THE INFLUENCE OF CARBON NANOTUBES ON THE PERFORMANCE OF CEMENT COMPOSITES
The usage of Carbon Nanotubes as an additive in cement composite has been investigated in previous and present research to improve the properties of cement composites in the construction industry. In this report, the performance of carbon nanotubes on the cement composite was presented. Comparison for both compressive and flexural strength of normal cement mortar between reference sample and carbon nanotubes mortar was performed in order to determine the optimum percentage of Carbon Nanotubes. The amount of Polycarboxylate-based Super Plasticizer were used as dispersant agent. The casting of cement mortar mix was done for four (4) batches consist of one (1) batch of reference sample and the other three (3) batch of cement mortar containing various percentage the amount of Carbon Nanotubes ranging from 0.5%, 0.75%, and 1.0% respectively. The samples were tested at 1, 3, 7 and 28 days on its compressive and flexural. Based on the collected data, cement mortar composites was found to enhance the mechanical behaviour of the mortar. The amount 0.5% of Carbon Nanotubes with respect to the weight of cement experienced the highest compressive and flexural strength on 28 days. Though this study has shown the improvement of cement mortar strength by applying an optimum amount Carbon Nanotubes as an additive in cement composites in practical used.
TABLE OF CONTENT
|DECLARATION BY CANDIDATE||i|
|TABLE OF CONTENT||iv|
|LIST OF FIGURES||vii|
|LIST OF TABLES||viii|
|CHAPTER 1: INTRODUCTION|
|1.1||Background of Research||1|
|1.3||Objective of Research||3|
|1.4||Scope of Research||3|
|1.5||Significance of result||4|
|CHAPTER 2: LITERATURE REVIEW|
|2.4.1 Carbon Nanotubes (CNTs)||10|
|188.8.131.52 Single Wall Carbon Nanotubes
|184.108.40.206 Multi Wall Carbon Nanotubes
|2.4.2 Dispersion of Multi Wall Carbon Nanotubes (MWCNTs)||12|
|2.5||Summary of Literature Review||13|
|2.6||Gap of Research||17|
|CHAPTER 3: METHODOLOGY|
|3.4||Preparation of Sample||24|
|3.5||Dispersion of Multi Wall Carbon Nanotubes (MWCNTs)||26|
|3.6||Cement Composite Strength Test||28|
|3.6.1||Compressive Strength Test||28|
|3.6.2||Flexural Strength Test||29|
|CHAPTER 4: RESULT AND DISCUSSION|
|4.2||Compressive and flexural strength||30|
|4.3||Discussion and analysis||35|
|4.3.3||Comparison of result with previous research||38|
|4.4||Optimum ratio of Carbon Nanotubes||39|
|CHAPTER 5: CONCLUSION AND RECOMMENDATIONS|
LIST OF FIGURES
|Figure 2.1||Arrangement of specimens for compressive strength test||6|
|Figure 2.2||Arrangement of specimens for flexural strength test||7|
|Figure 2.3||The solution of MWCNTs + polycarboxylate Super Plasticizer||13|
|Figure 3.1||Research Flowchart||20|
|Figure 3.2||(a) The cubic size (50mm x 50mm x 50mm) and (b) prism size (40mm x 40mm x 160mm) mould used||25|
|Figure 3.3||Sample were left for 24 hours after mould process.||25|
|Figure 3.4||Curing process of samples||25|
|Figure 3.5||Dispersion of MWCNTs flowchart||27|
|Figure 3.6||Ultrasonication process||27|
|Figure 3.7||Compressive strength testing||28|
|Figure 3.8||Tested Sample||28|
|Figure 3.||Flexural strength testing||29|
|Figure 3.10||Tested Sample||29|
|Figure 4.1||Compressive Strength (MPa) vs Curing Period graph (Days)||32|
|Figure 4.2||Flexural Strength (MPa) vs Curing Period graph (Days)||34|
|Figure 4.3||Compressive Strength (MPa) vs Weight Percentage of MWCNTs (wt. %)||36|
|Figure 4.4||Flexural Strength (MPa) vs Weight Percentage of MWCNTs (wt. %)||38|
|Figure 4.5||Comparison of result with previous research||39|
|Figure 4.6||Strength at days 28||40|
LIST OF TABLES
|Table 2.1||Gap of Research||17|
|Table 3.1||The chemical composition of OPC provided by Faculty’s Laboratory||22|
|Table 3.2||Weight percentage of Multi Wall Carbon Nanotubes with respect to weight percentage of cement and curing period for each sample. (Giuseppe, 2011)||22|
|Table 3.3||Properties of Multi Wall Carbon Nanotubes (MWCNTs) used provided by Cahaya Tech.||23|
|Table 3.4||Properties of Polycarboxylate-based super plasticizer (SP) provided by faculty’s laboratory||23|
|Table 4.1||Average value of compressive strength||31|
|Table 4.2||Average value of compressive strength||33|
1.1 BACKGROUND OF RESEARCH
Nowadays, everyone need a shelter place to ensure their safety in daily life such as by having a strong, tough and safe residential house. In order to have this type of building, developer or a contractor must use the quality material that achieve the standard provided by organization such as Eurocode, British Standard and Malaysian Standard. This situation can cause the feelings of desperation for human to develop or improve their quality and strength of material used for build a residential house for community by adding some additive to that material.
Since cement product is the primary material in construction, this material need to be strong or tough enough to prevent the failure of structure such as cracking. In the other word, if the cement based material’s strength in that particular project are not achieve their required standard, the developer or contractor for that project will be face high risk of failure for that project to be fail. Hence, we need to ensure that the material used in that project are achieve the standard.
However, Nanomaterial, such as Carbon Nanotubes (CNTs) can be the one of alternative way to increase the strength and toughness of cement composites. CNTs, are usually in size of hollow cylindrical nanostructure, are generally in size of few nanometer in diameter or even in several microns in length. By having the much more good properties of mechanical, electrical, chemical and thermal than the traditional fibre, this CNTs can be considered as a potential reinforcement in composites (Mohamed et al, 2013). At the same time, the process of dispersion for CNTs must be well conducted in order to enhance the properties of this nanomaterials.
Generally, CNTs can be divided into two types which is Single Wall Carbon Nanotubes (SWCNTs) and the other one is Multi Wall Carbon Nanotubes (MWCNTs). There is a few differences between SWCNTs and MWCNTs which is the looks of this two types CNTs were vary (Makar et al, 2005).
1.2 PROBLEM STATEMENT
The construction industry in Malaysia is expected to increase the country’s economic growth. Nowadays, construction industries was very active in Malaysia. There are many development of project has been planned and conducted throughout this era. This situation has increased the presence of many parties to be the part of material improvement’s industry.
On the positive side, with the increasing number of researcher, there are also many innovation has been made. Many of the researcher has focused on improvement of material quality in construction industry. The quality of the material is be the factor need to be considered in the construction since this factor has been the one of the project failure common caused.
In addition, material that used in the construction project must be in a good behaviour such as high in strength. In last few decades, there are several causes of common defect on construction industry has been studied. Since this defect are able to reduce the strength of structure, there are a few method has been applied to overcome this problem such as by adjusting the admixtures of cement mortar. However, the ability of cement mortar to increase the strength of structure has been questioned.
Hence, there is an idea to improve the strength of cement based material in order to overcome the problem on material strength behaviour. In fact, when the construction project using a good material, it will produce an excellent quality of construction project. For this reason, the use of Carbon Nanotubes (CNTs) as additive in cement composites (mortar) has been applied. By mixing this CNTs with mortar, the performance of mortar being enhanced and will reduce the risk of material defect.
1.3 OBJECTIVE OF RESEARCH
The aim of this study is to know the capability of Multiwall Carbon Nanotubes in mortar mixture. In order to achieve this aim, the specific objectives of this research are:
- To study the compressive and flexural strength of mortar containing Carbon Nanotubes.
- To determine the optimum percentage of Carbon Nanotubes for mortar mixture.
1.4 SCOPE OF RESEARCH
- The type of Carbon Nanotubes is Multi Wall Carbon Nanotubes (MWCNTs) provided by Cahaya Tech. The properties of MWCNTs used as in Table 1.1.
- The variation weight percentage of MWCNTs in mortar composition is 0.5%, 0.75% and 1.0% with respect to the weight of cement.
- The weight percentage of super plasticizer is constant for every each of sample which is 1.1% with respect to the weight of cement.
- Mixing process of MWCNTs and super plasticizer has involved the using of equipment which is ultrasonic device.
- The compressive strength test for sample has been referred to BS EN 12390-3: 2009 while BS EN 12390-5:2009 has been referred for flexural strength test.
1.5 SIGNIFICANCE OF RESULT
This research has been conducted by applying the Nanotechnology in cement mortar to improve its mechanical behaviour. Nanotechnology which are able to be use in design and construct process in construction industry because it can generates many unique products characteristic (Ganesh, 2012). Moreover, the application of nanomaterial are the one of nanotechnology nowadays. The ability of nanomaterials to improve the strength of cement mortar has been proved by Chuah (2014) if the mixture of the nanomaterials with cement mix are well dispersed.
Nanomaterial can be the alternative way regarding to improve the behaviour of material. Uniquely, (MWCNTs), with the material properties in Table 3.3, has been used in this research as nanomaterial that has to be mixed with cement mortar. This research was conducted to study that related to the relationship between the weight percentages of MWCNTs on cement composites. For this reason, the behaviour of cement mortar will be increased with the presence of this MWCNTs.
The variation types of cement mortar additive has attract the interest of researcher around the world to get involved in finding the most efficient additive due to its capability on improving mortar strength. In providing the optimum dosage of additive to the cement mortar mix combining with the proper procedure for samples preparation and samples testing, the strength of cement mortar are able to increase due to the ability of cement mortar additive. In this research, the optimum percentage for Multi Wall Carbon Nanotubes (MWCNTs) and the effect of MWCNTs to compressive and flexural strength of mortar containing MWCNTs was determined. Therefore, the research should be focusing on the basis and thus leading to more additive for cement mortar research results.
2.2 THEORETICAL BACKGROUND
Theoretically, the compressive strength and flexural testing are the main properties of concrete mixture. According to P. Bhatt (2006), the compressive strength of concrete were determined by calculating the stress exerted by the force to the surface area of material as shown in Eq. (1). The unit for stress are N/mm2 or kPa.
- The setting of accelerators or retarders.
- Plasticizing or water reducing for workability enhancement purpose.
- The increasing of resistance to damage from freezing and thawing by adding the air-entertaining admixtures.
- High range water reducing agent or super plasticizer, which can increase the efficiency.
- The increasing of strength by hardening the accelerators.
From the last decades, application of nanotechnology on enhancing or even producing an innovation of product was introduced. Nanotechnology also are able to be use in design and construct process in construction industry because it can generates many unique products characteristic (Ganesh, 2012). In addition, the successful of applying nanotechnology to cement was proved by the research conducted by Lelusz (2014).
The developing of nanotechnology was also increased in ascending rate throughout the years. Since the nanotechnology have the variation of definition, however it is generally can be refer to the understanding and manipulation of matter in Nano sizes which is from 0.1nm to 100 nm (Toma, 2004).
According to Baoguo et al (2014), the potentially new performance of the particles in nanometer scale was attracted higher numbers of scientist. Nano-particles are able to transformed the traditional building materials stronger and harder either it was used as additive or partial replacement depending to the desired special properties. Furthermore, the performance physics mechanical, volumetric stability, durability, sustainability or even the strength of material are the kind of properties that can be improve when the molecular structure was changed by nanotechnology process (Ganesh, 2012). With this in mind, the past research regarding nanotechnology were gave a lot of inspiration and encouragement for a new researcher to produce some innovation in construction materials industry.
Recently, there are many method has been carried out for improving the cement mortar properties. One of the alternative way to improve the cement mortar strength is by adding the supplementary elements into the cement mortar mixtures. There are many research has been conducted by several researcher regarding to improving the cement mortar strength by adding the supplementary nanomaterial element that can act as additive for the cement mortar mixture such as by using Carbon Nanotubes (CNTs). Furthermore, there are several research found that the carbon nanotubes are also considered as an attractive element to as the reinforcement of composite materials (Maria et al, 2010).
2.4.1 Carbon Nanotubes (CNTs)
CNTs are one of the discoveries in the field of nanomaterial, which being composed of tubes with the dimension up to 100 thousand times smaller than the diameter of human hair (Toma, 2004). According to Makar et al (2005), CNTs was discovered in 1991 with a unique form of carbon that has desirable thermal, electronic and mechanical properties. With its extraordinary resistance and strength characteristic, it make this CNTs cannot be compared with any other materials currently known thus gives this materials in high potential in various area in engineering construction industry. In addition, CNTs also can be described as a family of nanomaterials which made up by entirely of carbon. On this family, multi-walled carbon nanotubes (MWCNTs) were had a special interest for the industry and will be used as subject in this paper. The structure of MWCNTs were consisted of multiple layers of graphite superimposed and rolled in on themselves to form a tubular shape.
Moreover, carbon nanotubes can bear torsion and bending without breaking (Makar et al, 2005). Theoretically, the value of CNTs’ Young Modulus are approximately 1TPa which is indicate the elastic behaviour properties of CNTs exceptional the tensile strength is in the range of 20-100 GPa (Rashid et al, 2012). Furthermore, with elastic constant and high strength characteristics, it made CNTs as an additive with high aspect ratio, with the value can achieve until 2,500,000:1 higher than the typical value which is 1000:1. This situation means that the CNTs can be distribute on a much finer in order to fill up the pores in cement matrix (Makar et al, 2005). Since the aspect ratio of CNTs is much higher, using the CNTs are expected to improve significantly the cement mortar stronger and tougher.
This CNTs can be categorized into two major form which is Single Wall Carbon Nanotubes (SWCNTs) and Multi Wall Carbon Nanotubes (MWCNTs). MWCNTs are the nested arrays of SWCNTs since the SWCNTs are the composed of a single graphite rolled into a cylinder with long hollow section (Rashid et al, 2012). Typically, the average diameter of SWCNTs is 1nm whereas for MWCNTs is 10nm. However, in this family of CNTs, the MWCNTs had the special interest to be used in this research with its structural characteristic that consist of multiple layers of graphite superimpose and rolled in on themselves to form of tubular shape.
220.127.116.11 Single Wall Carbon Nanotubes (SWCNTs)
Normally, SWCNTs are in tubes of graphite shape with usually capped at the ends. Based on research conducted by Rashid et al (2012), the SWCNTs can be twisted and it is more pliable rather than MWCNTs. It is also can act as conductor that allow the flow of electric through it. The flow of that electric also can be stepped up or down by varying an electrical field. SWCNTs was divided into three types which are Armchair, Zigzag and Chiral. The properties of this three types were differ according to its character.
18.104.22.168 Multi wall Carbon nanotubes (MWCNTs)
While MWCNTs can be define as a concentric cylindrical graphite tubes made out of the groups of SWCNTs. The strength of MWCNTs are also were higher rather than SWCNTs. The shape of this MWCNTs can be determine by using microscope. Mohamed et al (2013) was state that the MWCNT are able to increase the Young’s Modulus, flexural toughness and flexural strength of cement composites.
2.4.2 Dispersion of MWCNTs
Dispersion of nanomaterial into the solution is one of the most important challenges in nanocomposite research since this nanomaterials like carbon nano filaments are usually entangled and grouped in nest (Vera-Agullo, 2009). Thus, dispersion process would be the importance factor need to be consider in order to provide the stable solution of MWCNTs in an aqueous solution. There are many ways can be used in dispersion of MWCNTs process such as by using ultra sonication device.
Furthermore, the ultra-sonication process can solve the problem on uneven dispersion of CNTs and the tendency of CNTs to aggregation occur (Lelusz, 2014). The several past researched has proved that CNTs were appeared poorly dispersed with forming a large agglomerates and bundles when there are no proper dispersion on CNTs techniques was used.
However, the addition of Super Plasticizer (SP) such as a Polycarboxylate is needed to ensure that solution was effectively mixed and stable for a certain period before it were add up to cement mortar mixture. This SP also was used to facilitating a dispersion of CNTs and to achieve a plastic consistency of mixture. According to Collins (2011), the addition of CNTs with Polycarboxylate SP has affect the increasing the compressive strength of OPC mixture almost 25% with the considerable of water/cement ratio must be greater than 0.35. The Polycarboxylate with the ability to act active as non-polar group to dispersed the non-polar group (CNT) with the polar group (cement and water) and had the possibility to contribute the higher stability and consistency of mix solution. The solution of MWCNTs plus with Polycarboxylate SP was shown in Figure 2.3.
Figure 2.3: The solution of MWCNTs + Polycarboxylate Super Plasticizer
2.5 SUMMARY OF LITERATURE REVIEW
According to the research that has been conducted by Byung et al (2007), Nano Silica (Nano-SiO2) also can be act as replacement or even additive nanomaterial in cement mortar composites. This Nano-SiO2 which is in nano size, are able to fill up the pores or voids to increase the strength of cement mortar. The form of hydrated product that filled the pores and voids, is due to the released of highly pozzolanic activity and calcium hydroxide during the hydration cement process occur. Moreover, the implement of Nano-SiO2 also can be more efficient and effective in pozzolanic reaction than that silica fume. Pozzolanic reaction is an occurrence of chemical reaction caused by the presence of pozzolan in Portland cement. Moreover, porosity values of mortar containing material with pozzolanic characteristics were equal or superior to the cement sample (Morsy et al, 2010).
However, the adjustment dosage of Nano-SiO2 are important and must be accompanied with water and dosage of super plasticizer in order to prevent the excessive self-desiccating and cracking of the cement mortar. The result for compressive strength of Nano-SiO2 mortar cement testing on this researched were higher than the control sample compressive strength. Another observation that has been conduct by Deyu et al (2012) was shown that the strength of mortar can be improve by incorporating of specimen with the Precipitate Silica (PS) with the cement. The research was investigate the strength of mortar by adding the PS that can agglomerate into the large size.
Even though this PS are in nano size and it can fill the void of mortar, there are constraints need to be consider to improve the strength of cement mortar. Theoretically, the higher dosage of PS added to the specimen can cause the microstructure of product more denser through the increment content of calcium silicate hydrate though the agglomerates will become larger size of grains. The research was showed that the enhancement of cement mortar only increase 6.8% with the addition of 1% of PS into specimen for 208 days of curing process. This situation is related to the existing of weak zones and weak agglomerates in the samples that prevent the improving of cement mortar strength when the pores are not fully filled (Deyu et al, 2012).
Providing the Nano-clay as nano material in cement paste sample also can improve the strength of cement mortar. Clay, which also has been used as pozzolanic materials, are able to fill up the void or pores in cement composites and definitely can enhance the strength of mortar. Morsy et al (2010) was conduct a research regarding to the effect of Nano-clay on Ordinary Portland Cement (OPC) paste was prove that the enhancing of cement paste strength can be predict occurred. Nano Meta Kaolin (NMK), are the one of Nano-clay types has founded that have a capability to increase the compressive strength of cement mortar in construction materials industry. From the research, the addition of NMK into cement matrix were increase the dense of cement microstructure when it is filled the voids in cement.
Furthermore, the pozzolanic materials, has caused the pozzolanic reaction of NMK with free lime released during hydration process produced the excess of calcium silicate hydrate (CSH) that gets deposited in pores thus resulting in the improvement of mechanical properties. Hence, the texture of hydrate products was denser and more compact. The researcher was founded that the NMK could improve the strength and microstructure of cement mortar when a small quantity of the nano-particles were uniformly dispersed in the cement mortar, then the hydrate products of cement will deposit on the nano-particles due to their great surface energy during hydration. This phenomenon also has increase the dense of mortar and the cement strength also was improved. However, the binding force between sand with the transmitter substance has an important role on the strength of cement mortar (Morsy et al, 2010).
The past research form Al-Salamia et al (2013) has shown that the ultra-fine size of Nano-Clay were efficiently distributed to fill up the void and therefore increased the strength of cement mortar by replaced the cement with Nano-Clay material. In spite the increment of mortar compressive strength occurred at the early stage, the compressive strength was slowly decrease throughout the samples hydrated at 3, 7 and also 28 days during the research period. This phenomenon were related to the agglomerated of NMK that retard the cement hydration on the cement mortar area. Hence, the weak zones area are easily developed thus the strength of mortar will decreased.
There are also a few research regarding to the using of CNTs as an additive in cement mortar mixed. Lelusz (2014) was doing a research regarding to the influence of CNTs to the compressive strength of cement mortar. The research was founded that the compressive strength of cement mortar was depends on the dosage of CNTs used and the period of curing process. Even though the strength of cement mortar will decrease after 7 days of curing, the strength were increase on the 28 days of curing. This phenomenon were conclude that the cement mortar containing CNTs have gone through the process of curing at least more than 7 days to get the higher compressive strength of cement mortar. However, this research was only used a little amount of wt. % of CNTs which is 0.06% and 0.12%. The time used for ultrasonication of CNTs process also was only 21 minutes.
Sergev et al (2013) also was conducted a research on the effect of MWCNTs to the cement mortar. It was stated that the addition of MWCNTs with SP were increased the compressive strength of cement mortar. The variation of MWCNTs dosage was ranged from 0.01% to 0.25% by weight percentage of cement. However, this research also was used different dosage of SP for each sample and it is resulted that the compressive strength also are vary within the samples. The researcher also were used the dry mixed of MWCNTs with the mineral acid for ultrasonication process. The purpose of using this “unpure” MWCNTs is for comparison with “pure” MWCNTs.
From the comparison of this three type of nanomaterial, the using of MWCNTs as an additive for cement concrete was choose. With the special capability and the extraordinary properties of MWCNTs was made this type of Nanomaterials was selected. Even though the function of this three nanomaterial was same, which is to fill up the void on cement mortar specimen, but there are various of strength result for each samples specimen because the properties of this nanomaterials itself (Lelusz, 2014)
Hence, after the study a few past researched, MWCNTs was elected to be an additive for cement mortar in order to provide a higher compressive strength of cement mortar. Although there are several research had been done by a few researcher regarding the use of MWCNTs as additive, this research was carried out a few different method and result within the others. This research was used a variation of MWCNTs dosage with ranged 0.05% to 1.00% by weight percentage of cement in order to determine the optimum dosage which can generate the height strength of cement mortar for construction industry (Sergev et al, 2013).
2.6 GAP OF RESEARCH
Table 2.1 shows the list of few nanomaterials that have been studied by previous researcher in enhancing concrete performance. The information was collected from reviewing the past research form several researches.
Table 2.1: Gap of Research
|Scope / Objectives||Nanomaterial|
|1||Byung et al.
|2||Deyu et al.
Table 2.1: Gap of Research (Continue)
|Scope / Objectives||Nanomaterial|
|3||Morsy et al.
|| Nano Meta Kaolin
|4||Al-Salamia et al. (2013)||
||Nano Meta Kaolin
|6.||Sergev et al. (2013)||
||Multi Wall Carbon Nanotubes
This chapter shows all related process regarding to the research framework and the research methodology. The process of conducting this research has been described through the conceptual framework.
3.2 RESEARCH FRAMEWORK
This section discussed about the whole process involved in this research. This research were carried out based on the flow chart in Figure 3.1. It is started from identifying the problem and objective, collecting the data, analysing the data and ended with making conclusion for this research.
After 1 day, take out the cube and rectangular sample from the mould. Proceed to curing process by placing the sample in the curing tank.
Preparation of sample:
- Deionized Water
- Super Plasticizer
- Multi Wall Carbon nanotubes (MWCNTs)
Two (2) testing were conducted after 1 day, 3 days, 7 days, and 28 days of curing.
- Compressive strength test
- Flexural strength test
Specimen were mixed by using mechanical mixer.
- Variation of MWCNTs ratio 0.5%, 0.75% and 1.0% with respect to the weight of cement. (G. Ferro et al, 2011)
- The weight percentage of super plasticizer were constant at 1.1 wt% with respect to the wt% of cement.
Result and Discussion
Specimen were poured into mould and was vibrated by mechanical vibrator.
- Cube mould
- Prism mould
Figure 3.1: Research Methodology
The Ordinary Portland Cement (OPC) was used for all specimens as a binder. This OPC was provided by Faculty Laboratory and the chemical composition of that cement as shown in Table 3.1. The ratio of cement for all types of specimen are constant with 1:2 with respect the ratio of water. While the mix proportion of all specimen is 1:2:4 for water, cement and sand ratio. Next, tap water was used in all the samples mixed while the deionized water has used in sonication of MWCNTs process. In addition, Carbon Nanotubes (CNTs) has been used as additive for cement mortar strength improvement. The Multi-Wall Carbon Nanotubes (MWCNTs) type was choose instead of Single-Wall Carbon Nanotubes (SWCNTs) as an additive for all specimens excluded the control sample.
However, the weight percentage of MWCNTs were vary for each specimen according to Table 3.2. The properties of MWCNTs used in this this research was shown in Table 3.3. Other than that, Polycarboxylate-based super plasticizer with specification as shown in Table 3.4 were also used in this research. The consumed amount of super plasticizer in the mortar mixed is constant with 1.1% with respect to weight percentage of cement.
Table 3.1: The chemical composition of OPC provided by Faculty of Civil Engineering
Table 3.2: Weight percentage of Multi Wall Carbon Nanotubes with respect to weight percentage of cement and curing period for each sample. (Giuseppe, 2011)
|Description||Weight percentage of MWCNTs
(wt % cement).
|Control Sample||0.00||1, 3, 7, 28|
|Batch 1||0.50||1, 3, 7, 28|
|Batch 2||0.75||1, 3, 7, 28|
|Batch 3||1.00||1, 3, 7, 28|
Table 3.3: Properties of Multi Wall Carbon Nanotubes (MWCNTs) used provided by Cahaya Tech
Table 3.4: Properties of Polycarboxylate-based Super Plasticizer (SP) provided by Faculty of Civil Engineering
|Visual Appearance||Light Yellow Powder|
|Bulk Density, kg/m3||510
|Drying Loss, %||2.0
℃), at 20% solution
|Solid Content, %||98.0
|Performance||Dosages for P.O Standard Cement (wt% of cement)|
|Cement Paste Flow||≥
|Water Reducing of Mortar||≥
3.4 PREPARATION OF SAMPLE
Once the dispersion of MWCNTs finished, the solution was added into the cement mixture with water cement ratio 0.5. The solution were mixed with the mixture cement proportion with ratio 1:2:4 which is 1 referred to proportion of water, and 2 is referred to cement weight while 4 is referred to sand weight. This mixture process has been conducted by using mechanical mixer. Every batch of sample were separated mix respectively according to the different dosage of MWCNTs.
Then, this sample mixture were poured into the two types of mould with different sizes for different purpose. The first mould is in cubic dimension which are 50mmx50mmx50mm size for compressive strength testing purpose. While the other one is in 40mmx40mmx160 prism mould for flexural strength testing as show on Figure 3.2. All the sample specimens were vibrated on mechanical vibrator in order to reduce the pore in sample that can decrease the strength of samples. Sample were left for 24 hours after mould process as shown in Figure 3.3. After that, the samples was demoulded after 1 day and followed by curing process for 1, 3, 7 and 28 days. All the sample were cured in a curing tank as shown in Figure 3.4. The compressive strength test and flexural strength test were conducted once the curing process for sample are done. However, there are originally control sample containing only SP were created in early stage for both type of testing for purpose of reference sample.
Figure 3.2: (a) The cubic size (50mm x 50mm x 50mm) and (b) prism size (40mm x 40mm x 160mm) mould used
Figure 3.3: Sample were left for 24 hours after mould process
Figure 3.4: Curing process of samples
3.5 DISPERSION OF MULTI WALL CARBON NANOTUBES (MWCNTs)
Dispersion of MWCNTs techniques is very important in order to ensure that the solution in stable before it is added to the cement mortar. This dispersion techniques will effect directly to the mechanical properties of MWCNTs if it is not well mixed. This research was used the dispersion technique as shown in Figure 3.5. The addition of super plasticizer (SP) is needed to stabilize the dispersed solution. The Polycarboxylate types of SP in liquid forms has been used to ease the mixing super plasticizer with cement mix in this research. The efficiency of this Polycarboxylate-based SP has been proved when it is mixed with CNTs powder. Figure 3.6 shown the Ultra-sonication process.
According to Mohamed, et al (2013), the liquid form Polycarboxylate-based SP were mixed with MWCNTs powder first. A ratio of Polycarboxylate-based SP has been fixed as 1.1 weight percentage with respect to the weight percentage cement used. While the dosages ratio of MWCNTs were vary respectively according to the Table 3.2 for each batch of samples. Then, the solution was sonicated for two (2) hours by ultra-sonication devices. This process has been repeated with different dosage of MWCNT with respect to the weight percentage of cement for each batch of samples. All process in samples preparation including ultra-sonication process were using distilled water (Hu, 2014).
Stir the MWCNTs and SP solution.
Use ultrasonic device to mix the solution for two (2) hour. (Mohamed et al, 2013)
Repeat the process with different weight percentage of MWCNTs according to Table 3.2.
Figure 3.5: Dispersion of MWCNTs flowchart
1)MWCNTs + SP 2) Stirring 3) Ultra sonication 4)Sonicated solution
Figure 3.6: Ultrasonication process
3.6 CEMENT COMPOSITES STRENGTH TESTING
There are two testing was conducted on this research in order to determine the compressive strength and flexural strength of cement mortar containing MWCNTs.
3.6.1 Compressive Strength Testing
The compressive strength testing procedure were referred to the BS EN 12390-3: 2009 to determine the strength of the cement mortar. In addition, this testing was used 50mm cubes size sample for testing purpose as shown in Figure 3.2 (a). The mortar cement consists of 1:2:4 mix proportion of water, cement and sand while the water binder ratio is 0.5 (Figure 3.7). Figure 3.8 showed the condition of sample after tested.
Figure 3.7: Compressive strength testing
Figure 3.8: Tested Sample
3.6.2 Flexural Strength Testing
The flexural strength testing procedure were referred to the BS EN 12390-5:2009 to determine the flexural strength of the cement mortar. In addition, this testing was used 40mmx40mmx160mm prism size sample for testing purpose as show in Figure 3.8. The mortar cement cmix proportion is 1:2:4 of water, cement and sand while the water binder ratio is 0.5(Figure 3.9). Figure 3.10 showed the condition of sample after tested.
Figure 3.9: Flexural strength testing
Figure 3.10 Tested Sample
RESULT AND DISCUSSION
This chapter will focus more on the discussion of findings from experimental work toward to achieve the research’s objectives. There are two (2) types of testing has been conducted through this study which is compressive testing and flexural testing. All testing was conducted properly as stated on methodology chapter. In addition, three (3) batch of cement composite samples containing differences weight percentage of MWCNTs as mentioned on Table 3.2 has been used for comparison purpose with control samples. For the control sample, the addition of SP into the cement composite mixture has been applied.
4.2 COMPRESSIVE AND FLEXURAL STRENGTH
After every single of testing completed, all the data were tabulated. All the samples included with the control sample were used the consistent volume and type of Super Plasticizer (SP). It is because by using the same volume and types of SP, the efficiency of using this MWCNTs as an additive in cement based material are more accurate and precise. While for the control sample, there were no MWCNTs was mix in the mixture since this sample acted as reference sample. Theoretically, there are few parameters need to be considered that can affect the result on this research regarding to the type of strength tested.
For the compressive strength testing, all result obtained were tabulate in Table 4.1. There were totally forty eight (48) sample containing different weight percentage of MWCNTs according to the batch has tested. The size of tested sample was 50mm x 50mm x 50mm. As a result, an average of the compressive strength result from the four (4) batch of sample tested with respect to the age of curing were calculated and depicted in form of graph as shown in Figure 4.1. The obtained results indicate the ability of MWCNTs to improve the compressive strength of cement composites mixture compared to the control samples that containing zero percentage of MWCNTs.
Table 4.1: Average value of compressive strength
|Compressive Strength, (MPa)|
(0 wt. % of MWCNTs)
(0.5 wt. % of MWCNTs)
(0.75 wt. % of MWCNTs)
(1% wt. of MWCNTs)
Figure 4.1: Compressive Strength (MPa) vs Curing Period graph (Days)
Figure 4.1 shows the Compressive Strength (MPa) vs Curing Period graph (Days). Sample Batch 1 which is containing 0.5 wt. % of MWCNTs shows that the strength were increase by the time when the curing period are increased. After 28 days of curing, the results showed that there are improvement of sample’s compressive strength occurred with the highest strength of sample was identified at the age of 28 days which is 80.34 MPa. Similar with the sample Batch 1, sample Batch 2 (0.75 wt. % MWCNTs) also have an increment on compressive strength. The higher compressive strength on this batch was at day 28 which is 76.87 MPa. While the highest compressive strength on the sample Batch 3 (1.0 wt. % MWCNTs) was only 60.32 MPa at age 28 days.
Whereas for the flexural strength testing, all result obtained were tabulate in Table 4.2. There were also totally forty eight (48) sample containing different weight percentage of MWCNTs similarly with the compressive strength testing according to the batch has tested. The size of tested sample was 40mm x 40mm x 160mm. As a result, an average of the flexural strength result from the four (4) batch of sample tested with respect to the age of curing were calculated and depicted in form of graph as shown in Figure 4.2. The obtained results indicate the ability of MWCNTs to improve the flexural strength of cement composites mixture compared to the control samples that containing zero percentage of MWCNTs.
Table 4.2: Average value of flexural strength
|Flexural Strength, (MPa)|
(0 wt. % of MWCNTs)
(0.5 wt. % of MWCNTs)
(0.75 wt. % of MWCNTs)
(1% wt. of MWCNTs)
Figure 4.2: Flexural Strength (MPa) vs Curing Period graph (Days)
Figure 4.2 shows that the sample from Batch 3 containing 1.0 wt. % of MWCNTs, indicate the higher value of flexural strength on every stage respectively. It shows that by increasing the value of % MWCNTs in the cement composites, the flexural strength were increased too. After 28 days of curing, the results showed that there are improvement of sample’s flexural strength occurred with the highest strength of sample was identified at the age of 28 days which is 9.21 MPa occurred on sample Batch 3.
Similar with the sample Batch 3, sample Batch 2 (0.75 wt. % MWCNTs) and Batch 1 (0.5 wt. % MWCNTs) were also experienced an increment on flexural strength with the higher rate of increment was shown at the period 3 to 7 days for the all samples. The higher increment rate of flexural strength was shown occurred on the sample Batch 2 which is 53.13%.
4.3 DISCUSSION AND ANALYSIS
All the obtained data were used in order to determine the availability to achieve the research’s objective.
4.3.1 Compressive Strength
As shown in Figure 4.1, variation of testing result was occurred due to the differences of curing period and the composition of MWCNTs between each samples, respectively. It can be seen that at the age of 3 days, all cement composites containing MWCNTs was shown an increasing of the compressive strength compared to the. While the highest improvement in the compressive strength was shown by Batch 1 sample with an increment of 23.29% compared to the control sample.
Furthermore, the composites’ behaviour changes were considered during the observation at the age of 7 days. The highest compressive strength at this age were obtained from sample Batch 2 which is 71.83 MPa with the increasing of 34.99% compared with the control sample. However, the compressive strength of sample Batch 1 and sample Batch 3 show a slightly increased with the small percentage of increment compared to the control sample. It can be said that the rate of strength increment were occurred slowly since the period of curing on this stage was too small. Fathollah (2011) was mention on his research that the curing period could influence the hydration process of cement composites.
After 28 days, all of the samples retrieved their strength values to become higher than the values at age 7 days. Anyhow, sample Batch 1 showed a significant an increase in the compressive strength, specifically 27.80% to the reference samples’ values. Simultaneously with the previous research by Sergev et al (2013), the strength will increase when the age of sample were increased. It was found that all the maximum stress in unit MPa, in every batch, was at age 28 days. Clearly, the compressive strength for each batch was vary due to the MWCNTs content respectively. One of the possible reason for this case was the proper selection of Super Plasticizer. According to Rafat (2013), a proper selection of Super Plasticizer as surfactant were prompted to an extreme increment of sample’s strength due to the low porosity of the sample since the SP was formed as a filler to filled the porosity.
It was observed that the using of MWCNTs with higher wt. % were decrease the compressive strength of sample (Figure 4.3). The compressive strength decreased slightly with an increase in the amount of MWCNTs. For instance, at the age of 28 days, the strength of sample were start to decrease from 83.25 MPa to 76.87 MPa with the increasing of MWCNTs. It is possible that MWCNTs in cement composites would still be agglomerated with such an increase, which induces local stress concentrations that impair strength. Thus, the dispersion of MWCNTs in hardened cement paste should be observed carefully when the amount of MWCNTs increases.
MPA = Mega Pascal (MPa)
Figure 4.3: Compressive Strength (MPa) vs Weight Percentage of MWCNTs (wt. %)
4.3.2 Flexural Strength
Figure 4.4 shows the result for flexural testing were vary due to the different wt. % of MWCNTs between each sample respectively. It can be seen that there were slowly increment of strength at the early age of sample for every batch. However, the improvement of sample’s flexural strength were occurred parallel with the increment of curing period. Relative to the control, flexural strength at the age of 7 days were showed there are increment of strength up to 30.88% and the strength at the age of 28 were 9.81 MPa, with an increment rate of 27.80% compared to control samples.
Simultaneously with the previous research done by Geng et al. (2014), one of possible reason the increment of flexural strength was due to the improvement of the composites microstructure. It was stated that the presence of MWCNTs could affected the occurrence of interfacial interaction between the MWCNTs and cement. In addition, the interaction leads to a strong covalent force on the interface of composites and MWCNTs. As a result, due to the presence of MWCNTs in the composition, the reduction of porosity in cement composite are improved and the pore size are fined. Therefore, the composite were become compacted and certainly, the flexural strength are enhanced.
MPA = Mega Pascal (MPa)
Figure 4.4: Flexural Strength (MPa) vs Weight Percentage of MWCNTs (wt. %)
4.3.3 Comparison of result with previous research
Figure 4.5 were created to compare the result from this research with a few previous research that has been done by Geng et al. (2005), Giuseppec et al. (2011) and Collins et al. (2011). The research’s result done by this three (3) researcher has been used as targeted result in this research. From the comparison graph, Figure 4.4, it showed that Furthermore, it can be seen on this figure that, at the age of 28 days, which is the matured period for cement composites, the sample were experience an increment of strength due to the presence of MWCNTs.
The reason for the increment strength and improvement in mechanical properties of this sample is the packing effect resulting from the small CNTs, acting as ﬁllers, ﬁlling the interstitial spaces in the hydration products thereby increasing cement density. However, according to Collins et al. (2011), there were parameter need to be considered in order to ensure the enhancement of MWNCTs cement composites. The first one is the dispersion method which is it should be conducted properly with the sufficient period of dispersion to ensure the solution is stable for mixing purpose. Figure 4.5 shows the different on dispersion period also would produce the strength of cement composite about 25.36% for compressive strength and 18.94% for flexural strength even the wt. % of MWCNTs for this three research were similar which is 0.5%.
MPA = Mega Pascal (MPa)
Figure 4.5: Comparison of result with previous research
4.4 Optimum ratio of Carbon Nanotubes
Based on the obtained result, Figure 4.6 were plotted to indicate the optimum value of MWCNTs for mortar mixture in order to improve the performance. There were two (2) factor has been considered which is compressive strength and flexural strength.
MPA = Mega Pascal (MPa)
Figure 4.6: Strength at days 28
Figure 4.6 shows that there are gradually slow decrement of compressive strength when the wt. % of MWCNTs were increased. While the flexural strength of the cement composite were experienced the increment of strength due to the increasing of MWCNTs content. However, the optimum value for the ratio of MWCNTs in mixture were define by considering the percentage of strength difference between compressive and flexural strength between each batch. It can be seen that sample Batch 1 has a highest compressive between the samples. At the same time, the highest flexural strength was determined on sample Batch 2.
By considering the percentage of differences between the strength, sample Batch 1 with the 0.5% wt. percentage of MWCNTs, were choosen as an optimum wt. % of MWCNTs with respect to the wt. % of cement since there were only 4% of different strength of flexural between sample Batch 1 and Batch 2. While the different for compressive strength are 7% between that samples. So then with the 83.24 MPa of compressive strength and 7.42 MPa of flexural strength, 0.5 wt. % of MWCNTs was defined as an optimum percentage in cement composites mixture.
CONCLUSIONS AND RECOMMENDATIONS
This chapter focused more on the conclusion of research. Futhermore, the ability of research to meets it objective were defined.
From the experiment results, several conclusions can be drawn related to the objective of study :
- This study indicated that the mortar containing Multi Wall Carbon Nanotubes improved the performance of cement composites in term of compressive strength and flexural strength.
- From the results obtained, it showed that the optimum value for weight percentage of Multi Wall Carbon Nanotubes to be added into the cement composites is 0.5 wt. % of Multi Wall Carbon Nanotubes with respect to the wt. % of cement with the percentage of strength increase of 27.80% for compressive strength and 10.38% for flexural strength compared to the control sample. The optimum value indicates the best volume of Multi Wall Carbon Nanotubes content in cement composites mixture to improve the performance of cement composites. It can be conclude that at 0.5 wt % of Multi Wall Carbon Nanotubes with 1.1% of Super Plasticizer respectively from the other 3 batches of samples.
- This study has identified that the use of Multi Wall Carbon Nanotubes as an additive in mortar mixtures give the positive effect of strength characteristic compared to control mortar enhanced in term of compressive and flexural strength of the mortar. The increased in strengths is mainly due to filling of the pores inside the cement mortar cubes with nano size material. It shows that the research’s objectives were achieved.
Further studies on Carbon Nanotubes cement composites are recommended to investigate the effects of incorporating the nano material to other aspects of concrete/mortar performance. It may be helpful and applicable for future and further research. Several recommendations are suggested for future research as follows:
- It is recommended to conduct the other test on the specimens. The other types of testing that can be performed to get the properties of mortar such as Scanning Electron Microscope (SEM).
- Use the other type of dispersion method with different types of dispersion period to determine the effect of dispersion onto the cement composites.
- Use the variation types of Super Plasticizer to determine the effectiveness of Super Plasticizer on cement cement composites.
- Long term investigations of the properties can also be carried out. For which, investigations are ongoing and will be presented in a future publications.
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