纤维、粉煤灰复合高性能道面混凝土应用研究

针对传统机场道面混凝土易开裂、耐久性不良的现象,采用在普通道面混凝土中掺加纤维、粉煤灰的技术路线,研究配制适合严寒干旱地区的新型高性能道面混凝土,并进行了抗裂、抗冻、抗渗、耐磨综合性能试验。试验结果表明：单掺粉煤灰或纤维,均能大大提高普通道面混凝土的抗裂性和耐久性,尤其是纤维、粉煤灰复合时,道面混凝土抗裂性和耐久性能进一步得到提高,是一种适合寒冷干旱地区的新型高性能道面混凝土。     

新型高性能道面混凝土抗裂性研究与应用

针对寒冷干旱地区机场道面铺筑水泥混凝土后经常出现早期裂缝的现象,为找到既能大幅度减少混凝土早期开裂又能满足设计要求的混凝土材料,采用在普通混凝土中单掺合成纤维或粉煤灰以及合成纤维与粉煤灰复合的技术路线,研究配制高抗裂的高性能道面混凝土,采用平板法对其早期抗裂性进行试验验证,并在多个机场道面工程中进行了应用,抗裂效果很好。     

高性能道面混凝土抗冻耐久性研究与应用

针对传统的普通道面混凝土施工和易性不易控制、强度储备偏低、道面表面品质差、耐久性不良等现象,通过掺加粉煤灰、引气剂、减水剂等外掺剂配制高性能道面混凝土。室内试验和现场应用效果均表明：与普通道面混凝土相比较,掺粉煤灰、引气减水剂的高性能道面混凝土施工方便,匀质性好,强度和抗冻性能均有显著提高。建议在严寒、寒冷地区修建的机场道面工程应大力推广应用掺外掺剂的高性能混凝土。     

克裂速纤维增强混凝土抗裂性能

用聚丙烯纤维来防止混凝土的早期塑性收缩裂缝是近年来为解决混凝土裂缝难题而采取的新措施。研究了两种聚丙烯纤维(Cemfiber和DF)的掺量、纤维种类等参数对塑性收缩裂缝的影响规律;分别采用圆形、平板状试件来研究砂浆、普通混凝土和高性能混凝土的抗裂性能。研究结果表明:(1) 聚丙烯纤维可以显著提高混凝土抗裂能力,纤维掺量越高,抗裂能力越强;(2) 为防止裂缝,应该尽可能降低水泥用量和提高骨料用量;(3) 聚丙烯纤维提高混凝土抗裂能力的主要原因是纤维提高混凝土的早期应变能力、减小收缩应变、提高塑性抗拉强度和减小毛细管的表面张力。     

纤维及矿物掺合料对煤矸石混凝土力学性能的改性研究

以煤矸石全替代普通混凝土中粗骨料的煤矸石混凝土为基础,研究不同体积掺量的聚乙烯醇(PVA)、聚丙烯(PP)及钢(ST)纤维对其力学性能的影响。选取最优力学性能下的纤维种类与掺量,继而探求其对单掺粉煤灰及粉煤灰/矿粉复掺替代部分水泥时的煤矸石混凝土力学性能的改性作用,得出最佳改性煤矸石混凝土配合比。结果表明,PVA、PP纤维掺量过多抑制了煤矸石混凝土的强度发展,存在最佳掺量,ST纤维在体积掺量为2%时,相较其他组可以最大幅度提高煤矸石混凝土的力学性能,其中对混凝土劈裂抗拉强度具有最佳改性效果。随着粉煤灰替代率的增加,降低了煤矸石混凝土的强度,30%替代率下粉煤灰/矿粉掺比为1∶2时煤矸石混凝土出现了矿物掺合料替代组合中的强度峰值,2%体积掺量的ST纤维对此时煤矸石混凝土改性后,使其达到了最优力学性能。     

聚丙烯纤维在厦门某工程地下室混凝土中的应用及其作用分析

本文阐述了一种新型的合成纤维--聚丙烯纤维在混凝土中的应用效果。实践表明,聚丙烯纤维掺加在混凝土中可以起到阻裂和细化裂缝的作用,明显地改善了混凝土的微观结构,使混凝土中原生的微裂纹减少、裂缝宽度减小,这必然使混凝土硬化体的抗渗性和韧性得到相当程度的提高,使混凝土表面光滑,进而使混凝土的耐久性得到大幅度的提高。使得聚丙烯抗裂纤维混凝土被广泛应用在大面积地下筏板、侧墙、顶板及道路面层、水工混凝土之中。     

纤维对开裂后混凝土渗透性及裂缝恢复的影响

通过劈裂试验和渗透试验,研究了结构型钢纤维、聚丙烯粗纤维和聚丙烯细纤维对开裂后混凝土的裂缝恢复率、劈裂韧性和渗透系数的影响。研究结果表明:钢纤维和聚丙烯粗纤维的掺入可限制裂缝扩展,使混凝土由脆性破坏转为韧性破坏,提高开裂混凝土在卸载后裂缝的恢复作用,显著减小开裂后混凝土的渗透系数。钢纤维掺量越高,裂缝恢复和渗透性降低越明显,钢纤维掺量由25kg/m~3增加至55kg/m3时,渗透系数减小了87%。钢纤维和聚丙烯粗纤维的掺入具有较好的正混杂效应,当裂缝宽度为150μm时卸载,单掺25kg/m~3钢纤维和4kg/m~3聚丙烯粗纤维与单掺35kg/m~3钢纤维相比,渗透系数减小了60%。而聚丙烯细纤维对开裂混凝土的裂缝恢复和渗透性影响较小。     

道面再生混凝土试验研究

采用掺加优质粉煤灰和高效外加剂的技术路线,进行了机场道面再生混凝土的强度、抗冻性、抗渗性和耐磨性等试验研究。结果表明：所配制的道面再生混凝土性能优于普通道面混凝土,满足机场道面要求,较普通道面混凝土,抗折强度提高4～11％;抗冻等级提高100％;抗渗等级提高300％以上;耐磨性提高18-36%。     

纤维混凝土的应用研究

通常队为,混凝士强度越高,其韧性越差,脆性越高,结构廷性和抗裂能力越不足,给结构抗震性能带来的安全隐患。在混凝土中掺入微细纤维的纤维混凝土不仅能够提高混凝土本身的延性和韧性,增强混凝土的抗裂性,而且对原材料加工几乎没有特别的要求,成本增加不大甚至还有可能降低。聚丙烯纤维具有耐化学腐蚀性强、强度高、加工性好、质轻、蠕变收缩小、价格低廉和在低掺量下对混凝土的抗裂、增韧效果显著等优良的技术经济性能,因而在建筑工程中得到越来越广泛的应用。聚丙烯纤维混凝土是一种掺入少量短切聚丙烯纤维来增强或改善混凝土性能的复合材料。聚丙烯纤维混凝土在国外应用较多,在我国的工程中应用也日渐增多。低掺量的聚丙烯纤维掺人混凝土后可显著控制混凝土早期收缩裂缝,提高混凝土的耐久性。     

聚丙烯纤维增强混凝土干接缝的抗剪性能

为了研究聚丙烯纤维对预制节段混凝土桥梁干接缝剪切性能的影响,本试验以接缝类型、键齿数量、混凝土类型、聚丙烯纤维掺量和水平正应力大小为试验参数,对C40普通混凝土和C40聚丙烯纤维增强混凝土试件进行抗剪性能的试验研究。记录了试件开裂载荷、极限载荷和残余载荷,同时也研究了试件开裂破坏模式和规范化剪应力-竖直位移曲线的关系。试验结果表明：聚丙烯纤维有利于提高干接缝试件的开裂荷载、极限荷载以及有利于试件的塑性变形;聚丙烯纤维对阻止干接缝试件开裂能起到一定的作用,但是聚丙烯纤维不同掺量的影响规律不明显。     

Effect of supplementary cementitious materials on shrinkage and crack development in concrete

The autogenous and drying shrinkage of Portland cement concrete, and binary and ternary binder concretes, were measured and compared. The binary and ternary binder concretes were formed by replacing part of the cement with fly ash, very fine fly ash and/or silica fume. Restrained shrinkage test was also performed to evaluate the effect of binder type on early age cracking. After the cracking of the restrained ring samples, crack widths were measured and compared with the results of an R-curve based model, which takes post-peak elastic and creep strains into account.The incorporation of fly ash and very fine fly ash decreased the autogenous shrinkage strain but increased the drying shrinkage strain. Since the total shrinkage strains of both the ternary and the binary concrete mixtures were similar, the strength development became an important factor in the cracking. The lower strength of the concrete with ternary binders led to earlier cracking compared to the binary binder concrete. Portland cement concrete cracked the earliest and had the greatest crack width. Measured crack widths were in accordance with the crack widths calculated with the R-curve model.     

聚丙烯纤维-钢筋/混凝土管节受力性能试验

顶管施工中钢筋/混凝土管节存在开裂现象,严重影响工程质量与后续营运。鉴于聚丙烯纤维具有改善混凝土抗拉、抗裂性能的作用,本文采用2种聚丙烯细纤维和1种聚丙烯粗纤维,设计了无纤维、单掺粗纤维及混掺三种尺度纤维的3组钢筋/混凝土管试件,进行了三点试验,对比分析管节的开裂破坏形态、荷载挠度曲线和开裂延性指标。并建立纤维混凝土管节三点试验的有限元模型,进一步探究聚丙烯纤维掺量对钢筋/混凝土管节受力性能的影响规律。结果表明,聚丙烯粗纤维可提高混凝土管的抗裂与承载能力,聚丙烯粗、细纤维的协同作用使管达到更高的使用和极限强度。相比无纤维管,混掺多尺度纤维提升管的使用强度和极限强度分别为28.7%和36.4%。此外,数值模拟合理地预测了纤维/混凝土管节的荷载挠度响应,并针对混凝土管节的极限强度值,得到单掺和混掺聚丙烯纤维时粗纤维的最佳掺量。      

自密实混凝土圆环约束收缩试验研究

进行了密封与沿环外侧面干燥两种条件下的自密实混凝土圆环约束收缩试验,分别研究自密实混凝土试件在自生收缩单独作用下,以及在干燥与自生收缩共同作用下钢环应变随混凝土龄期的发展规律及开裂性能,并与普通混凝土进行比较。配合比参数包括粉煤灰掺量、粉煤灰和矿渣复掺掺量、水胶比。揭示了配合比参数在两种不同条件下对钢环应变和开裂龄期的影响规律,并提出以“标准化”的钢环应变曲线作为开裂趋势曲线,以开裂系数为0.95时的龄期为“名义开裂龄期”作为圆环试验中混凝土开裂指标的建议。研究结果还表明,同一配合比参数对干燥约束收缩与自生约束收缩的作用有可能一致,也有可能完全相反,因此有必要对两种收缩分别研究;该文提出的“开裂趋势曲线”和“名义开裂龄期”能综合混凝土开裂中“作用”和“抗力”两个方面的影响,从而对混凝土的开裂性能进行动态、定量、综合的评价。     

Estimation of the risk for early thermal cracking for SCC containing fly ash

Cracking of concrete must be avoided during the hardening phase in order to minimize the risk of durability problems in the future, such as corrosion of the reinforcement, water tightness and damages due to frost. Estimation of the risk of early age cracking requires knowledge of the combined effects from temperature development and mechanical behaviour during the hydration. In the present paper, the influence of fly ash on the young concrete behaviour has been investigated. The concrete is based on a Swedish cement aimed for civil engineering structures, and the fly ash is of class F. A comparison of crack risks between concrete containing fly ash in different amounts with concrete without fly ash is presented. Also a previously tested concrete containing limestone filler is considered. The fly ash was added to replace a part of the aggregate, which gives a higher heat evolution. However, a numerical stress analysis showed that the risk for early age through cracking for a typical civil engineering structure is significantly decreased in the mixes containing fly ash. The denotation typical civil engineering structure is used here for concrete structures such as tunnels, bridges, and ramps of common cross-section dimensions. In the case of fly ash added to concrete by a partial replacement of cement, the crack risk will probably be further decreased. For a self-balancing structure of young concrete there is no restraint from adjacent structures, and the temperature and moisture gradients within the young concrete cause self-stresses governed by equilibrium with zero external forces for any cut. The estimated risk for surface cracking on a self-balancing wall or slab was not improved by an addition of fly ash. It is probably an effect of the increased heat development, which most likely counteracts the positive effect of the increased early age creep for concrete containing fly ash. If the heat evolution decreases when cement is partly replaced with fly ash, the use of fly ash might reduce the risk of surface cracks.     

Plastic shrinkage cracking of concrete incorporating mineral admixtures and its mitigation

In recent years, there has been a rapid increase in the use of mineral admixtures for high performance and durable concrete. Plastic shrinkage cracking in such concretes is a serious concern in large surface area/volume applications. The present study has two objectives: firstly, to investigate the influence of incorporating fly ash and granulated blast furnace slag (GGBS) on the susceptibility to such cracking; and secondly, to assess the techniques, such as fibre and shrinkage reducing admixture (SRA) addition, and spraying of curing compounds, to mitigate the cracking. The results indicate that replacement of ordinary Portland cement (OPC) with fly ash and GGBS increases the possibility of plastic shrinkage cracking significantly, with higher severity as the replacement level increases; 30% replacement of OPC with fly ash and GGBS doubled and quadrupled the crack area, respectively, mainly due to higher binder finesses, and the delay of setting and strength gain. Among the fibres tested, polypropylene and polyester fibres, at the recommended dosages of about 0.9 kg/m³, completely eliminated cracking in the most affected concrete (i.e., with 30% GGBS) while the dosages of the polyacrylonitrile and glass fibres had to be increased to provide a higher volume fraction. Two glycol-based SRAs, and two curing compounds based on acrylic resin and methacrylate mitigated cracking by significantly reducing evaporation from the surface of concrete.     

粉煤灰／海泡石纤维复合沥青混合料的制备与性能研究

从海泡石纤维和粉煤灰纤维的微观结构特性出发，进行粉煤灰，海泡石复合纤维增强沥青复合材料的制备。通过路用性能试验，研究了海泡石纤维和粉煤灰纤维对沥青混合料性能的影响以及结合机理。结果表明，添加适量海泡石和粉煤灰纤维可以制备性能优良的纤维复合沥青混合料。海泡石纤维对沥青表现极强吸持能力，有效调节沥青与胶浆的含量。粉煤灰纤维在沥青中主要起加固和改善混合料的作用。两种纤维的添加，使沥青混合料的高温变形性、水稳定性、低温抗裂性和抗疲劳性等显著提高。     

Structural behavior of alkali activated fly ash concrete. Part 2: structural testing and experimental findings

Alkali activated fly ash concrete (AAFAC) is an alternative form of concrete that uses coal fly ash as a 100 % replacement for ordinary portland cement (OPC). In this paper structural testing of nine steel reinforced AAFAC beams is explored. The test matrix included three over-reinforced, three under-reinforced, and three shear critical AAFAC beam samples, all tested in four point monotonic bending. For control purposes, an identical set of OPC concrete (OPCC) beams was fabricated and tested under identical conditions. Data collection during testing included load, deflection, top and side fiber concrete strains, and crack width. Test results show that AAFAC beams have very similar behavior to companion OPCC beams. This applies to load induced crack pattern, crack width magnitude, neutral axis location, flexural stiffness, and ultimate flexural and ultimate shear strengths. The research concludes that AAFAC flexural members can be designed using existing ACI 318-08 methods developed for OPCC, and that this applies to both the service and ultimate limit states.     

聚丙烯纤维对混凝土损伤渗透特性的影响

为研究损伤开裂后聚丙烯纤维/混凝土(PPF/PC)的渗透特性,通过圆盘劈裂试验预制了不同宽度的裂缝(100~400 μm),比较了PPF掺量对裂缝曲折度的影响。利用自行设计的渗透试验装置对混凝土损伤后的渗透率进行了研究,分析了不同PPF掺量、不同水压力下混凝土的损伤渗透率的变化规律。通过研究发现,加入PPF后,混凝土脆性较低,内部裂缝更易控制,裂缝曲折度相对于PC更高,且与PPF掺量成正比;相同水压力,相同有效裂缝宽度条件下,随着PPF掺量的增加,混凝土损伤渗透率降低,PPF的存在能够有效提高混凝土损伤后的抗渗性能;相同水压力下,相同PPF掺量的混凝土试件损伤渗透率整体上与有效裂缝宽度成正比;不同水压力下,相同PPF掺量的PPF/PC损伤渗透率在同一有效裂缝宽度情况下,随水压力增加而减小;修正后的泊肃叶渗流模型可以更好地评价PPF/PC损伤渗透特性。