Evaluation of Saw Dust Ash as Mineral Filler in Asphalt Mixture
CHAPTER ONE
Aim and Objectives
Aim
The aim of this research work is to evaluate the suitability of saw dust ash, as partial replacement for cement, as mineral filler in asphalt production. The aim of the study will be achieved through the following objectives.
Objectives
- To determine the chemical constituents of the material (saw dust ash).
- To determine its suitability as mineral filler in asphalt mixture as stipulated in AASHTO M17 and the Nigerian General Specification for Roads and Bridges (1997), volume II-Federal Ministry of Works.
- To subject its briquette to Marshall Test and compare result of tests with standards.
CHAPTER TWO
LITERATURE REVIEW
Asphalt Concrete
Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac in Great Britain) is a composite material used to form road surface, parking lots and runways. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted. The terms “asphalt (or asphaltic) concrete”, bituminous asphalt concrete and bituminous mixture are typically used in engineering and construction documents, to refer to asphalt. The different types of asphalt mixtures commonly used in pavement construction are hot-mix, hot-laid and cold-mix, cold laid. When used in the construction of highway pavements, it must resist deformation from imposed traffic loads, be skid resistant even when wet, and not affected easily by weathering forces. The degree to which an asphalt mixture achieves these characteristics mainly is dependent on the design of the mix used in producing the material (Garber and Hoel, 2010).
Composition of Asphalt
The main ingredients of asphalt mix are bitumen, and aggregates. Aggregates usually are categorized as coarse, fine, and fillers. Coarse aggregate ranging from 14 mm, 12 mm to 10 mm in sizes and fine aggregates are referred to as sand sizes, while the fines are the fillers (Atkins, 1997).
Bitumen
Bitumens used for road construction are viscous liquid or semi-solid materials consisting essentially of hydrocarbons and their derivatives, which are soluble in trichloroethylene (Brennan and O‟Flaherty, 2002).
There are different types of bitumen such as native asphalt, rock asphalt, tars and petroleum asphalt. The native asphalt is obtained from asphalt in Trinidad and other Caribbean areas. These were used in some earliest pavements in North America. Rock asphalts are rock deposits containing bituminous materials, which have been used for road surfaces in localities, where they occur. Tar bituminous materials are obtained from the destructive distillation of coal (Garber and Hoel, 2010).
The petroleum asphalts are products of the distillationof crude oil. These asphalts are the most common bituminous paving materials in use today. Bitumen is knownby its penetration grades. Their grades and temperature relationships are extremely important in the design of asphalt concrete. Viscosity decreases as temperature increases (Atkins, 1997).
Bitumen used in road works occurs in three forms; penetration-grade or straight run bitumen, cut-back bitumen and bitumen-emulsion. Penetration-grade bitumen is obtained directly from the traditional distillation of the crude petroleum as residue without mixing or refluxing with any diluents or solvent. The fractional distillation processes involve the separation of the different materials in the crude petroleum without significant changes in the chemical composition of each material. Ten grades of bitumen, from 15 pen (Hardest) to 450 pen (softest) are used in pavement materials in the United Kingdom. The harder grades (15 – 25pen) are used in mastic asphalts, the medium grades (35 – 70 pen) in hot rolled asphalts and the softer grades (100 – 450pen) in macadam. (Brennan and O‟Flaherty, 2002).
Cut-back bituments are obtained from the penetration grade bitumen through the addition of suitable diluents in order to reduce its viscosity. The bitumen cut-backs are slow curing bitumen, medium-curing bitumen, and rapid-curing bitumen. They are used mainly in cold-laid plant mixes, road mixes (mixed-in-place), and as surface treatments. Slow-curing (SC) bitumen can be obtained directly as slow-curing straights run bitumen or as slow-curing cutback bitumen by „cutting back‟ penetration grade bitumen with a heavy distillate, such as diesel oil. They have lower viscosities than the penetration grade bitumen and are very slow to harden. Slow-curing bitumen usually are designated as SC-70, SC-250, SC-800 or SC-3000, where the numbers relate to the approximate kinematic viscosity in centistokes at 60oC (1400F). They are used with dense-graded aggregate to provide a surface dressing in warm climate to act as a dust palliative (Garber and Hoel, 2010).
Medium-curing (MC) bitumen is produced by fluxing, or cutting back, the residual bitumen (usually 120 to 150 penetrations) with light fuel or kerosene. The term medium refers to the medium volatility of the kerosene-type diluter used. Medium curing cutback bitumen hardens faster than slow-curing liquid bitumen, although consistencies of the different grades are similar to those of slow-curing bitumen. However, the MC-30 is a unique grade in this series as it is very fluid and has no counterpart in the SC or RC series. The fluidity of the medium-curing bitumen depends on the amount of solvent in the material. MC-3000, for example, may have only 20 percent of the solvent by volume,
CHAPTER THREE
MATERIALS AND METHODS
Description of Materials
The main materials that are required for preparing asphalt mixes are bitumen, aggregate and fines (filler).
The aggregate consists of coarse and fine aggregates. The following are the materials used for this research work.
- Bitumen 60/70 pen grade
- Coarse aggregate (12mm and 10mm)
- Fine aggregate (Quarry fine)
- Ordinary Portland Cement (filler)-control
- Saw dust ash (filler)-investigation
Bitumen
Bitumen was sourced from NNPC refinery, Kaduna through EKSIOGULARRI Construction Company, Sabon Tasha, Kaduna.
Below are the main laboratory tests carried out on the bitumen:
Penetration Test (BS2000, 1983)
Bitumen penetration test is to determine the grade of the bitumen. Samples of bitumen were prepared and cured at a temperature of 25oC for about 45 minutes. Penetration was measured in millimeters where one unit equals 0.1mm. Three penetration tests were conducted and an average was taken to arrive at the penetration of the bitumen. The penetration test gives an empirical measurement of the consistency of a material in terms of the distance a standard needle sinks into the material under a prescribed loading and time. It is also used to indicate the viscosity of asphalt cements to ensure the exclusion of materials with very low penetration value at 25oC (77oF).
Practical Significance: Penetration values below 20 has been associated with bad cracking of the road surfacing while cracking rarely occurs when the penetration exceeds 30 for normal road work. The result of penetration test is presented in Table 3.1a.
CHAPTER FOUR
ANALYSIS, RESULTS AND DISCUSSION
Results
The results of the various laboratory tests conducted in this study are presented and discussed in this section. The specific gravity, aggregate crushing value and aggregate impact value test results of coarse and fine aggregates are presented in Table 4.1.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
Conclusion
Results of tests carried out on saw dust ash to determine its suitability for use as mineral filler show that it has a specific gravity value of 2.20, plasticity index value of 4 with 77.8% passing sieve No.200. These values are within the limit specified in the AASHTO M17, (1986) for mineral filler used in asphalt paving mixture.
Asphalt briquettes were prepared using 100% Portland cement as control. Saw dust ash was used to replace Portland cement at 0% to 100% with an increase of 10% respectively by weight of cement. For 100% Portland cement used as control in the research, 6.0% optimum bitumen content was obtained, maximum bulk density of 2.35g/cm3 was obtained, maximum stability of 11.85kN was attained, voids in total mix was 4.47%, voids filled with bitumen was 75.00% and the value of flow was 3.20mm. These values obtained are in accordance with the Nigerian General Specifications for Roads and Bridges (1997) and the AASHTO M17, (1986) specifications.
At the variation of percentages of Portland cement and saw dust ash at optimum bitumen content of 6.0% as contained in Table 4.5b, as percentage of saw dust ash increases, the value of bulk density of the mixture sample also decreases. At 100% Portland cement and 0% saw dust ash, the stability obtained was 5.00kN. At 10% saw dust ash, the stability value was 7.78kN which satisfies the Nigerian General Specifications for Roads and Bridges (1997) of not less than 3.5kN. Flow value of 2.90mm at 10% saw dust ash satisfies the Nigerian General Specifications for Roads and Bridges (1997). Flow values reduced from 2.90mm to a minimum value of 1.00mm when Portland cement was replaced with 100% saw dust ash. The bulk density generally reduces from 2.33g/cm3 at 100% cement to a minimum value of 2.03g/cm3 at 100% saw dust ash content. Voids in mix increases from 5.28% at 100% Portland cement to 15.06% maximum at 100% saw dust ash. The value of voids in total mix at 100% saw dust ash does not conform to the standard of Nigerian General Specifications for Roads and Bridges (1997). Voids in mineral aggregate also increased from 18.28% at 100% Portland cement to 26.32% at 100% saw dust ash. This value conforms with FMWH (2013) standard of not less than 15%. Voids filled with bitumen decreased from 71.12% at 100% Portland cement to a minimum value of 42.78% at 100% saw dust ash content. The value of voids filled with bitumen at 100% saw dust ash does not satisfy the requirement of the Nigerian General Specifications for Roads and Bridges (1997). The investigated saw dust ash can perform satisfactorily as mineral filler in asphalt mixture at 10%. Hence, it is generally suitable as mineral filler in asphalt mixture.
Recommendations
Based o+n results of the findings from the research, the partial replacement of Portland cement with 10% saw dust ash for use in asphalt production is recommended for use in Nigeria and any other part of the tropics.
From the chemical analysis of the saw dust ash, it was found out that it is a good pozzolanic material in accordance with the requirements in ASTMC 618 (1991).
Saw dust ash has a specific gravity value of 2.20, plasticity index of 4 with 77.8% passing sieve No. 200. These values show that saw dust ash is suitable as mineral filler in asphalt mixture in accordance with AASHTO M17 (1986).
At 10% saw dust ash content, the highest value of stability obtained is 7.78kN, its bulk density is 2.32g/cm3, the voids in total mix is 2.90mm and voids in mineral aggregate is 18.32%. These values are within the limits specified by the Nigerian General Specifications for Roads and Bridges (1997).
The percentage of cement replaced at 10% saw dust ash for asphalt production could be used for pedestrian walkways, out-door paving and Motorcycle Park.
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