【作者】 张健；

【导师】 张祖华； 史才军；

【作者基本信息】 湖南大学 ， 土木工程， 2019， 博士

【摘要】 波特兰水泥的生产和应用带来的环境问题日益加剧,碱激发水泥作为一种相对绿色低碳的材料正受到广泛研究,然而碱激发水泥混凝土的耐久性研究并不系统和清晰。本文研究了矿渣/粉煤灰比、激发剂Na₂O浓度、模数（Ms）和水胶比（w/b）对碱激发矿渣/粉煤灰水泥碳化、氯离子结合与抗硫酸盐侵蚀性能的影响,同时与波特兰水泥进行对比,提出了较为合理的测试方法,探究了碱激发水泥的碳化、氯离子结合与抗硫酸盐侵蚀反应机理,为碱激发水泥耐久性模型的建立和测试规范的完善提供了理论依据。本文首先研究了不同影响因素对自然和加速碳化碱激发矿渣/粉煤灰水泥碳化的影响以及碳化反应机理,同时与波特兰水泥对比分析。波特兰水泥碳化前期,Ca（OH）₂和C-S-H凝胶同时碳化,Ca（OH）₂完全消耗后,碳化主要发生在C-S-H凝胶上。而碱激发水泥的碳化机理与波特兰水泥不同,波特兰水泥常用的加速碳化测试方法不能直接在碱激发水泥中使用,特别是对于高钙碱激发体系（矿渣掺量≥60%）。碱激发矿渣/粉煤灰水泥的碳化产物主要与C-A-S-H凝胶的特性有关,水滑石起到CO₂吸附剂的作用,尤其是在自然碳化条件下。合适的矿渣/粉煤灰比可以有效降低碱激发矿渣/粉煤灰水泥凝胶相的碳化速率。碳化后C-A-S-H相脱钙会导致碳酸钙和硅胶的产生,而N-A-S-H相基本不发生改变。增大激发剂Na₂O浓度会使碱激发水泥中C-A-S-H相增多,碳化产生更多的碳酸钙,但对凝胶碳化速率影响不大;Na₂O浓度的增大还会促进粉煤灰的反应,更多N-A-S-H相的产生会降低凝胶碳化速率。w/b的降低（0.5-0.3）能够降低凝胶碳化速率,尤其是对高钙碱激发体系而言,且更多C-A-S-H相的碳化还会导致碳酸钙的量增多。在高钙碱激发体系中,激发剂Ms的增大（0-1.5）虽然能够降低凝胶碳化速率,但是碳化产生碳酸钙的量也会降低,因此合适的激发剂模数的选择还需要根据碱激发水泥碳化前后孔隙率和孔结构的变化进行具体分析。氯离子渗透是混凝土钢筋锈蚀的主要影响因素,而水泥的氯离子结合能力会影响氯离子的传输。本文采用吸附平衡法研究了不同因素对碱激发矿渣/粉煤灰水泥氯离子结合能力以及结合后产物相的影响,为碱激发水泥氯离子渗透模型的建立提供了理论基础。测试结果表明,Langmuir等温线能够较好地表征氯离子结合特性,且氯离子结合能力随着自由氯离子浓度的增大而增大。碱激发矿渣水泥的氯离子结合主要与C-A-S-H相的物理吸附有关,氯离子化学结合产物为Friedel’s盐;随着粉煤灰的掺入,碱激发水泥的氯离子结合能力随着N-A-S-H量的增大而增大,但无Friedel’s盐的产生。另外,碱激发水泥的氯离子结合能力随着w/b的增大显著增大。而激发剂Ms和Na₂O浓度对碱激发水泥氯离子结合能力的影响并不明确,这是因为采用的吸附平衡法在碱激发水泥氯离子结合测试中并不完善,各因素对碱激发水泥氯离子结合的影响很难单独进行分析,尤其是内外OH^-浓度对氯离子结合影响很大。因此,碱激发水泥氯离子结合影响因素以及测试方法还需要进一步研究和完善。硫酸盐侵蚀也是引起混凝土结构退化的重要因素。本文提出了一种较为合理的测试方法来研究Na₂SO₄和MgSO₄溶液对碱激发矿渣/粉煤灰水泥的侵蚀作用,为碱激发水泥在硫酸盐侵蚀环境中的应用提供了理论依据。波特兰水泥在5%Na₂SO₄溶液侵蚀后产生钙矾石,但无石膏的形成;由于Mg²⁺的作用,波特兰水泥在MgSO₄侵蚀后C-S-H脱钙分解,产生大量石膏和钙矾石,试样退化比Na₂SO₄侵蚀更为严重。而碱激发矿渣/粉煤灰水泥的硫酸盐侵蚀机理与波特兰水泥不同。碱激发矿渣水泥在Na₂SO₄侵蚀后虽然能够检测到少量钙矾石和石膏的产生,但C-A-S-H凝胶结构基本不发生改变。Na₂SO₄对碱激发矿渣水泥还有后续激发作用,且粉煤灰的掺入能够抑制钙矾石和石膏的形成。另一方面,碱激发水泥在MgSO₄侵蚀后,C-A-S-H凝胶脱钙分解,产生大量石膏,但未发现主要膨胀产物钙矾石的生成。因此,从反应产物上分析,碱激发矿渣/粉煤灰水泥的抗硫酸盐侵蚀性能要优于波特兰水泥。碱激发矿渣/粉煤灰水泥中,激发剂Ms对Na₂SO₄侵蚀产物种类影响不大。相比NaOH为激发剂（Ms=0）时,Na₂SO₃激发矿渣水泥的抗MgSO₄侵蚀性能更好,这是因为NaOH激发矿渣水泥在MgSO₄侵蚀后会检测到少量钙矾石的产生。激发剂Na₂O浓度和w/b对碱激发水泥Na₂SO₄和MgSO₄侵蚀产物种类影响不大,因此在研究Na₂O浓度和w/b对碱激发水泥抗硫酸盐侵蚀性能的影响时,更需考虑孔隙率或孔结构的影响。更多还原

【Abstract】 The environmental problems caused by the production and application of Portland cement are increasingly serious.As a relatively green and low-carbon material,alkali-activated cement（AAC）has been widely studied.However,the durability of AAC is not clear and needs syetemtatic research.In this paper,the effects of slag/fly ash ratio,Na₂O concentration,modulus（Ms）and water/binder ratio（w/b）on carbonation,chloride binding and sulfate resistance of alkali-activated slag/fly ash cement were studied,and compared with Portland cement.A more reasonable test method to study the carbonation,chloride ion binding and sulfate resistance mechanism of AAC was improved to provide a theoretical basis for the establishment of durability model and the improvement of test specifications.At first,the effects of different factors on natural and accelerated carbonation of alkali-activated slag/fly ash cement were studied.The results showed that at the early carbonation stage of Portland cement,Ca（OH）₂ and C-S-H gel are carbonized simultaneously.After Ca（OH）₂ is completely consumed,carbonation occurrs mainly on C-S-H gel.However,the carbonation mechanism of AAC is different from that of Portland cement.The accelerated carbonation test method of Portland cement cannot be directly applied to AAC,especially for the high-Ca AAC（slag content≥60%）.Carbonation products of alkali-activated slag/fly ash cement are mainly related to the characteristics of C-A-S-H gel,and hydrotalcite acts as CO2 adsorbent,especially under the natural condition.Appropriate slag/fly ash ratio can effectively reduce the carbonation rate of alkali-activated slag/fly ash cement.After carbonation,the decalcification of C-A-S-H phase will lead to the production of calcium carbonates and silica gel,while N-A-S-H phase is basically unchanged.The increase of Na2O concentration can increase the C-A-S-H phase in AAC,and more calcium carbonates generated after carbonation,but it has little effects on the carbonation rate of gel.The increase of Na₂O concentration will also promote the activation of fly ash,and produce more N-A-S-H phase that can reduce the gel carbonation rate.The reduction of w/b（0.5 to 0.3）can reduce the gel carbonation rate,especially for the high-Ca AAC,and more C-A-S-H will be carbonated,which can lead to producing more calcium carbonate.In the high-Ca alkali-activated system,although the increase of Ms（0 to 1.5）can reduce the gel carbonation rate,the amount of calcium carbonates decreases.Therefore,the appropriate Ms also requires specific analysis on the changes of porosity and pore structure before and after carbonation.Chloride penetration is the main factor affecting the corrosion of concrete reinforcement,and the chloride binding capacity of cement will affect the transport of chloride ion.In this paper,the adsorption equilibrium method was used to study the factors on binding capacity of alkali-activated slag/fly ash cement,which provided a theoretical basis for the establishment of chloride penetration model.The results of adsorption equilibrium test of Portland cement and alkali-activated slag/fly ash cement showed that the Langmuir isotherm can well characterize the chloride binding properties,and the chloride binding capacity increases with the increase of free chloride concentration.The chloride binding of alkali-activated slag cement is mainly related to the physical adsorption of C-A-S-H phase.With the incorporation of fly ash,the chloride binding capacity of alkali-activated cement increases with the increase of N-A-S-H,but no Friedel’s salt is detected.In addition,the chloride binding capacity of AAC increases significantly with the increase of w/b.However,the effects of Ms and Na₂O concentration on chloride binding are not clear,because the adsorption equilibrium method used in AAC is not perfect and affected by multiple factors,especially the effect of internal and external OH^-concentration.Therefore,a further study and improvement for the influencing factors of chloride binding and the test methods are needed.Sulfate attack is also an important factor causing the degradation of concrete structure.In this paper,a new test method was proposed to study the erosion effect of Na₂SO₄ and MgSO₄ solution on alkali-activated slag/fly ash cement,providing a theoretical basis for the application of AAC in sulfate environment.The results indicated that ettringite but no gypsum is detected in Portland cement exposed to 5%Na₂SO₄ solution.Due to the action of Mg²⁺,decalcification of C-S-H in Portland cement after MgSO₄ attack resulted in a large amount of gypsum and ettringite,and the degradation of sample is much more serious than Na₂SO₄ attack.The sulfate resistance mechanism of alkali-activated slag/fly ash cement is different from that of Portland cement.In alkali-activated slag cement,a small amount of ettringite and gypsum can be observed after Na₂SO₄ attack,the structure of C-A-S-H gel is basically unchanged.Furthermore,Na₂SO₄ has an activation effect on alkali-activated slag cement.In addition,the incorporation of fly ash can inhibit the formation of ettringite and gypsum.After MgSO₄ attack,the C-A-S-H gel of AAC is decalcified and decomposed,and a large amount of gypsum is formed,but the main expansion product,ettringite,cannot be detected.Therefore,in terms of the reaction products,alkali-activated slag/fly ash cement has a better sulfate resistance than Portland cement.In alkali-activated slag/fly ash cement,Ms has little effects on Na₂SO₄ reaction products.Compared with NaOH as the activator（Ms=0）,Na₂SO₃-activated slag cement has a better MgSO₄ resistance,because a small amount of ettringite is detected after MgSO₄ attack in NaOH-activated slag cement.The influence of Na₂O concentration and w/b on the types of reaction products after Na₂SO₄ and MgSO₄ attack on AAC is not significant.Therefore,the influence of porosity and pore structure should be considered.更多还原