International Journal of Modern Research in Engineering & Management (IJMREM) ||Volume|| 1||Issue|| 10 ||Pages|| 63-74 || November 2018|| ISSN: 2581-4540
Design of Cold Recycled Emulsified Asphalt Mixtures Using Portland Cement as A Partial Replacement of Aggregate Mineral Filler 1
Engr. Abdul Qudoos Malano, 2Prof. Dr. Naeem Aziz Memon, 3 Engr. Gulzar Hussain Jatoi and 4Engr. Abdul Hafeez Memon 1,2,3,4
Department of Civil Engineering, MUET Jamshoro, Sindh, Pakistan.
------------------------------------------------ABSTRACT----------------------------------------------------------Cold Recycling is getting popularity in research sector and construction industries because it overcomes all the issues of Hot Mix Asphalt of more consumption of natural resources, high production energy, central plant recycling, effect of greenhouse gases and non-feasibility in colder regions. In this research study, a cold recycled mixture is designed and compared in terms of mechanical and volumetric properties with control hot mix asphalt mixture, using 60% RAP (reclaimed asphalt pavement) aggregates and 40 % virgin aggregates to fulfill gradation requirements. Asphalt emulsion for cold recycled mixtures is used as a binder with varying five contents (4.3%, 4.8%, 5.3%, 5.8% and 6.3%). Also, a modified cold recycled mixture is prepared at optimum emulsion content of control cold recycled mixture by partially replacing conventional aggregate mineral filler with three different contents of Portland cement (2%, 3% and 4%) of total dry mass of aggregates. Marshall mix design procedure was adopted to calculate the optimum (bitumen, emulsion and filler content) for control hot mix asphalt, control cold recycled mixture and modified cold recycled mixtures respectively. Mechanical properties of each of these mixtures were compared with each other and it was found that modified cold recycled mixtures were better than controlled cold recycled mixture and comparable in properties to hot mix asphalt mixtures and Optimum filler content of Portland cement for modified cold recycled mixture was found to be at 4%.
KEYWORDS: Asphalt Emulsion, Cold Recycling, Hot mix asphalt, Marshall mix design and Marshall mix properties. ----------------------------------------------------------------------------------------------------------------------------- --------Date of Submission: Date, 16 November 2018 Date of Accepted: 21 November 2018 ------------------------------------------------------------------------------------------------------------------------------ --------
I.
INTRODUCTION
HMA is almost world widely used for the construction of flexible pavement because of early developed superior strengths and rapid availability to serve traffic loading soon after the construction. Besides, these merits HMA consumes more natural resources like (Aggregates, bitumen, high energy required for the production etc.) Recycling in case of HMA is done as a central plant recycling in which recycled material is mixed with fresh materials (i.e. Aggregates and bitumen) in the central plant and then transported to the site consuming energy, transport and labor cost. Also, the production of HMA adversely effects the environment due to the emission of toxic greenhouse gases. Due to the additional consumption of natural resources in HMA mixtures a new trend in the research and construction industries is being adopted for other feasible alternatives. Cold Recycling in this aspect is considered to be on the top of list. Cold Recycled Mixtures (CRM) reuse existing pavement materials, which is milled and mixed (with some portion of new aggregates if required) at the place i.e. (In Place Recycling) Unlike HMA. That reclaimed material contains aggregates and bitumen, which means cold recycling saves natural resources of aggregates and also favors less quantity of binder to be used in the mixture. CRM also saves energy required for the production because it is produced at ambient temperature due to the application of binders like Asphalt Emulsion, foamed bitumen and cut back etc. In HMA mixtures heat is required to lower the viscosity of the binder and hence, increase the workability of bitumen to be handled and mixed easily with aggregates and provide proper coating for the strong bonding and ultimately maximum stability. But Binders like Asphalt Emulsion, foamed bitumen and cut back etc. reduce or eliminate the need of heat. Binder like, Asphalt emulsion is a mixture of about 60% bitumen, 38 to 39% of water and 1 to 2% of emulsifier agent. Therefore, water present in emulsion reduces the viscosity of bitumen and eliminates the use of heat for the production. Therefore, it is environmentally friendly it decreases greenhouse effect and facilities the construction in cold regions. Even after all such benefits over HMA, CRM are only used for the small duties works like reinstatement works, repair work, patching works, paving of footpaths and are used for small and medium traffic roads.
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Design of Cold Recycled Emulsified Asphalt Mixtures… This is because of the facts that Cold Mixes are considered inferior in properties than HMA due to Low development of early strength, high porosity or air voids and long time required for curing (i.e. evaporation of water from the CRM and break of emulsion) to achieve full strength for maximum performance. Another hindrance in the adoptability of Cold mixes and CRM is the lack of proper standard design procedure. Presently, number of researches have contributed to use cold mixes and CRM in structural layers and this research also aims to use CRM in high duty pavements i.e. in structural layers in Pakistan. Strength of CRM depends upon the bonding of aggregate and emulsion which can be achieved after the breaking of emulsion which means the evaporation of the trapped water from the mixtures. In order to accelerate the process of breaking of emulsion i.e. evaporation of the water from the mix, additives are to be used which would reduce the porosity, time for curing and help in development of high early strength. Among various additives Portland cement is found out to be more effective as suggested by number of researches. When Portland cement is used in emulsion mixtures, it helps and accelerates emulsion breaking process by utilizing emulsion trapped water for the process of hydration i.e. water loss favors strength of the mix and secondly, Portland cement acts as a secondary binder i.e. additionally it imparts strength to the mixture of CRM and therefore problems of low early developed strength and longtime of curing are mitigated. Therefore, partial replacement of aggregate mineral filler is carried out by ordinary Portland cement used in three contents i.e. (2%, 3% and 4%) by mass of dry aggregates, total 9 specimens are prepared for modified CRM after finding the optimum emulsion content for CRM containing 60% RAP.
II.
LITERATURE REVIEW
In this research, experimental investigation was carried out to estimate and improve the properties of Cold Emulsion Mixtures. Properties of mixture under consideration were repeated load axial creep, indirect tensile stiffness modulus (ITSM) and fatigue. After estimation, comparison of these properties was carried out with control HMA mixture at 2000 MPa targeted (ITSM). The results of tests suggested that even in the absence of cement, when mixtures were efficiently designed and cured showed approximately the same stiffness as HMA mixtures. Further, when 1-2% cement was added in the cold mixtures, its performance was enhanced by means of strength gain, creep resistance and (ITSM). But fatigue performance was yet dominating in HMA mixtures. (I. N. A Thanaya Beng, 2009). This research work was done on the topic of “Characterize Cold Bituminous Emulsion Mixtures Incorporated Ordinary Portland Cement Filler for Local Surface Layer.” Objective of this study was to enhance the properties of Cold Bituminous Emulsion Mixtures (CBEM) i.e. Mechanical and durability properties for the hope of using it as a structural layer. In a trial, conventional filler was replaced by the three percentages of ordinary Portland cement; 0, 50%, and 100%. Mechanical properties of CBEM mixtures were determined in terms of Marshall stability, Flow, ITS and Wheel Track Test and the damage caused due to moisture was evaluated by Marshall Retained Stability. It was evaluated from the results of test that specimens with 100 % addition of OPC as a filler efficiently improved mechanical and durability properties of CBEM and 100 % OPC seemed promising for the use as structural layer, also there was the enhancement of mixtures about 1.9, 1.78, 9.4, 4.85 and 2.6 times than the untreated CBEM. It was also observed that CBEM with 100 % OPC was comparable to HMA and in terms of rutting resistance it performed 6.2 times higher than HMA. (MUSTAFA AMOORI KADHIM, SHAKIR FALEH AL-BUSALTAN AND RAID RAHMAN ALMUHANNA 2016.) “Performance Characteristic of Cold Recycled Mixture with Asphalt Emulsion and Chemical Additives.” The objective of this research was to see the effects of three different chemical additives i.e. Portland cement (PC), Hydrated lime (HL) and combined HL and ground-granulated blast furnace slag (GGBF), and investigation of these effects on (CREAM) by volumetric, strength, moisture susceptibility, rutting and low temperature bending tests along with microstructure images by environmental scanning electron microscope (ESEM). Additionally, A design procedure was proposed for a cold Recycled Mixture based on the selection of (OPWC) and (OEC). Design of cold recycled mixture was carried out by Modified Marshall mix design method. In RAP Premix water was added before introducing emulsified asphalt, then different additives were mixed i.e. CPC content was adapted from 1.5% to 3.5% at 1% intervals and the mass ratio of HL to GGBF was 1: 3. Specimen were prepared by 75 Marshall hammer blows and were cured for 24 hours in the mold and then specimen were cured in an oven at 60 0 C for 72 hours and then cooled at the room temperature for 24 hours. Asphalt emulsion was assumed as 4% for the determination of OPWC, specimens were prepared with premix water contents ranging from 1.5% to 3.5% at 0.5% intervals. OEC was determined using 3.0% to 5.5% range of emulsion content at 0.5% intervals. Results of tests concluded that the proper CPC can improve the ITS and lower the asphalt content, rutting and moisture resistance were proportional to CPC content, for anti-rutting and moisture damaged it was recommended to use CPC content or combination of HL and GGBF. (SHAOWEN DU 2015)
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Design of Cold Recycled Emulsified Asphalt Mixtures… Research was conducted on the “Effect of Portland cement (PC) and lime (HL) additives on properties of cold inplace recycled mixtures with asphalt emulsion.” These properties included, stability, durability, resilient modulus, permanent deformation and tensile strength. Objectives of this research were to the analyze and compare the effects of individual additive i.e. PC and HL on CIR emulsified mix, another objective was the evaluation of optimum PC and HL. Different asphalt emulsion contents and water content were used varying from (2.5 to 4.5) in 0.5% increments. Finally, optimum asphalt and water content were selected as 3.5 % and 3.6 %. It was summarized from the test results that PC and HL addition in recycled mixture enhanced stability, tensile strength, resilient modulus and bulk specific gravity, and decreased air void and flow. Both MSR and TSR outcomes indicated that both additives improved resistance to moisture damage. Creep test indicated that use of additives reduced rut depth. Though, both additives had better results but difficulty of lime slurry production compelled to use Portland cement. (Y. NIAZI, M. JALILI 2008.) In this investigation the effects of cement on Emulsified Asphalt Mixtures (EAM). Objectives of this research were to evaluate the influence of cement on (EAM) and enhance the mechanical properties of the mixtures and hoped to use (EAM) in structural layer. For that purpose, various laboratorial tests were conducted on (EAM) i.e. strength, water damage, temperature susceptibility, creep and permanent deformation. It was shown from results of tests that all the mechanical properties of EAM i.e. temperature susceptibility, water damage, creep, resilient modulus and permanent deformation were improved with inclusion of cement in the mixtures. Further, after curing rate of resilient modulus increased along with cement content up to 6%, creep, permanent deformation and resilient modulus were improved by cement addition and were comparable to HMA. Resilient modulus in HMA decreases with the increase of temperature and same trend is noticed in control EAM but in cement modified EAM, resilient modulus increases with increased cement content and decrease as temperature decreases. Unmodified EAM failed less than 30, 000 cycle this indicated poor resistance to permanent deformation. (Seref Oruc, 2007). This research was carried out to thoroughly analyze the effects of ordinary Portland cement (OPC) on bitumen emulsion mixtures. Dense graded mixtures were used for laboratory tests i.e. modulus of stiffness, resistance to fatigue cracking and permanent deformation. For vivid understanding of enhanced properties of mixtures measurement of rate of coalescence of bitumen droplet with aggregate was carried out and also various blends of emulsion with OPC and hydrated lime were analyzed. DSR tests of various blends were carried out to see the stiffening effects of OPC and HL and also electron microscopy was utilized to study crystalline structures of completely cured samples with and without OPC. It was concluded that the addition of OPC content up to 4% increased all the fore mentioned mechanical properties of the mixtures and those all were comparable to HMA mixes and these were increased due to the effect of hydration of cement, increased rate of coalescence and increased binder viscosity. (Brown and Needham, 2000) In this experimental work mechanical properties of modified emulsion mixtures with ordinary Portland cement (OPC) were investigated. Cold Bitumen Emulsion Mixtures (CBEM) were designed by replacement of filler with OPC and tested for mechanical properties like stiffness modulus, temperature sensitivity and moisture damage. It was concluded from the results of tests that addition of OPC increased the stiffness modulus and the maximum OPC content to be utilized is up to 6% and also faster curing was observed in CBEM mixtures at 6% OPC content. Resistance to water damage was also increased at 6% OPC content. Also, addition of OPC at 3% and 6% content in CBEM showed lower figs of temperature sensitivity than conventional mixtures. (Hayder Kamil Shanbara, 2018) This research was based on producing and characterizing the behavior of cold recycled asphalt pavement with high float emulsion and Portland cement. Objective of this research was to analyze the effect of Portland cement on the mix and determination of optimum emulsion and cement content. Testing was done on samples to evaluate the properties of mixtures i.e. soaked and un-soaked stability and for that samples were prepared at four different contents of Portland cement namely, 0%, 1%, 2% and 3% and at 3 different emulsion contents i.e. 1.5%, 2% and 2.5% and at 2% water. It was concluded from results of tests that both soaked and dry stability of mixtures increased with increase of cement content but under soaked condition effect were more. High dry stability was achieved with cement addition in mixtures with high content of emulsion but in mixes without cement stability decreases with increased emulsion content. Cold Recycled mixture with 2 % water, 2% high float emulsion and 1-2% cement content showed optimum performance in terms of properties than control Cold Recycled mixtures. (Rita I, Musharraf M.Z, Gerald & L. Senkowski, 2001)
III.
MATERIALS USED
Aggregates : The aggregate for this research was obtained from Noori-Abad quarry which is crushed limestone. Reclaimed asphalt pavement (RAP) material was collected from M9-motorway Hyderabad, Pakistan. Three types of mixtures were used for this research. Mix1 which is controlled HMA, Mix2 is CRM which consist of 60% RAP
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Design of Cold Recycled Emulsified Asphalt Mixtures… and 40% virgin aggregates and aggregate above 25mm was removed form RAP. Mix3 is modified CRM in which partial replacement of aggregate mineral filler of CRM is done with Portland cement. Gradation of aggregate for (Mix1, RAP extracted aggregate, and Mix2) is carried out according to ASTM C 117,136 given in the table 1. Physical properties of aggregates (coarse, fine and RAP) are given in table 2. Table 1. Gradation of All the mixtures SIEVE SIZE
Percentage Passing %
Inch
mm
Control HMA Mix
RAP Extracted Aggregate
Control CRM
Midpoint specification
Specification limit
1½“ 1” 3/4” 1/2” 3/8” #4 #8 #50 #200
38.1 25.4 19.1 12.7 9.52 4.76 2.40 0.30 0.075
100 100 96 79.3 63.9 41.8 30.2 7.9 2.8
100 100 84.8 45.5 28.6 7 1.9 0.6 0.3
100 100 91 67 57 41.5 30.5 8 3
100 100 95 --63 42.5 29 8.5 5
100 100 90- 100 --56-70 35-50 23-35 5-12 2-8
Cumulative % Passing
Particle Size Distribution Curve 100 90 80 70 60 50 40 30 20 10 0
Upper Mid point values lower Control HMA RAP Extracted Aggregate 0.01
0.1
1
10
100
Control CRM
Particle Size in (mm) Fig 1. particle size distribution of all mixtures Table 2. Results of various test of Aggregates Test Particulars Los Angeles Abrasion Value % Aggregate impact value % Water Absorption % Specific gravity of Coarse Aggregate Specific gravity of fine Aggregate Specific gravity of RAP Aggregate
Results obtained from tests 21 22.3 1.17% 2.613 2.615 2.498
RAP contained 2.5 % asphalt binder by RAP weight according to the results of Rotavapor extraction test. Properties of aged RAP binder are given in table 3.
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Design of Cold Recycled Emulsified Asphalt Mixtures‌ Table 3. Properties of Extracted Bitumen from RAP Properties Bitumen Content % Penetration at 25 0C, 0.1 mm Ductility at 25 0C, cm Softening point, 0C Specific gravity at 25 0C
Results 2.5 55 101 58 1.04
Bitumen : Bitumen used as a binder for the controlled HMA mixture was of 60/70 Grade which was obtained from Karachi refinery. After various tests, physical properties of bitumen were known which are presented in table 4. Table 4. Properties of Bitumen used in HMA Properties Penetration at 25 0C, 0.1 mm Ductility at 25 0C, cm Softening point, 0C Flash point, 0C Fire point, 0C Specific gravity at 25 0C
Results 66 130+ 46 3190 3630 1.006
Emulsion : In order to determine the type of emulsion to be used in the CRM whether cationic or Anionic emulsion, consideration of aggregate type is important. Aggregate reactivity depends upon proportion and distribution of negative charges. In case of acidic aggregates containing high silicon (SiO2) have negative charge on surface. These negative charged acidic aggregates show strong adhesion bonding with Cationic emulsion. In this research aggregates containing high silicon content were used and for better bonding with aggregates than other types Cationic Slow set emulsion was used namely (CSS-1h). After tests results of various properties are given in the table 5. Table 5. Properties of Cationic Slow Set Emulsion Properties Viscosity, Saybolt-Furol, 25 0C SFS Particle Charge test Specific gravity Residue by Distillation, % Penetration, 25 0C, 100gm, 5s mm Ductility, 25 0C, 5cm/min, cm Solubility in trichloroethylene %
Results 24 Positive 1.0185 60 62 100 98.5
Mineral Filler : Those aggregate materials having particle size less than 75 micron (No. 200 standard sieve) are known as mineral fillers and their function is to fill voids in aggregates and provide stability to the mixture against loads and failures. In this research work partial replacement of conventional aggregate mineral filler with Portland cement was done for modified CRM by three percentages namely (2%, 3% and 4%) by mass of total dry aggregates. Properties of conventional filler and ordinary Portland cement are given in the table 6. Table 6. Properties of Filler used Filler Aggregate Mineral Filer Ordinary Portland cement
IV.
Specific Gravity 2.615 3.11
Research Methodology
Mix1 which is controlled HMA was designed using Marshall mix design procedure for that purpose five varying bitumen contents namely (3%, 3.5%, 4.0%, 4.5% and 5.0%) three replicated of each so, total 15 samples were prepared for HMA. For preparing specimen a mixture of 1200gm containing (aggregates, filler, and bitumen) was taken. Aggregates and filler were heated to a temperature of 175 to 190OC, bitumen was heated to 121 to 125OC
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Design of Cold Recycled Emulsified Asphalt Mixtures‌ and asphalt (aggregates, filler and bitumen) were mixed at the temperature of 154 to 160OC. Mixture was placed in preheated mold having 10 cm dia and 7.5 cm height at the temperature of 138 to 149OC and compacted with 75 Marshall hammer blows on both sides of specimen. After compaction, specimen was placed at room temperature for 24 hours and then volumetric properties of mixture were determined. In order to determine physical properties of specimen (i.e. stability and flow) specimen was maintained at 60OC in water bath for 1 hour and then tested for stability and flow test. Optimum bitumen content (OBC) was determined taking average of three parameters (Maximum stability, unit weight of mix and air voids at 4%). For designing Mix2 which is controlled CRM a blend of 60% RAP and 40% virgin aggregates was mixed to fulfill gradation requirements ASTM C 117,136. Three mix design procedures were reviewed for CRM design namely Asphalt Institutes Manual Series MS (14), 1989, Asphalt Institutes Manual Series MS (19) 1997 and Asphalt Institute Manual Series MS (21), 2007. In order to removing the complexity in the design method, Asphalt Institutes Manual Series MS (14) was followed up to the determination of optimum total liquid content (OTLC) and Variation of Residual Asphalt content (RAC). Following are the steps involved for the determination of OTLC and RAC. Step:1 Gradation of aggregates using asphalt institute manual MS (14), 1989 for Dense Graded Mix. Step:2 Determination of initial residual asphalt content (IRAC) and initial emulsion content (IEC). IRAC is designated as P (% of IRAC) which is calculate by the following empirical formula. P = (0.05 A + 0.1 B + 0.5 C) Ă— (0.7) ----------- (1) Where A = % of aggregate retained on 2.36 mm sieve (8 no. sieve) B = % of aggregate passing 2.36 mm sieve and retained on 0.075 mm sieve and C = % of aggregate passing 0.075 mm sieve. (For Mixtures without RAP) (100− đ?‘&#x;)Ă—đ?‘ƒđ?‘ đ?‘? Pnb = P (For mixtures containing RAP) 100 (Asphalt Institute Manual Series MS (21), 2007.) Where, Pnb = Quantity of new emulsion asphalt to be added as (% of total aggregate weight) Psb = Asphalt content in RAP r = % of new aggregate to be added in CRM Initial emulsion content is calculated by the following equation. IEC = ( P/ X ) [%] ------------- (2) Where X is the asphalt content of emulsion in our case it is 60%. Table 7. Calculation of Pnb and IEC Initial Residual asphalt content (P) % 6.8
RAP %
% of new aggregate (r)
New asphalt emulsion (Pnb) %
Initial emulsion content (IEC)
60
40
5.3
9
Step: 3 Coating Test : For determine % coating based on visual observation specimen of 1200gm at IEC is dry mixed at room temperature with aggregates, RAP, filler and pre-wetted varied amount of water and afterward emulsion content is added and mixed for 2 to 3 minutes to obtain even coating. Different pre-wetted water contents starting from (2%, 2.5%, 3%, 3.5%) by weight of total mix and varied by (0.5%). Pre-wetted water content which gives best coating of emulsion with aggregate surface (with less amount of water) based on the visual observation is considered to be Optimum pre-wetted water content (OPWWC) which is 3% in our case. Step: 4 Determination of optimum total liquid content (OTLC) at compaction level. AT IEC and OPWWC specimen are compacted by 75 blows of Marshall hammer. Specimen at OPW WC are varied at compaction by 1% step by air drying i.e. (8, 7 and 6%) then specimens are tested for dry density. OTLC is consider on that mixture which contains maximum dry density. In our case OTLC was found out at 7%. Step: 5 Determination of variation of Residual Asphalt Content (RAC) Maintaining OTLC value, Residual asphalt content (RAC) was varied two points above and below by 0.5% step. I.e. (4.3%, 4.8%, 5.3%, 5.8% and 6.3%). 3 replicates of each content i.e. total 15 samples were compacted by 75 blows on of Marshall hammer on each side of specimen and then specimen was left in the mold for 24 hours and then it was extruded and placed in oven at 40oC for 72 hours (which is slightly modified from one day to 3 days) because of achieving good strength due to evaporation of water and then it was again maintained at room
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Design of Cold Recycled Emulsified Asphalt Mixtures‌ temperature for 24 hours and finally volumetric properties of specimen were determined and later tests for mechanical properties were conducted. Then using Marshall design procedure optimum residual asphalt content (ORAC) was determined in similar way as optimum bitumen content. For design of Mix3, Mix2 was modified by partial replacement of aggregate mineral filler with three different percentages of Portland cement (2%, 3% and 4%). Rest of the procedure was similar as for above mentioned Mix2.
V.
RESULTS
After conducting the various tests of physical and volumetric properties for all three types of mixes namely; Control HMA, Control CRM at 60% RAP and Modified CRM with the incorporation of cement, results and analysis are discussed in this section. Results of Controlled HMA. : Volumetric properties of mixtures were evaluated after compacting specimen i.e. Unit weight, VMA, VFA, and VTM. Afterwards, Marshall mix design equipment was utilized for calculating physical properties i.e. stability and flow values. Resulted are presented in table 8. The evaluated properties of mixture are also plotted against bitumen content. Table 8. Results of HMA Mixtures Properties Stability (Kgs) Unit weight g/cm2 Flow in 0.01� % V.T.M % V.M.A % V.F.A
Bitumen Content % 3.0 3.5 1304 1456 2.28 2.29 9.1 10.5 8.31 8.1 15.1 14.8 55 62
4.0 1950 2.37 11.3 5.82 15 71
2.5
3.5
4.5
2000 1900 1800 1700 1600 1500 1400 1300 1200
5.5
2.5
3.5
Bitumen Content (%)
14.0 12.0 10.0 8.0 6.0 4.5
5.5
Bitumen Content (%) fig 4. variation of flow values vs bitumen content
Air Voids % (VTM)
Flow Value (0.01")
VT M
16.0
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5.5
fig 3. variation of stability vs bitumen content
Fl ow
3.5
4.5
Bitumen Content (%)
fig 2. variation of unit weight vs bitumen content
2.5
5.0 1608 2.32 13.9 2.38 15.5 83
Stability (Kgs)
2.4 2.38 2.36 2.34 2.32 2.3 2.28 2.26
Stability (Kgs)
Unit weight (gm/cc)
Unit weight (gm/cc)
4.5 1504 2.33 12.8 4.9 15.3 80
12.0 10.0 8.0 6.0 4.0 2.0 0.0 2.5
3.5
4.5
5.5
Bitumen Content (%)
fig 5. variation of % air voids vs bitumen content
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Design of Cold Recycled Emulsified Asphalt Mixtures‌
Voi d s Fi l l ed Wi th Asp h al t (VFA) % 90
15.6 15.5 15.4 15.3 15.2 15.1 15 14.9 14.8 14.7
VFA (%)
VMA (%)
Voi d s In Mi n eral Aggregate (VMA) %
80 70 60 50
2.5
3
3.5
4
4.5
5
5.5
2.5
Bitumen Content (%)
3.5
4.5
5.5
Bitumen Content (%)
fig 6. variation of VMA vs bitumen content
fig 7. variation of VFA vs bitumen content
Fig 2. shows relationship between unit weight of compacted specimen vs bitumen content and it can be observed that unit weight values increase linearly with the increasing bitumen content up to 4% and maximum unit weight observed is 2.37. Later beyond 4% content values of unit weight decrease. First rise of the curve is due to the reduction of the air voids in the mixture and ultimately the reduction in the volume of the mixture and therefore unit weight increases. Beyond optimum point excessive amount of bitumen fills the voids of mineral aggregates with the bitumen and thereby bleeding of the mix increases and the sliding of the particles reduces unit weight. Fig 3. shows the relationship of stability (Kgs) with bitumen content and it can be seen that stability increases with increased bitumen content and maximum stability values of 1950 kgs is achieved at 4% bitumen content. Later, further increased bitumen content decreases stability value. Up to the optimum bitumen content point increasing bitumen favors better coating and ultimately increasing bonding and stability of mix and after optimum point excessive bitumen content causes bleeding of bitumen and reduce voids of mixture i.e. resulting in the lower stability value. Fig 4. shows Flow relationship vs bitumen values bearing liner relationship with bitumen content as it can be seen from the above fig it linearly increases with increased bitumen content. Maximum flow value is 14 at 5% content. This linear trend is due to the plastic deformation of the mixture at the failure point and it increases the segregation of mixture with increasing bitumen content. Fig 5. shows variation of air voids with bitumen content and it can be seen that air voids linearly decrease with increased binder content. 4% air void is achieved at 4.7 % binder content. Air voids in the mineral aggregate decreases with the increasing bitumen content because the voids of aggregates get filled more with the bitumen content and thereby reducing air voids. Fig 6. shows variation of Voids in mineral aggregate VMA with bitumen content. It can be observed that at 3.5 % binder content VMA is minimum and later VMA linearly increases with binder content. Fig 7. shows relationship of VFA with bitumen content. It is clear from the above graph that % of VFA increases continuously as bitumen content increases. Void in mineral aggregate by increasing bitumen content reduce the voids proportion filled by air and thereby increasing % VFA. Based on above results, determination of optimum bitumen content (OBC) is carried out by taking average of three bitumen content i.e. at maximum stability, at maximum unit weight and at 4% air voids. 4+4+4.7 OBC = , 3
OBC = 4.23 % Table 9. Results of Various Properties at OBC Properties Stability (Kgs) Unit weight (gm/cc) Flow (0.01�) VTM (%) VMA (%) VFA (%)
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OBC = 4.23 % 1750 2.36 11.9 5 15.2 76
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Design of Cold Recycled Emulsified Asphalt Mixtures‌ Results of CRM: Applying the same testing procedure for the calculation of volumetric and physical properties of Cold Recycled mixtures (CRM) as for HMA mixtures mentioned above. Table 10. Shows the results of CRM properties at varying emulsion content. After obtaining all the properties of CRM i.e. volumetric and physical properties graphs are plotted for each property against varying emulsion content. Table 10. Properties of CRM Properties Stability (Kgs) Unit weight g/cm2 Flow in 0.01� % V.T.M % V.M.A % V.F.A
Emulsion Content % 4.3 4.8 5.3 5.8 760 867 1000 912 2 2.1 2.2 2.16
6.3 804 2.12
2.5 16.3 21.4 34.1
4.8 8.8 21.9 65
3.2 11.5 17 46
3.9 6.6 18.1 61.5
4.3 7.7 20 63.3
Stability (Kgs)
Marshall Stability (Kgs) 1050 1000 950 900 850 800 750 700 650 3.8
4.8
5.8
6.8
Emulsion Content (%)
fig 8. variation of stability vs emulsion content
Unit Weight (gm/cc)
Unit Weight (gm/cc) 2.23 2.18 2.13 2.08 2.03 1.98 3.8
4.8
5.8
6.8
Emulsion Content (%) fig 9. variation of unit weight vs emulsion content
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Flow (0.01")
Voids in total mix (VMT) % Air voids (%)
Flow value
5 4 3 2 3.8
4.8
5.8
19.0 14.0 9.0 4.0
6.8
3.8
4.8
Emulsion Content (%)
6.8
Emulsion Content (%)
fig 10. variation of flow vs emulsion content
fig 11. variation of air voids vs emulsion content
Voids in Mineral Aggregate (VMA) %
Voids filled with asphalt (VFA) %
23.0 21.0 19.0 17.0 15.0
70
VFA (%)
VMA (%)
5.8
50 30
3.8
4.8
5.8
6.8
3.8
4.8
5.8
6.8
Emulsion Content (%)
Emulsion Content (%)
fig12. correlation b/w VMA vs emulsion content
fig 13. variation of VFA vs emulsion content
Fig 8. shows stability values linearly increasing with emulsion content up to 5.3% content and at this content maximum stability of 1000 kgs is achieved and beyond 5.3% emulsion content stability values linearly decrease with increased emulsion content. Fig 9. shows relationship between unit weight and emulsion content. It can be analyzed from the graph that unit weight is linearly increasing with increasing emulsion content up to 5.3% content and beyond this content further increase of emulsion content decreases unit weight value. Maximum value of unit weight observed is 2.2 gm/ cm3. Fig 10. shows linear increased trend of flow values with varying emulsion content and it can be seen that maximum flow value is achieved is 4.8 at 6.3% emulsion content. Fig 11. shows variation of % air voids with emulsion content and air voids linear decrease with increased emulsion content up to 5.3 % content and further increase of emulsion content increases air voids. But in actual increase of emulsion content should linear decrease air voids. Fig 12. shows that VMA linear decrease up to 4.8% emulsion content and further increase of emulsion content increases VMA. Fig 13. show relationship b/w VFA and emulsion content. It can be seen from above graph that VFA value increases with increasing emulsion content and Maximum value of VFA is 65 % achieved at 6.8 % emulsion content. At Optimum Emulsion content (OEC) or Optimum residual emulsion content (OREC) i.e. 5.3 % values of all the properties are already mentioned in table 10. Results of Modified CRM Table 11. Properties of Modified CRM Properties Stability (Kgs) Unit weight g/cm2 Flow in 0.01� % V.T.M % V.M.A % V.F.A
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At Optimum Emulsion Content (OEC) = 5.3 % 2% OPC 3% OPC 1174 1260 2.140 2.148 3.2 2.8 9.19 8.85 20.33 20.03 54.78 55.80
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4% OPC 1300 2.156 2.2 8.51 19.73 56.85
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Design of Cold Recycled Emulsified Asphalt Mixtures‌ From the above results of table 11. it can be analyzed that the addition of Portland cement follows a linear regression with the values of Stability, unit weight and VFA by increasing the content of cement from 2% to 4% this is due to the fact that increasing content of cement makes strong bonding due to the hydration process of the cement and further increasing hydration process utilize water present in emulsion and thereby breaking process of emulsion is accelerated and both these process results increasing stability, unit weight and further increasing cement content reduce air trapped in void of mineral aggregate and thereby increases VFA. Further, increasing cement content reduces the properties of mix i.e. Flow value, VTM and VMA. Increasing cement content from 2% to 4% fill the voids of aggregates and reduce trapped air thereby it reduces air voids of mix, flow value is the plastic deformation of mixture which is reduced due to the increasing cement content because cement adds rigidity and thereby flow deformation is reducing. Also, at 4% content of cement, stability and unit weight are found maximum so, the optimum content Portland cement to be used in the design mix is at 4%. After analyzing all the three types of the mixtures i.e. HMA, CRM and Cement modified CRM, three main properties of the mixtures i.e. Stability, unit weight and air voids are compared with each other. Mixture which is having greater value of stability, unit weight and minimum 4% value of air voids is considered to be better than other mixtures. HMA mixtures having stability value of 1750 kgs, unit weight of 2.36 gm/cc and 5% air voids at 4.23% optimum bitumen content. Whereas, in CRM at 5.3% optimum emulsion content stability is 1000 kgs, unit weight is 2.2 gm/cc and air voids are 6.6% and finally for modified CRM at 5.3% optimum emulsion content and 4% optimum filler content of Portland cement, stability achieved is 1300 kgs, unit weight is 2.16 gm/cc and air voids are 8.5%. It is clear from the above results that though HMA mixtures are rich in terms of properties than CRM and modified CRM, but results of CRM and modified CRM mixtures are comparable to HMA mixtures. But due to the more energy consumption requirement for the production, adverse environmental impacts and higher construction cost, HMA mixtures are not feasible. Whereas cold recycled mixtures are cost effective, saves natural aggregate resources, lowers binder requirement due to the utilization of aged binder and also, it is environmentally friendly. Further, cement modified cold recycled mixtures exhibits more increased strength due to the hydration of cement, it mitigates the lower early strength development problem by accelerating the breaking process of emulsion and it also, ensures the rapid availability of the pavement to serve traffic loading. However, problem of more air voids can be mitigated by heavy compaction i.e. applying 150 blows per face of specimen [1,10 and 11].
VI.
CONCLUSION
Following conclusions are drawn from this research based on experimental works on volumetric and physical properties of mixtures. 1- Cold Recycled Mixtures (CRM) favor less consumption of natural resources, save budget and are environmentally friendly. Also, CRM are equivalent in strengths and durability as HMA. i.e. Cold Recycled Mixture (CRM) can be used for high duty pavements. 2- CRM based on above mentioned physical and volumetric properties are comparable to HMA mixtures, as it is evident from the results that CRM and modified CRM are almost fulfilling all the requirements of Marshall mix design procedure for heavy traffic. i.e. Stability requirement in design is 815 kgs, achieved in CRM is 1000 and in modified CRM is 1300 kgs. Therefore, Modified CRM are preferred over HMA and CRM. However, air voids are achieved more than 4% so this problem as suggested by [1,10 and 11] is mitigated by heavy compaction (i.e. 150 blows per face of specimen). 3- Further, the issues of CRM regarding gaining low early strength and long time required for curing are mitigated by the addition of Portland cement as partial replacement of aggregate mineral filler and it was found that optimum filler content of Portland cement was found out to be at 4% by weight of dry aggregates of mixture. Recommendation 1- This research is based on materials and region of Hyderabad, Sindh, Pakistan. Further it can be conducted in other areas of the world. 2- This research utilizes only the determination of volumetric and physical properties of the mixtures. Further, performance-based properties can be evaluated. 3- Marshall mix design procedure was adopted for this research. further, this research can be conducted on Vheem and performance-based super-pave mix design method.
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