Based on the content of water reducer is fixed, alternative sand mine tailings at 40% and 50%, the dosage of different hydroxypropyl methylcellulose cellulose ether and a redispersible emulsion powder of mortar flow properties and compressive strength influences. As a result, it was found that increasing the amount of hydroxypropyl methyl cellulose ether, redispersible latex powder and tailing sand all reduced the strength of the mortar. The content of hydroxypropyl methyl cellulose ether and tailings sand increases, reducing the fluidity of the mortar, but the redispersible latex powder can significantly improve the fluidity of the mortar.
Natural sand resources are limited. As the amount of sand used for construction continues to increase, the price of natural sand will gradually increase. Using solid waste tailings to replace part of the sand can reduce sand costs, save resources, and reduce the risk of landslides caused by tailings. . In order to ensure that a large amount of tailings sand is added without significantly reducing the overall performance of the mortar, it is particularly meaningful to study the influence of the additive amount on the performance of the mortar, and the research on the effect of different compound admixtures on the performance of the mortar is not See more.
⑴Cement: Conch P·O42.5 cement is used, as shown in Table 1.
⑵River sand and tailings sand: respectively dry in a drying oven with an oven temperature of (105±5)℃ for 24h (equipment model: 101-2A electric heating blast drying oven).
⑶ Admixture 1: Hydroxypropyl methyl cellulose ether (HPMC) [2], its basic properties are shown in Table 4.
Additive 2: Polycarboxylic acid water reducing agent, hereinafter referred to as water reducing agent. Its basic performance is shown in Table 5.
Additive 3: Dispersible latex powder, hereinafter referred to as rubber powder. Its basic performance is shown in Table 6.
The test adopts the industry standard JGJ/T70-2009 "Test Method for Basic Performance of Building Mortar" for determination. The cube compressive strength test uses a mold of 70.7mm×70.7mm×70.7mm.
Test results and analysis
The cement quality is fixed at 450g. Tailings sand is used to replace part of the sand. The replacement amounts are 40% and 50% respectively. The ratio of lime to sand is 1:3, the ratio of water to cement is 0.5, the mass of water is 225g, and the mass percentage of admixture is mortar solid Based on the total mass of the material. In this experiment, three different functional additives were selected, and the mixing amount of two of them was changed. The specific experimental formula design is shown in Table 7.
4.1 The influence of additives on the flow properties of mortar
Figure 1 and Figure 2 are the test results of the influence of different admixtures on the flow properties of the mortar when tailings sand replaces 40% and 50% sand, respectively. Figure 1 and Figure 2 have the following two points in common: First, when the hydroxypropyl methyl cellulose ether admixture is increased to 0.2%, the consistency of the mortar decreases. The reason may be that the hydroxypropyl methyl cellulose Ether can improve the water retention performance of the mortar and improve the wet viscosity of the mortar. The viscosity of the mortar is increased, but the fluidity is weakened, which is not conducive to construction. The advantage is that the wall-hanging performance of ordinary dry mortar is improved; second, the content of dispersible latex powder is increased. The consistency gradually increases and the flow performance is improved. The reason is that the rubber powder has a certain air-entraining effect. With the increase of the rubber powder content, the bubbles in the mortar also increase simultaneously. These closed-pore bubbles are similar to "rolling balls" in the mortar. Improve the flow properties of the mortar.
Comparing Figure 1 and Figure 2, it is found that as the content of tailings sand increases, the consistency of the mortar decreases, and the flowability of the mortar decreases. Since the fineness modulus of tailings sand used in this test is lower than that of sand, the content of tailings sand increases, which reduces the overall fineness of fine aggregate particles, and the amount of cement slurry required to wrap fine aggregates will increase. In the case of cement mortar content, the cement slurry on the surface of the fine aggregate is reduced, resulting in a decrease in the fluidity of the mortar.
4.2 The influence of additives on the strength of mortar
Figure 3 and Figure 4 are the test results of the influence of different admixtures on the compressive strength of the mortar when tailings sand replaces 40% and 50% sand, respectively. It can be seen from Figure 3 and Figure 4 that the increase in the content of hydroxypropyl methyl cellulose ether and dispersible latex powder will reduce the compressive strength of the mortar. The reason is that the addition of these two additives may be in the cement stone. A flexible polymer structure system is formed, and its elastic modulus is lower than that of cement stone. When the mortar is subjected to external stress, the system cannot play a good rigid support function, which in turn reduces the compressive strength of the mortar; in addition, excessive additives increase An organic film may be formed on the surface of cement particles, hindering or weakening the hydration of the cement, resulting in the incomplete release of cement strength; finally, the rubber powder has a certain air-entraining effect, forming pores in the mortar, and the density of the mortar is reduced. It will also reduce the compressive strength of the mortar.
Comparing Figure 3 and Figure 4, the increase in tailing sand content also reduces the compressive strength of the mortar. The reason may be that the fineness modulus of tailings sand is smaller than that of sand. The amount of tailings sand to replace sand increases, and the content of fine aggregate in the formula increases, making the particle gradation unreasonable, reducing the density of mortar, increasing porosity, and reducing coarse particles. The effect of the mortar skeleton is weakened. When the cement content remains unchanged, too much tailings will reduce the strength of the mortar.
⑴Hydroxypropyl methyl cellulose ether can improve the water retention and wet viscosity of the mortar, but it reduces the fluidity and compressive strength of the mortar.
(2) Increasing the content of dispersible latex powder can significantly improve the fluidity of the mortar, but it increases the pore content in the mortar and reduces the compressive strength of the mortar.
(3) The increase in the replacement amount of tailings sand has reduced the fluidity and compressive strength of the mortar to a certain extent.
