Influence And Mechanism Of Seawater On Hydration Process Of Cement-based Composites

Due to the increasing shortage of building materials,seawater and sea sand have been used in many places at home and abroad to replace freshwater and river sand as building materials.However,there are still many problems in directly utilizing marine resources,so it has become a hot research topic.about how to apply seawater and sea sand to practical projects.Many researchers at home and abroad have already carried out relevant research,but most of the current results are concentrated on the mechanical properties and durability of seawater/sea sand concrete,and a systematic theoretical of the influence law and mechanism of seawater on cement hydration process in cement-based composites.system has not yet been formed.Therefore,this paper intends to study the influence law and mechanism of seawater and the main components of seawater including NaCl and Na₂SO₄ on the hydration process of cement-based composites by setting time test,mechanical strength test,hydration heat experiment and microscopic testing technology.Provide technical support for the practical engineering application of seawater in cement-based composites.The main research contents are as follows:Through the setting time test,it was found that seawater?SW?accelerates the hydration process of the cement,and the acceleration is mainly in the final setting time.Through hydration heat experiments,both SW and Cl^-accelerate the hydration heat release process of cement,while the SW group promotes the hydration heat release process more than the Cl^-group,indicating that SW promotes the cement hydration process with the complexation of various components in seawater.Through the MIP test,it was found that the seawater incorporation reduced the total porosity of the cement matrix and improved the internal pore structure during the hydration period from 1d to 28d,but the improvement effect was reduced in the later stage.The test of SEM-EDS shows that the incorporation of seawater changes the shape and size of the hydration product to some extent,and its effect varies with age.By analyzing the test results of compressive flexural strength,it can be seen that the incorporation of SW and NaCl promotes the strength,and the promotion is mainly before the hydration time 1d,and the promotion of compressive strength increase with the Cl^-increase.The effect of Na₂SO₄ on the strength development was promoted at12h-1d.The promoting effect began to decrease after 12h hydration,and its promoting effect decreased with the increase of the dosage.It was inhibited at 3d-28d and its inhibitory effect was increased with the amount of Na₂SO₄ increases.At the same time,the effect of NaCl on the strength is greater than that of Na₂SO₄,and the results show that in addition to NaCl and Na₂SO₄,there are still substances affecting the development of compressive strength.After 3 days of hydration time,the strength of SW group and NaCl group developed slowly and the intensity gradually approached the pure water group.The results still indicate that the intensity increase of each test group is mainly reflected in 1d-3d.The test of XCT results are consistent with the strength test results.Quantitative analysis of XRD and TGA results showed that the promotion of Ca?OH?₂ by SW and NC was mainly before the hydration time 1d,and the promotion of CH formation by NC group increased with the increase of the amount of NC.Na₂SO₄promoted the formation of CH at 4h-1d hydration,and its promotion effect was the highest before hydration for 4h,and the inhibition effect increased with the increase of the amount of Na₂SO₄ during the 3d-28d of hydration.By analyzing the percentage increase of CH in different hydration time intervals,it is found that the CH generation rate of SW group,NC group and PW group decreases with the increase of age,and the effect of Cl^-on CH content after 3 days of hydration is small.The CH generation rate of NS increased after 3d hydration,and the hydration degree of NS group was still lower than other test groups.The SW group promoted the formation of CH more than the NC group and the NS group,and the development trend of CH content was consistent with the intensity growth trend.