utilization of waste as a constituent ingredient for enhancing

Indian Journal of Science and Technology, Vol 9(37), DOI: 10.17485/ijst/2016/v9i37/87082, October 2016ISSN (Print) : 0974-6846

ISSN (Online) : 0974-5645

* Author for correspondence

1. Introduction

Sustainable development has taken center stage due to factors such as changes in the climate and depletion of resources. This concern has also been ably complimented by technological advancements within the construction sector. Many countries focus on the energy efficiency of buildings to create a sustainable environment. One way of enhancing the energy efficiency in buildings is to improve the heat insulation properties of the buildings. The conductive, convective and radioactive heat components and the micro-structure of the building material are decisive factors for thermal conductivity of materials. Thermal property of materials is closely related to constituent material and its microstructure. To

develop thermally efficient wall materials, detailed study of constituent material behavior is very crucial. Thermal comfort and energy efficiency is a global issue which needs much attention within the construction industry. Improvements in the properties of basic building material such as bricks, mortar, concrete, tiles, etc. can help to solve problems related to thermal comfort and energy efficiency up to a certain extent.

It is important to improve thermal performance of building envelope, as the energy efficiency of a building depends on the ability of the whole building envelope to retain internal heat, amongst other factors such as heat loss and moisture movement from a building through the walls. Building envelope consists of various elements which affect the functionality aspect of a building in terms

AbstractObjective: In view of the environmental regulations, practitioners have been inclined to use bricks with higher insulation capability, however with minimal attention to sustainable material composition, let alone waste material. From a research perspective, in the wake of the growing concerns for the environment, the use of waste material to develop bricks which can exhibit suitable characteristics attributed to the material composition has been on the rise. However, the extant literature on utilization of waste materials for brick mix design has neglected to provide detailed literature review on the influence of waste materials on the thermal performance of bricks. Methods: This paper provides detailed review of research conducted on thermal properties of bricks produced from various types of waste. Influence of the method of manufacturing and type of waste on thermal performance of bricks is discussed. A sustainability selection criteria format is provided to assist optimal decision making in considering alternative sustainable waste material. Findings: A sustainability selection criteria format is provided to assist optimal decision making in considering alternative sustainable waste material. Applications: The outcome of this paper can serve as a common reference for practitioners and researchers attempting to seek out solutions for further improving overall quality of thermally insulated waste-incorporated bricks, paving the way for more focused research on waste utilization in the development of more sustainable wall material based on the current brick production process.

Keywords: Heat Transfer, Sustainable Material, Thermally-Insulated Bricks, Waste

Utilization of Waste as a Constituent Ingredient for Enhancing Thermal Performance of

Bricks – A Review PaperAshwin Narendra Raut* and Christy Pathrose Gomez

Department of Construction Management, Universiti Tun Hussein Onn, Malaysia, Batu Pahat, Johor - 86400, Malaysia; [email protected], [email protected]

Vol 9 (37) | October 2016 | www.indjst.org Indian Journal of Science and Technology2

Utilization of Waste as a Constituent Ingredient for Enhancing Thermal Performance of Bricks – A Review Paper

of thermal comfort. Walls cover the majority of surface area that makes up the envelope of building. Despite being a very important feature of building envelope, wall material is generally overlooked in attempts to improve indoor air comfort levels.

Often the major concern within sustainable or green building initiatives with respect to energy efficiency is to focus on thermal transmittance (U-value) of the whole building envelope. However, the important consideration to incorporate waste material within the building envelope is not being given enough serious attention. Researchers have been diligently pursuing this ideal mainly by analyzing singular waste material incorporation that can impact on thermal performance, whilst often compromising other multi-functional performance parameters. This paper is part of a wider research towards developing wall systems incorporating waste material that can systematically improve energy efficiency within buildings. Thus, this paper provides a detailed analysis of the influence of waste materials on the thermal performance of bricks with the aim of developing more sustainable high thermal performance wall systems. This comprehensive review can serve as a common reference for practitioners and researchers attempting to seek out solutions for further improving overall quality of thermally insulated waste-incorporated bricks, paving the way for more focused research on waste utilization in the development of more sustainable wall material based on the current brick production process.

This review attempts to focus on various types of waste material and their utilization in bricks to meet the requirements of ecofriendly thermally efficient bricks. The bulk of the proportions of waste material being considered are that of agro-industrial waste material which has intrinsic characteristics that comply with the requirement of low heat conductance.

2. Previous Literature Studies on Utilization of Waste in Bricks

There has been lots of research done in the utilization of different categories of waste materials in brick/blocks1-5. However, there is limited review papers focused on summarizing the research outcomes on the use of waste materials in brick/blocks, with little attention being focused on thermal properties. These literature reviews have mainly focused on: 1. Particular

category of waste (municipal waste, agricultural waste, etc.); 2. Manufacturing methods; 3. Physico-mechanical properties such as compressive strength, water absorption, density, etc.; and 4. Characterization of waste material incorporated for preparation and their impact3-5. Additionally, the literature reviews have not been thorough in their approach1,2, with just a few published reviews standing out.

The review paper has differentiated the waste materials based on three methods of production of bricks: firing, cementing and geopolymerization3. The review paper focused on the incorporation of waste materials with respect to their sample size, specific criteria involved in the method of production as well as the results of standard tests that were conducted. Another such literature review work, focused on water absorption and compressive strength of the resultant brick incorporating waste material, specifically for bricks developed from industrial and agricultural solid waste4. In addition, the review paper further discussed some of the reasons regarding the lack of the utilization of waste materials in commercial brick production process3.

The review paper focused on the chemical properties of waste which they categorized into fuel waste, fly-ash, fluxing wastes, plastic reducing and plastifying wastes5. For each waste depending on their contribution in mix proportions as an additive, their High Heating Temperature (HHV) was compared. Also, effects of waste on various properties such as dry bending strength, drying shrinkage, waster absorption, linear firing shrinkage and compressive strength was also reviewed. A review on the characterization of clay incorporated with additives and their influence on the physico-mechanical properties of fired clay bricks6. Additives were categorized into four categories to summarize the effects of the addition of wastes on the basis of their nature viz. sewage sludge, ashes, inorganic residue, and organic wastes. These and other typical literature review work has not however highlighted the thermal performance of bricks incorporating waste material.

3. Review of Thermal Performance of Bricks Incorporating Waste Material

Much research has been done on various waste materials incorporated within bricks; however the focus of the

Ashwin Narendra Raut and Christy Pathrose Gomez

Vol 9 (37) | October 2016 | www.indjst.org Indian Journal of Science and Technology 3

literature review work here is to present studies specifically related to thermally insulated bricks developed by incorporating waste materials. Various researchers have been conducting experiments for the incorporation of industrial, agricultural and municipal waste in bricks by adopting different methods of production. Apart from sustainability attainment, researchers have been focusing on energy efficiency concerns in buildings by improving thermal performance of wall material (bricks), specifically in relation to the incorporation of waste material. In order to provide a developmental background to research into

the thermal properties of bricks, the following literature review that is focused on thermally insulated bricks is presented. It is broadly divided according to the two main methods of brick production i.e. 1. Fired bricks and; 2. Unfired bricks. Table 1 presents the various types of waste utilized along with its physico-mechanical and thermal properties for development of thermally efficient bricks. In a more specific sense, the higher aim of recycling of waste in bricks can lead to a more sustainable solution for waste management and can serve to address specific environmental concerns.

Table 1. Thermal performance of bricks made from waste materialSr. No.

Waste Material Used Type of brick

Test Conducted Min. Thermal Conductivity Achieved (W/mK)

Ref.

1 Bagasse (BG) (max. 2.5%) fired at temperature 950⁰C with clay

Fired Linear Shrinkage, Bulk Density, Water Absorption, Compressive Strength, Thermal Condctivity, SEM.

0.162 [19]

2 By-product of Glycerin (max. 15%) fired at temperature 1050⁰C with clay.

Fired Linear Shrinkage, Water Absorption, Bulk Density, Rate of Water Suction, Compressive Strength, Thermal Condctivity, Microstrctral Analysis (SEM).

0.1 [20]

3 Cigarette Butts (max. 10%) fired at 1050⁰C with brown silty clayey sand

Fired Compressive Strength, Flexural Strength, Density, Water Absorption, Initial Rate of Absorption, Leaching Test

0.45 [7]

4 Coconut coir fiber mixed with soil cement and sand.

Unfired Bulk Density, Compressive Strength, Thermal Condctivity

0.7187 [22]

5 Coffee Ground residue (CG) (max. 3%) fired at temperature 950⁰C with clay


0.142 [19]

6 Corn Cob Ash (max 25%) mixed with 1:3 ratio of cement and sand

Unfired Thermal Conductivity 0.51 [34]

7 Expanded vermiculite (max. 10%) fired at 1000⁰C with clay mixture.

Fired Bulk Density, Apparent Porosity And Water Absorption, Compresive Strength, Thermal Conductivity, Microstructral Properties (SEM).

0.65 [13]

8 Glass powder (max. 30%) mixed with Limestone powder and class-C flyash.

Unfired Compressive Strength, Flexural Strength, Water Absorption, Density, Thermal Condctivity

0.81 [23]

9 Ground Granulated Blast Furnace Slag (GGBS) mixed with lime or cement binder

Unfired Compressive Strength, Density, Rate of Water Absorption

0.2545 [21]

10 Marble Waste (max. 35%) fired at (950⁰C, 1050⁰C) with brick clay

Fired Bulk Density, Apparent Porosity, Water Absorption, Compressive Strength, Thermal Conductivity, SEM, EDS, XRD.

0.40 [15]

11 Millet Waste (0.122 kg) mixed with laterite soil (1 kg).

Unfired Thermal Conductivity 0.29 [26]

12 Olive mill wastewater (OMW) (max. 6.5%) fired at temperature 950⁰C with clay


0.143 [19]



13 Olive oil industrial waste (Pomace) (max. 10%) mixed with clay.

Unfired Loss Of Ignition, Linear Shrinkage, Bulk Density, Compression Test, Freeze-Thaw Test, Thermal Conduc-tivity, SEM.

0.72 [18]

14 Palm Kernel Shell (PKS) (max. 3%) fired at 1050⁰C with clay.

Fired Drying Shrinkage, Dry Density, Initial Rate Of Suction, Compressive Strength, Thermal Conductivity.

0.9283 [8]

15 Palm Oil Fibers (POF) (max. 3%) fired at 1050⁰C with clay.


0.8828 [8]

16 Palm oil fly ash (POFA) (max. 3%) fired at 1050⁰C with clay.


0.9638 [8]

17 Paper processing residue (PPR) (max.30%) fired at temperature of 1100⁰C with brick raw materials

Fired Loss On Ignition, Bulk Density, Ap-parent Porosity, Water Absorption, Thermal Conductivity

0.42±0.02 [14]

18 Polyurethane (PUR) + Expanded Polystyrene (EPS) (50:50 ratio) mixed together with curing tem-perature of (130⁰C, 140⁰C, 150⁰C).

Fired Bulk Density, Thermal Conductivity. 0.035 [27]

19 Rice Husk Ash (RHA) (max. 15%) by volume fired at temperature of (700⁰C, 800⁰C, 900⁰C, and 1000⁰C) with brick raw materials.

Fired Linear Shrinkage, Apprent Porosi-ty, Water Absorpton, Compressive Srength, Thermal Condctivity.

0.173 [16]

20 Rice Husk Ash (RHA) mixed with sand and cement in ratio (544:320:40) kg/m3

Unfired Bulk Density, Water Absorption, Compressive Strength, Thermal Conductivity.

0.33 [33]

21 Rice peel (max. 7%) fired at 900⁰C with yellow and grey clay

Fired Compressive Strength, Flexural Strength, Thermal Conducivity

0.20 [9]

22 Saw Dust (max. 15%) fired at 1050⁰C with Ifon clay.

Fired Apparent Porosity, Cold Crushing Strength, Thermal Shock Resistace, Bulk Density, Thermal Conductivity, SEM-EDX.

0.1 [17]

23 Saw Dust (max. 7%) fired at 900⁰c with yellow and grey clay


0.24 [9]

24 Sawdust (max. 9%) mixed with laterite soil and cement

Unfired Water Absorption, Thermal Conduc-tivity, Thermal Diffusivity, Compres-sion Strength.

0.50 [30]

25 Seed shell (max. 7%) fired at 900⁰c with yellow and grey clay


0.17 [9]

26 Sewage sludge ash was mixed with cement (max. C/S ratio 40%) and alumina (max. A/S ratio 0.3%)

Unfired Water Absorption, Bulk Density, Apparent Porosity, Compression Strength, Thermal Conductivity, Pore Srctre (MIP), Micrographic Exami-nation (SEM).

0.084 [31]

27 Sludge from Brewing industry (SBI) (max. 15%) fired at temperature 950⁰c with clay

Fired Linear Shrinkage, Bulk Density, Water Absorption, Compressive Strength, Thermal Condctivity, Sem.

0.150 [20]

28 Spent brewery grain (max. 15%) fired at 1000⁰c with brick ceramic paste

Fired Linear Shrinage, Mechanical Bending Strength, Water Absorption, Open Porosity, Bulk Density , Thermal Conductivity

0.37 ±0.01 [10]



3.1 Thermal Performance of Fired Bricks using Waste

Upon firing, clay bricks undergo through various mineralogical changes and changes in their texture and physical attributes as well as their porosity. The firing process could affect the physical and mechanical properties, colours and appearance of the manufactured brick. It has observed that manufacturing bricks by firing has a disadvantage in that it consumes huge amount of energy, to the extent of 2.0 kWh per brick on an average accompanied by large amount of greenhouse gas emissions. Owing to concerns about the environment, many researchers have tried to reduce the carbon footprint of fired clay brick by incorporating waste. Whilst a number of researchers have gone a step ahead and tried to enhance the physico-mechanical as well as thermal properties of fired bricks using waste materials.

Researcher developed fired clay bricks with the incorporation of cigarette butts up to an extent of 10%. Results pointed out that there was around 30% reduction in density of developed bricks as compared to the control sample7. The findings with respect to lower density caused the thermal conductivity of bricks cast together with cigarette butts was concluded by using mathematical modelling between dry density and thermal conductivity.

The cigarette butts utilization in fired clay bricks had significant impact on thermal conductivity performance values and it was found out to be a value of 0.45 W/mK. In another research studies were conducted on three different forms of palm oil waste within fired clay bricks. The waste generated from palm oil was differentiated into Palm Kernel Shell (PKS), palm oil fly ash and palm fibers8. Addition of all three forms of waste was done for different samples. All three types of palm waste showed slightly similar thermal properties ranging around 0.9 W/mK.

The Researchers developed bricks made from agricultural waste (sawdust, rice-peel and seed-shell) mixed in yellow clay and grey clay9. Sunflower seed shell showed greater reduction in thermal conductivity as compared to Saw dust and Rice-peel which was added in equal proportion (7%). Addition of seed shell to the basic clay reduced thermal conductivity to a level of 0.17 W/mK. Ferraz10 however utilized waste containing spent grain (barely malt and maize grit), one of the by-products of the brewing process. Spent Brewery Grains (SBG) were added in different proportions (5%, 10%, 15%) with clay mix and fixed at temperature 900°c, 950°c and 1000°c. The thermal conductivity analysis was conducted as per the standards of ASTM C51811 and ASTM E153012. The lowest value of thermal conductivity was observed at

29 Spent Earth from biodiesel filtra-tion (SEBF) (max. 20%) fired at temperature 1050⁰c with clay.

Fired Linear Shrinkage, Water Absorption, Bulk Density, Rate Of Water Suction, Compressive Strength, Thermal Condctivity, Microstrctral Analysis (SEM).

0.125 [19]

30 Straw mixed with clay cement/gypsum

Unfired Water Absorption, Density, Loss Of Wieght after 7 Days, Compressive Strength, Thermal Condctivity.

0.217 [24]

31 Sugarcane Bagasse Ash (SBA) (max. 80%) mixed with quarry dust and lime

Fired Dry Density, Waterabsorption, Effloroscence, Compressive Strength, Durabiliy Test (Chloride, Sulphate, And Carbonation), Environmental (Toxicity Characteristics Leaching Protocol (TCLP), Thermal Conduc-tivity.

0.455 [32]

32 Urban sewage sludge (SUW) (max. 15%) fired at temperature 950⁰c with clay

Fired Linear Shrinkage, Bulk Density, Water Absorption, Compressive Strength, Thermal Condctivity, Sem.

0.158 [19]

33 Recycled paper mill waste (RPMW) (max. 95%) mixed with cement as binder.

Unfired Density, Water Absorption, Efflo-rosence, Compressive Strength And Thermal Conductivity.

0.3 [33]

34 Olive husk (40% wt.) and straw (10% wt.) with clay fired at 125ºc for 5 hours, drying at 55ºc for 8 hrs.

Fired Compression Strength Test, Thermal Conductivity.

0.09±0.02 [25]



firing temperature of 1000°c for 15% addition of Spent Brewery Grains (SBG) and it was found to be 0.37±0.01 W/mK. A significant finding of this research was that the addition of SBG in red brick ceramic paste leads to increased water absorption and open porosity and, lower thermal conductivity and density.

The studies revealed that the weight of the fired clay bricks was reduced on addition of up to 35 wt. % waste marble powders by employing semi dry process and at firing temperatures of 950°C and 1050°c for 2 hrs13. Upon increasing the addition of waste marble powder up to 30 wt. % for all samples, the porosity ratios for the bricks increased up to about 40%. On the other hand, the compressive strength of the bricks decreased to 8.2 MPa. The strength of these bricks however was still in accordance to the standard values prescribed. For these samples, the thermal conductivity was lowered from 0.97 to 0.40 W/mK. Researchers utilized recycled paper processing residue in producing porous and light weight bricks14. Mixture consisting of the raw materials for the bricks and paper waste were dried before firing at 1100°C. Results showed decrease of 33% density as compared to the control mix which eventually contributed to lower thermal conductivity of <0.4 W/mK. Another study investigated the influence of the addition of expanded vermiculite to develop porous clay bricks15. The weight of the porous clay bricks was reduced by adding 2.5, 5, 7.5 and 10 wt.% expanded vermiculite, further it was dried and fired at 900°C and 1000°C. Vermiculite addition showed 45% improvement in porosity ratios, on the other hand compressive strength reduced. Increase in porosity contributed to improved thermal performance of the developed brick which decreased by 10%.

Researchers studied the effects of rice husk addition on the porosity and thermal conductivity properties of fired clay bricks16. They concluded, thermal conductivity values of rice husk incorporated brick samples increases with increase in firing temperature. Also, results showed that the thermal conductivity values decreased from 0.494 W/mK to 0.173 W/mK, compared to thermal conductivity of the brick without rice husks at 900°c firing temperature. But the drawback of addition of excess coarse rice husk of 15% made the brick fragile and did not provide enough binding strength.

The researchers studied the influence of composition of saw dust admixture with Ifon clay on the thermal properties of refractory17. The refractory was developed

by firing the clay and saw dust at a temperature of 1000°C. Along with thermal conductivity, several other mechanical properties were also studied. Thermal value of 0.05 W/mK was achieved with 30% addition of saw dust. Due to adverse impact on compressive strength, it was recommended that incorporation of just 10-15% of saw dust as an admixture for structural insulating bricks. 18The researcher assessed the use of assessed the use of “Pomace” i.e. olive oil industrial waste for the development of lightweight brick. As a result of adding the wet pomace, the brick porosity increased greatly. However, results indicated that for production of good quality bricks pomace should be restricted to 10 wt. %. A very high range of compressive strength was recorded with thermal performance attaining European standard value of 0.7 W/mK33.

Investigations were conducted on waste produced waste produced from biodiesel production plants, as Spent Earth from Biodiesel Filtration (SEBF) and the by-product of glycerine for the production of lightweight structural bricks19. Samples were prepared containing up to 20% mass of SEBF and 15% mass of glycerine with clay and it was fired at a temperature of 1050°C. The decrease in thermal conductivity values for SEBF and glycerine were 20% and 40% respectively. Lower thermal conductivity values of the glycerine–clay bricks could be attributed to the fact that waste produced a slightly different mineralogical composition with closed porosity and smaller pores.

Investigation was conducted on various types of industrial waste such as urban sewage sludge, bagasse and sludge from the brewing industry, olive mill wastewater, and coffee ground residue with clay which was then fired at 950°C20. The incorporation of urban sewage sludge, brewing industry sludge and bagasse in the body clay increased the number of open pores thus decreasing the compressive strength and slightly increasing the thermal insulation properties of the bricks. The incorporation of coffee grounds and olive mill wastewater in the body clay slightly increased the open porosity and the proportion of closed porosity, thus maintaining the compressive strength and improving the thermal insulation properties of the bricks by 19%. The thermal values achieved was 0.143 W/mK and 0.142 W/mK for 6.5% addition of olive mill wastewater and 3% coffee ground residue waste addition by weight percentage in bricks respectively.



3.2 Thermal Performance of Waste in Unfired Bricks

The method of preparation of unfired bricks requires a binding material having cementing properties to hold all the constituents elements together. Generally, unfired bricks preparation is based on hydration reactions similar to that in OPC to form mainly C-S-H and C-S-A-H phase contributing to strength3. Cement is vastly used as binder in production of unfired bricks which contributes to Greenhouse gases because of high embodied energy of cement. Incorporation of waste as a binding material can significantly reduce the overall embodied energy of brick.

The researchers incorporated Ground Granulated Blast furnace Slag (GGBS) as a binder to develop two different specimens by using Portland cement and quick lime21. It was observed that the mean thermal value for the unfired clay brick was 0.2545 W/mK and 0.2612 W/mK using the lime and cement binder specimens respectively. The thermal conductivity of the unfired clay bricks was approximated as a function of the material density and moisture content. 22The researchers soil-cement block by adding coconut coir fibres to achieve low thermal conductivity values. The developed soil-cement block had thermal conductivity levels of 0.651 W/mK and compressive strength of 39.55 kg/cm2. The increase in fiber content in blocks was attributed to be resulting in lowering the thermal conductivity but adverse effects were observed with regards to compressive strength.

The combination of glass powder and limestone powder along with class-C fly ash to develop bricks23. The compressive and flexural strengths, density, water absorption and thermal conductivity of the blocks were measured. It was observed that as the glass powder content increased the thermal performance of blocks, the reason being that the thermal conductivity value of glass was approximately 0.96 W/mK. Additionally, there was positive rise in the compressive and flexural strength of the blocks containing glass powder.

Fiber reinforced mud bricks was developed for thermal performance and mechanical properties according to ASTM and Turkish Standard24. Addition of straw with clay and cement showed lower thermal values around 0.2 W/mK. Alami25 utilized olive husk and straw as a filler material in clay bricks. The thermal conductivity (λ) value with 40% olive husk and 10% straw was found to be very low (0.09 W/mK). The thermal conductivity of bricks developed from millet waste mixed with laterite

powder26 from millet waste mixed with laterite powder was investigated. Addition of millet waste reduced the thermal conductivity from 1.4 W/mK to 0.29 W/mK for dry laterite soil blocks. Whilst, Zach et al. described the use of Polyurethane (PUR) waste of fraction 3-6 mm and Expanded Polystyrene (EPS) waste of fraction 1-4 mm27. Both the waste was mixed in 50:50 proportions, but samples were cured at three different set of temperatures. The thermal properties of samples were found to be around 0.035 W/mK. However their research does not provide any information regarding mechanical properties of sample.

Author investigated the performance of Rice Husk Ash (RHA) based sand–cement block28. Thermal conductivity tests were performed according to JIS R 2618:199529. The results showed significant reduction in thermal conductivity value of RHA block with a value of 0.33 W/mK as compared to commercially available clay bricks (0.72 W/mK). Thermal performance was found to be 54% better than that of commercial clay bricks. The researchers carried out experimental study on the effect of addition of pozzolan or sawdust in lateritic soil bricks. Sawdust was added to Lateritic soil along with cement in 9% wt. proportion30. The thermal conductivity of developed brick was 0.34 W/mK and 0.36 W/mK by using flash method and box method respectively at a compacting pressure of 10 bars.

The researchers studied pore structure influence on lightweight characteristic and thermal performance of material31. They studied the influence of pores generated from hydration of sewage sludge ash with cement along with metallic alumina powder. Addition of sewage sludge caused the thermal conductivity to be lowered, ranging between 0.085 to 0.102 W/mK, due to the increased volume of pores smaller than 10 µm. Interestingly, developed brick using sugarcane bagasse ash mixing it with constant composition of lime32. The thermal conductivity of the developed brick composition was obtained by Lee’s apparatus. The developed brick showed lower thermal conductivity values from 0.455−0.480 W/mK. It was reported that the thermal performance of developed bricks was found to be 62% and 54% lower than the commercially available clay bricks and fly ash bricks. Whilst33, another researcher utilized recycle paper mill waste as a basic ingredient constituting 80-95% of composition, and the binder material utilized was cement. The developed bricks were further used to assess indoor



temperature for developed sustainable material by using small scale model technique. The developed RPMW-cement bricks were found to have a lower thermal value of 0.3 W/mK.

3.3 Heat Transfer in Waste Incorporated Bricks

It is evident from the Table 1 that many of the agricultural as well as industrial waste has been tried and tested by many researchers to produce eco-friendly thermally efficient bricks. But, as we try to analyse these products comparing their physical performance such as density, water absorption and compressive strength with their thermal conductivity, most of products lack good thermal as well as physical properties. Figure 1-5 provides a representation of performance of eco-friendly thermally efficient bricks based on their properties. For a good quality thermally efficient brick the requirement is low thermal conductivity which will lower the heat transfer through wall components of the building envelope, higher compressive strength to provide durable structure and low density to reduce self-weight of structure.

Figure 1. Compressive strength vs Thermal conductivity of various waste materials used in fired bricks.

Figure 2. Compressive strength vs Thermal conductivity of various waste materials used in unfired bricks.

Figure 3. Porosity vs. Thermal conductivity of various waste materials used in fired bricks.

Figure 4. Density vs. Thermal conductivity of various waste materials used in fired bricks.

Figure 5. Density vs. Thermal conductivity of various waste materials used in unfired bricks.

The heat transfer phenomenon through bricks/blocks with additives is often complex. The concept of thermally efficient bricks lies with reducing the heat flow through material. The reduction in heat flow is brought by increasing porosity by various means such as addition of lighter material which has porous microstructure, addition of fibrous materials, and method of preparation i.e. firing/cementing technique. Basically porosity is one of the crucial factors which help in reduction of heat



flow rate through the material. Heat flow through porous matrix is largely attributed to pore geometry. Porosity, pore sizes and its distribution in the material greatly decides the heat transfer through the building envelope component, in this case thermally efficient bricks. Microstructure of materials plays a vital role which has solid matrix and pores consisting of fluid (water or air) which ultimately influences the heat transfer through conduction, convection and radiation. The components which contribute to heat transfer are:• Heat conduction in solid matrix/particles;• Heat conduction through pore fluid (air or water);• Heat conduction in micro-gaps that exist between

particles;• Particle contact heat conduction;• Heat transfer through pore fluid;• Radiation from solid surfaces of pores (particle to

particle radiation in pores)36.The pore forming additive used in burnt clay bricks are

generally classified into organic and inorganic substance. By the method of firing during its manufacturing stage, the increase in firing temperature increases the value of thermal conductivity which is mainly because of densification of matrix due to filling of the pores by the glassy mass during sintering stage. The presence of high content of calcite (CaCO3) either in clay or in additive results in a highly porous structure because of decomposition of calcite (CaCO3) into CaO and release of CO2

37. This is due to the fact that the compound formed during calcination process i.e. CaO is highly reactive which can readily react with different materials in the structure. As a result, calcium-alumino-silicates is formed after firing of clay body. Expansion due to CaO formation can cause increase in porosity of brick which enhances the thermal performance of bricks18. Most of the inorganic materials which can be used as additives possess carbonates of calcium and magnesium, and also silicates which have same kind of effect as described earlier. Combustion of organic additive with the release of CO2 creates pores which enhances the thermal efficiency of burnt clay brick. Thus, higher percentage of organic matter, greater the porosity; making the path of particles shorter for gas diffusion. Therefore, a higher organic additive content increases the open pore volume and decreases the bulk density of sintered specimen, thus lowering thermal conductivity38.

In case of unfired bricks the method of preparation

is by cementing technique. The thermal conductivity in unfired bricks is mostly dependent on the bulk density and porosity of constituent materials used. The lighter the constituent materials, the more porous it will be, which eventually results in lower thermal conductivity values. Organic materials are porous, having low density which results in lowered heat transfer rate. Agricultural waste mostly consists of fibrous material which is treated as low heat conducting material. This is due to the fact that in fibrous structure the air is trapped within the enclosure which possess very low heat transfer rate (approximately λ = 0.024 W/mK). Inclusion of natural fibers eventually lowers the overall thermal conductivity of material. In pozzolonic materials, the thermal values are partly related to high Silica (SiO2) content. Process of hardening of cement composites because of hydration reaction develops the pore structure39, resulting in void spaces occupied previously by water. The hydration reactions of cementitious materials mainly generate pores smaller than 0.1 µm25. However, thermal conductivity depends not only on the percentage of pores but also on their size and connectivity5,16,18,39. The pore parameters entirely rely upon the particle packing of material. Thus, the role of micro-structure of materials is very crucial in developing thermally efficient bricks.

3.4 Material Selection Strategy for Developing Sustainable Thermally Efficient Bricks

As was discussed earlier, for thermally efficient bricks, thermal conductivity is of utmost importance. Most researchers striving for this property try to select their raw materials and design mix proportions for minimal thermal conductivity, however in these cases other crucial criteria remain unattended. During the conceptual stage researchers have to select waste material for incorporation such that it can meet environmental, socio-economic and technical criteria during entire life cycle of the product. Table 2 presents detailed criteria for selecting waste for developing sustainable thermally efficient bricks. There are numerous waste materials having almost similar characteristics, with the potential to be incorporated as additives to enhance thermal performance of bricks, which makes the selection procedure quite complex. Additionally, the effects on other characteristics of the product need to be carefully considered. To overcome



this problem, it is proposed in this paper that the hierarchal method of optimal design be adopted. One of such method is the Pugh concept selection method which derives qualitative comparison of each alternative to a reference or datum alternative40. In this method formulation of decision matrix has to be done based on set of criterion based on which the potential option can be scored and then it can be ranked. The method is implemented by establishing an evaluation criteria matrix versus alternative embodiments.

The method is based on assuming that there are ‘n’ different and independent alternatives (A1, A2, A3......An) belonging to a particular group of waste, and similarly, W1, W2, W3…….Wn are different attributes corresponding to the alternatives. A simple decision matrix can be formed as shown in fig. 6 in which attributes are scored relative to other alternates. The (+) score can be consider as favourable feature whilst the (-) score can be considered as unfavourable characteristic, and (0) can be assigned to datum as a reference feature. The potential material can be awarded to the highest overall score. This simple

approach can be adopted by researchers who are striving to utilize materials having similar attributes or that fall in the same category.

Figure 6. Scoring Concept of decision matrix for selection of alternatives.

Velasco et. al.6 has categorised waste as a sustainable construction material according to its nature: 1. Sludge 2. Ashes, 3. Inorganic resides 4. Organic waste. Waste

Table 2. Selection criteria for potential waste material to be incorporated for developing thermally efficient sustainable bricksCriteria’s INPUT Process Output• Environmental • Non-Hazardous/Non-Toxic

• Sustainable

• Recycled

• Low Embodied Energy

• Waste reduction during operation

• Degradable

• Non-Hazardous/Non-Toxic

• Overall environmental Impact• Socio-Economic • Locally Available

• Affordable

• Easily Accessible

• Lower manufacturing Cost

• Safety and Health of labors

• Ease of plant setup and start-up

• Socially acceptable (perception)

• Low overall cost

• Technical • Low specific Gravity/low density

• Fibrous /Porous structure

• Supplementary cementitious properties

• Without Contaminants

• Durable

• Non-Volatile

• Less pre-processing pro-cedure

• Simplified operative tech-nique for labors

• Easy Applicability

• Low thermal Conductivity

• Low Density

• Acceptable Water Absorption, Compressive Strength.

• Highly Durable

• Fire resistant

• Freeze and thaw resistant

• Moisture resistant



belonging to particular category shows more or less similar attributes, selecting the waste as an additive becomes very confusing. Decision matrix aims at providing a simple tool of quantitative scoring of attributes to analyse various potential sustainable materials. The final product developed from the selected material then can have balanced attributes and this approach can be an efficient method to be adopted for industrial application.

4. Conclusion

Generation of solid waste is a serious problem and researchers have been trying to utilize the waste generated from various sectors in order to be more sustainable. The utilization of waste to develop eco-friendly thermally efficient wall systems is aimed at providing a sustainable solution. This paper provides a review of research on thermal performance for inclusion of waste materials in bricks which have shown the potential of being used for lowering the heat conductance of through wall. Previously, in developing thermally efficient bricks researchers only strive for thermal performance whilst other properties are left unattended failing to establish the developed brick as a truly sustainable building material that has immediate industrial application attributes. Hence, the aim of this paper is also to provide a methodology to seek out alternatives which proves to be thermally efficient as well as provide better durability option. As the building wall material consists of a complex network of pores and particles, the issue has to be addressed at microstructural level to develop such a material using locally available waste. Altering the microstructure of material used for commercially available brick is difficult. Use of such a sustainable material which can induce such a microstructure that lowers the heat transfer rate and also provides durability to the newly developed product is difficult with additional cost implications. To simply the selection dilemma among various wastes as alternatives it is thus proposed that a simple decision matrix system which can filter the best choice among the waste that has similar features. The aim is to adopt the types of waste that has the potential to develop building bricks that have primary thermal performance characteristics together with key combinatory performance criteria for immediate industrial application.

5. Acknowledgment

This research paper is an outcome of the research being undertaken at Universiti Tun Hussein Onn Malaysia (UTHM). A special thanks to the “Research, Innovation, Commercialization and Consultancy Management (ORICC)” Office at UTHM for the administrative support provided and for the Research Grant Vote No. U204 sponsorship.

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utilization of waste as a constituent ingredient for enhancing

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