硫酸和硫酸钠混合溶液对砂浆的腐蚀作用

用普通硅酸盐水泥和硫铝酸盐水泥的混合水泥以及磨细高炉矿渣和聚合物乳液配制了4种水泥砂浆,研究了这些水泥砂浆试样在1%(质量分数,下同)硫酸加10%硫酸钠的混合溶液中浸泡不同时间后的质量变化和强度变化.结果发现,混合溶液对4种水泥砂浆都具有强烈的腐蚀作用.磨细高炉矿渣能显著提高砂浆的耐腐蚀性能;进一步添加聚合物乳液(聚胶比为10%),则砂浆的抗表面剥落性能有很大改善,其中尤以苯丙乳液与丁苯乳液的混合乳液改性砂浆效果更好,但添加聚合物乳液会导致砂浆的抗压强度大大降低.此外,水泥砂浆试样在混合溶液及清水中浸泡后,它们的抗压强度比值要比它们的抗折强度比值对硫酸/硫酸钠腐蚀介质更为敏感.     

水泥混凝土用聚乙烯醇纤维的耐碱性能研究

为研究聚乙烯醇纤维(PVA)在水泥和混凝土中的稳定性,将聚乙烯醇纤维置于不同温度、不同碱性环境中来研究其性能变化规律。测试不同时间下,聚乙烯醇纤维浸泡后的直径变化、断裂强度保留率和断裂伸长率保留率。结果表明,聚乙烯醇纤维在碱溶液的浸泡下,随着时间延长,直径和断裂伸长率逐渐增加,强度逐渐降低;升高环境温度、增加浸泡溶液浓度,对聚乙烯醇纤维的性能有显著的影响。     

含矿渣水泥水化反应产物密度与强度变化特征

在P·Ⅱ52. 5级水泥中加入一定量的矿渣,并制备成水泥石样品,养护至不同的龄期,测定水泥石密度值、强度值与养护龄期的对应值,采用了XRD检测样品水化产物进行关联分析。试验结果分析表明:未加入矿渣的水泥石样品28 d前的强度持续增加,并高于含矿渣样品;养护至90 d,未加入矿渣的水泥石样品强度相对28 d发生了倒缩,而矿渣含量30%的水泥样品强度持续增长,并超过未加入矿渣的水泥石样品;XRD测试结果表明,矿渣的加入改变了水泥石的水化产物组成,且引起了水泥石水化产物的密度的变化,28 d后含矿渣水泥水化样品的密度呈不断增长的趋势。     

聚合物水泥砂浆的耐酸腐蚀性能

研究了聚合物水泥砂浆浸泡于盐酸、硫酸、醋酸溶液后的强度、质量损失率.实验表明:掺加聚合物乳液可改善水泥砂浆试件的耐酸腐蚀性能,且随着聚合物乳液掺量的增加,其改性效果明显;相比之下,掺加聚合物乳液对改善水泥砂浆试件的耐盐酸腐蚀性能较为明显,对耐硫酸、醋酸腐蚀的改性效果较差;聚合物乳液在水泥-水体系中,包覆于水泥水化产物表面,形成高分子聚合物膜,与水泥水化产物互相穿插,可提高水泥砂浆的强度,减少颗粒的剥蚀性,从而改善水泥砂浆的耐酸性.     

改性再生细骨料对胶砂性能影响的试验研究

采用2%盐酸溶液、硅烷溶液改性再生细骨料,研究了改性前后再生细骨料的物理性能和胶砂力学性能。研究结果表明,采用两种改性方法均降低了再生细骨料的吸水率、压碎指标,用其成型的水泥胶砂力学性能也均得到明显改善,其28 d的抗折强度趋近于天然细骨料水泥胶砂,硅烷浸泡再生细骨料水泥胶砂为天然细骨料水泥胶砂强度的109%,2%盐酸浸泡再生细骨料水泥胶砂抗压强度为天然细骨料胶砂强度的96%。对比2%盐酸溶液,硅烷浸泡改性再生细骨料效果更为显著。     

氧化石墨烯对碱矿渣水泥增韧效果研究

作为环保胶凝材料,碱矿渣水泥的低韧性限制了其大规模应用。采用改进Hummers法制备氧化石墨烯,研究不同掺量的氧化石墨烯对碱矿渣水泥水化放热、抗折强度、抗压强度和韧性的影响。结果表明:氧化石墨烯能够提高碱矿渣水泥后期水化放热,增大碱矿渣水泥后期水化程度;氧化石墨烯的掺入提高了碱矿渣水泥砂浆的抗折强度,略微降低其抗压强度,显著增加了碱矿渣水泥的韧性,当氧化石墨烯掺量为0.03%,碱矿渣水泥的韧性大幅提高,60 d折压比较空白组提高了51.9%。     

超细矿渣粉水化反应特征及活性评价

比较并改进流行的矿渣活性指标的测试方法,测试了超细矿渣粉的活性,并研究超细矿渣粉-水泥胶凝体系的水化机理及水化产物。试验结果表明超细矿渣粉-水泥胶凝体系Na OH溶液浸泡养护模式激发效果最好,活性指数达到116%。XRD分析表明超细矿渣粉-水泥胶凝体系的主要水化产物是、钙矾石。水化早期钙矾石峰随着矿粉掺入量而增强,胶凝体系的早期强度主要来自AFt晶体结构网络。随着超细矿渣粉逐渐消耗水泥水化产生的Ca(OH)2,体系后期强度主要来自超细矿渣粉在Ca(OH)2激发下反应得到的CSH凝胶网络。     

大掺量矿渣水泥抗硫酸盐侵蚀性能测试方法研究

对通过化学激发自制的大掺量矿渣水泥的抗硫酸盐侵蚀性能进行评定:首先采用长期浸泡方法进行测定,评判指标为线膨胀率和抗折强度比,结果表明该矿渣水泥具有优异的抵抗高浓度硫酸盐侵蚀的性能;其次采用GB/T 749-2001规定的快速试验方法进行测定,测定结果与长期浸泡方法有异.采用改进的快速试验方法,并以线膨胀率差(掺石膏粉试体14 d线膨胀率-正常试体14d线膨胀率)来评定矿渣水泥的抗硫酸盐侵蚀性能,可避免矿渣水泥水化过程中微膨胀所带来的附加干扰,从而使其测试结果与长期浸泡方法相同.     

改性聚丙烯纤维增强磷酸镁水泥砂浆的力学性能研究

增强磷酸镁水泥砂浆(MPCM)的抗弯韧性有利于促进其在混凝土路面修复领域的应用。为了增强MPCM的抗弯韧性,对比研究了未处理和硅烷偶联剂预处理的聚丙烯纤维对MPCM抗弯韧性的影响,分析了预处理聚丙烯纤维增韧MPCM的机制。结果表明,聚丙烯纤维质量掺量0.4%时,MPCM7d抗折强度增大23.5%;6-10mm聚丙烯纤维有利于提高MPCM的抗压强度,而10-19mm聚丙烯纤维更有利于提高MPCM的抗折强度;未处理聚丙烯纤维与磷酸镁水泥(MPC)水化产物之间为物理作用,聚丙烯纤维并未充分发挥增韧效果;用浓度20%的硅烷偶联剂溶液改性处理30~60min有利于改善聚丙烯纤维与MPC水化产物的界面粘结,使MPC水化产物和预处理后的聚丙烯纤维产生嵌合作用,显著地增强了MPCM的抗弯韧性。     

粉煤灰、矿渣对水泥水化热的影响

研究了不同水灰比硅酸盐水泥净浆的水化放热过程,以及用粉煤灰、矿渣粉配制成的混合水泥的水化放热过程,并研究了硅酸盐水泥和混合水泥的强度发展规律.试验结果表明:用粉煤灰、矿渣粉等量取代部分水泥,胶凝材料的水化热比硅酸盐水泥的水化热要低,但降低的幅度不完全与粉煤灰、矿渣粉的掺量成比例.单从降低胶凝材料水化热的角度看.掺粉煤灰的效果最好,掺矿渣粉的效果次之.强度试验结果表明,用粉煤灰和矿渣取代部分水泥的试件比同水灰比的水泥净浆试件的早期抗压强度小,但是后期强度增加快,从28 d强度看还是不及纯水泥净浆的强度.     

锈蚀后钢纤维和钢纤维混凝土的力学性能

通过对剪切型、铣削型、切断型3种钢纤维和钢纤维混凝土的快速锈蚀试验,研究了锈蚀前后钢纤维的外观、弯折性能和抗拉强度的变化,以及钢纤维混凝土经过不同锈蚀时间后的抗压强度和抗拉强度的变化规律.结果表明:随锈蚀时间的增加,钢纤维的锈蚀程度逐渐增大,弯折性能和抗拉强度逐渐降低,钢纤维混凝土的抗压强度和抗拉强度随之减小.但是抗压强度和抗拉强度的变化规律有所不同,当锈蚀时间较短时,抗压强度变化不明显,在锈蚀时间超过60d以后,抗压强度显著降低.而抗拉强度随锈蚀时间的增加逐渐下降.锈蚀时间相同时,抗拉强度的降低幅度比抗压强度的降低幅度小.切断型钢纤维的抗锈蚀能力相对较好,剪切型和铣削型钢纤维的抗锈蚀能力相对较差.     

玻璃纤维增强水泥耐久性研究的进展

玻璃纤维增强水泥(GRC)具有抗拉、抗弯、抗冲击、重量轻等多种优点。但长期性能降低限制其在更大范围内使用。对其长期性能降低的机理,国内外有许多学说,也提出了多种改善其耐久性的措施,例如改变玻璃纤维化学成分、基体改性、玻璃纤维表面涂覆处理、界面改善等。目前,其耐久性研究面对着确定加速老化试验方法及标准、搞清长期潮湿环境下GRC性能降低的机理、降低低碱度水泥的高成本、进一步改善普通硅酸盐水泥经掺合料改性后引起的早期强度降低和玻璃纤维性能等课题。     

亚微级纤维素纤维对水泥浆体微观结构的影响

以H_2SO_4溶液酸解脱脂棉的方法制备亚微级纤维素纤维(SCF),研究了其对水泥浆体微观结构的影响.结果表明:原始脱脂棉在酸解作用下,微原纤逐步剥离,形成尺度细小的亚微级纤维素纤维,且其直径随着H_2SO_4溶液质量分数的增大、酸解时间的延长而逐渐减小;亚微级纤维素纤维与水泥浆体具有很好的相容性,水泥水化产物依附于亚微级纤维素纤维表面生长;由于亚微级纤维素纤维在尺度上与C-S-H凝胶相匹配,因此随着水泥水化产物的不断生成、生长,该纤维逐渐被其包埋,从而起到诱导和桥接作用,使水泥浆体的微观结构更加均匀.     

化学沉积法改善纤维水泥基体的界面性能

为了改善合成纤维-水泥基体界面黏结性质,通过化学沉积纳米二氧化硅,制备了一系列的改性纤维.使用X射线能谱仪(EDS)确认二氧化硅的存在,采用扫描电镜(SEM)观察纳米颗粒在纤维表面的分布,从而评价化学沉积时间对沉积效果的影响,并通过单丝纤维拔出行为和塑性抗裂性能试验证实改性纤维的优势.结果表明:对聚丙烯(PP)纤维而言,合适的化学沉积时间为60 min,此时纳米二氧化硅粒子的平均粒径为300 nm;聚乙烯醇(PVA)纤维表面具有的亲水性质,使纳米二氧化硅在其上的分布形态与在PP纤维上明显不同;改性纤维的界面黏结强度显著提高,表现出优良的抗裂性能,其原因可能是由于二氧化硅的水化活性,水化产物在单丝拔出及塑性抗裂时起到了物理锚固及化学键合的双重作用.     

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement (CSA), ordinary Portland cement (OPC), and calcium sulfate (CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength (UCS), splitting tensile strength (STS), and volume change of fiber-added expansive mixtures were determined at different time periods (i.e. the strengths on the 28th day, and the volume changes on the 1st, 7th, 14th, 21st, and 28th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to 50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and 16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.     

碱激发矿渣净浆对氯离子的固化作用

为研究氯盐浸泡液pH值、激发剂种类对碱激发矿渣(AAS)净浆氯离子固化量的影响规律,采用氯盐暴露-平衡法、X射线衍射(XRD)、热分析(TGA-DSC)、扫描电镜(SEM)等分析了AAS净浆在氯盐浸泡前后的水化产物种类及微观形貌,同时对AAS净浆固化氯离子中的物理吸附和化学结合作用进行了量化评价.结果 表明:AAS净浆的氯离子固化量随着氯盐浸泡液pH值的增大而降低;水玻璃激发矿渣(WAS)净浆固化氯离子的能力大于NaOH激发矿渣(NAS)净浆;AAS净浆对氯离子的固化作用不仅包括物理吸附作用,还包括少量化学结合作用;氯离子固化过程中的物理吸附作用在NAS、WAS和普通硅酸盐水泥净浆中均占50％以上.     

国产碳纤维拉伸性能研究

通过单丝拉伸试验方法对国产碳纤维的单丝拉伸性能进行系统测试,并采用Weibull分布函数对拉伸强度进行统计分析。结果表明,国产碳纤维的单丝拉伸性能指标与东丽T700级和台丽TC36S型碳纤维仍存在较大差距。扫描电子显微镜SEM分析说明,东丽T700级碳纤维表面光滑平整,台丽TC36S型碳纤维表面有较浅沟槽,国产碳纤维单丝表面沟槽较宽、较深,表面结构的特点可能是导致国产碳纤维拉伸强度较低的主要原因。     

Performance of an alkali-activated slag concrete reinforced with steel fibers

This study investigated mechanical and permeability properties at early ages of an alkali-activated slag concrete (AASC) reinforced with steel fibers. The compressive, splitting tensile and flexural strengths, flexural notch sensitivity, pull-out and water absorption properties were evaluated. Test results reveal a reduction of AASC compressive strengths with fiber incorporations. However, splitting tensile and flexural strengths were largely improved with increasing fiber volume, varying from 3.75 to 4.64 MPa and from 6.40 to 8.86 MPa at 28 days of curing, respectively. The properties related to durability performance as water absorption, capillarity and water resistance penetration were enhanced with the steel fibers addition. The results show the enormous potential of AASC as building material with and without steel fiber reinforcement.     

Strain-hardening fiber cement optimization and component tailoring by means of a micromechanical model

It is well known that fibers can impart tensile ductility into fiber cement products. Specific rational guideline for engineering desirable fiber, matrix, and interface properties leading to optimized fiber cement product performance; however, is scarce. This paper discusses the theoretical basis for composite optimization of synthetic fiber reinforced cement that leads to maximum tensile ductility while minimizing the content of the expensive fiber component of fiber cement products. Specific tailoring of polyvinyl alcohol (PVA) fiber and polypropylene (PP) fiber and experimentally verified tensile ductility characteristics of the resulting fiber cement products are employed to illustrate the theoretical concepts. It is demonstrated that high product performance can be achieved with minimal amount of fibers via composite optimization. The theoretical tools developed are applicable to a wide range of fiber types and matrix types.     

Evaluation of fiber reinforcement on the strength behaviors of dredging slurry cemented at high water content

This study evaluates the strength behaviors of dredging slurry at high water content reinforced by polypropene fibers. Variables, including cement content, curing time, fiber content, fiber length, and water content, were applied to study the effects on the strength of the treated slurry. The unconfined compressive strength was lower with slurry at higher initial water content at 174% than that at 145% at given cement content regardless of fiber contents; and that increases with increasing fiber content at all cement contents at the water content of 174%; whereas, the effect was less significant at water content of 145%. The fiber length was not observed to affect the strength of the treated slurry in this study. The fiber-soil network would form and be enhanced by the hydration products of cement, limiting the development of cracks. The cement content and curing time dominate the stress–strain behaviors of dredging slurry. In addition, three forms of failure were observed with fiber-reinforced dredging slurry. The admixture of polypropylene fiber would restrict the development of cracks upon failure, improving the brittleness and increasing strain at failure of treated slurry.