Dry Mixed Mortar Formulation

In dry mixed mortar formulation, the key technical problems such as cement hydration, setting and hardening, drying shrinkage control and late stability should be fully considered, and the raw materials and reasonable formulation should be selected.

Keywords dry mixed mortar formulation, mortar technology, dry mixed mortar

1. Preface:

Many people think that mortar products technical performance as long as meet related standards or higher than standard value, product there will be no problem, the author thinks that this view is not very comprehensive, because quality testing in the standard is the normal temperature condition, within the stipulated time, after many times maintenance measure data, basically is conducted in laboratory conditions, And the construction engineering, especially the external wall engineering, the actual use environment and conditions of mortar products are much more complicated, there are high temperature and low temperature environment, rain and wet and dry environment, acid and alkali environment, a variety of different base materials, different construction technology methods and so on. It is required that mortar should not only have good performance and quality, but also have strong adaptability to meet various needs and requirements.

2, three key points of mortar formula design:

2.1, hydration condensation and water vapor action:

Mortar is hydraulic inorganic gelled material, it is gradually generated by cement hydration reaction with water, gel content, the better quality the better the performance of cement gel generated, no matter how many additives added, the poor quality of cement its mortar performance is ultimately impossible is good, therefore, no matter in formula design of ordinary mortar and special mortar, We must adhere to the use of high quality cement, less additives, because cement itself is cementing material, very stable, cheap cementing material.

2.2. Self-curing ability of mortar:

Cement hydration reaction, condensation hardening, achieve the ultimate strength, end of life, from beginning to end, are inseparable from a good water environment. This we can see through the cement pool and the cement ship in the 60-90's, as long as there has been water in the cement pool, the cement ship has been in the water, there will be no problem, if the pool is dry for a long time, the cement ship is put on shore for a long time, then it will be 100% water leakage. Still have Beijing imperial Palace, Shenyang imperial Palace, include the temple that hundreds of years ago, want us to brush paint on the wall of these ancient buildings only, emulsii paint, epoxy resin paint, easy and quick peel falls off, what reason? Because paint is airtight, chemical paint aging fast, afraid of acid and alkali.

We should make clear the properties of hydraulic, air-condensed inorganic materials and chemical materials. Mortar formula design should be based on the principle of geological polymer, its own ability to absorb water and gas, its advantage of microporous structure, make full use of environmental conditions, absorb and utilize water and gas and automatically balance, so as to achieve self-maintenance. Therefore, in addition to cement cementing materials used in the formula, can not block or close the cement pores, keep the pores unobstructed and its air permeability, moisture control function.

2.3, control drying shrinkage:

Cement mortar dry shrinkage, dry shrinkage of the larger mortar is easy to appear crack phenomenon, mortar turtle is a crack in the end, you wipe how thick and how much it will crack, a crack, crack before empty drum, fall off again, once the cracks, the crack size varies with the environment temperature and humidity of the air change 24 hours a day, is generally difficult to repair completely, Even if the use of high elastic materials, it does not help, because chemical high elastic materials aging fast, very short life, therefore, mortar or exterior wall putty belongs to high alkaline materials, is not suitable to add a large number of high elastic chemical emulsion. The formula of mortar should adopt gel principle, structure principle and water-air balance principle to control the drying shrinkage of mortar and prevent cracking phenomenon.

3. dry mixed mortar formula analysis:

formula Case 1:

Raw material name formula proportion

42.5 ordinary Portland cement 35-40%

Washed sand or quartz sand (20-40-80 mesh) 60-65%

RDP Powder of 8-10%

HPMC 0.2 0.35%

Analysis: the product in addition to cement added material less and fine, the product quality of the preparation is good. The proportion of cement and aggregate in the formula is reasonable, using the technical route of aggregate enhancement, according to the plastering thickness, using 20-40-80 mesh aggregate for reasonable grading, is correct, we can prove this technology in practice.

The use of better performance of redispersible polymer powder, its efficiency is better than the use of other products. redispersible polymer powder can react with silicon, aluminum, calcium, magnesium and other mineral components in mineral materials to generate gel with better performance and more stable network structure. This redispersible polymer powder has a significant effect of viscosity, enhancement and thickening, and has the ability to keep water and balance moisture. Can improve the mortar at the beginning of adhesion, later strength and stability, thixotropic lubrication, breathable moisture, anti-seepage water leakage, anti-condensation and so on, just like the Great Wall bricklaying adhesive and the palace Wall with plaster materials.

redispersible polymer powder from renewable natural plants, but also has anti-aging, acid and alkali resistance, freeze-thaw resistance, non-toxic, low carbon environmental protection and many other advantages, in mortar products and engineering has been used for more than 10 years, its quality is fully affirmed by the users.

Formula Case 2:

Raw material name formula proportion

42.5 ordinary Portland cement 35-40%

Washed sand or quartz sand 60-65%

Redispersible latex powder 0.15-25%

HPMC 0.2 0.35%

Ash calcium powder 5-10%

Coarse whiting powder, 5-10%

Wood fiber 2%

Starch ether 0.05 0.1%

Analysis: the material added in the formula is too much, the material is used improperly, the product stability is poor.

(1) The proportion of cement and aggregate in the formula is appropriate.

(2) the latex powder on the market is basically the use of polyvinyl acetate (referred to as EVA, ethylene and acetic acid and other copolymerization, but also the production of white latex commonly used chemical raw materials), EVA is afraid of water, poor bonding ability and stability, aging fast, easy degradation, mildew, is not suitable for large use in high alkaline materials. Cement strength is from weak to strong, chemical materials from strong to weak, both in curing and curing after the strength contrast is very big, chemical materials can close cement capillary hole, the use of cement mortar part or completely lose air permeability, moisture and self-maintenance ability. Due to the rapid aging and short acting time of chemical materials, the later strength and stability of hydraulic and air-condensed materials will be seriously affected. At the end of the eighties in the kitchen and toilet tiles, in cement mortar to join polyvinyl alcohol formaldehyde adhesive (polyvinyl alcohol, urea, formaldehyde, hydrochloric acid, etc., solid content of 8%, formaldehyde content 500mg/kg, 180. Peel strength 10N/25mm), just stick on the tile is very firm, but a few years later there will be a large area of flake off phenomenon. Now the ceramic tile of building exterior wall often appears to fall off, have certain relation with improper use of chemical adhesive in mortar, so, chemical material should be carefully used in mortar.

(3) HPMC is a commonly used water retaining material for mortar. The amount is not the more the better, the amount should be appropriate, adhesive mortar should be about 0.1-0.2%; Plastering mortar should be based on the plastering thickness, the amount of about 0.2-0.35%, that is, the thickness of the appropriate use less, the appropriate use of the thin.

(4) Gray calcium powder:

Some manufacturers in the mortar and exterior wall putty powder products add a certain amount of ash calcium powder, the main purpose is to increase with ash calcium powder mortar rapid hardening effect, ash, calcium has actually increased mortar rapid hardening effect, but the ash calcium powder increased mortar's hard at the same time, also contributed to the dry shrinkage of mortar, easy to cause crack, empty drum, fall off. Cement itself in production, according to different strength grade, with quicklime, gypsum, such as optional to mortar add ash calcium powder or fly ash, easy to cause mineral composition and chemical composition imbalance. Therefore, it is not recommended to use lime calcium powder or fly ash in mortar.

(5) Heavy calcium powder:

The main component of heavy calcium powder is calcium carbonate, and the commercial heavy calcium powder is basically more than 200 mesh. The addition of ultrafine powder materials in mortar affects the structural strength and stability, because the proportion of cement and aggregate in mortar is 3: The fineness of cement is about 200 mesh, and the fineness of aggregate is 20-80 mesh, which is reasonable gradation. If too much superfine materials such as heavy calcium, gray calcium, fly ash and micro mineral powder are added, it will obviously affect the setting capacity of mortar and weaken the effect of aggregate enhancement. Therefore, heavy calcium powder should not be used in mortar (except exterior wall putty).

(6) Wood fiber:

Wood fiber has a certain water absorption capacity and a certain anti-flow hanging effect, but the effect is very limited, even not very obvious. HYM series with better performance can be used without adding wood fiber in mortar.

(7) Starch ether:

Starch ether swelling, with a certain thickening, thixotropic ability, generally only with chemical latex and compound resin additives with the use of HYM series of better performance of plant redispersible polymer powder is not starch ether

Formula Case 3:

Raw material name formula proportion

42.5 ordinary Portland cement 35-40%

Washed sand or quartz sand 60-65%

Compound resin powder or base material 0.8-1%

HPMC 0.1 0.2%

Analysis: the proportion of cement, aggregate and HPMC in this formula is normal. Problem is the main distribution of resin powder and masterbatch, the former is mostly used chemical benzene class, esters and other volatile solvent oil and mineral powder by soaking or use a small amount of polymer, cellulose, a large number of micro mineral powder blend to sell packaging, the product is toxic, on human health and the natural ecological environment has a lot of harm, national production and use is prohibited, Basically plays no role in mortar, and will even destroy the quality and stability of mortar, mortar products produced by compound resin powder, poor quality, without any quality assurance, manufacturers should be vigilant. The latter compound type mother material, is to use a small amount of polymer and a large number of mineral powder, production is very simple, the manufacturer is more arbitrary, he wants to match, how to match, no technical content, products without any quality standards, more without technical guarantee.

Compound resin powder and master material cost is low, low price, poor quality, some manufacturers cogacious cheap, if there is a quality problem, the loss is the manufacturer, and even some manufacturers shut down.

Iv. Formula design and engineering practice:

Before production, the reliability and feasibility of the formula must be repeatedly demonstrated and verified. Must first find out theoretical basis and theoretical analysis, the theory must be pass, right, next to the main technical indicators and the comprehensive performance of the product of a large number of contrast analysis, careful observation, tracing investigation for engineering quality is already completed, the focus is on the stability of product quality, application technology and level of the manufacturer should not be limited in the laboratory, Must visit more, more investigation, more practice, and constantly summarize and improve.

V. Review:

Mortar formula should focus on the application, ensure the quality of the project, the quality should rely on the live, use good, use up stable. Everything comes from practice, which requires technical personnel to have excellent professional knowledge and rich practical experience.