Effect of cellulose ether on the water retention performance of ordinary mortar

Abstract: The effects of hydroxypropyl methylcellulose (HPMC) with different viscosities and different dosages on the water retention performance of ordinary mortar (masonry mortar and plastering mortar) were studied. Studies have found that HPMC can greatly improve the water retention of mortar and greatly improve the construction performance of mortar, and its suitable dosage is 0.4‰～0.5‰. Under the condition of the same viscosity and different dosage of HPMC, the water consumption of mortar remained basically unchanged, the apparent density increased slightly, and the water retention rate increased with the increase of HPMC dosage. Under the condition of different viscosities and the same dosage of HPMC, the water consumption of mortar is also basically the same. The apparent density also increases slightly, and the water retention rate increases with the increase of HPMC viscosity.

Key words: cellulose ether; water retention; masonry sand; plastering mortar

0.Preface

In order to meet the needs of the development of the modern construction industry, a new type of construction mortar with excellent properties is developing vigorously, which is dry-mixed mortar. Dry-mixed mortar refers to a kind of granule or powder produced by a professional manufacturer, which is mixed with dry and screened fine aggregate, inorganic binder, water-retaining thickening material, mineral admixture and additives in a certain proportion. shape mixture.

Dry-mixed mortar requires suitable consistency and workability, and traditional mortar is mostly realized by adding lime paste. A small amount of chemical additives is used in dry-mixed mortar to achieve water retention and thickening performance, which is one of the biggest differences from traditional mortar. As water retention and thickening agent, cellulose ether is mostly used at present.

The molecular composition of cellulose is (C6H10O5)n, which is a linear polysaccharide composed of a glucose bond and anhydrous D-hexacyclic glucose. It is a very important class of natural polymer compounds. Cellulose is composed of glucose ring chain link units, the molecular configuration is B-1.4 type, there is no disproportionation point, the molecular structure is very symmetrical, and a strong crystal structure is formed through the action of hydrogen bonds and other forces. It is precisely because of the good crystallization and the strong binding force between molecules that it is difficult to dissolve. However, there are a large number of highly reactive hydroxyl groups on the cellulose molecular chain, and many chemical substances with excellent properties can be prepared through chemical reactions. Cellulose ether is a kind of semi-synthetic polymer water-soluble polymer obtained by chemical modification of natural cellulose as raw material. It is a kind of hydrophilic polymer material that can dissolve or swell in water to form a solution or Dispersions.

In this paper, hydroxypropyl methylcellulose with different viscosities was selected. The effect of different dosages on the water retention of ordinary mortar (masonry mortar, plastering mortar) was studied.

1. Raw materials and test methods

1.1 Raw materials

Cement: P·O 42.5 grade cement produced by a company in Chongqing.

Fly ash: Class II fly ash (code: FI) produced by a company in Xinjiang. The particle sphericity of fly ash is better.

Sand: Dry sand from a certain place in Sichuan, with a fineness modulus of 1.9.

Cellulose ether: Hydroxypropyl methylcellulose (code: HPMC) produced by a company in Guangdong, divided into HPMC75000S, HPMCl00000S, and HPMC200000S according to viscosity.

Filter paper: choose ultra-white filter paper with a diameter of 110mm, and its performance index meets the requirements for fast-fixed filter paper specified in GB/T 1914-2007 "Chemical Analysis Filter Paper".

Gauze: commercially available medical gauze, the size is 110mm×110mm.

1.2 Sample mix ratio

According to the previous foundation work, determine the basic mix ratio of masonry mortar and plastering mortar. When studying the effect of cellulose ether on masonry mortar, the dosage of cellulose ether was 0.3‰, 0.4‰ and 0.5‰ respectively; when studying the effect of cellulose ether on plastering mortar, the content of cellulose ether The dosage is 0.3‰, 0.4‰ and 0.5‰ respectively.

1.3 Test method

The tests of consistency, apparent density and water retention are carried out according to the methods specified in JGJ/T70-2009 "Standards for Basic Performance Test Methods of Building Mortar".

2. Experimental results and discussion

2.1 Masonry mortar

Effect of different viscosity and different dosage of HPMC on properties of masonry mortar. When the amount of HPMC is above 0.4‰, the water retention of mortar can basically be kept above 90%.

Further, a comparative test was done on the water retention of masonry mortar without blending with HPMC.

The right half is the water retention of mortar without HPMC, and the left half is the water retention of HPMC. It can be seen that the filter paper is soaked by water without adding HPMC, and the surface of the mortar has no wet luster; the part with HPMC, the filter paper has no sign of being soaked, and the surface gloss of the slurry is good. Therefore, HPMC can well improve the water retention of masonry mortar.

It can be seen from the test that when no cellulose ether is added, the mortar will bleed severely, have poor fluidity and workability. The construction performance is not good. However, with the addition of HPMC, the water retention performance of the mortar is greatly improved, and its workability is good; but when the amount of HPMC is too high, the viscosity of the mortar is high, and sticking to knives often occurs, which is not conducive to construction. Therefore, under the premise of ensuring good workability and water retention performance, the amount of cellulose ether should be reduced as much as possible.

2.2 Plastering mortar

From the influence of different viscosities and different dosages of HPMC on the performance of plastering mortar, it can be seen that when the dosage of HPMC reaches more than 0.5‰, the water retention of mortar can be kept above 90%.

A comparative test was further conducted on the water retention of the plastering mortar without mixing with HPMC. The left half is the water retention without HPMC, and the right half is the water retention with HPMC. It can be seen that there is no part of HPMC doped. The filter paper is saturated with water, and the surface of the mortar has no wet luster: the part where HPMC is added. The filter paper showed no signs of wetting and the slurry surface was glossy. Therefore, HPMC can improve the water retention of plastering mortar very well.

It can be seen from the above tests that when no cellulose ether is added, the mortar will suffer from severe bleeding, poor fluidity, poor workability, and poor construction performance. With the addition of cellulose ether, the water retention performance of the mortar is greatly improved, and the workability is good, but when the amount of cellulose ether is too much, there will be sticking to the knife, which is not conducive to construction. Therefore, in the case of ensuring good workability, tensile bond strength and water retention performance, the amount of cellulose ether should be reduced as much as possible.

3. Conclusion

(1) For HPMC with the same viscosity, if the dosage is different, the water consumption of mortar remains basically unchanged; the apparent density of mortar increases slightly, and the water retention rate of mortar increases with the increase of HPMC dosage.

(2) If the amount of HPMC with different viscosities is the same, the water consumption of the mortar will remain basically the same; the apparent density of the mortar will also increase slightly. The water retention rate of mortar basically increases with the increase of HPMC viscosity.

(3) The addition of HPMC can greatly improve the water retention of mortar and improve the construction performance of mortar to a large extent.

(4) The optimum dosage of HPMC is 0.4‰~0.5‰.