Crushed brick blends with crushed rock for pavement systems

Transcription

1 Proceedings of the Institution of Civil Engineers Waste and Resource Management 163 February 1 Issue WR1 Pages doi: 1.16/warm Paper 35 Received 26/11/8 Accepted 15/7/9 Keywords: recycling & reuse of materials/ strength & testing of materials Thurairatnam Aatheesan PhD Candidate, Swinburne University of Technology, Melbourne, Australia Arul Arulrajah Senior Lecturer, Swinburne University of Technology, Melbourne, Australia Myint Win Bo Director (Geo-Services), DST Consulting Engineers, Ontario, Canada Binh Vuong Associate Professor of Civil Engineering, Swinburne University of Technology, Melbourne, Australia John Wilson Professor of Civil Engineering, Swinburne University of Technology, Melbourne, Australia Crushed brick blends with crushed rock for pavement systems T. Aatheesan BScEng, A. Arulrajah MEngSc, PhD, FIEAust, M. W. Bo DUC, MSc, PhD, FGS, FICE, CEng, CGeol, CEnv, CSci, PEng, PGeo, EurEng, EurGeol, B. Vuong MSc, PhD and J. Wilson MSc, PhD Construction and demolition materials account for a major proportion of the waste materials present in landfills in Australia. Crushed brick and crushed rock are, however, viable substitute materials for natural resources used as construction materials in engineering applications. Crushed brick is one of the major components of demolition materials. The crushed rock used in this study originates from basalt floaters or surface excavation rock (basalt), which commonly occurs near the surface to the north and west of Melbourne, Australia. The engineering characteristics of various proportions of crushed brick blends with crushed rock obtained from extensive laboratory testing are presented in this paper. The engineering properties obtained were compared with existing local road authority specifications for pavement sub-base or light-duty base material and backfill material for drainage systems to ascertain the potential use of crushed brick blends. The materials for the experimental works were collected from a recycling facility in Victoria, Australia. 1. INTRODUCTION Recycling and reuse of waste materials is a topic of global concern and great international interest. The urgent need for recycling is driven mainly by environmental considerations, due to the increased scarcity of natural resources and the increasing cost of landfill in most countries. Construction and demolition (C&D) materials are generated as a result of regeneration of infrastructure and demolition activities, and contribute to the major proportion of waste materials present in landfills in Australia. Recycled crushed brick and low-quality crushed rock are viable substitute materials for natural construction materials in engineering applications such as pavement sub-base material. Some countries have been using recycled C&D materials in civil engineering applications but there is still scope for wider engineering applications of such recycled materials. Poon and Chan (6) investigated the possibility of using recycled concrete aggregates and crushed clay bricks as aggregates in unbound sub-base materials in Hong Kong. The use of 1% recycled concrete aggregate increased the optimum moisture content and decreased the maximum dry density of the sub-base materials compared with those of natural sub-base materials. In addition, the replacement of recycled concrete aggregates by crushed clay bricks further increased the optimum moisture content and decreased the maximum dry density. Poon and Chan also reported that the California bearing ratio (CBR) value decreased with increasing coarse clay brick content. However, it was feasible to blend recycled concrete aggregates and crushed clay brick to produce a sub-base with a soaked CBR value of at least 35, which is a minimum requirement in Hong Kong. In Victoria, Australia, the total amount of recovered waste material was recorded as 6.13 Mt in 5 6 and around % of solid wastes were recycled over that period (Sustainability Victoria, 7). In the state of Victoria, more than three quarters (77% by weight) of the waste material mainly originated from C&D activities (51% by weight), followed by waste from commercial industry activities (26% by weight). C&D material in Victoria accounts for 47% of all material (by weight) recovered, followed by metals (24%). Furthermore, concrete was the major component of C&D material by weight, representing % of the total followed by rock/excavation stone (14%), brick/brick rubble (13%) and asphalt (5%). These materials could be used as alternatives to quarry-based products for works such as roads, footpaths, bridges and other civil engineering projects. In Melbourne, Victoria, soils are commonly classified into nine types. Heavy clay on younger basalts is one of these soil types and in regions where these are found, outcrops of basalt rock known as basalt floaters occur extensively (Van de Graaff and Wootton, 1996). The crushed rock used in this study originated from basalt floaters or surface excavation rock (basalt), which commonly occurs near the surface to the west and north of Melbourne. Traditionally, this material would have been discarded as waste, often into landfill. However, because this rock is generally hard and durable, the local authority for road works in Victoria has allowed (under controlled conditions) its use for pavement sub-base and other uses. The rock is often encountered in sub-divisional excavation for residential properties and in excavation works for drainage lines as well as other sub-surface infrastructure. This paper primarily focuses on crushed brick and crushed rock blends and their applicability and usage as a pavement sub-base or light-duty base material and as bedding and backfill material for drainage systems based on laboratory tests carried out in Victoria, Australia. The engineering properties of crushed brick with and without blending with crushed rock were investigated Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al. 29

2 Class 1 Class 2 Class 3 Class 4 Liquid limit (max): % Plasticity index (PI) California bearing ratio 15 (min): % Flakiness index (max): % PI % passing. 425 mm sieve (max) 45 Table 1. Physical properties of crushed rock (VicRoads, 6) and a suite of laboratory tests was conducted on blend mixes of crushed brick with crushed rock. The engineering properties of crushed brick blends were compared with the existing local authority specifications for flexible pavement sub-base and bedding and backfill material for drainage systems. 2. LOCAL AUTHORITY SPECIFICATIONS 2.1. Pavement sub-base VicRoads is the authorised governing body for local road and bridge work in the state of Victoria, Australia. VicRoads (6) classifies recycled crushed rock for pavement sub-base and light-duty base as class 1, class 2, class 3 or class 4; this classification is based on some of the physical and mechanical properties of crushed rock. Table 1 presents the physical properties of crushed rock accepted by VicRoads, while Table 2 presents the before- and after-compaction grading limits for mm crushed rock (class 3) sub-base in flexible pavements as specified by VicRoads (1995) Bedding and backfill material Melbourne Water is the authorised governing body for local drainage systems in the state of Victoria and classifies backfill and bedding material as grade A and grade B material. The specifications for the supply of crushed rock to Melbourne Water work sites are summarised in Tables 3 and 4 (Melbourne Water, 1). 3. METHODOLOGY AND EXPERIMENTAL WORK Samples of crushed rock and crushed brick were collected from Alex Fraser Group s recycling site at Laverton North, Victoria, located approximately km to the west of Melbourne, Australia. The laboratory tests on mixtures of crushed brick and crushed rock (class 3) were conducted at Swinburne University Sieve size: mm Before-compaction grading limits: % passing by mass After-compaction grading limits: % passing by mass Table 2. Grading limits for mm class 3 sub-base from all rocks (VicRoads, 1995) Sieve size: mm Limits of percentage passing sieve aperture by mass mm grade A mm grade B Table 3. Grading limits of crushed rock for drainage systems (Melbourne Water, 1) of Technology, Melbourne. A suite of blended mixtures of crushed brick and crushed rock was tested for particle size distribution, modified compaction, particle density, water absorption, CBR, Los Angeles abrasion, Atterberg limit, ph, organic content, 1% fines (wet and dry strength) and fines content. The crushed brick and crushed rock (class 3) had a maximum aggregate size of mm. The blend mixtures were prepared by hand-mixing to the required percentages by weight. Crushed brick from this site typically consists of 7% brick and 3% other materials such as asphalt, concrete and rock. The laboratory tests were undertaken in accordance with specifications published by Standards Australia (1999, ). As pavement sub-base is subjected to heavy loading, modified compactive effort was used to find the maximum dry density and optimum moisture content. In modified compaction, the weight of the hammer and the drop of the rammer are both higher than those used in standard compaction. A cylindrical mould (internal diameter 15 mm, effective height mm) was used for modified compaction tests. The blends were compacted into the mould in five layers each and compacted with 25 blows of a 4. 5 kg rammer falling freely from a height of 45 mm. California bearing ratio is a common bearing capacity test for pavement materials. As is common practice, the test samples were soaked in water for four days to simulate the worst scenario. In the modified CBR tests, samples were placed in a cylindrical mould (internal diameter 152 mm) and compacted in five layers, totalling an effective height of 117 mm by using a spacer disc inserted into the mould before compaction. Modified compactive effort was also used here as modified CBR values are applicable for pavement sub-base testing. mm grade A mm grade B Atterberg liquid limit: % Plasticity index (max) 4 16 Los Angeles abrasion loss 3 35 Table 4. Other requirements for crushed rock for drainage systems (Melbourne Water, 1) 3 Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al.

3 Sample 7CR3 75CR3* CR3 85CR3 9CR3 1CR3 Brick content by weight: % Particle density (coarse), series 1: t/m Particle density (coarse), series 2: t/m Particle density (fine): t/m Water absorption (coarse), series 1: % Water absorption (coarse), series 2: % Water absorption (fine): % California bearing ratio, series 1: % California bearing ratio, series 2: % Los Angeles abrasion loss Organic content: % ph Max. dry density (modified compaction): t/m Opt. moisture content (modified compaction): % Ten percent fines value (wet): kn Ten percent fines value (dry): kn Strength variation: % Plastic limit: % NOy NO NO NO NO NO Liquid limit: % NO NO NO NO NO NO Plasticity index NPz NP NP NP NP NP Clay content: % * For example, 7CR3 refers to 7% crushed rock (class 3) blended with 3% crushed brick by weight. y NO, not obtainable. z NP, non-plastic. Table 5. Engineering properties of crushed brick blended with crushed rock (class 3) Particle density and water absorption tests were undertaken on both coarse (retained on a mm sieve) and fine (passing a 4.75 mm sieve) material. The physical characteristics of crushed brick blends with crushed rock (class 3) obtained from the laboratory tests are summarised in Table 5. Two sampling series (series 1 and series 2) were undertaken several months apart and tests were repeated in the second series of sampling as indicated in Table 5. Particle size distribution tests for crushed brick blended with crushed rock (class 3) undertaken prior to and after compaction are summarised in Tables 6 and 7. As crushed brick originates from brick elements of structures, it contains cement mortar bonded to the brick. This cement mortar and fine clay brick particles increase the water absorption properties. The ph value of all the blends was over 7, indicating that the blends are alkaline by nature. 4. COMPARISON OF RESULTS 4.1. Pavement sub-base The before-compaction grading limits of all blends as compared with VicRoads requirements for mm class 3 crushed rock are shown in Figure 1 and are within VicRoads lower and upper bound limits for sub-base application. The grading curves of blended aggregates follow a well-graded particle size distribution, which indicates that smaller particles will fit into the voids created between larger particles and result in tight packing. This increases the workability and mix density of the blends thereby increasing their strength. The after-compaction grading limits of all blends compared satisfactorily with VicRoads requirements for class 3 crushed rock sub-base in flexible pavement (Figure 2). The before- and after-compaction grading limits of the crushed rock blends show that little breakdown occurs during compaction other than Sample 7CR3 75CR3 CR3 85CR3 9CR3 1CR3 Brick content by weight: % Particle size: mm Total passing: % Table 6. Particle size distribution (before compaction) of crushed brick blended with crushed rock (class 3) Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al. 31

4 Sample 7CR3 75CR3 CR3 85CR3 9CR3 1CR3 Brick content by weight: % Particle size: mm Total passing: % Table 7. Particle size distribution (after compaction) of crushed brick blended with crushed rock (class 3) that which would normally be experienced with a standard subbase material. This breakdown tends to occur mainly in crushed brick as it is weaker than crushed rock. This would suggest that a higher limit of 3% crushed brick could be added to the crushed rock mixes without any significant loss of performance taking into account breakdown during compaction. The crushed rock blends appear to remain well graded through the compaction process and this will generally aid compaction. As the clay content in all the blends was low, the plastic limit and liquid limit could not be obtained. This is because the Atterberg limit is directly related to clay mineralogy. The low clay levels may mean that some difficulties may occur with the workability of the crushed rock blends because cohesion of particles and a tight prepared surface is usually a desirable characteristic. The 1% fines value (wet and dry strength) test is an indicator of the durability of materials in saturated and completely dry conditions. The values of blends tested did not vary significantly between the saturated condition and completely dry condition, and this indicates that little breakdown occurred in the coarse fraction of the blend. Materials with a wet and dry strength variation of less than 35% are considered durable (Lay, 1998). The 1% fines values (wet and dry strength) showed low variations (less than 15%) for a number of the blends studied. Los Angeles abrasion test values are a useful indicator of durability and hardness of aggregates during crushing and compaction. The values achieved on the blended samples were within the VicRoads specified limit of 35 for a sub-base pavement material. The CBR values of crushed brick and crushed rock (class 3) blends are shown in Figure 3; the values were above 9%, which in turn is above the % requirement stipulated by VicRoads. Series 1 and series 2 data denote two separate 1 1 7CR3 CR3 9CR3 VicRoads upper bound 75CR3 85CR3 1CR3 VicRoads lower bound Total passing: % Particle size: mm Figure 1. Particle size distribution (before compaction) of crushed brick blended with crushed rock for pavement sub-base (class 3). For example, 75CR3 refers to 75% crushed rock (class 3) blended with 25% crushed brick by weight 32 Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al.

5 1 1 7CR3 CR3 9CR3 VicRoads upper bound 75CR3 85CR3 1CR3 VicRoads lower bound Total passing: % Particle size: mm Figure 2. Particle size distribution (after compaction) of crushed brick blended with crushed rock for pavement sub-base (class 3) sampling periods (three months apart from two different stockpiles) for quality control purposes. As series 1 and 2 sampling and testing were undertaken several months apart, the quality of aggregates may vary depending on their source. Blend 85CR3 of series 1 shows high a CBR value when compared with the other blends in series 1; this could be due to segregation of aggregates during compaction or minor fluctuations in the experimental works. The results achieved are acceptable and, along with other test results, indicate that the addition of varying percentages of crushed brick to crushed rock blends has little or no effect on overall performance. The laboratory test results indicated that potentially up to 3% crushed brick could be safely added to crushed rock (class 3) blends for pavement sub-base application Bedding and backfill for drainage systems The laboratory test results were also compared with local specifications for bedding and backfill material. The grading curves of all blends as compared with Melbourne Water specifications for grades A and B material are presented in 1 1 CBR, series 1 CBR, series CBR: % CR3 75CR3 CR3 85CR3 9CR3 1CR3 Sample Figure 3. CBR values of crushed brick blended with crushed rock (class 3) Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al. 33

6 1 1 7CR3 CR3 9CR3 Melbourne Water upper bound 75CR3 85CR3 1CR3 Melbourne Water lower bound Total passing: % Particle size: mm Figure 4. Particle size distribution of crushed brick blended with crushed rock (class 3) for bedding and backfill material (grade A) Figure 4 and Figure 5 respectively. The grading limits of all blends for grade A and grade B bedding and backfill material were found to be within the Melbourne Water specified lower and upper bounds, although some grade B finer particles were just on the limit. 5. CONCLUSION The laboratory testing undertaken in this research has revealed that incorporation of crushed brick into basaltic crushed rock (class 3) has a low to minimal effect on the physical and mechanical properties of the original material. The grading limits of all the crushed brick blends studied, before and after compaction, were also within VicRoads specified upper and lower bounds for crushed rock (class 3). The laboratory test results indicate that potentially up to 3% crushed brick could be safely added to crushed rock (class 3) blends for pavement sub-base application. VicRoads initially recommended up to 15% of crushed brick content in crushed rock (class 3) blends, but has stated that depending on the results of field trials it may be possible to increase the percentage of crushed brick added in the future CR3 CR3 9CR3 Melbourne Water upper bound 75CR3 85CR3 1CR3 Melbourne Water lower bound Total passing: % Particle size: mm Figure 5. Particle size distribution of crushed brick blended with crushed rock (class 3) for bedding and backfill material (grade B) 34 Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al.

7 The grading limits of all crushed brick blended with crushed rock (class 3), up to 3% crushed brick content, were found to be within Melbourne Water upper and lower bound curves for grade A and grade B backfill and bedding material. ACKNOWLEDGEMENT The authors would like to acknowledge Sustainability Victoria for funding this research project (contract no. 3887). They also acknowledge Alex Fraser Group for providing samples of crushed brick and crushed rock and technical assistance on this project. REFERENCES Lay MG (1998) Pavement materials. In Hand Book of Road Technology, 3rd edn. Gordon and Breach, The Netherlands. Melbourne Water (1) Sands, Crushed Rock and Crushed Scoria. MW, Melbourne, Specification 21.A.38. Poon CS and Chan D (6) Feasible use of recycled concrete aggregate and crushed brick as unbound road sub-base. Construction and Building Materials (8): Standards Australia (1999) Method for Sampling and Testing Aggregates. SA, Sydney, AS Standards Australia () Method of Testing Soils for Engineering Purposes. SA, Sydney, AS Sustainability Victoria (7) Annual Survey of Victorian Recycling Industries 5 6. SV, Melbourne, 7. Van de Graaff R and Wootton C (1996) Melbourne Soils. Department of Sustainability and Environment, State of Victoria, Land care notes, ISSN X. VicRoads (1995) Standard Specification for Road Works and Bridge Works. VicRoads, Melbourne, Section 34, Flexible pavement construction. VicRoads (6) Standard Specification for Road Works and Bridge Works. VicRoads, Melbourne, Section 812, Crushed rock for base and subbase pavement. What do you think? To discuss this paper, please up to 5 words to the editor at journals@ice.org.uk. Your contribution will be forwarded to the author(s) for a reply and, if considered appropriate by the editorial panel, will be published as a discussion in a future issue of the journal. Proceedings journals rely entirely on contributions sent in by civil engineering professionals, academics and students. Papers should be 5 words long (briefing papers should be 1 words long), with adequate illustrations and references. You can submit your paper online via where you will also find detailed author guidelines. Waste and Resource Management 163 Issue WR1 Crushed brick blends with crushed rock for pavement systems Aatheesan et al. 35

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