The performance differences between polycarboxylate-based admixtures and naphthalene-based admixtures:
1.The polycarboxylate-based superplasticizer has a higher water reduction rate compared to the naphthalene-based water reducer (solidification ratio ratio: 0.15%/0.6%), and has a larger molecular weight (MW5000/30000). The number of molecules present in each unit of concrete is much less than that of the polynaphthalene sulfonate molecules. The polycarboxylic acid has good compatibility with cement, and the flowability retention performance of freshly mixed concrete is good. It has a good reinforcing effect, good appearance quality, low shrinkage rate, and can significantly increase the usage of mineral admixtures, thereby reducing costs. The total amount of active ingredients, the content of sodium sulfate, and the chloride ion content are low, and they will not crystallize at low temperatures. They are clean and pollution-free, and environmentally friendly. At the same time, polycarboxylate-based superplasticizer can be developed into functional mother solutions according to different concrete requirements. However, due to its high water-reducing rate, it is relatively sensitive to water consumption, and relatively sensitive to the mud content of sand and gravel compared to naphthalene-based ones.
2. Polycarboxylate-based and naphthalene-based superplasticizer compounds exhibit a phenomenon of competing adsorption, causing some polycarboxylate to fail to exert its plasticizing effect, resulting in the failure of carboxylate and even possible premature setting and abnormal phenomena. They cannot be mixed, especially when naphthalene-based superplasticizer compounds are mixed into the carboxylate. Therefore, special attention should be paid when converting naphthalene-based compounds into carboxylate.
3. Low-strength concrete focuses on pumpability and slump retention, so the requirements for additives should have good water retention and thickening performance as well as long-term slump retention performance; high-strength concrete focuses on softness and fluidity, with less slump retention requirements, so the requirements for additives are to have a high water-reducing rate and general slump retention performance. Therefore, it is recommended that mixing stations use different additives for high and low-strength concrete under the condition of having the possibility.
Quality Control of Raw Materials at Entry:
1. Strengthen the inspection of raw materials upon entry. For cement, focus on checking its fluidity (water requirement); for admixtures (such as mineral powder and fly ash), pay special attention to the fineness and water requirement ratio. The fluidity can be tested by adding external agents, and the particle shape can be inspected using a microscope to evaluate the degree of its adsorption to the external agents.
2. Focus on checking the gradation and silt content of sand and stone materials. For washed sand, pay special attention to the gradation; for stone powder sand, pay attention to the silt content (the detection of the MB value). For stone chips, control the gradation and silt content, and keep the test data well recorded. Polycarboxylate superplasticizers are highly sensitive to the silt content of aggregates. This is mainly manifested in the increase in dosage as the silt content increases. Therefore, it is necessary to avoid using aggregates with excessive silt content. The adsorption speed of soil to polycarboxylate-based superplasticizers is 100 times that of cement, and the total amount of carboxylate external agents adsorbed is more than 20 times that of cement.
3. For the inspection of external agents upon entry, it is necessary to follow the testing methods agreed upon by both parties. The testing items can be selected between the fluidity of the pure paste and the concrete mix test. The main focus is on its retention performance, and parallel comparisons should be made.
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