Effect Of SAP On Mechanical Properties And Shrinkage Cracking Of Expanded Concrete

Super Absorbent Polymer(SAP)is a new type of internal curing material.It has strong water absorption capacity and strong water retention capacity.The water-absorbing SAP will absorb or release water in the concrete with the change of internal humidity.To improve the internal humidity of the concrete,the method is to maintain the concrete.The application of internal curing technology in concrete has attracted much attention.In the durability problem of concrete,shrinkage cracking is the most common problem.Although the use of expansion agent can improve the shrinkage of ordinary concrete,it is more suitable for water cement.The effect of low high-strength concrete is not obvious,because if the expansion agent is to play its role,it needs to ensure sufficient water for the reaction.Secondly,due to its high degree of compactness,traditional curing methods are difficult to achieve the expected curing effect,and concrete curing technology is one of the effective ways to solve these problems.In this paper,in the case of expansive concrete,it is mixed in a dry blending manner to study the effect of SAP content on the mechanical properties and shrinkage cracking of different water-to-gel ratio expansion concrete,and the reasonable dosage range of SAP is obtained,which is the actual engineering of SAP.The application provides an important reference basis;the main research contents and methods of this paper are as follows:(1)Water absorption performance tests were carried out on SAPs of four particle sizes(A(0.3-0.4 mm),B(0.2-0.3 mm),C(0.1-0.125 mm),D(<0.074 mm)),and it was found that In the first three minutes,SAP has the fastest water absorption rate and can reach the water saturation state within 60 minutes.The SAP with the particle size of 0.2-0.3mm has the best water absorption performance,and its water absorption rate is fast and the water absorption is large.Therefore,the particle size is selected.The SAP conducted subsequent experimental studies.(2)SAP’s super absorbent capacity will adversely affect the slump of concrete.Before the test,the cement paste fluidity test and concrete slump test will be carried out to determine the conditions without affecting the fluidity and slump.The reasonable dosage of SAP in concrete ranges from 0.1% to 0.5%.(3)Study the effect of SAP on the mechanical properties of expansive concrete,mainly through the concrete compressive strength test.For expansive concrete,when the water-binder ratio is the same,with the increase of SAP content,the compressive strength of expansive concrete first increases and then decreases,that is,SAP has a reasonable amount of content inside the expansive concrete,which is beyond reasonable.Within the range of the amount of the concrete,the compressive strength of the expanded concrete will increase negatively.When the water-to-binder ratio of the expanded concrete is different,the lower the water-to-binder ratio,the more obvious the effect of SAP,and the reasonable dosage range of SAP decreases with the decrease of the water-to-binder ratio;according to the compressive strength analysis of the expanded concrete,0.32 The optimum blending ratios of 0.35 and 0.38 for water-tobinder ratio SAP are 0.1%,0.3%,and 0.3%,respectively.(4)The influence of SAP on the shrinkage rate of cement paste is: SAP addition can effectively improve the shrinkage rate of cement paste.With the increase of SAP content,the shrinkage rate of cement paste is gradually reduced,and water gel.The lower the ratio,the more effective SAP is in improving the shrinkage of cement paste.In the test of early self-shrinkage of expanded concrete by non-contact method,the incorporation of SAP can better inhibit the self-shrinkage phenomenon of expanded concrete.The test data show that the self-shrinkage of expansive concrete mainly occurs in the first three days of curing age.With the increase of SAP content,the self-shrinkage phenomenon of expansive concrete is gradually weakened.(5)According to the hydration heat test of cement slurry,the peak temperature of the hydration reaction of cement slurry generally appears around the 13 th hour.At this moment,the hydration reaction of cement slurry is the most intense,and the hydration reaction releases the most heat;the addition of SAP can be reduced.The heat released by the early hydration reaction of the cement slurry,and the more the amount of SAP is added,the greater the reduction.(6)In the influence of SAP on the crack resistance of expansive concrete in the ring method,as the amount of SAP increases,the cracking time of the expansive concrete is pushed back,and the total number of cracks decreases,and the length and width of the crack are also reduced.The test results show that the addition of SAP can improve the crack resistance of expanded concrete,and the more the amount of SAP is,the more obvious the effect of improving the cracking of expanded concrete.(7)In the influence of SAP dosage on the pore structure of expansive concrete,it is found by the method of wire method and mercury intrusion test that the average pore diameter of expansive concrete increases with the increase of SAP content,and the most suitable pore diameter of expanded concrete First increase and then decrease,the porosity of the expanded concrete gradually increases.As a result of the analysis,an excessive amount of SAP adversely affects the pore structure of the expanded concrete,resulting in a decrease in the strength of the concrete.