Influence of cellulose ether on the properties of inorganic heat-insulating mortar

Abstract:The effect of cellulose ether on the water retention, consistency, dry apparent density, strength and volumetric water absorption of vitrified microbead thermal insulation mortar was studied. The research results show that: cellulose ether has the function of water retention and thickening, which can increase the consistency of thermal insulation mortar and improve its workability; with the increase of cellulose ether content, the compressive strength and flexural strength of thermal insulation mortar both increase first After the trend of decreasing, the optimal dosage is 0.4%; cellulose ether has obvious air-entraining effect, which can increase the closed porosity of mortar and reduce the volume water absorption of mortar.

Key words:vitrified microbeads; inorganic thermal insulation mortar; cellulose ether; water retention and thickening

0. Foreword

Scholars now mostly use vitrified microspheres and sepiolite as insulation materials, use Portland cement and fly ash as the main cementing materials, and add various auxiliary agents to prepare inorganic insulation mortar. Vitrified microbeads are a kind of acidic vitreous lava mineral (turpentine ore). After special technical treatment and production process, they become porous inside, vitrified and closed on the surface, and are in the form of spherical fine-diameter particles. A new type of inorganic lightweight thermal insulation material. As a new type of inorganic thermal insulation material, vitrified microbead thermal insulation mortar has excellent thermal insulation performance, anti-aging, weather resistance and fire resistance performance, and has high strength, good bonding performance, no hollowing and cracking phenomenon, and it can be mixed with water during on-site construction Ready to use and can be applied directly to drywall.

As an essential admixture in the preparation of inorganic thermal insulation mortar, cellulose ether will have a significant impact on the performance of thermal insulation mortar. Cellulose ether is obtained by reacting cellulose with NaOH, then reacting with various functional monomers such as monochloromethane, ethylene oxide, propylene oxide, etc., and washing the by-product salt and cellulose sodium. This experiment studies the water retention, consistency, dry apparent density, and strength of vitrified microbead thermal insulation mortar by studying cellulose ether, and the optimal blending of vitrified microbead thermal insulation mortar with water retention, consistency, dry apparent density, strength, and ether. The amount provides a theoretical reference for further research on cellulose ether inorganic thermal insulation mortar.

1. Test raw materials and methods

1.1 Raw materials

Chongqing Tianzhu ordinary 42.5R cement is used; the fly ash comes from the Class II fly ash produced by Xiamen Songyu Power Plant; the slaked lime uses Chongqing Zhengyang lime calcium powder; the vitrified microbeads are provided by Chongqing Tulip New Building Materials Co., Ltd.; it can be redispersed The latex powder is Wacker 5011 from Germany; the cellulose ether is hydroxypropylmethylcellulose (HPMC) produced by KIMA CHEMICAL CO.,LTD.

1.2 Test method

Base mix ratio: aggregate ratio 1 : 0.8, m (cement) : m (fly ash): m (slaked lime) is 7 : 2 : 1, and the amount of redispersible latex powder is 2% of the mass of the cementitious material , the water-binder ratio is 1.8. Cellulose ether is mixed according to the mass percentage of the gelling material, and the dosages are 0, 0.2%, 0.4%, 0.6%, and 0.8%, respectively.

The size is 70.7 mm × 70.7 mm × 70.7 mm test mold and 40 mm × 40 mm × 160 mm test mold molding, demoulding after 2 days, in the standard curing room [temperature (20 ± 2) ℃, relative humidity ≥ 95 %] to an age of 28 d. The molding method is carried out in accordance with GB/T 26000-2010 "expanded vitrified microbead thermal insulation mortar"; the consistency test is carried out in accordance with JGJ/T 70-2009 "standard performance test method for building mortar"; dry apparent density, compressive strength, resistance The flexural strength test was carried out in accordance with JG/T 283-2010 "Expanded vitrified microbead lightweight mortar".

2. Results and Analysis

2.1 Effect of cellulose ether on water retention of thermal insulation mortar

The thermal insulation mortar test block not mixed with cellulose ether is very rough, and the surface of the test block appears "pockmarked", and the cement paste cannot completely wrap the vitrified microbead thermal insulation aggregate, and is exposed outside. After adding 0.4% cellulose ether by mass, the thermal insulation mortar has no "pockmarked surface", and the surface is smooth and denser. Therefore, after adding cellulose ether, the construction performance of the vitrified microbead thermal insulation mortar is significantly improved, and the surface quality is significantly improved. This is mainly due to the fact that when the cellulose content is 0, the water retention of the thermal insulation mortar is extremely poor, and severe bleeding occurs, which causes the loss of cement paste and causes the phenomenon of "pockmarked surface"; after adding cellulose ether, the water retention performance is significantly improved, The loss of cement slurry is greatly reduced, so the construction performance of the test block mixed with cellulose ether is better.

2.2 Effect of cellulose ether on the consistency of thermal insulation mortar

From the effect of different cellulose ether content on the consistency of vitrified microbead thermal insulation mortar, it can be seen that with the increase of cellulose ether content, the consistency of the mortar first increases and then decreases, and the blank control without cellulose ether The group showed obvious bleeding phenomenon. This is mainly due to the significant water retention and thickening effect of cellulose ether. The addition of cellulose ether increases the water retention of the mortar, thereby reducing bleeding and increasing the fluidity of the mortar; at the same time, because cellulose ether has an air-entraining effect , Introduce a large number of stable micro-bubbles during the mortar preparation process to form a ball effect and further increase the fluidity of the mortar. When the amount of cellulose ether exceeds 0.6%, the consistency of the mortar decreases sharply, the viscosity increases, and the workability becomes poor. It can be seen that when the content of cellulose ether is 0.4%~0.6%, the thermal insulation mortar has better workability.

2.3 Effect of cellulose ether on the density of thermal insulation mortar

From the effect of different cellulose ether content on the dry apparent density of vitrified microbead thermal insulation mortar, it can be seen that with the increase of cellulose ether content, the dry apparent density of thermal insulation mortar first increases and then decreases. The mortar in the blank group had severe bleeding and could not be compacted, so the dry apparent density was low; in the test group, with the increase of cellulose ether content, the density gradually decreased. increase, bleeding decreases, the moisture in the slurry is absorbed by cement hydration and the pores left after evaporation increase, which reduces the dry apparent density; Reduced the apparent density of the mortar. Adding cellulose ether can increase the porosity of the mortar, reduce the apparent density, and its thermal insulation performance will also increase with the decrease of the density.

2.4 Effect of cellulose ether on the strength of thermal insulation mortar

From the influence of different cellulose ether content on the compressive strength and flexural strength of vitrified microbead thermal insulation mortar, it can be known that the compressive strength and flexural strength of thermal insulation mortar increase first and then decrease with the increase of cellulose ether content. The trend is small, and its compressive strength and flexural strength both reach the maximum when the cellulose ether parameter is 0.4%. After the cellulose ether is added, the fluidity and homogeneity of the mortar are increased, the cementitious material slurry in the mortar is more fully wrapped around the vitrified microbeads, and after the workability is improved, the mortar test block is denser, so the mortar strength will improve. With the further increase of the content of cellulose ether, the air-entraining effect on the strength becomes the dominant factor. With the increase of the content of cellulose ether, the more air bubbles are introduced, the lower the strength will be. The impact of cellulose ether on the strength of mortar is more significant. When the content is 0.4%, the compressive strength and flexural strength both reach the maximum.

2.5 Effect of cellulose ether on volumetric water absorption of thermal insulation mortar

From the effect of different cellulose ether content on the volume water absorption of vitrified microbead thermal insulation mortar, it can be seen that with the increase of cellulose ether content, the volume water absorption of thermal insulation mortar decreases gradually. From the above test results, it can be seen that after the cellulose ether is added, the apparent density of vitrified microbead insulation mortar gradually decreases, and the porosity gradually increases, but its volume water absorption does not increase with the increase of porosity, on the contrary decreased. This means that although the porosity of the mortar is increased after the addition of cellulose ether, the open porosity is reduced and the closed porosity is increased, so the volume water absorption decreases. Cellulose ether has an air-entraining effect and produces a large number of tiny, closed air bubbles. These air bubbles exist stably in the slurry and significantly improve the pore structure of the mortar. It can not only reduce the volumetric water absorption of the mortar, but also improve its thermal insulation performance.

3. Conclusion

(1) Cellulose ether has excellent water retention performance, which can significantly improve the workability of vitrified microbead insulation mortar and improve its surface quality.

(2) Cellulose ether has obvious water retention and thickening effect. With the increase of the dosage, the consistency first increases and then decreases. When the dosage of cellulose ether is 0.4%~0.6%, the thermal insulation mortar has better workability.

(3) Adding cellulose ether can increase the porosity of the mortar, reduce the apparent density and increase the thermal insulation performance.

 (4) With the increase of the content of cellulose ether, the compressive strength and flexural strength of the thermal insulation mortar first increased and then decreased, and the optimal content was 0.4% of the mass of the cementitious material.

(5) Cellulose ether has a strong air-entraining effect, which can reduce the dry apparent density of mortar, increase the closed porosity, and reduce the open porosity.