It is a high-efficiency concrete water-reducing agent. It was first developed and applied by Japan in the 20th century and was industrialized in the 1990s. It can improve the strength of concrete; or reduce the amount of cement while maintaining the same strength, saving cement and reducing costs. Now it has become a new type of concrete admixture widely used in construction. Compared with other high-efficiency water-reducing admixtures, water-reducing admixtures exhibit a series of more excellent properties, mainly in: low dosage and high dispersion. Its water reduction rate is as high as more than 30%, and a very small dosage (0.1%~0.2%) can give concrete high fluidity. Compared with other high-efficiency water-reducing agents, water-reducing agents have the following outstanding advantages:
(1) Good slump retention, with basically no loss of slump within 90 minutes; (2) Under the same fluidity Under normal circumstances, it has little impact on the cement setting time, and can well solve problems such as water reduction, air entrainment, retardation, and water bleeding; (3) It has good compatibility with cement; (4) The synthetic polymer backbone is The sources of raw materials are wide, and the monomers usually include: acrylic acid, methacrylic acid, maleic acid, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, vinyl acetate, sodium methylpropyl sulfonate, etc.; (5) Using similar water-reducing admixtures, more slag or fly ash can be used to replace cement, thereby reducing costs; (6) There is a large degree of freedom in the molecular structure, many controllable parameters in admixture manufacturing technology, and high performance It has great potential for polymerization; (7) Diversified polymerization pathways, such as copolymerization, grafting, block, etc. The synthesis process is relatively simple, and since no formaldehyde is used, it will not cause pollution to the environment.
The synthesis of water-reducing agent generally first synthesizes the macromonomer polyethyl alcohol monoacrylate through esterification, and then copolymerizes it with other monomers containing active groups. At present, this idea is basically followed in China. ongoing. This paper uses the above method to synthesize a kind of water reducing agent SP-1, and uses the post-ester method to synthesize another water reducing agent HZC, that is, first polymerizes to generate a polymer with a certain molecular weight, and then uses esterification reaction to introduce it on the side chain. Other functional groups with certain functions, and conduct comparative tests on these two products.
1 Molecular design of water-reducing agent
The molecular structure of water-reducing agent is distributed in a comb shape, with multiple active groups on the main chain, strong polarity, and side chains. It has hydrophilic polyether segments, long and large chains, and short hydrophobic molecular segments. A major feature of water reducing agents is that they can be designed through the molecular structure. The SP-1 and HZC water-reducing agents synthesized this time have similar molecular structures, but are different in terms of group ratios:
2 Synthesis of water-reducing agents
2.1 Raw materials
Acrylic acid (AR): analytical grade, Chengdu Kelong Chemical Reagent Factory.
Methacrylic acid: chemically pure, Suzhou Industrial Park Zhengxing Chemical Research Institute.
Polyethyl alcohol monomethyl ether (MPEG): degree of polymerization 23,10, Shanghai Taijie Chemical Co., Ltd.
Sodium methylpropyl sulfonate (MAS): 99.5%, Shandong Zibo Onasi Chemical Co., Ltd.
Ammonium persulfate: analytical grade, produced by Shanghai Aijian Reagent Co., Ltd. . Sodium sulfite: Wenzhou Dongsheng Chemical Reagent Factory, Zhejiang Province.
p-Toluenesulfonic acid: Shanghai Shanpu Chemical Co., Ltd.
Additives: homemade.
2.2 Synthesis of SP-1
Add polyethylene glycol monomethyl ether, p-toluenesulfonic acid, acrylic acid, and methacrylic acid to a three-necked flask equipped with a stirrer. and auxiliaries, react at 120°C for 5 to 8 hours to obtain macromonomer reaction products.
Add MAS, water and part of ammonium persulfate to a three-necked flask equipped with a stirrer and condenser tube, raise the temperature to 80°C and add dropwise macromonomer, acrylic acid, methacrylic acid and sodium sulfite. Mix the solution with the remaining ammonium persulfate and react for 4 to 8 hours to obtain a yellow product. Add NaOH to neutralize the solution to neutrality.
2.3 Synthesis of HZC
Add MAS, water and a part of ammonium persulfate to a three-neck flask equipped with a stirrer and condenser tube, stir and raise the temperature to 85°C, and slowly drip Add AA, sodium bisulfite and the remaining ammonium persulfate mixture, and react for 8 to 12 hours to obtain a light yellow liquid.
Cool the liquid to 50°C, distill away excess water under reduced pressure, add polyethylene glycol monomethyl ether and additives, and reflux the reaction at 95°C for 6 to 12 hours to obtain a red product, add water Make the solid content at 20%, then add NaOH to adjust the pH to neutral.
3 Performance test
3.1 Raw materials
Cement: P.O42.5R ordinary Portland cement, Chongqing Cement Factory.
Cement: P.O42.5R ordinary Portland cement, Chongqing Diwei Cement Factory. Fine aggregate: medium sand, Yueyang sand.
Coarse aggregate: gravel 5~25mm.
Naphthalene series water reducing agent: FDN, Chongqing Sansheng.
Water reducing agent: BASF, Germany, codenamed PC in this article.
3.2 Water slurry fluidity and retention test
The fluidity of cement slurry is measured according to the “Test Method for Homogeneity of Concrete Admixtures” (GB/T8077-2000). The mass of cement is 300g, W/C=0.29.
3.3 Concrete performance test
Refer to “Concrete Admixtures” (GB 8076-1997) to test the water reduction rate, slump retention and concrete compressive strength of different ages. Comparison test.
4 Results and Discussion
4. 1 Analysis of the fluidity test results of the clean slurry
P.O4 2.5R cement from Chongqing Cement Plant is used, and the water reducing agent is Test results of cement slurry fluidity under different dosages. It can be seen that compared to FDN, water reducing agents have better dispersion properties.��, especially PC and self-made SP-1, have better dispersion effects at a lower dosage (0.1%), while HZC has a cement slurry fluidity of 255mm when the dosage is 0.4%. . It can be seen that the dispersion properties of SP-1 and PC are basically close. The adsorption of naphthalene-based water-reducing agent FDN is straight adsorption, and the molecules are in the form of rod-shaped chains; while the water-reducing agent is distributed in a comb shape. The difference in molecular structure results in differences in the water-reducing mechanisms of the two water-reducing agents. The main electrostatic repulsion effect of naphthalene-based water-reducing agents is small. The negative Zeta potential of cement particles mixed with water-reducing agents decreases slightly, that is, the electrostatic repulsion is small. However, because its main chain is connected to the surface of the cement particles, the branch chains extend into The liquid phase forms a thicker adsorption layer of polymer molecules, which has a greater steric repulsive force and has a significant dispersion effect on cement particles when the dosage is small.
Using P.O4 2.5R cement from Chongqing Cement Plant, the relationship curve between cement slurry fluidity and time under a certain dosage of water-reducing agent, in which the dosage of SP-1 and PC are both 0.2%. , the HZC content is 0.4%, and the FDN content is 0.8%. It can be seen that the water reducing agent has better retention performance, among which homemade SP-1 and PC from BASF of Germany are better than HZC. It can be seen from the curve that the self-made HZC still has good dispersion retention performance, and although FDN also has good dispersion performance, the fluidity of cement slurry gradually decreases with the increase of time, and the curve attenuation is obvious. This is because unlike FDN, polyethers with long side chains are gradually hydrolyzed in an alkaline environment, releasing functional groups with water-reducing effects, which secondarily supplement the electrostatic repulsion between cement particles, thereby continuing to maintain the cement slurry. high liquidity.
4. 2 Analysis of concrete water reduction rate test results
The test used P.O42.5R cement from Chongqing Diwei Cement Factory and P.O42.5R cement from Chongqing Cement Factory. Four different water-reducing agents are added respectively, and concrete with the same slump is prepared according to the method specified in the standard “Concrete Admixtures” (GB8076-1997), and the corresponding water-reducing amount is calculated according to the method in the standard. Rate.
It can be seen that when the dosage is small, SP-1, PC and HZC all have high water reduction rates. When the dosage of SP-1 and PC is 0.2%, the water reduction rate is They are 30.7~32.9% and 29.7~32.5% respectively. When the dosage of HZC is 0.4%, the water reduction rate also reaches 24.2~24.8%.
4. 3 Analysis of concrete slump retention test results
Test results of adding different water-reducing agents in two cements. It can be seen that the concrete slump retention rate of PC is 93.2~95.3% at 1 hour, the slump retention rate of SP-1 is between 82.6% and 84.4% at 1 hour, and the slump retention rate of HZC is 86.4 at 1 hour. %~88.6%, which is significantly higher than FDN (62.8%~54.5%), indicating that the water-reducing agent has a better effect on maintaining the slump of concrete than the naphthalene series water-reducing agent. Because the naphthalene series water-reducing agent mainly uses the electric double layer repulsion effect to achieve the dispersion of cement particles; in addition to the double electric layer repulsion effect, the comb-shaped structure of the water-reducing agent also provides a steric hindrance effect, that is, the surface of the cement particles is It is stabilized by a block or graft copolymer dispersant to prevent random agglomeration. At the same time, (OH) and (COOH) in the water reducing agent molecules are adsorbed on the crystal nuclei of the hydrate, delaying the crystallization of the cement product. The speed of hydration hardening is more conducive to the slump retention of concrete.
4. 4 Analysis of concrete compressive strength test results
SP-1 and HZC P.O42.5R cement in Chongqing Cement Plant and P.O42 in Chongqing Diwei Cement Plant .5R cement shows good water reduction rate. In terms of intensity, SP-1 did not collect data due to the low intensity on 1d. Its intensity enhancement in the later period is quite obvious. The intensity ratio of HZC on 1d is 133~141%, the intensity ratio on 3d is 141~151%, and the intensity ratio on 7d is 142~ 148%, the 28d intensity ratio is 139~153%. There is a significant gap in strength between naphthalene-based FDN and water-reducing agents such as HZC and PC.
4.5 Modified HZC test results
From the above test results, it can be seen that compared with naphthalene series FDN, HZC has better dispersion and retention, but compared with German There is a certain gap between BASF’s PC and self-made SP-1. The introduction of other ingredients into HZC will play a greater role in improving the performance of HZC. The test uses a certain proportion of other mixture D, which is mainly based on sodium citrate and other additives, and other ingredients are added to form HZC*. The test results of the fluidity of HZC* in cement slurry after the introduction of Mixture D show that the dispersion performance of HZC* has been greatly improved after the introduction of Mixture D. These are the test results of the water reduction rate and strength ratio of HZC*. It can be seen that although the strength ratio at 1d decreased slightly after adding mixture D, the water reduction rate and strength ratio in the later period of HZC* were improved to a certain extent.
5 Conclusion
(1) By designing the molecular structure, using a reasonable monomer ratio, and using two different methods to synthesize a water-reducing agent with excellent performance.
(2) The cement slurry and concrete test results show that the water-reducing agents SP-1 and HZC synthesized this time have the advantages of low dosage, high water reduction rate, and obvious concrete strength enhancement effect. .
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