Experimental Study on Chloride Ion Penetration Resistance of Coal Gangue Concrete under Multi-Factor Comprehensive Action

In order to investigate the chloride ion penetration resistance of coal gangue concrete under multi-factor comprehensive action, the non-steady-state accelerated chloride ion migration test was used to test the chloride diffusion law of coal gangue concrete specimens by crack width, curing temperature and water-cement ratio. Three groups of crack width (0 mm, 0.05 - 0.12 mm, 0.12 - 0.2 mm), three curing temperatures (high temperature 45, medium temperature 25, low temperature 10), three water cement ratios (0.3, 0.4, 0.5) were set in the experiment. The results show that when the curing temperature and water cement ratio are constant, the crack width less than 0.12 mm has little effect on the chloride content and chloride diffusion coefficient. When the crack width is larger than 0.12 mm, the chloride penetration depth increases with the crack width. The resistance to chloride ion penetration of gangue concrete is greatly influenced by the water cement ratio. The influ-ence degree of three factors on chloride ion migration coefficient of gangue concrete is as follows: water cement ratio > crack width > curing temperature.

Spherical cavity-expansion model for penetration of reinforced-concrete targets

The feature of reinforcing bars is introduced into dynamic cavity-expansion theory. Based on the elastic-plastic response penetration model of plain (i.e., unreinforced) concrete (Forrestal and Tzou, 1997), a dynamic spherical cavity-expansion penetration model for reinforced-concrete targets is developed with consideration of the circumferential restriction effect derived from reinforcing bars in the crushed region. The theoretical solution and simplified calculation formula for the cavity radial stress in incompressible and compressible reinforced concrete are obtained by introducing a reinforcement ratio as the volume fraction of rebars in the concrete target. A damping function is presented to describe the restriction effect of a single layer of reinforcing bars on the surrounding concrete, thus establishing a model to calculate the penetration resistance of multilayer reinforced-concrete targets. Compared with test data for the penetration depth, this model considering the circumferential restriction effect produces better results compared with the existing theory.

Numerical study of size effect in concrete penetration with LDPM

Projectile size effect is of great importance since the scaling researches are extensively applied to concrete penetration investigations. This paper numerically deals with the projectile size effect on penetration resistance via the recently developed Lattice Discrete Particles Model(LDPM) which is featured with mesoscale constitutive laws governing the interaction between adjacent particles to account for cohesive fracture, strain hardening in compression and compaction due to pore collapse. Simulations of two different penetration tests are carried to shed some light on the size effect issue. The penetration numerical model is validated by matching the projectile deceleration curve of and predicting the depth of penetration(DOP). By constant velocity penetration simulations, the target resistance is found to be dependent on the projectile size. By best fitting numerical results of constant velocity penetration, a size effect law for target resistance is proposed and validated against literature data. Moreover, the size effect is numerically obtained in the projectile with longer extended nose part meanwhile the shorter extended nose is found to improve the DOP since the projectile nose is sharpened.

Chloride ion penetration into concrete under hydraulic pressure

The lining concrete of subsea tunnel services under combined hydraulic pressure, mechanical and environmental loads. The chloride ion and water penetrations into concrete under hydraulic pressure were investigated. The experimental results indicate that the water penetration depth, chloride ion transportation depth, and the concentration of chloride ion ingression into concrete increase with raised hydraulic pressure and hold press period. But the chloride ion transportation velocity is only 53% of that of water when concrete specimens are under hydraulic pressure. The chloride transportation coefficient of concrete decreases with hold press period as power function. And that would increase 500% 600% in chloride transportation coefficient when the hydraulic pressure increases from 0 to 1.2 MPa. The hydraulic pressure also decreases the bound chloride ion of concrete to about zero. Besides, the low water-cementitions materials and suitable content of mineral admixture(including fly ash and slag) improve the resistance capacity of chloride penetration, and binding capacity of concrete under hydraulic pressure.

Penetration Resistance of Composite Bucket Foundation with Eccentric Load for Offshore Wind Turbines

The penetration of the composite bucket foundation(CBF)is crucial in its construction process.In actual projects,the foundation is inevitably subjected to eccentric load caused by towers and turbines,as well as wind,wave,and flow,during the one-step installation.Moreover,the eccentric load is bound to affect the penetration method and penetration resistance of the foundation.To examine the above-mentioned issues,the penetration resistance of CBF with eccentric load was calculated and analyzed based on model tests,and the seepage field of the CBF under eccentric load was analyzed using ABAQUS.The influence of different magnitudes of eccentric load and various offset strategies on penetration resistance was analyzed,and the theoretical and measured values were compared.The result indicated that the negative pressure of the offset room was found to be smaller than that of other rooms when the CBF penetrated the soil under eccentric load.The penetration resistance of CBF under eccentric load was larger than that without eccentricity,and the larger the eccentric load is,the greater the penetration resistance.The influence of different eccentric load offset strategies on penetration resistance was found to be negligible.The calculated penetration resistance under eccentric load was in good agreement with the measured value.

Effect of Aggregate Gradation with Fuller Distribution on Properties of Sulphoaluminate Cement Concrete

Experimental investigations on mechanical property and durability of sulphoaluminate cement concrete with aggregate gradations according to Fuller distribution are presented in this paper. Compressive strength, water impermeability and resistance capability to sulfate attack of SACC have the same trend of concrete with fine aggregates of Fuller distribution gradation<concrete with coarse aggregates of Fuller distribution gradation<concrete with total aggregates of Fuller distribution gradation. The relationship between bulk density of aggregate and water penetration depth obeyed the second-order polynomial y=0.002x2-6.863 8x +5 862.3, and had a notable correlation R2=0.979 9. The sulphoaluminate cement concrete with total aggregate gradation with Fuller distribution for h=0.50 had the best resistance capability to sulfate attack. It was a second-order polynomial relationship between bulk density of aggregates and water penetration depth of y=0.002x2-6.863 8x+5 862.3 with R2=0.979 9, which indicated notable correlation. The fitting formula between bulk density of aggregates and sulfate resistance coefficient of SACC was y=0.000 5x+0.370 4 with R2=0.958 5.

Centrifuge experiment on the penetration test for evaluating undrained strength of deep-sea surface soils

Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration;however,a method considering the effect of ambient water on the surface penetration needs to be established urgently.In this study,penetrometers with multiple probes were developed and used to conduct centrifuge experiments on South China Sea soil and kaolin clay.First,the forces on the probes throughout the penetration process were systematically analyzed and quantified.Second,the spatial influence zone was determined by capturing the resistance changes and sample crack development,and the penetration depth for a sample to reach a stable failure mode was given.Third,the vane shear strength was used to invert the penetration resistance factor of the ball and determine the range of the penetration resistance factor values.Furthermore,a methodology to determine the penetration resistance factors for surface marine soils was established.Finally,the effect of the water cavity above various probes in the surface penetration was used to formulate an internal mechanism for variations in the penetration resistance factor.

Assessment of Curing Efficiency and Effect of Moist Curing on Performance of Fly Ash Concrete

This study was conducted to evaluate the sensitivity of compressive strength,water permeability and electrical resistance of near-surface layer concrete with different fly ash contents to curing conditions.It is shown that the sensitivity to curing condition and fly ash content descends in the following order：difference between internal and surface resistivity （ρ） at 28 days,water permeability and compressive strength;both of longer duration of moist curing and use of fly ash in concrete enhanced the water penetration resistance.It is indicated that the resistivity difference ρ at 28 days can reflect accurately the curing history of fly ash concrete regardless of mix proportions;and use of fly ash in concrete requires longer moist curing duration.

Concrete Based on Recycled Aggregates for Their Use in Construction: Case of Goma (DRC)

The following study is aimed at valorizing an important part of waste from building demolition, particularly concrete as a source of aggregates for their usage in new hydraulic concrete formulation. The experimental study mainly consisted of physical characterization of natural and recycled aggregates respectively and the impact of the latter on some properties of the new formulated concrete, actually their respective consistencies for fresh concrete and mechanical strength for the hardened one. The outcome of the study shows that the recycled aggregates are more heterogeneous and have a high capacity of water absorption, but which still respects the current standards of concrete. The need for additional water has been observed for recycled aggregates-based concrete so as to have the same workability. About the compressive strength, mechanical properties obviously show that, at 28 days from setting up, concretes from recycled aggregates can reach compressive strengths range between 20 and 25 MPa without any sophisticated technology. So, these results show that we can efficiently contribute to the protection of environment by valorizing waste from concrete-based building demolition on the one hand;and the preservation of natural reserve on the other. And both advantages contribute to sustainable development overall goals.

矿物掺和料对海水海砂混凝土抗氯离子渗透性的影响

通过10组试验,研究了10%~30%粉煤灰、10%~30%矿渣、5%~15%偏高岭土在单掺下对海水海砂混凝土抗氯离子渗透性能及化学组成的影响,并通过扫描电镜对微观结构进行分析.结果表明:海水海砂混凝土氯离子扩散系数随着粉煤灰掺量提高先减少后增大,随着矿渣掺量提高逐渐增大,随着偏高岭土掺量提高逐渐减小;偏高岭土、矿渣和20%以下粉煤灰掺入海水海砂混凝土后,均可见随着掺量的提高混凝土中的Friedel盐增多,自由氯离子及Ca(OH)2含量降低,混凝土孔溶液pH值降低;偏高岭土对海水海砂混凝土的氯离子化学结合和物理吸附作用及微观结构的改善最佳,20%以内掺量的粉煤灰次之.

基于PSO‑BPNN模型的氯氧镁水泥混凝土耐水性预测

为快速准确地获得具有优异耐水性氯氧镁水泥混凝土(MOCC)的配合比,设计了拓扑结构为4‑10‑2的粒子群优化(PSO)算法-反向传播(BP)神经网络(PSO‑BPNN)模型.该模型的输入层参数为n(MgO)/n(MgCl_(2))、粉煤灰掺量、磷酸掺量和磷肥掺量,输出层参数为MOCC的抗压强度和软化系数;模型数据集为144组,其中训练集数据为100组,验证集数据为22组,测试集数据为22组.结果表明:PSO‑BPNN模型在MOCC抗压强度预测中的评价参数——决定系数R^(2)=0.99、平均绝对误差S_(MAE)=0.52、平均绝对误差百分比S_(MAPE)=1.11、均方根误差S_(RMSE)=0.73;其在软化系数预测中的评价参数——R^(2)=0.99、S_(MAE)=0.44、S_(MAPE)=1.29、S_(RMSE)=0.62;与BP神经网络(BPNN)模型相比,PSO‑BPNN模型具有更强的双参数预测能力,可用于MOCC配合比的正向设计和反向指导.

不同侵蚀环境下水下不分散混凝土抗Cl-和SO_(4)^(2-)渗透性能研究

在不同侵蚀环境中的水下不分散混凝土会受到侵蚀离子的渗透,严重影响水下不分散混凝土的耐久性能。研究了不同强度等级的水下不分散混凝土在氯盐溶液、硫酸盐溶液和复合盐溶液3种侵蚀环境下抵抗侵蚀离子渗透的能力。通过分析不同矿渣掺量下抗侵蚀离子渗透性能的影响,探究Cl^(-)和SO_(4)^(2-)在渗透过程中的耦合作用,并利用AutoPoreIV9500压汞仪测试不同侵蚀龄期各试样的孔隙特征。结果表明:在距离侵蚀表面5 mm和30 mm处,C35混凝土比C25混凝土的离子浓度降低7%~60%;在相同侵蚀环境下,掺入矿渣粉可以显著减小水下不分散混凝土中侵蚀离子浓度;水下不分散混凝土中的孔隙组成以直径小于50 nm的介孔和微孔为主,矿渣的掺入细化了孔隙结构。即水下不分散混凝土的抗渗性能随着其抗压强度等级的提高而显著提高,并且矿渣粉的掺入使结构更加致密,从而有效提高混凝土抗Cl^(-)和SO_(4)^(2-)渗透性能。

内掺水泥基渗透结晶型防水材料混凝土配合比设计及性能研究

试验研究了不同掺量水泥基渗透结晶型防水材料(CCCW)对混凝土保水性、力学性能、抗渗性能、抗氯离子渗透性能及凝结时间的影响,并采用扫描电镜观察分析其微观形貌。试验结果表明:适量的CCCW能明显改善混凝土的保水性及力学性能,当CCCW掺量为0.8%时效果最佳;CCCW的掺入对混凝土的抗渗性能以及抗氯离子渗透性能也有提升,当CCCW掺量为1.0%时,抗渗压力比升高趋势更明显,电通量最低,随着CCCW掺量增加,混凝土凝结时间有所缩短;SEM照片显示CCCW的掺入能促进裂缝与空隙处的水化反应,生成枝蔓状结晶体,使得混凝土更加致密,提高了混凝土的力学性能与抗氯离子渗透性。

基于渗透结晶法的裂缝有效封堵对比研究

文中对比研究了BKN 88渗透结晶自修复剂和Feedar渗透结晶自修复剂宏观的修复效果,利用渗水系数来表征两种自修复剂的修复性能。结果表明,BKN 88渗透结晶自修复剂的修复效果较好。此外,文中研究了自修复剂掺量、开裂时间和裂缝宽度对自修复性能的影响。

外加剂对硫氧镁水泥泡沫混凝土性能影响

该文研究磷酸三钠、葡萄糖、有机酸C、有机酸盐D四种外加剂复掺对硫氧镁水泥泡沫混凝土抗压强度和耐水性的影响。并采用XRD、SEM表征硫氧镁水泥泡沫混凝土试样的物相组成和微观结构。结果表明,适当掺量的四种外加剂都能提高硫氧镁水泥泡沫混凝土抗压强度及耐水性,有机酸C对硫氧镁水泥泡沫混凝土抗压强度影响较大,有机酸C掺量为0.6%时,试块28 d抗压强度达到1.91 MPa;磷酸三钠可以有效改善硫氧镁水泥泡沫混凝土耐水性,当磷酸三钠掺量0.6%时,试块软化系数达0.8;复掺外加剂试样强度与耐水性得到提升,其28 d抗压强度达到2.1 MPa,是不掺外加剂试样的1.58倍,其软化系数达0.92。

混凝土碳化性能试验研究

混凝土作为重要的建筑材料,其耐久性能是影响使用寿命的重要因素。通过对常见种类的混凝土进行碳化性能测试,结果表明:掺合料降低了混凝土的抗碳化性能,矿渣粉对混凝土碳化性能的保持能力相对较好;高性能减水剂对混凝土碳化性能的改善作用优于高效减水剂;混凝土标准养护龄期延长,会增加其内部水化产物的数量和种类,从而增强其抗碳化性能。

高效缓凝减水剂与氧化镁膨胀剂对混凝土性能的影响

研究了不同高效缓凝减水剂(柠檬酸、葡萄糖酸钠、柠檬酸镁、柠檬酸锂)分别与氧化镁膨胀剂的共同作用对混凝土工作性、力学性能、干燥收缩、抗裂性能的影响。结果表明:柠檬酸锂对掺氧化镁膨胀剂混凝土拌合物的坍落度有负面影响,但柠檬酸、葡萄糖酸钠、柠檬酸镁能在一定程度上改善混凝土的工作性;各高效缓凝减水剂均可提高混凝土的力学性能;葡萄糖酸钠、柠檬酸镁、柠檬酸锂均可减少混凝土的干燥收缩;柠檬酸、葡萄糖酸钠、柠檬酸镁均对氧化镁膨胀剂在混凝土中的补偿收缩作用有正向影响,其中,柠檬酸镁、葡萄糖酸钠的效果相对更好;柠檬酸对掺氧化镁膨胀剂的混凝土早期开裂性能有负面影响,会促进裂缝的产生。

玄武岩-PVA混杂纤维对混凝土耐久性能影响研究

为了研究玄武岩纤维(BF)与聚乙烯醇纤维(PVA)复掺混杂纤维在混凝土体系中对混凝土耐久性能影响,通过耐久性试验研究做系统探究。结果表明:(1)玄武岩-PVA混杂纤维掺量0.2%时,干湿交替次数90次混凝土抗压强度耐腐蚀系数、质量损失率分别为75.5%、4.3%,抗硫酸盐等级为KS90。其他掺量抗硫酸盐等级均为KS60。表明玄武岩-PVA混杂纤维会提高混凝土抗硫酸盐侵蚀性能。(2)冻融循环200次,质量损失率最低降低值0.05%,最高降低值0.12%;相对动弹性模量最低提高值0.5%,最高提高值1.0%。表明玄武岩-PVA混杂纤维有助于提高混凝土抗冻性。(3)玄武岩-PVA混杂纤维掺量增加,混凝土试件电通量先减小后增大,在掺量0.2%时达到最低值1 700 C。表明适宜掺量提高混凝土抗氯离子渗透性能。