Dry-mixed mortar is a new type of building material combined with cement, fine aggregate, fly ash and other mineral admixtures and water-retaining and thickening materials, which has the advantages of stable quality, variety, and ease of construction, and it replaces the traditional mortar with its excellent performance. Raw materials are the main factors affecting the performance of mortar, how to ensure the quality of dry-mixed mortar is generally studied from the raw materials.

1 Impact of cement

Cement as an important component in dry mortar is an important factor in determining the performance of dry mortar. Cement strength, fineness, standard consistency water consumption, setting time will affect the performance of mortar. Cement fineness size affects the dry mortar water retention and cohesion, fineness increase water retention and cohesion will be improved, the hydration reaction is accelerated, but also improve the early strength of the dry mortar, fineness reduce cohesion will be correspondingly poor, will lead to the mortar appear urination and segregation, and at the same time will reduce the early strength of the dry mortar, but will be beneficial to the late strength growth; the size of the standard consistency of the cement water consumption The size of the water consumption of the standard consistency of cement has a corresponding relationship with the water consumption of dry mortar, the greater the water consumption of cement, the corresponding dry mortar water consumption will also increase, dry mortar water consumption increases will first reduce the strength of the mortar, the dry mortar will also have an impact on the long-term, durability; the strength of the cement is the most important factor affecting the strength of the dry mortar, the strength of the dry mortar will be with the strength of the cement and increase, the strength of the cement is reduced and reduced; the cement setting time length of time, the cement setting time, the cement setting time is not the same, but it is not the same. The strength of dry mortar will increase with the increase of cement strength and decrease with the decrease of cement strength; the setting time of cement will also affect the setting time of mortar.

2 Influence of fine aggregates

Fine aggregate in the mortar plays a skeleton role, it accounts for more than 70% in the mortar, its fineness modulus, the largest particle gradation are affecting the quality of dry-mixed mortar, used in dry-mixed mortar in the best fine aggregate should be consistent with the requirements of the sand. Through the test and references, it can be seen that the types of dry mortar are different, the fine aggregate required is not the same, ordinary dry mix masonry mortar fine aggregate should not be greater than the maximum particle size of 4.75mm, dry mix thin-layer plastering mortar with fine aggregate should not be greater than the maximum particle size of 2.36mm, the moisture content should not be greater than 0.5%. The mud content of river sand or the stone powder content of mechanism sand in the fine aggregate will affect the quality of dry-mixed mortar. Excessive mud content in river sand will not only reduce the strength of the mortar, but also accelerate the loss of consistency of the mortar. Mechanism sand in the stone powder content will make the mortar in the water demand increase, will also reduce the strength of the mortar, accelerate the loss of mortar consistency, but also increase the chance of mortar drum cracking. Through the test mechanism of sand in the stone powder can replace part of the cement in the dry mortar, as long as the dosage is properly controlled, but also to meet the strength of the dry mortar; stone powder content is too low will reduce the water retention rate of the mortar and cohesion, so that the mortar appears to urinate phenomenon.

3 The effect of mineral admixtures

The mineral admixtures mixed in ordinary dry-mixed mortar generally include fly ash and mineral powder. Fly ash, as the main constituent material in dry-mixed mortar, not only reduces the cost, but also improves the ease of mortar and mortar durability. The inclusion of fly ash will reduce the heat of hydration of mortar, resulting in a reduction of early strength growth, but will increase the late strength growth of mortar; the inclusion of fly ash will reduce the risk of cracking and cavitation of mortar. Mineral powder and fly ash are different, fly ash does not have its own hydration and hardening characteristics, only with the cement to stimulate its activity, the mineral powder itself will be hydrated and hardened, with a certain strength, with the cement together to stimulate its activity. Mineral powder can replace cement in equal amount, the replacement rate is also 20% to 50%, although it will affect the early strength of mortar, but the 28d strength basically has no effect, but also energy saving and consumption reduction. The specific surface area of mineral powder is greater than the specific surface area of cement, mixed with mineral powder, can increase the compactness of the mortar, improve the impermeability of the mortar. Specific surface area is too large to increase the water consumption of mortar, but the specific surface area is too small to make the water retention deteriorate; and mixing amount is too high to make the mortar setting time increase, and the ease of use deteriorate.

4 Effect of water retention and thickening materials

Dry mortar water retention and thickening materials mainly include cellulose ether, re-dispersible polymer powder, starch ether and so on. (1) cellulose ether is a water-soluble polymer material, can increase the water retention of mortar, adhesion, to prevent segregation of fresh mortar, water secretion, cellulose ether with the increase in the amount of water retention increased, but should not be mixed more than one, should be determined by test. (2) dispersible polymer powder is water-soluble material, it is suitable for thermal insulation mortar, tile adhesive, thin layer plaster mortar, it is in the mortar and cement complement each other to play a good bonding effect; dry mortar mixed with dispersible polymer powder can improve the ease of use of mortar, construction, water retention and mechanical properties. (3) starch ether can affect the consistency of mortar, generally used in ceramic tile adhesive, play a role in the construction of anti-sagging, improve the construction, generally starch ether and cellulose ether used together.

5 Conclusion

Dry mortar cement, fine aggregate, mineral admixture and water retention and thickening materials have an impact on the performance of mortar, especially mineral admixture and water retention and thickening materials on the performance of mortar is the most significant, water retention and thickening materials in the cellulose ether on the water retention of the mortar is the most significant, can be dispersed powder on the adhesive properties of the mortar has the greatest impact. Because of the different types of mortar, the raw materials needed are also different, should choose the appropriate raw materials to formulate dry mortar, in order to meet the requirements of construction.