Zainab Hataf Naji*
| Huda Mohammed Mubarak | Amer M. Ibrahim
© 2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
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In Iraq, certain rocks called porcelanite can be used to make lightweight concrete. The objective of this paper is to create lightweight self-compacting concrete (SCC) by utilizing 0.4 w/cm, coarse and fine porcelanite aggregate and adding nano silica to these mixtures. This study looks at a different way of doing things. Instead of using sand in concrete, they used varying amounts of fine porcelanite instead. We replaced 10%, 20%, 30%, 40%, and 50% of the sand with porcelanite to see how it would influence the concrete's thermal characteristics. Further examined the ratio of water to cement, using ratios of 0.4 and 0.5 by doing this, we wanted to see how both ratio of water to cement, and amount of porcelanite affected the thermal properties of the concrete. It was found that porcelanite makes self-compacting concrete harder to work with, and less able to conduct and spread heat. However, it does make the concrete hold more heat. When nano silica was used, it reduced workability of SCC. However, its effect on thermal properties was not of much significance.
nano materials, thermal conductivity, specific heat
At the present time, people are really concerned about energy and the environment. In the past few years, there has been a large increase in the number of people and factories, which has resulted in more energy being needed. One of the main reasons for this is because buildings use up a lot of energy [1]. Concrete is a commonly employed substance in constructing structures such as buildings and roads due to its economy, versatility, and availability [2]. Samson et al. [3] state that concrete is very popular in construction because it is cheap and lots of people use it. Recent statistics indicate that the production of regular concrete surpasses 26.8 billion tons annually across the globe [4]. Investigators have been working on creating new strong materials that have the advantages of self-compacting concrete and lightweight concrete. Lightweight self-compacting concrete (LWSCC), a novel concrete with the characteristics of both LWC and SCC, has been created. By substituting light weight aggregate (LWA) for normal weight aggregate (NWA) in SCC, LWSCC is created. ACI 213 [5] says that structural lightweight concrete should have a density between 1120 kg/m3 and 1920 kg/m3. Aggregates make up most of the weight of concrete and typically make up about 60% of the volume in SCC [6]. Due to its small perforations, LWA has the ability to lighten concrete and enhance its heat insulation abilities. Using LWSCC has many advantages. It makes things lighter, which helps make the construction process faster and cheaper. It also gets rid of noise from vibrating machines and provides better insulation for heat and sound because of the empty spaces in the material [7-9].
When evaluating the quantity of heat carried, the ability of cement-based materials to transmit heat should be taken into account. Buildings require more energy when heat escapes through the walls and roof. Thermal conductivity can be measured primarily in two ways: transiently and steadily. The way concrete conducts heat depends on a number of factors, including temperature, moisture content, kind of aggregate, type of cement, and density [10].
In most countries, buildings are responsible for using one third of all the energy and producing 30% of the greenhouse gases [11, 12]. Because people spend most of their time inside buildings, discussions about saving energy and maintaining a comfortable temperature are often debated [13]. The amount of energy needed to cool or heat a building and make it comfortable depends on the properties of the materials used for construction [14]. Ventilation and when heat escapes through materials are two reasons why buildings lose heat. Ventilation heat loss means that heat is transferred through the air when it is replaced via systems for ventilation, heating, and air conditioning. That being said, there is a connection between the heat loss of the fabric and the heat loss through the floors, walls, roof, and windows of a space. Concrete is thought to handle heat differently depending on its thermal conductivity, specific heat, and thermal diffusivity. Thermal conductivity is how well heat moves through concrete. It's a really important property that affects how heat is transferred by conduction [15]. Concrete that is difficult for heat to travel through keeps buildings cooler and uses less energy. According to Real et al. [16], when compared to normal weight concrete (NWC), the usage of structural lightweight aggregate concrete in European structures can save up to 15% on heating energy. There are many different ways to measure how well materials conduct heat. Various ways of measuring thermal conductivity may lead to different values [17]. Choosing the right way to measure how well heat travels through concrete is crucial for getting accurate numbers on how much energy buildings use. Also, it is important to mention that there are many things that can change the k-value of concrete [10].
In order to use "thermostone" as aggregate after crushing, Ibrahim et al. [18] measured the thermal characteristics (thermal diffusivity, specific heat & thermal conductivity) of concrete made by reusing the waste of clay brick. To accomplish this, they created three distinct blends. One of them used crushed clay brick instead of normal aggregate, and the other two used crushed thermostone in different amounts. Then compared these three mixes with a usual concrete mixture. Using a method called semi-adiabatic calorimeter, the specific heat was measured. Using the semi-adiabatic calorimeter method in the work, the specific heat was measured. While using the heating - cooling system method, thermal diffusion and specific heat were measured. To find thermal conductivity, they multiplied the thermal diffusivity, specific heat, and density. The researchers found in their experiments that as the concrete density increases, the ability of heat to spread out quickly also increases. However, the amount of heat that the concrete can hold decreases as its density increases. Thermal conductivity and thermal diffusivity are closely related. The amount of each ingredient in concrete affected how it handled heat.
Three different kinds of equipment were invented and built by Ahmed [19] to measure the thermal diffusivity, thermal conductivity and specific heat of concrete. These apparatuses are used to measure different properties of concrete. One tool measures how well concrete holds heat, another measures how heat moves through concrete, and a third measures how well concrete conducts heat. It was found that the lee disc method is a reliable way to measure how well heat moves through concrete. It is easy and convenient to use on a website to solve the problem of not having enough devices to measure thermal conductivity in building materials. In addition, they found that they could use a semi-diabatic calorimater method to detect the specific heat of any kind of concrete. A device that heats and cools the concrete can also be used to measure its thermal advantage, as long as the concrete density is within the range of 900-2400 kg/m3.
The goal of this work is to investigate how the characteristics of both fresh and hardened concrete are affected when LWA and nano Silica are added to an SCC mixture. This covers the heat-transfer and heat-holding capacities of the concrete. additionally examined the water-to-cement ratio, doing so with ratios of 0.4 and 0.5.
The experimental setup involved the casting of 120 (100*200 mm) cylinders for the assessment of specific heat and thermal diffusivity, 120 (280*280*40 mm) square plates for the measurement of thermal conductivity, and 120 (100*25 mm) discs for the measurement of thermal conductivity for various concrete mixes.
2.1 Material
Portland cement (Type I) was used in this work. The cement chemical and physical characteristics demonstrate that it satisfies the criteria of Iraq standard No. (5)-1984. The crushed gravel supply from Al-Soddor region was used. It was known as porcelainnite and had a maximum size of 12.5 mm. The test results for the physical properties and chemical compositions of the coarse porcelanite aggregate are shown in Tables 1 and 2, respectively. Al-Ukhaider, a natural sand, was sieved using a 4.75 mm sieve size before being utilized as a fine aggregate. Grading of fine porcelanite and its properties are shown in Tables 3 and 4. In our study, we employed a high range water-reducing admixture called glenium 51. The supplier of silica fume (SF) was SIKA Company. Table 5 lists the features of the used SF. AEROSIL ® Company powdered silica nanoparticles, imported from North America, were employed in this experiment. The physical and chemical characteristics are displayed in Tables 6 and 7.
Table 1. Physical properties of course porcelanite aggregate
|
Physical Properties |
Results |
|
Absorption % |
32 |
|
Saturation percentage |
3.6 |
|
Bulk density Kg/m3 |
891 |
Table 2. Chemical analysis of porcelanite stone aggregate
|
Analysis of Porcelanite Stone Chemically Aggregate |
Percentage |
|
Silicon dioxide |
62.2% |
|
Calcium oxide |
11.5% |
|
Magnesium oxide |
7.2% |
|
Aluminium oxide |
2.7% |
|
Iron (III) oxide |
0.8% |
|
Titanium dioxide |
0.2% |
|
Sulfur trioxide |
0.3% |
|
Letter of intent |
13.8% |
Table 3. Grading of fine porcelanite
|
Sieve Size (mm) |
%Passing |
|
9.5 |
100 |
|
4.75 |
99 |
|
1.18 |
53 |
|
0.3 |
23 |
|
0.15 |
15 |
Table 4. Physical properties of fine porcelanite
|
Physical Properties |
Test Result |
|
Absorption% |
32 |
|
Specific gravity |
1.38 |
|
Loose bulk density (SSD) Kg/m3 |
977 |
Table 5. The properties of silica fume
|
Type |
Densified Silica Fume |
ASTM C1240-05 |
|
Form |
Powder |
- |
|
Color |
Gray |
- |
|
Surface area |
2400-2800 m2/kg |
≥15000 m2/kg |
|
SiO2 |
≥90% |
≥85% |
|
SO3 |
≤0.29% |
- |
|
CaO |
≤0.8% |
- |
|
Cr |
≤0.035% |
- |
|
Strength activity index |
106% |
≥105% |
Table 6. Physical properties of SiO2 nano particles
|
Form |
Powder |
|
Color |
White |
|
Specific surface area |
200 m2/k |
|
Diameter size |
4 nm |
Table 7. SiO2 nano particles chemical analysis
|
SiO2 Content Based on Ignited Material |
99.8% |
|
PH |
3.7-4.5 |
|
L.O. I |
≤1% |
Table 8. The details of the mixes
|
Group |
Mixture Name |
Cement (Kg/$\mathrm{m}^{3}$) |
Silica Fume (Kg/$\mathrm{m}^{3}$) |
Nano Silica Replacement (%) by Weight of Cement |
Fine Aggregate |
Coarse Aggregate |
W/P |
Water (kg/$\mathrm{m}^{3}$) |
HRWRA (L/$\mathrm{m}^{3}$) |
||
|
Sand (Kg/$\mathrm{m}^{3}$) |
Fine Porcelinite (%) Replacement by Volume of Sand |
Gravel (kg/$\mathrm{m}^{3}$) |
Coarse Porcelinite Replacement (%) by Volume of Gravel |
||||||||
|
1 |
0.5C |
510 |
90 |
0 |
785 |
0 |
890 |
0 |
0.5 |
300 |
5 |
|
M1 |
510 |
90 |
0 |
706.5 |
10 |
890 |
0 |
0.5 |
300 |
5 |
|
|
M2 |
510 |
90 |
0 |
628 |
20 |
890 |
0 |
0.5 |
300 |
5 |
|
|
M3 |
510 |
90 |
0 |
549.5 |
30 |
890 |
0 |
0.5 |
300 |
5 |
|
|
M4 |
510 |
90 |
0 |
471 |
40 |
890 |
0 |
0.5 |
300 |
6 |
|
|
M5 |
510 |
90 |
0 |
392.5 |
50 |
890 |
0 |
0.5 |
300 |
6 |
|
|
2 |
0.4C |
510 |
90 |
0 |
785 |
0 |
890 |
0 |
0.4 |
240 |
9 |
|
M6 |
510 |
90 |
0 |
706.5 |
10 |
890 |
0 |
0.4 |
240 |
9 |
|
|
M7 |
510 |
90 |
0 |
628 |
20 |
890 |
0 |
0.4 |
240 |
9 |
|
|
M8 |
510 |
90 |
0 |
549.5 |
30 |
890 |
0 |
0.4 |
240 |
10 |
|
|
M9 |
510 |
90 |
0 |
471 |
40 |
890 |
0 |
0.4 |
240 |
10 |
|
|
M10 |
510 |
90 |
0 |
392.5 |
50 |
890 |
0 |
0.4 |
240 |
10 |
|
|
3 |
M11 |
494.7 |
90 |
3 |
785 |
0 |
890 |
0 |
0.4 |
240 |
13 |
|
M12 |
484.5 |
90 |
5 |
785 |
0 |
890 |
0 |
0.4 |
240 |
16 |
|
|
4 |
M13 |
517.6 |
90 |
0 |
0 |
100 |
890 |
0 |
0.4 |
240 |
12 |
|
M14 |
494.7 |
90 |
3 |
0 |
100 |
890 |
0 |
0.4 |
240 |
17 |
|
|
M15 |
484.5 |
90 |
5 |
0 |
100 |
890 |
0 |
0.4 |
240 |
22 |
|
|
5 |
M16 |
517.6 |
90 |
0 |
785 |
0 |
0 |
100 |
0.4 |
240 |
10 |
|
M17 |
494.7 |
90 |
3 |
785 |
0 |
0 |
100 |
0.4 |
240 |
14 |
|
|
M18 |
484.5 |
90 |
5 |
785 |
0 |
0 |
100 |
0.4 |
240 |
18 |
|
2.2 Concrete mixture amount
2.2.1 Mix details
In this search, we made and tried out twenty different mixtures. We divided them into five groups to test them. ACI 237R-07 [20] was used to design a self-compacting concrete mixture for reference. To make LWSSC, they used coarse porcelanite aggregate instead of gravel and fine porcelanite aggregate instead of sand. Table 8 shous the information about the combinations.
2.2.2. Mixing procedure
Before mixing, make sure the inside surface of mixer is dry and too clean. Initially, aggregate (Coarse and fine) is mixed for one minute. Then, the cement and binder materials (silica fume, and nano silica) are blended with the aggregate for one minute. Next step, two-thirds of the water is mixing with mixture and we continue mixing it for two minutes. Then, glenium 51 is blended with one-third of water and added to mixture. At last, the mixing continues for an additional 2 minutes.
2.2.3 Casting and curing of test specimens
To keep the concrete from adhering to the mold once it hardens, it's crucial to clean it well and oil it before pouring the concrete into its. After the molds are filled, a trowel is used to make the top surface even and smooth. Before removing the specimens, they are covered in nylon sheets for 24 hours. This reduces the probability of the drying and prevents cracking. The samples were removed from the molds and submerged in tap water until the testing phase.
2.2.4 Test method
As for the evaluation of fluidity of SCC, Slump flow and T50 test, J-ring test L-Box test [21] were used in laboratory. The test for heated guarded plates is the accepted gold standard for figuring out the flat slab's homogenous insulating material's heat transmission properties. The steady state test protocol has been standardized by ASTM C 177 [22]. The capacity of a material to transfer heat is indicated by its thermal conductivity, often represented by the symbol (k). These properties are measured using the Ahmed technique [19]. Concrete thermal diffusivity was measured using a heating-cooling apparatus [19]. Concrete's specific heat can be determined using a variety of techniques, including electrical and calorimetric approaches. This study makes use of a calorimeter. Concrete using the semi-adiabatic calorimeter approach [19].
3.1 Workability
The workability test result for SCC mixtures is presented in Figures 1, 2, 3 and 4. All of the test results are within specified limits of [21]. It can be inferred from these figures that the utilization of additional fine porcelanite results in a decrease in the workability of SCC mixtures. Two factors are thought to be responsible for this effect: first, the high absorption of porcelanite reduces the amount of water needed to mix the material in order to achieve the necessary workability; second, the laminar form of the fine porcelanite may provide additional challenges for workability. By using HRWRA, the impact of these elements was reduced.
Figure 1. Slump flow test results
Figure 2. T50 test results
Figure 3. L-Box test results
Figure 4. J-Ring test results
3.2 Using hot guarded plate method (HGP) & Lee’s disc method to measure thermal conductivity (k) plate
Figure 5 displays the results of thermal conductivity for saturated surface dry case (SSD) and oven dry case at ages 7 and 28 days using the "HGP" technique. As well as the results of thermal conductivity in oven dry case at ages 28 days using Lee's disc method for all SCC mixes. It is evident that for all SCC mixes (SSD case and oven dry case) at 28 days the results of thermal conductivity are greater than thermal conductivity for mixtures at 7 days. This happens because hydration products are constantly formed, which makes the concrete matrix denser and increases its ability to conduct heat. The thermal conductivity of concrete is higher when it is in a saturated surface dry (SSD) state compared to when it is completely dry. Water contained within the pores of the micro - structure of concrete causes the increase in thermal conductivity. This is true for both 7 and 28 days (see Figure 6). Additionally, using the HGP approach, it displays the proportionate growth in SSD thermal conductivity and oven dry thermal conductivity between the ages of 7 and 28 days. Figures 7 and 8 show that when the replacement % of fine porcelanite aggregate increases, the thermal conductivity for both SSD and oven dry decrease at 7 and 28 days. This behavior happens because the porcelanite aggregate has lots of tiny holes. When the fine and coarse porcelanite aggregate is fully replaced with a water to cement ratio of 0.4, the thermal conductivity of self-consolidating concrete (SCC) decreases because of the pores present in the porcelanite aggregate. Because fine porcelanite aggregate contains fewer interior holes filled with air, which reduce thermal conductivity, the thermal conductivity is higher in the case of fine porcelanite than in the case of coarse porcelanite. Figures 8, 9, and 10 show when the proportion of nano silicarises, thermal conductivity also rises for SCC mixes (SSD and oven dry) at 7 and 28 days. The decrease in accessible pores brought on by a rise in nano silica concentration is the reason for this behavior. It was hardly a noteworthy rise, though.
3.3 Thermal diffusivity and specific heat
The material thermal diffusivity determines the rate at which temperature changes may occur inside a unit mass [23]. The thermal diffusivity for each SCC combination at age 28 days is displayed in Table 9 and Figure 11. It is evident that when concrete's density drops, so does its thermal diffusivity. Thermal diffusivity in the SCC mixture is not greatly increased by adding nano silica. The term "specific heat" refers to the amount of heat required to change the temperature of a given quantity of material by a specific degree [23]. The specific heat for each SCC combination at age 28 days is displayed in Table 9 and Figure 12. It is evident that when concrete's density drops, the specific heat rises. The specific heat of the SCC mixture is unaffected by the addition of nano silica.
Figure 5. Test results for thermal conductivity (k) for every mixture
Figure 6. Results of the thermal conductivity (k) test for each mixture in G1
Figure 7. Test results for thermal conductivity (k) for every mixture in G2
Figure 8. Results of the thermal conductivity (k) test for each mixture in G3
Figure 9. Results of the thermal conductivity (k) test for each mixture in the G4 and 0.4C mixes
Figure 10. Results of the thermal conductivity (k) test for the 0.4C mixture and all mixtures in G5
Figure 11. Oven dry thermal diffusivity at 28 days for all SCC mixtures
Figure 12. Oven dry specific heat at 28 days for all SCC mixtures
Table 9. Specific heat and oven-dry thermal diffusivity for all SCC mixes at 28 days
|
Groups |
Designation of Mixtures |
Density of Oven Dry at 28 Days (kg/m3) |
Thermal Diffusivity of Oven Dry (m2/sec) *10-7 at 28 Days |
Specific Heat of Oven Dry (J/kg.) at 28 Days |
|
1 |
0.5C |
2177.4 |
7.66 |
1066 |
|
M1 |
2145.1 |
7.35 |
1086 |
|
|
M2 |
2115.9 |
7.01 |
1101 |
|
|
M3 |
2085.5 |
6.83 |
1118 |
|
|
M4 |
2059.3 |
6.55 |
1141 |
|
|
M5 |
2028.1 |
6.31 |
1167 |
|
|
2 |
0.4C |
2317 |
9.13 |
971 |
|
M6 |
2287.1 |
8.64 |
992 |
|
|
M7 |
2255.3 |
8.28 |
1008 |
|
|
M8 |
2227.8 |
7.95 |
1030 |
|
|
M9 |
2194.3 |
7.76 |
1059 |
|
|
M10 |
2166.2 |
7.47 |
1074 |
|
|
3 |
M11 |
2323.1 |
9.24 |
962 |
|
M12 |
2327.9 |
9.37 |
955 |
|
|
4 |
M13 |
1985.1 |
5.27 |
1193 |
|
M14 |
1990.7 |
5.39 |
1185 |
|
|
M15 |
1996.2 |
5.46 |
1173 |
|
|
5 |
M16 |
1864.4 |
4.9 |
1274 |
|
M17 |
1869.6 |
5.01 |
1266 |
|
|
M18 |
1872.8 |
5.13 |
1252 |
In this paper, we studied the nano materials and the applications of lightweight aggregates in self-compacting concretes. So, we discuss thermal properties SCC and the fresh properties, based on that, it is concluded that:
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