Universal slabs for hydro-and heat insulation

. The article deals with the creating of a universal material for protecting underground structures from groundwater as well as providing their thermal protection. The article presents a method for waterproofing and drainage of underground walling structures using drainage slabs made of filtration polystyrene foam and considers the possibility of using these slabs for reducing heat losses of heated underground structures. Thermal engineering characteristics of filtration polystyrene foam are determined, and calculations of heat losses of underground walling structures with slabs made of this material are given. The results of studies of the kinetics of water drainage by filtration polystyrene slabs are shown. The dependence of the heat conductivity of filtration polystyrene on humidity and other factors are also presented. Calculations of heat losses through the walls of heated underground premises are given, taking into account the temperature distribution in the ground along the depth of the structure. A comparative analysis of heat losses with the use of filtration polystyrene foam slabs and without them has been carried out. Based on the experimental results obtained, it was revealed that filtration polystyrene foam has not only high filtration characteristics, but is also an effective material for thermal protection of underground structures.


Introduction
The main methods for protecting the underground parts of buildings and structures from the impact of groundwater is the use of various types of drainage systems (wall drainage, bed drainage, pipe-draining, etc.) in combination with waterproofing materials (rolling, coating, sheet, etc.) [1][2][3][4][5][6][7][8][9][10].However, often the quality of work does not meet the necessary requirements, since ensuring reliable protection of structures is associated with timeconsuming work on preparing the foundation (usually concrete) and laying waterproofing materials, as well as with the qualitative selection and arrangement of filter materials and systems.
Slabs made of filtration concretes and plastics, multilayer polymer shells with geotextile materials and rolled plastic membranes with rounded protrusions are used as wall drainages [11][12][13][14][15]. Materials based on bituminous binders, cements, as well as metal sheets are used as waterproofing.However, the materials used for the purpose of waterproofing and drainage are not always combined with each other due to differences in physical, mechanical, chemical, thermal and other characteristics.One of the consequences of such incomparability of materials can be the low adhesion of waterproofing and drainage materials, which entails a violation of the protective coating continuity and the penetration of water into the underground structure.In addition, with an unsatisfactory insulation system, heat losses through underground structures increase significantly (more than 10%) [16].
Thus, the task of creating protective systems of underground structures that combine both waterproofing, drainage and thermal insulation functions is very urgent.

Methods
In this work, slabs of filtration polystyrene foam (FP) obtained as a result of sintering at the contact points of pre-foamed granules at a temperature of 90-95°C and a pressure of 0.02 MPa were studied and used as wall drainage.This material was chosen due to its high filtration capacity (the filtration coefficient is 500-800 m/day) and low water-retaining ability relating to a low wettability of expanded polystyrene [17].
The absence of capillary pores and low wettability of FP contributes to the fact that its water-retaining capacity is very low and 10-12 hours after the material is completely saturated, the water drains completely, leaving the material practically dry.Moreover, the FP with greater porosity, and, consequently, lower density, loses water faster.Thus, FP slabs with a porosity of 30-32% become dry already 10 hours after saturation with water, and FP slabs with a porosity of 20-23% -after 12 hours (fig 1).As studies have shown, already at 30% (by mass) saturation with water, the heat conductivity coefficient stabilizes, and with a further increase in humidity, it does not change, because water rapidly flows down the system of pore channels (fig.2).This shows that with constant moisture exposure to the material, the filtration rate of which is 1-1.5 cm/s, it will contain no more than 30% (by weight) of moisture, and, therefore, the heat conductivity coefficient will be constant and not exceed 0.053 W /m•°C.
Calculations of heat losses are carried out for the conditions of the winter period.At the same time, the height of slabs placing up to the basement floor is conditionally divided into two zones (fig.3).The distribution of temperature over the depth of the ground is taken in accordance with the climatic conditions of Moscow.The calculation is performed for each zone separately.Heat losses for the first zone is determined by the formula (1): Q 1 * -heat losses for the first three conditional zones; Q 1 ** -heat losses for the fourth conditional zone, located below the freezing zone.
Heat losses Q 1 * (W•h) are calculated by the formula (2): t in -temperature inside the basement,°С; t in = 13°С; t g i -ground temperature, °С (taken in accordance with the temperature distribution in the ground for each conditional zone); A i -surface area, m 2 ; R g1 -heat resistance of the ground, equal to 2.10 for the first zone (m 2 •°С)/W [18]; R in -heat exchange resistance on the inner surface, equal to 0.1 (m  δ c -concrete wall thickness, equal to 0.4 m; λ c -heat conductivity coefficient of concrete, W/(m•°С); δ FP -slab FP thickness, accepted in the calculation 0.1 m [19].
For Moscow conditions, the maximum depth of ground freezing is 1.65 m [20].There is no hygroscopic water in the freezing layer in FP slabs and the heat conductivity coefficient (λ FP ) is 0.035-0.040W/(m•°C).
Heat losses Q 1 ** (W•h) are calculated by the formula (4): In this case, K 1 ** (W/(m 2 •°С) is calculated as follows: The maximum specific inflow Q max (m 3 /day) to the drainage is calculated by the formula (6) [21]: K -filtration coefficient of the backfill ground, taken 5 m/day; H -height of the wall drainage, m.
At a depth of up to two meters, Q max is 7.4 m 3 /day.With a ground filtration coefficient of 5 m/day and a filtration coefficient of FP slabs of 500-800 m/day, the watering pass layer of the slabs is 10-15 mm.At this case the lateral ground pressure (about 0.0152 MPa) on the slab has practically no effect on the filtration coefficient and heat conductivity of the material.
As a result of calculations according to the formulas ( 2) and ( 4), heat losses in the first zone are: .819 W•h.Heat losses for the second zone (fig.5) are calculated by the formula (7): t g2 -average ground temperature in the second zone, t g2 = 2.7°С; A 2 -surface are, m 2 , A 2 = h 2 •1.0 m; h 2 -height of the second zone, equal to 0.5 m; τ -time, h; К 2 -heat transfer coefficient, W/(m 2 •°С): R g2 -heat resistance of the ground, equal to the second zone 4.3 (m 2 •°С)/Вт [18]; R in , δ c , λ c , t in , τ -similar to those used in the calculation of the first zone.To calculate the second zone, with the depth of the laying 2.5 m, the thickness of the water pass layer of the slabs is 12-19 mm (with a ground filtration coefficient of 5 m/day and a FP filtration coefficient of 500-800 m/day).In this regard, for the water-saturated part of the slab with the thickness δ FP3 = 0.019 m, we take λ FP3 = 0.053 W/ (m•°C), and for the dry part of the slab with the thickness δ FP4 = 0.08 m, we take λ FP4 = 0.040 W/ (m•°C).
By placing the obtained values in the formula (7), we determine Q 2 = 0.736 W•h.

Results
The next stage of our research is to conduct a comparative analysis of heat losses in winter for a heated basement without FP slabs and with slabs.For the convenience of comparative calculations, the thickness of the slabs is assumed to be 0.1 m.Heat losses data obtained for the first and second calculation zones, as well as the difference in heat losses, are shown in table 1. Analyzing the data obtained when calculating the heat losses of the basement with and without the use of FP slabs, we can conclude that the use of FP slabs as a heat-insulating material reduces the heat losses of the basement by 2 times.

Discussion
Depending on the depth of the underground structure, the lateral pressure of the ground on the wall drainage changes.In this regard, when using FP slabs, one should take into account the fact that under load the watering pass capacity of the slabs decreases, the structure becomes denser and, consequently, the heat conductivity of the material increases.Thus, with a short-term compression from 2 to 10%, the average density of filtration polystyrene foam decreases by 2.5-3.6 times.With a constant long-term load (for three months) in the range from 0.02 to 0.06 MPa, the deformation increases to a greater extent in the initial period, then the deformations stop and the relative compression is no more than 2%.For the efficient operation of the material, slabs with a thickness of 0.1m and average density of 17 kg/m3 should be used.
Thereby, drainage FP slabs are effective when the depth of underground structures is up to 10 m, which corresponds to most residential and industrial buildings.By deeper installation of slabs, their density and heat conductivity become higher, and their filtration characteristics -lower.

Conclusion
Analyzing the results obtained, the following conclusions can be drawn.
Taking into account the fact that the FP slabs are both an effective wall drainage with high water-removing characteristics and good heat insulation material, it can be calculated that the economic costs of their use are 3.5-4.5 times lower compared to traditional systems of protection of heated underground structures using extruded polystyrene foam and wall drainage from various filtration materials.Thus, the use of lightweight, large-sized, resistant to aggressive groundwater FP slabs in underground construction can significantly improve the quality of wall drainage and thermal protection, cut down construction expenses and reduce labor costs.

Fig. 1 .
Fig. 1.Kinetics of water drainage from the FP slab after saturation.

Fig. 3 .
Fig. 3. Calculation scheme of heat losses through walling structures with a ground base t in -temperature inside the basement,°С; t g I -ground temperature in the first calculation zone,°С; t g II -ground temperature in the second calculation zone,°СThe first zone, in turn, is divided by height into four conditional zones; in each zone the temperature varies within no more than 5°C (fig.4).When passing through 0°C in the

Fig. 4 .
Fig. 4. Temperature distribution in the first calculation zone t out -outside air temperature, °C; t sur -surface temperature, °C; t I -average temperature in the first conditional zone, °C; t II -average temperature in the second conditional zone, °C; t III -average temperature in the third conditional zone, °C; t IV -average temperature in the fourth conditional zone, °C; δ FP -thickness of the FP slab; δ c -thickness of the concrete wall

Table 1 .
Comparison of heat losses with and without FP slabs