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In engineering construction, water-reducing agents are often combined with retarders to produce composite admixtures with dual retardant and water-reducing effects. These admixtures are then applied to engineering materials to meet the engineering expectations and performance requirements of cement. In particular, by adding water-reducing and retarding composite admixtures to cement mixing trucks and extending the setting time of concrete, cement mixing trucks can travel longer distances, providing greater convenience for long-distance engineering cement construction.
Mr. Huang studied the combination of phosphate and water-reducing agents and found that sodium pyrophosphate, sodium hexametaphosphate, and sodium tripolyphosphate can all be used as retarders in combination with polycarboxylates.
Mr. Liu compared the performance of various retarders in water-reducing agents and concluded that the combination of retarders and water-reducing agents can enhance the later strength of mortar.
Ms. He studied combinations of various retarders and naphthalene-based water reducers and found that combining multiple retarders with naphthalene-based water reducers had good effects and increased the setting time of cement slurry to varying degrees.
Mr. Wang synthesized a phosphate retarder and polycarboxylate superplasticizer (PCE) independently and studied PCE performance at different temperatures. The results showed that phosphate could reduce PCE dispersibility at low temperatures, while it could improve PCE dispersibility and retention performance at both normal and high temperatures.
Mr. Zhang studied the effects of sucrose and homemade retarder HNJ-10 on the flowability of cement mortar. The results showed that as the dosage of sucrose and HNJ-10 increased, the flowability of cement mortar continued to increase within 0-2 hours. Thunder developed a cementing retarder (XCT600) through aqueous solution polymerization, and experiments showed that the product has strong temperature resistance and still has a strong retarding effect on cement at 160 ℃.
The author studied and analyzed the effects of combining hydroxycarboxylic acid retarders (lactic acid, salicylic acid, malic acid, citric acid, tartaric acid) with polycarboxylate superplasticizer on cement slurry flowability and retardation time, providing scientific experimental references for selecting hydroxycarboxylic acid retarders in engineering practice.
Lactic acid, purity 85.0%~90.0%; Malic acid, purity ≥ 99.5%; Citric acid, purity ≥ 99.5%; Tartaric acid, purity ≥ 99.5%; polycarboxylate superplasticizer , solid content: 7.5%; Ordinary Portland cement, strength grade: 42.5R.
The flowability test and standard consistency setting time test of cement slurry are carried out in accordance with national standards GB/T8077-2012 and GB/T1346-2011.
Lactic acid, salicylic acid, malic acid, citric acid, and tartaric acid are the most commonly used types of hydroxycarboxylic acid retarders. Because of their wide availability, sufficient production, and low cost, they were selected as the test objects for this hydroxycarboxylic acid retarder experiment, providing a scientific basis for selecting retarder types in practical engineering.
In organic retarders, the general dosage is not greater than 0.1%. Therefore, in this experiment, the hydroxycarboxylic acid retarder dosage gradient is 0%, 0.01%, 0.03%, 0.05%, 0.07%, and 0.09%, and it is compounded with polycarboxylate superplasticizer. A previous test confirmed the optimal dosage of polycarboxylate superplasticizer for cement slurry flowability. The test showed that the optimal dosage of commercial polycarboxylate superplasticizer, with a solid content of 7.5% and a water reduction rate of 26.2%, is 2.4%, and the cement flowability is best at a water-cement ratio of 0.29.
The degree of influence on the flowability and setting time of cement slurry is that the flowability of cement slurry is relatively minimum when the lactic acid dosage is 0.01%. When the lactic acid dosage increases from 0.01% to 0.05% (in 0.02% increments), flowability increases slightly and reaches an optimal level. After that, increasing the lactic acid dosage to 0.07% and 0.09% results in a relatively small change in cement flowability, with basically no change. Comprehensive analysis shows that lactic acid has little effect on cement flowability and a slight weakening effect at low dosages.
At an initial lactic acid dosage of 0.01%, increasing the dosage in 0.02% increments showed no effect on cement setting time up to 0.09%. In the lactic acid-relatedacid-related experiments, lactic acid exhibited a phenomenon similar to bleeding with increasing dosage, with more water above the cement test block, but no bubbles generated.
Overall, these results indicate that lactic acid is not suitable for use as a retarder in combination with polycarboxylate superplasticizer.
When the initial salicylic acid dosage is 0.01% and increases in a gradient from 0.02% to 0.09%, the cement slurry’s flowability decreases at different rates and shows an overall downward trend. The cement slurry’s flowability is worst at a salicylic acid dosage of 0.07%. When the initial salicylic acid dosage is 0.01% and increases in 0.02% increments to 0.09%, it does not affect cement setting time.
During testing of salicylic acid-related phenomena, we found that different salicylic acid dosages in the retarding test can cause varying degrees of irregular bubble precipitation in the cement test block. When the cement test block is fully set, bubble precipitation can cause an undesirable honeycomb and rough surface above the cement test block, which can affect the block’s density.
From the experimental results above, it can be concluded that lactic acid is not suitable as a retarder in combination with polycarboxylate superplasticizer.
The degree of influence on net slurry flowability and setting time is that the initial flowability of the cement slurry is lowest when the malic acid content is 0.03%, and the flowability of the cement is worst after 60 minutes when the content is 0.09%. When the initial malic acid content is 0.01%, and the dosage increase gradient is 0.02%, the cement setting time steadily increases, and the rate of increase at each stage is similar.
No adverse effects were observed in the cement test block during the malic acid-related test, with no bleeding, bubble precipitation, honeycomb, or rough surface after drying.
These results indicate that malic acid can be used as a retarder in combination with a polycarboxylate superplasticizer.
The influence of net slurry flowability and setting time shows that at 0.01% dosage, the flowability of the cement matrix increases slightly. However, with a 0.02% increase in citric acid dosage, the flowability of the cement matrix deteriorates. Flowability decreases fastest when the citric acid dosage increases from 0.05% to 0.07%, and deteriorates most when the dosage increases to 0.09%.
When the initial dosage of citric acid is 0.01% and the dosage gradient is 0.02% and increased to 0.09%, the slow setting time of the cement test block increases at different growth rates and is divided into three stages: the first stage is when the dosage of the admixture is increased from 0 to 0.01%, the setting time of the test block remains stable and unchanged, and steadily increases from 0.01% to 0.05% and from 0.07% to 0.09%. In the third stage, the citric acid dosage increased from 0.05% to 0.07%; the final setting time was the highest and similar to that of cement at 0.09%.
The experimental results show that increasing citric acid content leads to excessive thickening and severe wall adhesion of the slurry. From the experimental results, although citric acid can be used as a retarder, it significantly reduces cement fluidity. Therefore, when using it, pay attention to dosage to avoid negative effects, such as excessive citric acid dosage leading to a serious decline in overall material workability and resulting in product inspection failure.
The influence of an initial tartaric acid dosage of 0.01% and a dosage-increase gradient of 0.02% to 0.09% on cement flowability shows both a gain effect and a weakening effect, with an overall “W”-shaped trend of irregular influence and almost no effect.
The retardation time of tartaric acid on cement test blocks is different from the other four groups, and its gain effect is the best. The rate of increase in retardation time also steadily accelerates with the increase of dosage gradient (dosage gradient of 0.02%), and the rate of increase in retardation time is also the fastest among the five groups of retarder tests.
The experimental results show no negative impact on the cement test block. From the experimental results, tartaric acid performed best and was the most suitable retarder and polycarboxylic acid compound for practical engineering applications among the five groups.
From the experimental data chart on the influence of 5 groups of hydroxycarboxylic acid compounds on cement flowability, it can be seen that different additives affect cement flowability to varying degrees at different dosages. Overall, however, hydroxycarboxylic acids have little effect, and only the dosages of salicylic acid and citric acid additives are notable.
From the data of cement setting time test, it can be seen that salicylic acid and lactic acid are not suitable as retarders because they do not affect on the cement setting time; Although citric acid has the effect of increasing the setting time of cement, it will have a serious impact on the workability of cement, so a low dosage is sufficient when using it; Malic acid and tartaric acid are the additives that perform well and have the least impact among the five sets of experimental data. Both can be used as retarders, but tartaric acid performs best overall. Therefore, tartaric acid is the most suitable retarder.
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