聚羧酸減水劑對水泥水化的影響及相關(guān)機(jī)理研究
發(fā)布時(shí)間：2018-09-03 20:07
【摘要】：水泥及其外加劑化學(xué)是設(shè)計(jì)和改善混凝土各種性能的理論基礎(chǔ)。本論文以凝膠滲透色譜、ζ電位分析、X-射線衍射、差示掃描量熱分析以及掃描電鏡等,研究了聚羧酸減水劑對水泥水化的影響及其作用機(jī)理,并探討了減水劑對水化產(chǎn)物結(jié)晶習(xí)性和微觀形貌的影響。研究以聚羧酸減水劑的吸附為重要線索,將水泥水化研究和單礦水化研究相結(jié)合。主要研究內(nèi)容及創(chuàng)新點(diǎn)如下:1.研究了不同結(jié)構(gòu)的聚羧酸減水劑在水泥單礦C3S表面及其水化產(chǎn)物Ca(OH)2表面的吸附以及對C3S水化的影響。結(jié)果表明,水化60 min,C3S對聚羧酸減水劑的吸附量為5.5~6.5 mg/g,相應(yīng)的ζ電位為-3.2 mV。此時(shí),Ca(OH)2的吸附量為1.9 mg/g,相應(yīng)的ζ電位為-4.32 mV。綜合數(shù)據(jù)研究表明,C3S對減水劑的吸附發(fā)生在C3S及其水化層表面,并對C3S水化產(chǎn)生重要影響。誘導(dǎo)前期,減水劑的吸附增大C3S水化放熱量,促進(jìn)C3S表面Ca2+溶解;誘導(dǎo)期和減速期,放熱滯后,C3S水化延遲,且水化相分布、形貌也發(fā)生明顯變化,Ca(OH)2晶粒明顯細(xì)小。減水劑摻量越高,分子羧基密度越大,C3S水化延緩的效應(yīng)越明顯。模擬的Ca(OH)2晶體合成實(shí)驗(yàn)表明,不摻聚羧酸減水劑的Ca(OH)2晶粒尺寸約為0.5~1μm,而摻0.2%聚羧酸減水劑的Ca(OH)2晶粒尺寸僅為0.2~0.5μm。上述研究表明,在硅酸鹽水泥漿體中,聚羧酸減水劑不僅起到高效減水和改善混凝土氣孔結(jié)構(gòu)的作用,而且通過吸附影響到C3S的水化及其水化相形態(tài)。這為聚羧酸減水劑提高混凝土密實(shí)性和力學(xué)性能提供了新的依據(jù)。2.研究了不同結(jié)構(gòu)的聚羧酸減水劑在C3A、Ca2SO4·2H2O及其水化產(chǎn)物AFt表面的吸附以及對C3A水化的影響。結(jié)果表明,C3A、AFt和Ca2SO4·2H2O的ζ電位分別為+12、+4.1和-0.6 mV。水化60 min,C3A對三種聚羧酸減水劑的吸附量在9~12 mg/g,此時(shí)AFt和Ca2SO4·2H2O對聚羧酸減水劑的吸附量分別為13~15 mg/g和0.21 mg/g左右。減水劑主要吸附在C3A和AFt的表面,羧基密度越大,吸附量相對越高。聚羧酸減水劑吸附對C3A水化產(chǎn)生重要影響。誘導(dǎo)前期,C3A和Ca2SO4·2H2O的溶解均受到減緩,從而使誘導(dǎo)期被延長1~2 h,并抑制了加速期AFt向AFm的轉(zhuǎn)化,低羧基密度的聚羧酸減水劑對C3A水化的抑制作用表現(xiàn)得更加強(qiáng)烈。AFt對聚羧酸減水劑較強(qiáng)的吸附作用導(dǎo)致其晶體的生長、形貌及其分布形態(tài)受到嚴(yán)重影響。溶液結(jié)晶法模擬實(shí)驗(yàn)制備的AFt為2μm左右針狀晶體,且相互聚集。但聚羧酸減水劑存在條件下得到的AFt晶體外形為1μm左右長的棒狀,分散且生成量大。3.研究了不同結(jié)構(gòu)聚羧酸減水劑在水泥顆粒表面的吸附及其對水泥水化的影響。結(jié)果表明,聚羧酸減水劑在水泥顆粒表面的吸附量隨時(shí)間延長逐漸增大。水化60 min,水泥顆粒對聚羧酸減水劑的吸附量為1.3~1.6 mg/g之間,吸附平衡的ζ電位在-9~-12 mV范圍。這一吸附量雖然比上述C3S和C3A單礦的吸附量都低,但卻與混凝土工程中聚羧酸減水劑的常規(guī)摻量相一致,原因可能與水泥中C2S的礦物含量以及水泥中的助磨劑有關(guān)。聚羧酸減水劑對水泥水化的影響是:誘導(dǎo)期延長,水化速率減慢;減水劑摻量增加,誘導(dǎo)期延長越明顯,這與C3S和C3A單礦的水化情況相一致。另外,由于水化相中Ca(OH)2、AFt被C-S-H凝膠所覆蓋,其形貌特征不明顯。但從聚羧酸減水劑影響單礦水化產(chǎn)物Ca(OH)2、AFt的結(jié)果來看,聚羧酸減水劑可以細(xì)化AFt、Ca(OH)2的晶粒,因此會(huì)對水泥石的強(qiáng)度產(chǎn)生貢獻(xiàn)。4.為了進(jìn)一步驗(yàn)證吸附是影響水泥及其單礦水化的主要原因,本論文還研究了有機(jī)膦酸HEDP在水泥表面的吸附及其對水泥水化的影響。結(jié)果表明,HEDP的吸附能力比聚羧酸減水劑強(qiáng),在摻量0.02~0.2%的范圍,吸附率達(dá)到摻量的98%以上且未達(dá)到飽和。0.2%摻量時(shí)水泥水化溫峰出現(xiàn)時(shí)間也從正常的11 h延長至50 h。HEDP摻量越大,其水化誘導(dǎo)期越長。進(jìn)一步的巖相研究表明,HEDP的吸附明顯抑制了AFt和Ca(OH)2的形成與生長,得到的水化產(chǎn)物由正常的短纖維狀變?yōu)楠?dú)特的毛絨狀。HEDP的緩凝機(jī)理可被認(rèn)為是通過“吸附”和“螯合沉淀”使水泥水化受到抑制作用。
[Abstract]:Chemistry of cement and its admixtures is the theoretical basis for designing and improving various properties of concrete. In this paper, the effects of polycarboxylic superplasticizer on cement hydration and its mechanism are studied by gel permeation chromatography, zeta potential analysis, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, and the bonding of hydration products is also discussed. The main research contents and innovations are as follows: 1. The adsorption of polycarboxylic acid superplasticizers on the surface of C3S and its hydrated product Ca (OH) 2, and the adsorption of C3S water on the surface of C3S were studied. The results show that the adsorption capacity of C3S on polycarboxylic superplasticizer is 5.5-6.5 mg/g and the corresponding_potential is - 3.2 mV at 60 min of hydration. At this time, the adsorption capacity of Ca (OH) 2 is 1.9 mg/g and the corresponding_potential is - 4.32 mV. In the early stage of induction, the adsorption of water reducer increases the heat release of C3S hydration and promotes the dissolution of Ca2+ on the surface of C3S; in the induction and deceleration stages, the heat release lags, the hydration delay of C3S, and the distribution of hydration phases and morphology of Ca (OH) 2 grains are obviously changed. The higher the dosage of water reducer, the higher the molecular carboxyl density, the more obvious the effect of C3S hydration retardation. The experimental results of Ca(OH)2 crystal synthesis show that the grain size of Ca(OH)2 without polycarboxylic acid superplasticizer is about 0.5-1 micron, while that of Ca(OH)2 with 0.2% polycarboxylic acid superplasticizer is only 0.2-0.5 micron. The above studies show that the polycarboxylic acid superplasticizer not only plays an important role in reducing water and improving the pore structure of concrete, but also plays an important role in the Portland cement paste. Adsorption of polycarboxylic acid superplasticizers on the surface of C3A, Ca2SO4.2H2O and its hydration products AFt and their effects on the hydration of C3A were studied. The_potential of H2O is +12, +4.1 and -0.6 mV, respectively. The adsorption capacity of C3A to the three polycarboxylic superplasticizers is 9-12 mg/g after 60 min of hydration. At this time, the adsorption capacity of AFt and Ca2SO4.2H2O to the polycarboxylic superplasticizers is about 13-15 mg/g and 0.21 mg/g respectively. The superplasticizer is mainly adsorbed on the surface of C3A and AFt. The higher the density of carboxyl group is, the higher the adsorption capacity is. The solubility of C3A and Ca2SO4.2H2O was slowed down at the early stage of induction, which prolonged the induction period by 1-2 hours and inhibited the transformation of AFt to AFm. The inhibition of polycarboxylic acid superplasticizer with low carboxyl density on the hydration of C3A was stronger. The growth, morphology and distribution of AFt crystals are seriously affected by the action. The AFt crystals prepared by solution crystallization method are about 2 micron acicular crystals and aggregate with each other. However, the AFt crystals obtained in the presence of polycarboxylic acid superplasticizer have a rod shape of about 1 micron long, dispersed and produced a large amount of AFt crystals. The results show that the adsorption capacity of polycarboxylic superplasticizer on the surface of cement particles increases with time. The adsorption capacity of cement particles on the surface of polycarboxylic superplasticizer is between 1.3 mg/g and 1.6 mg/g after 60 min of hydration, and the zeta potential of adsorption equilibrium is between - 9 mV and - 12 mV. However, the adsorption capacity of C3S and C3A is lower than that of C3S and C3A, but it is consistent with the conventional dosage of polycarboxylate superplasticizer in concrete engineering. The reason may be related to the mineral content of C2S in cement and the grinding aids in cement. In addition, the morphology of AFt covered by C-S-H gel is not obvious because of Ca (OH) 2 in the hydration phase. But from the results of polycarboxylic acid superplasticizer affecting Ca (OH) 2, AFt can refine the grain of AFt and Ca (OH) 2 in cement. In order to further verify that adsorption is the main factor affecting the hydration of cement and its single mineral, this paper also studies the adsorption of organic phosphonic acid HEDP on cement surface and its effect on cement hydration. When the content of HEDP is more than 98% and less than 0.2%, the occurrence time of hydration temperature peak is prolonged from 11 h to 50 H. The larger the content of HEDP, the longer the hydration induction period. Further lithofacies studies show that the adsorption of HEDP obviously inhibits the formation and growth of AFt and Ca (OH) 2, and the hydration products are changed from short fibrillar to independent. The retarding mechanism of HEDP can be considered as the inhibition of cement hydration by "adsorption" and "chelating precipitation".
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ172.1
本文編號(hào)：2221039
[Abstract]:Chemistry of cement and its admixtures is the theoretical basis for designing and improving various properties of concrete. In this paper, the effects of polycarboxylic superplasticizer on cement hydration and its mechanism are studied by gel permeation chromatography, zeta potential analysis, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, and the bonding of hydration products is also discussed. The main research contents and innovations are as follows: 1. The adsorption of polycarboxylic acid superplasticizers on the surface of C3S and its hydrated product Ca (OH) 2, and the adsorption of C3S water on the surface of C3S were studied. The results show that the adsorption capacity of C3S on polycarboxylic superplasticizer is 5.5-6.5 mg/g and the corresponding_potential is - 3.2 mV at 60 min of hydration. At this time, the adsorption capacity of Ca (OH) 2 is 1.9 mg/g and the corresponding_potential is - 4.32 mV. In the early stage of induction, the adsorption of water reducer increases the heat release of C3S hydration and promotes the dissolution of Ca2+ on the surface of C3S; in the induction and deceleration stages, the heat release lags, the hydration delay of C3S, and the distribution of hydration phases and morphology of Ca (OH) 2 grains are obviously changed. The higher the dosage of water reducer, the higher the molecular carboxyl density, the more obvious the effect of C3S hydration retardation. The experimental results of Ca(OH)2 crystal synthesis show that the grain size of Ca(OH)2 without polycarboxylic acid superplasticizer is about 0.5-1 micron, while that of Ca(OH)2 with 0.2% polycarboxylic acid superplasticizer is only 0.2-0.5 micron. The above studies show that the polycarboxylic acid superplasticizer not only plays an important role in reducing water and improving the pore structure of concrete, but also plays an important role in the Portland cement paste. Adsorption of polycarboxylic acid superplasticizers on the surface of C3A, Ca2SO4.2H2O and its hydration products AFt and their effects on the hydration of C3A were studied. The_potential of H2O is +12, +4.1 and -0.6 mV, respectively. The adsorption capacity of C3A to the three polycarboxylic superplasticizers is 9-12 mg/g after 60 min of hydration. At this time, the adsorption capacity of AFt and Ca2SO4.2H2O to the polycarboxylic superplasticizers is about 13-15 mg/g and 0.21 mg/g respectively. The superplasticizer is mainly adsorbed on the surface of C3A and AFt. The higher the density of carboxyl group is, the higher the adsorption capacity is. The solubility of C3A and Ca2SO4.2H2O was slowed down at the early stage of induction, which prolonged the induction period by 1-2 hours and inhibited the transformation of AFt to AFm. The inhibition of polycarboxylic acid superplasticizer with low carboxyl density on the hydration of C3A was stronger. The growth, morphology and distribution of AFt crystals are seriously affected by the action. The AFt crystals prepared by solution crystallization method are about 2 micron acicular crystals and aggregate with each other. However, the AFt crystals obtained in the presence of polycarboxylic acid superplasticizer have a rod shape of about 1 micron long, dispersed and produced a large amount of AFt crystals. The results show that the adsorption capacity of polycarboxylic superplasticizer on the surface of cement particles increases with time. The adsorption capacity of cement particles on the surface of polycarboxylic superplasticizer is between 1.3 mg/g and 1.6 mg/g after 60 min of hydration, and the zeta potential of adsorption equilibrium is between - 9 mV and - 12 mV. However, the adsorption capacity of C3S and C3A is lower than that of C3S and C3A, but it is consistent with the conventional dosage of polycarboxylate superplasticizer in concrete engineering. The reason may be related to the mineral content of C2S in cement and the grinding aids in cement. In addition, the morphology of AFt covered by C-S-H gel is not obvious because of Ca (OH) 2 in the hydration phase. But from the results of polycarboxylic acid superplasticizer affecting Ca (OH) 2, AFt can refine the grain of AFt and Ca (OH) 2 in cement. In order to further verify that adsorption is the main factor affecting the hydration of cement and its single mineral, this paper also studies the adsorption of organic phosphonic acid HEDP on cement surface and its effect on cement hydration. When the content of HEDP is more than 98% and less than 0.2%, the occurrence time of hydration temperature peak is prolonged from 11 h to 50 H. The larger the content of HEDP, the longer the hydration induction period. Further lithofacies studies show that the adsorption of HEDP obviously inhibits the formation and growth of AFt and Ca (OH) 2, and the hydration products are changed from short fibrillar to independent. The retarding mechanism of HEDP can be considered as the inhibition of cement hydration by "adsorption" and "chelating precipitation".
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ172.1
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