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Although Portland cement is composed of four main minerals, in the process of cement clinker formation, due to the doping and solid solution of other elements, the formation process and conditions of various minerals in cement and single mineral firing There is a significant difference. The adsorption amount of cement on superplasticizer is not a simple superposition of several mineral adsorption amounts. It is necessary to systematically study the adsorption characteristics of high-performance water-reducing agents for cements with different mineral compositions. The research on the adsorption characteristics of Portland cement to superplasticizers is divided into two parts. Firstly, Portland cement with different mineral compositions was fired using chemical reagents as raw materials, and the adsorption law of this series of cements on the water-reducing agent was determined. Then, a series of cement clinker close to the actual production cement composition is fired with industrial raw materials, and Portland cement is prepared according to the regulations, and the adsorption amount and adsorption law of these cements for different superplasticizers are determined, and the mixing is determined differently. The rheological properties of superplasticizers.
9.2.1 Adsorption of superplasticizer by Portland cement fired by purifying reagent
According to the above four kinds of single minerals c3s, c2s, c3a, c4af adsorption additives, it is found that among the four minerals c3s, c2s, c3a and c4af of cement clinker, the transition phase C3A has the largest adsorption capacity of water reducing agent. The order of the adsorption of various minerals to the superplasticizer is c3a>c4af>c3s>c2s. In order to study the adsorption of superplasticizers by four different minerals c3s, C2S, C3A and C4AF in cement clinker, two groups (S group and I group) were burned with different c3s/c2s ratios and different C3A/C4AF ratios. Cement, tested the adsorption enthalpy of naphthalene-based superplasticizer (UNF-5) with different mineral composition cements. In Group S cement, the number of C3A and C4AF remained unchanged, changing the C3S/C2S ratio. In group I, the number of c3s and c2s remained unchanged, changing the proportion of c3a, /c4af, see Table 9-10. The mineral composition of the clinker and the results of the free calcium oxide (f-CaO) titration are shown in Table 9-10.
Table 9-10 Mineral composition of clinker
|Sample No||Mineral composition /%|
The apparent adsorption capacity of the naphthalene-based superplasticizer on the two groups of cement is shown in Figures 9-33 and 9-34. The adsorption of the naphthalene-based superplasticizer UNF-5 from the cement prepared by the purification reagent shows that the adsorption capacity of the superplasticizer is higher when the ratio of C3S/C2S and C3A/C4AF in the mineral of cement clinker is higher. Big. According to the adsorption amount of the cement clinker, it can be considered that C3S adsorbs more naphthalene-based superplasticizer than C2S. Under the conditions of the same transition phase content, the cement with high C3S content has a higher adsorption capacity for the superplasticizer than the cement with high C2S content. Also from the results of the adsorption of cement clinker Nos. 1-1 and #2, it can be clearly seen that C3A adsorbs more Naphthalene based superplasticizer than C4AF. The C3A content of 1-2 is 8%, which is 5% higher than 3% of C1A content of 1-1, and the maximum adsorption amount of 1-2 cement to naphthalene superplasticizer is about 1-1 cement. Times! The sample results again demonstrate the significant effect of C3 A content in cement clinker on the amount of superplasticizer adsorbed. According to the adsorption data of cement single mineral to superplasticizer, the amount of C3A adsorption superplasticizer is about 10 times that of silicate phase. Therefore, for adsorbing superplasticizer, increasing 1% of C3A is equivalent to increasing. 10% C3S, C3A content changes have a greater impact on the amount of cement adsorption superplasticizer. The effects of various minerals in cement clinker on the adsorption of hemoplastic water reducer and the adsorption of single mineral on superplasticizer are consistent. Regarding the influence of the adsorption of single mineral C3A on the admixture, the results of this study are consistent with the conclusions obtained by other researchers, but the effect of C4AF on the adsorption capacity of the water reducer is not as large as previously reported. The results of the adsorption of c4af on superplasticizers in cement single minerals and cement clinker minerals show that the adsorption capacity of c4af on superplasticizer is much lower than that of c3A. Therefore, by reducing the ratio of (:3厶/(:4-8?), it is possible to control the adsorption capacity of cement clinker to the superplasticizer, thereby controlling the rheological properties of cement concrete mixed with superplasticizer. In addition, in cement In the study of single mineral adsorption, the adsorption of all single minerals on the water-reducing agent showed a tendency to increase the adsorption amount with the increase of the concentration of the water reducing agent, and in the purely fired cement, with the concentration of the superplasticizer The increase of the amount of adsorption increases rapidly, and then the concentration of the water reducing agent increases, and the amount of adsorption decreases. The same trend appears in the two groups of cement.
9. 2. 2 Industrial raw materials fired Portland cement adsorption of high efficiency water reducer
Portland cement with different mineral compositions is fired from industrial raw materials, see Table 9-11. The sulfamate superplasticizer (AS), aliphatic superplasticizer (FAS) and naphthalene superplasticizer (UNF-5) were tested on the surface of cement particles. Adsorption capacity.
Table 9-11 Mineral composition of cement clinker
|Clinker||Clinker rate||Clinker mineral composition address /%|
|Numbering||Density / (g / cm3)||Specific surface area / (m2 / kg >||C3S||C2S||c3a||C4AF|
|A-1||3.15||390||54. 61||23. 17||7. 85||11.85|
|A-2||3.12||390||55.26||23. 45||8. 55||10. 22|
|A-3||3.16||410||56. 56||24. 00||8. 51||8. 42|
|B-1||3.16||420||60. 86||16. 98||8. 95||10. 69|
|Br2||3.15||390||61. 63||17. 20||9. 38||9. 28|
|B-3||3.14||400||63. 63||17. 75||6. 42||9.69|
|C-1||3.15||420||66. 88||11.08||9.82||9. 71|
|C-2||3.16||410||68. 38||11. 32||7. 08||10. 69|
|C-3||3.15||400||69. 86||11. 57||7.31||8. 74|
According to the design value of cement clinker, C3S and QS are basically the same in the same series of cement clinker, and the aluminate mineral can be adjusted appropriately. The C3S content of the three series of cements increased in turn, and the CzS content decreased in turn. The CsS of C series cement clinker has exceeded 65%, which belongs to high C3S clinker. The facies analysis of the cement clinker composed of different minerals was carried out under the mirror, and the mineral composition, morphology and distribution of the clinker were observed. The clinker samples were coarsely ground, washed, and polished, and then etched with a 1% nitric acid-ethanol solution for 108. After drying, the samples were observed under a light microscope, and the experimental results are shown in Fig. 9-35.
As can be seen from Fig. 9-35, the cement clinker of the A (KH = 0.88) series contains more round granular B ore. As the lime saturation coefficient KH increases, the A ore in the clinker increases. Al (KH=0.88; SM=2.4; IM = 1.4) Clinker can be seen in comparison with C-3 (KH = 0.94, SM = 3.0, IM = 1.6) clinker, the latter A mine Significantly more than the former. In Bl (KH = 0.91, SM = 2. 4; IM = 1. 6) clinker, B-2 (SM = 2. 6; IM = 1.8; KH = 0.91) clinker and Cl (KH = 0) 94, SM = 2.4; IM = 1.8) In the clinker sample, the A ore is more long and columnar. Long columnar A ore often exists in clinker with more intermediate phases, indicating that the content of intermediate phases of these three clinker is relatively large. B-2 (KH=0.91, SM = 2.6; IM=1.8) clinker and Cl (KH = 0. 94; SM = 2. 4; IM=1. 8) C3A in the clinker sample can be observed from the photograph. The content of C4AF was higher in the clinker of Bl (KH = 0.91; SM=2.4; IM = 1.6). The results of the anti-photoelectric mirror confirmed that the fired clinker was consistent with the experimental design.
9. 2. 2.1 Adsorption of naphthalene-based water reducer on the surface of different cement particles
The adsorption capacity of UNF-5 on the surface of different cement particles is shown in Figure 9-36 to Figure 9-38. From the adsorption of naphthalene-based superplasticizer UNF-5 on cements with different mineral compositions, it is seen that with the increase of the concentration of superplasticizer, the adsorption capacity of cement particles to superplasticizer increases, but when the concentration of superplasticizer increases When it is increased to a certain extent, the adsorption amount increases slowly, and some even decrease (such as B>2 cement with KH = 0.91, SM = 2. 6, IM = 1. 8). In the A series of cement, the mineral composition does not change much. With the increase of C3S and C3A content, the adsorption amount also increases, but the difference is not big. The maximum adsorption capacity of the A series cement for the naphthalene series superplasticizer is 6~7mg. /g cement. In B series cement, the adsorption capacity of B~2 is significantly higher than that of the other two kinds of cement. The maximum adsorption capacity is 11~12mg/g cement, the maximum adsorption capacity of B-3 is 8mg/g cement, and the maximum of B-1. The adsorption capacity is only 6 mg / g cement. B-2 exhibits the largest amount of adsorption because of its maximum C3S and C3A content, which further demonstrates the sensitivity of the two minerals to admixture adsorption. The C3S content in C series cement is further improved. Except C-1 content in C-1 is higher than 9%, the other two C3A contents are not high, C-1 shows the maximum adsorption capacity, C-2 adsorption is the second, C-3 The amount of adsorption is the smallest.
9.2. 2.2 Adsorption of aliphatic sulfonate water reducer on different cement particles
The adsorption amount of FAS on the surface of different cement particles is shown in Figure 9-39 to Figure 9-41. From the adsorption of aliphatic superplasticizer FAS on different mineral cements, it can be seen that it has a similar rule with UNF-5 superplasticizer. Cement B>2 with large adsorption capacity of naphthalene-based superplasticizer also showed the largest adsorption amount of FAS, but the adsorption amount of FAS by various cements was lower than that of naphthalene UNF at the same equilibrium concentration. The adsorption amount of C-1 on FAS is larger than that on the naphthalene series. The increase is obvious. C-1 cement (KH = 0.94; SM = 2.4, IM = 1.8) is effective for water reduction? | The adsorption amount is as high as 13. 4 mg / g.
9. 2. 2. Adsorption of 3 sulfamate on the surface of different cement particles
The adsorption amount of AS on the surface of different cement particles is shown in Figure 9-42 to Figure 9-44. With the increase of AS concentration of sulfamate-based high water reducer, the adsorption capacity of AS on A series cement quickly reached the maximum value, and then the adsorption of AS on the A series (KH = 0.88) cement began. The maximum amount is about 3. 5 mg / g cement, obviously small amount of f UNF-5 and FAS adsorption.
Adsorption on cement particles of the B series (KH = 0.91) and C series (KH = 0. 94) is similar to the highly efficient water reduction I UNF-5 and FAS adsorption. It can be seen that as the cement lime saturation coefficient KH increases, the maximum adsorption capacity of cement particles increases, and C-1 cement (KH = 0.94; SM = 2.4; IM = 1.8) is expected to reduce the AS effect. 4重量/克。 The large adsorption amount of up to 9. 4mg / g.
The maximum adsorption capacity of three superplasticizers of UNF-5, FAS and AS on different mineral cements is shown in Table 9-12.
Therefore, it can be seen that among the four minerals of cement, C3A has the greatest influence on the adaptability of cement and admixture. From the data in Table 9-12, it can be found that with the increase of C3S content in cement, the maximum adsorption amount is also Significantly increased, the maximum adsorption capacity of the cement sample of the strontium lime saturation coefficient (C series, ie KH = 0.94) on the superplasticizer, and the cement sample with low lime saturation coefficient (A series, ie KH = 0.88) Compared with the latter, the maximum adsorption capacity of the water reducing agent is significantly higher than that of the latter; the cement with the highest C3S content (C-3 sample, ie KH = 0.94, SM = 3.0, IM = 1.6) ), the maximum adsorption capacity of superplasticizer, almost the lowest C3S cement (A-1 sample) twice the maximum adsorption capacity of high-efficiency water reducer, sometimes for high-efficiency water reducer varieties (such as AS) Even up to nearly three times, as shown in Figure 9-45.
Different high-efficiency water reducing agents in cement with Cl (KH = 0. 94; SM = 2.4; IM=1.8), B-2 (KH = 0.91 ? SM = 2. 6; IM=1. 8) C-3 (KH = 0. 94; SM = 3. 0; IM = 1. 6) cement, Bl (KH = 0.91; SM = 2. 4; IM = 1.6) cement and A- The adsorption on the cement of 3 (KH = 0.88, SM = 3. 0; IM = 1.8) is shown in Figure 9-46 to Figure 9-50.
From the above adsorption of different superplasticizers, the amount of AS absorbed on the surface of cement particles is small, followed by FAS, and the amount of UNF-5 adsorbed on cement particles is larger. The adsorption amounts of the three high-efficiency i-water agents in all the experimental studies all increased firstly with the change of the equilibrium concentration, and then decreased after reaching the maximum value, especially the high-efficiency water-reducing agent and the equilibrium concentration of the high-efficiency water-reducing agent increased. The amount of adsorption decreased significantly. The reason why the adsorption amount increases with the increase of the equilibrium concentration is not clear, and may be related to the adsorption mode of the superplasticizer. It is reported that the superplasticizer wash adsorbs on the adsorption point on the surface of the cement particles (ie, the site where the molecules of the superplasticizer are adsorbed). The adsorption on the naphthalene-based high-efficiency water-reducing agent ice-grain particles is a plane adsorption, and the high-efficiency water-reducing agent molecules are horizontally laid on the cement particles, and the adsorption amount is large. The adsorption of the aromatic sulfonate (AS) on the cement particles is high. In the state of being curled, some active adsorption sites are adsorbed on the surface of the cement particles, and the linear molecules are irregularly extended into the interior of the solution, and the adsorption amount is small. The larger adsorption of UNF-5 on cement particles may also be related to the more sulfonic acid functional groups contained in UNF-5. The suction of the superplasticizer on the cement particles is carried out by a combination of physical and chemical effects. Its instantaneous physical adsorption with the cement particles is guided by the position of chemical adsorption in the first few minutes of hydration. Due to the non-uniformity of the phases on the surface of the cement particles, those sites with more active enthalpy are more likely to adsorb the water-reducing agent molecules. In this way, the distribution of the cement particles initially to the high-efficiency i-water molecule can be considered as such that the high-efficiency water-reducing agent molecules are concentrated in the higher activity sites, and the high-efficiency water-reducing molecules are adsorbed on other parts of the cement particles.
Whether the adsorption of the admixture occurs in a special or normal manner, it will affect the hydration process of the cement. The presence of organic molecules at the solid-liquid interface can cause nucleation and growth of the crystal. Adsorption at the center of the nucleus prevents the nucleus from achieving a minimum critical dimension. On the other hand, the presence of the adsorbent admixture may cause the growth of the hydration product to cause structural changes due to the embedding of the admixture, and the morphology of the hydrated product particles may also vary.