Dry-mixed mortar is a kind of granule and powder that is uniformly mixed with additives such as fine aggregates and inorganic binders, water-retaining and thickening materials, water-reducing agents, anti-cracking agents, and defoaming agents in a certain proportion after drying and screening. The mixture is transported to the construction site by a special tanker or sealed waterproof paper bag, and then mixed with water. In addition to cement and sand, the most widely used dry-mixed mortar is redispersible and redispersible polymer powder. Because of its high price and great influence on the performance of mortar, it is the focus of attention. This paper discusses the effect of dispersible polymer powder on the properties of mortar.
1 Test method
In order to determine the effect of dispersible polymer powder content on the properties of polymer mortar, several groups of formulas were designed by orthogonal test method and tested according to the method of “Quality Inspection Standard of Polymer Mortar for External Wall Thermal Insulation” DBJOI-63-2002. It is used to determine the influence of polymer mortar on the tensile bond strength, compressive shear bond strength of concrete base and the compressive strength, flexural strength and compression-to-fold ratio of polymer mortar itself.
The main raw materials are P-04 2.5 ordinary silica cement; RE5044 and R1551Z redispersible and redispersible latex powder; 70-140 mesh quartz sand; other additives.
2 Influence of dispersible polymer powder on the properties of polymer mortar
2.1 Tensile bonding and compression shear bonding properties
With the increase of dispersible polymer powder content, the tensile bond strength and compressive shear bond strength of polymer mortar and cement mortar also increased, and the five curves moved up in parallel with the increase of cement content. The weighted average of each relevant point can quantitatively analyze the degree of the influence of the content of redispersible polymer powder on the performance of cement mortar. The compressive shear strength shows a linear growth trend. The overall trend is that the tensile bond strength increases by 0.2 MPa and the compressive shear bond strength increases by 0.45 MPa for every 1% increase in the dispersible polymer powder.
2.2 Compression/folding properties of mortar itself
With the increase of redispersible polymer powder content, the compressive strength and flexural strength of the polymer mortar itself decreased, indicating that the polymer has a hindering effect on the hydration of cement. The effect of dispersible polymer powder content on the compression ratio of polymer mortar itself is shown in Figure 4. , with the increase of the redispersible latex powder content, the compression ratio of the polymer mortar itself decreases, indicating that the polymer improves the toughness of the mortar. The weighted average of each relevant point can quantitatively analyze the degree of influence of the redispersible polymer powder content on the performance of the polymer mortar itself. With the increase of the redispersible polymer powder content, the compressive strength, flexural strength and The indentation ratio shows a linear decreasing trend. For every 1% increase of dispersible polymer powder, the compressive strength decreases by 1.21 MPa, the flexural strength decreases by 0.14 MPa, and the compression-to-fold ratio decreases by 0.18. It can also be seen that the flexibility of the mortar is improved due to the increase in the amount of dispersible polymer powder.
2.3 Quantitative analysis of the effect of lime-sand ratio on the properties of polymer mortar
In polymer mortar, the interaction between lime-sand ratio and redispersible polymer powder content directly affects the performance of mortar, so it is necessary to discuss the effect of lime-sand ratio separately. According to the orthogonal test data processing method, different lime-sand ratios are used as variable factors, and the related redispersible polymer powder content is used as a constant factor to draw a quantitative diagram of the influence of lime-sand ratio changes on mortar. It can be seen that, With the increase of lime-sand ratio, the performance of polymer mortar to cement mortar and the performance of polymer mortar itself show a linear decreasing trend. The bond strength is reduced by 0.12MPa, the compressive shear bond strength is reduced by 0.37MPa, the compressive strength of the polymer mortar itself is reduced by 4.14MPa, the flexural strength is reduced by 0.72MPa, and the compression-to-fold ratio is reduced by 0.270
3 The effect of redispersible latex powder containing f on the tensile bonding of polymer mortar and EPS foamed polystyrene board The bonding of polymer mortar to cement mortar and the bonding of EPS board proposed by DB JOI-63-2002 standard is Conflicting.
The former requires high rigidity of polymer mortar, while the latter requires high flexibility, but considering that the external thermal insulation project needs to stick to both rigid walls and flexible EPS boards, at the same time, it is necessary to ensure that the cost is not too high. Therefore, the author lists the effect of dispersible polymer powder content on the flexible bonding properties of polymer mortar separately to emphasize its importance.
3.1 Influence of the type of dispersible polymer powder on the bond strength of EPS board
Redispersible latex powders are selected from foreign R5, C1, P23; Taiwanese D2, D4 2; domestic S1, S2 2, a total of 7; polystyrene board selected Beijing 18kg / EPS board. According to DBJ01-63-2002 standard, the EPS board can be stretched and bonded. Redispersible latex powder can meet the requirements of rigid and flexible stretch bonding properties of polymer mortar at the same time.