Analysis of Tensile and Shear Strength Research Results of a Deformable Adhesive in a Lightweight Floor System

The article statistically analyzes experimental tests on a light floor system (LFS) without screeds. The results of over two years of experiments in which the strength of C2S1 and C2S2 cement deformable adhesive for tensile and shearing were tested allow to determine the confidence interval for the expected value of these strengths along with determining the relative precision of the estimation. In the article, only the C2S1 adhesive was analyzed because it meets two important criteria. It has relatively high mechanical strength and is more economically advantageous (purchase price 2-3 times lower than C2S2). The obtained data also allowed to verify the hypothesis regarding the minimum strength of the C2S1 adhesive during the pull-off test and shear strength.


Introduction
Tests of tensile and shear strength of mortars adhesive, after the preparation of samples, took place from July 2016 to October 2018. Tensile strength tests of adhesives perpendicular to the frontal surfaces (tensile strength) were carried out in dry conditions and water absorption in accordance with the standard [1]. The shear strength of adhesives was made by using PressoMess according to the manufacturer's instructions. These tests were described in [2][3][4], and concerned a lightweight floor system, where the underlaying material was EPS 200 hydro or XPS 300 thermal insulation with a rough or waffle surface. The floor made from tiles was directly attached to the insulating underlay using deformable mortars adhesive of the C2S1 or C2S2 class, reinforced with a glass fiber mesh of various weights from 145-320g/m 2 . The test results indicate their insignificant dependence on the weight of the mesh embedded in the adhesive, as described in [4]. An exemplary vertical section of a light floor system is shown in Figure 1, and photographs of test stands in (Figures 2-4). The results of all tests are given in tables 1 and 2. In the conclusions of the article [4], it was found that after the tests of tensile and shear strength optimal construction of a lightweight floor in terms of economic and strength, meeting even the criteria for stronger dispersion adhesives acc. [5] is composed of:     Copyrights @ Jacek Karpiesiuk. 142

II.
Verify the hypothesis regarding the minimum strength of the C2S1 adhesive for the pull-off method and shear strength tests.

Results of Calculation
Determination of the confidence interval for the value of the expected tensile and shear strength of the C2S1 adhesive together with the determination of the relative precision of the estimation, according to [6]. Table 3 lists the test results from the sample, after rejecting the selected extreme stress values given in Table 1, considered as errors in sample preparation. Based on these data, the necessary calculations were made according to designs (1), (2) and they were placed at the bottom of Table 3. The calculation assumes a 90% confidence level due to the fact that assuming a 95% confidence level, the relative precision of estimation in some of the test samples was greater than 10%. The calculation was based on the formula for the range of interval estimation of the expected tensile and shear strength value for the C2S1 adhesive mortar (1) and the formula for the relative precision of estimation δ (2).
Where:  Comparing the obtained result with the critical value t2 ,s = t0.2; 12 = 1.356 read from the Student's t-charts [6] at the righthanded alternative hypothesis, we can conclude that the test result is higher than the critical value (located in the critical area), which authorizes the rejection of the null hypothesis in favor of the alternative hypothesis. This means that for 90% certainty, the expected strength value of the C2S1 adhesive in EPS isolation using the pull-off method (dry conditions) is higher than 0.1955 MPa. In order to estimate the minimum strength of the C2S1 adhesive with EPS isolation using the pull-off method (dry conditions), with the results obtained from the carried-out samples, for α = 0.10 we can make calculations using the formula for the t-test: The obtained result can be treated with 90% certainty as the minimum strength of the C2S1 adhesive with EPS insulation for pull-off method with dry conditions.
Using the above procedure, the data from Table 3