Research On The Effects Of Sustained-Release Polycarboxylate Superplasticizer On Concrete Performance

In recent years,construction projects have developed rapidly in our country,concrete is one of the most important engineering materials,the requirements on workability,durability and so on for the concrete construction in the market are getting higher and higher.The advantages and disadvantages of the polycarboxylate superplasticizer is closely related to the performance of concrete.Low addition,high water reduction,high slump retaining and a series of advantages of a new generation of high performance water reducing agent-polycarboxylate superplasticizer has been used widely.But when transporting concrete at long distances or in hot weather,excessive evaporation of water leads to excessive loss of concrete slump.Therefore,the better stability of the sustained-release polycarboxylate superplasticizer has been rapid development.However,the research on the application performance of sustained-release polycarboxylate superplasticizer is rarely published and its research hasn't formed a complete system.Therefore,it is necessary to further study the effect of concrete raw materials and adding methods of the superplasticizer on the efficiency of the sustained-release polycarboxylate superplasticizer.This not only provides theoretical basis for the better utilize of water reducing and slow releasing properties of the sustained-release polycarboxylate superplasticizer,but also has a positive significance in the popularizing of its use in practical concrete projects.In this paper,the common type polycarboxylate superplasticizer(PC)is used as a reference,the changes in functional groups of sustained-release polycarboxylate superplasticizers(PCS)in different concentrations of alkali solution,the performance of polycarboxylate superplasticizer about different alkali content and C3 A content of cement,different stone powder content,lithology,MB value of artifical sand and different ways to add polycarboxylate superplasticizer were studied by infrared spectroscopy,adsorption,hydration heat,cement paste fluidity and setting time,mortar fluidity,concrete slump and strength test.The mechanism of the effect of various factors on the performance of polycarboxylate superplasticizer is discussed,which is of positive significance to promote the application of polycarboxylate superplasticizer in concrete.The results show:(1)The content of Na2 Oeq increased from 0.67% to 1.13%,the number of groups of PCS decreased,the amount of adsorbed on the surface of cement particles decreased,the initial amount of adsorption decreased less than PC,the fluidity of cement paste and concrete with PCS is reduced,but its fluidity retention is more excellent than the PC.In addition,the initial and final setting time is shortened,the rate of cement hydration is accelerated,the total hydration heat is reduced and the concrete strength is improved.(2)The content of C3 A increased from 8.49% to 11.49%,the amount of adsorbed on the surface of cement particles with PCS increased,the initial adsorption growth rate is lower than the PC,but the adsorption capacity increased significantly than PC over time,the fluidity of cement paste and concrete with PC and PCS is reduced,the decrease of the initial fluidity is more than that of paste with PC.In addition,the initial and final setting time are shortened,the hydration rate of the cement hydration is accelerated,the total heat hydration is increased and the strength of the concrete is improved.(3)When the addition is twice,the smaller the ratio of the first and the second dosage,the more beneficial to maintain fluidity.Comparison of multiple addition and twice addition,when the addtion is four times,the workability retaining of the cement paste and the concrete is more excellent.When the ratio and the number of addition were constant,whether it is added multiple or twice,the later addition time and the larger dosage lead better slump retaining.Multiple addition of PCS is helpful to avoid ing bleeding caused by the lager addition of PCS.(4)With the content of arfitical gravel powder increased from 8% to 18%,the fluidity of mortar and concrete with PCS is decreased,and the strength increased.The concrete of limestone sand is larger than that of pebble concrete,but its strength is lower than that of pebble concrete.When the MB value increased from 1.1 to 2.6,the fluidity of the mortar and the concrete with PC and PCS are reduced,but the sensitivity of the PCS-doped system to the MB value is smaller than that of the PC.Whether it is the increase in the content of stone powder or MB value,the PCS-doped concrete has a better stability than PC-doped concrete.With the increase of MB value,the strength of PCS-doped increased slightly and then decreased.