- Email: [email protected]
Influence of recycled coarse aggregate derived from construction and demolition waste (CDW) on abrasion resistance of pavement concrete
Construction and Building Materials 142 (2017) 248–255
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of recycled coarse aggregate derived from construction and demolition waste (CDW) on abrasion resistance of pavement concrete Rakesh Kumar Rigid Pavements Division, CSIR-Central Road Research Institute, Delhi Mathura Road, New Delhi 110 025, India
h i g h l i g h t s 4.75–10 mm and 10–20 mm size RCA were used to replace NCA of similar size range. Abrasion resistance of concrete made with RCA was investigated. RCA reduces abrasion resistance of paving concrete but not beyond acceptable limit. RCA can be used in paving concrete mixes.
a r t i c l e
i n f o
Article history: Received 9 December 2016 Received in revised form 23 February 2017 Accepted 9 March 2017
Keywords: Concrete Recycled concrete aggregate Compressive strength Abrasion CDW
a b s t r a c t Coarse aggregate has notable influence on concrete properties. The sustainability in concrete is generally achieved through reduced mining of natural resources required for the manufacturing of its basic constituents, by recycling of suitable industrial by-products or post-consumer materials including construction and demolition waste (CDW). CDW is composed of several materials depending on its locality of the origin. Recycled concrete aggregate (RCA) is obtained by crushing the concretized components of CDW. RCA is inhomogeneous with respect to its dynamic properties unlike natural coarse aggregate (NCA). A pavement concrete has to possess a proper strength and adequate abrasion resistance to resist surface wearing due to a moving traffic. This study presents the influence of using RCA as a replacement of NCA in paving concrete. Two series of concrete mixes, at two different water-cement ratios, that is, 0.44 and 0.38, were used in this study. The study exhibited that RCA reduces the abrasion resistance significantly yet it could be effectively used in pavement concrete. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The global demand for construction quality aggregates is expected to be more than 51 billion metric tons by 2019 [1]. The mining, processing, and transport operations for such a large quantity of aggregates consume a huge amount of energy and adversely affect the ecology of the areas and riverbeds [2]. Ever increasing demand for quality aggregates has resulted in a faster rate of depletion of natural resources such as rocks, river, as well as land quarried sand, in many parts of the world endangering sustainable developments. Though the demand for aggregates is entirely based upon region to region, depending upon economic growth; generally, the availability of good aggregates is getting scarce everywhere. In concrete, the sustainability is generally achieved through a reduced mining of natural resources for the manufacturing of its basic constituents, by recycling of suitable industrial byproducts or post-consumer materials including construction and E-mail address: [email protected] http://dx.doi.org/10.1016/j.conbuildmat.2017.03.077 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
demolition waste (CDW). Such usage requires that the durability of the concrete is not compromised but enhanced. The scarcity of availability of aggregates followed by rapid growth in infrastructural development calls for finding suitable alternative sources for it. Among all the alternate sources for aggregates, the recycling of construction and demolition waste (CDW) has grown in popularity because it is generally available everywhere [3]. Further, across several measures, use of RCA has a lower environmental impact than NCA [2]. CDW is generated whenever a building, road, bridge, industrial structure or a manufacturing facility is constructed, repaired or rehabilitated or demolished. A majority of RCA material comes from building renovations and demolition. Such demolition activities pollute the environment by releasing dust particles. CDW is typically composed of wood, plaster, concrete, asphaltic cement, roofing materials, glass, plastics, metal, insulating materials, carpeting, and other similar material depending on its locality of the origin. The construction and demolition is a continuous process, which seemingly will continue forever. The world needs to address a judicious management of the solid waste
R. Kumar / Construction and Building Materials 142 (2017) 248–255
that it generates from construction and demolition processes. Table 1 shows CDW generated and recycled in few countries across the world. Attempts to utilize CDW, in order to produce concrete aggregates have been made since the World War II [5] and possibly even before. However, it is important to note that the RCA derived from CDW is inhomogeneous unlike NCA derived from a rock. Recycled aggregate contains other deleterious materials, which make it difficult for complete replacement of a good quality natural aggregate for concrete; and, therefore, restricting its many applications such as in reinforced concrete structural elements. Several studies [6– 16] have shown that the fresh and hardened state properties of concrete made with RCA widely depend upon the quality of the parent concrete from CDW. The maximum nominal size of recycled aggregate influences the amount of mortar attached to the recycled aggregate. The finer the aggregate, more mortar content is attached to it [7–10]. Due to this reason, specific broad conclusions are difficult to make for the use of RCA. A general conclusion for the reference purposes about the properties of concrete made with recycled aggregate with respect to natural aggregate with same water-to-cement (W/C) ratio is shown in Table 2. However, it is important to note that the quality of the concrete made with recycled aggregate depends entirely upon the quality of recycled aggregate; the proportion at which it has replaced natural aggregate, the amount of cement paste adhered to it, and other similar factors. Due to a wide variation in the available literature, it is apparent that numerous experimental data are generated for the in-house needs, using local RCA, in order to draw any specific conclusion for a given project activity. A lower density, higher water absorption, higher porosity and a lower specific gravity for the mortar content attached to the recycled aggregate in comparison with natural aggregate result in a decrease in compressive strength, modulus of elasticity, density, as well as durability factor of concrete. In a recent study Knaack and Kurama [25] have reported an insignificant influence on the rate of strength gain of RCA concrete compared to NCA concrete. An extensive study by Silva et al. [26] suggests that a performance based classification of RCA based on its physical properties for the use of RCA in concrete can minimize the variation in the properties of concrete containing it. Concrete used in the construction of road surfaces, bridge decks, airfield runways, parking lots, and other similar applications is Table 1 CDW waste generated and recycled [4]. Country
Waste generated (Mt)
Percentage of recycling
Percentage of landfill
USA Germany UK France Italy India
180 59 30 24 20 12
56 17 45 15 9 NA
44 83 55 85 91 NA
249
generally known as a pavement concrete or pavement-quality concrete. This concrete undergoes dynamic loading due to moving traffic and ambient environment. Therefore, this concrete has to possess a proper strength and durability properties relevant to its use in pavements. Deterioration of concrete surfaces occurs due to various forms of wear such as erosion, cavitations, and abrasion due to various exposures. Abrasion wear occurs due to rubbing, scraping, skidding, or sliding of objects on the concrete surface. This form of surface wear is observed in pavements, floors, or other surfaces on which friction forces are applied due to relative motion between the surface and the moving traffic. Concrete abrasion resistance is markedly influenced by a number of factors including concrete strength, aggregate properties, surface finishing, curing, and other similar factors. The characteristics of coarse aggregate have noticeable impact on the performance of the concrete pavements. Numerous studies [27–32] have indicated that the abrasion resistance of concrete is mainly dependent upon the concrete’s compressive strength. The factors such as water to-cementitious materials ratio, type of aggregates and their properties, air entrainment, and other similar factors, which affect the concrete strength also influence the abrasion resistance. According to ACI Committee 201 [27], concrete subjected to abrasion should have a compressive strength at least 28 MPa. In general, a hardened cement paste possesses low resistance to abrasion. In order to develop a concrete for a high abrasion resistance, it is desirable to use a hard coarse aggregate, and paste having low porosity and high strength [28]. Sufficient information on the abrasion resistance of concrete containing RCA is not readily available. Therefore, this research project was undertaken to investigate the abrasion resistance of concrete incorporating RCA derived from the CDW generated in New Delhi, India. The paper presents the comparative properties of RCA against NCA. The influences of the replacement of NCA by RCA in size range 10–20 mm and 4.75 to 20 mm on strength and abrasion resistance of pavement concrete mixes are presented. 2. Experimental study The experimental study includes the evaluation of the suitability of the recycled concrete aggregates and comparison of their properties with natural coarse aggregates of similar size range, evaluation of sand, testing of cement, preparation and testing of concrete specimens for the study of influences of the replacement of NCA with RCA on concrete properties for pavement construction. 2.1. Materials
Table 2 Properties of concrete with RCA vis-a-vis NCA. Property
RCA compared to NCA
References
Compressive strength Splitting and flexural tensile strength Modulus of elasticity Drying shrinkage Creep Water absorption Freezing and thawing resistance Carbonation depth Chloride penetration
Decrease up to 25% Decrease up to 10%
[6,10–12] [6,7,11–14]
Decrease up to 45% Increase up to 50% Increase up to 50% Increased up to 50% Decreased Similar Similar or slightly increased
[6,8,9,12,13] [15–18] [15,17,19] [13,17] [19,20] [21,22] [22–24]
The materials used include; an ordinary portland cement (OPC), crushed quartzite natural and recycled aggregate in size range of 4.75 mm to 20 mm msa, land quarried sand for concrete, tap water, and polycarboxylate ether-based high range water reducing agent (HRWRA). The basic properties of the OPC used in the study are presented in Table 3. The gradation of fine aggregate (sand) is presented in Table 4. The water absorption, specific gravity, and bulk density of sand were 1.0%, 2.65, and 1600 kg/m3, respectively. Potable water available at CSIR-CRRI laboratory was used for the mixing of the concrete mixes and for the curing of the concrete specimens. A high-range water reducing agent (HWRA) was used to get the desire workability for the concrete. 2.2. Recycled verses natural coarse aggregate RCA in the size range of 4.75–10 mm and 10–20 mm was collected from a commercial recycling plant from time to assess the variation in its composition, as well as physical and mechanical
250
R. Kumar / Construction and Building Materials 142 (2017) 248–255
Table 3 Physical properties and compressive strength of cement. Physical Properties
Value
Permissible range as per IS 8112
Specific gravity Normal consistency (%) Initial setting time (min) Final setting time (min)
3.12 32 120 240
3.10–3.15 28–32 >30 <600
Compressive strength 7 Days (MPa) 28 Days (MPa)
35.6 50.5
>33 >43
Table 4 Gradation of fine aggregate based on sieve analysis data. Sieve opening size (mm)
% Passing
10.0 4.75 2.36 1.18 0.6 0.300 0.150
100 100 99 89 59 17 6
Grading zone of sand Grading of sand lies in between Zones II & III.
properties. A natural crushed quartzite aggregate of the same size range was also taken for the comparison of aggregate properties of RCA. Both types of the aggregate were evaluated in accordance with the relevant Indian Standards for their suitability for the use in the concrete for pavement. Since RCA was inhomogeneous, unlike natural aggregate, therefore, RCA was required to be evaluated thoroughly for its compositions and other physical properties. Fig. 1 and Fig. 2 show as received RCA of size range 4.75–10 mm and 10–20 mm, respectively, while Fig. 3 and Fig. 4 show natural aggregate. The composition of RCA was evaluated by determining the presence of different materials in it. Fig. 5 presents the composition of RCA for size range of 10–20 mm. For this purpose, three different samples weighing 4 kg each were randomly taken out from three stock piles of RCA (10–20 mm). The average values obtained on these three samples for different constituents of RCA along with water absorption are given in Table 5. The average brick aggregate content in RCA by mass was about 0.4%. The presence of different materials was not evaluated in RCA of size range 4.75–10 mm. The sieve analysis of RCA in the size range of 10 to 20 mm for RCA was very similar to the gradation of the NCA (Table 6). However, 4.75–10 mm size range of RCA had about 27% of the aggregate finer than 4.75 mm. Therefore, coarse aggregate of this size range was used only after screening from 3 mm wire net. Table 6 shows
Fig. 2. RCA of size range10–20 mm.
Fig. 3. NCA of size range 4.75–10 mm.
Fig. 4. NCA of size range10–20 mm.
Fig. 1. RCA of size range 4.75–10 mm.
the gradation of both types of aggregate in size range of 10–20 mm and 4.75–10 mm. It is obvious that RCA of size range 4.75–10 mm used in the study was much finer than NCA (Table 6). Therefore, before using RCA of 4.75–10 mm, it was sieved from a sieve of 4.75 mm size.
R. Kumar / Construction and Building Materials 142 (2017) 248–255
251
the soundness test. The comparison of the properties of the RCA with the NCA shows that the RCA properties are generally inferior to NCA. Hence, it is difficult for RCA to be 100% substitute for any good quality natural aggregate.
2.3. Mix proportions
Fig. 5. Different components of RCA.
Table 5 Composition and water absorption by components of RCA. Components
% by mass
Water absorption,%
Sand stone (Red) Mable Aggregate adhered with mortar Brick Concrete aggregate Cement Mortar
3.1 0.4 5.5 0.4 85.9 4.4
Negligible Negligible 7.6 14.7 0.29 16.9
Table 6 Gradation of RCA vis-à-vis NCA. Sieve size (mm)
25 20 12.5 10 4.75 2.36
Percentage passing, 20 mm msa
Percentage passing, 10 mm msa
RCA
NCA
RCA
NCA
100 91 19.6 2.3 0.7 –
100 91.5 17.6 3 0.4 –
– – 100 85.3 3.8 0.11
– – 100 90 27.4 9.1
Proper determination of water absorption by RCA is very important as it is very dynamic in nature. The different constituents present in RCA make it difficult to restrict the water absorption within the permissible limit of 2% as prescribed in Indian Standard IS:456, 2010 [33]. Water absorption by different constituents present in RCA is reported in Table 5. The comparative physical properties of RCA and NCA are presented in Table 7. The smaller size range of RCA had a higher value for water absorption than a larger size range of the RCA. The weigh loss of RCA in soundness test was more than three folds of NCA. Fig. 6 shows RCA before and after
It is well established that cement content, water-tocementicious materials ratio, slump, air content, type of finish, and curing, affect the characteristics of the pavement concrete surface layer including abrasion resistance [29]. Numerous studies [30–32] have shown that compressive strength is the most important factor governing the abrasion resistance of concrete. Laplante et al. [32] have reported that concrete resistance to abrasion is strongly influenced by the relative abrasion resistance of its constituent materials that are, coarse aggregate and mortar. Generally, concretes made with hard rock such as granite and quartzite as coarse aggregate exhibit a higher abrasion resistance compared to the softer rock such as limestone aggregate. A number of investigators have shown that both surface finishing techniques and types of curing practice also have a strong influence on the abrasion resistance of concrete [34–35]. Therefore, two series of concrete mixes were prepared, concrete mixes containing replacement of NCA in size range of 10–20 mm by RCA, 100% RCA i.e. replacement of NCA by RCA that is, from 4.75 mm to 20 mm. A control mix comprising of all NCA i.e. 100% NCA was also prepared. The NCA was replaced by RCA on mass to mass basis. The higher water absorption by RCA was accounted for in mixes by the addition of extra water needed to bring RCA in SSD condition. The free water-to-cement ratio for Series 1 mixes was kept 0.44, while the same for Series 2 mixes was 0.38. The mix proportions by mass for, cement, sand, coarse aggregate, water-to-cement ratio, HRWRA used were 1:2.1:3.86:0.44: 0.0067 and 1: 1.84: 3.26: 0.38: 0.0063 for Series 1 and Series 2 concrete mixes. Mix details and mix designations are shown in Table 8.
2.3.1. Mixing and specimens preparation Mixing and concrete specimen’s preparations were carried out in accordance with the Indian standard procedure. The raw materials, coarse and fine aggregates, and cement were mixed in a dry state in a tilted drum type mixer for about 30 s. After that two third of the water required was added and the mix was further mixed for two minutes. Then the remaining 1/3rd water containing HRWRA was added and mixing was further continued for 3–4 min before evaluating the fresh properties of the concrete mixes. The standard specimens were cast for the evaluation of compressive (150 mm cubes), 100 mm 100 mm 500 mm beams for flexural strength, and 100 mm cubes for abrasion resistance of the concrete. The samples were demolded after 24 h and then cured in a curing tank until the time of testing.
2.4. Slump and density of concrete
Table 7 Comparative physical properties of aggregates (RCA and NCA). Physical properties
RCA
NCA
Specific gravity Aggregate crushing value (%) Bulk Density (kg/m3) Water absorption (%) Water absorption (%) Soundness (by Sodium Sulphate solution), % Impact Value, (WAIV) % LA Abrasion (%)
2.24, 2.45 23.8–30.7 1470–1520 4.23 (10–20 mm) 6.8 (4.75–10 mm) 16.17
2.71 20.2–28.17 1570–1650 0.48 0.74 4.97
18.5–21.1 30.2–33.8
12.4 21.3–21.6
The slump and fresh density of concrete mixes were determined to understand the influences on the fresh properties of the concrete on the replacement of natural aggregates by RCA. The density of the concrete is related to its strength and durability. The concrete density varies depending on the amount and density of the aggregate, how much air is entrapped or purposely entrained, the amount of cement, and the maximum size of the aggregate used. Average fresh density of concrete was determined by dividing the mass of the concrete filled and compacted in known volume of cubes and beams.
252
R. Kumar / Construction and Building Materials 142 (2017) 248–255
(a) RCA before soundness test.
(b) RCA after soundness test.
Fig. 6. .RCA before and after soundness test.
Table 8 Mix designations and details about coarse aggregates. Mix designation
Description
M30 M31
100% Natural coarse aggregates (4.75–20 mm) Natural coarse aggregates replaced in size range 10–20 mm by RCA 100% Recycled coarse aggregates (4.75–20 mm) 100% Natural coarse aggregates (4.75–20 mm) Natural coarse aggregates replaced in size range 10–20 mm by RCA 100% Recycled coarse aggregates (4.75–20 mm)
M32 M40 M41 M42
Series 1, w/c = 0.44
Series 2, w/c = 0.38
2.5. Mechanical testing of concrete Prior to the mechanical testing, the concrete specimens were removed from the curing tank. The compressive strength and flexural strength were determined in accordance with the IS 516: 1959 [36]. Average compressive strength and flexural strength obtained on triplicate test specimens are reported. 2.5.1. Abrasion resistance Abrasion resistance of the pavement concrete is one of the parameters to measure its durability. Abrasion loss of concrete was determined by sand blasting method in accordance with the IS: 9284-1993[37]. This method determines the abrasion resistance of concrete under physical effects only by subjecting the test cubes of 100 mm to the impingement of air-driven silica sand. Silica sand conforming to IS: 650-1991 [38] graded to pass 1.00 mm IS sieve and retained on 0.50 mm IS sieve was used in this method (Fig. 7). Abrasive charge of 4000 gm impinging with a pressure of 0.14 N/mm2 on the side faces of the cube was applied and the abrasion loss of specimen was recorded as the loss in mass in grams for two separate impressions on the same face of the concrete cube under test. Fig. 8 shows a typical cube specimen before and after the abrasion testing. 3. Results and discussion 3.1. Slump and density of fresh concrete Table 9 shows the slump and fresh density of the concrete mixes. With an increase in replacement of NCA by RCA a decrease
Fig. 7. A concrete specimen under abrasion testing by sand blasting method.
in slump and fresh density of concrete was observed. The reduction in the slump was mainly due to the change in the nature of particle shape and surface texture of RCA compared to NCA. The replacement of NCA with RCA reduced the fresh density of the concrete, which was mainly due to a lower specific gravity of RCA and further due to the comparatively higher content of entrapped air due to more angular particle shape and surface texture. 3.2. Compressive strength The compressive strength developed at 7 and 28 days by concrete mixes of Series 1and Series 2 are given in Fig. 9 and Fig. 10, respectively. The replacement of natural coarse aggregate with RCA decreases the compressive strength of concrete mixes. For Series 1 mixes, mix M30 developed maximum compressive strength followed by mix M31 where only 10–20 mm size coarse aggregate was replaced. Mix M32 developed least strength in this series. All concrete mixes of Series 1 developed the 28-day compressive strength of more than 28 MPa. Even mix M32 developed a compressive strength of 28.9 MPa. In mix M32, NCA was completely replaced with RCA. It is apparent that concrete mix M31 developed about 10% less compressive strength than mix M30. However, mix M32 developed about 20% less compressive strength compared to mix M30. Similar trends were also observed for Series 2 concrete mixes. The reduction in the compressive strength was mainly
R. Kumar / Construction and Building Materials 142 (2017) 248–255
(a) Before test
253
(b) After abrasion test
Fig. 8. Cube face of the test specimen before and after abrasion testing.
Table 9 The slump and the fresh density of concrete mixes. Mix No.
Series
Slump (mm)
Fresh density (kg/m3)
M30 M31 M32 M40 M41 M42
Series 1
40 35 25 25 15 25
2460 2390 2370 2485 2370 2485
Series 2
attributed to the presence of many micro pores and cracks in the mortar attached with aggregates from RCA and also due to the presence of soft aggregates such as pieces of brick. The percentage reduction in strength for concrete mixes of Series 2 was slightly more than that for Series 1. It can be thus concluded that the complete replacement of NCA by RCA (from 4.75 mm to 20 mm) reduces compressive strength more than the replacement of 10 mm–20 mm size of NCA by RCA in a concrete mix. It is worth to note that this finding may differ for RCA obtained from CDW of other locations or recycling plants. 3.3. Flexural strength
Fig. 9. Development of compressive strength of series 1 mixes.
The 28-day flexural strength developed by the concrete mixes is presented in Table 10. Concrete mix containing only NCA (mix M30) developed the maximum flexural strength followed by the concrete mix made with replacement of 10–20 mm NCA by RCA. Concrete mixes with 100% replacement of all the coarse aggregates (from 4.75 mm to 20 mm) developed least flexural strength (mixes M32 and M42). The trend for the reduction of the flexural strength was similar to that of the compressive strength. It is important to note that there was insignificant reduction in flexural strength of concrete containing RCA as a replacement of larger size of NCA i.e. 10– 20 mm. However, the replacement of the smaller size of natural coarse aggregate i.e. 4.75–10 mm influenced more adversely the development of the flexural strength (a reduction up to 20%) than the larger size of the aggregate. The requirement of more paste compared to the case of large size aggregates might be responsible for such behavior. 3.4. Abrasion resistance
Fig. 10. Development of compressive strength of series 2 mixes.
The abrasion resistance characteristic of the concrete test cubes was determined at the age of 28 days by subjecting it to the impingement of air driven silica sand. The results are shown in Table 11. The mass loss in concrete after test gives an indication about its resistance to abrasion. A lower value of the abrasion loss indicates a higher resistance to abrasion for the concrete. It can be seen that there was a noticeable increase in the mass loss representing a decrease in the resistance to abrasion due to the replacement of NCA by RCA. The complete replacement of NCA by RCA increased the mass loss in concrete test cubes which indicated a decrease in the abrasion resistance. The decrease in the abrasion resistance of concrete varies from 18% to 22%. The mixes containing complete replacement of NCA by RCA exhibited the lowest
254
R. Kumar / Construction and Building Materials 142 (2017) 248–255
Table 10 Flexural strength of concrete mixes. Flexural strength, MPa
Concrete mix series 1
7-day 28-day
Concrete mix series 2
M30 (100% NCA)
M31 (10 to 20 mm NCA replaced by RCA)
M32 (100% NCA)
M40 (100% NCA)
M41 (10 to 20 mm NCA replaced by RCA)
M42 (100% RCA)
4.2 5.0
4.0 4.6
3.6 3.9
5.3 6.1
4.9 5.8
4.6 5.1
Table 11 Abrasion resistance of concrete mixes of series 1 and series 2. Abrasion loss
Avg. mass loss, %
Concrete mix series 1
Concrete mix series 2
M30 (100% NCA)
M31 (10 to 20 mm NAC replaced by RCA)
M32 (100% NCA)
M40 (100% NCA)
M41 (10 to 20 mm NAC replaced by RCA)
M42 (100% RCA)
0.204
0.226
0.240
0.179
0.213
0.220
Table 12 Guidelines for different catagories of concrete surfacing based on the abrasion loss of the concrete [37]. Sl. No.
Surfacing category
1.
Concrete Pavement: a) With mixed traffic including iron-tyred traffic b) With pneumatic tyred traffic only Factory floor Dockyard Railway platform Foot path
2. 3. 4. 5.
Maximum values of abrasion loss, % by mass 0.16 0.24 0.16 0.16 0.24 0.40
abrasion resistance and highest mass loss. The decrease in abrasion resistance of the concrete is believed mainly due to the comparatively inferior quality of RCA (Table 7) and relatively poor quality of the cement paste matrix of concrete adhering to RCA; i.e. an increase in the porosity, which is mainly due to the presence of two transition zones, cracks and pores in mortar attached with aggregate, and due to reduction in density of concrete. In addition, a lower compressive strength is also responsible for it. Therefore, this study indicates that the abrasion resistance of concrete incorporating RCA is significantly lower than the concrete containing NCA. It is important to note that all concrete mixes used in this study can be used in pavement construction meant for pneumatic tyred traffic in accordance with the guidelines of IS 9282: 1993 [37] (Table 12). Finally, it is suggested that recycled aggregate can be used to replace natural aggregate without affecting abrasion resistance characteristic beyond the limit that make a concrete unfit for the pavement construction. 4. Conclusions The influence of replacing natural coarse aggregates in concrete mixes with recycled concrete aggregates of similar size obtained from recycling of CDW on abrasion resistance of pavement concrete is reported in this study. Its impact on compressive and flexural strengths of concrete, were examined also. The important finding from the study are given as follows. In interpretting the findings, it should be noted that the results are limited to the RCA and mixes used in the study. The physical properties of recycled coarse aggregate were inferior to the natural coarse aggregate. The replacement of natural aggregate with recycled one reduces the fresh density of the concrete mixes by 6–8%.
Compressive and flexural strength of the concrete made with recycled aggregate were less than the concrete with natural aggregate. This decrease is much more prominent when all natural aggregate i.e. from 4.75 to 20 mm is replaced by recycled aggregate. The abrasion resistance of concrete with recycled aggregate was significantly less compared to concrete with natural aggregate. The concrete mixes made with replacement of only larger size recycled aggregate i.e.10–20 mm showed better resistance to abrasion than mixes mixes with all recycled aggregate that is, from 4.75 to 20 mm. However, all concrete mixes show abrasion resistance characteristics acceptable for paving concrete. Recycled aggregate can be used to replace natural aggregate from paving concrete without adversely affecting its abrasion resistance characteristic.
Acknowledgements The permission of the Director, CSIR-CRRI (Prof. Satish Chandra) to publish this research study is gratefully acknowledged. The RCA material provided by the manufacturer is thankfully acknowledged. The help rendered by Prof. T. R. Naik of UW-M, USA for the improvement of the paper is gratefully acknowledged. The support provided during the experimental work by Mr. Ishan Sinha, Shekhawat, Vijay Kumar, Rishi and other laboratory staff of the CSIR-CRRI is thankfully acknowledged.
References [1] K. Yanik, Report-global demand for aggregates to rise,, (20 June 2016). [2] M. Davis, A. de la Rosa, B. Weldon, Y.C. Kurama, M.J. McGinnis, Environmental considerations of recycled concrete aggregates (RCA) for improved sustainability of reinforced concrete building structures, Proc. of SCMT 4, Las Vegas, USA, 2016, August. [3] T.R. Naik, R. Kumar, Sustainable Concrete with Industrial and Postconsumer by-Product Materials, in: G.M. Sabnis (Ed.), Green Building with Concrete: Sustainable Design and Construction, Taylor & Francis Group, New York, 2015, pp. 337–372. [4] V. Krishna, R. Kumar, Recycling cement concrete roads: an innovative advent to sustainability, Int. J. Res. Eng. Technol. 2 (2013) 59–65. [5] S.W. Tabsh, A.S. Abdelfatah, Influence of recycled concrete aggregates on strength properties of concrete, Constr. Build. Mater. 23 (2009) 1163–1167. [6] A. Ajdukiewicz, A. Klisczewicz, Influence of recycled aggregates on mechanical properties of HS/HPC, Cem. Concr. Compos. 24 (2002) 269–279. [7] A.K. Padmini, K. Ramamurthy, M.S. Mathews, Influence of parent concrete on the properties of recycled aggregate concrete, Constr. Build. Mater. 23 (2009) 829–836. [8] M. Batayneh, I. Marie, I. Asi, Use of selected waste materials in concrete mixes, Waste Manage. 27 (2007) 1870–1876.
R. Kumar / Construction and Building Materials 142 (2017) 248–255 [9] C.S. Poon, Z.H. Shui, C.S. Lam, H. Fok, S.C. Kou, Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete, Cem. Concr. Res. 34 (2004) 31–36. [10] K. Rahal, Mechanical properties of concrete with recycled coarse aggregate, Build. Environ. 42 (2007) 407–415. [11] K.H. Yang, H.S. Chung, A. Ashour, Influence of type and replacement level of recycled aggregates on concrete properties, ACI Mater. J. 105 (2008) 289–296. [12] T.C. Hansen, H. Narud, Strength of recycled concrete made from crushed concrete coarse aggregate, ACI Concr. Int. 5 (1987) 79–83. [13] J. Xiao, J. Li, C. Zhang, Mechanical properties of recycled aggregate concrete under uniaxial loading, Cem. Concr. Res. 35 (2005) 1187–1194. [14] R. Kumar, C. Shekhawat, Commercially available construction and demolition waste recycled coarse aggregate in the manufacture of concrete, Ind. Concr. J. 90 (2016) 27–35. [15] C.S. Poon, Z.H. Shui, L. Lam, Effect of microstructure of ITZ on compressive strength of concrete prepared with recycled aggregates, Constr. Build. Mater. 18 (2004) 461–468. [16] M. Tavakoli, P. Soroushin, Strength of recycled aggregate concrete made using field-demolished concrete as aggregate, ACI Mater. J. 93 (1996) 182–188. [17] A. Domingo-Cabo, C. Lázaro, F. López-Gayarre, M.A. Serrano-López, P. Serna, J. O. Castaño-Tabares, Creep and shrinkage of recycled aggregate concrete, Constr. Build. Mater. 23 (2009) 2545–2553. [18] J.M.V. Gómez-Soberón, Porosity of recycled concrete with substitution of recycled concrete aggregate an experimental study, Cem. Concr. Res. 32 (2002) 1301–1311. [19] R.M. Salem, E.G. Burdette, N.M. Jackson, Resistance to freezing and thawing of recycled aggregate concrete, ACI Mater. J. 100 (2003) 216–230. [20] R. Zaharieva, F. Buyle-Bodin, E. Wirguin, Frost resistance of recycled aggregate concrete, Cem. Concr. Res. 34 (2004) 1927–1932. [21] S.M. Levy, P. Helene, Durability of recycled aggregates concrete: a safe way to sustainable development, Cem. Concr. Res. 34 (2004) 1975–1980. [22] N. Otsuki, M. Asce, S. Miyazato, W. Yodsudjai, Influence of recycled aggregate on interfacial transition zone, strength, chloride penetration and carbonation of concrete, ASCE J. Mater. Civ. Eng. 15 (2003) 443–451.
255
[23] K.Y. Ann, H.Y. Moon, Y.B. Kim, J. Ryou, Durability of recycled aggregate concrete using pozzolanic materials, Waste Manage. 28 (2008) 993–999. [24] F.T. Olorunsogo, N. Padayachee, Performance of recycled aggregate concrete monitored by durability indexes, Cem. Concr. Res. 32 (2002) 179–185. [25] A.M. Knaack, Y.C. Kurama, Design of concrete mixtures with recycled concrete aggregates, ACI Mater. J. 110 (2013) 483–493. [26] R.V. Silva, J. de Brito, R.K. Dhir, Properties and composition of recycled aggregates from construction and demolition waste suitable for concrete production, Const. Build. Mater. 65 (2014) 201–217. [27] ACI Committee 201 Report, Guide to Durable Concrete, Title No. 74–53, ACI, 1977. [28] P.K. Mehta, Concrete Structure, Properties and Materials, Prentice-Hall International, 1986. [29] M.E. Prior, Abrasion Resistance: Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM STP-169A, ASTM, Philadelphia, 1966, pp. 246–260. [30] K.M. Hadchti, R.L. Carrasquillo, Abrasion resistance and scaling resistance of concrete containing fly ash, Center for Transportation Research, Bureau of Engineering Research, University of Texas at Austin, Research Report: 481–3, August 1988. [31] L.P. Witte, J.E. Backstrom, Some properties affecting the abrasion resistance of air-entrained concrete, ASTM Proc. 51 (1951) 1141–1155. [32] P. Laplante, P.C. Aifcin, Vezina, Abrasion resistance of concrete, J. Mater. Civ. Eng. 3 (1991) 19–30. [33] I. Standard, Plain and reinforced concrete-code of practice, IS 456, 2000. [34] R.F. Ytterburg, Wear-resistant industrial floors of portland cement concrete, ASCE Civ. Eng. 41 (1971) 68–71. [35] A. Nanni, Curing of roller compacted concrete and strength development, ASCE J. Transp. Eng. 114 (1988) 684–694. [36] I. Standard, Method of Test for Strength of Concrete, IS 516, 1959. [37] I. Standard, Method of Test for Abrasion Resistance of Concrete, IS 9284, 1993. [38] I. Standard, Standard Sand for Testing of Cement Specification, IS 650, 1991.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of recycled coarse aggregate derived from construction and demolition waste (CDW) on abrasion resistance of pavement concrete Rakesh Kumar Rigid Pavements Division, CSIR-Central Road Research Institute, Delhi Mathura Road, New Delhi 110 025, India
h i g h l i g h t s 4.75–10 mm and 10–20 mm size RCA were used to replace NCA of similar size range. Abrasion resistance of concrete made with RCA was investigated. RCA reduces abrasion resistance of paving concrete but not beyond acceptable limit. RCA can be used in paving concrete mixes.
a r t i c l e
i n f o
Article history: Received 9 December 2016 Received in revised form 23 February 2017 Accepted 9 March 2017
Keywords: Concrete Recycled concrete aggregate Compressive strength Abrasion CDW
a b s t r a c t Coarse aggregate has notable influence on concrete properties. The sustainability in concrete is generally achieved through reduced mining of natural resources required for the manufacturing of its basic constituents, by recycling of suitable industrial by-products or post-consumer materials including construction and demolition waste (CDW). CDW is composed of several materials depending on its locality of the origin. Recycled concrete aggregate (RCA) is obtained by crushing the concretized components of CDW. RCA is inhomogeneous with respect to its dynamic properties unlike natural coarse aggregate (NCA). A pavement concrete has to possess a proper strength and adequate abrasion resistance to resist surface wearing due to a moving traffic. This study presents the influence of using RCA as a replacement of NCA in paving concrete. Two series of concrete mixes, at two different water-cement ratios, that is, 0.44 and 0.38, were used in this study. The study exhibited that RCA reduces the abrasion resistance significantly yet it could be effectively used in pavement concrete. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The global demand for construction quality aggregates is expected to be more than 51 billion metric tons by 2019 [1]. The mining, processing, and transport operations for such a large quantity of aggregates consume a huge amount of energy and adversely affect the ecology of the areas and riverbeds [2]. Ever increasing demand for quality aggregates has resulted in a faster rate of depletion of natural resources such as rocks, river, as well as land quarried sand, in many parts of the world endangering sustainable developments. Though the demand for aggregates is entirely based upon region to region, depending upon economic growth; generally, the availability of good aggregates is getting scarce everywhere. In concrete, the sustainability is generally achieved through a reduced mining of natural resources for the manufacturing of its basic constituents, by recycling of suitable industrial byproducts or post-consumer materials including construction and E-mail address: [email protected] http://dx.doi.org/10.1016/j.conbuildmat.2017.03.077 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
demolition waste (CDW). Such usage requires that the durability of the concrete is not compromised but enhanced. The scarcity of availability of aggregates followed by rapid growth in infrastructural development calls for finding suitable alternative sources for it. Among all the alternate sources for aggregates, the recycling of construction and demolition waste (CDW) has grown in popularity because it is generally available everywhere [3]. Further, across several measures, use of RCA has a lower environmental impact than NCA [2]. CDW is generated whenever a building, road, bridge, industrial structure or a manufacturing facility is constructed, repaired or rehabilitated or demolished. A majority of RCA material comes from building renovations and demolition. Such demolition activities pollute the environment by releasing dust particles. CDW is typically composed of wood, plaster, concrete, asphaltic cement, roofing materials, glass, plastics, metal, insulating materials, carpeting, and other similar material depending on its locality of the origin. The construction and demolition is a continuous process, which seemingly will continue forever. The world needs to address a judicious management of the solid waste
R. Kumar / Construction and Building Materials 142 (2017) 248–255
that it generates from construction and demolition processes. Table 1 shows CDW generated and recycled in few countries across the world. Attempts to utilize CDW, in order to produce concrete aggregates have been made since the World War II [5] and possibly even before. However, it is important to note that the RCA derived from CDW is inhomogeneous unlike NCA derived from a rock. Recycled aggregate contains other deleterious materials, which make it difficult for complete replacement of a good quality natural aggregate for concrete; and, therefore, restricting its many applications such as in reinforced concrete structural elements. Several studies [6– 16] have shown that the fresh and hardened state properties of concrete made with RCA widely depend upon the quality of the parent concrete from CDW. The maximum nominal size of recycled aggregate influences the amount of mortar attached to the recycled aggregate. The finer the aggregate, more mortar content is attached to it [7–10]. Due to this reason, specific broad conclusions are difficult to make for the use of RCA. A general conclusion for the reference purposes about the properties of concrete made with recycled aggregate with respect to natural aggregate with same water-to-cement (W/C) ratio is shown in Table 2. However, it is important to note that the quality of the concrete made with recycled aggregate depends entirely upon the quality of recycled aggregate; the proportion at which it has replaced natural aggregate, the amount of cement paste adhered to it, and other similar factors. Due to a wide variation in the available literature, it is apparent that numerous experimental data are generated for the in-house needs, using local RCA, in order to draw any specific conclusion for a given project activity. A lower density, higher water absorption, higher porosity and a lower specific gravity for the mortar content attached to the recycled aggregate in comparison with natural aggregate result in a decrease in compressive strength, modulus of elasticity, density, as well as durability factor of concrete. In a recent study Knaack and Kurama [25] have reported an insignificant influence on the rate of strength gain of RCA concrete compared to NCA concrete. An extensive study by Silva et al. [26] suggests that a performance based classification of RCA based on its physical properties for the use of RCA in concrete can minimize the variation in the properties of concrete containing it. Concrete used in the construction of road surfaces, bridge decks, airfield runways, parking lots, and other similar applications is Table 1 CDW waste generated and recycled [4]. Country
Waste generated (Mt)
Percentage of recycling
Percentage of landfill
USA Germany UK France Italy India
180 59 30 24 20 12
56 17 45 15 9 NA
44 83 55 85 91 NA
249
generally known as a pavement concrete or pavement-quality concrete. This concrete undergoes dynamic loading due to moving traffic and ambient environment. Therefore, this concrete has to possess a proper strength and durability properties relevant to its use in pavements. Deterioration of concrete surfaces occurs due to various forms of wear such as erosion, cavitations, and abrasion due to various exposures. Abrasion wear occurs due to rubbing, scraping, skidding, or sliding of objects on the concrete surface. This form of surface wear is observed in pavements, floors, or other surfaces on which friction forces are applied due to relative motion between the surface and the moving traffic. Concrete abrasion resistance is markedly influenced by a number of factors including concrete strength, aggregate properties, surface finishing, curing, and other similar factors. The characteristics of coarse aggregate have noticeable impact on the performance of the concrete pavements. Numerous studies [27–32] have indicated that the abrasion resistance of concrete is mainly dependent upon the concrete’s compressive strength. The factors such as water to-cementitious materials ratio, type of aggregates and their properties, air entrainment, and other similar factors, which affect the concrete strength also influence the abrasion resistance. According to ACI Committee 201 [27], concrete subjected to abrasion should have a compressive strength at least 28 MPa. In general, a hardened cement paste possesses low resistance to abrasion. In order to develop a concrete for a high abrasion resistance, it is desirable to use a hard coarse aggregate, and paste having low porosity and high strength [28]. Sufficient information on the abrasion resistance of concrete containing RCA is not readily available. Therefore, this research project was undertaken to investigate the abrasion resistance of concrete incorporating RCA derived from the CDW generated in New Delhi, India. The paper presents the comparative properties of RCA against NCA. The influences of the replacement of NCA by RCA in size range 10–20 mm and 4.75 to 20 mm on strength and abrasion resistance of pavement concrete mixes are presented. 2. Experimental study The experimental study includes the evaluation of the suitability of the recycled concrete aggregates and comparison of their properties with natural coarse aggregates of similar size range, evaluation of sand, testing of cement, preparation and testing of concrete specimens for the study of influences of the replacement of NCA with RCA on concrete properties for pavement construction. 2.1. Materials
Table 2 Properties of concrete with RCA vis-a-vis NCA. Property
RCA compared to NCA
References
Compressive strength Splitting and flexural tensile strength Modulus of elasticity Drying shrinkage Creep Water absorption Freezing and thawing resistance Carbonation depth Chloride penetration
Decrease up to 25% Decrease up to 10%
[6,10–12] [6,7,11–14]
Decrease up to 45% Increase up to 50% Increase up to 50% Increased up to 50% Decreased Similar Similar or slightly increased
[6,8,9,12,13] [15–18] [15,17,19] [13,17] [19,20] [21,22] [22–24]
The materials used include; an ordinary portland cement (OPC), crushed quartzite natural and recycled aggregate in size range of 4.75 mm to 20 mm msa, land quarried sand for concrete, tap water, and polycarboxylate ether-based high range water reducing agent (HRWRA). The basic properties of the OPC used in the study are presented in Table 3. The gradation of fine aggregate (sand) is presented in Table 4. The water absorption, specific gravity, and bulk density of sand were 1.0%, 2.65, and 1600 kg/m3, respectively. Potable water available at CSIR-CRRI laboratory was used for the mixing of the concrete mixes and for the curing of the concrete specimens. A high-range water reducing agent (HWRA) was used to get the desire workability for the concrete. 2.2. Recycled verses natural coarse aggregate RCA in the size range of 4.75–10 mm and 10–20 mm was collected from a commercial recycling plant from time to assess the variation in its composition, as well as physical and mechanical
250
R. Kumar / Construction and Building Materials 142 (2017) 248–255
Table 3 Physical properties and compressive strength of cement. Physical Properties
Value
Permissible range as per IS 8112
Specific gravity Normal consistency (%) Initial setting time (min) Final setting time (min)
3.12 32 120 240
3.10–3.15 28–32 >30 <600
Compressive strength 7 Days (MPa) 28 Days (MPa)
35.6 50.5
>33 >43
Table 4 Gradation of fine aggregate based on sieve analysis data. Sieve opening size (mm)
% Passing
10.0 4.75 2.36 1.18 0.6 0.300 0.150
100 100 99 89 59 17 6
Grading zone of sand Grading of sand lies in between Zones II & III.
properties. A natural crushed quartzite aggregate of the same size range was also taken for the comparison of aggregate properties of RCA. Both types of the aggregate were evaluated in accordance with the relevant Indian Standards for their suitability for the use in the concrete for pavement. Since RCA was inhomogeneous, unlike natural aggregate, therefore, RCA was required to be evaluated thoroughly for its compositions and other physical properties. Fig. 1 and Fig. 2 show as received RCA of size range 4.75–10 mm and 10–20 mm, respectively, while Fig. 3 and Fig. 4 show natural aggregate. The composition of RCA was evaluated by determining the presence of different materials in it. Fig. 5 presents the composition of RCA for size range of 10–20 mm. For this purpose, three different samples weighing 4 kg each were randomly taken out from three stock piles of RCA (10–20 mm). The average values obtained on these three samples for different constituents of RCA along with water absorption are given in Table 5. The average brick aggregate content in RCA by mass was about 0.4%. The presence of different materials was not evaluated in RCA of size range 4.75–10 mm. The sieve analysis of RCA in the size range of 10 to 20 mm for RCA was very similar to the gradation of the NCA (Table 6). However, 4.75–10 mm size range of RCA had about 27% of the aggregate finer than 4.75 mm. Therefore, coarse aggregate of this size range was used only after screening from 3 mm wire net. Table 6 shows
Fig. 2. RCA of size range10–20 mm.
Fig. 3. NCA of size range 4.75–10 mm.
Fig. 4. NCA of size range10–20 mm.
Fig. 1. RCA of size range 4.75–10 mm.
the gradation of both types of aggregate in size range of 10–20 mm and 4.75–10 mm. It is obvious that RCA of size range 4.75–10 mm used in the study was much finer than NCA (Table 6). Therefore, before using RCA of 4.75–10 mm, it was sieved from a sieve of 4.75 mm size.
R. Kumar / Construction and Building Materials 142 (2017) 248–255
251
the soundness test. The comparison of the properties of the RCA with the NCA shows that the RCA properties are generally inferior to NCA. Hence, it is difficult for RCA to be 100% substitute for any good quality natural aggregate.
2.3. Mix proportions
Fig. 5. Different components of RCA.
Table 5 Composition and water absorption by components of RCA. Components
% by mass
Water absorption,%
Sand stone (Red) Mable Aggregate adhered with mortar Brick Concrete aggregate Cement Mortar
3.1 0.4 5.5 0.4 85.9 4.4
Negligible Negligible 7.6 14.7 0.29 16.9
Table 6 Gradation of RCA vis-à-vis NCA. Sieve size (mm)
25 20 12.5 10 4.75 2.36
Percentage passing, 20 mm msa
Percentage passing, 10 mm msa
RCA
NCA
RCA
NCA
100 91 19.6 2.3 0.7 –
100 91.5 17.6 3 0.4 –
– – 100 85.3 3.8 0.11
– – 100 90 27.4 9.1
Proper determination of water absorption by RCA is very important as it is very dynamic in nature. The different constituents present in RCA make it difficult to restrict the water absorption within the permissible limit of 2% as prescribed in Indian Standard IS:456, 2010 [33]. Water absorption by different constituents present in RCA is reported in Table 5. The comparative physical properties of RCA and NCA are presented in Table 7. The smaller size range of RCA had a higher value for water absorption than a larger size range of the RCA. The weigh loss of RCA in soundness test was more than three folds of NCA. Fig. 6 shows RCA before and after
It is well established that cement content, water-tocementicious materials ratio, slump, air content, type of finish, and curing, affect the characteristics of the pavement concrete surface layer including abrasion resistance [29]. Numerous studies [30–32] have shown that compressive strength is the most important factor governing the abrasion resistance of concrete. Laplante et al. [32] have reported that concrete resistance to abrasion is strongly influenced by the relative abrasion resistance of its constituent materials that are, coarse aggregate and mortar. Generally, concretes made with hard rock such as granite and quartzite as coarse aggregate exhibit a higher abrasion resistance compared to the softer rock such as limestone aggregate. A number of investigators have shown that both surface finishing techniques and types of curing practice also have a strong influence on the abrasion resistance of concrete [34–35]. Therefore, two series of concrete mixes were prepared, concrete mixes containing replacement of NCA in size range of 10–20 mm by RCA, 100% RCA i.e. replacement of NCA by RCA that is, from 4.75 mm to 20 mm. A control mix comprising of all NCA i.e. 100% NCA was also prepared. The NCA was replaced by RCA on mass to mass basis. The higher water absorption by RCA was accounted for in mixes by the addition of extra water needed to bring RCA in SSD condition. The free water-to-cement ratio for Series 1 mixes was kept 0.44, while the same for Series 2 mixes was 0.38. The mix proportions by mass for, cement, sand, coarse aggregate, water-to-cement ratio, HRWRA used were 1:2.1:3.86:0.44: 0.0067 and 1: 1.84: 3.26: 0.38: 0.0063 for Series 1 and Series 2 concrete mixes. Mix details and mix designations are shown in Table 8.
2.3.1. Mixing and specimens preparation Mixing and concrete specimen’s preparations were carried out in accordance with the Indian standard procedure. The raw materials, coarse and fine aggregates, and cement were mixed in a dry state in a tilted drum type mixer for about 30 s. After that two third of the water required was added and the mix was further mixed for two minutes. Then the remaining 1/3rd water containing HRWRA was added and mixing was further continued for 3–4 min before evaluating the fresh properties of the concrete mixes. The standard specimens were cast for the evaluation of compressive (150 mm cubes), 100 mm 100 mm 500 mm beams for flexural strength, and 100 mm cubes for abrasion resistance of the concrete. The samples were demolded after 24 h and then cured in a curing tank until the time of testing.
2.4. Slump and density of concrete
Table 7 Comparative physical properties of aggregates (RCA and NCA). Physical properties
RCA
NCA
Specific gravity Aggregate crushing value (%) Bulk Density (kg/m3) Water absorption (%) Water absorption (%) Soundness (by Sodium Sulphate solution), % Impact Value, (WAIV) % LA Abrasion (%)
2.24, 2.45 23.8–30.7 1470–1520 4.23 (10–20 mm) 6.8 (4.75–10 mm) 16.17
2.71 20.2–28.17 1570–1650 0.48 0.74 4.97
18.5–21.1 30.2–33.8
12.4 21.3–21.6
The slump and fresh density of concrete mixes were determined to understand the influences on the fresh properties of the concrete on the replacement of natural aggregates by RCA. The density of the concrete is related to its strength and durability. The concrete density varies depending on the amount and density of the aggregate, how much air is entrapped or purposely entrained, the amount of cement, and the maximum size of the aggregate used. Average fresh density of concrete was determined by dividing the mass of the concrete filled and compacted in known volume of cubes and beams.
252
R. Kumar / Construction and Building Materials 142 (2017) 248–255
(a) RCA before soundness test.
(b) RCA after soundness test.
Fig. 6. .RCA before and after soundness test.
Table 8 Mix designations and details about coarse aggregates. Mix designation
Description
M30 M31
100% Natural coarse aggregates (4.75–20 mm) Natural coarse aggregates replaced in size range 10–20 mm by RCA 100% Recycled coarse aggregates (4.75–20 mm) 100% Natural coarse aggregates (4.75–20 mm) Natural coarse aggregates replaced in size range 10–20 mm by RCA 100% Recycled coarse aggregates (4.75–20 mm)
M32 M40 M41 M42
Series 1, w/c = 0.44
Series 2, w/c = 0.38
2.5. Mechanical testing of concrete Prior to the mechanical testing, the concrete specimens were removed from the curing tank. The compressive strength and flexural strength were determined in accordance with the IS 516: 1959 [36]. Average compressive strength and flexural strength obtained on triplicate test specimens are reported. 2.5.1. Abrasion resistance Abrasion resistance of the pavement concrete is one of the parameters to measure its durability. Abrasion loss of concrete was determined by sand blasting method in accordance with the IS: 9284-1993[37]. This method determines the abrasion resistance of concrete under physical effects only by subjecting the test cubes of 100 mm to the impingement of air-driven silica sand. Silica sand conforming to IS: 650-1991 [38] graded to pass 1.00 mm IS sieve and retained on 0.50 mm IS sieve was used in this method (Fig. 7). Abrasive charge of 4000 gm impinging with a pressure of 0.14 N/mm2 on the side faces of the cube was applied and the abrasion loss of specimen was recorded as the loss in mass in grams for two separate impressions on the same face of the concrete cube under test. Fig. 8 shows a typical cube specimen before and after the abrasion testing. 3. Results and discussion 3.1. Slump and density of fresh concrete Table 9 shows the slump and fresh density of the concrete mixes. With an increase in replacement of NCA by RCA a decrease
Fig. 7. A concrete specimen under abrasion testing by sand blasting method.
in slump and fresh density of concrete was observed. The reduction in the slump was mainly due to the change in the nature of particle shape and surface texture of RCA compared to NCA. The replacement of NCA with RCA reduced the fresh density of the concrete, which was mainly due to a lower specific gravity of RCA and further due to the comparatively higher content of entrapped air due to more angular particle shape and surface texture. 3.2. Compressive strength The compressive strength developed at 7 and 28 days by concrete mixes of Series 1and Series 2 are given in Fig. 9 and Fig. 10, respectively. The replacement of natural coarse aggregate with RCA decreases the compressive strength of concrete mixes. For Series 1 mixes, mix M30 developed maximum compressive strength followed by mix M31 where only 10–20 mm size coarse aggregate was replaced. Mix M32 developed least strength in this series. All concrete mixes of Series 1 developed the 28-day compressive strength of more than 28 MPa. Even mix M32 developed a compressive strength of 28.9 MPa. In mix M32, NCA was completely replaced with RCA. It is apparent that concrete mix M31 developed about 10% less compressive strength than mix M30. However, mix M32 developed about 20% less compressive strength compared to mix M30. Similar trends were also observed for Series 2 concrete mixes. The reduction in the compressive strength was mainly
R. Kumar / Construction and Building Materials 142 (2017) 248–255
(a) Before test
253
(b) After abrasion test
Fig. 8. Cube face of the test specimen before and after abrasion testing.
Table 9 The slump and the fresh density of concrete mixes. Mix No.
Series
Slump (mm)
Fresh density (kg/m3)
M30 M31 M32 M40 M41 M42
Series 1
40 35 25 25 15 25
2460 2390 2370 2485 2370 2485
Series 2
attributed to the presence of many micro pores and cracks in the mortar attached with aggregates from RCA and also due to the presence of soft aggregates such as pieces of brick. The percentage reduction in strength for concrete mixes of Series 2 was slightly more than that for Series 1. It can be thus concluded that the complete replacement of NCA by RCA (from 4.75 mm to 20 mm) reduces compressive strength more than the replacement of 10 mm–20 mm size of NCA by RCA in a concrete mix. It is worth to note that this finding may differ for RCA obtained from CDW of other locations or recycling plants. 3.3. Flexural strength
Fig. 9. Development of compressive strength of series 1 mixes.
The 28-day flexural strength developed by the concrete mixes is presented in Table 10. Concrete mix containing only NCA (mix M30) developed the maximum flexural strength followed by the concrete mix made with replacement of 10–20 mm NCA by RCA. Concrete mixes with 100% replacement of all the coarse aggregates (from 4.75 mm to 20 mm) developed least flexural strength (mixes M32 and M42). The trend for the reduction of the flexural strength was similar to that of the compressive strength. It is important to note that there was insignificant reduction in flexural strength of concrete containing RCA as a replacement of larger size of NCA i.e. 10– 20 mm. However, the replacement of the smaller size of natural coarse aggregate i.e. 4.75–10 mm influenced more adversely the development of the flexural strength (a reduction up to 20%) than the larger size of the aggregate. The requirement of more paste compared to the case of large size aggregates might be responsible for such behavior. 3.4. Abrasion resistance
Fig. 10. Development of compressive strength of series 2 mixes.
The abrasion resistance characteristic of the concrete test cubes was determined at the age of 28 days by subjecting it to the impingement of air driven silica sand. The results are shown in Table 11. The mass loss in concrete after test gives an indication about its resistance to abrasion. A lower value of the abrasion loss indicates a higher resistance to abrasion for the concrete. It can be seen that there was a noticeable increase in the mass loss representing a decrease in the resistance to abrasion due to the replacement of NCA by RCA. The complete replacement of NCA by RCA increased the mass loss in concrete test cubes which indicated a decrease in the abrasion resistance. The decrease in the abrasion resistance of concrete varies from 18% to 22%. The mixes containing complete replacement of NCA by RCA exhibited the lowest
254
R. Kumar / Construction and Building Materials 142 (2017) 248–255
Table 10 Flexural strength of concrete mixes. Flexural strength, MPa
Concrete mix series 1
7-day 28-day
Concrete mix series 2
M30 (100% NCA)
M31 (10 to 20 mm NCA replaced by RCA)
M32 (100% NCA)
M40 (100% NCA)
M41 (10 to 20 mm NCA replaced by RCA)
M42 (100% RCA)
4.2 5.0
4.0 4.6
3.6 3.9
5.3 6.1
4.9 5.8
4.6 5.1
Table 11 Abrasion resistance of concrete mixes of series 1 and series 2. Abrasion loss
Avg. mass loss, %
Concrete mix series 1
Concrete mix series 2
M30 (100% NCA)
M31 (10 to 20 mm NAC replaced by RCA)
M32 (100% NCA)
M40 (100% NCA)
M41 (10 to 20 mm NAC replaced by RCA)
M42 (100% RCA)
0.204
0.226
0.240
0.179
0.213
0.220
Table 12 Guidelines for different catagories of concrete surfacing based on the abrasion loss of the concrete [37]. Sl. No.
Surfacing category
1.
Concrete Pavement: a) With mixed traffic including iron-tyred traffic b) With pneumatic tyred traffic only Factory floor Dockyard Railway platform Foot path
2. 3. 4. 5.
Maximum values of abrasion loss, % by mass 0.16 0.24 0.16 0.16 0.24 0.40
abrasion resistance and highest mass loss. The decrease in abrasion resistance of the concrete is believed mainly due to the comparatively inferior quality of RCA (Table 7) and relatively poor quality of the cement paste matrix of concrete adhering to RCA; i.e. an increase in the porosity, which is mainly due to the presence of two transition zones, cracks and pores in mortar attached with aggregate, and due to reduction in density of concrete. In addition, a lower compressive strength is also responsible for it. Therefore, this study indicates that the abrasion resistance of concrete incorporating RCA is significantly lower than the concrete containing NCA. It is important to note that all concrete mixes used in this study can be used in pavement construction meant for pneumatic tyred traffic in accordance with the guidelines of IS 9282: 1993 [37] (Table 12). Finally, it is suggested that recycled aggregate can be used to replace natural aggregate without affecting abrasion resistance characteristic beyond the limit that make a concrete unfit for the pavement construction. 4. Conclusions The influence of replacing natural coarse aggregates in concrete mixes with recycled concrete aggregates of similar size obtained from recycling of CDW on abrasion resistance of pavement concrete is reported in this study. Its impact on compressive and flexural strengths of concrete, were examined also. The important finding from the study are given as follows. In interpretting the findings, it should be noted that the results are limited to the RCA and mixes used in the study. The physical properties of recycled coarse aggregate were inferior to the natural coarse aggregate. The replacement of natural aggregate with recycled one reduces the fresh density of the concrete mixes by 6–8%.
Compressive and flexural strength of the concrete made with recycled aggregate were less than the concrete with natural aggregate. This decrease is much more prominent when all natural aggregate i.e. from 4.75 to 20 mm is replaced by recycled aggregate. The abrasion resistance of concrete with recycled aggregate was significantly less compared to concrete with natural aggregate. The concrete mixes made with replacement of only larger size recycled aggregate i.e.10–20 mm showed better resistance to abrasion than mixes mixes with all recycled aggregate that is, from 4.75 to 20 mm. However, all concrete mixes show abrasion resistance characteristics acceptable for paving concrete. Recycled aggregate can be used to replace natural aggregate from paving concrete without adversely affecting its abrasion resistance characteristic.
Acknowledgements The permission of the Director, CSIR-CRRI (Prof. Satish Chandra) to publish this research study is gratefully acknowledged. The RCA material provided by the manufacturer is thankfully acknowledged. The help rendered by Prof. T. R. Naik of UW-M, USA for the improvement of the paper is gratefully acknowledged. The support provided during the experimental work by Mr. Ishan Sinha, Shekhawat, Vijay Kumar, Rishi and other laboratory staff of the CSIR-CRRI is thankfully acknowledged.
References [1] K. Yanik, Report-global demand for aggregates to rise,
R. Kumar / Construction and Building Materials 142 (2017) 248–255 [9] C.S. Poon, Z.H. Shui, C.S. Lam, H. Fok, S.C. Kou, Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete, Cem. Concr. Res. 34 (2004) 31–36. [10] K. Rahal, Mechanical properties of concrete with recycled coarse aggregate, Build. Environ. 42 (2007) 407–415. [11] K.H. Yang, H.S. Chung, A. Ashour, Influence of type and replacement level of recycled aggregates on concrete properties, ACI Mater. J. 105 (2008) 289–296. [12] T.C. Hansen, H. Narud, Strength of recycled concrete made from crushed concrete coarse aggregate, ACI Concr. Int. 5 (1987) 79–83. [13] J. Xiao, J. Li, C. Zhang, Mechanical properties of recycled aggregate concrete under uniaxial loading, Cem. Concr. Res. 35 (2005) 1187–1194. [14] R. Kumar, C. Shekhawat, Commercially available construction and demolition waste recycled coarse aggregate in the manufacture of concrete, Ind. Concr. J. 90 (2016) 27–35. [15] C.S. Poon, Z.H. Shui, L. Lam, Effect of microstructure of ITZ on compressive strength of concrete prepared with recycled aggregates, Constr. Build. Mater. 18 (2004) 461–468. [16] M. Tavakoli, P. Soroushin, Strength of recycled aggregate concrete made using field-demolished concrete as aggregate, ACI Mater. J. 93 (1996) 182–188. [17] A. Domingo-Cabo, C. Lázaro, F. López-Gayarre, M.A. Serrano-López, P. Serna, J. O. Castaño-Tabares, Creep and shrinkage of recycled aggregate concrete, Constr. Build. Mater. 23 (2009) 2545–2553. [18] J.M.V. Gómez-Soberón, Porosity of recycled concrete with substitution of recycled concrete aggregate an experimental study, Cem. Concr. Res. 32 (2002) 1301–1311. [19] R.M. Salem, E.G. Burdette, N.M. Jackson, Resistance to freezing and thawing of recycled aggregate concrete, ACI Mater. J. 100 (2003) 216–230. [20] R. Zaharieva, F. Buyle-Bodin, E. Wirguin, Frost resistance of recycled aggregate concrete, Cem. Concr. Res. 34 (2004) 1927–1932. [21] S.M. Levy, P. Helene, Durability of recycled aggregates concrete: a safe way to sustainable development, Cem. Concr. Res. 34 (2004) 1975–1980. [22] N. Otsuki, M. Asce, S. Miyazato, W. Yodsudjai, Influence of recycled aggregate on interfacial transition zone, strength, chloride penetration and carbonation of concrete, ASCE J. Mater. Civ. Eng. 15 (2003) 443–451.
255
[23] K.Y. Ann, H.Y. Moon, Y.B. Kim, J. Ryou, Durability of recycled aggregate concrete using pozzolanic materials, Waste Manage. 28 (2008) 993–999. [24] F.T. Olorunsogo, N. Padayachee, Performance of recycled aggregate concrete monitored by durability indexes, Cem. Concr. Res. 32 (2002) 179–185. [25] A.M. Knaack, Y.C. Kurama, Design of concrete mixtures with recycled concrete aggregates, ACI Mater. J. 110 (2013) 483–493. [26] R.V. Silva, J. de Brito, R.K. Dhir, Properties and composition of recycled aggregates from construction and demolition waste suitable for concrete production, Const. Build. Mater. 65 (2014) 201–217. [27] ACI Committee 201 Report, Guide to Durable Concrete, Title No. 74–53, ACI, 1977. [28] P.K. Mehta, Concrete Structure, Properties and Materials, Prentice-Hall International, 1986. [29] M.E. Prior, Abrasion Resistance: Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM STP-169A, ASTM, Philadelphia, 1966, pp. 246–260. [30] K.M. Hadchti, R.L. Carrasquillo, Abrasion resistance and scaling resistance of concrete containing fly ash, Center for Transportation Research, Bureau of Engineering Research, University of Texas at Austin, Research Report: 481–3, August 1988. [31] L.P. Witte, J.E. Backstrom, Some properties affecting the abrasion resistance of air-entrained concrete, ASTM Proc. 51 (1951) 1141–1155. [32] P. Laplante, P.C. Aifcin, Vezina, Abrasion resistance of concrete, J. Mater. Civ. Eng. 3 (1991) 19–30. [33] I. Standard, Plain and reinforced concrete-code of practice, IS 456, 2000. [34] R.F. Ytterburg, Wear-resistant industrial floors of portland cement concrete, ASCE Civ. Eng. 41 (1971) 68–71. [35] A. Nanni, Curing of roller compacted concrete and strength development, ASCE J. Transp. Eng. 114 (1988) 684–694. [36] I. Standard, Method of Test for Strength of Concrete, IS 516, 1959. [37] I. Standard, Method of Test for Abrasion Resistance of Concrete, IS 9284, 1993. [38] I. Standard, Standard Sand for Testing of Cement Specification, IS 650, 1991.