Synthesis and Application of Sodium-carboxymethylcellulose Type Superplasticizer in Cement Mortars

The polymeric admixture, the sodium-carboxymethylcellulose(CMC)/poly sodium p-styrene sulfonate(PSS)/poly vinyl acetate(PVAc) was synthesized and applied in cement mortars. The polymer was tested by FTIR and SEM, and the results indicate that the ideal molecular structure is synthesized. The effect of addition amount of polymeric admixture and water-to-cement ratio on mechanical properties of cement mortars was studied. The polymer-modified mortars under the optimum water cement ratio and optimum polymer cement ratio, the flexural strength of polymer-modified mortars are 1.45, 1.21, and 1.17 times higher than the plain cement mortar at age of 3, 7, and 28 d, respectively. The compressive strength of polymer-modified mortars at age of 3, 7, and 28 d are 1.55, 1.40, and 1.2941 times higher than that of the plain cement mortar,respectively. Scanning electron microscope(SEM), FTIR and TG were used to analyze the effect of polymer emulsion on cement hydration reaction. The results show that the polymer emulsion can promote the hydration reaction of cement.     

Effect of Waterborne Epoxy on Performances of Cement Asphalt Mortar

The waterborne epoxy modified cement asphalt mortars were prepared with varying content waterborne epoxy and a constant fluidity. The effects of waterborne epoxy emulsion on water/cement ratio,compressive and flexural strength,tensile bond strength,freezing and thawing damage,corrosion resistance of cement asphalt mortar cured for 7 and 28 d have been investigated. The results show that waterborne epoxy is very beneficial to the improvement of mechianical properties and durability of cement asphalt mortar. Waterborne epoxy can improve the flowing ability of cement asphalt mortar. With the increasing of waterborne epoxy content,compressive strength,flexural strength and bond strength all have increased obviously. The modified mortar shows higher resistance to corrosion and the freezing and thawing compared with control mortar.     

PB-g-PS胶乳改性水泥砂浆的性能研究

PB-g-PS胶乳常用于改性水泥砂浆,聚丁二烯对苯乙烯的重量比的范围从70/30,50/50到30/70.保持水灰比为0.5的常数,在20°、相对湿度为90%的空气中养护24 h,接下来在20°的水中养护27 d.这项研究考察了聚丁二烯与苯乙烯的重量比和聚灰比对PB-g-PS胶乳改性水泥砂浆的流动度,抗压、抗折强度及吸...     

粉煤灰对砂浆强度影响的实验研究

探讨了高烧失量粉煤灰对砂浆强度的影响。用不同掺量的粉煤灰做了两组实验，测试结果表明：粉煤灰砂浆的用水量随着粉煤灰掺量的增加而增加；在蒸养后，粉煤灰砂浆试块的抗压和抗折强度比无粉煤灰试块有较大的提高；当粉煤灰掺量占水泥量的３０％时，其抗压和抗折强度最高；在标差２８ｄ后，粉煤灰掺量大于３０％的砂浆试块抗压和抗折强度比无粉煤灰试块有所降低。     

温度对聚丙烯纤维砂浆及测强曲线的影响

目的研究温度对聚丙烯纤维砂浆及测强曲线的影响,为以后工程防火加固选用砂胶比提供依据,从而达到降低成本的目的．方法通过测试不同胶砂质量比的聚丙烯纤维砂浆的初始流动度、终凝时间、抗压强度和抗折强度,研究不同温度下不同碳纤维掺量的聚丙烯纤维砂浆的耐高温性能．结果当碳纤维体积分数为0．3％、胶砂质量比为1．5时,聚丙烯纤维砂浆流动度大于320mm,终凝时间60min左右,28d抗压强度大于80MPa,1000℃高温燃烧后,残余50％以上强度,各龄期的测强曲线与实测强度有较好的拟合关系．结论采用普通硅酸盐水泥、铝酸盐水泥、石膏三元体系,通过添加碳纤维、偏高岭土掺合料及多种化学添加剂,可满足工程实际需要,并且具有良好的经济性．     

Strength and chloride resistance of blended Portland cement mortar containing palm oil fuel ash and fly ash

This paper presented a study on the strength and chloride resistance of mortars made with ternary blends of ordinary Portland cement (OPC), ground palm oil fuel ash (POA), and classified fly ash (FA). The mortar mixtures were made with Portland cement type I containing 0-40wt% FA and POA. FA and POA with 1wt%-3wt% retained on a sieve No.325 were used. The compressive strength and rapid chloride penetration depth of mortars were determined. The results reveal that the use of ternary blended cements produces ...     

Mechanical Properties and Microstructure of CaSO_4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker(CaSO_4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO_4 whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO_4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO_4 whiskers were identified by X-ray diffraction(XRD) and scanning electron microscope(SEM). Conclusion can be drawn that CaSO_4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO_4 whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry(MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.     

超细粉煤灰与原灰在水泥砂浆中的水化特征对比研究

主要对比研究了粉煤灰原灰颗粒和超细粉磨后的粉煤灰颗粒在水泥砂浆中的水化过程,利用SEM对水化行为进行了微观观察,并结合砂浆试块3 d7、d、28d抗折、抗压强度.结果表明:粉煤灰的细度对试块的强度影响最大,尤其是后期对抗压强度,在相同掺量下,强度相差达2倍左右;粒径在5μm左右的粉煤灰颗粒在养护初期就已经开始水化,且水化速率较快,在28 d时水化程度已经很充分,粉煤灰原灰颗粒即使养护到28 d龄期时,水化程度仍然很低;掺入细灰的试体各个龄期的结构均比原灰的要致密,且钙矾石的生长更快.     

Effect of Sand Content on Strength and Pore Structure of Cement Mortar

The effects of four sand contents on the compressive, flexural and splitting-tensile strength of cement mortars were evaluated. Moreover, we experimentally investigated the pore structure of cement mortar brought about by changing the sand content and water/cement ratio. The changes in the pore structure were quantified by measuring the porosity and pore size distribution obtained by using mercury intrusion porosimetry(MIP) technique. The test results show that the strengths of cement mortar increase with increasing sand content. It is also suggested that the traditional water/cement ratio law can be applied to cement mortar with different sand contents, provided that a slight modification is introduced. Sand content is an important parameter influencing the pore structure of cement mortar. Moreover, there is a good relationship between the pore structure and strength of cement mortar.     

Properties of cementitious rendering mortar prepared with recycled fine aggregates

The results of an experimental study on investigating the properties of cementitious rendering mortars prepared with a recycled fine aggregate (RA) were presented. The RA was obtained from a recycling plant in which mixed demolition wastes were processed by mechanical crushing, sieving and sorting operations. Two series of rendering mortar mixes were prepared with a constant water/cement and a constant aggregate/cement ratios of 0.55 and 3 respectively. River sand and natural crushed rock fine were originally used in the two series separately, and they were consistently replaced by 25%, 50%, 75% and 100% by the recycled aggregate. The experimental results showed that mechanical properties, such as compressive strength, flexural strength and modulus of elasticity of the mortars prepared with the RA were lower than the mortars made with the natural aggregates. Nevertheless, the bond strength at the interface between the mortar and masonry bricks determined by the Triplet test was found to be higher for the mortars prepared with the RA.     

Influence of Superplasticizers on Strength and Shrinkage Cracking of Cement Mortar under Drying Conditions

The effects of polynaphthalene series superplasticizers（PNS） with a low content of sodium sulfate （H-UNF）,with a high content of sodium sulfate（C-UNF） and polycarboxylate type superplasticizer （PC） on strength and shrinkage cracking of cement mortar under drying conditions were investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase the initial cracking time of mortars, and decrease the cracking sensitivity of mortars. As for decreasing the cracking sensitivity of mortars, PC〉H-UNF〉C-UNF. To incorporate superplasticizers is apparently to increase the free shrinkage of mortars when keeping the constant w/b ratio and the content of cement pastes. As for the effect of controlling the volume stability of mortars, PC〉C-UNF〉H-UNF. Maximum crack width of mortars containing PC is lower, but the development rate of maximum crack width of mortars containing H-UNF is faster in comparison with control mortars. The flexural and compressive strengths of mortars at 28-day increase with increasing superplasticizer dosages under drying conditions. PC was superior to PNS in the aspect of increasing strength.     

CA砂浆强度影响因素及强度机理研究

为制得满足高速铁路建设的CA砂浆,制备了不同配比的CA砂浆,通过考查CA砂浆的强度并利用扫描电子显微镜观测微观结构,研究砂的级配、砂灰比、乳化沥青与水泥比等因素对CA砂浆固化体不同龄期强度的影响．研究表明：选择粒径为0．15—0．3mm与0．3—0．6mm的组合砂能有效地降低高强型CA砂浆材料的分离度,而对CA砂浆28...     

水泥混凝土地坪"起砂露石"的薄层修复砂浆研究

通过对多种配方修补砂浆的抗压强度、抗折强度、抗拉强度、粘结强度、折压比、拉压比、干缩变形性能、弹性模量、耐磨性能的对比研究，发现了施工性能、力学性能、变形性能、耐久性能完全能满足“起砂露石”的混凝土地坪修补要求的砂浆，避免了采用板块拆除重浇、环氧砂浆罩面等修补方式所造成的费工耗时、色差严重、变形不同步或老化而导致粘结失效等问题。     

Production and mechanical properties of aligned multi-walled carbon nanotubes-M140 composites

This study investigated the production of M140, aligned multi-walled carbon nanotubes (A-MWNTs) reinforced M140 composites (A-MWNTs-M140) and their mechanical properties including their compressive and bending properties as well as their microstructure characteristic of bend fracture surface. M140 was first produced by speed change mixing technics with commercial materials, water-bath curing at normal temperature. In addition, two different A-MWNTs dispersions including carbonyl dispersions of A-MWNTs (C-A-MWNTs) and aqueous dispersions of A-MWNTs (A-A-MWNTs) with the addition of 0.01wt% A-MWNTs were utilized to obtain enhanced mechanical properties with respect to plain M140. The results indicated that the use of A-MWNTs dispersions allows increasing compressive strength and flexural strength by 8.4% and 5.4%, respectively for the C-A-MWNTs-M140, and by 15.9% and 20.7% for the A-A-MWNTs-M140, respectively. The SEM and EPMA examinations of fracture surface also showed that the bond interface between the nanotubes and matrix is moderate and the main reinforcing mechanisms are microfilling effect, CNTs pull-out and debond. The aqueous dispersion of A-MWNTs is an appropriate method and is more compatible with the M140. Supported by the National Natural Science Foundation of China (Grant No. 50438010)     

水泥掺量对纤维改性聚合物树脂混凝土力学性能的影响

利用抗压试验、抗折试验、扫描电镜等方法,探讨了水泥掺量对聚合物砂浆性能的影响.试验结果表明：当水泥掺量为115%时与水泥掺量0%时相比,聚合物砂浆的抗折强度提高95%,抗压强度提高74%,折压比也相应有所提高.但加入量高于115%时,导致水泥比表面积过大,抗折强度和抗压强度均有所下降.     

纳米高岭土颗粒改性水泥基复合材料的性能

研究了纳米高岭土颗粒对不同龄期水泥基材料微观结构（微孔结构、微观结构）及物理力学性能（工作性、抗弯强度、抗压强度、氯离子渗透性）的影响。结果表明,纳米高岭土颗粒的填充效应及其对水泥水化的促进作用改善了水泥基材料的微观孔结构,限制了氯离子在水泥基材料中的渗透扩散。当高岭土为水泥质量的1％时,水泥浆1、3、7、90 d抗弯强度分别提高30．41％、39．04％、36．27％和38．32％;当高岭土为水泥质量的5％时,水泥砂浆氯离子扩散系数降低53．03％;混凝土氯离子扩散系数随高岭土掺量增加呈指数递减;当高岭土为水泥质量的5％时,氯离子扩散系数降低18．87％;抗压强度分别提高28．4％;改性混凝土28 d抗压强度与混凝土氯离子扩散系数呈线性增加关系。     

再生纤维素纤维增强水泥砂浆的早期抗裂和自收缩行为

早期收缩开裂是导致混凝土劣化的重要因素之一,纤维的加入可以延缓甚至减少裂缝的延伸及扩展。使用具有吸水特性的再生纤维素纤维,与UF500纤维素纤维和无吸水的聚丙烯短纤维对比,研究再生纤维素纤维对水泥砂浆早期抗裂和自收缩行为的影响规律。将掺量为水泥质量1%或2%的各类纤维掺入水泥砂浆,密封养护,分析水泥砂浆强度、折压比及自收缩应变。研究结果表明：水灰比0.3时,添加再生纤维素纤维不能增强砂浆的抗裂性能和自收缩性能;水灰比大于0.35时,添加1%的再生纤维素纤维虽然降低了砂浆的抗折强度和抗压强度,但提高了该样品的折压比,增强了砂浆的抗裂性能和减缩效应。     

Properties and Acceleration Mechanism of Cement Mortar Added with Low Alkaline Liquid State Setting Accelerator

Low alkaline liquid state setting accelerator(LSA) for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement with addition of LSA relating to its setting time and strength development as well as its resistance to sulfate attack for short and long term exposure were experimentally examined. The experimental results showed that 5%-7% addition of LSA significantly accelerated the initial and final setting of Portland cement in the presence or absence of the blending of mineral admixtures, the initial and final setting time being less than 3 min and 6 min respectively. Meanwhile, the early 1 day curing age compressive strength increased remarkably by 20%, while the late 28 th day curing age compressive strength remained almost unchanged as compared with that of the reference accelerator free cement mortar specimen. Furthermore, mortar specimens of cement added with LSA and exposed to 5% Na2SO4 solution showed their excellent resistance to sulfate attack, with their short and long term curing age resistance coefficient to sulfate attack being around 1.04 to 1.17, all larger than 1.0. XRD analysis on hardened cement paste specimens at very early curing ages of several minutes disclosed the existence of more ettringite in specimens added with LSA than that of the reference specimens, meanwhile SEM observation also revealed the existence of well crystallized ettringite at very early hydration stage, suggesting that the accelerated setting of Portland cement can be attributed to the early and rapid formation of ettringite over the whole cement paste matrix due to the introduction of LSA. MIP measurement revealed that hardened cement paste specimens with the addition of LSA presented less medium diameter pores, more proportion of small pores and less proportion of large capillary pores, which is in a very good coincidence with the improvement of strength development of cement mortars added with LSA.     

废旧塑料改性砂浆力学性能研究

用片状和圆柱状塑料骨料等取代砂浆中的砂子,研究塑料骨料取代量、形状对水泥砂浆流动度、抗弯强度、抗压强度、抗弯挠度和断裂韧性的影响.结果表明,随片状塑料骨料掺量增加,砂浆流动度、抗压强度、抗弯强度、断裂韧性都快速下降,抗弯挠度增加;随圆柱状塑料骨料掺量增加,砂浆流动度增加,抗压强度下降,抗弯强度在低掺量时变化不明显,断裂韧性先增加后下降,抗弯挠度逐渐增加.     

Mechanical and morphological properties of highly dispersed carbon nanotubes reinforced cement based materials

Stable homogeneous suspensions of multi-walled carbon nanotubes (MWCNTs) were prepared using gum arabic (GA) as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy (UV-vis), and the concentration measurement shows that the optimum concentration of GA is 0.45 g L-1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% (by weight of cement). The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry (MIP), and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy (FESEM) and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.