Use of different barium salts to inhibit the thaumasite form of sulfate attack in cement-based materials

We investigated the effects of different barium compounds on the thaumasite form of sulphate attack(TSA)resistance of cement-based materials when they were used as admixtures in mortars.Moreover,we analyzed the inhibition mechanisms within different types of barium salts,namely BaCO_3 and Ba(OH)_2,on the thaumasite formation.The controlcement mortar and mortars with barium salts to cement and limestone weight ratios of 0.5%,1.0%,and 1.5% were immersed in 5%(by weight)MgSO_4 solution at 5 ℃ to mimic TSA.Appearance,mass,and compressive strength of the mortar samples were monitored and measured to assess the generaldegradation extent of these samples.The products of sulphate attack were further analyzed by XRD,FTIR,and SEM,respectively.Experimentalresults show that different degradation extent is evident in allmortars cured in MgSO_4 solution.However,barium salts can greatly inhibit such degradation.Barium in hydroxide form has better effectiveness in protection against TSA than carbonate form,which may be due to their solubility difference in alkaline cement pore solution,and the presence of these barium compounds can reduce the degree of TSA by comparison with the almost completely decomposed controlsamples.     

硅灰改性高韧性水泥基材料性能试验研究

工程水泥复合材料（ECC）具有良好的韧性和裂缝控制能力,可用于解决地下和水工工程中的混凝土开裂和渗漏水问题。高水灰比ECC(w/c=1.03)流动度好,但抗渗性能差,且水灰比过高使得材料坍落度大、黏聚性差,不满足可喷射性的指标要求。为了解决上述问题,将硅灰（SF）以不同的SF/水泥质量比引入高水灰比ECC中,以改善其工作性能、抗渗性能、微观结构和力学性能。结果表明,当SF/水泥比为15％时,高水灰比ECC的工作性能大大提高,达到新拌材料可泵送及可喷射的指标要求,高水灰比ECC的抗渗性能提高至P8以上;扫描电镜(SEM)和能量分散光谱仪（EDS）的观察结果证实,添加SF使ECC的显微组织更致密,而且还可以减少碱性物质的产生,从而抑制碱集料反应,提高耐久性。对ECC展开韧性、抗渗性及工作性能(可泵送及可喷涂)研究,获得了高韧性、高抗渗、可喷可泵的ECC配合比,为其在实际工程中的推广及应用奠定了基础。     

胶凝材料组成对混凝土TSA硫酸盐侵蚀的影响

研究不同水泥品种、矿物掺合料对混凝土抗TSA侵蚀性能的影响规律,采用掺30%石灰石粉填料的胶砂件,测试各砂浆在5±1℃的2%MgSO4溶液中浸泡1年后的外观破损与强度损失情况,通过X-射线衍射仪分析各砂浆的矿物成分.结果表明:不同品种水泥的抗TSA侵蚀能力由高到低依次为:硫铝酸盐水泥 硅酸盐水泥复合>硫铝酸盐水泥>抗硫酸盐水泥>普硅水泥.掺硅灰和矿渣细粉均能明显改善混凝土抗TSA侵蚀性能,且矿渣粉掺量越大效果越明显.由于粉煤灰活性低,掺量较少时可在一定程度上减缓TSA侵蚀过程,但掺量过多时反而产生不利影响.     

掺纳米白炭黑对新拌和硬化水泥基材料性能的影响

通过TEM,SEM,BET和激光粒度分析测试,对比研究了沉淀法纳米白炭黑(precipitated silica,PS)与纳米SiO2微粉(nano-silica powder,NS)的纳米特性及其团聚特性,并通过流变、凝结时间、强度和氯离子渗透深度测定,研究了掺PS和NS对新拌和硬化水泥基材料性能的影响及机理.结果表明:PS的团聚程度远大于NS,未经球磨分散处理时呈双峰粒度分布,团聚颗粒粒径很大,D50和D90分别高达58.187 μm和105.326 μm,大大超过52.5水泥的颗粒粒度.NS掺量低于1.0％时对水泥净浆稠度影响不大,但PS掺量对净浆稠度有明显影响,低于0.75％时缓慢增长,超过1％时则明显增大.掺PS和NS均可促进水泥水化,在1.0％掺量范围内,随PS掺量增加,水泥砂浆的强度和抗氯离子渗透性能均可得以有效改善.     

Effects of silica fume and steel fiber on chloride ion penetration and corrosion behavior of cement-based composites

This project was aimed to evaluate the chloride permeability and corrosion behavior of cement-based composites which comprised fibers and silica fume in the mixes. Resistivity, polarization resistance, ponding and rapid chloride penetration results of specimens were obtained through tests. Test results indicate that resistivity, open circuit potentials and direct current polarization of specimens with w/b ratio of 0.35 are higher than those of specimens with w/b ratio of 0.55. For length-diameter ratio of 65, resistivity and direct current polarization of specimens with fiber length of 35 mm were similar to those of 60 mm. In addition, the open circuit potentials of specimens with fiber length of 60 mm were slightly higher that those of 35 mm. The resistivity decreased with increasing steel fiber content, and the open circuit potential and direct current polarization increased with increasing steel fiber content. The specimens containing silica fume were found to provide higher resistivity, open circuit potentials and direct current polarization than the control specimens. The incorporation of steel fiber and silica fume in composites achieved more significantly decreases in resistivity and increases in direct current polarization than steel fiber composites or silica fume composites. The penetration depth and six-hour total charge passed of specimens for w/b ratio of 0.35 were lower than those for w/b ratio of 0.55. For length-diameter ratio of 65, the penetration depth of specimens for fiber length of 35 mm was similar to that of 60 mm. The penetration depth decreased with increased steel fiber content in the composites. By regression analysis, a good correlation between open circuit potential and direct current polarization, and chloride penetration depth and direct current polarization.     

氯氧镁水泥基材料体积稳定性研究

采用不同掺合料与骨料配制氯氧镁水泥基材料,分别在干燥和潮湿环境下,对氯氧镁水泥基材料的干燥收缩和潮湿膨胀变形进行实验研究与变形机理分析.结果表明,在干燥状态下,氯氧镁水泥净浆42 d的收缩率达到1400×10-6,单掺稻壳粉后收缩率明显提高,单掺粉煤灰后收缩率提高不多.单掺砂和复掺硅灰及粉煤灰后收缩率明显降低;在潮湿状态下,氯氧镁水泥净浆42 d的膨胀率为6898×10-6,单掺稻壳粉水泥的膨胀率比氯氧镁水泥净浆略有提高,单掺粉煤灰、砂和复掺硅灰及粉煤灰的水泥膨胀率均明显降低.     

硅灰粉煤灰对喷射混凝土性能影响

为了解决现场喷射混凝土普遍存在强度低、喷层易开裂、回弹量大、粉尘浓度高等问题,在喷射混凝土中加入不同掺量的硅灰、粉煤灰替代水泥,并通过室内试验和现场试验研究硅灰、粉煤灰对添加铝酸盐液态速凝剂喷射混凝土性能的影响。结果表明:铝酸盐液态速凝剂掺量为3%时,凝结效果最好;单掺8%的硅灰能有效促进铝酸盐液态速凝剂的凝结效果,提高混凝土强度,增加粘聚性;单掺粉煤灰可以降低速凝剂的促凝效果、降低混凝土强度、提高和易性。硅灰、粉煤灰和铝酸盐液态速凝剂混掺,对混凝土1 d抗压强度影响由主到次为粉煤灰掺量>速凝剂掺量>硅灰掺量,28 d抗压强度影响由主到次为速凝剂掺量>硅灰掺量>粉煤灰掺量,从而得出三者最佳组合。并结合新型喷射工艺进行现场试验,得出最佳组合能有效减少水泥用量、提高喷射混凝土强度、减少开裂、降低回弹和粉尘的结论。     

煅烧对微硅粉性能的影响

采用同步热分析法、X射线衍射、扫描电镜、比表面积和白度等测试手段对煅烧前后的微硅粉样品进行了分析.实验结果表明:在600℃、4 h煅烧时微硅粉的除碳效果最佳,煅烧后样品中碳的质量分数由1.96%下降到0.65%;样品主要成分二氧化硅晶体结构并未变化,仍旧为非晶态,煅烧后仍出现了碳化硅的特征峰,表明煅烧去除的主要为游离碳;微观形貌分析表明,煅烧后样品微观颗粒粒径在长大,片状物质的含量却明显减少,但是组成颗粒的一次粒子长大并不明显;比表面积测试表明煅烧前后比表面积变化不大,但白度由31.04提高到70.14.     

Reaction degree of silica fume and its effect on compressive strength of cement-silica fume blends

The compressive strength of the cement-silica fume blends with 5mass%, 10mass%, 20mass% and 30mass% of silica fume and water to binder ratio of 0.28, 0.32 and 0.36 from three days to ninety days were investigated. The reaction degree of silica fume was calculated from the Q4 silica tetrahedron, which was used as a probe obtained from 29 Si solid state nuclear magnetic resonance analysis. The fl at of compressive strength after 28 days disappeared for blended cement with inereasing reaction degree of silica fume. The compressive strength of the blended cement pastes approached that of P.I. cement pastes after 56 days and exceeded that after 90 days. The addition of silica fume and the w/b ratio of blends are both critical to the reaction degree of silica fume. The appropriate addition of silica fume, high silica fume reaction degree and low w/b ratio are benefi cial to the compressive strength of the cement-silica fume blends.     

Form and mechanism of sulfate attack on cement-based material made of limestone powder at low water-binder ratio under low temperature conditions

The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.     

川藏铁路石灰石粉–水泥基材料抗低温硫酸盐侵蚀研究

为研究川藏铁路掺石灰石粉混凝土抗低温硫酸盐侵蚀性能,通过对低温硫酸盐溶液浸泡侵蚀和电脉冲低温硫酸盐侵蚀作用下掺不同石灰石粉的水泥基材料的外观侵蚀变化等级、质量评价参数、抗压强度评价参数、孔隙特征以及侵蚀产物的测试,研究了低温环境下石灰石粉掺量对水泥基材料硫酸盐侵蚀行为的影响规律,并建立非单调Wiener随机过程模型对低温环境下石灰石粉-水泥基材料硫酸盐侵蚀服役寿命进行了预测。结果表明:（1）低温环境下硫酸盐浸泡侵蚀反应缓慢,侵蚀周期内,石灰石粉-水泥基试件外观未出现可见剥落、质量持续增加;强度先提高后降低,在侵蚀120d时出现转折;孔隙先细化后劣化,在侵蚀90d时出现转折;在侵蚀180d时有少量碳硫硅钙石生成。（2）电脉冲加速了低温环境下石灰石粉-水泥基硫酸盐侵蚀反应,电脉冲低温硫酸盐侵蚀60d时,试件表面开始剥落,质量和强度下降,内部孔隙劣化。石灰石粉掺量越多,碳硫硅钙石侵蚀破坏就越严重,石灰石粉掺量为40%的试件在侵蚀60d时就有碳硫硅钙石生成,而石灰石粉掺量为10%、20%的试件在侵蚀90d才生成碳硫硅钙石。（3）基于Wiener随机过程的可靠性寿命退化分析表明,电脉冲低温硫酸盐侵蚀作用下掺10%、20%和40%石灰石粉-水泥基材料室内加速侵蚀寿命分别为265d、130d及105d。     

美国混凝土硫酸盐侵蚀试验方法评析

指出混凝土硫酸盐侵蚀破坏的本质与其暴露条件如持续浸泡、干湿交替、溶液pH值、质量分数和温度相关．在阐明混凝土硫酸盐侵蚀反应类型和侵蚀机理的基础上，分析实验室5种硫酸盐试验加速途径，评述美国现行5种硫酸盐侵蚀试验方法，指出现行硫酸盐侵蚀试验方法，在测试时间、侵蚀破坏指标、多因素分析和模拟现场侵蚀破坏的有效性方面需要改进．     

Effects of Thaumasite Formation on the Performance of Portland-limestone Concrete Stored in Magnesium Sulfate Solution

The influence of theaumasite formation on the performance of Portland-limestone cement concrete stored in magnesium sulfate solution was studied.The experimental results show that the deterioration of Portlandlimestone cement concrete is higher than that of Portland cement concrete.The more the content of limestone,the more serious the deterioration of concrete,and also the lower the temperature,the earlier the deterioration of concrete.Thaumasite was detected to form in the Portland-limestone pastes when stored in 10wt% MgSO4 solution at 3-10℃ and is was easy to form at lower temperatures.     

Unsaturated Water Transport of Cement-based Materials

The slice-weighing method was used to investigate the unsaturated water transport of different cement pastes. The experimental results show that a sharp wetting front existed during water transport, the transport can be described by a non-linear diffusion equation, and transport coefficient of different materials exhibit various rules with water content of materials. The addition of fly-ash decreases transport coefficient of cement pastes in all the various water contents, even changes the transport mechanism.     

纳米硅粉水泥土固化机理研究

将具有优异性能的纳米硅粉作为外掺剂应用于水泥土改性研究.通过室内无侧限抗压强度试验,探讨了纳米硅粉掺人比和龄期对水泥土强度的影响规律;结合水泥石强度试验和X射线衍射(XRD)试验,研究了纳米硅粉对水泥浆的改性效果和改性机理;通过扫描电镜(SEM)测试,分析了纳米硅粉水泥土的微结构特点及微结构形成过程;在纳米硅粉-土相互作用分析的基础上,提出了纳米硅粉水泥土的固化机理,该研究将为纳米硅粉在水泥土中的进一步应用奠定理论和试验基础.     

减缩剂对水泥基材料早期水化及收缩变形性能的影响

采用非接触式电阻率测定仪和半绝热实验方法分别研究了减缩剂对常温和半绝热条件下的水泥浆体早期水化的电阻率和温升的影响,对比研究了减缩剂对水泥砂浆在干燥条件和常温水中养护时的线性长度变化与强度发展情况的影响,应用五路裂缝测定仪研究了减缩剂在水泥砂浆中的抗裂效果.结果表明:在常温条件下减缩剂会延缓水泥早期水化,而在半绝热条件下则会加速水泥早期水化;减缩剂主要提高干燥环境下的水泥砂浆的抗裂性能,降低其线性收缩值与强度增长,推迟其约束收缩初始开裂时间,而对水中养护的砂浆无补偿收缩效应,因此不利于控制热裂缝.分析表明,减缩剂在水泥基材料中应用时不仅具有物理作用,而且具有化学作用.     

Effect of Al in slag blended cement paste under sulfate attack

Unilateral sulfate attack of cementitious materials containing 40% slag with different water to binder ratios was investigated. The results showed that the degradation of slag blended cement pastes was nearly from the corners of paste surface with cracking and spallings, water-to-binder(w/b) ratio made a significant sense to the damage that low w/b ratio led to little weight loss, less cracking and spalling damage and vice versa. Microstructural experimental results demonstrated that in the three different stages of sulfate attack, degradation of pastes was primarily associated with the migration behavior and bonding configuration of aluminum, in the early ages Al was mostly present in C-(A)-S-H, and thus, the damage of pastes hardly appeared while at later ones Al had been largely transferred from C-(A)-S-H into AFt, leading to expansive damage.     

不掺硅粉的活性粉末混凝土配合比试验

在遵循活性粉末混凝土(RPC)基本配制原则的基础上,不掺入硅粉,采用超细水泥、普通水泥、掺合料(粒化高炉矿渣和粉煤灰)、砂、水、减水剂、钢纤维进行配合比试验。试验结果表明:不采用硅粉制备RPC是可行的;在制备RPC时,将超细水泥与适量掺合料混掺后,可以在保证材料强度和流动性的同时提高材料的经济性;用普通水泥取代大部分超细水泥后,材料的性能仍可保证,且更加经济。另外,研究了钢纤维掺量对材料性能(抗压、抗折、流动性及弯曲韧性)的影响规律。     

自诊断机敏水泥基材料力-电性能测试方法研究

用不同的方法对组分确定的机敏水泥基材料力-电性能进行测试，所得到的数据有很大的差别．通过对直流电路、直流电桥、交流电路及交流电桥等方法的分析比较，指出直流电路和电桥的方法不能消除机敏水泥基材料本身存在的极化，使得反映其力-电性能的阻抗趋于稳定；而交流电路和电桥方法则可以得到稳定的阻抗值．比较数字电桥在串联和并联等效方式下的交流阻抗结果可知，串联等效方式的交流阻抗值小且稳定性好．     

A Comparative Study on the Pozzolanic Activity between Nano-SiO2 and Silica Fume

The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction （ XRD ） , differential scanning calorimetry （DSC）, scanning electron micrascopy （SEM） and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca（OH）2 and nano-SiO2, the reaction rate of Ca（ OH）2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca （ OH）2 with nano-SiO2 showed marked increases over those of Ca（ OH）2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca（ OH）2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.