Due to its self-leveling, low material usage, autoclave-free, low thermal conductivity and light weight, air-entrained concrete is considered one of the most useful porous materials used in modern civil and industrial constructions. Using aerated concrete is a good way to reduce CO2 emissions by reducing the amount of cement used. In addition, the pores in aerated concrete can be used to contain the CO2.
Given the mechanical and morphological properties of conventional aerated concrete, it is crucial to find the perfect concrete mix to create a carbon dioxide-filled aerated concrete brick with comparable or better properties and quality compared to conventional aerated concrete bricks. This research deals with the evaluation of the performance of these special concrete masonry units during tests such as pressure test, water absorption test, field emission scanning microscopy (FESEM), mercury intrusion porosimetry (MIP) and response surface methodology (RSM). The results obtained show that CO2 foamed concrete with a density higher than the Control density can be produced using 0.08 kg to 0.16 kg of foam and 0.20 kg to 0.30 kg of fine aggregate.
Second, CO2 entrained foam concrete with similar or higher compressive strength compared to Control can be produced using 0.08kg to 0.16kg of foam and 0.25kg to 0.30kg of fine aggregate.
- Background of Study
- Problem Statement
- Objectives
- Scope of Study
While cement plays an important role in shaping our built environment, it has an extremely large carbon footprint, accounting for approximately 8% of global carbon dioxide emissions. In addition, the oil and gas industry is also responsible for a large part of the world's carbon dioxide emissions. In order to eliminate or reduce the greenhouse effect, it is crucial to identify as soon as possible possible methods to deal with the emitted carbon dioxide to improve the sustainability of the construction and oil and gas industries.
For a more sustainable use of carbon dioxide gas, foam concrete is a great way to include a huge amount of this greenhouse gas, making it a very useful building material. While cement is the most widely used construction material, its production contributes to approximately 8% of the world's total carbon dioxide emissions. Although several methods were used to try to reduce this greenhouse gas, for example: recycling, use of renewable energy sources, the world's total carbon dioxide emission is still at a record high level.
Studying the compressive strength and water absorption properties of carbon dioxide-filled foamed concrete blocks.
- Aerated Concrete
- Autoclaved Aerated Concrete (AAC)
- Foamed Concrete
- Mechanical Properties of Foamed Concrete
- Carbon Dioxide Emission from Construction and Oil & Gas Industry
- CO 2 Sequestration into Concrete Bricks
- Concrete Carbonation
The most important variables in determining the applicability of foam concrete in its hardened state are its mechanical properties. The volume of foaming agent, by which the amount of air spaces in hardened foam concrete fluctuates, is one of the primary controlling variables in compressive strength. On the other hand, water-cement ratio also affects the compressive strength of foam concrete.
Subsequently, an excessive amount of natural sand will change the pore size in the paste, resulting in a reduction in the strength of foam concrete. This proves that the amount of sand in relation to the binder influences the compressive strength of foam concrete (Y.H. Mugahed Amran, 2015). Finally, when fly ash and silica fume were used as cement substitutes, the compressive strength of foam concrete mix was compromised.
Fly ash was used to replace up to 65% of the volume of foam concrete without loss of strength.
- Project Flowchart
- Casting and Curing of CO2 Filled Foamed Concrete Bricks
- Foam Solution Preparation
- Compressive Strength Test
- Water Absorption Test
- Response Surface Methodology (RSM)
- RSM Variable Proportioning and Materials Quantities
- Field Emission Scanning Electron Microscopy (FESEM)
- Mercury Intrusion Porosimetry (MIP)
On the other hand, CO2-filled foam concrete bricks will also be used for the following tests. Field Emission Scanning Electron Microscopy (FESEM): performed to visualize the topography details of the CO2-filled foam concrete stones. During this process, it is important to continuously mix the foam and concrete mixture until an even mixture is achieved.
Moreover, the inclusion of sodium acetate had no effect on the compressive strength of the material. Crystal formation within the concrete pores, which leads to increased permeability, is confirmed by a scanning electron microscope test result of a 5% sodium acetate sample. The purpose of this test is to measure the ability of CO2-filled foamed concrete to carry loads on its surface without cracking or deflection.
The molding compound will be poured into 15 cm x 15 cm x 15 cm cubes and well vibrated to ensure that there are no voids. The load will operate at a rate of 140 kg/cm2 per minute until the bricks collapse. The compressive strength of the brick can then be obtained by dividing the load at failure by the area of the brick.
Three samples are placed at least 25 mm apart and any drying surfaces in a drying oven. Apart from that, it is also crucial to ensure that the samples have unrestricted access to air. The longitudinal axis of the specimens shall be horizontal and the water surface shall be 25 mm above the top of the specimen.
After 300 minutes, the samples are removed and dried with a towel to remove excess water. For all mixtures produced, the amounts of water and cement were kept constant, as illustrated in Table 3.1 below.
Test Results
- Density of CO 2 Aerated Foamed Concrete Brick
- Compressive Strength of CO 2 Aerated Foamed Concrete Brick
- Water Absorption of CO 2 Aerated Foamed Concrete Brick
In addition to the amount of foam, the amount of fine aggregate also affects the density of CO2 air-foamed concrete blocks. This is because as the amount of fine aggregate increases, the mass also increases, increasing the overall density of the brick. Based on Figures 4.1 and 4.2 above, all mixes except r5 exhibit higher density compared to the control stone, which has an average density of 1.249 g/cm3.
Figure 4.5 shows that the amount of foam in CO2 aerated concrete foam is inversely proportional to the compressive strength. Based on the tread line, the higher the amount of foam, the lower the compressive strength. This is because as the amount of foam increases, the amount of air bubbles will also increase, which then increases the porosity of the stone and thus decreases its compressive strength.
On the other hand, the amount of fine aggregate directly affects the compressive strength of the CO2 aerated foamed concrete blocks. According to the tread line in Figure 4.6, the compressive strength increases proportionally with the amount of fine aggregate used. When the amount of fine aggregate in a stone increases, the air voids in the stone decrease, increasing the compressive strength of the stone.
Based on Figure 4.9, it can be seen from the trend line that the amount of foam used is directly proportional to the water absorption of the bricks. This is because as the amount of foam used in the brick increases, the density of the brick decreases, thus increasing the air voids, which in turn allows the brick to absorb more water. In Figure 4.10, it can be seen from the trend line that the amount of fine aggregate used in the brick is inversely proportional to the water absorption capacity.
This is because the more the amount of fine aggregate used in a brick, the greater the mass and density, which reduces the porosity of the brick, and therefore decreases its water absorption capacity. Based on Figures 4.9 and 4.10, only Mixture r5 has a higher water absorption capacity compared to the control brick, which has an average water absorption of 39.41%.
RSM Modelling and ANOVA Analysis
Therefore, it is safe to say that the generated density, compressive strength and water absorption models all had significant p-values of 0.0415, respectively. The higher the R2 number (on a scale of 0 to 100 percent), the better the model fits the data in general. As shown in Table 4.2, the R2 values for the models made in this study are 49.35 percent, 74.3 percent, and 58.18 percent for the density, compressive strength, and water absorption models, respectively.
Similarly, for the model to fit, the difference between the adjusted R2 and the predicted R2 must be less than 0.2. In addition, the Adequate Precision value (Adeq. Precision) determines the signal-to-noise ratio, with a value greater than 4 being preferred. The adequate precision values for density, compressive strength and water absorption are 7.0875 respectively for the developed models.
These numbers indicate that the signal is strong and that the models can be used to traverse the design space. Ordinary residual plots and actual versus predicted plots are two of the most common model diagnostic tools. The pattern of distribution of data points around the fit lines, as shown in Figures 4.10 to 4.12, suggests that the models are.
RSM Optimization
Mercury Porosimetry Intrusion
Control has the largest total pore volume and largest pore diameter as shown in Table 4.3. On the other hand, when the average pore diameter of a brick increases, the total volume of cement mix in the brick decreases, resulting in a decreased density. This explains how Control has the lowest average density compared to Run 6 and Run 8.
When the three mixes are compared in terms of density, Control has the lowest density, making it the best option. Further, while Run 6 has a higher compressive strength than Control, it also has higher absorbency while having a lower density. Despite having a greater density than the Control, it has a lower compressive strength when compared to the Control.
Therefore, it can be said that Control is the most optimal sample of the three. According to the FESEM test analysis results as shown in Figure 4.19 to Figure 4.22, Run 5 is shown to have the largest amount of air voids, followed by Control, Run 4 and Run 8. However, through this analysis, it is shown that while the Control has the second lowest density, it has the highest compressive strength among the four mixes.
On the other hand, although Run 4 has a higher density compared to Control, its water absorption capacity is also higher. With its lowest density of the four mixtures, namely 1.126 g/cm3, it has the lowest compressive strength and the highest water absorption. Nevertheless, its extremely low compressive strength and high water absorption capacity does not make it the best mix between the other 3.
Finally, although Run 8 has the highest density, its compressive strength and water absorption capacity are below par when compared to the Control. In conclusion, it can be said that the Control is the most optimal specimen out of the four.
Conclusion
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