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Influence of Cellulose Ethers on the Consistency, Water Retention and

Adhesion of Renovating Plasters(4)

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2.3. Methodology of research on the influence of cellulose admixtures on the ability to retain water in

fresh renovation plaster

The retention of water in fresh mortar is described by the percentage of water that remains in the mortar

after a brief draining of water through the filter paper [18]. In laboratory conditions, the measurement

consisted of placing fresh mortar in a plastic ring with a diameter of 140 mm and a thickness of 10 mm,

set on a filter paper and a plate also made of plastic. The mortar flow in the ring was covered with a

plastic plate and left for 5 minutes. The amount of water adsorbed by the filter paper was adopted as the

measure on the basis of which the water retention value (WRV) was calculated as a percentage

determined from equation (1):

WRV =100-W (1)

where: WRV - water retention value, W - relative loss of water in the mortar (%).

The water content in mortars was constant and amounted to 25% in relation to all dry ingredients,

the w/c ratio was 1.04.

2.4. Methodology of research on the influence of cellulose admixtures on the adhesion of hardened

mortars to the substrate

The adhesion of renovation plasters was determined in accordance with PN-EN 1015-12:2016-08E

standard [19], as the value of critical stress during which adhesive or cohesive detachment of the layer

of applied material from the substrate took place. For this purpose, the mortar was applied to a thickness

of 10 mm on a concrete block. After 28 days of seasoning, 50 mm diameter discs were cut out of the

plaster. After cleaning the surface of the samples, five steel discs were attached with epoxy glue at the

points of incision. The critical strain was measured using the "Pull-off" device on the ProceqDyna Pull

off Tester Z-16. The consistency of the mortars was constant at the flow of 170 mm±5 mm determined

by the flow table test.

3. Research results and discussion

The test results are shown in table 3.

3.1. Study of the influence of cellulose admixtures on the consistency of mortar

The results of the influence of cellulose admixtures, differing in the modification and viscosity, on the

consistency change determined using the flow table method are shown in Figure 2. To quantify the

influence of the admixture on consistency, the amount of mixing water which must be added to the
mortar in order to obtain a consistency of the mortar had without cellulose admixture, which was
170±5mm (determined by the flow table test).
Table 3. Research results showing the influence of chemical composition and viscosity of cellulose
admixtures on consistency determined by the shock table method, water retention value (WRV),
adhesion to concrete substrate and air content in fresh mortar.
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Figure 2. Influence of the type of cellulose admixture on the amount of mixing water necessary to
obtain a consistency of flow 170±5 mm, determined by the flow table method (a), the relationship
between the viscosity of cellulose admixtures, determined for 2% solutions (Brookfield viscosity
gauge) and the amount of mixing water (flow 170±5 mm) (b)
Analysing the results presented in figure 2a, it can be concluded that with the increase in viscosity
of cellulose admixtures, the consistency of fresh mortar increases unevenly. The greatest changes in the
amount of mixing water were observed when the viscosity changed from 6,000 MPa·s to 28,000 MPa·s
for HPMC, from 6,500 to 36,000 MPa·s for HEMC, and in the case of MEHEC in the viscosity change
from 6,000 to 31,000 MPa·s. It was also found that the degree of influence of individual admixtures on
mortar consistency depends on their type of cellulose admixture. The greatest influence on the
consistency was that of HPMC and HEMC-based admixtures, figure 2b.