碱式硫酸镁水泥的基本理论及其在土木工程中的应用技术研究

发布时间：2018-09-06 13:18

【摘要】：硫氧镁水泥具有轻质、碱度低、防火、装饰效果好等优点,但其存在强度低、抗水性差的缺点,限制了其大规模应用。本文采用外加剂技术制备了一种高强、抗水、抗腐蚀、抗碳化及具有良好护筋性能的碱式硫酸镁水泥,并系统研究了碱式硫酸镁水泥的物相结构、水化产物、力学性能、耐久性能及在土木工程中的应用技术,取得主要研究成果如下:1.合成了纯的碱式硫酸镁新相,结合初始原料配比、XRD分析、化学分析和热分析结果,确定其组成为5Mg(OH)2·Mg SO4·7H2O,形貌为针杆状晶体;在Topas 4.2软件中采用模拟退火法解析出5Mg(OH)2·Mg SO4·7H2O为单斜晶体,所属空间群为C121,晶胞参数为:a=15.14?、b=6.31?、c=10.26?、β=103.98o,晶体密度为1.87 g/cm3。该晶体是由Mg-O八面体为骨架,SO42-、H2O和OH-为填充离子(或分子)的层状结构。2.外加剂K2、K7、K8、K19、K21、K27、K30、K31、K32和K34均可明显改善碱式硫酸镁水泥的强度。硫酸镁溶液浓度一定时,碱式硫酸镁水泥的强度随Mg O/Mg SO4摩尔比增加而提高。相同摩尔比时,碱式硫酸镁水泥的强度高于氯氧镁水泥,且碱式硫酸镁水泥不易出现吸潮返卤现象。与硅酸盐水泥相比,碱式硫酸镁水泥具有更低的孔隙率;与氯氧镁水泥相比,碱式硫酸镁水泥的孔隙溶液浓度更低,且电阻率远大于氯氧镁水泥。碱式硫酸镁水泥的强度高于硫氧镁水泥的主要原因是其水化完全,且致密的微观结构中含有大量针状5Mg(OH)2·Mg SO4·7H2O。3.传统硫氧镁水泥净浆试件泡水28d后开裂、奔溃,原因是低活性Mg O水化产生结晶应力,破坏水泥结构。碱式硫酸镁水泥具有更加优异的抗水性能,无矿物掺合料时,碱式硫酸镁水泥净浆试件泡水180d的软化系数可达0.85以上。掺加粉煤灰的碱式硫酸镁水泥的抗水性能可进一步提高,泡水180d软化系数可达0.98。原因在于外加剂延缓了Mg O在水中水化的速度,削弱了Mg O水化产生的结晶应力,且强度相5Mg(OH)2·Mg SO4·7H2O的溶解度较低(0.034 g/100 g)。4.碱式硫酸镁水泥与传统硫氧镁水泥相比具有优异的抗水热、抗氯化镁溶液腐蚀、抗碳化和护筋性能。掺加矿渣的碱式硫酸镁水泥在80℃下水热处理14d不出现开裂。浸泡卤水8个月,碱式硫酸镁水泥强度不降反升。碱式硫酸镁水泥在加速碳化环境中,不出现碳化现象。碱式硫酸镁水泥中钢筋锈蚀程度远低于在氯氧镁水泥中的情况。碱式硫酸镁水泥中钢筋的早期锈蚀速率高于硅酸盐水泥,后期逐渐降低,甚至会低于硅酸盐水泥中的钢筋锈蚀速率。掺加少量亚硝酸盐阻锈剂时,碱式硫酸镁水泥中钢筋几乎不锈蚀。5.碱式硫酸镁水泥有望大规模应用于土木工程。以碱式硫酸镁水泥为主要胶凝材料制备的闭孔膨胀珍珠岩砂浆、化学发泡、物理发泡等保温材料,具有强度高、密度低、保温效果好、防火等性能。内掺40%粉煤灰的碱式硫酸镁水泥胶砂试件的28d抗压强度达57.7MPa,达到52.5R硅酸盐水泥的强度,抗折强度达16.2MPa,是62.5硅酸盐水泥的2倍。以碱式硫酸镁水泥为胶凝材料可制备出C20~C50等强度等级的砂石混凝土,且其抗冻性优于普通硅酸盐水泥混凝土。以碱式硫酸镁水泥为可制备具有韧性好、承载力高的钢筋混凝土构件,其中钢筋的锈蚀速率较低,四个月内钢筋的锈蚀率仅为2‰~3.5‰,平均锈蚀速率仅为氯氧镁水泥混凝土中的2‰左右,是矿渣硅酸盐水泥混凝土中的6‰左右。
[Abstract]:Magnesium oxysulfate cement has the advantages of light weight, low alkalinity, fire protection and good decorative effect, but its disadvantages of low strength and poor water resistance limit its large-scale application.In this paper, a kind of high strength, water resistance, corrosion resistance, carbonization resistance and good reinforcement protection performance of magnesium oxysulfate cement was prepared by using additive technology. The main research results are as follows: 1. Pure basic magnesium sulfate new phase was synthesized and its composition was determined to be 5Mg(OH)2.Mg SO4.7H2O by XRD analysis, chemical analysis and thermal analysis. In Topas 4.2 software, 5Mg(OH)2.Mg SO4.7H2O was determined as monoclinic crystal by simulated annealing. The space group belongs to C121. The cell parameters are: a = 15.14?, B = 6.31?, C = 10.26?, beta = 103.98o, and the crystal density is 1.87 g/cm 3. The crystal is a layered structure with Mg-O octahedron as skeleton, SO42-, H2O and OH - as filling ions (or molecules). K2, K7, K8, K19, K21, K27, K30, K31, K32 and K34 can obviously improve the strength of basic magnesium sulfate cement. When the concentration of magnesium sulfate solution is constant, the strength of basic magnesium sulfate cement increases with the increase of molar ratio of Mg O/Mg SO4. At the same molar ratio, the strength of basic magnesium sulfate cement is higher than that of magnesium oxychloride cement, and basic magnesium sulfate cement is not easy to appear. Compared with Portland cement, basic magnesium sulfate cement has lower porosity; compared with magnesium oxychloride cement, basic magnesium sulfate cement has lower concentration of pore solution, and its resistivity is much higher than that of magnesium oxychloride cement. There are a lot of acicular 5Mg(OH)2.Mg SO4.7H2O.3 in the microstructure. The traditional magnesium sulfate cement paste cracks after soaking for 28 days, which is due to the crystallization stress produced by the hydration of low active Mg O and the destruction of cement structure. The softening coefficient of alkaline magnesium sulfate cement mixed with fly ash can be further improved, and the softening coefficient can reach 0.98 after soaking for 180 days. The reason is that the admixture retards the hydration rate of Mg O in water, weakens the crystallization stress produced by hydration of Mg O, and the solubility of the strength phase 5Mg(OH)2.Mg SO4.7H2O is lower (0.03). 4 g/100 g). 4. Compared with the traditional magnesium sulfate cement, the basic magnesium sulfate cement has excellent hydrothermal resistance, resistance to magnesium chloride solution corrosion, resistance to carbonization and reinforcement protection properties. The basic magnesium sulfate cement with slag does not crack after hydrothermal treatment at 80 C for 14 days. After soaking in brine for 8 months, the strength of the basic magnesium sulfate cement does not decrease but rises. In the accelerated carbonation environment, there is no carbonation. The corrosion degree of steel bars in the basic magnesium sulfate cement is much lower than that in the magnesium oxychloride cement. Basic magnesium sulfate cement is expected to be widely used in civil engineering. Closed-cell expanded perlite mortar, chemical foaming, physical foaming and other insulation materials made of basic magnesium sulfate cement as the main cementing material, have high strength, low density, good insulation effect, fire protection and other properties. The 28-day compressive strength of the basic magnesium sulfate cement mortar with 40% fly ash is 57.7 MPa and 52.5 R Portland cement. The flexural strength is 16.2 MPa, twice that of 62.5 Portland cement. The sand-stone concrete with strength grades of C20~C50 can be prepared by using basic magnesium sulfate cement as cementing material, and its frost resistance is better than that of ordinary silicon cement. Portland cement concrete. Making use of basic magnesium sulfate cement as a kind of reinforced concrete component with good toughness and high bearing capacity, the corrosion rate of steel bars is low, the corrosion rate of steel bars is only 2~3.5, the average corrosion rate is only about 2 in magnesium oxychloride cement concrete, which is 6 in slag Portland cement concrete. About a thousand per thousand.
【学位授予单位】：中国科学院研究生院(青海盐湖研究所)
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TQ172.1

【参考文献】