WANG Juan1，KOU Yude2，CHEN Ning1 （1.Shanghai Academy of Building Research，Shanghai 201108，China； 2.Shanghai Construction Building Materials Market Management Station，Shanghai 200032，China）
Abstract：The variation of the properties of tile adhesives with different amounts of emulsion powder and cement in water immersion，freezing and thawing and high temperature conditions was studied，and the influencing factors and improvement techniques of its durability were analyzed in depth. The results show that the bonding strength of 28 d for tile adhesive is mainly related to the content of cement and the content of emulsion powder. When the content of emulsion powder is lower than 1%，the tensile bonding strength is not improved obviously，the water-resistant bonding strength is mainly related to the amount of cement， when the cement content is low，the water resistance decreased，but the dosage of cement should not be too high，that will form a compact surface which decrease the force of mechanical anchor. Meanwhile，the emulsion powder dispersed and had swelling behavior facing with water，so increasing powder content is good for its water resistance property. The freeze-thaw resistance bond strength of tile adhesive require both ability of water resistance and stress deformation，so the powder content should not be too low，the main factors affecting the bond strength of aging resistance of tile adhesive is the emulsion powder content and moisture content of the substrate.
Tile adhesive is mainly used in interior and exterior walls, floors, bathrooms, kitchens and other building decoration places. It can reduce the amount of bonding material, reduce the thickness and weight of tile bonding, reduce tile weight, reduce delamination and peeling. The problem. Excellent tile adhesive should be firmly bonded to the substrate and the tile, with good flexibility, can adapt to the thermal expansion and contraction caused by environmental reasons, and adapt to the changes in environmental temperature in each season. Waterproof and water-retaining properties, effectively isolate water from erosion. Its performance indicators are mainly reflected in the tensile bond strength index. Durability is simplified by measuring the tensile bond strength after thermal aging, water immersion and freeze-thaw. As tile adhesives are more and more widely accepted by engineering, many scholars have carried out research on their additives and their adaptability to ceramic tile and waterproof slurry substrates. Xiong Youming et al. Studied the effects of redispersible polymer powder and polyvinyl alcohol on the tensile bond strength and flexibility of tile adhesives. Wen et al. Studied the effects of cement dosage, sand gradation, and rubber powder dosage on the tensile bond strength, water immersion strength, and heat resistance of cement-based tile adhesives. Li Yuhai discussed the influence of cement amount and standard brick type on the tensile strength of tile adhesive under different curing conditions. Wu Hongxia et al.  studied the adhesive strength of cement-based adhesives and the performance of wet-mixed mortar with three types of tiles with different water absorption. Dong Fengliang et al. Studied the compatibility of waterproof pastes with different polymer contents and tile adhesive materials in wet house systems. The above studies focused on the effects of adhesive powders and tiles on tensile bond strength, the adaptability of tile adhesives to substrates, and did not analyze the degradation mechanism of tile adhesives and the factors affecting durability. This article analyzes the deterioration mechanism of ceramic tile adhesive and its influencing factors from the perspectives of different rubber powder content, cement dosage, and moisture content of the substrate. It can be used to analyze the reasons for deterioration of building tile peeling and the durability of ceramic tile manufacturers Sexual improvement provides some reference.
1.1 Raw materials
Cement (C): P · O42.5, Shanghai Wanan, the main properties are shown in Table 1; sand (S): 30 ~ 90 mesh river sand, the particle size distribution is shown in Table 2, the fineness modulus is 1.6; cellulose ether (E): viscosity 40 Pa · s, Zhejiang Zhongwei Co., Ltd .; latex powder (P): vinyl acetate and ethylene copolymerizable redispersible polymer powder (EVA, P1), styrene and acrylic acid copolymer redispersible polymer powder P2, the minimum film-forming temperature is 0 ℃, produced by ELOTEX; other additives include starch ethers, early strength agents, expressed as O.
1.2 Test method
Refer to JC / T 547-2017 “Ceramic Tile Adhesive” for mixing and forming test specimens. Tile gel curing conditions include four conditions: 28 d standard culture, 7 d standard culture and 21 d water culture, 7 d standard culture + 21 d water culture and freeze-thaw cycles, and 14 d standard culture + 14 d 70 ℃. The concrete slabs used in the middle distribution ratio are dry and non-drying. The substrate was purchased from Shanghai Zengsi Industry and Trade Co., Ltd., which complies with the standard requirements.
1.3 Mixing ratio
Table 3 shows the mixing ratio of the test tile adhesive. The water-to-powder ratio is 0.22. Among them, 1 # ~ 5 # formulas adopt two types of concrete slabs for drying and non-drying, and the remaining properties are all undried concrete slabs. 6 # ~ 9 # all adopt dry concrete slab.
2 Test results and discussion
2.1 Effect of EVA rubber powder content on the durability of tile adhesive
2.1.1 Effect of EVA rubber powder content on tile adhesive 28 d tensile bond strength (see Figure 1)
It can be seen from Fig. 1 that the 28-day tensile adhesive strength of the tile adhesive (1 # ～ 5 #) is increasing with the increase of the amount of rubber powder. The 28-day tensile adhesive strength when the rubber powder is not added is 1.25 MPa, when the rubber powder content is 0.5%, the tensile bond strength is reduced to 1.19 MPa, and when the rubber powder content is 1.0%, the tensile bond strength is 1.37 MPa, which is slightly higher than when the rubber powder is not added. After the increase, the tensile bond strength increased more significantly with the increase of the rubber powder content. Adding redispersible rubber powder can form a polymer film (latex film) and form part of the pore wall, thus sealing the high pore structure of the mortar. The latex film has a self-stretching mechanism, which can apply tension to the place where it is anchored to the mortar. Through these internal forces, the mortar is kept as a whole. When the amount of EVA rubber powder is less than 0.5%, the effect of improving the tensile bond strength is not obvious. The amount of rubber powder has a significant effect on the film formation amount. The recommended amount of rubber powder is not less than 1.0%.
2.1.2 The influence of the amount of EVA powder and the state of the base material on the thermal aging bond strength of tile adhesive The
latest standard JC / T 547-2017 requires that all concrete slabs should be dried concrete slabs before the standard is revised. The concrete slab is controlled below a certain moisture content. Two types of concrete slabs were used in the study. One was directly molded after one month of standard curing, and the other was dried at 105 ℃ for 5 hours and cured for 24 hours. Figure 2 shows the effect of the amount of EVA redispersible emulsion powder on the thermal aging tensile bond strength of tile adhesive.
It can be seen from Figure 2 that the heat-aged tensile bond strength of both the dried and undried concrete slab tile adhesive 1 # sample without EVA rubber powder is less than 0.5 MPa; when the rubber powder content is 0.5%, drying is used. The tensile adhesive strength of the tile adhesive of the board is 0.72 MPa, and the unseasoned board is 0.26 MPa; when the rubber powder content is 1.0%, the tensile strength of the tile adhesive of the dried board is 1.23 MPa. The unseasoned board is 0.24 MPa; when the content of the rubber powder is 2.0%, the tile adhesive with heat-aged tensile bond strength is 1.78 MPa, and the unseasoned board is 0.69 MPa. To sum up, the heat-resistant aging tensile bond strength of the tile adhesive after drying the concrete slab is generally higher than that of the unseasoned board. The tensile bond strength of the tile adhesive using the dry board increases with the amount of rubber powder. Significantly increased, 1.0 MPa can be achieved when the rubber powder content is 1.0%. The tensile adhesive strength of tile adhesives using unbaked boards does not increase significantly at low levels of rubber powder. The tensile adhesive strength is greater than 0.5 MPa when the rubber powder is added at 2%. The reason is that the tile adhesive is thermally aged in a 70 ℃ oven for 14 days. At the high temperature, the tile adhesive undergoes fatigue strain. The polymer film formed by the rubber powder has a strong deformation ability, which is the main factor to resist the tile adhesive strain. The moisture in the concrete slab continuously evaporates under high temperature conditions. The less the moisture in the concrete slab, the lower the pressure generated by the moisture during evaporation, and the more favorable the interface tensile bond strength of the tile adhesive. When the concrete slab is not dried, the amount of rubber powder needs to be increased to more than 2.0% to help resist the loss of tensile bond strength caused by the pressure of water evaporation.
2.1.3 Effect of EVA rubber powder content on tile adhesive water immersion and freeze-thaw tensile bond strength
Figure 3 shows the effect of EVA rubber powder content on tile rubber water immersion and freeze-thaw tensile bond strength. The immersion conditions are standard. After 7 d soaking in water for 21 d, the freeze-thaw resistance conditions are standard culture for 7 d, soaking water for 21 d, and freeze-thaw cycles, so the dried and un-dried concrete slabs have little effect on water immersion and freeze-thaw resistance. Therefore, the differences between the two concrete substrates are not compared.
It can be known from Fig. 3 that the immersion in water and freeze-thaw tensile strength of the 1 # sample without EVA rubber powder were 0.35 and 0.38 MPa, respectively. With the increase of the rubber powder content, the increase in water immersion and freeze-thaw strength is not obvious. When the rubber powder content is 2.0%, the water immersion and freeze-thaw strength are greater than 0.5 MPa. The results show that when the cement content is 35%, the tile adhesive with low EVA powder content has poor soaking and freeze-thaw cycles. When the cement content is 35%, the density of the tile adhesive is not good. The water continuously penetrates through the pores and voids to the tile adhesive and the concrete slab, as well as the interface between the tile adhesive and the tile. A water vapor layer is formed at the interface to reduce the tensile bond of the tile adhesive. Strength, when the amount of rubber powder is small, the amount of emulsified film is low, and the hydrophilic group is continuously dispersed and swelled under the action of water. Only when the amount of rubber powder is high, it can play a binding role. The freeze-thaw cycle requires that the tile adhesive be resistant to both water and freezing. During this process, the water continuously freezes and melts to generate expansion and contraction stress. Under the effect of stress fatigue, micro cracks will occur on the tile adhesive interface and inside. The crack is a weak link for waterproofing. With the continuous accumulation of water erosion and stress and deformation, the crack continues to expand. When the rubber powder content is high, a continuous film can be formed in the tile adhesive, and then the cracks can be prevented from spreading and the adhesive effect can continue to be exerted.
2.2 Effect of cement content on the durability of tile adhesives
Figure 4 shows the effects of different cement content on the durability of tile adhesives, which are 5 # ~ 9 # formulas, in which the cement content is increased from 35% to 43%.
It can be seen from Figure 4 that the thermal adhesive aging tensile bond strength of the tile adhesive is similar to the 28 d tensile bond strength, and even higher than the initial value of 28 d with the increase of the amount of the rubber powder. With the increase of cement content, the tensile bond strength at 28 d has been increasing.
The immersion tensile bond strength reached a maximum value of 1.89 MPa when the cement content was 40%, and then decreased to 1.6 MPa. The freeze-thaw resistance tensile bond strength also tends to increase first and then decrease as the cement content increases. It reaches a maximum at 40% cement content and 1% rubber powder content, and then increases with the increase of cement content. By the drop. Figure 5 shows the interface of the tensile bond strength test of four groups of samples after freeze-thaw resistance.
Figure 5 (a) shows that when the tile adhesive with 35% cement content and 2% EVA powder content is freeze-thaw tensile strength, the failure interface is located inside the tile adhesive. The tile adhesive is not dense and there are some pores. . Figure 5 (b) shows that the failure interface is located on the surface of the tile adhesive. The tile adhesive with 38% cement content and 2% EVA powder content is denser, and the freeze-thaw tensile bond strength is greater than 1.0 MPa. Figure 5 (c) shows that the failure interface is located on a small part of the surface of the tile adhesive. It is observed that the surface of the tile adhesive with 40% cement content and 3% styrene-acrylic powder content is dense. Its freeze-thaw tensile bond strength is greater than 1.0 MPa, which is lower than the freeze-thaw tensile bond strength of 7 # formula with the same amount of cement and 2% EVA powder. Figure 5 (d) shows that some of the failure interfaces are located on a small part of the surface of the tile adhesive, and some surfaces are dense and flat without tensile damage. The actual freeze-thaw tensile bond strength is reduced to 0.68 when compared with 40% cement. MPa. In summary, the excessive cement content makes the tile adhesive too dense, which reduces the mechanical anchoring force with the tile. Under freeze-thaw conditions, the interface is under repeated expansion and contraction stress, and the tensile bond strength is continuously reduced.
(1) The 28-day tensile bond strength of tile adhesive is mainly related to the cement and rubber powder content. When the amount of rubber powder is less than 1%, the film formation is low, and the improvement of tensile bond strength is limited.
(2) The tensile bond strength of ceramic tile soaked in water is mainly related to the cement content. When the cement content is low, the water resistance decreases. However, the cement content should not be too high, and the dense surface of the tile adhesive is not conducive to the mechanical anchoring force of the tile. After the rubber powder is emulsified and formed into a film, it will easily swell in water. It is necessary to increase the amount of rubber powder to ensure the same bonding effect. Certain additives ensure that the cement content should not be less than 35% and not more than 40%, and the rubber powder content should be higher than 2%, and it should be appropriately increased according to different tensile bond strength requirements.
(3) The freeze-thaw resistance of ceramic tile adhesives requires both water resistance and a certain degree of resistance to stress and deformation. The cement content should also not be too high, because the dense surface is subject to the expansion and contraction stress of the freeze-thaw cycle. The anchoring force will be further reduced, and the amount of rubber powder should not be too low. Certain admixtures ensure that the cement content should not be less than 35% and not more than 40%, and the content of rubber powder should be more than 2%, and it should be appropriately increased according to different tensile bond strength requirements.
(4) The heat-resistant aging tensile bond strength of tile adhesive requires strong resistance to high temperature deformation. At the same time, if the moisture content of the substrate is high at high temperature, the moisture continuously penetrates into the tile adhesive and concrete slab, as well as the tile adhesive and tile, through the pores and voids. At the interface, a water vapor layer is formed at the weak interface to reduce the tensile bond strength of the tile adhesive. Therefore, the main factors affecting its high temperature resistance are the content of rubber powder and the moisture content of the substrate.