Water reducing agent is a new type of environmentally friendly water reducing agent. It is a hot topic in water reducing agent research at home and abroad. It is also considered to be the third breakthrough in concrete technology after reinforced concrete and prestressed reinforced concrete technology. Among them, water-reducing agents are the most prominent. However, in recent years, due to the environmental protection situation, the quality of cement, sand and gravel and other materials has fluctuated frequently. Due to factors such as sensitivity to the above-mentioned materials, however, when the concrete water-reducing agent encounters the soil in the sand and gravel, What should be done?
In addition to cement, sand, stone and water, it is an essential fifth component in modern high-performance concrete. Among them, the high-performance water-reducing agent and the naphthalene-based high-performance water-reducing agent are the two most widely used admixtures in engineering. In particular, the high-performance water-reducing agent has low dosage, good dispersion performance, high water reduction rate, and significant enhancement effect. Excellent slump retention performance and many other advantages.
However, in actual projects, the performance of water-reducing agents is affected by many factors, especially the mud content in the raw materials of sand and gravel, which affects its water-reducing performance. To achieve the same fluidity when using sand with a higher mud content, the amount of water-reducing agent needs to be increased by 30%-50%, or even doubled. This not only makes it more difficult to control the water-reducing agent in the construction process, but also greatly increases the cost investment, which has a great negative impact on the wide application of water-reducing agent. Therefore, it is necessary to study the impact of the mud content of sand and gravel on water-reducing admixtures, explore the rules and mechanisms of its influence on the performance of water-reducing agents, and obtain the allowable mud content of sand and gravel, in order to provide high-performance water-reducing agents and Provide theoretical guidance for the application of naphthalene series high-efficiency water reducing agents in engineering.
1. Test raw materials
1.1 Cement: Ordinary Portland P·O42.5 cement, its physical properties.
1.2 Ordinary river sand: See its physical properties and sand gradation analysis.
Sand with different mud content is adjusted through calculation of original sand and yellow mud. The original sand is medium sand with a mud content of 3.4%. When the mud content of the test sand is higher than the mud content of the original sand, wash the sand again and add yellow mud for manual preparation; when the mud content of the test sand is lower than the mud content of the original sand, calculate the amount of yellow mud added to Meet the test mud content requirements.
1.3 Water-reducing agent: high-performance water-reducing agent, liquid, solid content 39%; naphthalene-based high-efficiency water-reducing agent, powder.
1.4 Mud: yellow mud, which is dried and manually ground into powder.
2. Test plan
2.1 Research on the influence of sand and mud content in mortar on the effect of water reducing agent
According to the actual application situation of the project, the sand and mud content were selected respectively. When the dosage (the dosage is 0.0%, 1.4%, 2.5%, 3.0%, 3.4%, 4.4%, 5.4% respectively), for different dosages of high-performance water reducing agent (the dosage is 0.20%, 0.26%, 0.32%) , 0.38%) and naphthalene series high-efficiency water-reducing agent (dosage of 0.50%, 0.75%, 1.00%, 1.25%). Based on the fluidity of mortar reaching (180±5) mm, the water reduction rate of high-performance water-reducing agent and naphthalene-based high-efficiency water-reducing agent in mortar was measured, and the mechanism and sensitivity analysis were conducted.
2.2 The influence of aggregate mud content on the effect of water-reducing agent in concrete and the mechanical properties of concrete
Select the naphthalene series water-reducing agent content to be 0.75%, and the water-reducing agent content should be 0.75%. The amount is 0.32%, and the effect of aggregate mud content (0.6%, 1.4%, 2.5%, 3.0%, 3.4%, 4.4%, 5.4%) on the water reduction rate and hardening of the water-reducing agent in the concrete mixture is studied. The influence of concrete strength can lead to the control limit of sand mud content.
Concrete is prepared according to the actual mix ratio of a certain construction site. Based on the concrete mixture reaching the same slump (100±5) mm, the water reducing rate of the water reducing agent in the concrete is measured. According to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" GB/T50081-2002, the compressive strength of concrete cubes after standard curing for 7 days and 28 days was measured.
3. Results and Analysis
3.1 The influence of sand mud content on water reducing performance of water reducing agent
Sand mud content, high performance water reducing agent mixing The amount affects its water-reducing performance. The mud content of sand and the dosage of naphthalene-based high-efficiency water-reducing agent influence its water-reducing performance.
As the mud content of sand increases, the high-performance water-reducing admixture shows a trend of first slowly decreasing, then rapidly decreasing, and finally stabilizing. When the sand mud content is between 0.0% and 2.5%, the water reduction rate decreases slowly; when the sand mud content increases from 2.5% to 3.4%, the water reduction rate decreases rapidly; then as the mud content continues to increase, Its water reduction rate tends to be stable. When the sand mud content is 3.4%, the water reducing rate of high-performance water-reducing agent is the lowest.
As we all know, the water-reducing mechanism of water-reducing agents is mainly due to the steric hindrance effect. In its molecular structure, groups such as carboxylate groups on the main chain are adsorbed on the surface of cement particles, and the side chains extend into the solution. , thereby achieving the dispersion of cement particles. The adsorption of the soil itself in the sand, the directional adsorption of hydrophobic groups, and the chelation of metal ions in the clay may be the mechanism for the clay to adsorb the water-reducing agent. Due to the adsorption of water-reducing agents by clay, the number of high-performance water-reducing agents that are adsorbed between cement particles and exert steric hindrance, electrostatic repulsion, air entrainment isolation, etc. is reduced. The dispersion effect of water-reducing agents on cement is reduced, and its water-reducing properties are reduced. Effectiveness decreases. The test results show that when the mud content of the sand is low (the dosage is less than 2.5%), the adsorption effect of the clay is not significant, and the water-reducing rate of the water-reducing agent is slightly reduced. As the mud content increases (the dosage is between 2.5% and 3.4%), the number of adsorbed macromolecules increases, and the water-reducing performance decreases significantly. When the mud content is greater than 3.4%, the adsorption effect of the clay tends to be saturated, and the water reducing rate of the water reducing agent also tends to bePressure intensity sensitivity coefficient.
When the water-reducing rate of the naphthalene-based water-reducing agent concrete specimen with a dosage of 0.75% naphthalene-based water-reducing agent is 12.8%, the strength of the concrete specimen mixed with the naphthalene-based water-reducing agent is 12.8%. The water-reducing rate of the water-reducing agent is the most sensitive; when the water-reducing rate of the concrete block with a water-reducing agent content of 0.32% is 23.6%, the strength of the concrete block containing the water-reducing agent has a significant impact on the water-reducing rate. The water reduction rate of the agent is the most sensitive. The sensitivity of the strength of the concrete block mixed with water-reducing agent to the water-reducing rate of the water-reducing agent is much higher than the sensitivity of the strength of the concrete block mixed with naphthalene-based water-reducing agent to the water-reducing rate of the naphthalene-based water-reducing agent.
IV. Conclusion
4.1 When the mud content of the sand is 3.0%~3.4%, the water-reducing effect of the water-reducing agent is most sensitive to the mud content of the sand.
4.2 When the mud content of the sand is 3.4%, the water-reducing effect of the water-reducing agent is more sensitive to the mud content of the sand than that of the naphthalene series water-reducing agent; and as the amount of water-reducing agent increases As the sand mud content increases, the impact of sand mud content on its water-reducing effect increases.
4.3 Large amounts of naphthalene-based water-reducing admixtures are less sensitive to mud content. Contains trace amounts of clay, which can improve the water-reducing effect of naphthalene-based water-reducing agents. </p
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