a b s t r a c tIn Cameroon, these last centuries, an increase in energy demand for cooling and heating in buildings has been witnessed all over the world. Solutions must be proposed by researchers and specialists of buildings to remedy this situation. In this study, a literature review on the thermal insulation applications to external walls of buildings was presented, and a case was investigated in a tropical wet and hot climate. The economic model including the cost of insulation material and the present value of energy consumption and the cost over a lifetime of 22 years of the building, were used to find the optimum insulation thickness, energy saving, and payback period, for buildings in Cameroon. Materials that extruded polystyrene were chosen and used for two typical wall structures (Concrete block (HCB) and compressed stabilized earth block wall (CSEB)). The yearly cooling transmission loads, according to wall orientations and percentage of radiation blocked were calculated using the explicit finite-difference method under steady periodic conditions. As a result, it was found that the lowest value of optimum insulation thickness (0.09 m) and energy savings (79.80%) were obtained for the south-oriented wall, while the payback period (4.73years) was the highest on the same face compared to all wall orientations. Insulation optimum thickness was higher in the HCB wall (0.0983 m) than in CSEB wall (0.0958 m), however, the payback period was the weakest for the HCB wall compared to the other wall type.

a b s t r a c tToday, more than ever, the human energy requirements are enormous and still growing. Worldwide, all the countries need energy, which is the main source of development. However, the development of African continent is still very slow because of the limited policy interest and investment levels. The effective use of energy is crucial because of the continuous depletion of energy resources, especially for developing countries which are currently experiencing rapid economic and population growth. The aim of this article is to review the status and current trends in resource potential, energy consumption, and energy policies in the residential sector, both globally and in Cameroon. It was found that the world's energy needs are constantly growing and should exceed 50% of current levels by 2030. In Africa, most of the substantially renewable energy resources are under-exploited. We found that 83% of the rural population in Africa, 92% in Sub-Saharan Africa, and 70% in South Asia have no access to electricity. Especially in Cameroon, the energy consumption in the residential sector is about 70% of the total energy consumption, which is higher compared to the world level that is around 27%. Energy efficiency is very important in the context of sustainable development. Currently, traditional biomass is the main source of energy in Sub-Saharan Africa.

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Since twenty years, Madagascar suffered, by the advanced level of pollution due to the proliferation of plastic bags. They are always discarded in nature and constitute an increasingly important visual and environmental pollution in cities. And because they are easily carried and deposited everywhere by the wind, it has more negative consequences on the environment and thus on the health of the population. Plastics are among the most persistent pollutants and the problem appears when they reach the waste stage. The degradation of these plastic bags requiring more than four centuries, so the search for solutions for the use of these products is very solicited to preserve the environment. That’s why our research is consecrated into the transformation of plastic bags into pavers or bricks at a lower cost. The combustion of plastics releases large quantities of thick and toxic fumes. So, to avoid this phenomenon, our so-called “wet” process consists in heating a mixture of a Rich Carbon of Waste Element (RCWE), fusing the plastic bags as a binder and adding the sand as agglomerate. We obtain a quantity of product 3 times higher than the quantity of plastic bags used (to have 60 kg of product, we need 20 kg of plastic bags) unlike the other processes providing 5 kg of product for 20 kg of plastic bags, ie the plastic is reduced by ¼. The rest of the study focused on the melting temperature of the plastic bag in the RCWE which is approximately 110° C, the proportions between the RCWE and the plastic bag for the optimization of the cost of energy : we showed that the energy is optimal for a proportion of half (100g of RCWE for 50g of plastic), the proportions between plastics and sand (binder and agglomerate) : by weight, the binder must always be less than the agglomerate (the result is optimal in the proportion of agglomerate -binder 80 -20), the mechanical behavior : the result shows that when the quantity of plastics is the higher, the maximum stress is high, but the plastic area is low. The product is among the ductile materials, the property of which a material can permanently deform before breaking (an important factor for the deformation of materials), the permeability, and the adhesion test with the rubber.

Madagascar undergoes, like all countries in the world, the effects of climate change. in fact, since the last 5 years, in the coastal regions and the basins, the temperature has raised from 2 to 2.5 ° and varies between 34 to 36 ° in the shadow during the rainy season and on the high hills, the temperature diminishes from 2 to 2.5 ° during the dry period and varies from 4 ° to 8 °. However, the structure of lodging of 60% of the people are not adapted to this temperature change. Particularly, in the coastal regions, the walls of the houses are made of sheet iron. The inside of these houses is very hot when the weather is hot and very cold when it is cold. The inhabitants can't afford the houses made in bricks or breeze block and the natural sources of aggregates are in the process of exhaustion. In the other part, we have seen that tons of paper are ready to be burned at the administrative services (public treasury, public financing, universities, ...) and the newspaper publishers. So, it becomes a must to find another way to the construction materials, justifying in that case our research axis. This study aims at the developing of construction material based on recycled paper, binder and aggregate. It deals of picking up or gathering all waste of papers and outdates newspapers and transforming them into brick for building constructions. What's more, papers have prominent thermal insulating properties. Our work is focused on the study of variants on the different manufacturing processes, the choice of binder, the preparation of the specimens with different binders and different dosages, the mechanical compression tests for different binders, the evaluation of thermal conductivity for different binders and the numerical simulation of the thermo mechanical behavior of samples. The result is a lightweight brick with good thermal insulation. Tests have also made it possible to declare that the material has acceptable mechanical properties : the compressive strength is 1.56 [N/mm2], higher than the value prescribed by the standard for lightweight concrete blocks for construction of 1.1 [N/mm2], the value of thermal conductivity is 0.114 [W/mK], ten times less conductive heat than concrete and it can replace glass wool for a double its thickness. The specific weight is 57.5 [kg/m2].The practical results were confirmed by finite element simulations.