氯离子在掺不同矿物质掺合料高性能混凝土中的扩散性能

采用改进型电迁移法测试了氯离子在掺不同矿物质掺合料高性能混凝土中的扩散性能．研究表明：在混凝土中分别内掺磨细矿渣、粉煤灰、硅灰、膨胀剂均可提高混凝土的抗渗透性能(Cl^-扩散系数降低),其中以单掺硅灰效果最优;在混凝土中复掺膨胀剂和磨细矿渣或膨胀剂和粉煤灰,对提高混凝土抗渗透性能的效果优于单掺二者之一,也优于单掺效果最好的硅灰混凝土．复掺膨胀剂和细掺料后混凝土内部结构进一步优化、微观结构致密、微缺陷减少,由此,开发了一种低成本配制超高抗渗性混凝土的新途径。     

塑性膨胀剂对预应力孔道压浆料体积变形与亚微观结构的影响

针对预应力孔道压浆料普遍存在的体积收缩问题,研究了含氮有机化合物作塑性膨胀剂对其塑性及硬化阶段变形行为的影响,并通过孔结构和扫描电镜测试,探讨了塑性膨胀剂的作用机理.结果表明:含氮有机化合物品种和掺量对压浆料的自由膨胀率和强度有很大影响,以亚硝基化合物SP-B作塑性膨胀剂较为适宜,掺量以0.02％～0.06％为佳;SP-B塑性膨胀剂通过在压浆料浆体内部释放氮气,产生了均匀、微细的气泡而引发适度的塑性膨胀,有效补偿了浆体的早期体积收缩,且对硬化浆体亚微观结构和力学性能无显著不利影响;掺SP-B塑性膨胀剂的压浆料浆体的早期膨胀过程分为快速膨胀期、缓慢膨胀期和膨胀稳定期三个阶段,进一步复掺UEA膨胀剂,提高了硬化浆体中后期的体积稳定性.     

固硫灰做水泥混合材及缓凝剂的研究

研究固硫灰做水泥混合材及缓凝剂,其细度和掺量对水泥性能的影响.试验结果表明,10％～30％不同细度的固硫灰掺入硅酸盐水泥熟料中后,所制备的水泥安定性合格、凝结时间正常;强度随着细度的增加而增加,随着掺量的增加先增加后降低;磨细处理有利于降低水泥的总膨胀能.同时通过研究发现,固硫灰的掺量和细度对水泥早期水化产物的形成有较大的影响,掺磨细固硫灰水泥所形成的AFt是粗大的针棒状结构,而掺未磨细固硫灰水泥形成细小的AFt和大量的AFm.     

掺多膨胀源膨胀剂复合胶凝体系的膨胀性能及力学性能研究

为研究不同膨胀源膨胀剂对复合胶凝体系膨胀性能及力学性能的影响,对单掺及复配多膨胀源膨胀剂补偿收缩复合胶凝体系的限制膨胀率及抗折、抗压强度等开展了试验研究.结果表明:氧化镁和氧化钙-硫铝酸钙(简称CA膨胀剂)两种膨胀剂在单掺情况下,CA膨胀剂膨胀量远大于氧化镁;CA膨胀剂的膨胀速率随掺量的减小而变缓,膨胀稳定期变长,而MgO膨胀剂的膨胀速率不受掺量的影响.复掺情况下,高活性MgO的限制膨胀率始终大于低活性MgO,且后期膨胀差距会随着MgO膨胀剂掺量的增加逐渐增大.当CA、MgO两种膨胀剂在质量比为1:1复配情况下,可采用叠加原理来较为准确地预测多膨胀源膨胀剂的膨胀经时发展规律以及膨胀量.对于强度而言,相同掺量下MgO膨胀剂对强度的影响小于CA膨胀剂.此外,复掺试验组限制膨胀与限制强度随龄期发展的协调性取决于该配合比中对膨胀能贡献更大的单类型膨胀剂的协调性.     

水胶比和粉煤灰掺量对补偿收缩混凝土自收缩特性的影响

通过测定基准混凝土和补偿收缩混凝土的自收缩,研究添加硫铝酸钙–氧化钙类膨胀剂的补偿收缩混凝土的自收缩特性,以及水胶比和粉煤灰掺量对于膨胀剂补偿效果的影响。结果显示:在前20h内硫铝酸钙–氧化钙类膨胀剂因为没有足够的强度约束而无法对混凝土自收缩产生补偿作用,在20～168h龄期内膨胀剂开始发挥补偿作用,自收缩减小。膨胀剂对自收缩的补偿效率受水胶比和粉煤灰掺量的影响很大,水胶比越大,膨胀剂对混凝土自收缩的补偿效率越高;粉煤灰掺量越大,膨胀剂的补偿效率越高。水胶比为0.34,粉煤灰掺量为45%时,适当掺量(6%)的膨胀剂产生的膨胀可以补偿全部的自收缩,使混凝土在30h后持续保持膨胀变形。     

养护温度和粉煤灰对补偿收缩混凝土膨胀效能的影响

研究了养护温度和粉煤灰掺量对补偿收缩混凝土的膨胀效能和强度的影响。结果表明：20、40℃养护时混凝土的各龄期强度均匀增长;60℃养护能极大地促进早期强度增长,后期强度增长缓慢。粉煤灰在不同养护温度下对混凝土的早期强度发展都有抑制作用;长期高温养护后,粉煤灰活性逐渐显现,显著促进混凝土的强度增长,且粉煤灰掺量越大,混凝土强度增幅越大。硫铝酸钙–氧化钙类膨胀剂的膨胀效能发挥对温度非常敏感,养护温度越高,膨胀剂的水化速度越快,膨胀作用发挥越早;适量掺加粉煤灰有利于膨胀效能的发挥,掺量越大,膨胀随温度增长的增幅越大。大掺量粉煤灰补偿收缩混凝土的强度发展和限制膨胀率的温度敏感性均很高。     

掺MgO膨胀剂水泥净浆变形性能研究

通过对含镁尾矿的处理,采用一定工艺制备了MgO膨胀剂,研究了不同煅烧温度下的MgO膨胀剂的膨胀性能,并进一步研究MgO膨胀剂的掺量和细度以及粉煤灰对不同养护条件下水泥净浆自由变形性能的影响.结果表明:煅烧温度1050℃时膨胀剂膨胀性能较好;水泥净浆的自由变形随掺量的增加和龄期的延长以及养护温度的升高而增大;在早期细度较小的膨胀剂具有较好的膨胀效果,而后期细度大的膨胀剂的膨胀效果高于细度小的膨胀剂;粉煤灰对膨胀剂早期膨胀和后期膨胀都有显著的抑制作用.     

水泥-膨胀剂-磨细矿渣复合胶凝材料膨胀与强度发展的协调性研究

研究了水泥-膨胀剂二元复合胶凝材料和水泥-膨胀剂-磨细矿渣三元复合胶凝材料, 这两种胶凝材料可以用于制备具有良好体积稳定性的高性能膨胀混凝土(HPEC).研究表明, 存在一个最优辅助胶凝材料掺量组合, 在此条件下胶凝材料具有良好的膨胀与强度的协调性, 在水泥-膨胀剂体系中, 膨胀剂的掺量范围在6%～12%, 其中掺6%～8%时用于配制补偿收缩混凝土, 掺8%～12%时用于配制填充性膨胀混凝土.在水泥-膨胀剂-矿渣体系中, 矿渣的掺量范围是20%～40%, 对应膨胀剂的掺量及胶凝材料的适用范围为膨胀剂6%～10%时用于配制补偿收缩混凝土, 掺8%～15%时用于配制填充性膨胀混凝土.矿渣的掺入可以削减由于膨胀剂过量而导致的过高的膨胀率, 从而避免由此造成的膨胀破坏现象.     

内养护与膨胀剂复合作用对混凝土综合抗裂性能的影响

为了评价内养护与膨胀剂复合作用对混凝土综合抗裂性能的改善效果,采用温度–应力试验法研究了在实际温度历程下受强约束状态时,掺高分子吸水树脂(SAP)和膨胀剂(UEA)的混凝土的温度–应力发展,并研究了SAP和UEA复掺对混凝土工作性、力学性能和长期变形性能的影响。结果表明:SAP和UEA复掺,增大了混凝土升温阶段的压应力,降低了降温阶段拉应力发展速率和混凝土的开裂温度,开裂温降提高了10℃以上,延长了混凝土的开裂时间。SAP和UEA复掺对混凝土工作性影响不明显,略微降低了混凝土的抗压强度。变形性能试验表明:SAP和UEA复掺使混凝土的极限拉伸值提高了10%~30%,混凝土的干燥收缩降低了10%~20%;14 d水养护混凝土限制膨胀率在0.05%左右,转为恒温恒湿的空气中养护时,42 d膨胀率在0.04%左右。因此,内养护与膨胀剂复合作用显著改善了混凝土的综合抗裂性能。     

抗收缩工程水泥基复合材料力学性能研究

工程水泥基复合材料(ECC)具有较好的延性和抗拉性能,但成型收缩率较大,容易导致试件成型开裂,严重影响结构的耐久性。在ECC中掺入高性能硫铝酸钙(HCSA)膨胀剂以减小ECC成型收缩率,研究了不同掺量的膨胀剂对ECC收缩率和力学性能的影响。结果表明：膨胀剂掺量为6%～8%(质量分数,下同)时可明显改善ECC的收缩率,膨胀剂掺量过高会使ECC出现膨胀现象;膨胀剂掺量为4%～6%时可明显提高ECC的抗压强度,但对抗拉强度影响较小;膨胀剂掺量为2%～4%时可明显提高ECC的剪切韧性,但对抗剪强度影响较小;膨胀剂掺量为6%～8%时可明显提高ECC的极限弯曲强度。     

纳米颗粒对道路粉煤灰混凝土耐磨性能的影响及作用机理

为探讨纳米颗粒对道路粉煤灰混凝土耐磨性能的影响,采用纳米材料和超细粉煤灰等量取代水泥制备了纳米改性粉煤灰水泥砂浆,在此基础上制备出三种纳米改性道路粉煤灰混凝土:纳米SiO2 (NS)混凝土、纳米SiC(NC)混凝土和纳米复掺混凝土,并研究了两种纳米材料对粉煤灰水泥砂浆力学性能和道路粉煤灰混凝土耐磨性能的影响及作用机理.结果表明:混凝土中掺入纳米材料能显著提高其耐磨性能.单掺NS混凝土中NS最优掺量为2％,单掺NC混凝土中NC最优掺量为3％;而复掺2％ NS、2％ NC时,纳米复掺混凝土耐磨性最佳,与基准混凝土相比,磨损量降低了75％.分析认为:纳米材料的表面效应、活性效应和微集料填充效应使其具有较大的表面能,在水泥浆体中与Ca(OH)2晶体发生二次水化反应,改善了Ca(OH)2的取向程度,强化了水泥石微细观结构,优化了水泥基体内孔径分布与孔结构,使其更加密实,从而提高了道路粉煤灰混凝土的耐磨性能.     

Influence of fly ash fineness on strength, drying shrinkage and sulfate resistance of blended cement mortar

In this paper, the influence of fineness of fly ash on water demand and some of the properties of hardened mortar are examined. In addition to the original fly ash (OFA), five different fineness values of fly ash were obtained by sieving and by using an air separator. Two sieves, Nos. 200 and 325, were used to obtain two lots of graded fine fly ash. For the classification using air separator, the OFA was separated into fine, medium and coarse portions. The fly ash dosage of 40% by weight of binder was used throughout the experiment. From the tests, it was found that the compressive strength of mortar depended on the fineness of fly ash. The strength of mortar containing fine fly ash was better than that of OFA mortar at all ages with the very fine fly ash giving the highest strength. The use of all fly ashes resulted in significant improvement in drying shrinkage with the coarse fly ash showing the least improvement owing primarily to the high water to binder ratio (W/B) of the mix. Significant improvement of resistance to sulfate expansion was obtained for all fineness values except for the coarse fly ash where greater expansion was observed. The resistance to sulfuric acid attack was also improved with the incorporation of all fly ashes. In this case the coarse fly ash gave the best performance with the lowest rate of the weight loss owing probably to the better bonding of the coarse fly ash particles to the cement matrix and less hydration products. It is suggested that the fine fly ash is more reactive and its use resulted in a denser cement matrix and better mechanical properties of mortar.     

Early longitudinal dimensional changes of fresh fly ash mortar exposed to drying conditions

The present work examines the effect of fly ash (ASTM Class F) on early longitudinal dimensional changes in fresh cement-fly ash (10, 25 and 40 percent cement replacement) mortar mixes exposed to drying conditions immediately after casting at elevated temperature (30 C, 86 F).

It was found that the fly ash affects expansion in the fresh mortar mix: the larger the cement replacement percentage (i.e. increased amount of fly ash in the mix), the higher the expansion values and the longer its duration. However, the effect of the fly ash on plastic shrinkage during drying has no clear trend, as it is governed both by the preceding expansion and by the duration of the shrinkage phase (both influenced in turn by the specific chemical composition and physical properties of the fly ash and the cement).     

The role of activating solution concentration on alkali–silica reaction in alkali-activated fly ash concrete

To enable commercial use of alkali-activated fly ash concrete, its durability must be better understood. Alkali–silica reaction is a primary concern since highly alkaline solutions are generally used for activation. This study investigated the effect of NaOH activating solution concentration on pore solution alkalinity and subsequent alkali–silica reaction in alkali-activated fly ash concrete. It was found that pore solution alkalinity increased with increasing activating solution NaOH concentration, and this effect was amplified at concentrations above an optimum, defined as the concentration that resulted in the highest mortar compressive strength. Expansion of concrete prisms containing highly reactive fine aggregate and activating solution concentrations above the optimum concentration was approximately three times that of concrete with optimum activating solution concentrations, but only about 5% of the expansion observed in the ordinary portland cement control. The low expansion may be attributed to the low calcium levels in the alkali-activated fly ash concrete.     

粉煤灰混凝土的势能化

根据势能的观点和混凝土工程性质的要求，给出混凝土中粉煤灰经化势，固化势和免疫势的定义，以及粉煤灰砂浆体或粉煤灰混凝土材料的协同工作特性的数学表达；通过图解的方法，对粉煤灰材料的质量等级以及粉煤灰混凝土双掺技术的应用进行了势能化的初步探讨。     

等强度条件下粉煤灰对补偿收缩混凝土变形性能的影响

通过测定水中限制膨胀率和水养7d转干空后的限制膨胀率,计算干燥收缩落差,讨论粉煤灰在等强度条件下对补偿收缩混凝土变形性能的影响.结果表明:等强度条件下掺加适量粉煤灰可以明显地促进限制膨胀率的增长;掺量过大容易导致早期约束不足,降低对限制膨胀的促进作用.粉煤灰可以明显降低混凝土转干空后早期的干燥收缩落差.随着粉煤灰掺量增加,干燥收缩落差进一步降低,空气中放置28 d后均表现为膨胀.对于硫铝酸钙-氧化钙类膨胀剂和粉煤灰复掺的补偿收缩混凝土,膨胀剂最小用量的要求可以适当降低.     

粉煤灰及锂盐对水泥砂浆碱集料反应复合抑制效果的探讨

通过砂浆棒快速法考察掺入粉煤灰和锂盐对砂浆棒膨胀率的影响,研究向水泥砂浆中同时添加粉煤灰和锂盐对碱集料反应（AAR）的抑制效果。结果表明,适量掺人粉煤灰和锂盐可以较好的起到对碱集料反应的抑制作用。     

粉煤灰加气混凝土砌体力学性能与节能效应分析

利用室内试验方法制备了粉煤灰加气混凝土砌块和砌体,分别测试了混凝土砌块的抗拉抗压强度和砌体的抗拉和抗剪强度,分析了砌体抗压和抗剪强度随砂浆厚度的变化规律。在此基础上,建立了粉煤灰加气混凝土砌体节能效应的FLAC 3D数值计算模型。研究表明:(1)粉煤灰加气混凝土砌块的抗拉压强度平均值分别为4.53 MPa和0.75MPa;(2)粉煤灰加气混凝土砌体的整体抗压和抗剪强度随砂浆厚度的增大而分别减小和增大;(3)粉煤灰加气混凝土砌体的平均传热系数小于普通灰砂砖砌体,且随砂浆厚度的增大而减小。     

UEA水泥砂浆与混凝土长期性能的研究

采用差热分析、Ｘ射线衍射曲线、扫描电镜对掺ＵＥＡ膨胀剂水泥２８ｄ及１０ａ龄期的水化产物进行比较研究,并且采用高压水银侧孔仪对２８ｄ及１０ａ龄期的ＵＥＡ砂浆的孔结构进行分析。结果表明随着龄期的增长,掺ＵＥＡ膨胀剂的水泥石结构趋于密实,通过对掺ＵＥＡ的水泥砂浆和混凝土长期物理力学性能和膨胀性能的研究,表明掺ＵＥＡ混缔造长剂的砂浆和混凝土是稳定的。本工作对补偿收缩混凝土应用具有指导意义。     

Effect of steam curing on class C high-volume fly ash concrete mixtures

The effect of steam curing on concrete incorporating ASTM Class C fly ash (FA), which is widely available in Turkey, was investigated. Cement was replaced with up to 70% fly ash, and concrete mixtures with 360 kg/m³ cementitious content and a constant water/binder ratio of 0.4 were made. Compressive strength of concrete, volume stability of mortar bar specimens, and setting times of pastes were investigated. Test results indicate that, under standard curing conditions, only 1-day strength of fly ash concrete was low. At later ages, the strength values of even 50% and 60% fly ash concretes were satisfactory. Steam curing accelerated the 1-day strength but the long-term strength was greatly reduced. Setting time of fly ash-cement pastes and volume stability of mortars with 50% or less fly ash content were found to be satisfactory for standard specimens. In addition, for steam curing, this properties were acceptable for all replacement ratios.