Study On Preparation And Properties Of Special Repair Mortars

Whether ancient buildings in the old age or modern concrete buildings that are widely used all over the world, are facing the problem of damage due to different kinds of factors, such as the environment, human effects and problems of the materials itself. Many ancient buildings represent the politics, economy, art, architecture and technology of that time, so they contain a lot of information about the history and culture. But they are quite fragile having been affected by the environment and human. Therefor they especially need to be protected and repaired carefully. While, concrete may be affected by physical or chemical factors such as atmosphere, water or biological erosion, and also can be damaged during service. These damage might lead to esthetic problems or economic losses, which may cause inconvenience to people's daily life and production. Moreover, these damage will also bring security risks. Consequently, it is an urgent problem to study and develop proper repair materials which is suitable for the special condition.In this paper, based on metakaolin, two kinds of repair mortars was prepared, which were for geotechnical buildings and modern concrete buildings respectively. One of them is lime-metakaolin repair mortar, and another is geopolymer repair mortar. Some basic properties of the two kinds of repair mortars were systematically studied. The main contents and conclusions of the study are as follows:A kind of repair mortar for geotechnical buildings was prepared with lime and metakaolin as major binding materials. Two kinds of water-repellent admixtures(tung oil and calcium stearate) were used to improve the water resistance of the mortars. Different properties of the mortars were evaluated: strength, the process of reaction, water absorption, softening coefficient and shrinkage. Phase and microstructure analysis of the mortars were carried out through XRD and SEM. The results show that tung oil and calcium stearate can improve water resistance of the mortars significantly. Water absorption of the mortars with tung oil or calcium stearate can be below 2.5%, and the softening coefficient of them can be above 0.85. Tung oil and calcium stearate can form membrane in the mortars and hinder the pozzolanic reaction of metakaolin, which as a result decrease the mortars' strength. But 28 d compressive strength of the mortars are all above 5 MPa and meet the strength requirement of repair mortars. Also, tung oil and calcium stearate can regulate the growth of products and affect the micromorphology and structure of mortars. Tung oil make the particle size smaller and the structure more compact, while calcium stearate leads to a looser structure. Considering both the mortar strength and water resistance, the optimum dosage of tung oil and calcium stearate was 5% and 1.5% respectively.Then, a series of geopolymer repair mortars was prepared, with metakaolin as the major binding material. Different factors that affect the setting time of geopolymer pastes were studied. Geopolymer mortars of three different strength levels(high, medium and low levels) was designed and prepared for different repair conditions. The influence of slag content, fly ash content and curing system on the strength of geopolymer mortars was studied. Also, the influence of slag content and fly ash content on the bonding strength of geopolymer mortars was studied. Phase analysis of geopolymer products was carried out though XRD. The results show that the setting time of geopolymer was affected by many factors, such as the modulus of sodium silicate, alkali content and water-binder ratio. Slag can shorten the setting time of geopolymer, but fly ash has little effect on the setting time of geopolymer. Slag did not have negative impacts on the strength of geopolymer mortars, while fly ash may decrease the strength of geopolymer mortars. Higher curing temperature is beneficial to the development of the early strength of the geopolymer mortars, but it has little effect on the ultimate strength. The bonding strength of the geopolymer mortars has some correlation with the strength of the geopolymer mortars itself, but even the geopolymer mortars of low strength level also showed good bonding performance. Slag can make the product of the geopolymer has subtle changes, CaO may be a cause of the differences.