4 1. Overview What is Chip sealing? Comparative Studies and success stories from round the world.Cost effectiveness of chip sealing compared to other preventive maintenance techniques.Chip Sealing is the application of bituminous binder immediately followed by the application of aggregate. Rolling is then performed to embed the aggregate into binder. Depending on the kind of chip seal being applied multiple layers can be applied.The different types of seal coating that could be applied include Single chip seal, multiple chip seal, Cape seals, Fabric seals, thin overlay and scrub seals. Out of all these chip sealing has been proved to be the most durable and most economical.
7 2. Objectives of the Research To evaluate the effectiveness of Idaho’s existing chip seal practice.To identify the reasons for the loss of aggregate from the pavement surface.To study the materials used and suggest the best material to improve the chip seal practice.To evaluate the performance of different kinds of binders.To establish a better rational design method based on experiments performed in this project.
8 3. Scope of Work Determine the properties of aggregate. Utilize the parameters in design calcs.Establish a better aggregate of the six districts of IdahoEstablishing a better rational design method which suites the conditions of Idaho.
9 II. Laboratory Tests Sieve Analysis Flakiness Index Test Loose Unit WeightCleanliness Value TestVialit TestsSieve analysis is a process of grading the aggregate into different sizes. The % aggregate passing was plotted against the sieve size in inches. From the plot obtained which looks like the above graph the sieve size through which 50% of aggregate passes is calculated. This value is the Median Size of the aggregate. The median size of the aggregate combined with the flakiness index value of the aggregate gives the average least dimension of the aggregate, which is an essential property in determining the amount of aggregate and binder through McLeod method.
11 b) Flakiness Index Test Flakiness Index value is an important test that determines weather the aggregate is flaky or round. If the aggregate is flaky, during rolling the aggregate might settle down on its largest cross sectional area possible. This might lead to bleeding. The flakiness index test plate consists of slots for aggregate that passed through one sieve and retained on the next consecutive sieve. Example, the aggregate that passed through ½ inch sieve and retained on 3/8 inch sieve is allowed to pass through the slot 3. the weight of aggregate passing and weight of aggregate retained on the slot 3 were noted. Similarly the weight of aggregate passing and retained through different slots were observed. Flakiness index is the % of the ratio of the total aggregate passing to total aggregate weight.
12 c) Loose Unit WeightWt of Aggregate = lb. Volume of the Container = 0.1 cubic feet. Loose Unit Wt = 9.519/ 0.1 = lb/cubic feetLoose unit weight of the aggregate is a property through which the void ratio can be determined. Void ratio is an important factor in the calculation of amount of binder and amount of aggregate. The aggregate was freely dropped into the container of known volume from a height not less than 2 inches to the brim of the container. The weight of aggregate in the container was noted. Knowing the volume and the weight, the loose unit weight could be calculated.
13 d) Cleanliness Value Test Although Cleanliness index value has no relevance with any design method, it was performed in order to see how effective it is when compared to sieve analysis to know the amount of percentage fines.
14 e) Vialit TestAlso known as the aggregate retention test. The plate used in the test represents the existing surface of the pavement. The surface of the plate was roughened in order to simulate it to the field. The amount of aggregate and binders as per the design method were sprayed and spread respectively. The sample was then rolled with a roller which weighed 25 pounds for ten times. The sample was then cooled and cured at various temperatures depending on the type of analysis. Every district was subjected to various binders, various temperatures and various levels of cleanliness.
15 III. Design Methodologies McLeod Design MethodModified Kearby MethodNew Zealand Chip Seal Design methodUnited Kingdom Road Note 39McLeod method and Modified Kearby method are the most popular among the methods adopted by United States of America. New Zealand Chip Seal design method has been the most successful among all the design methods available. Pavements in New Zealand which have been seal coated, last generally from 10 to 12 years. The road note 39 was similar to McLeod method except that it determined the average least dimension using a nomograph instead of using the formula as in McLeod method. The other methods that are used world wide are AustoRoad chip seal design method and South African TRH-3.
16 1. McLeod Design MethodThe amount of aggregate is determined using the formula:A = 46.8 (1-0.4V) ×H×G×E
17 McLeod Design Method Cont’d Amount of binder to be used is given by:The amount of aggregate is calculated the average least dimension and then the maximum median size and the average of the two is taken as the total amount of binder.
18 2. Modified Kearby Method The amount of aggregate is determined by:Need to explain the design with an example
19 2. Modified Kearby Method The asphalt spread ratio is determined by:
20 3. New Zealand Chip Seals Method The residue asphalt content is determined:Apart explaining with an example also explain the sand patch method which is performed to determine the average texture depth.
22 IV. Results and Discussions Median SizeFlakiness IndexAverage Least DimensionLoose Unit WeightVoid RatioCleanliness Value TestVialit TestDistrict 5 had the least amount of fines and it also had the most round aggregate. A correlation chart between the average least dimension of the aggregate and the aggregate retained in the Vialit test was compared to a correlation chart between a factor M/FI and the weight of the aggregate retained. The correlation of the M/FI value when compared to ALD was much close to 1.
23 1. Median Size of the Particle The median size varied from inches to inches, the lowest for District 2 and the highest for District 1.The void ratio and its correlation with the aggregate retained for each district was subjected to a regression analysis and the results showed a negligible correlation between the two. The use of void ratio in the design method in the design method of McLeod is not properly justified. The flakiness index values varied from 5.44 to 21.08, the lowest for District 5 and the highest for District 2. The median size varied from inches to inches, the lowest for District 2 and the highest for District 1.
24 2. Flakiness Index ValueThe flakiness index values varied from 5.44 to 21.08, the lowest for District 5 and the highest for District 2.The void ratio and its correlation with the aggregate retained for each district was subjected to a regression analysis and the results showed a negligible correlation between the two. The use of void ratio in the design method in the design method of McLeod is not properly justified. The average least dimension of the aggregate for the District 2 was the least and District 6 was the maximum. District 5 had the highest loose unit weight of and District 6 had the lowest ofThe void ratio of District 5 was the lowest and that of District 6 was the highest.
25 3. Average Least Dimension VS M/FI DistrictALDM/FI10.2692.1120.1751.1430.2162.9140.2172.8350.2395.2760.2783.11From the above table, the average least dimensions of the aggregate does not show much variation which corresponds to the aggregate retained on the plate after the test. The M/FI clearly shows the exact correlation with the aggregate retained. The amount of aggregate retained for District 2 was the least and that for District 5 was the highest, and it is the same in the case of M/FI value. The correlation charts that were plotted show the same result. The correlation of ALD with aggregate retained is 0.16 odd compared to the correlation of the M/FI which was 0.91 odd. This shows considerate amount of proof to change the ALD with a value such as M/FI.
26 4. Loose Unit WeightDistrict 5 had the highest loose unit weight of and District 6 had the least ofThe void ratio and its correlation with the aggregate retained for each district was subjected to a regression analysis and the results showed a negligible correlation between the two. The use of void ratio in the design method in the design method of McLeod is not properly justified.
27 5. Void Ratio District Void Ratio 1 0.449 2 0.427 3 0.450 4 5 0.412 6 0.477The correlation of the void ratio when plotted against the aggregate retained in the vialit test had barely any correlation with each other.
28 6. Cleanliness Value Index DistrictCV (%)Height of Sediment (in)187.570.44279.040.81392.210.27490.600.33592.320.26688.660.40
29 7. Vialit Test Results The Vialit Tests Washed Aggregate Retention (%) Unwashed Aggregate (%)95.1389.4495.0491.2992.690.6893.2490.4294.0090.47The percent of aggregate retained in case of samples that were washed and oven dried was 94% and the aggregate retained in case of sample that was unwashed and contained fines was 90.47%. There was a difference of 4 % of aggregate retained due to the presence of fines. The binder used was CRS-2R and the aggregate samples were representative samples of District 5. All the samples were cured and cooled at the room temperature.
30 Vialit Test Results Cont’d Vialit Test for Different BindersCRS-2RCRS-2PCRS-2LCRS-2S89.4491.1987.7388.6491.2993.8093.0689.7090.6892.7890.3789.3290.4792.5989.22The percent of aggregate retained for CRS-2P was higher than other binders CRS-2R, CRS-2S and CRS-2L. The binder CRS-2S had the lowest percent of aggregate retained. There was a difference of about 3% in the amount of aggregate retained when CRS-2P and CRS-2S were used. District 5 unwashed aggregate was used in all cases and the samples were all cooled and cured at room temperature.
31 Vialit Test Results Cont’d Vialit Test Cured at different temperatures-10 Degrees C25 Degrees C40 Degrees C60 Degrees C54.8389.4495.5893.452.9391.2997.1294.655.0690.6895.3292.854.2790.4795.9293.6When the aggregate sample was cooled for one day and then cured at -10 degree centigrade then the percentage of aggregate retained was recorded as the lowest and the percent of aggregate retained was highest when the sample was cured at a temperature of 40 degree centigrade. After 40 degrees if the sample was cured at 60 degrees then the percent of aggregate retained showed a slight decline. The temperature in the summer is generally around 40 degree centigrade and this shows that summer is a right time for executing chip seals, and also the temperature around winter which may be -10 degrees indicates that winter is not an appropriate temperature for chip sealing.
32 7. Vialit Test ResultsThe percent of aggregate retained for district 5 was the highest and the percent of aggregate retained for district 2 was the lowest. This clearly reflects at the aggregate properties of the districts. District 5 aggregate was round and with least amount of fines and the District 2 had most flaky and dusty aggregate.
33 Vialit Test Results Cont’d The amount of aggregate swept for different bindersCRS-2RCRS-2PCRS-2SCRS-2L153.7155.8150.8135.9
34 V. Conclusions and Recommendations In countries such as Australia and New Zealand where seal coating has been very successful, good quality aggregates are transported from places as far away as 500 miles from the job site.
35 1. Conclusions M/FI factor better than ALD Void Ratio and its significance in the design.Effect of fines on the aggregate retentionEffect of different binders on Aggregate retention.
36 Conclusions Cont’d Effect of different aggregate on CRS-2R Effect of temperature of curing on aggregate retention.Cleanliness Value compared to Percentage fines.
37 2. RecommendationsUsing washed aggregate or aggregate with least amount of fines is recommended.Using aggregate which is more round in shape and is uniform in size are preferred.
38 Recommendations Cont’d Quantities of binder and aggregate should be used as per calculated in the design method procedure.Using Digital Imagery technique and Finite element analysis.Wheel Tracking better than dropping a ball.