两种乳胶粉对三元胶凝体系饰面砂浆性能的影响

研究了乙烯-醋酸乙烯共聚物(乳胶粉A)及乙烯-醋酸乙烯-丙烯酸酯三元共聚物(乳胶粉B)对铝酸盐水泥-硅酸盐水泥-半水石膏三元体系饰面砂浆抗泛白性、耐沾污性、吸水性及力学性能的影响。结果表明,乳胶粉B对各项性能的作用效果均优于乳胶粉A。乳胶粉B掺量为0~6%时砂浆7d泛白等级为0级;适当掺量的乳胶粉B能改善砂浆的耐沾污性,在其掺量大于等于12%时,砂浆的耐沾污性优于未掺乳胶粉的砂浆;乳胶粉A的掺量为3%~9%时,乳胶粉B掺量为3%~15%时可改善砂浆的吸水性;乳胶粉A能提高砂浆抗折强度及拉伸粘结强度,但会降低砂浆的抗压强度,而乳胶粉B能同时提高砂浆的抗折强度、抗压强度及拉伸粘结强度。     

聚合物水泥砂浆的力学性能

本文采用美国产ＭＴＳ试验机,分别研究了掺聚醛酸乙烯水泥砂浆的轴拉和轴压应力－应变关系及抗弯性能。试验结果表明,随着聚醛酸乙烯的掺入,砂浆的轴压强度和弹性模量显著下降,但极限应变却明显增大;砂浆的轴拉强度和抗弯强度均略有提高,而极限应变、拉压强度比和弯压强度比则显著增加。因此,掺入聚醛酸乙烯能有效改善砂浆的变形力学性能。根据１２年龄期的粘结抗弯强度试验结果,聚醛酸乙烯砂浆不但具有优良的粘结性能,还具有良好的耐久性,可广泛用于新老混凝土的粘结、修补及结构加固中的钢板粘贴和表面粉刷等。     

核壳结构苯丙乳胶粉的制备与表征

采用半连续种子乳液聚合法,合成了具有核壳结构的丙烯酸酯聚合物乳液,利用喷雾干燥技术制得可再分散苯丙乳胶粉.研究了乳胶粉的再分散性、乳胶粉粉体颗粒到成膜过程的微观状态、核壳比例对乳胶粒核壳结构的影响、乳化剂用量对再分散性的影响及乳胶粉在干混砂浆中的成膜性能.结果表明,乳胶粉无团聚,再分散可以恢复到原乳液的纳米尺寸,成膜时蓝光明显;乳化剂用量为0.9％时,聚合稳定性和再分散性较好.透射电镜测试表明核壳比为8∶2、5∶5均得到了清晰的核壳结构的乳胶粒,扫描电镜测试表明乳胶粉在干混砂浆中可以起到良好的粘结作用.     

丁苯乳液改性水泥砂浆的物理性能

本文研究了丁苯乳液SD622S改性水泥砂浆的物理性能,包括新拌砂浆的减水率、保水率、体积密度、凝结时间,硬化砂浆的体积密度、孔隙率、毛细孔吸水率等.实验结果表明:丁苯乳液可提高砂浆的减水率和保水率,使砂浆的凝结时间延长.随着丁苯乳液掺量的增加,硬化砂浆的毛细孔吸水率降低.丁苯乳液使新拌砂浆和硬化砂浆的体积密度减小,但随聚合物掺量的增加有所回升.硬化砂浆的孔隙率随聚合物掺量的变化趋势正好相反.     

PVAc胶乳改性水泥砂浆的性能

采用聚醋酸乙烯酯(PVAc)胶乳制备了改性水泥砂浆,研究了PVAc胶乳对砂浆工作性能、粘结强度、力学强度和吸水率的影响;通过扫描电镜(SEM)表征了改性砂浆的微观形貌。结果表明:当PVAc掺量由0增加到25%,改性砂浆的粘结强度增长幅度超过90%;PVAc胶乳掺量小于13%时对延长砂浆的凝结时间、提高砂浆的韧性有显著作用,并可大幅度降低压折比、吸水率;当PVAc掺量超过18%,改性砂浆的吸水率低于1%;SEM测试结果表明PVAc胶乳固化物可有效填充水泥砂浆的内部孔隙,在水化物与集料之间起到桥接作用,使水泥石结构更致密。     

可再分散乳胶粉对硫铁矿尾砂自流平砂浆性能的影响

探究硫铁尾矿砂在自流平砂浆的资源化利用途径,以硫铁矿尾砂为细集料制备水泥基自流平砂浆,分析了可再分散乳胶粉掺量对砂浆流动度、力学性能及耐磨性的影响。结果表明：乳胶粉掺量可以显著降低20 min、60 min 后的流动度经时损失,乳胶粉掺量为2.0%时,砂浆的拉伸粘结强度为1.9 MPa,并在天然河砂与尾砂复配情况下,尾砂替代率为75%时,磨损量仅有0.09 kg/m2。     

三氟氯乙烯-醋酸乙烯酯-叔碳酸乙烯酯含氟乳液的合成

以三氟氯乙烯、醋酸乙烯酯、叔碳酸乙烯酯为主要原料,制备固相质量分数约为33%,乳胶粒子粒径为151～205 nm的一系列稳定的三元含氟共聚物乳液,并对聚合物结构进行红外光谱表征,通过透射电镜观察乳胶粒子的形态,讨论乳化剂全氟辛酸铵用量、引发剂过硫酸钾用量及反应温度对共聚胶乳粒径的影响和单体配比对乳液最低成膜温度和聚合物玻璃化温度的影响。结果表明,随着全氟辛酸铵用量和过硫酸钾用量增大和反应温度升高,乳液中乳胶粒子的粒径变小;随着过硫酸钾、全氟辛酸铵用量增加,乳胶粒子数量逐渐增加;随着叔碳酸乙烯酯用量的增加,乳液最低成膜温度和聚合物玻璃化温度都变小。     

核壳结构苯丙乳胶粉的制备与表征

采用半连续种子乳液聚合法,合成了具有核壳结构的丙烯酸酯聚合物乳液,利用喷雾干燥技术制得可再分散苯丙乳胶粉。研究了乳胶粉的再分散性、乳胶粉粉体颗粒到成膜过程的微观状态、核壳比例对乳胶粒核壳结构的影响、乳化剂用量对再分散性的影响及乳胶粉在干混砂浆中的成膜性能。结果表明,乳胶粉无团聚,再分散可以恢复到原乳液的纳米尺寸,成膜时...     

有机纤维与聚合物复掺改性水泥砂浆力学性能研究

要 在固定水灰比为0.35条件下,分别研究了聚酯纤维、聚合物丁苯乳液单掺与复掺时对水泥混凝土抗压抗折强度、折压比的影响.结果表明:单掺聚酯纤维在一定掺量下可以不同程度地提高水泥砂浆的抗压抗折强度,折压比随着聚酯纤维含量的增加呈先减小后增加的趋势;单掺聚合物乳液降低了水泥砂浆的抗压强度,而折压比则随聚合物乳液掺量增加呈现逐步变大的趋势;聚酯纤维与聚合物乳液复掺时,聚合物乳液的掺入使聚酯纤维混凝土的抗压强度出现小幅降低,增强了其抗折强度,提高了其折压比,当纤维体积掺量为0.1％、聚灰比为15％时,聚酯纤维聚合物水泥混凝土的柔性最大;纤维-聚合物复掺能够使其性能得到进一步改善,效果优于两者的单掺效果.并通过扫描电镜探讨了聚酯纤维与聚合物乳液在水泥砂浆中的作用机理,表明两者复掺有效填充了水泥基材料内部的宏观与微观缺陷,提高了界面过渡区的密实程度.     

橡胶微粉对无机聚合物胶凝材料力学性能的影响

主要研究了橡胶微粉对无机聚合物砂浆和水泥砂浆力学性能的影响.实验结果表明,随着橡胶微粉掺量的增加,无机聚合物砂浆和水泥砂浆的抗压强度、抗折强度均有所下降,其中无机聚合物砂浆弹性模量降低、变形能力增强、弯曲韧性系数稍有降低;水泥砂浆弹性模量升高、变形能力下降、弯曲韧性系数下降.分析材料微观破坏形貌后发现,与水泥砂浆相比,橡胶微粉与无机聚合物砂浆界面粘结较好,粘结强度高,从而造成无机聚合物砂浆和水泥砂浆这两种材料体系在橡胶微粉掺杂后力学性能的差异.     

Study of cement mortars modified by emulsifier-free latexes

Cationic copolymer latex of vinyl acetate (VA) with methacryloxyethyl trimethylammonium chloride (MTC) and anionic copolymer latex of VA with sodium acrylate (SA) were prepared via emulsifier-free emulsion copolymerization. Modifications of cement mortars by these copolymer latexes were studied, and the results were compared with mortars modified by homopolymer of VA (PVA) as well as with blank mortars. The experimental results showed that flow of the mortars modified by PVA homopolymer and P(VA–MTC) copolymer latexes were increased compared with the blank, whereas a decrease was observed for that modified by P(VA–SA) anionic copolymer latex; a volume expansion was detected in polymer modified mortars by PVA and P(VA–MTC), while no volume expansion was observed in the anionic P(VA–SA) modified mortars; the flexural strength of mortars modified by P(VA–MTC) increased by 79.5% compared to unmodified mortars after 5 day water curing plus 21 day air curing. This value reached 95% when the curing process was followed by a supplementary 24 h vacuum curing. These polymer modified mortars were then subjected to hydration analysis through X-Ray diffraction (XRD). Mechanisms of the mortar modification are discussed based on the characterization results.     

Function of styrene-acrylic ester copolymer latex in cement mortar

This paper focuses on the effect of the styrene-acrylic ester copolymer (SAE) latex on the performance of cement mortar, through studying on the water-reduction and water-retention effects of the SAE latex in the mortar, and the influence of the SAE latex on the air-content and the bulk density of the fresh mortar and the bulk density, compressive and flexural strengths, shrinkage rate, water capillary adsorption and anti-penetration capacity of the hardened mortar. The experimental results show that the SAE latex has good water-reduction and water-retention effects in mortar. The SAE latex has also air entrainment effect, increasing the air content and reducing the bulk density of the fresh mortar. The apparent bulk density and dry bulk density of the hardened mortars decrease with the increase of the SAE latex/cement-ratio (m_p/m_c) and the change is in accordance with that for the bulk density of the fresh mortar. The SAE latex influences the development of the compressive strength but slightly on the flexural strength, and improves the toughness, shrinkage property, waterproofing quality and anti-penetration capacity of the mortar significantly.     

Compressive strength of mortar containing natural pozzolan under various curing temperature

A first set of mortar specimens was made with 0%, 10%, 20%, 30% and 40% of natural pozzolan replacement and cured under constant curing temperature of 20, 40 and 60 °C with saturated humidity. The second set incorporating only 20% of natural pozzolan was exposed to elevated temperatures for 1, 3 and 7 days and then cured in saturated environment under a temperature of 20 °C. This paper presents the experimental results of the mortar properties such as the ultimate strength, the half age of strength and the activation energy. The introduction of the pozzolan enhances the ultimate compressive strengths and increases the activation energy which indicates the slow reactivity. The effect of the temperature on the ultimate strengths is evaluated by a new model. By using the equivalent time method, we could estimate the strength at 28 and 90 days of the second set mortar. This method satisfactorily predicts the strength of concrete cured at any temperature history.     

低温快速固化环氧导电胶的制备与性能

采用E-51型环氧树脂为导电胶基体树脂, 低分子量聚酰胺树脂(PA)为固化剂, 填加经硅烷偶联剂(KH550)改性后的纳米级和微米级铜粉及助剂制备导电胶。首次采用了液态固化剂(低分子量的聚酰胺酯), 以解决导电胶制备过程中填料用量受限的难题。通过正交试验方法探讨了导电胶中导电填料的含量、导电填料配比、硅烷偶联剂用量和还原剂添加量对导电胶粘接性能和导电性能的影响, 对导电胶的制备工艺进行了优化, 获得了制备导电胶的最佳方案。测试结果表明该导电胶能够在60 ℃下4 h内快速固化。在填料质量分数为65%时, 导电胶具有最低的体积电阻率3.6×10-4 Ω·cm; 导电胶的抗剪切强度达到17.6 MPa。在温度为85 ℃、湿度(RH)为85%的环境下经过1000 h老化测试后导电胶电阻率的变化和剪切强度的变化均不超过10%。      

两种沥青胶浆的疲劳及自愈合性能试验

为了研究沥青胶浆的疲劳及自愈合特性,利用动态剪切流变仪（DSR）进行时间扫描及疲劳-愈合-再疲劳测试,并通过原子力显微镜（AFM）对细观结构进行观测,比较分析了不同粉胶比下基质沥青胶浆和苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）改性沥青胶浆的疲劳性能,以及在常温（25℃）下3个不同间歇期的自愈合性能。试验发现：SBS沥青胶浆具有更好的疲劳和自愈合性能,两种沥青胶浆疲劳寿命均随粉胶比的增大而增加,同一粉胶比条件下,更长的间歇期有利于其自愈合,过大或者过小的粉胶比都会降低沥青胶浆的自愈合性能;AFM观测结果表明：基质沥青胶浆出现明显的"蜂状结构",粉胶比增加,矿粉吸附更多的沥青质,"蜂状结构"变多,与沥青界面内聚力作用增强,提高了抗疲劳性能,SBS改性剂与沥青相容性良好,改性沥青胶浆没有出现"蜂状结构",改性剂的加入增强了分子间内聚力,有助于提高抗疲劳性能,因此建议路面材料选用改性沥青胶浆。     

Styrene–butadiene latex modified calcium aluminate cement mortar

This paper investigates properties of calcium aluminate cement (CAC) mortar modified with the styrene–butadiene-rubber (SBR) latex. This material may be advantageously applied as a rapid repair mortar. Mortar specimens were prepared with constant water-to-cement mass ratio; polymer solid content of latex was varied from 0% to 9%, and Li₂CO₃ was investigated as an accelerator. Specimens were treated at different curing conditions: 1, 7 days and transformation of metastable hydration products at 70 °C. The heat of hydration evolution of mortar specimens was measured by means of a self adopted isoperibol calorimeter.The measurement results indicate that SBR latex improves workability of fresh state mortar and retards nucleation and growth of hydration products. Due to polymer coagulation process and co-matrix formation permeability, stiffness and compressive strength decrease while adhesion strength to old concrete substrate, and flexural strength increase with amount of added latex.     

丙烯酸酯改性EVA乳液胶黏剂的黏结性能研究

采用单一变量法,选择醋丙乳液、纯丙乳液、苯丙乳液、硅丙乳液分别改性EVA乳液胶黏剂,研究丙烯酸酯乳液与EVA乳液的共混效果,以及不同类型的丙烯酸酯乳液对EVA乳液胶黏剂黏结性能的增黏效果。热力学、差示量热扫描、红外光谱测试结果表明,丙烯酸酯乳液能够与EVA乳液互溶。剥离强度、高温黏结性能、低温黏结性能测试结果表明,经丙烯酸酯改性的EVA乳液胶黏剂的黏结性能整体得到提高,其中,经醋丙乳液改性的EVA乳液胶黏剂的综合性能最优,能够满足实际使用要求。     

活化煤矸石改性沥青胶浆流变性能实验研究

煤矸石是我国目前排放量最大的工业固体废弃物之一,以粉体煤矸石为填料对沥青进行改性在国内外鲜有研究涉及。采用锥入度实验、动态剪切流变实验(DSR)和弯曲梁流变实验(BBR),研究了不同粉胶比条件下活化煤矸石改性沥青胶浆的剪切强度及高、低温流变性能变化规律,并与矿粉改性沥青胶浆进行对比;在此基础上,初探了活化煤矸石改性沥青胶浆作用机理。结果表明,采用活化煤矸石替代矿粉后,沥青胶浆的抗剪强度和高温性能大幅提高,低温性能则基本相当。研究成果为活化煤矸石替代矿粉作为沥青混合料填料的可行性提供了依据。     

An explanation for the negative effect of elevated temperature at early ages on the late-age strength of concrete

Elevated curing temperature at early ages usually has a negative effect on the late-age strength of concrete. This article aims to study the mechanism of this phenomenon. The results show that elevated curing temperature at early ages has a negative effect on the late-age strength of hardened cement paste, but it has a greater negative effect on the late-age strength of cement mortar. After elevated temperature curing at early ages, the late hydration of cement is hindered, but the late reaction of fly ash is not influenced. Owing to the continuous reaction of fly ash, the late-age pore structure of cement–fly ash paste under elevated curing temperature is finer than that under standard curing temperature, and the late-age strength of cement–fly ash paste under elevated curing temperature is higher. However, the late-age strength of cement–fly ash mortar under elevated curing temperature is lower. Apparently, there are differences between the effects of elevated curing temperature on hardened paste and mortar. It is the deterioration of transition zone between hardened paste and aggregate that makes the negative effect of elevated curing temperature on the mortar (or concrete) be greater than the hardened paste. As the water-to-binder ratio decreases, the negative effect of elevated curing temperature on the transition zone tends to be less.     

Bond strength of PCC pavement repairs using metakaolin-based geopolymer mortar

In order to use geopolymer mortar as a pavement repair material, a splitting test and a slant shear test are performed to characterize the bond strength of the geopolymer and conventional cement mortar interfaces. Effect of curing time, degradation of the cement mortar under different acid conditions on the bond strength of geopolymer with conventional cement mortar, and comparison of the metakaolin geopolymer with other pavement repair materials are analyzed. It was found that curing time affects the interface bond strength greatly. Metakaolin geopolymer reaches 80% of its 28 day strength in 3 days curing, but shows low strength in 24 h curing. Curing temperature affects the strength of metakaolin geopolymer, however metakaolin geopolymer cured in ambient temperature and the bond strength of 3 days curing through splitting and slant shear tests reaches 3.63 MPa and 16.32 MPa, respectively. Degradation of cement mortar negatively affects the bond strength of geopolymer and conventional cement mortar. Possibility of using metakaolin geopolymer as a repair material is discussed by comparison of this experimental result with these of other repair materials.