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Effect of hydroxypropyl methylcellulose ether on the pore structure and performance of modified foamed cement insulation board

Views: 0     Author: Site Editor     Publish Time: 2023-06-05      Origin: Site

Abstract: Taking the foamed cement with a dry apparent density of 250 kg/m3 prepared by ordinary Portland cement as the object, the effects of hydroxypropyl methylcellulose ether (HPMC) on the pore size, strength, water absorption and Influence of thermal conductivity. The results show that the porosity of the foamed cement insulation board does not change with the increase of the amount of HPMC, but the addition of HPMC can significantly reduce the pore size of the foamed cement insulation board. With the increase of HPMC content, the compressive strength and flexural strength of the foamed cement insulation board first increased and then decreased, the water absorption first decreased and then increased, and the thermal conductivity decreased continuously. When the amount of HPMC was 0.02% of the cement mass, the 28-day compressive strength and flexural strength of the foamed cement insulation board increased by 14.1% and 16.67%, respectively, and the volume water absorption decreased by 18.21%. Reduced by 0.004 W/(m·K).

Key words: foamed cement insulation board; hydroxypropyl methylcellulose ether; porosity; strength; water absorption; thermal conductivity

0. Preface

As a grade A non-combustible building energy-saving material, the foamed cement insulation board is very suitable for building envelope insulation and fire protection belt engineering, and meets the urgent needs of the building energy-saving market for fireproof and safe insulation materials. The strength and thermal conductivity of foamed cement mainly depend on its dry density, but the pore structure and physical characteristics of the pore wall of foamed cement also have a great influence on the performance of foamed cement. Roβler et al. studied the influence of porosity, pore size and pore shape on the strength of foamed concrete. The results showed that the smaller the pore size of foamed concrete, the higher the strength; There are many studies on the pore structure of cellulose ether; the effect of methyl cellulose on the pore structure of foamed cement has also been studied; the effect of cellulose ether on cement paste and its effect mechanism have also been studied, but it is not systematic enough. This paper intends to study the effect of cellulose ether on the pore structure and performance of low density (250 kg/m3) foamed cement insulation board.

1. Experiment

1.1 Experimental raw materials

Cement: P·O42.5R cement produced by Chongqing Xiaonanhai Cement Factory; Fly ash: Class II, Chongqing Hualuo Fly Ash Development Co., Ltd.; Silica fume: SF2201 microsilica fume, Chongqing Jinyuda Trading Co., Ltd. Foaming agent: industrial hydrogen peroxide, concentration 27.5%, commercially available; polycarboxylate water reducer: pale yellow liquid, solid content 9.1%, water reducing rate 21%; foam stabilizer: industrial calcium stearate, commercially available ; Coagulant: developed by Chongqing Sibeiken Energy Saving Technology Development Co., Ltd.; fiber: polypropylene fiber, length (12±2) mm, commercially available; cellulose ether: hydroxypropyl methyl fiber with a viscosity of 100 Pa s Monoether (HPMC).

1.2 Experimental method

1.2.1 Preparation method of foamed cement

Add water reducer, PP fiber, coagulant and foam stabilizer to the quantitative water and stir evenly, then add HPMC accounting for 0, 0.01%, 0.02%, 0.03%, 0.04%, and 0.05% of the cement mass respectively, and mix the cement, powder Add coal ash, silica fume and other powder materials into the above aqueous solution and stir for 180 s to make cement paste, then add a certain amount of foaming agent hydrogen peroxide (concentration 27.5%) and stir for 7 to 9 s, then put it into the mold and remove the green body from the mold Afterwards, it is maintained under natural conditions to the specified age. Throughout the test, the same benchmark formula and foam volume were guaranteed each time, and the apparent density of foam cement was controlled at 240-250 kg/m3.

1.2.2 Performance test

(1) Test of apparent density: Cut the foamed cement insulation body that has been naturally cured for 28 days into 150mm×150mm×30mm specimens, and follow GB/T 5486—2008 "Inorganic Hard Thermal Insulation Products Test Method "Test the dry apparent density of the foamed cement insulation board.

(2) Test of porosity: Grind the foamed cement sample finely with an agate mortar, pass through a 0.08 mm square hole sieve, and then dry it in an oven at (110±5)°C to constant weight; Pour into the Lee's bottle to above the 0-point scale line, rotate to discharge the air, and record its volume V0 after standing still; accurately weigh the mass m0 of the ground foamed cement powder, put the powder into the Lee's bottle, and record the volume V1, Calculate the true density ρ of the foamed cement.

(3) Test of strength and volumetric water absorption: Cut the foamed cement that has been naturally cured to the specified age into specified sizes, and test the 3, 7, 14 and 28 days of the foamed cement insulation board according to GB/T 5486-2008 Compressive strength, 28 d flexural strength and volumetric water absorption. The size of the compressive strength test piece is 100 mm × 100 mm × 30 mm, the size of the flexural strength test piece is 300 mm × 100 mm × 30 mm, and the size of the volume water absorption test piece is 400 mm × 300 mm × 30 mm.

(4) Test of thermal conductivity: Cut the foamed cement that has been naturally cured to the specified age into 300mm×300mm×30mm specimens, and according to GB/T 10294-2008 "Steady-state thermal resistance and related characteristics of thermal insulation materials" Determination of the protective hot plate method" to test the thermal conductivity of foamed cement insulation boards.

2. Results and Analysis

2.1 Effect of HPMC content on dry apparent density of foamed cement insulation board

When the content of HPMC is 0-0.05%, the dry apparent density of the foamed cement insulation board is very close, both in the range of 248-250 kg/m3.

2.2 Effect of HPMC content on porosity of foamed cement insulation board

The porosity of the 250 kg/m3 foamed cement insulation board prepared with different dosages of HPMC is basically consistent, fluctuating around 86.75%, and there is no major change. This is because the quality of the raw materials is the same and the foaming volume is the same, so the apparent density of the foamed cement insulation board is basically the same, that is, when the apparent density of the foamed cement insulation board is constant, the porosity does not change with the amount of HPMC And change.

2.3 The effect of HPMC content on the pore size of foamed cement insulation board

Adding 0.02% HPMC can significantly reduce the pore size of the foamed cement insulation board. This is because the incorporation of HPMC can increase the viscosity of the slurry, which increases the surface tension of the cement slurry, and the pore size of the formed pores becomes smaller and the distribution is relatively uniform. Further observe the two types of foamed cement insulation board samples under a microscope, randomly delineate three straight lines of 30-40 mm at a distance of 20 mm from the edge of the specimen, observe the small holes on the straight line, and record the total number of small holes, Then calculate the pore size of the two foamed cement insulation board samples. The average pore size of the sample without HPMC is 5.4 mm, while the average pore size of the sample mixed with 0.02% HPMC is 1.2 mm.

2.4 Effect of HPMC content on compressive strength of foamed cement insulation board

The compressive strength of foamed cement insulation board increases with the prolongation of curing age, and with the increase of HPMC content, the compressive strength of foamed cement insulation board increases first and then decreases. When the content of HPMC increased to 0.02%, the compressive strength of the foamed cement insulation board reached the maximum value at 14 d and 28 d, and the compressive strength at 3, 7, 14, and 28 d was 0, 1.6 higher than that without HPMC, respectively. %, 10.9% and 14.1%.

2.5 Effect of HPMC content on the flexural strength of foamed cement insulation board

With the increase of HPMC content, the 28-day flexural strength of the foamed cement insulation board first increased and then decreased. When the HPMC content was 0.01%, the flexural strength of the foamed cement insulation board reached the maximum value. When the HPMC content When the content is 0.04%, the flexural strength of the foamed cement insulation board is lower than that without adding HPMC. As the amount of HPMC continues to increase, the flexural strength of the foamed cement insulation board continues to decrease.

2.6 Effect of HPMC content on volumetric water absorption of foamed cement insulation board

With the increase of HPMC content, the water absorption of the foamed cement insulation board decreases first and then increases. When the HPMC content is 0.02%, the volumetric water absorption of the foamed cement insulation board is the lowest, only 5.75%, which is lower than that of the non-added cement board. The reduction of HPMC was 18.21%. With the continuous increase of HPMC content, the volume water absorption rate gradually increased.

2.7 Effect of HPMC content on thermal conductivity of foamed cement insulation board

With the increase of HPMC content, the thermal conductivity of foamed cement insulation board decreased gradually. When the amount of HPMC is 0.02%, the thermal conductivity of the foamed cement insulation board is 0.004 W/(m K) lower than that without HPMC. When the amount of HPMC continues to increase to 0.05%, the thermal conductivity of the foamed cement insulation board The thermal conductivity is 0.007 W/(m·K) lower than that of undoped HPMC. This is because the addition of HPMC makes the pore size of the foamed cement insulation board smaller and uniform, the movement of air molecules in the pores slows down, the air fluidity decreases, and the heat transfer is slower, so the thermal conductivity decreases.

3. Conclusion

(1) As the amount of HPMC increases, the porosity of the foamed cement insulation board basically does not change, but the pore size decreases.

(2) With the increase of HPMC content, the compressive strength and flexural strength of the foamed cement insulation board first increased and then decreased, and the volume water absorption first decreased and then increased.

(3) As the amount of HPMC increases, the thermal conductivity of the foamed cement insulation board decreases gradually.

(4) The incorporation of HPMC can improve the performance of the foamed cement insulation board to a certain extent. According to the comprehensive analysis of various properties, the recommended dosage of HPMC is 0.02% of the cement mass. The foamed cement insulation board prepared at this time is 28 days The compressive strength and flexural strength were increased by 14.1% and 16.67% respectively compared with those without HPMC, the volumetric water absorption decreased by 18.21%, and the thermal conductivity decreased by 0.004 W/(m·K).