稻壳灰对本地化高延性水泥基材料性能的影响

为了降低高延性水泥基复合材料的生产成本和提高废弃稻壳的建材资源化利用,首先利用国产涂油PVA纤维和天然河砂分别替代进口PVA和石英砂探究了本地化高延性水泥基复合材料的配制工艺,在此基础上试验研究了稻壳灰作为辅助胶凝材料替代部分水泥（10%、30%和50%,质量分数）对高延性水泥基复合材料流动度、抗压强度、拉伸性能和弯曲性能的影响规律。研究结果表明：采用国产涂油PVA纤维和天然河砂可成功配制强度等级可达C30且14 d的极限拉伸应变可达到1.44%的国产化高延性水泥基复合材料。水胶比和PVA纤维掺量分别是影响高延性水泥基复合材料抗压强度和拉伸强度的主要因素。相比对照组,随着稻壳灰替代率的增加,浆体流动度由于稻壳灰的吸水性逐渐下降,最大可降低10%;基体14 d抗压强度略有提高后大幅降低;试件抗拉强度呈略微下降趋势,而极限拉伸应变则显著提高可高达2.94%;基体弯曲强度呈先增加后逐渐降低的趋势,,且纯弯段裂纹数量明显增多,且裂纹宽度均低于100μm。可见,稻壳灰替代10%的水泥有利于高延性水泥基复合材料抗压强度、极限拉应变和弯曲强度的提高,同时对浆体流动度影响较小。微观分析可知,具有良好火山灰活性的稻壳灰可与水泥水化产物反应提高胶凝产物总量,同时降低Ca(OH)2数量,进而增强了高延性水泥基复合材料的强度。     

聚乙烯醇纤维水泥基复合材料

介绍了聚乙烯醇纤维的特点和聚乙烯醇纤维水泥基复合材料的高延性、耐久性、抗疲劳性能和抗破坏能力．     

骨料级配对应变硬化水泥基材料力学性能的影响

水泥基复合材料的高脆性是诱发结构开裂、腐蚀甚至失去承载能力的主要原因.PVA纤维增强水泥基复合材料（SHCC）的应变硬化特性和多微缝开裂特征可显著改善此类材料的性能.通过三点受弯和直拉试验对比了骨料颗粒级配合理与否对SHCC材料力学性能的影响.结果表明：适宜的颗粒级配可以显著改善SHCC的应变硬化特性,骨料的最大粒径可以由ECC材料常用的110μm放大到1.25 mm,便于此类材料在实际工程中的推广应用.     

混杂聚乙烯醇-玄武岩纤维延性水泥基材料的高温后力学性能

本文试验研究了混杂聚乙烯醇(PVA)-玄武岩纤维延性水泥基材料(ECC)暴露于高温后的力学性能.测试了混杂和单掺纤维ECC分别经历20,50,100,200和400℃温度后的残余抗压、抗拉和抗弯力学行为.结果表明:相较于单掺纤维ECC在400℃的脆性破坏,玄武岩纤维部分取代PVA纤维可使ECC获得更高的抗压韧性;在拉伸...     

PVA纤维水泥基材料力学性能试验研究

为了制备超高韧性的水泥基复合材料(ultra high toughness cementitious composites,UHTCC),通过抗压、抗折以及直接拉伸试验,结合扫描电镜(SEM)测试,探讨粉煤灰掺量、石英砂掺量对UHTCC力学性能的影响;通过粉煤灰-石英砂复配,研究超高韧性水泥基材料的最优粉煤灰-石英砂掺量配比.结果表明:随着粉煤灰掺量的增加,抗压、抗折强度降低,拉伸变形增大,但是当粉煤灰质量/水泥质量(m(FA)/m(C))大于2.7后,拉伸变形提高缓慢;当石英砂质量/胶凝材料的质量(m(S)/m(B))为0.36时,拉伸变形性能最好;本文确定的最优粉煤灰-石英砂体系掺量为:m(FA)/m(C)-m(S)/m(B)=1.2-0.48,m(FA)/m(C)-m(S)/m(B)=2.2-0.36.     

掺粉煤灰PVA纤维增强水泥基复合材料的试验研究

研究了粉煤灰掺量对PVA纤维增强水泥基复合材料（ECC）的新拌性能、弯曲性能、抗压抗折强度、开裂模式及微观结构的影响.结果表明：随着粉煤灰掺量的增加,水泥净浆的屈服剪切应力和塑性黏度不断降低,ECC的流动度增加.ECC的初始开裂荷载降低、抗折和抗压强度逐渐降低,ECC的跨中挠度提高,ECC的平均裂缝宽度变小.在满足抗压强度的前提下,适当增加粉煤灰掺量有助于提高ECC的韧性和延性.     

掺钢渣粉超高韧性水泥基材料拉伸性能研究

从固废利用和材料高性能化出发,通过掺加钢渣粉来制备超高韧性水泥基复合材料。考虑了水胶比(0.25、0.35)、钢渣粉(0、20%、40%、60%、80%)两个因素,采用立方体抗压试验和直接拉伸试验探究掺钢渣粉的PVA纤维增强水泥基复合材料基本力学性能。结果表明:利用钢渣制备超韧性水泥基复合材料是可行,钢渣粉掺量不超过60%时,掺钢渣PVA纤维增强水泥基复合材料能满足一般工程对抗压强度的需求;钢渣粉的掺入使水泥基复合材料表现出明显的应变硬化特点,拉伸极限应变得到了极大的提升。     

养护制度与组分对含石灰石粉水泥基材料力学性能的影响

从胶凝材料组成、硬化水泥石基本物相出发,探讨了标准养护、蒸汽养护和蒸压养护制度下含石灰石粉水泥基胶砂力学性能。结果表明,对于35%石灰石粉+65%硅酸盐水泥体系,标准养护、蒸汽养护对水泥胶砂柔韧性无明显影响,蒸压养护显著增加其脆性;用矿粉等量取代含石灰石粉水泥,蒸压养护显著增加其脆性,明显降低其抗裂性;蒸汽养护也增加其脆性,但增幅低于蒸压养护;用粉煤灰等量取代含石灰石粉水泥,标准养护提高其柔韧性,蒸汽养护对其柔韧性无明显影响,蒸压养护明显降低其柔韧性,但提高其抗裂性;标准养护下,硬化水泥石中出现碳铝酸盐,蒸汽养护和蒸压养护制度下,碳铝酸盐不能稳定存在。     

BF-SHCC高温力学性能及延性变化机理

为深入研究高温对玄武岩纤维高延性水泥基复合材料(BF-SHCC)力学性能的影响,对高温后BF-SHCC试件进行了单轴拉伸、四点弯曲和抗压强度试验,研究其延性和强度的变化规律;利用热重-差热分析(TGA-DSC)和电子显微镜分析(SEM)从微观结构解释高温后BF-SHCC延性的变化机理.研究表明:随着过火温度升高至200...     

减水剂对PVA-ECC高温后力学性能的影响试验

对加入减水剂和未加入减水剂的聚乙烯醇纤维增强水泥基复合材料(PVA-ECC)测定了不同温度作用后的立方体抗压、棱柱体抗折及薄板抗弯强度.发现加减水剂PVA-ECC的各项残余力学性能均比无减水剂PVA-ECC的对应值大;室温状态下的立方体抗压强度增加85%,棱柱体抗折强度增加38%,薄板抗弯强度增加60%.与室温值相比,无减水剂试件在200℃时的立方体抗压强度和棱柱体抗折强度分别增加3.9%、8.7%,薄板3点抗弯强度下降14.1%,加减水剂试件对应的3项力学性能则分别降低31.4%、55.3%、39.7%.而当达到400℃时,无减水剂试件的棱柱体抗折和薄板抗弯强度损失率分别达75.7%和62.5%.600℃时,无减水剂薄板只剩1块,其余2块已经剥落.800℃时,无减水剂立方体试件已经剥落,加减水剂立方体试件的抗压强度损失率也已达80.1%.     

Impact properties of engineered cementitious composites with high volume fly ash using SHPB test

The split Hopkinson pressure bar (SHPB) testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites (ECCs) with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete (RPC) and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.     

Shrinkage reducing measures for engineering cementitious composites

Inhibition measurement of shrinkage of engineering cementitious composites （ECC） was investigated due to typical ECC with higher free drying shrinkage.The effects of expanded admixture （EA）,shrinkage reducing admixture （SRA）,coarse sand＋stone powder （CS＋SP） and superabsorbent polymer （SAP） on drying shrinkage and mechanical properties were studied.The experimental results show that ECC incorporating EA,SRA and coarse sand can retain around 60% of the typical ECC＇s free drying shrinkage.Superabsorbent polymerl（SAP） can delay the development of free drying shrinkage of ECC at different ages,and the effect of SAP is not distinct like the actions of EA,superabsorbent polymer（SRA） and coarse sand.Significantly,SAP may act as artificial flaw to form a more homogeneous defect system that increases the potential of saturated multiple cracking,hence the ductility of ECC will be improved greatly.     

PVA-ECC与BFRP筋黏结性能试验分析

为研究聚乙烯醇纤维增强工程水泥基复合材料(polyvinyl alcohol fiber reinforced engineered cementitious composites, PVA-ECC)与玄武岩纤维增强复材筋(basalt fiber reinforced polymer bars, BFRP筋)的黏结性能,以BFRP筋表面形式(缠绕带肋、喷砂缠绕带肋)、锚固长度(5d、7d、9d)、直径(8、10、12 mm)、PVA-ECC保护层厚度(70、25、15、5 mm)和PVA-ECC强度(C50、C80)为参数,设计制作28个PVA-ECC与BFRP筋黏结锚固试件进行拔出试验。通过观察和分析各试件的破坏形态、黏结强度和黏结滑移曲线,探究了各因素对PVA-ECC和BFRP筋的黏结性能的影响规律。最后,通过分析已有本构模型的适用性,根据试验结果建立了BFRP筋与PVA-ECC的黏结滑移本构模型。研究结果表明：较小保护层厚度(5 mm)的试件容易发生劈裂破坏,且黏结强度仅为正常试件的39.59%;BFRP筋表面喷砂可提高最大平均黏结应力;随着锚固长度的降低,BFRP筋与PVA-...     

Electromagnetic shielding and absorption properties of fiber reinforced cementitious composites

In order to investigate the electromagnetic shielding effectiveness (SE) and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol (PVA) fiber reinforced concrete were researched. The results show that with the increase of fiber volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI(electromagnetic interference) prevention buildings by attenuating and reflecting electromagnetic wave energy.     

Fracture and tensile properties of polyvinyl alcohol fiber reinforced cementitous composites

Experiments were carried out to design polyvinyl alcohol （PVA） fiber reinforced cementitous composites （PVA-FRCCs） holding high ductility and energy consumption ability. Besides, the properties of each ingredients in composites, mixing method and technology for fresh mixture were described in detail. Then, the pseudo-strain-hardening （PSH） behavior was investigated in uniaxial tension test. As a result, the maximum ultimate tensile strain can reach 0.7 percent. On the other hand, the single edge notch （SEN） thin sheet specimens were employed to gain the normal tensile load via crack mouth opening displacement （CMOD） curves, which can show obvious PSH behavior. In addition, the curves can be divided into four zones whose fracture toughness calculation methods were discussed. The wedge splitting （WS） test method can be applied to discuss the fracture toughness. Moreover, fracture energy of SEN and WS specimens were both approximately evaluated.     

Mechanical properties of gangue-containing aluminosilicate based cementitious materials

High performance aluminosilicate based cementitious materials were produced using calcined gangue as one of the major raw materials. The gangue was calcined at 500℃. The main constituent was calcined gangue, fly ash and slag, while alkali-silicate solutions were used as the diagenetic agent. The structure of gangue-containing aluminosilicate based cementitious materials was studied by the methods of IR, NMR and SEM. The results show that the mechanical properties are affected by the mass ratio between the gangue, slag and fly ash, the kind of activator and additional salt. For 28-day curing time, the compressive strength of the sample with a mass proportion of 2：1：1 （gangue： slag： fly ash） is 58.9 MPa, while the compressive strength of the sample containing 80wt% gangue can still be up to 52.3 MPa. The larger K^＋ favors the formation of large silicate oligomers with which AI（OH）4- prefers to bind. Therefore, in Na-K compounding activator solutions more oligomers exist which result in a stronger compressive strength of aluminosilicate-based cementitious materials than in the case of Na-containing activator. The reasons for this were found through IR and NMR analysis. Glauber＇s salt reduces the 3-day compressive strength of the paste, but increases its 7-day and 28-day compressive strengths.     

混杂PVA-ECC配合比优化设计及力学性能试验研究

为了降低工程用水泥基复合材料(ECC, Engineered Cementitious Composites)制造成本,使ECC能够在实际工程中大规模应用,将中国产PVA纤维和日本产PVA纤维以一定的比例混合,配制混杂PVA-ECC。基于ECC的材料设计理论,兼顾抗压强度和受拉能力,对掺有硅粉的混杂PVA-ECC中的纤维体积含量进行了优化设计。通过四点弯曲试验和轴心抗压试验,研究了混杂PVA-ECC在不同龄期下的弯曲性能和抗压性能。试验结果表明,混杂PVA-ECC试件均表现出明显的应变硬化和多缝开裂的特征,此外,其抗压强度后期增长明显。基于UM法,提出一种改进的反分析方法,可利用四点弯曲试验结果推导ECC的极限拉伸应变,并与试验结果进行了比较,结果表明,通过建议的反分析方法得到的预测值与试验值吻合较好。     

超高性能水泥基材料的力学行为及机理分析

研究安防系统对超高性能水泥基复合材料工作性及超高力学性能的特殊要求,以大掺量超细工业废渣取代水泥,掺加超高硬度细集料,采用高温干热养护制度,成功制备出一种超高性能水泥基复合材料.对其工作性及不同养护温度和养护时间下的力学性能进行测试,结果表明,制备的材料具有较好的工作特性及超高力学性能,可满足安保产品要求,其抗压强度最高可达240 MPa.采用X射线衍射技术、差热-热重分析方法及扫描电镜对其微观结构形成进行分析,结果显示,超高硬度细集料与胶凝材料的强物理结合使其在复合材料中起增强相的作用,高温养护加速了水泥的水化及矿物惨合料的火山灰反应,降低了材料中Ca(OH)2的含量,增加了C-S-H凝胶的含量,提高了材料的密实度,改善了界面微观结构,提高了超高性能水泥基复合材料的宏观力学性能.     

环保型胶凝材料的制备及其力学性能研究

利用硅酸盐水泥熟料、矿渣、粉煤灰、硅灰、石膏及其他组分制备出环保型胶凝材料Ⅰ和Ⅱ,并测试了其性能。结果表明,环保型胶凝材料的硅酸盐水泥熟料掺量(30%～50%),具有较低的需水量和正常的凝结时间,其标准稠度需水量为23%,净浆和配制的混凝土都具有较高的流动性,且有较小的流动性经时损失,标准养护28天的胶砂试件抗压强度可以达到50MPa以上,可以配制出C50 C60高流态的高性能混凝土.     

盐-干湿循环作用下低温养护纤维水泥土的力学性能试验研究

为探明玄武岩纤维水泥土在盐溶液(Na2SO4)和干湿循环耦合作用下的力学特性,将玄武岩纤维按一定比例掺入水泥土中,试块分批分次放入不同浓度的盐溶液中浸泡,而后放入烘干箱中烘干,如此实现若干次干湿循环,并基于无侧限抗压强度试验,研究低温和常温养护条件下纤维水泥土的强度变化规律,在此基础上,探讨盐溶液浓度和干湿循环次数对试...