Technological capabilities of manufacturing heat insulating materials based on crushed cotton plant stems

. Today’s priority in construction lies in three primary areas: ecology, energy efficiency and cost-effectiveness. It means that the most important task it to construct environmental, energy-efficient and cost-effective buildings and structures. To erect houses having such characteristics, primary elements of a structure (brick block, etc.) must be made subject to the conditions that provide for the above characteristics. The prevailing trend in construction is the production of environmental, energy-efficient and cost-effective construction materials. This research is intended to develop an energy efficient procedure to make heat-insulating materials based on crushed cotton plant stems. To achieve this goal, the authors have addressed the following issues: describing the process of making a heat-insulating material based on crush cotton plant stems; analysis of energy-efficient characteristics of manufacturing materials based on crushed cotton plant stems; and analysis of environmental friendliness of such a material. The research applies the deductive method based on mathematical modelling. The subject of the research is the procedure to make a material based on crushed cotton plant stems. The primary conclusion and outcome of this research is that papercrete based on crushed cotton plant stems has such advantages as cost-effectiveness, environmental friendliness, energy efficiency and low resource demand in manufacturing and operation. The resulting strength of papercrete allows using it as a heat insulating material to erect low-rise buildings.


Introduction
Society development is directly or indirectly related to construction development.Progress in the field of construction is achieved, among other things, also by evolution of construction materials.Construction materials represent natural or artificial materials, compositions and products made of them, used in construction to manufacture structures and to erect buildings and structures.Today, the use of secondary agricultural resources as important feedstock for making construction materials is of high importance, especially in the Republic of Chad located in the central part of the African continent and having developed agricultural production.Moreover, using the wastes of the energy industry to partially replace the primary binder in concretes and cement mortars is also a perspective trend of scientific progress in the construction industry [1].
Using secondary resources of agriculture and industry wastes will reduce the use of natural mineral resources and will improve the environmental situation.Moreover, this improves strength characteristics of materials and increases the life cycle of structures [2].
It must be noted that materials and procedures to manufacture and use them in the area of construction must be energy-saving.Using the principles of energy saving ensures the following advantages: reducing the demand in energy when making construction materials thanks to the use of low-energy production technologies; using efficient heat-insulating materials for the construction of residential and public buildings, which can reduce heat losses via enclosing structures [2].Therefore, developing new energy-saving manufacturing technologies for heat-insulating materials using large-tonnage man-made wastes will make it possible to manufacture cheap construction materials and address the issues of secondary agriculture and industry resources.
This paper is intended to develop an energy-efficient procedure to manufacture heatinsulating materials based on crushed cotton-plant stems.This goal is achieved by solving the following tasks: describing the process sequence for making heat-insulating materials based on crushed cotton plant stems; analyzing energy-efficient characteristics of its manufacture procedure; analyzing the environmental profile of the material.The subject matter of this research is the procedure to manufacture a material based on crushed cotton plant stems.Research methods are principles of mathematical modelling of nonstationary heat and mass transfer.

2
Materials and methods

Procedure for making heat-insulating papercrete based on crushed cotton plant stems
The process of making a heat-insulating material based on crushed cotton plant stems includes the following stages: collection and crushing of cotton plant stems; soaking the crushed stems; preparing the papercrete mixture; pressing and vibration; drying; inspection of finished products; consumption.Figure 1 schematically shows the manufacturing process of papercrete blocks made of crushed cotton plant stems.
The preparation process of manufacturing the heat-insulating papercrete starts with collection of cotton plant stems, their crushing, rejection according to screening parameters, transportation to the production site, and stacking.The crushed cotton plant stems should be less than 40 mm long, 10 mm wide and 5 mm thick [3].Crushing is followed the soaking for no more than 2 days to decrease the concentration of sugars and gluconates, which reduces the cement core effect on delayed setting of the papercrete mixture and curing of papercrete and improves the final fire resistance [4].This is followed by drying and sieving of the crushed product to sort the most optimum parts.
The primary manufacturing process of the heat-insulating papercrete using crushed cotton plant stems includes the following primary operations: preparation of the feedstock mixture; molding; pressing and vibration; drying and removal from the mold.To improve strength properties of papercrete, the feedstock mixture is injected with a low amount of chemical additives of various purpose: curing accelerators (calcium chloride, calcium nitrate, aluminum sulphate); porosity regulators (liquid-glass foaming agent, liquid glass, neutralized air-entraining resin); those improving protection against steel reinforcement bars (alkylsulfate paste); improving bactericide and insecticide properties (saponified wood tar, saponified wood pitch), and those simultaneously regulating various properties (sodium ethylsilicate, sodium methylsilicate, polyhydrosiloxane) [5].If regulatory requirements are met, papercrete products have the following characteristics represented in Tables 1 and 2 [5,6].Table 1.Strength of papercrete dried to constant mass [6].

Energy efficient procedure to manufacture structural heat-insulating materials based on crushed cotton plant stems
A new trend in construction is energy-efficient materials and technologies.Energy use is taken into account at all life cycle stages of the construction material, product or structure.
The main indicator of efficiency in the production of construction materials or erecting buildings is the reduced prime cost at all stages of the facility life cycle.Energy efficient materials have improved physical and mechanical properties.They reduce expenses for the period of operation.This approach is formulated in Federal Law No. 261 On Energy Saving and Improving Energy Efficiency and Making Changes to Certain Legal Acts of the Russian Federation [7].Table 3 gives primary energy expenses for the most common construction materials [2].To manufacture energy-saving materials such as heat-insulating papercrete, the initial feedstock (crushed cotton plant stems) is an organic filler that provides reduced weight of products and gives a solution of environmental issues [8].The evaluation of environmental effects of construction materials is given in Table 4 [2].Table 4 gives assessment of negative effects for each eco-factor: 3 pointshighest negative effect; 2 pointsmedium negative effect; 1 pointlowest negative effect.In accordance with the level of negative effect for each eco-factor, we must define the scale of total negative environmental burden and human burden for the materials given in the table: 1 to 6low burden; 7 to 12medium burden; 13 to 18high burden [9].According to the indicators represented in Tables 3 and 4, construction materials made of vegetable feedstock have a high environmental score.Therefore, a structural heat-insulating material based on crushed cotton plant stems is environmentally friendly, and its use as an energy-efficient material will save heat and energy for the operation period of buildings and structures.
This material may serve a basis for environmental comfort of people, guarantee its health safety and promote environmental protection against contamination with man-made wastes.Using breathing materials keeps the harmony between people, their dwelling and nature without detrimental effects on future generations.Materials with environmental characteristics have the following advantages: safety for human health and environment and minimal burden, high repairability and easy interchangeability, as well as ability to dispose after the end of life.

Results
When developing the sequence of process operations for manufacturing the structural heatinsulating material based on crushed cotton plant stems, the authors have developed a mathematical model describing each specific process.The essence of the mathematical model is developing experimental data to find dependencies of heat-physical characteristics of the material (heat conductivity, heat capacity) versus humidity and temperature, as well as transfer coefficients (heat loss, weight loss, weight conductivity) versus drying process parameters [9].For the heat flux with evaporated moisture, the following equation is true [10,11]: where  is the weight loss coefficient, s/m;   () is the partial pressure of saturated water vapor above evaporation surface, Pa;   () is the partial pressure of water vapor in the air environment, Pa.Traditionally, in [10,11], the problem of nonstationary weight conductivity (moisture diffusion) along the block thickness is recorded as follows: In what follows, we omit index i to simplify the calculations.The initial condition (moisture distribution by block thickness) looks as follows: In a partial case of even initial condition, it is recorded as follows: Boundary conditions: а) on the external surface of the block: where   is the dry material density, kg/м 3 .
This condition defines density of the moisture flux supplied from the internal layers to the surface.b) on the lower surface of the block: It means that the moisture flux coming from internal layers to the lower surface must be equal to the flux coming to the soil under the filtration transfer mechanism.
To make it dimensionless, let us divide by   : [2] = − Let us place    0 under the integral sign: Let us multiply and divide by the complex Let us transform the third addend: Further transformations give:

Fig. 1 .
Fig. 1.Process of manufacturing papercrete blocks made of crushed cotton plant stems.
ℎ  ,  = 2  ℎ  where (, ) is the function defining the moisture value at time  in the pint with coordinate , k is the weight conductivity coefficient (moisture diffusion coefficient in solid), (m 2 /s).

Table 3 .
[2]mple of primary energy expenses for the most common construction materials and their environmental comparison[2].

Table 4 .
Evaluation of environmental effects of construction materials.

Negative effects of production and use of construction material as per its life cycle stages
, Т   ℎ   ℎ  , ℃, ;   ,   is the ambient temperature, ℃, .