复合水泥净浆化学收缩影响因素研究

发布时间：2018-05-16 01:38

  本文选题：水泥净浆 + 化学收缩　； 参考：《长沙理工大学》2013年硕士论文

【摘要】：继矿物掺合材与外加剂双掺技术日趋成熟后，混凝土又引入纳米级超细组分，其早期体积变形是现代混凝土材料的关键性基础问题之一，而化学收缩行为无疑更加复杂。本文以水泥净浆的化学收缩为主题，采用ASTM C1608实验方法（恒温水浴环境密闭小容器绝对体积法），，系统研究复合水泥净浆化学收缩的影响因素，包括：水泥品种及细度、水胶比、矿物掺合材、外加剂、纳米材料以及养护温度等。主要结论如下： 1、水泥熟料含量对水泥净浆化学收缩值起决定性作用。在四种矿物熟料成分中，C_3A收缩最大，C_2S早期反应较慢，所引起的早期化学收缩相应较小。细度越大，水泥颗粒早期水化越快，引起早期化学收缩值越大。 2、水泥净浆化学收缩随着水灰比/水胶比增大而增大，如水灰比为0.38水泥浆7d化学收缩值较0.26水灰比的增加48%。不同水胶比复合水泥浆早期化学收缩差异非常显著。 3、采用粉煤灰、矿渣、硅粉和石膏，按不同比例等质量取代水泥，制备复合水泥净浆，研究矿物掺合材对其化学收缩的影响： （1）粉煤灰由于其微集料密实填充作用，对早期化学收缩表现出极强的抑制效果。掺加45%I级粉煤灰3d收缩值较水泥净浆收缩值减小41%；而粉煤灰后期参与二次水化，对化学收缩抑制作用显著减小。掺加II级粉煤灰复合水泥浆对早期收缩的抑制效果明显小于I级粉煤灰。 （2）硅粉的加入使复合水泥浆早期化学收缩值较水泥净浆略有增加，且随着掺量增大，收缩值增大。如：硅粉掺量为12%时，3d化学收缩值较水泥净浆增长12%。而掺8%纳米SiO_2复合水泥浆28d化学收缩值较水泥净浆降低19%。显然，掺纳米SiO_2复合水泥浆后期化学收缩增长速度明显降低。 （3）矿渣复合水泥浆早期化学收缩值较水泥净浆显著减小，且收缩值随着矿渣掺量的增大而减小。掺45%矿渣复合水泥浆3d化学收缩值比同水灰比净浆收缩值减少53%。随着龄期增长，矿渣参与水化反应，抑制收缩的作用逐渐减缓。 （4）粉煤灰与脱硫石膏复掺时，粉煤灰在30%掺量不变的条件下，石膏掺量越大，化学收缩值越小，这与石膏在水泥水化过程中结晶自膨胀有关。采用I、II级粉煤灰与脱硫石膏复掺，3d化学收缩值较水泥净浆分别减小11%和37%。 （5）粉煤灰与矿渣复掺复合水泥浆早期化学收缩较水泥净浆明显降低，复掺比例在一定范围内波动对收缩值的影响不显著。如：25%粉煤灰和15%矿渣复合水泥浆3d化学收缩较水泥净浆降低超过35%，中后期化学收缩增长速率加快，至28d收缩值达3.15ml/100g。 4、采用三种纳米材料：活性材料纳米SiO_2、功能型材料纳米TiO_2、惰性材料纳米CaCO_3。在同掺量同水胶比条件下，掺不同纳米材料复合水泥浆化学收缩值排序为：SiO_2TiO_2CaCO_3。其中，低掺量（1-3%）纳米SiO_2增加化学收缩，且收缩值随着掺量增加而增长。高掺量（4-8%）SiO_2对中后期化学收缩有明显抑制作用。纳米材料与矿物掺合材复掺能显著降低化学收缩值，如在粉煤灰和矿渣双掺体系中掺5%纳米CaCO_3，复合水泥浆3d收缩值较同龄期水泥净浆减少46%，较未掺纳米材料粉煤灰和矿渣复合水泥浆减小11%。这与纳米材料的掺入使得复合粉体形成更紧密堆积状态纳米效应有关。 5、在实验采用的外加剂及其掺量范围内，缓凝剂掺量为0.15%水泥浆3d化学收缩较水泥净浆减少63%，这说明掺缓凝剂水泥浆早期化学收缩发展缓慢，中后期化学收缩发展迅速，甚至超过水泥净浆；萘系减水剂由于含膨胀剂成分，导致早期出现细微膨胀现象，且整个龄期内收缩值都非常小。引气剂与早强剂在常用掺量范围内对化学收缩值影响不显著。 6、养护温度显著影响水化速率，进而显著影响水泥浆体的化学收缩。较高温度养护条件下，水泥净浆早期化学收缩增长迅速。40℃恒温水浴环境养护与15℃养护相比，水泥浆早期（7d前）化学收缩值增长超过50%，后期（7-28d）不同养护温度引起的差异减小。 此外，本文通过自创等效堆积密度及流动度实验，探索不同粒度分布干态复合粉体颗粒堆积状态及其对填充水和吸附水的影响，进而分析颗粒堆积对水泥净浆化学收缩的影响，得出初步结论。
[Abstract]:In this paper , the influence factors of chemical shrinkage of cement paste are studied by using ASTM C1608 experiment method ( constant temperature water bath environment closed small container absolute volume method ) , including cement variety and fineness , water - cement ratio , mineral admixture , admixture , nano - material and curing temperature . The main conclusions are as follows :

1 . The cement clinker content plays a decisive role in the chemical shrinkage value of cement paste . In the four kinds of mineral clinker components , the shrinkage of C _ 3A is the largest , the early reaction of C _ 2S is slow , the early chemical shrinkage is correspondingly small . The larger the fineness , the faster the early hydration of cement particles , the greater the early chemical shrinkage value .

2 . The chemical shrinkage of cement paste increases with the increase of cement ratio / water cement ratio , such as the ratio of water to cement ratio is 0.38 , the chemical shrinkage value of cement paste is increased by 48 % than that of 0.26 % .

3 . Fly ash , slag , silicon powder and gypsum are used to replace the cement according to different proportions , so as to prepare the composite cement paste , and the influence of the mineral admixture on the chemical shrinkage of the cement is studied :

( 1 ) The fly ash has strong inhibition effect on early chemical shrinkage due to the dense filling effect of its micro - aggregate , and the shrinkage value of cement paste with 45 % grade I fly ash is reduced by 41 % than that of cement paste .
however , that effect of compound cement slurry with grade II fly ash on early shrinkage is obviously less than that of grade I fly ash .

( 2 ) The chemical shrinkage value of the composite cement paste increased slightly with the addition of silicon powder , and the shrinkage value increased with the increase of the mixing amount . For example , the chemical shrinkage value of the 3d chemical shrinkage was 12 % when the content of silicon powder was 12 % . The chemical shrinkage value of the 28 % nano - SiO _ 2 composite cement slurry decreased by 19 % than that of cement paste .

( 3 ) The early chemical shrinkage value of the slag composite cement paste is obviously reduced than that of the cement paste , and the shrinkage value decreases with the increase of the slag content . The 3d chemical shrinkage value of the 45 % slag composite cement slurry is reduced by 53 % than that of the cement mortar . As the age increases , the slag participates in the hydration reaction , and the effect of inhibiting shrinkage gradually slows down .

( 4 ) When the fly ash is mixed with the desulfurization gypsum , the larger the amount of the fly ash is added , the smaller the amount of gypsum is , the smaller the chemical shrinkage value , which is related to the self - expansion of the crystal self - expansion during the hydration of the cement .

( 5 ) The early chemical shrinkage of fly ash and slag complex compound cement slurry is obviously lower than that of cement paste , and the effect of fluctuation on shrinkage value is not obvious within a certain range . For example : 25 % fly ash and 15 % slag composite cement paste 3d chemical shrinkage is more than 35 % lower than that of cement paste , the rate of chemical shrinkage increase in middle and late stage is accelerated , and the shrinkage value of 28d is 3.15ml / 100g .

4 . Three kinds of nano - materials : nano - SiO _ 2 of active material , nano - TiO _ 2 of functional material and nano - CaCO _ 3 of inert material were used . The chemical shrinkage of nano - SiO _ 2TiO _ 2CaCO _ 3 was increased with the ratio of co - doping with water - cement ratio .

5 . During the experiment , the amount of retarder added is 0.15 % , the chemical shrinkage of cement slurry is reduced by 63 % than that of cement paste , which indicates that the early chemical shrinkage of the retarder cement slurry is slow , the chemical shrinkage develops rapidly in the middle and late stages , and even exceeds the cement paste ;
Due to the swelling agent component , naphthalene series water reducing agent causes early slight swelling phenomenon , and the shrinkage value in the whole age is very small . The influence of entraining agent and early strength agent on chemical shrinkage value is not significant in the range of common doping amount .

6 . The curing temperature significantly affects the hydration rate , which can significantly affect the chemical shrinkage of cement slurry . The chemical shrinkage of cement paste increases rapidly at the higher temperature curing condition . Compared with the curing at 15 鈩

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