for entire concrete structures to function properly as the interface is the core link between the repairing material and the substrate concrete. Thus, to investigate the interface bonding performance is essential for ensuring a favorable support provided by the repairing material and long-term durability of concrete structures [18], [19], [20], [21].
Although previous studies have been carried out to investigate the bonding performance of aqueous epoxy resin modified PCRMs, systematic research including the synthesis of aqueous epoxy resin, investigations of basic properties of the corresponding PCRMs and related interface bonding properties is still quite limited. In the present study, an aqueous epoxy resin modified PCRM was first made which was then explored with regards to basic properties (including flowability and mechanical properties) and different interface bonding strengths. A type of polypropylene (PP fiber) was employed to improve the anti-crack toughness of the epoxy resin modified PCRMs and OPC was partially replaced by fly ash to enhance the fiber dispersion as well as reducing the usage of OPC [17]. Finally, related micro-bonding mechanisms behind the enhanced flexural toughness and interface bonding properties due to the introduction of the aqueous epoxy resin were discussed based on the microstructural analysis and other experimental results.
Section snippets
Materials
The ordinary Portland cement (OPC) with strength class 42.5 and fly ash (Grade I) were used as the binder with a specific density at 2900 kg/m3 and 2200 kg/m3 respectively. Their chemical compositions determined by X-ray fluorescence are shown in Table 1. ISO quartz sand purchased from Qingdao kangluda Instrument Equipment Co., LTD. (Shandong, China) was used as the fine aggregate for mortar mixing. Moreover, polycarboxylate-type superplasticizer (SP) was used to ensure that all mortar mixes
Flowability
Fig. 4 shows the flowability of the epoxy resin modified OPC-based mortars as a function of epoxy resin contents. It is apparent that the flowability gradually decreases as the amount of the aqueous epoxy resin increases. For instance, the flowability of the epoxy resin modified mortar was 220 mm, 180 mm and 135 mm for the control mortar and the epoxy resin modified mortar with epoxy resin dosages at 5% and 10% respectively. This phenomenon is probably due to the high viscosity of the aqueous
Conclusions
The purpose of this study is to systematically and comprehensively investigate the mechanical properties and interface bonding performance of the aqueous epoxy resin modified OPC-based mortar using different dosages. The same OPC-based mortar without epoxy resin was used as the control. Based on the experimental results and microstructural analysis, an optimal dosage level was determined and related mechanisms were also proposed. Several conclusions can be drawn as below.
- (1)
The flexural strength
CRediT authorship contribution statement
Jie Ren: Partial funding acquisition, writing-review & editing, partial supervision. Siyao Guo: Funding acquisition, partial supervision and review. Xu Zhang: Experimental conduction and data collection. Ji-Zhou Chen: Minor editing and/or experimental aiding. Ben Mou: Minor editing and/or experimental aiding. Huai-Shuai Shang: Minor editing and/or experimental aiding. Pan Wang minor editing and/or experimental aiding. Lihai Zhang: Minor editing and/or experimental aiding.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (51978354), major program of Shandong province (GG201809170147), open Fund of Key Laboratory of Large Structure Health Monitoring and Control (KLLSHMC1906). The first author also would like to acknowledge the fellowship support received from the Tai Shan Scholar Programme, Qing Chuang technology plan of Shandong provincial institutions.
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