橡胶粒子-PVA纤维复合改性水泥砂浆抗裂性能的研究

针对水泥基材料收缩裂缝问题,进行了利用橡胶粒子与PVA纤维复合改善水泥砂浆抗裂性的试验研究,并对橡胶粒子与PVA纤维在水泥砂浆中的阻裂机理进行了初步探讨。试验结果表明,复掺橡胶粒子与PVA纤维能明显提高水泥砂浆的抗裂性能。当橡胶粒子掺量为10%、PVA纤维掺量为0.5%时,可完全消除水泥砂浆的宏观收缩裂缝。     

再生纤维素纤维增强水泥砂浆的早期抗裂和自收缩行为

早期收缩开裂是导致混凝土劣化的重要因素之一,纤维的加入可以延缓甚至减少裂缝的延伸及扩展。使用具有吸水特性的再生纤维素纤维,与UF500纤维素纤维和无吸水的聚丙烯短纤维对比,研究再生纤维素纤维对水泥砂浆早期抗裂和自收缩行为的影响规律。将掺量为水泥质量1%或2%的各类纤维掺入水泥砂浆,密封养护,分析水泥砂浆强度、折压比及自收缩应变。研究结果表明：水灰比0.3时,添加再生纤维素纤维不能增强砂浆的抗裂性能和自收缩性能;水灰比大于0.35时,添加1%的再生纤维素纤维虽然降低了砂浆的抗折强度和抗压强度,但提高了该样品的折压比,增强了砂浆的抗裂性能和减缩效应。     

聚丙烯纤维控制特细砂混凝土塑性收缩裂缝试验研究

特细砂具有平均粒径小、比表面积大的特点，用其配制的大流动性混凝土极易出现塑性收缩裂缝。因此，对特细砂混凝土塑性收缩防裂措施进行研究，具有重要的现实意义。通过平板端约束试验，研究了聚丙烯纤维掺量对特细砂混凝土塑性收缩裂缝面积、裂缝宽度以及水分蒸发速率的影响，探讨了该纤维的阻裂机理。     

有机纤维对“客运专线”用C40高性能混凝土性能的影响

目的为增强混凝土早期抗塑性开裂性能及耐久性,研究了有机纤维种类、长度及掺量对混凝土工作性能、力学性能及抗碳化性能的影响．方法采用坍落度试验、抗压与抗折强度试验、混凝土碳化试验及平板约束法测试进行研究．结果聚丙烯腈（PAN）纤维对混凝土工作性能影响最大,坍落度降幅达86％;掺入19mm聚丙烯（PP）单丝纤维,坍落度下降25％;加入0．15％PP纤维,坍落度降幅达28．7％,含气量增加25．9％;掺入聚乙烯醇（PVA）纤维后,混凝土7d、28d抗压强度降幅最大,分别达30．4％、23．5％;12mmPP单丝纤维体积掺量为0．15％时混凝土的抗裂效果明显好于0．05％掺量,而碳化深度较基准低30％．结论混凝土中掺入有机纤维后,早期抗塑性开裂性能明显增强;混凝土的抗裂效果随纤维长度和掺量增加,效果越来越明显;有机纤维的加入明显提高混凝土的抗碳化力,力学性能有所降低,但降幅不大．     

索塔锚固区用HPFRC的塑性收缩与干燥收缩

钢锚箱锚固区部位所处环境复杂，为确保其耐久性，制备了专用高性能纤维混凝土（HPFRC）.模拟干热环境，对优选出的泵送性能优异的高性能混凝土（HPC）和高性能纤维混凝土（HPFRC）进行了塑性收缩试验；研究了纤维掺量和种类对塑性收缩和干燥收缩性能的影响，并对其机理进行了探讨。研究表明：随着纤维掺量的增加，塑性收缩的开裂总面积下降，混凝土的抗裂等级提高；当钢纤维的体积掺量超过0．8％，高性能铜纤维混凝土自由干燥66d的收缩值同高性能混凝土相比下降了50％；纤维体积率为0．1％的聚丙烯纤维与体积率为0．6t％的钢纤维混杂后，对抑制塑性收缩和干燥收缩效果显著？     

聚丙烯纤维对桥面铺装轻骨料混凝土性能影响

试验研究了聚丙烯纤维对桥面铺装轻骨料混凝土工作性能和强度的影响,探讨了对轻骨料预湿、掺入聚丙烯纤维及钢纤维与开裂时间、开裂面积、裂缝数量的关系.结果表明:聚丙烯纤维的掺入降低了轻骨料混凝土的流动性,当聚丙烯纤维掺量为1.2 kg/m3时,混凝土初始坍落度和扩展度仅为未掺聚丙烯纤维混凝土的69%和64%,当聚丙烯纤维掺量为0.6 kg/m3时,混凝土分层度较小;聚丙烯纤维在轻骨料混凝土中存在一个最佳掺量,当聚丙烯掺量为0.6 kg/m3时,混凝土28 d抗压强度变化不大,28 d抗折强度有一定提高.抗裂试验表明:对轻集料进行预湿处理和掺入纤维可以阻止和延缓混凝土早期塑性收缩产生的裂缝,提高混凝土的早期抗裂性能.     

水灰比对混凝土塑性收缩裂缝的影响

试验研究了水灰比对新拌混凝土塑性收缩裂缝面积和水分蒸发速率的影响。结果表明，水泥和集料用量一定的的条件下，在0．35-0.65范围内，混凝土拌合物的水分蒸发速率随水灰比的增加而增大；混凝土塑性收缩面积最大值对应的水灰比约为0．5，当水灰比小于0．5时，混凝土塑性收缩面积随水灰比的提高而增大，当水灰比大于0．5时，混凝土塑性收缩面积随水灰比的提高而减小。     

聚丙烯纤维混凝土早期塑性开裂特征及分形评价

目的研究了聚丙烯纤维对混凝土塑性开裂特征的影响,为改善混凝土塑性开裂提供理论依据.方法采用平板约束法,研究不同掺量、不同长度的聚丙烯纤维对混凝土塑性开裂特征的影响,并应用分形理论,计算了聚丙烯纤维混凝土塑性开裂的分形维数.结果聚丙烯纤维的掺入阻碍了裂缝的产生和发展,且随着体积掺量的增加、长度的增长阻裂效果增强;裂缝分形维数的发展随着纤维掺量的增加、长度的增长而减缓,裂缝复杂化程度减缓.结论聚丙烯纤维能有效地延缓裂缝的产生和发展;应用分形理论分析评价混凝土早期塑性开裂特征是十分有效的.     

大掺量钢渣矿粉抗裂水泥砂浆的试验研究

为降低砂浆的体积收缩,提高其抗裂性能,以30%、50%超细钢渣矿粉取代部分水泥,同时掺入纤维,用于制备水泥砂浆,研究了砂浆的物理力学性能、体积收缩性能,并用平板法研究了砂浆的抗裂性能.结果表明,与空白试样对比,超细钢渣矿粉和纤维的合理掺入可降低砂浆的体积收缩(56 d时可降低20%-30%),提高砂浆的的抗裂性能.     

芳纶纤维橡胶混凝土的塑性开裂与韧性研究

为探究掺加芳纶纤维对橡胶混凝土的韧性、抗裂性的影响,将40目橡胶粉等体积替换7.5％细骨料制成橡胶混凝土,并加入不同掺量的芳纶纤维,采用平板试验及落锤试验,分别研究了纤维橡胶混凝土的抗裂性能及冲击韧性.结果 表明:掺入芳纶纤维对橡胶混凝土的抗压强度提升不明显,但显著提高了冲击韧性和抗塑性开裂;在芳纶纤维掺量为0.7％时,试件的抗冲击韧性比达到最大值4.125,比橡胶混凝土增加了大约3倍;芳纶纤维掺量分别为0．3％、0.5％、0.7％时,混凝土未出现裂缝,有效提高了混凝土抵抗开裂的能力.     

聚丙烯纤维和膨胀剂复合对砂浆塑性收缩的影响

混凝土的塑性收缩裂缝,是其结构原生缺陷的主要来源,无论是否可见,都会影响混凝土的耐久性.文章研究了聚丙烯纤维和膨胀剂复合对砂浆塑性收缩裂缝的影响,结果显示,纤维与膨胀剂复合,在减少塑性收缩裂缝数量和细化裂缝两个方面均优于纤维或膨胀剂的单独作用,砂浆抵抗塑性收缩开裂能力显著提高.     

减缩剂对水泥基材料减缩效果的研究

综述水泥基材料各类常见收缩的特点、机理及对水泥基开裂的影响.通过自由收缩、质量损失、强度、平板抗裂性等试验研究减缩剂(SRA)的减缩抗裂效果.加入SRA,砂浆早期收缩明显减小,且减缩率前7d最大.而质量损失早期高于未加SRA的,后期则趋于平缓;SRA降低砂浆抗压、抗折强度.这与SRA降低砂浆孔隙水表面张力、延缓水泥水化、改变孔结构有关.平板抗裂对比试验表明:抗裂效果聚丙烯纤维最好,减缩剂次之,膨胀剂最差.     

水泥砂浆在载荷作用下的电学模型研究

水泥砂浆试块在载荷作用下会产生电信号（电压或电流），推导了这种力电效应的电学模型。载荷作用下的水泥砂浆试块相当于一个电流源，电解质水溶液在孔隙中流动会遇到阻力形成内阻，电极和其中的水泥砂浆电介质构成电容。并分析了模型中每个元件的构成和大小，根据这个模型较好的解释了水泥砂浆试块的力电效应。     

Effect of Waterborne Epoxy on Performances of Cement Asphalt Mortar

The waterborne epoxy modified cement asphalt mortars were prepared with varying content waterborne epoxy and a constant fluidity. The effects of waterborne epoxy emulsion on water/cement ratio,compressive and flexural strength,tensile bond strength,freezing and thawing damage,corrosion resistance of cement asphalt mortar cured for 7 and 28 d have been investigated. The results show that waterborne epoxy is very beneficial to the improvement of mechianical properties and durability of cement asphalt mortar. Waterborne epoxy can improve the flowing ability of cement asphalt mortar. With the increasing of waterborne epoxy content,compressive strength,flexural strength and bond strength all have increased obviously. The modified mortar shows higher resistance to corrosion and the freezing and thawing compared with control mortar.     

Numerical simulation on moisture transport in cracked cement-based materials in view of self-healing of crack

The moisture transport in cracked cement-based materials was investigated with priority by numerical simulation. The cracked cement-basis material was treated as two components system, including the cracks and cementitious mortar. The mass balance between the water in the cracks and in the cement mortar was considered. From the modeling results, it was seen that the water or vapor filled the crack immediately when the cracked cementitious mortar was put into contact with the water or vapor. The water/vapor penetrates into the mortar from the crack surfaces, as well as the external surface exposed in the outside condition. The existence of cracks increases the penetration of water/vapor into the cementitious mortar. As the basis for studying the self-healing in cracked concrete, the simulation on moisture transport provided important information about the water distribution and movement inside the cracked concrete.     

水泥砂浆外涂有机硅烷防护效果研究

为了研究外涂有机硅水泥砂浆材料的防护效果,用有机硅涂料对水泥砂浆进行表面涂层处理,并与未涂层水泥砂浆和涂丙烯酸的水泥砂浆相比较,系统研究了改性有机硅涂层对防水抗渗性能、抗碳化性能、抗氯离子渗透等性能的影响。试验结果表明：有机硅外涂水泥砂浆呈现出较好地疏水效果,使用有机硅外涂水泥砂浆的防水抗渗性能大大改善了;与空白组、丙烯酸组相比,涂有有机硅涂层的砂浆的氯离子扩散系数显著降低,约为空白组的1／4,约为丙烯酸组的1／3;随着养护时间的增加,涂有有机硅涂层的试块的碳化程度明显低于空白组和丙烯酸组,而且碳化深度增长速度明显变慢;空白样水泥砂浆密实性较差,表面粗糙多孔,试块结构疏松,而加了硅烷的试块涂料与水泥浆表面粘结紧密,界面区并不明显。为烷氧基有机硅烷作为水泥砂浆防护材料实际工程应用奠定一定的基础。     

硅烷偶联剂改性对聚丙烯纤维抗裂效果的影响

采用乙烯基三乙氧基硅烷偶联剂(SCA-1613)对聚丙烯纤维分别进行浸泡和表面接枝改性,并研究了最佳改性工艺条件;通过对开裂指数和断裂能的测试,研究了偶联剂改性对聚丙烯纤维在砂浆中的抗裂性能的影响。结果表明,与未改性纤维相比,经硅烷浸泡处理后的纤维,可明显提高水泥基材料的抗塑性开裂性能,其最佳的纤维体积掺量为0.08%,改性效果较突出。     

Influences of polypropylene fiber and SBR polymer latex on abrasion resistance of cement mortar

Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexural strength, brittleness index (σ_F/σ_C) and abrasion resistance can be improved significantly by the addition of PP fiber and SBR polymer latex. The relationship between the flexural strength and abrasion resistance was analyzed, showing a good linear relationship between them. The reinforced mechanism of PP fiber and SBR polymer latex on cement mortar was analyzed by some microscopic tests. The test results show that the addition of SBR polymer latex has no significant influence on the cement hydration after 7 d curing. Adding SBR polymer latex into cement mortar can form a polymer transition layer in the interfaces of PP fiber and cement hydrates, which improves the bonding properties between the PP fiber and cement mortar matrix effectively.     

Properties and Acceleration Mechanism of Cement Mortar Added with Low Alkaline Liquid State Setting Accelerator

Low alkaline liquid state setting accelerator(LSA) for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement with addition of LSA relating to its setting time and strength development as well as its resistance to sulfate attack for short and long term exposure were experimentally examined. The experimental results showed that 5%-7% addition of LSA significantly accelerated the initial and final setting of Portland cement in the presence or absence of the blending of mineral admixtures, the initial and final setting time being less than 3 min and 6 min respectively. Meanwhile, the early 1 day curing age compressive strength increased remarkably by 20%, while the late 28 th day curing age compressive strength remained almost unchanged as compared with that of the reference accelerator free cement mortar specimen. Furthermore, mortar specimens of cement added with LSA and exposed to 5% Na2SO4 solution showed their excellent resistance to sulfate attack, with their short and long term curing age resistance coefficient to sulfate attack being around 1.04 to 1.17, all larger than 1.0. XRD analysis on hardened cement paste specimens at very early curing ages of several minutes disclosed the existence of more ettringite in specimens added with LSA than that of the reference specimens, meanwhile SEM observation also revealed the existence of well crystallized ettringite at very early hydration stage, suggesting that the accelerated setting of Portland cement can be attributed to the early and rapid formation of ettringite over the whole cement paste matrix due to the introduction of LSA. MIP measurement revealed that hardened cement paste specimens with the addition of LSA presented less medium diameter pores, more proportion of small pores and less proportion of large capillary pores, which is in a very good coincidence with the improvement of strength development of cement mortars added with LSA.