Experimental Study On Self-toughening Of Quaternary System Magnesium Cementitious Materials And Concrete

This thesis intends to use the chemical products in the ocean as the main raw material to make the quaternary system of magnesium cementitious materials,and the well-graded coral reefs are aggregates and seawater for mixing water to prepare a high-strength magnesium.Coral concrete to meet the construction needs of the island reef project during the development of China's oceans.In this paper,the relevant knowledge of physical chemistry is used to calculate the reaction entropy of magnesium oxysulphate whiskers?MOWs?.The size of the reaction entropy is used to determine whether MOWs is formed in the magnesium cementitious material at normal temperature.Then,using Mg O powder,Mg Cl₂ crystal,Mg SO₄ crystal and seawater as reaction materials,the effect of magnesium sulfate content on the number and appearance of MOWs was studied by changing the amount of Mg SO₄ crystal.Citric acid and ammonium dihydrogen phosphate were selected to modify the magnesium cementitious material,and the modification law of the modifier on the amount and morphology of MOWs was studied.At the same time,the cement specimen with modifier added was studied.Mechanical experiments were carried out to study the influence of modifiers on the compressive and flexural strength of magnesium alkali salt cement and its mechanism.The high-performance magnesium basic salt coral concrete is prepared by using the best ratio of cementing material,uniform coral reef and seawater mixing.Multiple sets of magnesia coral concrete buckling ratio test were designed to study the effects of bone-binder ratio on compressive,flexural and tensile strength of magnesia coral concrete,and the coral concrete was modified with citric acid and ammonium dihydrogen phosphate.To increase the strength of concrete.Through the experimental scheme of the above design,the research shows that when Mg O:Mg Cl₂: Mg SO₄=1:0.1:0.11,the whiskers appear in the cement matrix are the most,and the morphology is the best.At the same time,the amount and morphology of MOWs were improved by using citric acid and ammonium dihydrogen phosphate.The 131,311 and 318 phases of MOWs were found by XRD diffraction analysis.The mechanical experiments found that the 1% content of citric acid can increase the flexural strength of the quaternary magnesium cementitious material by 1.3 times,and can increase the flexural strength of the magnesium cementitious material by 36 per cents.The 0.5%content of ammonium dihydrogen phosphate can increase the flexural strength and compressive strength of the magnesium cementitious material by 24 per cents and 45 per cents,respectively.Finally,through the optimization of the aggregate-binder ratio and the strengthening and toughening of the MOWs to the coral concrete,the magnesia coralconcrete has a concrete compressive strength of 38.6 MPa,tensile strength and flexural strength of 6.75 MPa and 8.95 MPa,respectively.