IntroductionWith the exponential growth in number of automobiles in India during recent years, the demand of tyres as original equipment and as replacement has also increased. The quantity of scrap tyres produced in India is not exactly available but the increasing trend of use of road transportation will definitely create a problem of disposal in very near future. The total number of registered buses, trucks, cars/jeeps/taxis and two wheelers up to 1997 in India were 0.5 million, 2.25 million, 4.7 million and 26 million, respectively. An annual cumulative growth rate of 8% is expected (Automan, 1999, Statistical Yearbook, 2000). Considering the average life of the tyres used in these vehicles as 10 years after rethreading twice, the total number of waste disposable tyres will be in the order of 112 million per year. Some of the current uses for used tyres in India include tyre rethreading applications, tyre derived fuel for making bricks, making belts for running shafts and making gaskets. This consumes only a fraction of the total tyres discarded every year. The previous common practice of use as fuel is now prohibited by the Indian Government as it causes serious environmental degradation.
The major significance of this research work is to ascertain the replacement of the natural stone aggregate as good quality conventional natural resources like sand, gravel, aggregates etc are depleting very fast with the increase in construction activities in the country and a ban on new quarries are inevitable due to environmental problem. As such, there is a growing search for alternative materials. Keeping in view of the aforesaid reason, a comprehensive experimental investigation was carried out to study the properties of fresh rubberised concrete which in turn provide a useful guideline for its use in concrete.
Ordinary Portland Cement (53 Grade) conforming to IS: 12269 – 1987 was used in this investigation. The specific gravity and specific surface of the cement was found out to be 3.15 and 3350gm2/gm respectively. The normal consistency of the cement as determined by Vicat Apparatus was found to be 29%.
SandFine grained sand of Dihing River near Dibrugarh was used in this investigation. The sand used was medium sand with fineness modulus as determined was 2.35 and specific gravity is equal to 2.62.
|Table 1. Properties of Natural Aggregate|
|Name of the Properties||Value|
|Flakiness Index (%)||1.5|
|Elongation Index (%)||2.75|
|Crushing Value (%)||5.0|
WaterWater used for making the concrete was treated water of potable standard which is available in the concrete testing laboratory of Dibrugarh Polytechnic. The water was further tested in the Environmental Engineering Laboratory and found to conform to potable water standard.
Tyre chipsTyre chips was made by cutting the scrap truck tyres into sizes of 12mm and 16mm and used by mixing them in proportion of 2:3. The cutting of tyre was done by hand by labour with chisels & cutters. The maximum and minimum size of chips was 16mm and 12mm respectively. The specific gravity and water absorption was as determined in the laboratory was 0.96 and 0.45% respectively.
Preparation of Concrete Mixture and Test ProcedureA design mix of M25 grade was used in this experimental investigation. The proportion of the design mix was 1: 0.98:2.1 with water cement ratio of 0.39. The percentage of replacement natural coarse aggregate with tyre chips starts from 10% and ends at 30% in increments of 10%. The tyre chips was prepared by cutting the whole scrap tyre into the sizes ranging from 12mm - 16mm without the use of any equipment or machine. A normal concrete of natural aggregate without any replacement (0%) is used for the purpose of reference. Indian Standard Methods of Sampling and Analysis of Concrete (IS: 1199 – 1959) was used to determine the workability and compaction factor of the fresh concrete. The concrete mix was prepared manually and then poured into the cube mould and compacted with surface vibration. The details of the test series are given in Table 1.
The standard procedure as outlined in Indian Standard Code of practice for slump test was followed in this experimental investigation.
The compacting factor of the fresh concrete was also determined to ascertain the workability of fresh concrete as per IS: 1199 – 1959. The standard apparatus as outlined in I.S code was used is for the determination of Compacting factor of the fresh concrete.
Results and DiscussionProperties of fresh Rubberised Concrete: Based on the test conducted on fresh concrete the workability of the concrete in terms of slump value is tabulated in Table 2. It was observed that the workability of the rubberised concrete increases with the increase in tyre chips content. But the compaction factor slightly decreases with increase in rubber content which is negligible. The increase in the value of slump may be due to the lower water absorption capacity of the tyre chips and slight decrease in compaction factor may be due to the cushioning effect provided by the tyre chips aggregate.
|Table 2: Workability of the Concrete in terms of Slump Value|
|Sl. No||Test Series||Workability (Slump)|
|1||Normal Concrete||85 mm|
|2||Rubberised concrete (10%)||100 mm|
|3||Rubberised concrete (15%)||125 mm|
|4||Rubberised concrete (30%)||150 mm|
|Table 3: Unit weight of rubberised concrete|
|Type of Concrete||Unit Weight (Kg/m3)||% reduction|
|Rubberised (10% replacement)||2350||6|
|Rubberised (20% replacement)||2250||10|
|Rubberised (30% replacement)||2200||12|
|Table 4: Compressive strength of rubberised concrete|
|Type of Mix (1:1.5:3, w/c = 0.45)||Compressive Strength (MPa)|
|Rubberised concrete (10% replacement)||27||32|
|Rubberised concrete (15% replacement)||24||28|
|Rubberised concrete (30% replacement)||18||22|
The compaction factor as determined was found to be in the range of 0.8-0.9 and satisfactory.
Properties of rubberised concrete in hardened state: The properties of concrete prepared with partial replacement of natural aggregate with tyre chips aggregate was tested for its weight and compressive strength and the results obtained are tabulated in Table 3 and 4. The photographic view of the compression testing machine (2500kN) and the tested cube containing tyre chips are shown in Fig.1 and 2.
|Figure 1: Compression testing machine (Capacity 2500kN)||Figure 2: Photograph of the concrete cubes containing tyre chips after compression test|
ConclusionBased on the experimental investigations conducted on rubberised concrete and the subsequent results, the following major conclusions can be drawn.
- The workability of the rubberised concrete increases with the increase in rubber content. This may be due to the lower water absorption capacity of the tyre chips.
- Due to lower water absorption capacity of the tyre chips, the good workability can be achieved with lower water cement ratio and hence may be useful for high performance concrete having low water cement ratio. This property may lead to the reduction in use of plasticizer and super plasticizer in those concrete.
- The use of rubberised concrete may be very much beneficial for a country like India where the problem of scrap tyre disposal is at the very initial stage.
- The rubberised concrete may be useful for the bases of foundation which in turn reduces the use of natural aggregates and hence mining.
- To be used in reinforced cement concrete, it needs further investigations and field tests.
- The unit weight of rubberised concrete decreases with the increase in tyre chips content and hence may be suitable for lightweight construction.
- The compressive strength of the concrete with tyre chips does not show any remarkable decrease upto 15% replacement of natural aggregate with tyre chips.
- It will offer an opportunity for new entrepreneurs to set up industries for production of tyre chips and hence help in saving our environment as well as employment generation.
- The cost analysis reveals that rubberised concrete is cheaper than normal concrete as the scrap tyres are available with nominal cost. There is a direct cost reduction of 10% for optimum replacement percentage of tyre chips.
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