Effect of Compactive Efforts on the Strength Properties of Groundnut Shell Ash Stabilized Reclaimed Asphalt Pavement

Advanced Materials Research Vol. 824 (2013) pp 12-20 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.824.12 Effect o...
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Advanced Materials Research Vol. 824 (2013) pp 12-20 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.824.12

Effect of Compactive Efforts on the Strength Properties of Groundnut Shell Ash Stabilized Reclaimed Asphalt Pavement Edeh, Joseph Ejelikwu1, a, Eberemu, Adrian Oshioname2,b and Aburabul, James Mzuaor3,c 1,3

Department of Civil Engineering, University of Agriculture, Makurdi, 970001, Nigeria. 2 Department of Civil Engineering, Ahmadu Bello University, Zaria 810001, Nigeria. a [email protected] (corresponding author), [email protected], c [email protected]

Keywords: California bearing ratio, flexible highway pavement, groundnut shell ash, reclaimed asphalt pavements, stabilization.

Abstract. Large quantities of groundnut shell ash (GSA) are generated from the combustion of groundnut shell, disposed in large quantities on production sites while large volume of reclaimed asphalt pavements (RAP) aggregates are also generated during pavement rehabilitation and reconstruction and disposed along road alignments. This paper presents results of the laboratory evaluation of the effect of compactive efforts on the strength properties of GSA stabilized RAP with a view to determining its suitability as highway pavement material in pavement constructions. The RAP-GSA mixtures were subjected to Reduced British Standard light, RBSL (reduced Proctor); British Standard light, BSL (standard Proctor); West African Standard, WAS and British Standard heavy, BSH (modified Proctor) compactive efforts to determine the compaction characteristics, California bearing ratio (CBR), durability and water absorption characteristics. Test results show that the properties of RAP improved with GSA treatment. The particle grading improved from 99.13 % coarse aggregate and 0.87 % fines, with AASHTO classification of A-1-b for 100 % RAP, and 9.08 % coarse aggregate and 90.92 % fines, with AASHTO classification of A-4 for 100 % GSA to 15.66–91.72 % coarse aggregate and 8.28–84.32 % fines, with AASHTO classification in the range A-4 (silty soil) to A-1-a (granular materials), for the various RAP-GSA mixes. Maximum dry density (MDD) decreased while the optimum moisture content (OMC) increased with higher GSA content in the RAP + GSA mixes and with decreased compactive effort from BSH to RBSL. Optimum CBR values of 35.1% (unsoaked) and 44.1% (soaked) recorded for 90% RAP + 10% GSA mix achieved with BSH compactive effort, satisfied the durability requirements with insignificant expansion and water absorption and can be used as subbase material in flexible pavements construction. This research provides the results of evaluation of the effect of compactive efforts on the strength properties of GSA stabilized RAP as highway construction material, as it is based on CBR determination. Further work may be encouraged to assess resilient modulus of this material under cyclic load. Introduction Massive road construction has depleted once plentiful aggregate supplies and continuing to exhaust the valuable resources to rebuild existing roads only propagates and accelerates the problem [1]. It is quite common, in countries with tropical climate that the soil found in the construction place do not satisfy the technical requirements of the project [2]. Therefore, there is a need to resort to one of the suitable methods of low cost road construction, followed by a process of stage development of the roads using the appropriate compactive efforts, to meet the growing needs of the road traffic. Additionally, if old asphalt and road base materials are not recycled, they must be disposed of or stockpiled, increasing transportation cost, utilizing valuable land space and increasing environmental and health hazards. Stabilization of reclaimed asphalt pavements (RAP) with groundnut shell ash (GSA) may make the reconstruction of old roads a largely self-sustaining process. Some researchers [2,3] tried with soils, which are available everywhere [4].

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 41.206.11.17, Ahmadu Bello University, Zaria, Nigeria-19/09/13,06:38:29)

Advanced Materials Research Vol. 824

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Reclaimed asphalt pavement (RAP) is an existing asphalt mixture that has been pulverized, usually by milling, and is used like an aggregate in recycled asphalt pavement [5]. During pavement rehabilitation and reconstruction, large quantities of this materials are generated especially when asphalt pavement are removed. Properly crushed and screened RAP consists of high-quality, well graded aggregates coated by asphalt cement [6]. The properties of RAP are largely dependent on the properties of the constituent materials and asphalt concrete type used in the old pavement. Research has established typical range of particle size distribution, physical, chemical, engineering and mechanical properties of RAP [3,6]. Groundnut shell (GS) is the outer cover of the groundnut grain with very high concentration of silica as major compound. The particles size distribution range from 15 to 30µm, having irregular shapes. Research has also established the chemical properties of GSA [7]. It is a highly pozzolanic material [8] with about 6% ash content [9]. It has found a known use as biomass ash filters for high temperature applications in India [10] and as partial replacement of cement in concrete [11]. This paper considers the results of the effect of the compactive efforts of Reduced British Standard light, RBSL (reduced Proctor); British Standard light, BSL (standard Proctor); West African Standard (WAS) and British Standard heavy, BSH (modified Proctor) on the strength properties of GSA stabilized RAP as highway pavement material. Materials and Methods Materials: Reclaimed asphalt pavements: The reclaimed asphalt pavement (RAP) used in this study was obtained from North Bank (lies between latitude: 7o35' - 7o53'N and longitude: 8o24' 8o42' E) in Makurdi, Benue State, Nigeria. The RAP consists of high-quality, well graded aggregate coated with asphalt cement. Groundnut shell ash: The groundnut shell ash used in this work was obtained from the incineration of groundnut shell at a groundnut processing yard in Ugba (lies between latitude: 7o5' 7o15'N and longitude: 9o00' - 9o06' E), headquarter of Logo Local Government Area in Benue state, Nigeria. The groundnut shell was burnt into ashes in a kiln at a regulated temperature of 600 oC, airdried before use for this study [12]. Methods: Samples of RAP and GSA were tested to determine the index properties, particle size distribution, soil classification, Atterberg limits, specific gravity, compaction characteristics, California bearing ratio, durability and water absorption characteristics in accordance with procedures outlined in BS 1377 [13]. RAP in increasing stepped concentration of 10% (i.e., 0, 10, 20, 30, 40 up to 100%) was stabilized with GSA in decreasing stepped concentration of 10% (i.e., 100, 90, 80, 70, 60 down to 0%), and the optimum proportion was determined during the preliminary mix design tests. Attempt to determine the Atterberg limits were not successful as RAP, GSA and the RAP-GSA mixes were not cohesive and could not be rolled into threads, indicating that RAP, GSA and RAP-GSA mixes are non-plastic. Hence, Atterberg limits are taken as minimum from the classification chart [14]. The specification relating to the use of these indices for highway design and construction in Nigeria are given in the Nigerian General Specifications [15]. RAP-GSA mix design and the determination of Atterberg limits: The key design parameter for stabilizing processed RAP with GSA is the blending ratio of RAP to GSA that is needed to provide adequate bearing capacity. The ratio adopted for this work is to alternately vary the RAP and GSA contents. That is, while one component is increasing in the mix, the other will be decreasing. Table 1 gives detail mix proportions for RAP-GSA mixes.

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Advances in Materials and Systems Technologies IV

RAP (%) 0 10 20 30 40 50 60 70 80 90 100

Table 1: RAP-GSA mix ratios. GSA (%) Resulting combinations (%) 100 100% GSA 90 10% RAP + 90% GSA 80 20% RAP + 80% GSA 70 30% RAP + 70% GSA 60 40% RAP + 60% GSA 50 50% RAP + 50% GSA 40 60% RAP + 40% GSA 30 70% RAP + 30% GSA 20 80% RAP + 20% GSA 10 90% RAP + 10% GSA 0 100% RAP

Results and Discussion Oxide composition of groundnut shell ash: The oxide composition of the groundnut shell ash (GSA) is given in Table 2. Calcium oxide (CaO) content is 20.7% and silicon dioxide (SiO2) content is 43.4%. CaO/SiO2 ratio, which is indicative of cementing potential, is 0.67, SiO2 + Fe2O3 + Al2O3 = 36.1% and Loss on ignition (LOI), which is the indication of the amount of unburnt carbon in the GSA is 4.12%. According to ASTM C 618-92a [16], the GSA used for this study is self-cementing. Table 2: Oxide composition of groundnut shell ash (GSA). Oxides CaO SiO2 Al2O3 P2O5 Fe2O3 MnO K2O TiO2 SO3 ZnO Ag2O LOI Concentrations 20.7 30.9 7.32 4.18 5.19 0.59 27.8 2.01 4.23 0.13 3.16 4.12 (%)

Particle size distribution: The particle size distribution curves of 100% RAP, 100% GSA and the various RAP + GSA mixes are shown in Figure 1. The gradation of 100% RAP is composed of 99.13% coarse aggregates and 0.87% fines with coefficient of uniformity, Cu = 16.7 and coefficient of grading, Cz = 0.3, and falls under the AASHTO classification of A-1-b (granular materials). 100% RAP does not satisfy the requirements of grading (Cu>6 and 1

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