偏高岭土改善海工混凝土抗氯离子侵蚀性的效果及机理

以不同掺量偏高岭土单掺以及与粉煤灰、矿粉复掺制备混凝土,分别采用浸泡法和RCM法测试混凝土氯离子扩散系数,采用压汞法测试混凝土的孔结构;同时制备相应掺NaCl水泥净浆,采用自动电位滴定仪测试水泥浆中总氯离子和游离氯离子量,计算氯离子固化率,并通过XRD法分析其物相组成。结果表明,偏高岭土可显著降低混凝土氯离子扩散系数,其与粉煤灰或矿粉复掺时效果更优,且与粉煤灰复掺时对后期氯离子扩散系数的降低作用显著;偏高岭土提高了水泥浆对氯离子的固化率,提高掺量可改善固化效果;偏高岭土复掺粉煤灰或矿粉进一步增强了固化效果,且与粉煤灰复掺效果最优;偏高岭土细化了混凝土孔结构,降低了毛细孔含量,促进了含氯水泥浆中F盐的生成,从减少氯离子传输通道和提高氯离子固化作用两方面改善海工混凝土的抗氯离子侵蚀性能。     

钢纤维和聚丙烯粗纤维对活性粉末混凝土强度和延性的影响

众所周知,混凝土强度越高,脆性越显著,特别是超高强度混凝土。本文就钢纤维和聚丙烯粗纤维对掺偏高岭土活性粉末混凝土抗压强度和延性的影响进行了研究,结果表明:掺入一定量的钢纤维,可以改善混凝土内部孔隙结构,延迟和阻碍裂缝的形成和发展,从而提高混凝土的抗压强度,改善混凝土的脆性;掺入一定量的聚丙烯粗纤维,混凝土强度不会提高,但具有改善混凝土脆性的作用。     

偏高岭土对混凝土抗碳化性能的影响

为了提高混凝土的抗碳化性能,在混凝土中掺入偏高岭土并进行碳化实验.实验结果表明:随着偏高岭土掺量的增加,混凝土的抗碳化能力也相应的提高了,且当矿物掺合料总掺量为35%,其中偏高岭土掺量为15%时,混凝土抗碳化能力最大的提高率达到38.02%.实验结果可为提高混凝土抗碳化性能提供一种新的思路.     

掺石灰石粉混凝土的性能及其改善途径

采用不同掺量的石灰石粉取代水泥配制混凝土,同时配制复掺6%偏高岭土和20%石灰石粉的混凝土,并采用相同的胶凝材料体系制备水泥净浆,开展Na_2SO_4溶液浸泡试验。测试了混凝土抗压强度,采用RCM法和硫酸盐干湿循环侵蚀试验分别测试混凝土的氯离子扩散系数和抗硫酸盐侵蚀性,采用MIP法测试混凝土孔结构,进一步采用SEM观察浸泡后净浆试件的微观形貌。结果表明,石灰石粉对混凝土抗压强度、抗氯离子渗透性和抗硫酸盐侵蚀性均有一定的不良影响。采用偏高岭土与石灰石粉复掺可以有效提高掺偏高岭土混凝土的强度、抗氯离子渗透性和抗硫酸盐侵蚀性。其机理主要在于优化了混凝土孔结构,降低了有害离子在混凝土中的传输速度,阻止了混凝土在硫酸盐环境中钙钒石、石膏等侵蚀产物的形成。     

插层材料-偏高岭土复合改性混凝土抗硫酸盐侵蚀

以插层材料(LDHs)和偏高岭土(MK)为主要功能组分改善混凝土耐久性能,针对混凝土的工作性能、力学性能和抗硫酸盐侵蚀性能进行研究。结果表明,LDHs材料可有效吸附外界侵入的硫酸根离子,而MK在混凝土中的火山灰特性可促进水泥的水化过程,改善混凝土内部的显微结构。LDHs与MK的复合可实现吸附硫酸根离子和优化孔结构的叠加效应,从而大幅度增强混凝土的早期抗压强度和抗硫酸盐侵蚀性能。     

LDHs-MK复合改性混凝土抗氯离子渗透性能的研究

以LDHs材料和偏高岭土为主要功能组分开展混凝土试验,针对混凝土的工作性能、力学性能和抗氯离子渗透性能进行研究。结果表明,偏高岭土在混凝土中的火山灰作用可促进水泥的水化进程,改善混凝土内部的显微结构,而LDHs材料可有效固化外界侵入的氯离子,从而在混凝土内部形成一个防御屏障。LDHs与MK的复合可实现固化氯离子和优化孔结构的叠加效应,从而大幅度增强混凝土的抗压强度和抗氯离子渗透性能。     

偏高岭土和硅灰影响砂浆干燥收缩的对比研究

采用偏高岭土、硅灰取代水泥制备砂浆,经不同预养护时间后测试砂浆干燥过程中的收缩和质量损失,对比分析偏高岭土和硅灰对砂浆干缩的影响。结果表明,偏高岭土和硅灰均减小了砂浆90d干缩,偏高岭土改善砂浆抗干缩性更优,延长预养护时间有利于提高偏高岭土和硅灰降低砂浆干缩的效果;在一定掺量范围内,随掺量上升,掺偏高岭土砂浆干缩不断变小,掺硅灰砂浆则先变小后变大;硅灰和偏高岭土砂浆中复掺粉煤灰能进一步改善砂浆抗干缩性,而复掺矿粉则不利于降低砂浆干缩。预养护3d的偏高岭土砂浆和硅灰砂浆质量损失在一定范围内与干缩呈线性关系,粉煤灰和矿粉的加入降低了线性拟合度;预养护14d的砂浆干燥质量损失与干缩线性关系良好。     

偏高岭土对水泥净浆火山灰效应强度贡献率的影响

根据蒲心诚教授提出的偏高岭土火山灰效应定量分析方法,进行了偏高岭土对水泥净浆(以下简称净浆)火山灰效应强度贡献率(以下简称强度贡献率)的影响研究.结果表明:随着偏高岭土掺量的增加,其净浆强度贡献率增加;随着养护龄期的增加,其净浆强度贡献率呈现先减少后增加的趋势,且7,d时出现最低值;3、28,d时小粒径偏高岭土(2.5和3.75,μm)的净浆强度贡献率明显高于7,d时的值,这说明偏高岭土火山灰效应主要是发生在早期(3,d)和后期(28,d);而大粒径偏高岭土和补充激发剂则有利于提高其中期(7,d)净浆强度.     

无机矿粉对碱激发碳酸盐胶凝材料性能的影响

研究了矿渣、粉煤灰和偏高岭土时碱激发碳酸盐胶凝材料的强度、抗渗性能以及凝胶时间的影响，探讨了该材料浆体的流变特性。研究表明：1)矿渣可大幅度提高该材料的强度和抗渗性能，但会显著缩短凝胶时间；偏高岭土有利于强度的提高，但时抗渗性能和凝胶时间的影响不显著；粉煤灰时这些性能的影响均不显著；2)无机矿粉复合后，可使材料28d的抗压强度达43MPa以上，抗渗压力达1.5MPa以上；3)该胶凝材料的浆体为宾汉型流体；4)该胶凝材料中掺加粉煤灰，其浆体的流动性优于掺加矿渣和偏高岭土的浆体流动性。     

碱激发S-MK复合固化剂固化黏土早期强度试验研究

采用偏高岭土对钢渣进行成分增补,同时使用氢氧化钠激发钢渣-偏高岭土(S-MK)复合固化剂对黏土进行固化处理,并在自然条件下养护7 d,研究S-MK复合固化剂固化黏土早期强度特性和各组分材料的最优配比.结果表明:固化黏土的早期抗压强度随着偏高岭土含量的增加表现为先增加后减小,偏高岭土掺量存在临界值,固化土早期抗压强度增长趋势平缓;固化土早期强度随着NaOH浓度的增加而增加,早期强度增长趋势表现为随浓度先平稳发展而后迅速增长,最后趋于平稳;当NaOH和偏高岭土共同作用时,偏高岭土掺量的临界值,随着NaOH浓度的增大而增大,且当NaOH浓度为7％、偏高岭土掺量10％时,试件达到最大抗压强度.     

Properties of High Volume Fly Ash Concrete Compensated by Metakaolin or Silica Fume

The compressive strength and dynamic modulus of high volume fly ash concrete with incorporation of either metakaolin or silica fume were investigated. The water to cementitious materials ratio was kept at 0.4 for all mixtures. The use of high volume fly ash in concrete greatly reduces the strength and dynamic modulus during the first 28 days. The decreased properties during the short term of high volume fly ash concrete is effectively compensated by the incorporation of metakaolin or silica fume. The DTA results confirmed that metakaolin or silica fume increase the amount of the hydration products. An empirical relationship between dynamic modulus and compressive strength of concrete has been obtained. This relation provides a nondestructive evaluation for estimating the strength of concrete by use of the dynamic modulus.     

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5%,10% and 20% metakaolin were prepared at a water/cementitious material ratio (W/C) of 0.30.In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison.The specimens were cured in water at 27℃ for 3 to 90 days .The results show that at the early age of curing(3 days and 7 days),metakaolin re-placements increase the compressine strength ,but silica fume replacement slightly reduces the compressine strength.At the age of and after 28 days ,the compressive strength of the concrete with metakaolin and silica fume replace-ment increases.A strong reduction in the total porosity and average pore diameter were observed in the conctete with MK 20% and 10% in the first 7 days.     

添加不同纤维的高性能混凝土力学性能试验

通过试验研究了弹性模量具有明显差异的3种纤维对于混凝土的力学性能改善所起的作用,以及钢纤维、碳纤维和聚丙烯纤维单掺或复掺对于混凝土的抗压强度、劈裂抗拉强度和弹性模量的影响。结果表明：添加0．5％高弹性模量的钢纤维对于混凝土的强度和弹性模量均有提高作用,复掺0．3％钢纤维和0．2％碳纤维的混凝土抗拉强度的提高大于抗压强度;添加0．5％钢纤维的混凝土HPC-2的弹性模量最大,比基准混凝土提高6．5％;添加0．2％聚丙烯纤维的混凝土HPC-3的弹性模量最小,且小于基准混凝土;此外,混凝土抗压强度的影响程度与纤维的弹性模量的关系更为直接,混凝土劈裂抗拉强度的改善与纤维的抗拉强度的关系更为直接,纤维的弹性模量与基体弹性模量的比值,对复合材料的弹性模量有直接的影响。     

Effects of Polypropylene Fibers on the Physical and Mechanical Properties of Recycled Aggregate Concrete

The viability of using polypropylene fibers(PPF) in concrete was largely studied. Yet, few of the existing research studies investigated the effects of PPF on the properties of concrete containing recycled concrete aggregate(RCA). Mixes with different RCA replacement ratios and different PPF content were designed and tested. The test results showed that the addition of PPF did not change significantly the compressive strength and the density of the concrete, but slightly decreased its modulus of elasticity and Poisson's ratio. The drop in the splitting tensile strength and the flexural strength due to RCA inclusions was to a large extent compensated by the PPF addition. The water absorption decreased and the percent voids increased with increased PPF addition. Correlations between the RCA content, the PPF content and the properties of concrete were studied. Useful regression models were proposed to predict the properties of concrete in relevant ranges of RCA and PPF content.     

单轴受压下再生混凝土的损伤特性研究

利用超声检测技术,以超声波波速的衰减来度量损伤,对单轴受压条件下不同再生粗骨料取代率再生混凝土的损伤进行实时超声试验。通过试验研究了不同再生粗骨料取代率下再生混凝土损伤随单轴压应力的变化规律.试验结果表明再生粗骨料取代率对单轴压应力下混凝土损伤影响显著,且不应忽视混凝土在极限压应力以前的损伤。在考虑单轴压应力、再生混凝土初始强度影响因素下,建立了再生混凝土损伤关系模型。     

高性能再生骨料混凝土的基本性能试验研究

对高性能商品再生骨料混凝土的基本性能进行了试验研究，试验结果表明：采用常规材料和适当的途径完全可以使再生骨料混凝土实现高性能化，高性能再生骨料混凝土的抗压强度、抗拉强度均稍低于高性能天然骨料混凝土，而其弹性模量明显低于高性能天然骨料混凝土且随强度的提高而提高。试验显示再生骨料混凝土的破坏基本是界面破坏，并通过回归分析得出了高性能再生骨料混凝土的轴心抗压强度与立方体抗压强度之间的关系以及弹性模量的参考计算公式。     

尾矿砂塑性混凝土的力学特性

针对塑性混凝土具有弹性模量低、抗渗性及塑性变形特性良好等特点,利用尾矿砂配置了不同尾矿砂砂率和不同水泥掺量的塑性混凝土,对尾矿砂塑性混凝土试件分别进行了立方体抗压强度、轴心抗压强度以及弹性模量等试验.利用极差分析探讨了砂率和水泥掺量等对尾矿砂塑性混凝土的立方体抗压强度、轴心抗压强度以及弹性模量的影响,得到了立方体抗压强度、轴心抗压强度以及弹性模量随砂率和水泥掺量的变化规律.试验结果表明,尾矿砂塑性混凝土立方体抗压强度和轴心抗压强度随砂率的增加而降低,随着水泥掺量的增加,其立方体抗压强度和轴心抗压强度均逐步增大,弹性模量在砂率为50%处达到最大,随着水泥掺量的增加其弹性模量也逐步增大.     

钢纤维自密实混凝土抗压性能试验研究

通过立方体试块的抗压试验,研究了钢纤维体积率、钢纤维类型、浇筑方式、粉煤灰置换率对自密实混凝土抗压强度的影响.结果表明,钢纤维提高了自密实混凝土的抗压强度;在钢纤维体积率的一定范围内,振捣改善了钢纤维对自密实混凝土抗压强度的增强效果;自密实混凝土的抗压强度随着粉煤灰置换率的增加而降低,随着龄期的增长而逐渐提高.在试验研究的基础上,给出了粉煤灰置换率为20%,30%的自密实混凝土立方抗压强度随龄期变化的计算公式.     

基于试验二维随机骨料再生混凝土抗压强度研究

制作42个再生混凝土立方体试块并测试其立方体抗压强度,基于二维随机骨料理论推导符合试验用粗骨料级配的二维骨料分布曲线,生成二维随机骨料混凝土有限元模型模拟其抗压强度并与试验结果进行对比.结果表明：再生混凝土抗压强度总体上随再生粗骨料取代率的上升而降低,但再生粗骨料取代率为50%时,试验与有限元模拟结果均存在强度升高的变异现象.随着再生粗骨料取代率的上升,再生混凝土抗压强度峰值应力对应的平均应变有所延后.     

Self-healing of cracks in concrete with various crystalline mineral additives in underground environment

Cracks can deteriorate mechanical properties and/or durability of concrete. A few studies have shown that, cracks can autogenously heal under a certain conditions besides the traditional passive repair with a deliberate external intervention. For underground concrete structures, the presence of water, as a necessity for chemical reactions of the healing additives, is beneficial to healing concrete. In this paper, a natural healing method by mineral additives was developed according to the chemical and physical characteristics of underground environment. The healing capacity of three different crystalline mineral materials classified namely, carbonate, calcium sulphoaluminate expansive agent and natural metakaolin due to permeation- crystallization, expansion and pozzolanic reaction, has been assessed from the mechanical properties, referring to the relative elastic modulus, the strength restoration, and the water permeability of the healed specimens. In addition, the morphology of the healing products in the vicinity of the crack was observed. The results indicate that the specimens incorporated with the three mineral additives show different healing capacity according to the improved mechanical properties and permeability. The permeability of the host matrix decreased a lot after crack healing by natural metakaolin followed by carbonate whereas no noticeable improvement of water permeability has been observed for the specimens mixed with expansive agent. The specimens incorporated with carbonate show the best mechanical restoration in terms of relative elastic modulus and compressive strength. Although the dominate element is CaCO3 by reaction of CO32-, either from the dissolved CO2 or from the additives, and Ca2＋ in the cementitious system to fill the cracks, the healing capacity depends greatly on the morphology and the properties of the newly formed products.