Quality control of raw materials
1. Cementing materials
The cementitious materials in dry mortar mainly include cement, gypsum and lime. At present, the largest amount is cement, followed by gypsum. Cement is one of the basic raw materials in cement-based dry-mixed mortar, and the quality of cement has a great impact on the quality of construction projects. Therefore, strengthening the testing of cement quality is of great significance to ensure the quality of construction projects.
The cement in dry-mixed mortar should adopt general-purpose silicate cement, and should adopt bulk cement in accordance with the regulations. The incoming cement should have quality certification documents. The main technical requirements of cement can be divided into two categories: chemical index and physical index. The laboratory mainly tests the physical indexes of cement.
2. Aggregate
Aggregate selection should be analyzed in terms of mud content, stone powder content, particle gradation, harmful substances, firmness, bulk density, porosity, etc. Aggregate must be tested for its particle gradation, mud content, mud content, stone powder content, and firmness before it is imported into the factory, while other items need to be sampled according to the batch. Among them, in order to improve the strength of cement and mortar, it is necessary to use particles of different sizes for proportioning, i.e., particle grading. Mud content is the content of sand with a nominal particle size of less than 80μm, while mud content is the content of sand with a nominal particle size of more than 125mm, and less than 630μm after washing or hand-kneading treatment. If the mud content and mud block content in sand is too much, it will affect the strength and durability of mortar, etc. Generally, the mud content should be controlled to be ≤3.0% and the mud block content to be ≤2.0%.
3. Admixture
Admixtures used in mortar are divided into active filler and inert filler. Active filler refers to itself does not have hydration activity or only weak hydration activity, but in an alkaline environment or the presence of sulfate can be hydrated, and produce strength of the filler. Commonly used active fillers are fly ash, granulated blast furnace slag powder, silica fume, zeolite powder, steel slag powder. Inert fillers are substances that are not active and cannot produce strength, such as ground quartz sand, limestone, hard slag and other materials, the fineness of which is generally similar to or finer than cement. Adding inert fillers in mortar can reduce the amount of cementitious materials and lower production costs. Admixtures used in mortar should comply with the relevant national and industry standards.
4. Additives
Additives used in dry mortar in a small amount, but can largely improve the working performance of mortar. Commonly used mortar additives are cellulose ether, re-dispersible latex powder, starch ether, water reducer, air-entraining agent, defoamer, anti-cracking fiber. In the production of different varieties of mortar to choose different admixtures used to modify the mortar.
5. Construction process control
The thickness of each layer of plaster should not be greater than 10mm when plastering mortar is used, when the thickness of plaster is greater than 10mm, it should be plastered in layers, and should be carried out after the previous layer of mortar has set and hardened, and then the next layer of plastering. Each layer of mortar shall be compacted and smoothed respectively, and the smoothing shall be completed before setting. When the thickness of plaster is greater than or equal to 35mm, reinforcement measures should be taken, such as adding mesh cloth and steel wire mesh. The mortar should be prevented from quick drying, water rushing, impact, vibration and freezing before setting. When the temperature or construction environment temperature is lower than 5℃, dry mortar shall not be constructed without effective heat preservation and anti-freezing measures.
6. Maintenance
Mortar construction is completed, the surface layer condensation, it must be timely moisturizing maintenance, in order to prevent the mortar early plastic cracking, mortar maintenance time shall not be less than one week. In case of summer high temperature season, ensure that the water is drenched every 4 hours during the day not less than once.
Finished product control
1. Production process control
The whole production process should have a detailed record, do a good job in the sand baking process control, batching, mixing and online primary inspection and other aspects of the original record. The sand drying process should be determined in accordance with the specified frequency of sand moisture content and particle gradation, the moisture content of the drying sand is controlled within 0.5%, and the particle gradation is guaranteed to meet the requirements of the mortar ratio. Mixing should choose to use mechanical forced mixing, mixing process should be carried out in strict accordance with the mortar ratio, and do a good job of mixing equipment status and parameter records.
2. Performance testing and control
Dry mortar performance indicators are divided into rapid detection indicators and long-term performance indicators, of which the rapid detection indicators are divided into water retention rate, setting time and 2h consistency loss rate, etc. If all the indicators are qualified, the batch of mortar can be shipped out, and issue factory inspection reports. In addition, other long-term performance indicators, such as 14d tensile bond strength, 28d shrinkage, etc., the manufacturer should be reported to the site within 3d after all the performance results.
Conclusion
As a new type of construction material, dry mortar has a broad application prospect, but it also faces a series of quality problems. By strictly controlling the quality of raw materials, strengthening the construction process control and finished product testing, the quality of dry-mixed mortar can be effectively improved to ensure the safety and durability of construction projects. In the future, it is necessary to continuously explore and improve the production and application technology of dry-mixed mortar to meet the growing demand of the construction market.
