CHAPTER 4 PERFORMANCE OF COCONUT SHELL AGGREGATE

Transcription

1 74 CHAPTER 4 PERFORMANCE OF COCONUT SHELL AGGREGATE 4.1 GENERAL This chapter discusses the physical and mechanical properties of CSA such as water absorption, specific gravity, grading, fineness modulus, flakiness and elongation index, bulk density, impact resistance, crushing strength, and abrasion value of CSA. The method of reducing the degradability of CSA by quality improvement technique is also analyzed and exhibited. 4.2 COCONUT SHELL The coconut shells were collected from the local oil mills and household wastes from South India, particularly from the Kanyakumari district. They were well seasoned. Seasoning was done by getting rid of the fibers and immersing them in water for 24 hours and then drying them in the air for one day. Coconut shells were sun dried for one month before they were broken into small pieces, which is depicted in Figure 4.1. The seasoned CS is crushed manually by applying a hammer to the required size range. The different sizes of the aggregates were maintained in a range of 4.75 to 12.5mm and 2.36 to 10 mm. CS aggregates were tested for their physical and mechanical properties.

2 75 Figure 4.1 Crushing of coconut shell aggregate 4.3 PHYSICAL PROPERTIES OF CSA The physical properties of coconut shell aggregate are studied as per the Indian standards and the results are compared with conventional aggregates. The test results are summarized in Table 4.1. Table 4.1. Properties of granite aggregate and CS Physical and mechanical properties Granite aggregate of size 20mm CSA of size 4.75 to 12.5mm CSA of size 2.36 to 10mm Water absorption (24h) (%) Specific gravity Impact value (%) Crushing value (%) Fineness modulus (%) Shell thickness (mm) Loose Bulk density (kg/m 3 ) Compacted bulk density (kg/m 3 ) Abrasion value (%) Flakiness index (%) Elongation index

3 Water Absorption of CS Aggregate The measured water absorption of CS was 17.67%. The absorption capacity signifies the porosity of an aggregate. This value implies that the CSA has a high water absorption compared to conventional granite aggregates that usually have water absorption of 1.5%. This high water absorption could be due to the high pore content. Because of the high water absorption, shells may have a chance to absorb water from the concrete mix during the manufacture of concrete. This may be abbreviated by applying the aggregate in SSD condition. The water absorption capacity of CS aggregate was satisfying the limit of absorption capacity of the LWA, that is, 5 20% (ACI Education Bulletin E1-07). Similar results were obtained for other lightweight aggregate OPS which have water absorption of approximately 20% (Shafigh et al 2013a) and volcanic pumices, have values of almost 37% (Hossain 2004). Mannan et al (2006) have reported that the water absorption capacity of OPS aggregate can be reduced by using pre-treatment methods such as 20% PVA solution. This diminished the water absorption of OPS significantly from 23.3 to 4.2% Unit Weight and Specific Gravity of CS Aggregate The average unit weight of CS was 570 kg/m 3 while that of coarse aggregate was found to be 1644 kg/m 3. The percentage of reduction in unit weight of CSA is found to be 65% when compared to conventional aggregate. The unit weight of CS is within the range of 480 to 1040 kg/m 3 (ACI Education Bulletin E1-07). The specific gravity of CS and CA were 1.16 & 2.78 respectively. This figure fall in the range of 1/3 to 2/3 of specific gravity of normal weight aggregate (ACI 213R-87). This meant that CSA can be classed as LWA.

4 Thickness of CS Coconut shells were selected at random and their thicknesses were measured using Vernier calipers at different positions in a shell, and then the average was taken. The thickness of CS varied in the range 3-8 mm. Figure 4.2 shows the CSA of different sizes. Figure 4.2 Different size of CS aggregate Grading of CSA Grading refers to the particle size distribution of a material. The grading is determined by using the codal provision IS 2386 (Part I):1963. Using the sieve analysis test, the particle size distribution was performed and the results are presented in Figure 4.3. The fineness modulus was calculated from the results of the sieve analysis test Fineness Modulus of CSA The fineness modulus of the CS aggregate was found to be 6.56% and this value lies in the limiting values of fineness modulus of conventional aggregates, which is (Shetty 2006). The Fineness modulus of granite aggregate and fine aggregate is 7.68 and 2.8 respectively. This showed

5 Cumulative passing (%) 78 that the concrete produced using CS as coarse aggregate falls in the category of LWC. 100 CS 4.75 to 12.5mm granite aggregate CS 2.36 to 10mm Sieve size (mm) Figure 4.3 Particle size distribution of CS aggregate and granite aggregate 4.4 MECHANICAL PROPERTIES OF CSA From the Table 4.1, the average crushing value (CV) and the average impact value (IV) of the CS were found to be 2.3% and 7.8%, respectively, which satisfies the requirement as per IS (Part IV). However, the crushing and impact value of the granite aggregate were found to be 8.4% and 19.8% respectively. The low value of the IV and CV indicates that CS has good energy absorbing materials. Hence, CS can offer better resistance against crushing and impact, compared to conventional aggregate. When CS is used as aggregate in concrete, the good energy absorbing capacity would be advantageous to structures which are likely to be exposed to dynamic or shock loading (Gunasekaran et al 2011). These results satisfy the requirement as per IS (shall not exceed 30%). According to

6 79 Indian Road Congress, an aggregate having an impact value lesser than 35% can be used as a wearing course and the one having the impact value lesser than 45% can be used as a wearing surface. Hence CSA with an impact value of 10% can be both practiced as a wearing course and wearing surface. 4.5 DURABILITY OF CSA Durability of an aggregate is a measure of its resistance to wear, moisture penetration, decay and disintegration which relies on the hardness of the aggregate. The hardness of CS was measured by using the Los Angels abrasion method. The test outcomes (Table 4.1) showed that the abrasion value is higher in CS than CA which implies that concrete with CS will possess a high level of resistance to wear and is used to produce pavements and floors. Basri et al (1999) have reported that the Los Angeles abrasion value of the OPS aggregate was 4.8%. The average percentage loss in abrasion test on the CS was found to be 1.92%. 4.6 QUALITY IMPROVEMENT OF CSA Need for Quality Improvement of CSA Coconut shell is an agricultural waste which is not commonly used in the construction industry. CS had been shown to be used as building material in the LWC production (Gunasekaran et al 2011). CS aggregate may have a chance to degrade and decompose over a period of time in aggressive environment which is similar to other biodegradable materials. Hence, before using the CS aggregates in the preparation of LWC, it has to be checked against the degradability by placing the aggregate in acid, alkaline and sulphate solution and, if required, proper pre treatments can be given to enhance their properties. So, to check the degradability of CSA, a quality test was performed using preservative technique as similar to OPS aggregate

7 80 (Mannan et al 2006). Although CS had been examined by the previous researches (Gunasekaran et al 2011; Olanipekun et al 2006) to produce LWC, an improvement on the quality of CSA was not done. To check the quality and degradability of well seasoned aggregates under aggressive environment, the CSA was subjected to acid and alkaline solutions and tested their physical and mechanical properties. This was achieved by surface treatment of the coconut shell with chemicals. Then the treated shells were checked for its quality and durability. The best pre treatment was chosen after suitable tests and the concrete prepared is tested for its strength Pretreatment Materials and Methods Pre treatment aims at giving some chemical coating to the aggregate to ensure that proper covering is provided on the top of the aggregate to protect it from any kind of degradation Chemicals for Pretreatment Some of the common wood preservative chemicals are Sodium Dichromate Solution, Poly vinyl Alcohol, Acetic acid Solution, Ferrous Sulphate Solution, etc. (Santos et al 1999) which are listed in Table 4.2. Sodium dichromate (Na 2 Cr 2 O 7 ) is a chemical, which is considered to be used as a good wood preservative. Ferrous sulphate (FeSO 4 ) is the chemical utilized as a lawn conditioner and moss killer. Acetic acid solution is used to reduce the water absorption of wood and rendering the wood dimensionally more stable and extremely durable. Hence aceticacid solution is used for wood preservation. Poly vinyl alcohol (PVA) has excellent film forming, emulsifying and adhesive properties. It has high tensile strength and flexibility properties. It is used for wood preservation. The above mentioned chemicals were taken in various percentages and treatment was given separately.

8 81 Table 4.2 List of chemicals used for pretreatment Sl No. Designation Chemicals 1 A Non treated CS 2 B 1 5% Sodium Dichromate 3 B 2 10% Sodium Dichromate 4 B 3 20% Sodium Dichromate 5 C 1 5% Ferrous Sulphate 6 C 2 10% Ferrous Sulphate 7 C 3 20% Ferrous Sulphate 8 D 1 5% Acetic Acid 9 D 2 10% Acetic Acid 10 E 1 10% Poly vinyl Alcohol 11 E 2 20% Poly vinyl Alcohol Methods for Pretreatment The coconut shell aggregates were prepared by properly removing all fibers from the shell. Then the shells were crushed and sieved. The coconut shell passing the 12.5 mm sieve and retained on 4.75 mm sieve was used up to meet the test requirements. Various methods for pretreatment are dipping (or) immersing, spraying, painting and pressure treatment. In this study, immersing technique was used to treat the CSA. The aggregate was immersed in water for one day and further taken out and dried thoroughly under the sun for another day. This is done to ensure that the chemical is properly absorbed by the dry surface.

9 Pretreatment of CS Aggregates Even though the role of CS in concrete is aimed at waste recycling and cost reduction, the quality of the concrete prepared cannot be compromised. Hence, to achieve good quality, with long term service from CSC, it is required to have a quality control on the CSA since it is an agricultural waste. This concept focused on providing some pretreatment to CSA by some known and available chemicals as similar to wood treatment chemicals (Degroot & Baker 1981). The prepared CS aggregate was taken for pretreatment. The pretreatment adopted in this work was performed by simply dipping or immersing chemical solutions in varying percentages which are proved to be good enough to be considered as wood preserving chemicals. The pretreatment of CSA immersed in PVA solution is presented in Figure 4.4. The CS aggregates were dipped for three days in the chemical solution and then packed out and dried and tested their basic properties like water absorption, impact value and crushing value and the results are shown in Table 4.3. The Figure 4.5 shows the CSA after pretreatment with PVA. Figure 4.4 CSA immersed in PVA soulution for pretreatment

10 83 Figure 4.5 CSA after pretreatment with PVA Table 4.3 Physical and mechanical properties of treated CSA Designation Aggregate Impact Value (%) Aggregate Crushing value (%) Water absorption (%) A B B B C C C D D E E

11 84 Based on the results, the most effective pre treatment chemicals were identified by comparing with treated and non treated aggregates. From the above Table 4.3, it is evident that, even though some chemicals provide good mechanical properties, a lower water absorption value cannot be assured. Since CS is woody in nature, it can absorb water in any adverse condition and possibly be decayed. The treatment with PVA gave promising water absorption values. Hence, from the above Table 4.3, PVA can be proposed as a reliable pre-treatment chemical Observation on Treated and Nontreated CS Aggregate Water absorption The water absorption of treated CS aggregate with various chemicals is presented in Table 4.3. No impressive changes were seen in the pretreated and nontreated CS aggregate, apart from the ones treated with PVA. The water absorption for CS pre-treated with 20% PVA was 10.2%, whereas for the non-treated CS, it was 17.67%. The improvement in the water absorption of treated CSA was due to the formation of thin film coating by PVA which reduced the absorption of the aggregate Impact value The strength of the CS aggregate was attained by means of the aggregate impact value (IV) test and the results are presented in Table 4.3. In all the treated CSA some minor improvement was found in the IV value, whereas CSA treated with 20% PVA showed 42% improvement in the IV when compared to non treated CSA. This showed that the PVA coating enhanced the property of CS aggregate.

12 Crushing value The Table 4.3 summerizes the crushing value (CV) of the CS aggregate treated with various chemicals. CSA treated with 10% and 15% ferrous sulphate solution showed some marginal improvement (6.5%) in their CV compared to non-treated CSA. But their water absorption values were higher than that of non-treated CSA. Thus, no considerable amount of improvements were observed for CV with the different pre-treatments except for the CS treated with PVA Exposure to Aggressive Environment After finding an effective pre treatment chemical for CSA (20% PVA), non-treated and PVA treated CS aggregates were subjected to different aggressive environmental conditions. such as alkaline, acidic and sulphate solutions. Similar to the pre-treatment of OPS aggregate reported by Mannan et al (2006), CSA was immersed in different aggressive solutions for 7 days. The aggressive environment used for CSA was namely (i) 1 mol of sodium hydroxide (NaOH) for alkali attack; (ii) 0.1 mol of sulphuric acid (H 2 SO 4 ) for acid attack, and (iii) 5.2% of magnesium sulphate (MgSO 4 ) for sulphate attack. After subjecting the CS to various adverse environmental conditions, tests like water absorption, aggregate impact value, aggregate crushing value, etc. were found out and the noted changes were registered. The water absorption value increased drastically in all the three environments. Also, there was a notable change in the impact and crushing values. The Table 4.4 shows the properties of treated and non-treated CS after durability test. A comparison was made of PVA treated and non-treated CSA subjected to aggressive environment which is depicted in Figure 4.6 and 4.7.

13 Water absorption(%) Impact and Crushing Values (%) IV of CS CV of CS IV of PVA treated CS CV of PVA treated CS Acid Attack Alkali Attack Sulphate Attack CS subjected to Extreme Environments Figure 4.6 Impact and crushing value of PVA treated and nontreated CSA subjected to extreme environments Water Absorption of nontreated CS Water Absorption of PVA treated CS Figure 4.7 Acid Attack Alkali Attack Sulphate Attack Treated and nontreated CS subjected to extreme environments Water absorption of PVA treated and nontreated CSA subjected to extreme environments

14 87 Table 4.4 Properties of PVA treated and nontreated CSA exposed to different extreme conditions Extreme environment PH Impact Crushing Water Value value (%) value (%) absorption (%) Non treated CSA 1 mol NaOH solution (alkali attack) 0.1mol H 2 SO 4 solution (acid attack) 5.2% MgSO 4 solution (sulphate attack) PVA treated CSA 1 mol NaOH solution (alkali attack) 0.1mol H 2 SO 4 solution (acid attack) 5.2% MgSO 4 solution (sulphate attack) Acid attack on CSA The resistance to acid attack was found out by exposing the coconut shell to 0.1 mol of sulphuric acid for seven days. After 7 days, they were checked for their physical changes and mechanical properties once again to study the influence of acid on the CS. The physical observation showed a slight colour change of coconut shell to light brownish colour as shown in Figure 4.8. The water absorption, impact and crushing value of non treated CSA due to acid attack was 55.2%, 7.1% and 5.25%, respectively, whereas these values were 17.67%, 5.5% and 2.3% for non-treated CSA without subjecting to aggressive environment. The water absorption, impact and

15 88 crushing value of PVA treated CSA due to acid attack was 22.94%, 6.3% and 5.1%, respectively, whereas these values were 10.2%, 3.2% and 2.0% for PVA treated CSA without being subjected to aggressive environment. From the Figure 4.6 and 4.7, it is evident that PVA coated aggregate gave better results than non-treated CSA. Figure 4.8 Coconut shell aggregate subjected to acid attack Alkali attack on CSA Resistance to alkali attack is checked by exposing the coconut shell to 1 mol of sodium hydroxide for seven days which was tabulated in Table 4.4. On alkali attack, the colour of the coconut shell changed dark brown indicating severity of attack or deterioration which is shown in Figure 4.9. The impact value changed to 6.58% from 5.5% indicating a loss in impact value. That is, the impact value decreased 19.6% due to alkali attack. The water absorption and crushing value of non treated CSA due to alkali attack was 60% and 3%, respectively whereas these values were 17.67% and 2.3% for non-treated CSA without being subjected to aggressive environment. The water absorption, impact and crushing value of PVA treated CSA due to acid

16 89 attack was 46.32%, 5.65% and 2.7% respectively. From the Figure 4.6 and 4.7, when comparing the treated and non-treated CSA when subjected to alkaline solution, there was an enhancement in their performance due to the coating of 20% PVA solution. Figure 4.9 Coconut shell aggregate subjected to alkali attack Sulphate attack on CSA Resistance to sulphate attack is determined by exposing the coconut shell to 5.2% of magnesium sulphate for seven days. On alkali attack, the colour of the coconut shell changed to brown indicating deterioration as shown in Figure From the Table 4.4, the water absorption, impact and crushing value of non treated CSA due to sulphate attack was 54.3%, 6.34% and 2.75%, respectively, whereas these values were 25.77%, 4.9% and 2.6% for PVA treated CSA when subjected to aggressive environment. These values showed a better performance for PVA treated CSA when compared to non-treated CSA.

17 90 Figure 4.10 Coconut shell aggregate subjected to sulphate attack. 4.7 CONCLUDING REMARKS In this chapter, physical and mechanical properties of CS aggregate were determined. The degradability of the CSA under aggressive environments was also studied and quality improvement was carried out using pre-treatment which is similar to pretreatment of wood with various chemicals. Based on the results obtained, the following conclusions are drawn Properties of Coconut Shell The water absorption (17.67%) capacity of CS is higher when compared to conventional granite aggregate. Hence CSA must be used in saturated surface dry condition before mixing with concrete. The specific gravity of CS is low (1.16) compared to normal aggregate (2.85) due to its porosity. The low bulk density (570 kg/m 3 ) of CS suggests that LWC can be made by using CS aggregate. CS has more resistance against crushing, impact

18 91 and abrasion, compared to crushed granite aggregate which shows that CSC is suitable for producing pavements. Coconut shell, an agricultural lightweight waste material has been found as a useful building material as a replacement for coarse aggregate Properties of Treated Coconut Shell The CS aggregate is a wood based material and it may have a chance to degrade under aggressive environment. Different pre-treatment methods were used to enhance the quality of CS aggregates. The most desirable pre-treatment was using 20% PVA, giving outstanding results on the resulting concrete properties. The water absorption for CS pre-treated with 20% PVA was 10.2%, whereas for the non-treated CS, it was 17.67%. The PVA solution formed a thin layer on the CS surface and this prevented water from penetrating into the CS. The impact value for CS aggregate pre-treated with 20% PVA was about 58.18% of non-treated CS, indicating good shock absorbing properties without breaking the CS into small pieces.