MOISTURE CONTENT EFFECT ON PERMANENT DEFORMATION BEHAVIOUR OF UNBOUND GRANULAR MATERIALS

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 10, October 2018, pp , Article ID: IJCIET_09_10_184 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed MOISTURE CONTENT EFFECT ON PERMANENT DEFORMATION BEHAVIOUR OF UNBOUND GRANULAR MATERIALS Ali Alnedawi*, Kali Prasad Nepal and Riyadh Al-Ameri School of Engineering, Deakin University, Geelong, Australia Corresponding author* ABSTRACT The performance of unbound granular materials is generally assessed by their strength, modulus, and resistance to breakage. The mechanical properties of the unbound granular materials are not considered in most of the specifications of the local pavement base materials such as Vic Roads. Moreover, there is a little information about the effect of the local unbound granular materials properties on the permanent deformation due to the complexity of the materials (i.e. nonlinear) and difficulties to conduct long term laboratory permanent deformation test. Thus, this study aims to test the effect of the moisture content on the permanent deformation of the local base materials under repeated loads. Three different samples prepared over three different moisture contents were tested in the laboratory using a repeated load triaxial test. The results showed that as soon as the moisture content increases the permanent deformation of unbound granular materials also increases. When the moisture content was above the optimum (+OMC), a dramatic collapse is noticed in the permanent deformation resistance of B1, B2 and G1 respectively. Whilst, a high resistance to permanent deformation was noticed when samples prepared at a moisture content below the optimum (-OMC). The regression analysis showed that when the moisture content was below the optimum, low values for parameter c and B, and high values for parameter S are observed, except for sample G1. It was also concluded that the investigated regression model is material dependent due to the high-observed quality of fit for sample G1. Key words: flexible pavement; unbound granular materials; repeated load triaxial test; permanent deformation; constitutive models; moisture content Cite this Article: Ali Alnedawi, Kali Prasad Nepal and Riyadh Al-Ameri, Moisture Content Effect On Permanent Deformation Behaviour Of Unbound Granular Materials, International Journal of Civil Engineering and Technology, 9(10), 2018, pp editor@iaeme.com

2 Ali Alnedawi, Kali Prasad Nepal and Riyadh Al-Ameri 1. INTRODUCTION The unbound granular materials (UGMs) are materials consist of different graded particles without binder, workable and able to be compacted, such as soil aggregate, gravel, crushed rocks, and recycled concrete. The absence of natural aggregate imposes the need for alternatives such as processed crushed rock [1]. Typically, crushed rock manufacturing begins with blasting massive rocks and is followed by several crushing stages. Crushed rock is one of the main UGMs that used as base and sub base materials in the flexible pavement[2]. The performance of UGMs is generally assessed by their strength, modulus, and resistance to breakage. The most common distresses of UGMs are rutting, shoving, and disintegration. For the Empirical design method, UGMs are usually characterized according to their CBR. While for the Mechanistic Empirical design method, elastic modulus and Poisson s ratio are generally used for characterization. The structural and functional requirements of the UGMs can be determined from the deformation resistance, durability, strength, and tendency to cracking. Generally, the physical properties of the UGMs have the main features of the characterizations, which include among others, hardness and crushing strength, surface texture, particle shape, particle size distribution, fines content, plasticity, density, and moisture content. The specification for pavement base and sub base crushed rock in Victoria-Australia is described by VicRoads [3], which have requires minimum tests such as are grading, unsound rock content, Plasticity Index, CBR, Degradation Factor, and permeability. Unfortunately, the mechanical properties of the UGMs are not considered in these requirements. One of these mechanical properties is permanent deformation (PD), which is the accumulated plastic strain under repeated loads [4]. This deformation is important for determining pavement layer thicknesses and evaluating pavement performance [5-7]. There are many factors that influence the PD of the UGMs such as stresses, number of load cycles, moisture content and fines content. However, the recent guide to pavement technology by Austroads [8] stated that there is a little information about the effect of the local UGMs properties on the PD due to the complexity of the materials (i.e. nonlinear) and difficulties to conduct long term laboratory PD test. Moreover, Increasing in pavement service life, improving in construction quality, and reduction in asphalt thickness could be achieved by a proper selection of UGMs[9]. Thus, this study aims to test the effect of the moisture content on the permanent deformation of the local base materials under repeated loads as one main materials property. 2. EXPERIMENTAL INVESTIGATION 2.1. Materials Two types of Class 2 crushed rocks, basalt (B1, B2), and granite (G1) are a widely used as unbound flexible pavement material in Victoria, Australia, as recommended by Roads Corporation of Victoria (VicRoads). These materials were collected from two different quarries, located in Victoria, Australia. Gradation, classifications, maximum dry density (MDD), and optimum moisture content (OMC) are tabulated in Table editor@iaeme.com

3 Moisture Content Effect On Permanent Deformation Behaviour Of Unbound Granular Materials Table 1 Physical and geotechnical properties of the tested materials Physical properties B1 B2 G1 D10 (mm) D30 (mm) D50 (mm) D60 (mm) Fines<0.075mm Coefficient of uniformity (C u ) Coefficient of curvature (C c ) AASHTO classification A-1-a A-1-a A-1-a Compaction (Modified): MDD Compaction (Modified): OMC Plasticity Index Specimen fabrication Samples are compacted into cylindrical specimens with a range of moisture content (MC) as shown in Table 2 and lined with a rubber membrane. The membrane helps to distribute the confining water pressure and to prevent contact with the water medium. Figure 1 shows a new fabricated specimen over the triaxial pedestal. Material Table 2 Experimental testing matrix Moisture content (%) - OMC OMC +OMC B B G Figure 1 New moulded specimen editor@iaeme.com

4 Ali Alnedawi, Kali Prasad Nepal and Riyadh Al-Ameri 2.3. Repeated Load Triaxial test procedure The repeated load triaxial test (RLTT) procedure was followed in accordance withaustroads [10]. Trapezoidal vertical loading waveform was applied at a loading frequency of 0.5 Hz. Multi-stage of stresses was applied as shown in Table 3. Table 3 Stress sequences for permanent deformation test Stages σ 3 (kpa) * σ d (kpa) ** Load cycles * confining pressure ** Deviator stress 3. TEST RESULTS AND DISCUSSION In flexible pavements, the unbound base layer is generally prepared to reach the MDD. The presence of moisture in the mix helps the granular particles to slide and roll during the compaction process. Figure 2 shows the PD of the tested crushed rocks against several amounts of moisture contents. The results are presented in three distinct graphs to characterize each stress stage individually and to observe the exclusive effect of MC during each stage. Low coefficient of determination is anticipated due to the wide covered range of MC and materials. It can be clearly seen that as soon as the moisture content increases the PD of UGMs also increases. For instance, in Figure 2.a when the applied σ d was 350 kpa, the PDs of specimen B1 prepared at MCs of 7.6, 8.6, 9.6% were 0.60,1.39, and 1.68% respectively. This observation is consistent with the previous studies conducted by [11-15]. (a) stage editor@iaeme.com

5 Moisture Content Effect On Permanent Deformation Behaviour Of Unbound Granular Materials (b) stage 2 (c) stage 3 Figure 2 Permanent deformation versus moisture content Table 4 shows the influence of moisture contents on PD of the tested materials. The amount of PD change (increase/decrease) was calculated with respect to the PD at OMC. When the MC was above the optimum (+OMC), a dramatic collapse is noticed in the PD resistance of B1, B2 and G1 respectively. Whilst, a high resistance to PD was noticed when samples prepared at MC below the optimum (-OMC). For instance, G1 prepared at +OMC showed an increase in the PD by 33.8, 35.0, 205.8% at load cycles 10000, 20000, and respectively. Whereas, when the same sample prepared at -OMC showed a reduction in the PD by 15.6, 31.2, 29.8% at load cycles 10000, 20000, and respectively editor@iaeme.com

6 Ali Alnedawi, Kali Prasad Nepal and Riyadh Al-Ameri Material Table 4 Influence of moisture contents on PD of the tested materials Prepared MC Change in PD cycles B1 - OMC -53.0% -42.9% -31.6% +OMC 20.6% 25.4% 36.3% B2 - OMC -56.7% -50.4% -41.6% + OMC 49.9% 42.5% 49.9% G1 - OMC -15.6% -31.2% -29.8% + OMC 33.8% 35.0% 205.8% For further investigation of the effect of MC, regression analysis was conducted using the RLTT database. The PD prediction models by Theyse, De Beer [16]was used for this purpose. This constitutive model consists of two predictive variables (stress and no. of load cycles) and three regression parameters as shown in Equation (1). (1) Where, PD= permanent deformation, N = number of cycles,σ c = vertical stress (kpa), and c, s & B = regression parameters. Table 5 shows the regression parameters and the coefficient of determination R 2 for the tested materials using Equation 1. When the MC was below the optimum, low values for parameter c and B, and high values for parameter S are observed, except for sample G1. It was found the parameter c, B, and S are materials dependent since the different trend was noticed between basalt (B1, B2) and granite (G1) rocks.in addition, high quality of fit withr 2 was observed for sample G1, which supports the conclusion that the model in Equation 1 is material dependent. Sample Table 5 Regression parameters Moisture content (%) Equation 1 c B S R 2 B E B E B E B E B E B E G E G E G E editor@iaeme.com

7 Moisture Content Effect On Permanent Deformation Behaviour Of Unbound Granular Materials 4. CONCLUSION A number of observations can be made from this study. First, as soon as the moisture content increases the permanent deformation of unbound granular materials also increases.when the moisture content was above the optimum (+OMC), a dramatic collapse is noticed in the permanent deformation resistance of B1, B2 and G1 respectively. Whilst, a high resistance to permanent deformation was noticed when samples prepared at a moisture content below the optimum (-OMC). Second, the regression analysis shows that the model in Equation 1 is material dependent due to the high quality of fit withr 2 was observed for sample G1. Moreover, when the moisture content was below the optimum, low values for parameter c and B, and high values for parameter S are observed, except for sample G1, which supports the conclusion that the model in Equation 1 is material dependent. REFERENCES [1] USGS, Mineral Yearbook. 2000, United State Geological Service [2] Alnedawi, A., K.P. Nepal, and R. Al-Ameri, A comparison study between basalt and granite crushed rocks under repeated traffic loads, in The First MoHESR and HCED Iraqi Scholars Conference in Australasia. 2017: Melbourne, Australia. [3] VicRoads, SECTION CRUSHED ROCK FOR PAVEMENT BASE AND SUBBASE. 2011, Roads Corporation of Victoria (VicRoads): Australia. p. 13. [4] Bodin, D. and J. Kraft, Effect of moisture content and laboratory preparation conditions on the permanent deformation of unbound granular materials [5] Huang, Y.H., Pavement Analysis and Design. Pearson Prentice Hall, Pearson Education, Inc., 2004(2): p [6] Englund, J., Analyses of Resilient Behavior of Unbound Materials for the Purpose of Predicting Permanent Deformation Behavior. 2011: Chalmers University of Technology. [7] Alnedawi, A., K.P. Nepal, and R. Al-Ameri, Mechanistic behavior of open and dense graded unbound granular materials under traffic loads. International Journal of GEOMATE, : p [8] Austroads, Guide to Pavement Technology / Part 4A: Granular Base and Subbase Materials. Austroads Publication, 2008: p [9] Niekerk, V., Mechanical behavior and performance of granular bases and sub-bases in pavements. 2002: TU Delft, Delft University of Technology. [10] Austroads, Austroads repeated load triaxial test method: Determination of permanent deformation and resilient modulus characteristics of unbound granular materials under drained conditions, AG-PT/T , Austroads Publication. p [11] Barksdale, R.D. Laboratory evaluation of rutting in base course materials. in Presented at the Third International Conference on the Structural Design of Asphalt Pavements, Grosvenor House, Park Lane, London, England, Sept , [12] Dawson, A., N. Thom, and J. Paute, Mechanical characteristics of unbound granular materials as a function of condition. Gomes Correia, Balkema, Rotterdam, 1996: p [13] Saevarsdottir, T. and S. Erlingsson, Water impact on the behaviour of flexible pavement structures in an accelerated test. Road Materials and Pavement Design, (2): p [14] Azam, A.M., D.A. Cameron, and M.M. Rahman, Permanent Strain of Unsaturated Unbound Granular Materials from Construction and Demolition Waste. Journal of Materials in Civil Engineering, (3). [15] Rahman, M.S. and S. Erlingsson, A model for predicting permanent deformation of unbound granular materials. Road Materials and Pavement Design, (3): p [16] Theyse, H., M. De Beer, and F. Rust, Overview of South African mechanistic pavement design method. Transportation Research Record: Journal of the Transportation Research Board, 1996(1539): p editor@iaeme.com