水泥基材料早期收縮研究及數(shù)值模擬
發(fā)布時間：2018-09-08 08:18
【摘要】：本文研究重點為水泥基材料早期收縮,包括混凝土中礦物摻合料、減水劑和增效劑對混凝土早期收縮的影響,尋找水泥凈漿早期收縮和相對蒸發(fā)量及孔徑分布之間的量化關系,并進行初步的混凝土早期收縮數(shù)值模擬探索,建立工程實際環(huán)境和數(shù)值模擬之間的橋梁。 采用自行研制的混凝土及水泥凈漿早期收縮裝置,分別研究了礦物摻合料、增效劑、水化熱對水泥基材料的早期收縮影響,更是深入探究了減水劑對水泥基材料相對蒸發(fā)量以及內(nèi)部孔徑分布的影響,獲得了相對蒸發(fā)量和孔徑分布與水泥凈漿干燥收縮值之間的量化關系：研究表明粉煤灰和礦粉都能夠減少混凝土早期收縮,但是規(guī)律并不相同,粉煤灰減少早期收縮的作用在摻量超過20%后下降,而礦粉只有在摻量大于20%才能顯著減少混凝土早期收縮；增效劑能夠提高水泥凈漿的和易性,提高粘聚性,防止混凝土離析,并能夠降低單方水泥用量、節(jié)約成本,但收縮試驗表明增效劑加快了混凝土初凝后10小時的收縮速率,從而可能導致最終收縮大于不摻增效劑的基準配合比；研究表明減水劑細化了水泥凈漿的孔隙分布,改變了水分蒸發(fā)規(guī)律,而相對蒸發(fā)率的變化和孔徑小于50nm的毛細孔數(shù)量變化之間的乘積能夠較好的反應收縮實測值的變化,并在相對蒸發(fā)率這一因素進行了更深入的探究,表明水灰比不同的水泥凈漿早期收縮在不同風速下引起的不同相對蒸發(fā)率上依然能夠滿足該量化規(guī)律,這是前人研究所未有的；針對水泥基材料中的膨脹階段,進行了一系列探索性試驗以尋找膨脹的機理,排除了骨料化學性質(zhì)差異、水泥成分變化、減水劑、水化熱、骨料物理移動等因素,得出與單方水泥用量以及自由水含量呈正相關關系。此外還初步研究了通過數(shù)值模擬來模擬實際工程中混凝土早期收縮的可靠方法。 在前述的研究基礎上對未來的繼續(xù)深入研究提出想法：如可以研究混凝土收縮和水分蒸發(fā)之間的量化關系,通過表面影響因子將數(shù)值模擬和實際工程環(huán)境相聯(lián)系,通過對水泥基材料試件埋入濕度探頭來獲得混凝土內(nèi)部的濕度變化,研究濕度與收縮之間的量化關系,并可以將數(shù)值模擬得出的混凝土內(nèi)部濕度結果進行比較,從而可以對數(shù)值模擬結果進行修正和完善。
[Abstract]:This paper focuses on the early shrinkage of cement based materials, including the effects of mineral admixture, water reducer and synergist on the early shrinkage of concrete, and to find out the quantitative relationship between the early shrinkage of cement paste and the relative evaporation and pore size distribution. The initial numerical simulation of early shrinkage of concrete is carried out to establish the bridge between the engineering environment and the numerical simulation. The effects of mineral admixture, synergist and hydration heat on the early shrinkage of cement based materials were studied by using the self-developed early shrinkage device of concrete and cement paste. The effect of water reducer on relative evaporation and internal pore size distribution of cement-based materials is also discussed. The quantitative relationship between the relative evaporation and pore size distribution and the drying shrinkage of cement paste is obtained. The results show that both fly ash and mineral powder can reduce the early shrinkage of concrete, but the rules are different. The effect of fly ash on reducing early shrinkage decreases after the addition of more than 20%, but only when the amount of mineral powder is more than 20% can it significantly reduce the early shrinkage of concrete, and the synergist can improve the easiness of cement paste, improve the cohesion and prevent concrete segregation. It can reduce the amount of unilateral cement and save the cost, but the shrinkage test shows that the synergist accelerates the shrinkage rate of 10 hours after the initial setting of concrete, which may lead to the final shrinkage larger than the standard mix ratio without synergist. The results show that the water reducer refines the pore distribution of cement paste and changes the water evaporation law, and the product between the relative evaporation rate and the change of the number of pores with pore diameter smaller than 50nm can better respond to the change of measured values of shrinkage. The relative evaporation rate of cement paste with different water / cement ratio can still satisfy the quantitative law under different wind speed, which has not been found in previous studies, and the relative evaporation rate of cement paste with different water / cement ratio is studied in a more in-depth way. The results show that the relative evaporation rate of cement paste with different water / cement ratio can still satisfy this quantitative rule under different wind speed. In view of the expansion stage of cement based materials, a series of exploratory tests were carried out to find out the mechanism of expansion. The factors such as the difference in the chemical properties of aggregate, the change of cement composition, the water reducing agent, the heat of hydration and the physical movement of aggregate were excluded. It is found that there is a positive correlation between the content of single cement and the free water content. In addition, the reliable method of simulating the early shrinkage of concrete in practical engineering by numerical simulation is studied preliminarily. On the basis of the above research, the following ideas are put forward: for example, the quantitative relationship between concrete shrinkage and water evaporation can be studied, and the numerical simulation can be linked to the actual engineering environment through surface influence factors. The moisture change in concrete is obtained by embedding a humidity probe into the cement based material specimen, and the quantitative relationship between humidity and shrinkage is studied, and the results obtained by numerical simulation can be compared. Thus, the numerical simulation results can be modified and improved.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU528
本文編號：2229945
[Abstract]:This paper focuses on the early shrinkage of cement based materials, including the effects of mineral admixture, water reducer and synergist on the early shrinkage of concrete, and to find out the quantitative relationship between the early shrinkage of cement paste and the relative evaporation and pore size distribution. The initial numerical simulation of early shrinkage of concrete is carried out to establish the bridge between the engineering environment and the numerical simulation. The effects of mineral admixture, synergist and hydration heat on the early shrinkage of cement based materials were studied by using the self-developed early shrinkage device of concrete and cement paste. The effect of water reducer on relative evaporation and internal pore size distribution of cement-based materials is also discussed. The quantitative relationship between the relative evaporation and pore size distribution and the drying shrinkage of cement paste is obtained. The results show that both fly ash and mineral powder can reduce the early shrinkage of concrete, but the rules are different. The effect of fly ash on reducing early shrinkage decreases after the addition of more than 20%, but only when the amount of mineral powder is more than 20% can it significantly reduce the early shrinkage of concrete, and the synergist can improve the easiness of cement paste, improve the cohesion and prevent concrete segregation. It can reduce the amount of unilateral cement and save the cost, but the shrinkage test shows that the synergist accelerates the shrinkage rate of 10 hours after the initial setting of concrete, which may lead to the final shrinkage larger than the standard mix ratio without synergist. The results show that the water reducer refines the pore distribution of cement paste and changes the water evaporation law, and the product between the relative evaporation rate and the change of the number of pores with pore diameter smaller than 50nm can better respond to the change of measured values of shrinkage. The relative evaporation rate of cement paste with different water / cement ratio can still satisfy the quantitative law under different wind speed, which has not been found in previous studies, and the relative evaporation rate of cement paste with different water / cement ratio is studied in a more in-depth way. The results show that the relative evaporation rate of cement paste with different water / cement ratio can still satisfy this quantitative rule under different wind speed. In view of the expansion stage of cement based materials, a series of exploratory tests were carried out to find out the mechanism of expansion. The factors such as the difference in the chemical properties of aggregate, the change of cement composition, the water reducing agent, the heat of hydration and the physical movement of aggregate were excluded. It is found that there is a positive correlation between the content of single cement and the free water content. In addition, the reliable method of simulating the early shrinkage of concrete in practical engineering by numerical simulation is studied preliminarily. On the basis of the above research, the following ideas are put forward: for example, the quantitative relationship between concrete shrinkage and water evaporation can be studied, and the numerical simulation can be linked to the actual engineering environment through surface influence factors. The moisture change in concrete is obtained by embedding a humidity probe into the cement based material specimen, and the quantitative relationship between humidity and shrinkage is studied, and the results obtained by numerical simulation can be compared. Thus, the numerical simulation results can be modified and improved.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU528
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