The adaptability of polycarboxylic acid admixture and other raw materials of concrete
Concrete Admixture have been introduced into China and popularized since the 1930s, especially the development and successful production and application of polycarboxylic acid water reducing agent at the end of the 20th century, which created a new era of Concrete Admixture. This kind of water reducing agent because of low dosage, high water reduction rate, small slump loss of concrete and other characteristics, has been respected by the industry engineering circles, but also led to the rapid development of concrete technology. However, due to the accelerated process of infrastructure construction in recent years, the construction enterprises have also increased, the supply of raw materials is increasingly tense, and the quality of raw materials is uneven. Scarcity of river sand resources ban, the mechanism of sand fineness modulus, mud content exceeds the standard, poor grading; cement composite admixture proportion increases and other reasons, seriously affect the quality of concrete, so polycarboxylic acid admixture with other raw materials has become an important factor affecting the impact of the quality of concrete.
1 The influence of cement and Concrete Admixture adaptability on concrete quality
Cement is one of the most important components of concrete, and is also the most important part of the decision of the performance of concrete, and the current cement factory only focuses on strength, excessive grinding, which seriously affects the quality of concrete.
In the past, cement admixture is generally 10% to 15%, 42.5 cement 28 days compressive strength of cement can basically be maintained at about 50MPa, now the cement factory in order to reduce the cost of admixture to 20% to 30%, 42.5 cement 28 days compressive strength of cement is difficult to reach 48MPa.
The fineness of the cement is not the greater the better, the fineness is too large to achieve the same workability under the premise of the concrete water demand will increase, the loss of concrete slump will also become larger. If the content of tricalcium aluminate in cement is high, or the amount of gypsum hemihydrate and sodium sulfate in cement are also high, the slump loss of concrete is especially large, and it will lose fluidity in about half an hour, which seriously affects the construction.
(1) When the alkali content in cement is high, there will be a decrease in the flow of concrete and an increase in the slump loss over time, especially when using low sulfate content water reducing agent, the effect is more obvious, while the effect of the water reducing agent with higher sulfate content can significantly improve the situation. This is mainly because the calcium sulfate contained in the low concentration of water reducing agent is produced in the synthesis of neutralization, water solubility is very good. Therefore, when encountering the use of high alkali cement, adding a certain amount of sodium sulfate and hydroxyl hydroxylate retarder in the water reducing agent compounding, the concrete flow as well as slump is better.
(2) When the alkali content in cement is high, and the pH value of polycarboxylic acid water reducing agent is low, the concrete will firstly produce acid-base neutralization reaction, and the concrete will not only increase the temperature, but also accelerate the hydration of the cement, and the fluidity and slump of the concrete will be relatively large loss in a short time. Therefore, when encountering similar cement, do not use citric acid retarder but use alkaline retarder, such as sodium hexametaphosphate, sodium polyphosphate, etc. The effect is better.
(3) When the alkali content of cement is low, the fluidity of concrete is also poor, and the effect of appropriate increase in admixture is not very obvious, and the concrete is also easy to urinate. The main reason for this phenomenon is that the sulfate ion content in cement is not enough to reduce the hydration effect of inhibiting tricalcium aluminate in cement. At this time in the compounding need to add a certain amount of sodium thiosulfate and other sulfates to supplement the soluble alkali in the cement.
(4) when the concrete appears to urinate yellow slurry, pinhole, bubbles, basically can be concluded that the mother liquor and cement is difficult to adapt to the cause, then can be ether and ester, and aliphatic and other kinds of different mother liquor compounding, at the same time, we need to consider pure water-reducing mother liquor to reduce the amount of melamine and sodium hexametaphosphate and then with the appropriate amount of antifoam agent. Do not use products such as thickening, the use of thickening agent bubbles can not come out, resulting in excessive gas content, concrete weight reduction and strength drop significantly.
(5) when the cement in the grinding agent foaming ingredients, concrete is also easy to urinate yellow slurry and static for about 10 seconds in a very poor state, sometimes mistakenly thought to be a water reducing agent compounding water reduction rate is high or gas-inducing add more, in fact, it is the problem of cement grinding agent. This problem must be encountered according to the amount of foam to use antifoaming agent, in the compounding can not be used again air-entraining agent.
2 Mechanism sand quality and the adaptability of Concrete Admixture on the quality of concrete
Various regions of the mechanism of sand parent rock and production technology varies greatly, the mechanism of sand water absorption to a certain extent affects the slump loss of concrete, and the mechanism of sand mud powder content is too high not only affects the strength of concrete, especially the entity rebound strength, durability, resulting in the phenomenon of powdering the surface of the concrete, and at the same time on the mixing plant cost control is also unfavorable. The current production of mechanism sand fineness modulus is basically 3.5 ~ 3.8, or even 4.0, and grading serious breaks unreasonable, 1.18 ~ 0.03mm between the proportion of very few, for pumping concrete is a challenge.
(1) The production of mechanism sand must strictly control the stone powder content of about 6%, as well as the mud content of 3% or less, for the broken grade mechanism sand the stone powder content is a good supplement.
(2) In the preparation of concrete, try to maintain a certain amount of stone powder content to achieve the gradation and rationalization, especially the need to control the amount of 2.36mm or more.
(3) In order to ensure the strength of concrete under the premise of controlling the sand rate, the proportion of large and small gravel is reasonable, you can appropriately increase the amount of small gravel.
(4) Water washer sand is basically precipitated with flocculant to remove mud, and a considerable part of flocculant will remain in the finished sand. High molecular weight flocculants have a particularly large impact on water reducing agent, doubling the admixture of admixtures at the same time as the concrete flow and slump loss is particularly large.
3 Other concrete mixture and Concrete Admixture adaptability to the impact of concrete quality
Power plant fly ash has been a scarcity of material, grinding fly ash came into being, conscientious point of the enterprise will add a certain proportion of the original ash, black hearted enterprises are all stone powder, fly ash loss of burned seriously exceeded the standard, water demand ratio is too large, the activity is basically in the range of 50% to 60%. Fly ash mixed in the amount of limestone powder will not only affect the amount of fly ash burn loss will also affect its activity.
(1) Strengthen the testing of milled fly ash, grasp the change of its loss on fire, and pay close attention to the water demand ratio.
(2) A certain amount of clinker can be added into the milled fly ash to increase the activity.
(3) It is strictly prohibited to use gangue or shale and other materials with great water absorption rate to grind fly ash.
(4) In the grinding of fly ash can be appropriate to add a certain amount of water-reducing components of the product, to control the water demand ratio has a certain effect. Different material quality on the state of concrete are particularly obvious, to solve the problem of adaptability needs a careful analysis process.
