**3. Methodology of Controlling the Technological Process of Executing Floors made of Cement-Based Materials**

The developed methodology for controlling the technological process of executing floors made of cement-based materials is described below and graphically presented in Figures 2–5. Figure 2 presents the general, and Figures 3–5 the detailed scheme of this methodology.

**Figure 2.** General diagram illustrating the developed methodology.

In Stage 1, which was presented in Figure 3, the conditions that need to be met must be checked in order to make the decision to start executing the floor.

**Figure 3.** Methodology of controlling the technological process of executing floors made of cement-based materials—Stage 1 (control before starting the floor).

**Figure 4.** Methodology of controlling the technological process of executing floors made of cement-based materials—Stage 2 (ongoing control during execution of the floor).

Stage 1 begins from checking whether the window and door joinery has been built into the building. After ensuring this condition, the relative humidity of the air in the building and the air and substrate temperature on which the floor will be laid are in the required ranges [7]. The next step is to check the evenness of the upper surface of the concrete base. Unevenness of the upper surface of the concrete base is permissible, but the upper and lower deviations need to be maintained according to [30–35]. If these conditions are met, insulating foil can be laid on the substrate. The 2nd stage then begins, in which the ongoing process of floor control takes place (Figure 4).

As it can be seen from Figure 4 the first step of Stage 2 is to check the evenness of the insulation foil on the surface of the concrete substrate, reinforced concrete ceiling or foamed polystyrene. In this step, it should be borne in mind that corrugation of the insulation foil laid under the floor is not allowed. The next step is to control the mixing and homogenization of the cement mix according to the mix manufacturer's requirements. When laying the cement mix, the thickness of the mortar layer and the evenness of the top surface of the floor and its deviation from the horizontal plane should be checked. Peripheral expansion joints are then checked, which should be made of non-absorbent flexible foam, usually with a minimum thickness of 7 mm for the full thickness of the floors. Unevenness of the upper floor surface is only permissible if the upper and lower deviations are maintained, according to [30–35]. The next step is to make sure that expansion joints are cut in the first 24 h after executing the floor. Ongoing floor care, consisting of moisturizing it, should then be carried out. Then proceed to the control strength tests after the floor (stage 3).

Stage 3 consists of carrying out control strength tests of the floor, without which there should be no final acceptance and commissioning (Figure 5). This stage requires a slightly broader and more detailed explanation. As illustrated in Figure 5, the first step in Stage 3 is to check the subsurface tensile strength of the floor using the semi-destructive pull-off method in randomly made places, 28 days after concreting, and in accordance with EN 1542 [36]. The pull-off tests should begin with selecting representative measuring places and preparing the surface. Then, in these places, an incision should be made in the floor at least 15 mm deep where a steel measuring disc with a diameter of 50 mm is then attached with glue. This disc should then be pulled-off from the floor (Figure 6) and the value of the subsurface tensile strength should be determined in accordance with EN 1542 [36].

**Figure 5.** Methodology of controlling the technological process of executing floors made of cement-based materials—Stage 3 (control strength tests after finishing the execution of the floor).

**Figure 6.** Control of the subsurface tensile strength of the floor using the pull-off method: (**a**) pull-off apparatus; (**b**) scheme of the method; (**c**) view of the glued steel disc; (**d**) view of the floor surface after the pull-off tests.

A fragment of the floor, with such a size that at least six beam samples with a length of 160 mm, a width of 40 mm and a height equal to the floor thickness can be obtained, should then be cut off in order to check both the compressive strength of the cement mortar along the thickness and the flexural and compressive strength of the floor. The test samples should first be subjected to ultrasonic testing along the direction of concreting the floor. For ultrasonic testing, it is proposed to use an ultrasonic probe that has special exponential heads with a frequency of 40 kHz and point contact with the tested surface. According to [37] this frequency is optimum for testing cement floor samples with a dimension of 40 <sup>×</sup> <sup>40</sup> <sup>×</sup> 160 mm3. The measuring points should be applied to the lateral surfaces of the samples at a spacing of 5 mm in three rows (Figure 7).

**Figure 7.** Example view: (**a**) head and probe for ultrasonic testing; (**b**) floor sample tested using the ultrasonic method.

After performing the ultrasonic tests, the lower zone of the beam samples should be cut so that their thickness is 40 mm, and then subjected to flexural and compressive strength tests. On the basis of the conducted ultrasonic tests, a correlation relationship (or possibly a hypothetical relationship from the literature) between the velocity of the longitudinal ultrasonic wave and the compressive strength of cement mortar should be developed for the tested floors. This relationship will be used to identify the course of compressive strength along the thickness of the tested floor. The compressive strength in the upper zone should not be less than 10% when compared to the strength in the middle zone. However, the flexural and compressive strength should not be less than the values for the floor that were specified by the designer. After meeting the above strength conditions, the floor can be approved for use. In the event of non-compliance with strength conditions, the floor, after consulting the designer, should be either allowed to be used, or removed.
