Study On The Autogenous Shrinkage And Mechanism Of High Strength Concrete With Super Absorbent Polymer

High-strength concrete, characterized with large amount of cement and low waterbinder ratio, has a high hydration heat, autogenous shrinkage and easily early-cracking, which have dramatically caused a poor effect on its service performance and durability, leading to a restrictedapplication in practical engineering.Super Absorbent Polymers(SAP) is a kind of polymer materials which has strong water absorption groups such as carboxyl and hydroxyl, and a three-dimensional network structure. Meanwhile, the SAP can fix free water inside the polymer network through water hydration and swelling effect. Once the SAP was applied to the High-strength concrete, a good curing condition can be achieved. In general, SAP, as a kind of internal curing materials, caneffectively inhibit the autogenous shrinkage and improve anti-cracking performance of concrete, which has a broad application prospect. However, how to make a better use of the water absorption and release of SAP and effectively control the autogenous shrinkage of high-strength concrete, is the fundamental research point to its widespread application. Therefore the influence of the SAP on the properties of high strength concrete has a great significance.In this paper, types of super absorbent resins, as well as its water absorption, contents and extra water-binder ratios were taken into account on the autogenous shrinkage, mechanical property and durability of the high-strength concrete. what’s more, mechanism of the influence of SAP on the properties of concrete was also investigated by using relative humidity monitoring, mercury intrusion porosimetry(MIP), X-ray diffraction(XRD), scanning electron microscope(SEM) and microcalorimetric. The main results can be concluded as follows.① In the condition of the same particles of the four types of SAP, the water absorption ability was mainly affected by the synthetic process, ratio of the raw material and also the kind of the solutions. The ratio of pores solutions absorption of D type SAP obtained by solution polymerization was greater than other kinds of SAP obtained by reverse suspension polymerization. Additionally, the ratio of water absorption of the D type SAP prepared by reverse suspension polymerization had a close connection with the using proportion of acrylic acid. According to the results, the ratios of the water absorption of the four kinds of SAP soaked in different solutions were separately 16.6g/g, 10.6g/g, 40.1g/g and 18.0g/g in deionized water, 15.2g/g, 10.9g/g, 35.2g/g and 21.5g/g in tap water, and as well 20.1g/g, 23.8g/g, 26.8g/g and 32.6g/g in simulative pore solutions of cement pastes. According to the water-releasing regulation of the type A cured in the sealed condition, the rate of the water-releasing was relatively significant in the first 3 days, thereafter slowed down.② The appropriate contents of the SAP and the extra water-binder ratio could inhibit the autogenous shrinkage of the concrete. And the greater the ratio of water absorption of the SAP was, the more effective the inhibitory effect was, leading to a significant decrease in autogenous shrinkage about 65.3%. However, in order to avoid the poor effects on the fluidity of the fresh concrete caused by great ratio of water absorption, the contents of SAP with a high ration of water absorption should be appropriately decreased or the low ratio of water absorption of SAP should be used. as a result of comprehensive consideration of the workability, mechanical property, durability and the inhibitory effect on the autogenous shrinkage of the concrete, the type A SAP had an outstanding performance.③ In the case of the same water-binder ratio, autogenous shrinkage of concrete should be deceased with the increasing of the dosage of SAP. Inhibition effect for autogenous shrinkage would be most excellent when using type A, which could makethe reduction of shrinkage compared to the reference increase to 15.7% when the dosage varied from 0.3% to 0.4%. Whilethe decrese of autogenous shrinkage could be merely reduced no more than 9.0% with other three kinds of SAP. With the certain dosage of SAP, enlarging water-binder ratio could make autogenous shrinkage of concrete reduce firstly, but then increase, finally the value of shrinkage was larger than the reference if thevalid water-binder ratio was greater than its. Therefore appropriate additional water-binder ratio should becontrolled seriously when using SAP as a key technologyto reduce autogenous shrinkage of concrete.④ As suction volume of SAP was small in the case of low water-binder ratio, the compressive strength of concrete varied in the small range along with the change of SAP types and water absorption rate. However, in the case of the same water-binder ratio, compressive strength of concrete could be improved because of the decease of effective water-cement ratio with dosage of SAPincreased.With the same dosage of SAP, strength of concrete could be little improved with additional water-cement ratio, but decresed when additional water-cement ratio increase to a certain value.⑤ The incorporation of SAP into the system of cement material could be benefit to the improvement ofdurabilitiesof concrete in a certain extent, such as resistance to chloride ion permeability, anti-freeze performance and carbonation resistance. It could be concluded from Microscopic analysis study that the number of macroporous(> 10mm) in pore structure of cement hydration products with SAP rised, whereas with more closed spherical hole. With the evolution of hydration, as a result of the release of interior water of SAP, further hydration could take place so as to improve the density of hydration products around.