Study on Preparation of Polymeric Germanium from Slag and Metakaolin

Ancient concrete, mortar buildings (such as the Egyptian pyramids, Roman Colosseum) has a very excellent durability, it can remain for thousands of years in a relatively harsh environment, even thousands of years without failure. In contrast, under the same conditions, modern concrete prepared with Portland cement has an average life of only 40 to 50 years, and the longest is no more than 100 years. In a short period of only a few years, it is seriously damaged. The reason is that there is an amorphous substance not found in Portland cement in ancient cockroaches. The structure of this material is similar to the three-dimensional framework of organic polymer, but its main body is inorganic Si04 and A10n. Tetrahedron, French material scientist J. Davidovits calls it Geopolymer (Geop01ymer).

The amount of metakaolin is a polymer and a small amount of alkaline solution with a large excitation natural or artificial aluminum silicate material is mixed, at room temperature curing conditions even at less than 150 deg.] C under no cement clinker gel to give different intensity levels of material. Compared with the conventional inorganic Si-Al cementitious materials, the geopolymer has the following characteristics: it has excellent durability: in the preparation: the process does not use a large amount of resources and energy such as the production of Portland cement. "Two grinding and one burning" calcination: process, and basically does not emit CO ₂ , and the raw materials used are natural or artificial low-calcium Si-Al materials with abundant resources and low price; fast hard, early strength, and long-term strength High, the geopolymer generally obtains 70% of the final strength, and the late compressive strength can reach 20-100 MPa; the low shrinkage, the shrinkage of the 7, 28d of the geopolymer is only 0.2 ‰, 0.5, respectively. ‰, while the Portland cement hardened slurry 7, 28d has a shrinkage of up to 1.0‰, 3.3‰; low permeability, its chloride ion permeability coefficient is 10 ^{- 9} cm ² /s, similar to granite ^{(10 - 1 0 cm 2 /} s); high temperature resistance, good heat insulation effect, can resist a high temperature of 1000 ~ 1200 ℃ without damaging the burner for a thermal conductivity of 0.24 ~ 0.38W / m. K, comparable lightweight refractory brick clay (0.3 ~ 0.438W / m.K). These characteristics make geopolymers and their defects have broad application prospects in municipal, bridge, road, water, underground, marine and military fields, and will become an alternative to Portland cement.

Of steel slag produced in the smelting plant byproduct of pig iron, slag reaches annual emissions of l million tons, taking into account the slag material is Si-Al, having high activity after finely ground slag powder thus replace part Utilization The preparation of geopolymers from metakaolin has important social, economic and technical benefits.

1. Raw materials and experimental methods

(1) Raw materials

Metakaolin: calcined kaolin at 700 ° C for 12h; slag powder: ground slag provided by Jiangnan Cement Plant: sodium hydroxide: chemically pure flake sample: sodium silicate: 40βBe liquid sodium silicate, M=3.0~ 3.3, solid content is about 37%: fine aggregate: fineness modulus M = 1.34 yellow sand, mud content is 0.42%, when used to sieve particles below 5mm: coarse aggregate: 5 ~ 15mm continuous grade of limestone crushed stone. The technical specifications of the above raw materials are shown in Table 1.

Table 1 Chemical composition and physical properties of raw materials

Note 1: MK - metakaolin, SL - slag powder

(2) Experimental methods

1. Forming method

First, the metakaolin, slag powder and aggregate were stirred with a mortar mixer for 3 min, then slowly added to the prepared high alkali solution, stirred for 3 min, and the mixed slurry was poured into a 40×40×160 mm ³ triple mold, vibrating. After 1 min, ld was demolished, cured under the prescribed maintenance system, and then subjected to compression and flexural tests. The pure ground polymer paste base mix ratio without slag powder is:

The mixing ratio is the optimized optimal ratio

2, impermeability test

According to JTJ270-98 "Quick Test of Concrete Resistance to Chloride Ion Penetration", the electrical resistance and relative chloride ion permeability coefficient of ruthenium were determined. Three test pieces were prepared from the geopolymer, and the average value was taken as the final value.

3. Anti-freeze-thaw test of geopolymer bismuth

Refer to GBH82-85 "Test method for long-term performance and durability of ordinary concrete" in the "quick freezing method". The acoustic time and amplitude are measured every 25 times with an ultrasonic detector, and the internal damage is reflected by the increase in sound time and the attenuation of the amplitude.

2. Preparation of geopolymer bismuth mixed with slag powder

(1) Optimization and optimization of polymer mortar base for slag powder

1. Determination of the amount of slag powder

In this study, an equal amount of substitution method was used to incorporate 10, 30, 50, 70% slag powder into metakaolin. The water-cement ratio of the five groups of tests was 0.35, and the ratio of sand to sand was 1:1. After 28 days of standard curing, the compressive strength and flexural strength of the five geopolymers were tested. The experimental scheme and results are shown in Table 2.

Table 2 Experimental scheme and results

2. Optimization of maintenance system

The experiment used three kinds of maintenance systems: standard 3d, 80 °C steaming (2h, 4h, 8h), 150 °C steaming 2h.

Curingregime

Figure 1 Effect of curing system on mechanical properties

It can be seen from Figure 1 that under different maintenance systems, the strengths vary greatly. Standard curing has the lowest intensity, followed by steaming and steaming. The same as the steamed test piece, with the extension of the steaming time, the strength of the test piece also increased accordingly. After steaming at 80 °C for 2h, the compressive strength increased by 19.11%. The effect of steaming has been initially shown, but due to the short time, its potential has not been fully exerted, so the growth rate is small; steaming for 4h, compressive strength It increased rapidly by 46.03%; after steaming for 8 hours, the compressive strength increased rapidly by 53.16%. Obviously, prolonging the steaming time in an appropriate amount is very advantageous for accelerating the reaction speed of the polymer of the slag powder and increasing the early strength. The strength of the steamed test piece is lower than that of the steamed test piece, probably because the activity of the slag is relatively high, and the steaming is enough to make it react quickly and completely: excessive curing temperature (pressure steaming) is easy to cause In a very short period of time, a large amount of hydration products are rapidly formed on the surface of the slag particles, which is too late to diffuse, resulting in a stage of bond strength between the particles: on the other hand, steaming may also cause a change in the hydration product.

In contrast, the effect of the maintenance system against the strength of the fold is consistent with its effect on the compressive strength, but the extent of the impact is relatively small. It can be seen that with 80 ° C steaming for 8 h, the compressive strength is increased by 53.16%, and the flexural strength is only increased by 28.99%.

From the experimental results, steaming has the best effect on improving the polymer strength of slag powder, and the energy consumption is not too high, and it is convenient to operate. Comprehensive consideration of the final 80 ° C steam curing 8h as a test piece maintenance system.

(2) Preparation of polymer strontium of slag powder

The coarse aggregate is introduced on the basis of the optimal slag powder ground polymer mortar (SL50PSS) determined by (1). After the coarse aggregate is added, the fluidity of the mixture is reduced, and the water-to-binder ratio is increased from 0.35 to 0.40 for easy molding. After the test piece is formed, the mold is cured by a system of steaming for 8 hours at 80 ° C, and then subjected to compression and flexural tests. The mixing ratio and experimental results are shown in Table 3.

Table 3 ç ¼ mix ratio and experimental results

Third, the durability of slag powder geopolymer

(1) Resistance to chlorine separation

Table 4 Chloride ion diffusion coefficient

It can be seen from Table 4 that the chloride ion diffusion coefficient of the polymerized strontium powder is relatively small, and its order of magnitude is 10 ^{- 9} , indicating that its impermeability is very excellent. Compared with several common building materials (see Table 5), it can be seen that the impermeability of the geopolymer is between granite and kaolinite, which indicates that the geopolymer has excellent impermeability and can be combined with some Natural rock is comparable.

Table 5 Cl ^- permeability coefficient of several common building materials

(2) Resistance to freezing and thawing

Figure 3 Weight loss rate of thorium in freeze-thaw cycles Figure 4 Growth of thorium in freeze-thaw cycles

Figures 3 to 5 show the weight loss, acoustic growth and acoustic amplitude attenuation curves of the geopolymer strontium slag powder during the freeze-thaw cycle. It can be found that as the number of freeze-thaw cycles increases, the weight loss, the increase in sound time, and the attenuation rate of the acoustic wave amplitude gradually increase. If the weight loss rate reaches 5.0% as the evaluation standard for the number of freeze-thaw cycles, the number of freeze-thaw cycles of the geopolymer strontium slag powder can be calculated to be 119 times.

Figure 5 Amplitude attenuation of helium in a freeze-thaw cycle

Fourth, mechanism research

(a) X-ray diffraction analysis 0mi))

Fig.6 XRl) line diagram of metakaolin and slag powder polymer

As it can be seen in FIG. 6, Slag XRD spectrum of the polymer in the dispersion was 20 ~ 40 ^o, the bread-like, indicating that both the structure of the main polymer is amorphous; Comparative XRD spectrum at 20 ~ The size of 40 ^o , the ground polymer of the slag powder contains more amorphous matter than the pure polymer, and we also observed sharp peaks of a small amount of crystalline matter (4.23A, 3.33A, 1.81A, 1.37A). ), for identification of its analysis, the quartz crystal is determined, comparing the XRD spectrum metakaolin, quartz understood by those metakaolin introduced, and the polymerization process of the quartz crystal does not participate in the reaction.

(2) Infrared analysis (IR)

Figure 7 IR spectrum of metakaolin Figure 8 IR spectrum of geopolymer with slag powder

The positions of the main characteristic peaks and the types of corresponding groups in the above IR line graph are shown in Table 6.

Table 6 Location of main characteristic peaks and corresponding groups in the IR spectrum of metakaolin and slag powder

The IR spectrum of the geopolymer of metakaolin and slag powder was found to be:

1. The wave number corresponding to the strongest characteristic peak on the IR spectrum of metakaolin is 1086 cm ^-1 , and the IR spectrum of the geopolymer becomes 1033 cm ^-1 , indicating that the wave number of 1086 cm ^{-1 is} in the process of geopolymerization. The peak shifts toward the low wavenumber direction. It is noted that 1086 cm ^-1 corresponds to the Si-O symmetric stretching vibration peak in metakaolin, and 1033 cm ^-1 corresponds to the Si-O non-uniform stretching vibration peak. The characteristic peak shifts to the low wave number, indicating that A1O ₄ may replace part of the SiO ₄ group on the uniform Si-O-Si chain structure in the original metakaolin, causing the environment around SiO ₄ to change, thus affecting the internal structural atmosphere of the system. The stretching vibration peak of Si-O is affected to some extent, showing peak position shift.

2. The wave number of the melon line on the metakaolin is 914 and 798 cm ^-1 respectively corresponding to the 6-coordinate Al-OH vibration peak and the 6-coordinate Al-O vibration peak. After the geopolymer is formed, the peak is weakened. Instead of firing, a weak absorption peak appears at a wavenumber of about 700 cm ^-1 . Looking at the 1R line card, this peak corresponds to the vibration of the 4-coordinate AlO ₄ . This indicates that during the geopolymerization process, the 6-coordinate A1 remaining in the metakaolin is converted into the 4-coordinate A1.

V. Conclusion

(1) In this paper, slag powder is used as a Si-Al material for preparing geopolymer. Through the optimization of slag powder content and three curing systems, the optimal ratio and curing process of slag powder ground polymer mortar are obtained. The slag powder content is 50%, and steaming at 80 °C for 8 hours. At this time, the compressive strength of the geopolymer mortar is 75.2 MPa, and the flexural strength is 10.1 MPa.

(2) By studying the durability of polymer slag of slag powder, it is found that this cockroach has excellent resistance to chloride ion penetration and freeze-thaw resistance.

(3) The formation mechanism and structural nature of the geopolymer were analyzed by infrared and X-ray diffraction. It was found that the geopolymer was an amorphous product, and the infrared vibration peak of 1086 cm ^-1 corresponding to SiO _{4 was} low during the synthesis. Wavenumber shift, 6 coordination A1 is also converted to 4 coordination.

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