机场道面除冰液作用下大掺量粉煤灰混凝土的抗冻性

通过大掺量粉煤灰混凝土（HFCC）试件在质量分数为3.5%,12.5%,25%机场道面除冰液（CMA溶液）、质量分数为3.5％的NaCl溶液、质量分数为3.5％的飞机除冰液（AD溶液）、质量分数为25%的商品飞机除冰液与水中快速冻融试验,获得了冻融过程中HFCC的质量损失率和相对弹性模量的变化规律。结果表明:在质量分数为3.5%的介质中,HFCC在NaCl溶液中的冻融破坏以表面剥落为主,在AD,CMA溶液中以内部冻融损伤为主;与水中冻融条件相比,质量分数为3.5%的CMA溶液延缓了HFCC的冻融破坏作用;HFCC在CMA溶液作用下的冻融破坏与其质量分数密切相关,CMA溶液质量分数越高,HFCC的冻融破坏作用越小,当CMA溶液的质量分数在12.5%以上时,即使经受600次快速冻融循环,其质量损失率和相对动弹性模量损失均很小;在质量分数为25%的冻融介质中,HFCC在商品飞机除冰液中的抗冻性较差,在机场道面除冰液中抗冻性较好;HFCC完全能够应用于较高质量分数CMA溶液进行冬季除冰雪作业的水泥混凝土机场跑道。     

除冰剂对机场跑道混凝土抗冻性能影响

采用单面冻融法,以试件表面剥落量作为混凝土抗冻性能的评定参数,探讨了经不同浓度乙二醇溶液浸泡后的机场道面混凝土的抗冻性能。结果表明,混凝土经中低浓度乙二醇溶液浸泡后,冻融破坏严重,当乙二醇浓度为3%时,冻融破坏达最大值;通过机场道面混凝土破坏机理分析,破坏主要受混凝土中溶液吸入率、除冰剂自结冰膨胀率影响显著。     

高性能混凝土经飞机除冰液长期作用的化学腐蚀

飞机除冰液对机场高性能混凝土(HPC)长期作用的腐蚀性未知,采用浸泡腐蚀法经过4 a测定了普通水泥混凝土(OPC)和HPC分别在水、25%乙二醇(飞机除冰液)和25%商用飞机除冰液(LBR-A除冰液)中的抗腐蚀性。结果表明,除冰液与OPC表层的CH发生化学腐蚀反应,产生结晶腐蚀产物,使得混凝土试件质量不减反增,LBR-A除冰液对混凝土表层的腐蚀性比乙二醇更强一些。但除冰液的长期作用并不能对水泥混凝土的内部结构造成实质性影响,仅限于表层的逐层剥蚀。因此,在商用飞机除冰液的长期腐蚀作用下,用硅酸盐水泥掺加40%粉煤灰(FA)配制的HPC抗腐蚀性最好,用抗硫酸盐硅酸盐水泥掺加40%FA配制的HPC抗腐蚀性次之,OPC抗腐蚀性较差。     

混凝土的除冰盐剥落性能与机理研究

进行了混凝土在浓度3．5％氯化钠溶液中快速冻融的试验研究,结果表明,盐溶液对混凝土抗冻性的影响具有双重性,盐溶液使混凝土试件表面饱和程度的提高导致严重剥落,重量损失大幅度增加,溶液降低冰点的作用使混凝土内部破坏程度较小,相对动弹性模量下降略为缓慢。混凝土的耐久性系数应该考虑相对动弹性模量和重量损失两个指标。     

甲酸钾除冰液作用下机场道面混凝土单面冻融试验研究

采用单面冻融法,研究了不同甲酸钾除冰液浓度作用下机场道面混凝土冻融前后的性能,并对机场道面混凝土表面剥落物质量、介质吸入率、超声波相对动弹性模量和孔结构进行了测定。结果表明：在除冰液作用下,混凝土的孔隙水饱和度显著提升,使混凝土冻融后的破坏程度加剧;在除冰液浓度作用下,混凝土冻融时的表面剥落物质量和介质吸入率与冻融介质的性质及混凝土孔隙水饱和度有关,大小顺序皆为：6%>12%>24%>0,超声波相对动弹性模量与混凝土内部结构复杂程度有关,除冰液浓度对超声波相对动弹性模量下降影响大小顺序为：24%>6%>12%>0;随除冰液浓度（6%、12%、24%）增加,单面冻融后混凝土的平均孔径呈先增大后减小的趋势。     

混合侵蚀与冻融交替作用下混凝土性能劣化试验

以质量分数为3％的氯化钠和5％的硫酸钠混合溶液为侵蚀介质,采用慢冻法,对立方体抗压强度为54.7 MPa的混凝土试件进行0,100,200,300次冻融循环试验,并测定各组试件的质量损失、抗压强度、相对动弹性模量和应力、应变等试验数据.结果表明:随着冻融循环次数的增多,混凝土试件表面剥蚀加剧,表观质量和相对动弹性模量无...     

粉煤灰高性能混凝土在醋酸钙镁溶液中的化学腐蚀与机理分析

机场道面除冰液对机场高性能混凝土具有一定的腐蚀性,采用浸泡腐蚀法研究了粉煤灰高性能混凝土在25%的醋酸钙镁(机场道面除冰液主要成分)溶液中的抗腐蚀性。结果表明,25%的醋酸钙镁溶液长期作用下对于粉煤灰高性能混凝土内部没有化学腐蚀作用,当粉煤灰掺量越高,高性能混凝土的抗醋酸钙镁剥蚀能力越强。相对抗硫酸盐水泥高性能混凝土而言,硅酸盐水泥高性能混凝土表现出更为出色的抗醋酸钙镁剥蚀能力。因此,采用较大掺量的粉煤灰作为矿物掺合料,以硅酸盐水泥作为胶凝材料,制备的高性能混凝土具有非常好的抗醋酸钙镁表面剥蚀性能。     

碳化高性能混凝土的抗硫酸盐腐蚀性能研究

采用长期自然浸泡的方法,研究了经过快速碳化试验后的粉煤灰混凝土和掺加粉煤灰,矿渣,硅灰的高性能混凝土在5%硫酸镁溶液中的抗腐蚀性能。结果表明:碳化一定程度密实混凝土的表层,但降低混凝土的抗硫酸盐腐蚀性能。碳化HPC比碳化FAC具有更优的抗硫酸镁腐蚀性能。碳化混凝土在硫酸镁腐蚀作用下的破坏形态主要是混凝土开裂,混凝土开裂时并无明显表面剥落现象。     

甲酸钠除冰剂对机场跑道混凝土抗冻性的影响

采用单面冻融法测试了机场道面混凝土在不同浓度甲酸钠溶液中的抗冻性,并用试件表面剥落量作为混凝土抗冻性评定参数。结果表明,混凝土在中低浓度甲酸钠溶液中冻融破坏最严重,在高浓度和水中破坏较轻。并从混凝土吸水率和除冰剂结冰膨胀率两方面对试验结果进行了分析。结果表明,在冻融过程中混凝土吸水率大小和除冰剂本身结冰膨胀率大小共同决定了混凝土在除冰剂中的冻融破坏速率。     

化学外加剂对3D打印水泥基材料抗冻性的影响

为探究3D打印成型水泥基材料的抗冻耐久性,制备了不同外加剂掺量的水泥基3D打印试件,通过加速冻融试验研究3D打印试件的质量损失和动弹性模量变化。结果表明,随着速凝剂掺量的增加,水泥基材料3D打印试件的质量损失增大,相对动弹性模量降低,抗冻耐久性变差。引气剂的加入可以减轻但无法完全阻止3D打印试件的表面剥落破坏,且未能明显减轻试件的内部损伤。随着增稠剂掺量的增加,3D打印试件的表面剥落量增大,相对动弹性模量的降低速率减缓,试件的内部损伤有所减轻。本研究对于3D打印水泥基材料用化学外加剂的选择、油墨材料组成设计及3D打印制品的服役性能评价均具有一定的指导意义。     

NaCl除冰盐作用下混凝土的抗冻能力分析

通过存质量浓度为3.5%的NaCl溶液中的冻融循环试验,测试了普通混凝土、引气混凝土、粉煤灰混凝土和硅灰混凝土的相对动弹性模量和质量损失率,分析了不同混凝土的抗盐冻的能力.结果表明:适当的引气能够明显改善混凝土的抗盐冻性能,掺加20%粉煤灰时,混凝土仍具有较高的抗盐冻能力,掺量达到40%时混凝土的抗盐冻性能明显下降,掺加10%硅灰明显提高混凝土的抗盐冻能力.     

Corrosion rate of ordinary and high-performance concrete subjected to chloride attack by AC impedance spectroscopy

Corrosion of reinforcing steel in concrete is studied by using AC impedance. Subjected to different conditions and chloride concentrations, a laboratory study was conducted to estimate the corrosion rate of reinforcing steel embedded in ordinary Portland concrete (OPC) and high-performance concrete (HPC).One hundred and four OPC and HPC concrete cylinders embedded with a single reinforcing steel bar were exposed to sodium chloride solution with 0%, 1%, 3% and 5% concentrations. Specimens were also subjected to pre-conditioning and drying-wetting cycles.The AC Impedance technique (IS) was used to determine the corrosion rate of the reinforced concrete cylinders. In order to interpret the AC impedance spectra, several electrical equivalent circuits were employed.This investigation aims to compare IS with commonly used corrosion assessment techniques, such as Tafel plot (TP) and linear Polarization (LP).Results confirm that data obtained from AC impedance can be used to calculate the corrosion rate of reinforcing steel. A reasonable agreement with the results of TP and LP techniques is demonstrated. It is found that the corrosion rates obtained by AC impedance technique are lower than TP by 5–20%, while results of LP are 20–30% higher than those of TP.     

Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.     

泡沫混凝土弹性模量的测试方法探讨

为获得密度为800 kg/m3的泡沫混凝土的弹性模量数据,设计了一种振弦式应变计测试的方法,并采用该方法测试了采用普通水泥和双快水泥配制的两种泡沫混凝土的应力应变,绘制了变化曲线,计算了弹性模量.采用普通水泥配制的泡沫混凝土,7 d的弹性模量在200～300MPa之间,采用双快水泥配制的泡沫混凝土,2 h的弹性模量在350～500MPa之间.测试表明该方法操作方便、速度快、测试结果离散性小、数值符合泡沫混凝土的特点和强度水平.     

气泡特征对混凝土抗盐冻性能的影响

采用快冻法研究了普通混凝土(OPC)、引气混凝土(APC)和高性能混凝土(HPC)在质量分数为3.5％的NaCl溶液中的抗盐冻性能,并借助低真空扫描电子显微镜(SEM)观测了水泥浆体中气泡特征,研究了混凝土气孔结构对混凝土抗盐冻性能的影响规律.结果表明:在水胶比0.50的OPC浆体中,引入直径小于30 μm、间距小于6...     

海工混凝土的氯离子扩散性与寿命评估

通过现场海洋曝露试验和实验室海水浸泡试验,采取分层取样和化学分析方法,应用氯离子三维扩散理论,研究了普通混凝土和高性能混凝土在海洋大气区、潮汐区、水下区和实验室海水浸泡下的C1-扩散系数变化规律.结果表明,混凝土的C1-一扩散系数随着曝露时间的增加而降低,高性能混凝土的抗C1-扩散性优于普通混凝土.在Khatri计算模型的基础上,提出了考虑劣化效应系数的海工混凝土使用寿命计算模型.该模型计算结果与Clear经验模型基本吻合,解决了Khatri计算模型结果与实际寿命不相符的问题.     

海水侵蚀环境下混凝土耐久性的研究

采用普通硅酸盐水泥和矿渣硅酸盐水泥，分别配制了水灰比在0．45～0．60范围内的混凝土试件，采用加速腐蚀试验研究了在海水侵蚀后，其强度、重量损失随时间变化的规律及原因，并为试件损伤状态定量化解析提供了试验数据。结果表明，在相同的试验条件下，矿渣硅酸盐水泥混凝土耐久性优于普通硅酸盐水泥混凝土：混凝土试件的抗蚀系数为0．8时，与美国ASTM标准规定的强度损失25％的界限值吻合较好。     

Corrosion protection performance of microsilica added concretes in NaCl and seawater environments

In a hardened concrete structure, diffusion of oxygen, carbon dioxide, aggressive ions and moisture from the concrete/environment to the concrete/rebar interfaces takes place through the pores. This results in the failure of the passivation provided by the alkalinity of the cement to the rebars. Microsilica is a mineral that improves the corrosion protection and strength of concrete by reducing the permeability of the concrete and forming more calcium silicate hydrate (CSH) which provides strength and durability to concrete. In order to study the corrosion protection behavior of microsilica in ordinary Portland cement (OPC) and sulfate resistant cement (SRC), carbon steel reinforced concrete specimens of above cements containing 10% each of densified (DMS) and undensified (UDMS) microsilica were exposed to 5% NaCl solution and seawater. Corrosion of rebars was monitored using open circuit potential (OCP) measurements. Diffusion of ions into the concrete was studied by salt ingress, salt fog and rapid chloride permeability tests. It has been noted that densified microsilica provides better corrosion protection to the rebars than the undensified one. In addition to this its protective effect with SRC is much more than with OPC. An attempt has been made to explain the mechanism of corrosion protection behavior of microsilica added concrete immersed in seawater and NaCl solution.     

高强高性能混凝土配合比设计和试验

本文采嗣P·Ⅱ52．5硅酸盐水泥．掺加S95级矿粉、二级粉煤灰、高效泵送剂．配制C60-C80强度等级的试验。