No abstract

There is a great need for an easy-to-use tool to simulate drying of concrete floors. In order to model practical situations, the tool should take into account changing conditions, especially wetting at worksite, but also temperature. For this purpose, a simulation program was developed for drying time estimations for concrete floors, which was published in 2021 and is named as the “by2020 Concrete drying time estimate”. This study presents the results of the laboratory test series conducted to calibrate the drying time estimations of the by2020 software. As all possible scenarios for practical situations were not possible to study in the test series, results from the literature were partly used for calibration and validation of the tool. A methodology for test series for calibration of the drying time estimation model is proposed based on this study. It was found that a model suitable for practical applications can be implemented based on relative humidity measurements only. However, the tests series of relative humidity measurements should take into account the influence of various factors such as wetting period and different temperature conditions.

Excess moisture in concrete structures is a major problem in building industry. It is claimed that degradation of the finishing materials of concrete slabs is the largest source of volatile organic compound in the building stock in the Nordic countries. Considering concrete wall panels, the choice of the insulation material influences concrete drying considerably and causes a risk for moisture accumulation on the interior surface, if vapor tight finishing materials are used or if finishing materials are installed prematurely. Mineral wool insulation, which has predominately been used in Finland, is a vapor open material. However, vapor tight plastic foam insulation materials are nowadays more commonplace. Here we show that the overall rate of drying of the concrete panel with a vapor open insulation material is higher in comparison to the concrete panel with vapor tight insulation materials. However, relative humidity distribution near the inner surface of the concrete panel at the end of the drying phase is almost identical irrespective of the insulation material and the water vapor resistance of the interior surface material has a greater impact on the relative humidity level on the inner concrete surface. Moisture behavior of concrete panel walls is studied under a certain building schedule in Finnish environment and building conditions by numerical simulation. The model for drying of concrete is calibrated based on laboratory measurements. According to our study, self-desiccation and changing diffusivity due to the hydration process of the concrete cannot be ignored when evaluating the moisture behavior of the concrete wall panel structure with a low water binder ratio ( w/ b < 0.5). Measurements indicate that the early age humidity drop is by up to 10 percentage points.

Moisture management in building site has improved significantly in recent years. However, problems with concrete floors are repeatedly found. One possible reason for the failure may be that the time required for adequate drying of the concrete has not been properly considered when scheduling the building process and because the pressure to complete the building, the floor covering has been installed too early. In building industry, there is a clear need for better understanding of the adequate drying times of concrete structures, as well as tools to make sufficient drying estimates. The new tool BY2020 provides a new approach to drying and moisture risk estimations. The simulation tool is a FEM-based model that allows change in geometry with time so that the material layers are automatically added into the model, based on the determined schedule. The boundary conditions are also changing with time based on the schedule. In addition, the water vapor resistance of the flooring material can be modelled to evaluate the long-term moisture behavior of the floor structure. Preliminary results are encouraging and the feedback on the new approach has been positive. Validation process is ongoing and target completion time for the tool is late 2020.