本文關(guān)鍵詞：海水多因素侵蝕下混凝土力學性能劣化特征　出處：《寧波大學》2014年碩士論文　論文類型：學位論文

  更多相關(guān)文章： 海水腐蝕 混凝土 損傷演化 劣化

【摘要】：海水中含有大量的氯離子、硫酸根離子和鎂離子。這些離子對混凝土的侵蝕作用將會導(dǎo)致混凝土力學性能的劣化以及耐久性的降低。因此,海洋環(huán)境下混凝土結(jié)構(gòu)力學性能的演化成為了該領(lǐng)域研究的熱點問題。本文對混凝土材料在海水多因素(氯離子、硫酸根離子和鎂離子)耦合侵蝕下的強度、動彈模量以及蠕變性能的演化進行了研究。通常情況下,氯離子會侵蝕混凝土中的鋼筋(加強筋),硫酸根離子主要侵蝕混凝土。本文重點研究了氯離子對硫酸根離子侵蝕混凝土作用的影響。通過檢測氯化鈉溶液、硫酸鈉溶液和氯化鈉-硫酸鈉混合溶液腐蝕下的混凝土抗壓強度、動彈性模量以及表面硬度的變化,得到了混凝土材料在侵蝕作用下的力學性能演化結(jié)果。研究結(jié)果表明氯離子在氯鹽-硫酸鹽侵蝕混凝土的交互作用中,對硫酸根離子侵蝕混凝土的影響可分為三個階段。第一階段:氯離子對硫酸根離子侵蝕混凝土的抑制作用隨時間的增長呈單調(diào)遞增趨勢;第二階段:氯離子對硫酸根離子侵蝕混凝土的抑制作用隨時間的增長呈單調(diào)遞減趨勢;第三階段:氯離子對硫酸根離子侵蝕混凝土的抑制作用消失,轉(zhuǎn)變?yōu)榇龠M硫酸根離子對混凝土的侵蝕作用,揭示了氯離子對硫酸根離子侵蝕的抑制-轉(zhuǎn)戾現(xiàn)象。論文在第三和第四章對水泥砂漿在硫酸鈉、硫酸鎂兩種溶液侵蝕下的力學性能進行了研究。通過水泥砂漿侵蝕后動彈性模量以及形貌的變化,分析鎂離子-硫酸根離子耦合侵蝕混凝土的作用機理。在鎂離子和硫酸根離子共同腐蝕下混凝土的損傷可分為三個階段:Ⅰ.填充混凝土內(nèi)部孔隙的第一階段。(延時鈣礬石和氫氧化鎂固體填充混凝土孔隙,導(dǎo)致混凝土力學性能的增強,故也稱該階段為負損傷階段。);Ⅱ.鈣礬石和氫氧化鎂填充導(dǎo)致的混凝土力學性能增強與混凝土內(nèi)部微裂紋劣化并存的“競爭”階段;Ⅲ.混凝土內(nèi)部微裂紋擴展占主導(dǎo)作用的材料劣化階段。實驗結(jié)果驗證了添加粉煤灰不僅降低了混凝土中C3A的含量,同時改善了混凝土的內(nèi)部結(jié)構(gòu),抑制了混凝土的損傷劣化提高了混凝土抗硫酸鹽腐蝕的性能。硫酸鹽侵蝕下混凝土損傷劣化的新模型。該模型采用微裂紋的數(shù)密度表征不同尺度的微裂紋。微裂紋發(fā)展的驅(qū)動力包括兩個方面:遠場荷載和侵蝕內(nèi)膨脹力。根據(jù)混凝土的拉伸強度本文給出了微裂紋的起裂條件,再由微裂紋成核率的“白模型”,得到了損傷驅(qū)動應(yīng)力相關(guān)的微裂紋成核率方程。在假定微裂紋的長大服從Seaman擴展方程的基礎(chǔ)上,結(jié)合微裂紋數(shù)密度演化的平衡方程,得到了特征線上的微裂紋數(shù)密度演化的一階常微分方程。通過對微裂紋的體積積分,得到了混凝土損傷劣化的新模型。該模型的相關(guān)參數(shù)由實驗結(jié)果確定。研究結(jié)果表明:本文得到的損傷劣化模型可以比較好地反映混凝土侵蝕損傷演化規(guī)律。
[Abstract]:Seawater contains a large number of chloride ions, sulfate ions and magnesium ions. The erosion of concrete by these ions will lead to the deterioration of the mechanical properties of concrete and the deterioration of durability. The evolution of mechanical properties of concrete structures in marine environment has become a hot issue in this field. In this paper, the strength of concrete materials under the coupling erosion of seawater (chloride ion, sulfate ion and magnesium ion) is studied. The evolution of dynamic modulus of elasticity and creep properties has been studied. In general, chloride ions will erode the reinforced bars (reinforced bars) in concrete. The effect of chloride ion on the effect of sulfate ion on concrete erosion was studied. The sodium chloride solution was detected. The changes of compressive strength, dynamic elastic modulus and surface hardness of concrete under corrosion of sodium sulfate solution and sodium chloride sodium sulfate mixed solution. The results of mechanical properties evolution of concrete materials under erosion are obtained. The results show that chloride ion is in the interaction of chloride salt and sulfate erosion concrete. The influence of sulfate ion on the concrete erosion can be divided into three stages: the first stage: the inhibition effect of chloride ion on the sulfate ion erosion concrete shows a monotone increasing trend with the increase of time; The second stage: the inhibition effect of chloride ion on sulfate ion erosion concrete shows a monotone decreasing trend with the increase of time. The third stage: the inhibition effect of chloride ion on sulfate ion erosion concrete disappeared and changed to promote sulfate ion erosion effect on concrete. The inhibition of chloride ions on sulfate ion erosion is revealed. Chapter 3 and 4th of this paper discuss the effect of sodium sulfate on cement mortar. The mechanical properties of magnesium sulfate under two kinds of solution erosion were studied. The dynamic elastic modulus and morphology of cement mortar were changed after erosion. The mechanism of mg ~ (2 +) -sulfate ion coupling erosion concrete is analyzed. The damage of concrete can be divided into three stages under the condition of magnesium ion and sulfate ion corrosion together. I. the first stage of filling the inner pores of concrete. Delay ettringite and magnesium hydroxide solid filled concrete pores. The mechanical properties of concrete are enhanced, so this stage is also called negative damage stage. II. The "competitive" stage in which the mechanical properties of concrete filled with ettringite and magnesium hydroxide coexist with the degradation of microcracks in concrete; The experimental results show that the addition of fly ash not only reduces the content of C3A in concrete, but also improves the internal structure of concrete. A new model for damage deterioration of concrete under sulfate erosion is proposed. The model uses the number density of microcracks to characterize microcracks of different scales. The driving forces of grain development include two aspects:. According to the tensile strength of concrete, the crack initiation conditions are given. Based on the "white model" of microcrack nucleation rate, the damage driven stress related microcrack nucleation rate equation is obtained. It is assumed that the growth of microcrack is based on the Seaman propagation equation. Combining the equilibrium equation of microcrack number density evolution, the first order ordinary differential equation of microcrack number density evolution on characteristic line is obtained. A new model of concrete damage deterioration is obtained. The relevant parameters of the model are determined by the experimental results. The results show that the damage deterioration model presented in this paper can better reflect the evolution law of concrete erosion damage.
【學位授予單位】：寧波大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU528
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本文編號：1383131