Abstract
The main purpose of this study was to develop a type of concrete block which can serve as a thermal and sound insulator. Expanded polystyrene (EPS) was selected as an insulating materials and to protect the EPS from external effect it was covered with sand-cement mortar. As EPS can withstand against a very little amount of compressive force so cement mortar should be a rich one. The block was casted in a simple mold and demolded after 24 hours. Then it was tested followed by specified days of curing. Also, through this study, economic proportion of sand-cement mortar and usability of strength gaining admixture was investigated and it was found that 1:3 cement mortars with admixture gives satisfactory results in terms of durability and strength.

1.   Introduction:

Brick is the main building material for the construction industry, which has been growing at about 5.6 percent annually between 1995 and 2005, leading to an estimated growth rate of 2–3 percent for the brick sector.

Annually about 17.2 billion burnt clay bricks are produced allover Bangladesh whose output value is about Tk. 83 billion (BUET 2007). With about 5,000 operating kilns, brick-making is a significant sector in Bangladesh, (The World Bank, ESMAP-2011) contributing about 1 percent to the country‘s gross domestic product (GDP) and generating employment for about 1 million people (BUET 2007). These vast amounts of clay bricks consume 45 million tons of clay, 3.5 million tons of coal and 2 million tons of fire wood. The Fixed Chimney Kiln (FCK) dominates the brick sector in Bangladesh, despite its highly polluting and energy-intensive features. Most operating kilns consume about 18–22 tons of coal to produce 100,000 bricks (BUET 2007). Coal burning by kilns releases pollutants into the atmosphere, leading to harmful effects on health (e.g., from PM) and agricultural yields (e.g., from NOx) and contributing to global warming and climate change (e.g., from CO2). Annually 9.8 million tons of CO2 is emitted due to burning of bricks in Bangladesh (BUET 2007).

Also, the clay is being collected from agricultural land.  Research indicates that about 42000 acres of agricultural land is being diminished annually due to unplanned brick field and collection of clay from agricultural top soil. If these processes continue our food security will be in danger very soon.

Considering above facts Housing and Building Research Institute (HBRI) has taken a number of research programs regarding alternative to burnt clay bricks. Thermal block is one of them.

The thermal block is a type of concrete block where expanded polystyrene is used to increase the thermal resistant properties of the block and to lighten the gross block weight. Cement mortar is casted over EPS and cured for specified period. As no burning is required so this block will be environment friendly, sustainable, and cost effective. The wall made of this block will provide comfortable indoor environment both in summer and winter. Due to its lightweight characteristics this will save structural cost and uses of this block in multi storied buildings will be suitable in earth quake point of view.

2.  Literature Review:

Extensive searching of literature was performed during and prior to study process. A handful amount of literature is available on thermal blocks. Thermal blocks are widely used in the region of harsh temperature, especially in Europe where average temperature in winter is below freezing point and Middle Eastern countries where average temperature in summer is more than 40ºC. We tried to follow the specifications, instructions, and standard provided by Dubai Municipality, a well-established institute in Middle Eastern region. In some cases we modified some parameter due to the local condition, especially in case of materials used.

2.1.  Cement Concrete Literature:

Concreteis a composite material composed mainly of water, aggregate, and cement. Often, additives and reinforcements are included in the mixture to achieve the desired physical properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily molded into shape. Over time, the cement forms a hard matrix which binds the rest of the ingredients together into a durable stone-like material with many uses. To make thermal bricks in this laboratory, Ordinary Portland Cement (OPC) is used with coarse grained sand collected from Sylhet. Different engineering properties both for cement and sand were determined prior to casting the thermal bricks. Water reducing and strengthening admixture (Daracem) was also used for another set of sample.

2.2.     Properties of Cement:

The cement used for our research work was collected from local market. Different tests were conducted on this cement to obtain its properties. The test results are summarized below.

1.  Introduction:

Brick is the main building material for the construction industry, which has been growing at about 5.6 percent annually between 1995 and 2005, leading to an estimated growth rate of 2–3 percent for the brick sector.

Annually about 17.2 billion burnt clay bricks are produced allover Bangladesh whose output value is about Tk. 83 billion (BUET 2007). With about 5,000 operating kilns, brick-making is a significant sector in Bangladesh, (The World Bank, ESMAP-2011) contributing about 1 percent to the country‘s gross domestic product (GDP) and generating employment for about 1 million people (BUET 2007). These vast amounts of clay bricks consume 45 million tons of clay, 3.5 million tons of coal and 2 million tons of fire wood. The Fixed Chimney Kiln (FCK) dominates the brick sector in Bangladesh, despite its highly polluting and energy-intensive features. Most operating kilns consume about 18–22 tons of coal to produce 100,000 bricks (BUET 2007). Coal burning by kilns releases pollutants into the atmosphere, leading to harmful effects on health (e.g., from PM) and agricultural yields (e.g., from NOx) and contributing to global warming and climate change (e.g., from CO2). Annually 9.8 million tons of CO2 is emitted due to burning of bricks in Bangladesh (BUET 2007).

Also, the clay is being collected from agricultural land.  Research indicates that about 42000 acres of agricultural land is being diminished annually due to unplanned brick field and collection of clay from agricultural top soil. If these processes continue our food security will be in danger very soon.

Considering above facts Housing and Building Research Institute (HBRI) has taken a number of research programs regarding alternative to burnt clay bricks. Thermal block is one of them.

The thermal block is a type of concrete block where expanded polystyrene is used to increase the thermal resistant properties of the block and to lighten the gross block weight. Cement mortar is casted over EPS and cured for specified period. As no burning is required so this block will be environment friendly, sustainable, and cost effective. The wall made of this block will provide comfortable indoor environment both in summer and winter. Due to its lightweight characteristics this will save structural cost and uses of this block in multi storied buildings will be suitable in earth quake point of view.

2. Literature Review:

Extensive searching of literature was performed during and prior to study process. A handful amount of literature is available on thermal blocks. Thermal blocks are widely used in the region of harsh temperature, especially in Europe where average temperature in winter is below freezing point and Middle Eastern countries where average temperature in summer is more than 40ºC. We tried to follow the specifications, instructions, and standard provided by Dubai Municipality, a well-established institute in Middle Eastern region. In some cases we modified some parameter due to the local condition, especially in case of materials used.

2.1.     Cement Concrete Literature:

Concreteis a composite material composed mainly of water, aggregate, and cement. Often, additives and reinforcements are included in the mixture to achieve the desired physical properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily molded into shape. Over time, the cement forms a hard matrix which binds the rest of the ingredients together into a durable stone-like material with many uses. To make thermal bricks in this laboratory, Ordinary Portland Cement (OPC) is used with coarse grained sand collected from Sylhet. Different engineering properties both for cement and sand were determined prior to casting the thermal bricks. Water reducing and strengthening admixture (Daracem) was also used for another set of sample.

2.2.     Properties of Cement:

The cement used for our research work was collected from local market. Different tests were conducted on this cement to obtain its properties. The test results are summarized below.

SL	Test conducted	Test Result
1.	Normal consistency	25%
2.	Initial Setting Time	135 Min
3.	Final setting Time	185 Min
4.	Compressive Strength	3 Days- 1986 psi 7 Days- 2990 psi 28 Days- 4142 psi
5.	Tensile Strength
6.	Fineness	99.4% passing in #100 US sieve
7.	Specific Gravity	3.14

1.1.1.                                               Properties of Sand:

 

In Bangladesh two types of sands are commonly used. Locally available sand collected from different rivers. This sand is finer in size. FM varies from 1.5 to 2.2. Building designers do not recommend this sand for structural construction. This is only used in non-bearing partition wall construction and plastering works. Other type of sand is Sylhet sand collected from hilly rivers of Sylhet. This sand is coarser in size and its size is more consistent than other types of sand.  Its FM varies from 2.3 to 2.9. In this test we used clean sand Sylhet sand, its FM was 2.72. Figure 1.1 showed the sieve size versus percent finer curve of Sylhet sand.

 

Sieve analysis of Sand and sub-sequent result:

 

Sieve No (ASTM)	Sieve Openings (mm)	Quantity Retained (gm)	Percentage Retained (%)	Cumulative Percentage Retained (%)	Percent Passing to the nearest Sieve	Fineness Modulus (FM)
4	4.75	0.00	0.00	0.00	100.00	2.79
8	2.35	18.30	3.66	3.66	96.34
16	1.18	100.30	20.06	23.72	76.28
30	600 µm	194.60	38.92	62.64	37.36
50	300 µm	138.80	27.76	90.40	9.60
100	150 µm	39.10	7.82	98.22	1.78
Pan		8.90
Total		500.00	98.22	278.64

 

Figure: Sieve Size vs % Finer curve of Sylhet sand

1.1.                                      EPS Literature:

EPS is a type of insulation that is molded or expanded to produce coarse, closed cells containing air. Expansion is achieved by virtue of small amount of pentene gas dissolved into the polystyrene base material during production. EPS foam products whether used for insulation or packaging are lightweight, versatile, sanitary, energy efficient, and most importantly cost effective.

 

1.1.1.                                               Density:

EPS densities for practical civil applications range between 11 and 30 kg/m3. For other applications like insulation higher densities are more efficient (van Dorp, 1988). In our test EPS25 (25 kg/m3 from Advance Technologies Ltd. was used.

 

1.1.2.                                               Compressive strength and stress strain curve:

Figure 2-3 shows the uniaxial compression stress strain curve of EPS for two different densities. The two densities shown are considered the extreme values for most engineering applications done so far. Specimens are 0.05m cubes tested at a displacement rate of 0.005m/min. From the figure the stress strain curve can be simply divided into two main straight lines connected with a curved portion. The slope of the straight line portions increase with density. The stress at any strain level also increases with the density. The bead size has no important effect on the compressibility of cut specimens (BASF Corp., 1968).

EPS under confining compression Sun (1997) reported that with in-crease in confining stress the strength and initial tangent modulus decrease. Sun concluded these results based on axial deviator stress strain curves, which are important for submerged EPS.

1.                    Making of Thermal Block

Full size (4’X8’) EPS panel collected from factory is first cut to size to make thermal blocks. After proper sizing and grooving the EPS pieces are placed into the steel mold. The molds are rectangular steel box open in one side. Cement mortar is then placed in the gap between the mold wall and EPS. These are de-molded after 24 hours and then blocks are kept for curing. The blocks can be used after 28 days of proper curing with water. The complete process of making thermal blocks can be best described by the following pictorial presentation.

1.                    Test Program

 

1.1.              Compressive strength test:Compressive strength of thermal block was tested in accordance with appendix B of BS 6073: Part 2 of five samples.  Average result based on the gross area of thermal block of each test was considered for the particular proportion. Compressive strength of 7 days, 14 days, and 28 days was measured for each set of sample.

1.2.              Water Absorption Test: Water absorption test of thermal block was done after 28 days of water curing and 14 days of air curing following the water curing period. The test was performed in accordance with ASTM C20-00 Standard. The percentage of water absorption by thermal blocks of different proportion was calculated for the gross weight of the blocks. Besides water absorption test of burnt clay bricks randomly collected from local market was done to compare the water absorption characteristics of two types of block/bricks. The test result is presented in later sections.

 

2.                    Test Result and Discussion:

2.1.              Compressive strength test:Result of compressive strength test is shown in table below. It is observed that compressive strength of tested thermal block increased with increasing cement content. Also the compressive strength was considerably higher of the sample (1% of cement used) containing admixture although the proportion
of cement is same.

SL	Cement used (in % of  Mix)	Admixture Used (in % of Cement)	Curing Age (Days)
			7	14	28
			Compressive Strength (psi)
1	50	0%	830	981	1189
2	50	1%	986	1145	1350
3	33	0%	755	839	1056
4	33	1%	820	1000	1228
5	25	0%	620	780	945
6	25	1%	760	820	1080
7	20	0%	562	700	836
8	20	1%	600	765	865

 

The discrete data can be best understood by the following figures which compared the result of compressive strength test with different proportion of cement and admixture used.

From the graph-1 and chart-1 we observe that for sample without any admixture used, 28 days compressive strength increses by 13%, 26%, and 42%  when cement content is increased to 25%, 33%, and 50% respectively.  Almost similar phnoena occur in case of sample with admixture used. In this case the incresing amount is 24%, 42%, and 56%   when cement content is increased to 25%, 33%, and 50% respectively. We see the increasing rate in sample with admixture is higher than the sample without admixture. Almost same result can be obtained from 33% cement with admixture and 50% cement without admixture use. To understand the phenomena more clearly let us examine the follwing graph (graph-2).

In graph-2 we see the compressive strength of thermal block having 50% cement withou any admixture is almost same (1200psi) as that of block having 33% cement with admixture (1% of cement). Also that compressive strength (1200 psi) satisfy th standards (Dubai Municipality as an example).

 

1.1.              Water Absorption Test: Water absorption test result of thermal block and burnt clay bricks are presented in the table below. Ten samples were tested as per ASTM standard. Different sample was taken from different proportion of cement and admixture used. It is observed that water absorption of no sample exceed 6% and average water absorption 5% for all ten samples. On the other hand, most of the burnt clay bricks soak more than 20% water of their initial gross weight.

 

 

 

 

 

Sample No.	Thermal Block			Burnt Clay Brick
	Initial Weight  (gm)	Final Weight (gm)	Water Absorption (%)	Initial Weight (gm)	Final Weight (gm)	Water Absorption (%)
1	1407	1470	4.47	2538	3085	21.55
2	1398	1470	5.15	2666	3295	23.59
3	1752	1820	3.88	2625	3230	23.04
4	1442	1525	5.75	2735	3225	17.91
5	1250	1305	4.40	2635	3325	26.18
6	1236	1303	5.42	2535	2960	16.76
7	1162	1226	5.50	2650	3167	19.50
8	1390	1468	5.61	2750	3280	19.27
9	1405	1485	5.69	2735	3350	22.48
10	1438	1504	4.58	2715	3210	18.23
Average	1388	1457	5.01	2658	3212	20.85

1.                    Conclusions:

From the test result and related literature study following conclusions can be drawn for the feasibility of the study on thermal block.

a.        As saving agricultural top soil from the aggression of brickfield is our supreme priority so we must find the alternative to burnt clay bricks. Considering compressive strength and water absorption thermal block can be a good alternative to burnt clay bricks to construct non-load bearing walls.

b.        Thermal block is 50% lower in weight compared to burnt clay bricks. So usage of thermal block in high-rise building may save the cost of foundation considerably.

c.        As thermal conductivity of EPS is very low compared to the burnt clay brick so usage of thermal block in interior wall will provide a comfortable interior environment.

d.        At present thermal blocks are casted manually. It involves cutting the EPS sheet in pieces with groove, casting the mortar, molding and demolding etc. So cost per piece is a little higher than burnt clay bricks. Once the industrial process is adopted the cost per piece will be within the range of burnt clay bricks.

 

2.                    References:

1.        Dubai Municipality Standard,  DMS 1: Part 5: 2004

2.        IS 10262: (1982) Recommended Guidelines for Concrete Mix Design, Indian Standards Institution, New Delhi.

3.        K. Ganesh Babu, et al.(1992): Concrete Mix Design-An Appraisal of the Current Codal Provisions, The Indian Concrete Journal, February 1992, pp. 87-95.

4.        Nagataki S, Fujiwara H. In; Malhotra VM, editor. Self-compacting property of highly flowable concrete,Vol. Sp 154.American Concrete Institute:1995. P.30114.

5.        EFNARC. Specification and guidelines for self-compacting concrete, English edition. European Federation for Specialist Construction Chemicals and Concrete systems. Norfolk, UK February 2002.

6.        Khayat KH, Guizani Z.Use of viscosity-modifying admixture to enhance stability of fluid concrete. ACI Mater J 1997; 94(4).

7.        A Reclamation Manual Specialist Supplement: Concrete Manual, Fifth Edition 1953, Denver, Cplorado, USA.

8.        Santi Sridorunkatum and Chalermichai Ngourungsi: Technology Manual on Concrete Hollow Blocks, A project Funded by UNDP 1987, printed and published in Thailand and the Philippines.