Different amounts of cellulose ether and starch ether were compounded into dry-mixed mortar, and the consistency, apparent density, compressive strength and bonding strength of the mortar were studied experimentally. The results show that cellulose ether and starch ether can significantly improve the relative performance of mortar, and when they are used in proper dosage, the comprehensive performance of mortar will be better.
Key words: cellulose ether; starch ether; dry-mixed mortar
Traditional mortar has the disadvantages of easy bleeding, cracking, and low strength. It is not easy to meet the quality requirements of high-quality buildings, and it is easy to cause noise and environmental pollution during the production process. With the improvement of people’s requirements for building quality and ecological environment, dry-mixed mortar with better comprehensive performance has been more widely used. Dry-mixed mortar, also known as dry-mixed mortar, is a semi-finished product that is uniformly mixed with cementitious materials, fine aggregates, and admixtures in a certain proportion. It is transported to the construction site in bags or in bulk for mixing with water.
Cellulose ether and starch ether are the two most common building mortar admixtures. Cellulose ether is the basic unit structure of anhydroglucose obtained from natural cellulose through etherification reaction. It is a water-soluble polymer material and usually acts as a lubricant in mortar. Moreover, it can reduce the consistency value of the mortar, improve the workability of the mortar, increase the water retention rate of the mortar, and reduce the cracking probability of the mortar coating. Starch ether is a starch substituent ether formed by the reaction of hydroxyl groups in starch molecules with active substances. It has very good rapid thickening ability, and very low dosage can achieve good results. It is usually mixed with cellulose in construction mortar Use with ether.
1. Experiment
1.1 Raw materials
Cement: Ishii P·O42.5R cement, standard consistency water consumption 26.6%.
Sand: medium sand, fineness modulus 2.7.
Cellulose ether: hydroxypropyl methylcellulose ether (HPMC), viscosity 90000MPa·s (2% aqueous solution, 20°C), provided by Shandong Yiteng New Material Co., Ltd.
Starch ether: hydroxypropyl starch ether (HPS), provided by Guangzhou Moke Building Materials Technology Co., Ltd.
Water: tap water.
1.2 Test method
According to the methods stipulated in “Standards for Basic Performance Test Methods of Building Mortar” JGJ/T70 and “Technical Regulations for Plastering Mortar” JGJ/T220, the preparation of samples and the detection of performance parameters are carried out.
In this test, the water consumption of the benchmark mortar DP-M15 is determined with a consistency of 98mm, and the mortar ratio is cement: sand: water = 1:4:0.8. The dosage of cellulose ether in the mortar is 0-0.6%, and the dosage of starch ether is 0-0.07%. By changing the dosage of cellulose ether and starch ether, it is found out that the change of the dosage of admixture has an effect on the mortar. impact on related performance. The content of cellulose ether and starch ether is calculated as a percentage of cement mass.
2. Test results and analysis
2.1 Test results and analysis of single-doped admixture
According to the ratio of the above-mentioned experimental plan, the experiment was carried out, and the effect of the single-mixed admixture on the consistency, apparent density, compressive strength and bonding strength of the dry-mixed mortar was obtained.
Analyzing the test results of single-mixing admixtures, it can be seen that when starch ether is mixed alone, the consistency of the mortar decreases continuously compared with the benchmark mortar with the increase of the amount of starch ether, and the apparent density of the mortar will increase with the increase of the amount. Decreasing, but always greater than the benchmark mortar apparent density, mortar 3d and 28d compressive strength will continue to decrease, and always less than the benchmark mortar compressive strength, and for the index of bonding strength, with the addition of starch ether increases, the bond strength first increases and then decreases, and is always greater than the value of the benchmark mortar. When cellulose ether is mixed with cellulose ether alone, as the amount of cellulose ether increases from 0 to 0.6%, the consistency of the mortar decreases continuously compared with the reference mortar, but it is not less than 90mm, which ensures good construction of the mortar, and the apparent density has At the same time, the compressive strength of 3d and 28d is lower than that of the reference mortar, and it decreases continuously with the increase of the dosage, while the bonding strength is greatly improved. When the dosage of cellulose ether is 0.4% , the mortar bonding strength is the largest, almost twice the benchmark mortar bonding strength.
2.2 The test results of mixed admixture
According to the design mix ratio in the admixture ratio, the mixed admixture mortar sample was prepared and tested, and the results of mortar consistency, apparent density, compressive strength and bonding strength were obtained.
2.2.1 The influence of compound admixture on the consistency of mortar
The consistency curve is obtained according to the test results of compounding admixtures. It can be seen from this that when the amount of cellulose ether is 0.2% to 0.6%, and the amount of starch ether is 0.03% to 0.07%, the two are mixed into the mortar In the end, while maintaining the amount of one of the admixtures, increasing the amount of the other admixture will lead to a decrease in the consistency of the mortar. Since the cellulose ether and starch ether structures contain hydroxyl groups and ether bonds, the hydrogen atoms on these groups and the free water molecules in the mixture can form hydrogen bonds, so that more bound water appears in the mortar and reduces the flow of the mortar , causing the consistency value of the mortar to gradually decrease.
2.2.2 The effect of compounding admixture on the apparent density of mortar
When cellulose ether and starch ether are blended into the mortar at a certain dosage, the apparent density of the mortar will change. It can be seen from the results that the blending of cellulose ether and starch ether at the designed dosage After mortar, the apparent density of the mortar remains at about 1750kg/m³, while the apparent density of the reference mortar is 2110kg/m³, and the combination of the two into the mortar makes the apparent density drop by about 17%. It can be seen that compounding cellulose ether and starch ether can effectively reduce the apparent density of mortar and make the mortar lighter. This is because cellulose ether and starch ether, as etherification products, are admixtures with a strong air-entraining effect. Adding these two admixtures to mortar can significantly reduce the apparent density of mortar.
2.2.3 The effect of mixed admixture on the compressive strength of mortar
The 3d and 28d compressive strength curves of the mortar are obtained from the results of the mortar test. The compressive strengths of benchmark mortar 3d and 28d are 15.4MPa and 22.0MPa, respectively, and after the cellulose ether and starch ether are blended into the mortar, the compressive strengths of mortar 3d and 28d are 12.8MPa and 19.3MPa, respectively, which are lower than those without the two. A benchmark mortar with an admixture. From the influence of compound admixtures on compressive strength, it can be seen that no matter whether the curing period is 3d or 28d, the compressive strength of mortar decreases with the increase of the compounding amount of cellulose ether and starch ether. This is because after the cellulose ether and starch ether are mixed, the latex particles will form a thin layer of waterproof polymer with the cement, which hinders the hydration of the cement and reduces the compressive strength of the mortar.
2.2.4 Influence of mixed admixture on the bond strength of mortar
It can be seen from the influence of cellulose ether and starch ether on the adhesive strength of mortar after the designed dosage is compounded and mixed into mortar. When the dosage of cellulose ether is 0.2%~0.6%, the dosage of starch ether is 0.03%~0.07% %, after the two are compounded into the mortar, with the increase of the amount of the two, the bonding strength of the mortar will gradually increase first, and after reaching a certain value, with the increase of the compounding amount, the adhesive strength of the mortar will gradually increase. The bonding strength will gradually decrease, but it is still greater than the value of the benchmark mortar bonding strength. When compounding with 0.4% cellulose ether and 0.05% starch ether, the bonding strength of the mortar reaches the maximum, which is about 1.5 times higher than that of the benchmark mortar. However, when the ratio is exceeded, not only the viscosity of the mortar is too large, the construction is difficult, but also the bonding strength of the mortar is reduced.
3. Conclusion
(1) Both cellulose ether and starch ether can significantly reduce the consistency of mortar, and the effect will be better when the two are used together in a certain amount.
⑵Because the etherification product has strong air-entraining performance, after adding cellulose ether and starch ether, there will be more gas inside the mortar, so that after adding cellulose ether and starch ether, the wet surface of the mortar will The apparent density will be significantly reduced, which will lead to a corresponding reduction in the compressive strength of the mortar.
(3) A certain amount of cellulose ether and starch ether can improve the bonding strength of mortar, and when the two are used in combination, the effect of improving the bonding strength of mortar is more significant. When compounding cellulose ether and starch ether, it is necessary to ensure that the compounding amount is appropriate. Too large an amount not only wastes materials, but also reduces the bonding strength of the mortar.
(4) Cellulose ether and starch ether, as commonly used mortar admixtures, can significantly change the relevant properties of the mortar, especially in improving the mortar consistency and bonding strength, and provide reference for the proportioning production of dry-mixed plastering mortar admixtures .