Common admixture of concrete batching plant uses the erroneous zone and correct method

1, common admixtures use errors

Author inspected Guangdong area more than wet mix concrete batch plant, found some mixing has always been difficult to improve concrete strength. If you want to increase the strength of concrete, in the fierce market competition environment and the confused faces increased costs, lower profits. Through in-depth research, analysis, we find that most of these mixing into concrete admixtures use errors, as follows:

1.1 low-price purchase admixture

Due to fierce competition in the market, and strict control of mixing station for the procurement of raw materials. Mixing hope with the minimum purchase prices of raw materials, concrete admixture as well.

Mixing the additive the purchase price down, will inevitably lead to additive manufacturers to reduce the levels of quality. Mixing admixture of procurement contracts are rarely clear acceptance criteria. Even if there is, it is clearly in accordance with the national standard and national standard is the minimum standard. This leads to additive manufacturers in the case of low bid, supply lower quality additives, usually barely reached national standards, it is difficult to meet the functional requirements of mixing additive.

1.2 limit the amount of admixture

Mixing decision-making to meet stricter than the cost, even the amount of cement, admixtures were specifically requested. This necessarily led to the technology sector in the mix design, can't break through the decision-making admixture of high volume requirements.

1.3 lack of admixtures for quality control and test validation

At present, the additive storage testing, most of the mixing station is a solid content, water rates, density, paste and other technical indicators in the 1~2 test, very few concrete batching plants.

In practice, we found that even though the additive content of solid, water rates, density, paste and other technical specifications to meet the requirements, concrete tests still may not meet the test results, that is, insufficient water for concrete, bad or adaptability.

2, improper use of admixtures on concrete quality and cost of

Due to the low levels of admixture of low price purchase quality, in order to achieve adequate water and effect technical departments tend to increase the amount of additives, resulting in additive consequences of low quality. Instead, quality control and stability, better cost control of mix proportion of mixing station using admixtures of better quality and higher prices, due to low quality, additive cost reduction rather than unilaterally.

Some mixing stations limit the amount of additives. In the case of lack of concrete slump, technology sector or to reduce the moisture content of sand, stone, or concrete unilateral water, directly led to the decline of strength of concrete. Quality-conscious technology sector will be indirect or direct unilateral water consumption of concrete at the same time, increased content of cementitious materials (keep the water cement ratio unchanged), leading to concrete costs increase.

Admixture of mixing station is a lack of quality control and test validation. Quality fluctuation in admixture (down), the technology sector still uses the original mix. To meet the slump of concrete requirements, concrete of actual consumption increases, water cement ratio and concrete strength.

3, the action mechanism of additives

Current naphthalene admixture and admixture of poly-carboxylic acid salts, are relatively high molecular weight (typically 1500~10000) organic compounds belong to the category of surfactant.

Surfactant molecules have polar structure, its end is a non-polar lipophilic groups (or nonpolar hydrophobic groups), and the other end for the polar hydrophilic. Surface active agents dissolved in water, reducing surface tension at the same time, dispersing, wetting, emulsification, foaming, wash and other effects.

3.1 adsorption and dispersion

Concrete mix liquidity depending on the amount of free water in concrete. After joining the admixtures in concrete, because the surface of cement particles directed molecular adsorption admixture, leading to cement the mutual electrostatic repulsion between particles dispersed. Undermining the structure of cement flocculation, releasing large amounts of free water, greatly increasing the fluidity of concrete mix.

3.2 wetting

Due to the admixture of orientation of molecules on the surface of cement particles, forming a single molecule solvated water. The water film on the one hand increases the contact area of the cement particles and water, on the other hand has a wetting effect. Therefore, full hydration of the cement, cement strength rising rapidly.

4, the fundamental role of additives

(1) in the case of unit water consumption is not reduced, and water to Binder ratio unchanged, improve the workability of the fresh concrete to improve liquidity; because of the cement particles and water greatly increases the contact area, full of cement hydration, water to Binder ratio unchanged, tend to have a certain degree of increase of concrete strength.

(2) maintain a certain degrees, reduce water consumption, water to Binder ratio decreases, increases the strength of the concrete.

(3) maintain a strength of case, reduce the amount of cementitious material, reducing water consumption, water to Binder ratio unchanged, saving cement and other cementitious materials.

5, how to purchase and use admixtures

Correct purchase and using additives, can produce huge economic and technological value. Not only can improve the strength of concrete, can reduce the cost of concrete mix. Specific methods are as follows:

5.1 testing links

Admixture testing various technical indicators, is prior to the negotiation of important links. Through tests, additives should be determined by the specification of the eligibility criteria. Including the solid content of admixtures, water rates, density, water reduction of cement paste fluidity and concrete and other technical indicators. Suggested concrete rate as a key indicator to measure the level of quality of additives.

5.2 procurement

After the admixture of clear eligibility criteria, you can start purchasing negotiations. Recommended test for determining the eligibility criteria, the additive manufacturers are bidding. Additive supply quality level is not lower than the tender requirements under supplies even at low price to determine manufacturer.

Meanwhile, the choice of additive manufacturers, should consider the manufacturers size, distance and transport capacity, large-scale mixing station or a large level of project delivery experience and quality of supply, as well as after-sales service ability and level, not manufacturer filter price as the only indicator.

5.3 checking links

Mixing admixture admixture of storage prior to testing, testing results against contracting standards qualified before storage. Recommends that the distinction between key indicators and indexes. Through long-term practice, in my opinion, admixture of key indicators to rate (mortar) and concrete water; reference density (specific gravity), the solid content and the fluidity of cement paste. Due to time reasons, general acceptance link testing specification is density, fluidity of cement paste and water reduction (mortar).

Storage display admixture is not qualified and recommended treatment plan are as follows:

(1) return: when formulating admixture of the eligibility criteria, will have a upper and lower the permitted fluctuation limits. If rate lower eligibility criteria limit the test results should be returned.

(2) the demotion: in case of an emergency, such as admixture inventory to meet production needs, by mutual agreement, do the downgrade, due to inadequate water-reducing rate of lead additives the additive manufacturers are responsible for the increased portion; or by mutual consensus, also make downgrade, solution as above.

On the admixture of unqualified handling, and recommendations stated in the purchase contract, avoiding both in admixture unqualified without law and disputes.

5.4 use the link

(1) generally, inspectors should strictly adhere to established concrete mix, including the amount of additive in the mix;

(2) every day before and during the production process, quality inspector should test the moisture content of sand and stone aggregate, used to guide production; production of actual moisture of sand, stone, a more accurate reflection of the actual amount of water consumption in a single, which reflects the water requirement of cementitious materials and aggregate fluctuations, and admixture rate fluctuations;

(3) properties of raw material when fluctuations occur, timely adjustment of concrete mix. The increase of water demand of cementitious materials and aggregate and admixture rate of decline, lack of water consumption can cause unilateral. Right approach is appropriate admixture dosage, making water do not exceed those established in a single concrete mix, keeping the same water to Binder ratio to ensure the strength of concrete.

5.5 routine testing

Additive after detection before storage, in line with the stipulated standards before granting the contract of storage. Because the rate of testing results and concrete mix would have some access, it is recommended that after storage General detection of admixtures. Test items include water for concrete, solid content, and so on. Among them, the water as the key indicator for concrete, must comply with the requirements.

After a routine examination, such as the concrete rate volatility, should take out admixture of qualified samples were compared in the past, analysis of changes in raw materials is additive or other raw materials. And adjusted according to the results inform the inspectors concrete admixture dosage to ensure water to Binder ratio does not exceed the design value, so as to guarantee the strength of concrete is not affected. And shall immediately notify the change of raw material suppliers quality improvement.

5.6 test validation

In order to ensure the rationality of the production mix, it is recommended that at least monthly to common concrete mix for no less than 2 times the test validation. I found that the most stirring of the high cost of a concrete problem or lack of common concrete mix ratio test to verify.

Concrete test validation, from the raw material quality, workability and strength of concrete and comprehensive verification.

6, conclusion

(1) mixing admixture of errors because of the action mechanism of additives and basic lack of understanding, as well as the degree of influence of water-Binder ratio on strength of concrete failure to comprehend;

(2) misunderstanding of correct mixing additives, testing links, purchasing, checking links, use links, routine testing, test to verify all aspects of the system under control, in which the key to ensuring the strength of concrete is that controlling the production of actual consumption, ensure the water cement ratio is not greater than the design values;

(3) the additive under low levels of quality, water reduction to achieve the desired effect, you must increase the amount of additives. Practice has proved that the procurement and use of low-dosage of admixtures for high standards, low standards compared with high admixture, in terms of the strength of concrete, or admixture of unilateral cost control, there are advantages;

(4) blind limits admixture dosage is not a scientific approach. This approach often leads to concrete unilateral water and cementitious material in a single overall improvement, so as to greatly enhance the mix costs. Recommended according to the testing, determine the water cement ratio and water consumption in a single ceiling to control maximum weight in proportion cost part (binder), on this basis, identify best meet the requirements of concrete slump admixture dosage;

(5) lack of quality control and test validation on the admixture, admixture levels of quality are likely to decline. In that case, keep the same admixture dosage as a result of the unilateral increase in water consumption, will have a disastrous effect on concrete strength. Therefore, strengthen the quality control of admixtures, directly related to the compressive strength of the concrete can be guaranteed or is stable.

In short, as long as we mastered the proper use of additives, you can on the premise of maintaining the mix of constant cost, increasing concrete strength; or maintain the concrete strength of the premise, reduce the cost of mix, creating tremendous technical economic value for concrete batching plant.