Study on Compatibility of the Ternary System of the Water Reducing Agent and Retarder

Study on Compatibility of the Ternary System of the Water Reducing Agent and Retarder
Concrete admixtures can improve the working performance of fresh concrete, improve the construction environment, improve the mechanical properties and durability of hardened concrete, save cement, reduce costs, and speed up construction, so concrete admixtures are widely used. However, some admixtures, including ordinary water reducing agent, high range water reducing agent, retarder (organic retarder, retarding water reducing agent, inorganic retarder), have adaptability problems with cement in the process of use, resulting in great differences in their effects.
In this paper, the compatibility of Nylon superplasticizer with three different cements was studied, and the effects of different dosage of superplasticizer on the initial fluidity and 1h fluidity loss of cement paste were observed; The effect of retarder on the initial fluidity of cement paste was observed (the water cement ratio was the same, compared with the initial fluidity of cement paste without retarder); The compatibility between superplasticizer and cement ternary system mixed with different kinds of retarders was observed, the experimental results were analyzed, and the existing problems were put forward. 1 Raw materials, experimental methods and instruments
1.1 Experimental materials
1.1.1 Cement
Qinling 42.5 ordinary Portland cement (hereinafter referred to as QL); Zhengzhou Longyuan 42.5 ordinary Portland cement (hereinafter referred to as LY); Grade 42.5 ordinary Portland cement for overpass (hereinafter referred to as TQ); Shield stone 42.5 ordinary Portland cement (hereinafter referred to as DS).
1.1.2 High range water reducing agent
Tianjin produced low concentration naphthalene sulfonate formaldehyde condensate (hereinafter referred to as NX).
1.1.3 Retarder
Sodium polyphosphate; Citric acid; D-sodium gluconate.
1.2 Experimental methods and instruments
The cement paste diffusion test shall be conducted according to GB8077.
The water cement ratio of the net slurry is 0.29. Change the amount of superplasticizer added. Compare the differences in the compatibility between different cements and superplasticizer by measuring the initial fluidity of the slurry 5 min after adding water (that is, the end of mixing) and the fluidity of the slurry 1 h after standing. The water cement ratio of the net slurry is 0.29. Change the dosage of superplasticizer, mix a retarder (fixed dosage), compare the initial fluidity of the slurry 5 min after adding water (i.e. the end of mixing) and the fluidity of the slurry after standing for 1 h (%), and verify the improvement effect of adding retarder on the compatibility of the same cement and superplasticizer; Under the same conditions, properly increase the dosage of retarder, and compare the influence of the dosage of retarder; Change the type of cement, carry out the above research, and compare the compatibility of retarder to three different cements and superplasticizer
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Whether the functions of are the same.
Similarly, change the type of retarder, do the above research, and compare the difference of the influence of different retarders on the compatibility of cement and superplasticizer.
2 Experimental results and discussion
2.1 Compatibility between naphthalene superplasticizer and cement binary system
Generally speaking, when the fluidity of cement paste is fixed, the dirty water cement ratio will increase with the increase of the amount of superplasticizer. After reaching a certain amount, the fluidity will not increase, or the increase is very small. At this time, the amount of superplasticizer is called the saturation point. When the mixing amount exceeds this point too much, the cost will be increased, and the segregation of cement slurry and aggregate will be caused. Figure 1 shows the experimental results of fluidity changes of three kinds of cement mixed with water (W/C=O.29) under the change of NX content. Among them, NX and LY cement have good compatibility, showing obvious saturation point, and when the content exceeds 0.8%, the 1h fluidity loss is very small. The compatibility of NX with TQ cement and QL cement is poor, because TQ cement has high initial fluidity, but its fluidity loss in 1h is too large. However, the initial fluidity of QL cement is not high and the fluidity loss in 1h is large. The mixing amount is 0.4% No.9%, and F60 is basically not increased.
Fig. 1 Fluidity Change with NX Dosage Change
(a) LY cement; (b) TQ cement; (c) QL cement
2.2 Compatibility of retarder and cement binary system
The main function of retarder is to delay the setting and hardening rate of cement, so that the concrete mixture can maintain plasticity for a long time. According to its function, it can be divided into retarding and water reducing agents with retarding and water reducing functions. In this experiment, the water cement ratio is 0.29. Add 0.1% ～ 0.3% sodium polyphosphate to the three kinds of cement respectively. With the increase of the dosage, the retarder has no change compared with the blank experiment (cement and water), which proves that sodium polyphosphate has no water reducing effect. Similarly, the control blank experiment (cement and water) of adding 0.01% ～ 0.1% citric acid to three kinds of cements proves that citric acid has no water reducing effect. In the experiment, it was also found that 0.01 ～ 0.1% D-gluconate sodium was added, and with the increase of the amount of D-gluconate, the consistency of cement paste increased compared with the blank experiment (cement and water), which proved that D-gluconate sodium had a weak water reducing effect.
2.3 Compatibility of ternary system of cement, naphthalene superplasticizer and retarder
The compatibility between superplasticizer and cement is improved through the composite use of additives. The composite use of superplasticizer and retarder can effectively control the concrete slump loss over time. It is shown that when a certain retarder is added at the same water cement ratio and the amount of superplasticizer, the fluidity value of cement paste and 1h fluidity are improved, indicating that the ternary system of cement, naphthalene superplasticizer and retarder has good compatibility. At the same time, in the experiment, we found that the compatibility between some kinds of cement and naphthalene superplasticizer was very poor, which showed that the content of naphthalene superplasticizer was very high (up to 0.8%), and there was still no fluidity. However, after the proper amount of retarder is compounded, a large initial fluidity can be obtained even when the dosage of naphthalene superplasticizer is very low. However, the 1h fluidity of ternary system has no significant change compared with that of binary system.
For example, when TQ cement and NX with different content are mixed with 0.1% - 0.3% sodium polyphosphate, when the content of superplasticizer is less than 0.6%, the composite sodium polyphosphate has an obvious effect on increasing the initial fluidity value and 1h fluidity value of the paste, and reduces the 1h fluidity loss value. Compared with the original binary system, the saturation point of superplasticizer in the ternary system is earlier. When the amount of superplasticizer is greater than 0.6%, although it has no obvious effect on increasing the initial fluidity value and 1h fluidity value, it still effectively inhibits the lh fluidity loss.
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The experiment of QL cement and LY cement shows the similar rule.
2.4 Compatibility of cement, naphthalene superplasticizer and D-sodium gluconate ternary system
DS and QL cement were used to test. The initial fluidity of cement paste of the original binary system was increased when the dosage of D-sodium gluconate was 0.01% ～ 0.1%, but the requirements for the dosage of D-sodium gluconate were different when the two cements were used to maximize the initial fluidity. DS cement is 3/10000, and QL cement has the most obvious effect when the dosage of D-sodium gluconate is 10/10000.
2.5 Compatibility of cement, naphthalene superplasticizer and citric acid ternary system
The test was carried out with LY cement mixed with 0.01% - 0.1% citric acid with different content of NX. After adding citric acid, the fluidity value of cement paste and 1h fluidity value did not increase compared with the original binary system. And with the increase of citric acid content, the initial fluidity of the clear pulp tends to decrease.
2.6 Analysis of compatibility factors
2.6.1 Mineral composition, fineness and calcium sulfate form of cement
The research shows that the mineral composition of cement clinker, gypsum type and content, alkali content, free calcium oxide content, mixture type and content, cement fineness and particle composition will affect the compatibility of superplasticizer and cement. The lower the content of CA and C4F in cement, the better the compatibility between naphthalene superplasticizer and cement binary system, because the adsorption capacity of CA to superplasticizer is stronger than other mineral components. With the increase of cement fineness, the influence of C3A is more obvious.
Because the concentration of sulfate ions in the liquid phase controls the rheological behavior of the slurry, when its dissolution is slow, it needs to affect C. When the amount of A is relatively high, due to the lack of sulfate ions, more C is produced. A will be hydrated locally, and the superplasticizer will be adsorbed on C. A and its hydrated products reduce the concentration of effective water reducer in the liquid phase, and the dispersion effect is small. Therefore, the cement containing dihydrate gypsum and hemihydrate gypsum is better than anhydrite, because the first two release sulfate ions faster than the latter.
2.6.2 High range water reducing agent
The molecular structure, polar group type, non-polar group type, average molecular weight and molecular weight distribution, degree of polymerization and impurity content of water reducer all affect its adaptability to cement.
2.6.3 Retarder
Theoretically, sodium polyphosphate can prolong the induction period of cement hydration, and make C. The hydration rate of A slows down because phosphate ionizes phosphate ions and reacts with cement hydration products, forming a dense and insoluble phosphate thin layer on the surface of cement particles, which inhibits the penetration of water molecules and hinders the normal hydration of cement. Thus, the hydration of C, A and the formation of ettringite are delayed and play a retarding role.
3 Conclusions and problems
Through the study on the compatibility of the ternary system of cement, naphthalene based superplasticizer and retarder, the following conclusions are obtained:
(1) The compatibility between the same superplasticizer and ordinary Portland cement produced by different manufacturers is different.
(2) The compatibility of different retarders with the binary system composed of the same ordinary Portland cement and naphthalene superplasticizer is different.
(3) Some retarders have similar effects on the compatibility of binary system composed of ordinary Portland cement produced by different manufacturers and the same naphthalene superplasticizer.
The problem to be further studied is to change the types of sugar retarders and hydroxyl hydroxy acid retarders, find out the universal laws and analyze them from the perspective of retarding mechanism, and verify the above experimental results through mortar experiments.
reference
[1] He Tingshu. Concrete Admixture. Xi'an. Shaanxi Science and Technology Press, 2003
[2] Qin Weizu. Study on the compatibility and testing method of cement superplasticizer. Concrete, 1996 (2): 11-17
[3] Ding Zhu et al. Study on the compatibility of cement and water reducer. Design and Research, 1998 (10)
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