Laboratory evaluation of the characteristics of continuously reinforced concrete pavement incorporating recycled concrete aggregate.
Globally, the concrete industry consumes large quantities of natural resources, which are becoming scarce to meet increasing demands. At the same time, utility of old structure is diminishing. These infrastructures are demolished to pave way for new and modern construction. Buildings are demolished due to various reasons, such as reconstruction for better economic gains, natural disasters and war-inflicted damages. The rate of demolition is increasing day by day, and at the same time, the cost of dumping is increasing due to non-availability of appropriate dumping sites. Besides scarcity of land, other problems associated with the landfill option include their location, transportation cost and public opposition. Thus, recycling has been gaining wider attention as a viable option for the handling of waste materials. Utilisation of recycled concrete aggregate (RCA) in concrete has been engaged due to awareness of society in natural resources protection. The application of Recycled Aggregate as coarse aggregate in concrete mixes has been initiated so as to make effective use of the waste materials (Singla 2013).
Properties of RCA are necessary to determine its suitability for use as an aggregate in new concrete pavements and for proper design of the concrete mix design. According to Singla (2013) the advantages of RCA are sustainability, reduction in the amount of material that would be delivered to a landfill, and reduction in the need of virgin aggregate to be created.
According to Keith, Jeff, and Mark (2009), the reasons for considering the use of RCA as a source of aggregate for the new pavement are: (a) Dwindling supplies of high-quality virgin aggregates, dwindling landfill space and increased disposal costs, (b) Sustainability (conservation of natural resources) and overall reduction in project costs. The Los Angeles abrasion test is a method for determining an aggregate's resistance to abrasion. It can be used as a measure of an aggregate's suitability for use in concrete because higher loss values often indicate undesirable softness of an aggregate (Snyder 2006). Typical values of mass loss for RCA are 20-45% compared to 15-30% for NA (Snyder 2006). The values usually indicate internal structural strength of the aggregates and the quality of the aggregate. Additional loss occurs for recycled aggregates in this test, dependent on the amounts of adhered mortar, due to the weakness of mortar-to-aggregate bond strengths (Amorim, De Brito, and Evangelista 2012).
Previous studies of the effects of using RCA in new Portland cement concrete have varied in their conclusions, largely because aggregate quality varied widely in the original concrete from which the RCA was produced. The quality and properties of RCA has been found to be similar to the quality and properties of the original aggregate (Garber et al. 2011), and RCA quality impacts the quality of the concrete in which it is incorporated (Limbachiya, Meddah, and Ouchagour 2012). Thus, recycling concrete where the original aggregates were of low quality would likely yield RCA which is inadequate for use. It has been recognised by Gonzalez and Moo-Young (2004) that choosing to not reuse high-quality aggregate could be wasteful, and that exploring RCA could provide relief to the exhaustion of natural aggregate resources and construction budget.
Concrete workability can be a concern regardless of whether or not RCA is used to replace NA, but a mix with RCA - tends to lose workability faster and is often a harsher mix (Garber et al. 2011). This harshness is due to the more angular surface typical of RCA, compared to NA, which is a result of the crushing process used to obtain it. One study found that - the RCA's average shape index is 120% higher than the NCA's (natural coarse aggregate), meaning that RCA is more angulated than the NCA (Amorim, De Brito, and Evangelista 2012). The workability of a mix affects slump, how easily the concrete can be placed, and how well it will compacted.
Higher and more variable air contents are common in fresh concrete made with RCA. This is due to the higher porosity of the recycled aggregates themselves and to the entrained air in the original mortar. Therefore, the target air content of mixtures containing RCA must be higher to achieve the same durability as conventional mixes (Keith, Jeff, and Mark 2009). Butler, West, and Tighe (2011) however, concluded that recycled coarse aggregate concrete had higher compressive strength values than the natural aggregate concrete. This is likely due to the stronger mortar-aggregate bond between the RCA and the new mortar.
Chen, Yen, and Chen (2003) study, washed RA was used as coarse aggregate. They found that washed RA comprised higher strength than that of unwashed RA. Greater bond effects were produced when impurities, powder and harmful materials on aggregate surface in RA are washed away. They also identified that at low w/c ratio, the compressive strength ratio of recycled concretes to normal concretes are decreased. Main factor which lead to this result is strength of the paste is increase at low w/c ratio. Based on composite material theory, they revealed that RA will become a weak material and its bearing capacity become smaller which influenced to decrease in strength.
Amnon Katz (2003), tested the properties of the recycled aggregate and of the new concrete made from it, with nearly 100% of aggregate replacement, and found that the concrete made with 100% recycled aggregates was weaker than concrete made with natural aggregates at the same water to cement ratio. It was also found that the properties of aggregates made from crushed concrete and the effect of the aggregates on the new concrete (strength, modulus of elasticity, etc.) resemble those of lightweight aggregate concrete.
The flexural strength drops by 13% with the 100% replacement of coarse aggregate (Rao, Jha, and Misra 2007). The strength of RCA is reported to be less by about 10% compared to normal concrete (Sagoe-Crentsil, Brown, and Taylor 2001). Drying shrinkage is a long-term property of concrete. It depends upon the amount of excess mix water, paste content, and how well the aggregate restrains paste shrinkage. The use of coarse RCA results in excess water in the pores of the RCA as well as an increase in paste content. Thus, coarse RCA replacement of coarse NA typically results in an increase in drying shrinkage (Snyder 2006).
One of the major applications of RCA is in the construction of continuously reinforced concrete pavements (CRCP). CRCPs are designed and constructed to provide a durable and comfortable driving surface and these are ideal for heavy-traffic highways and airport pavements. CRCP is fully reinforced along the entire length. CRCP naturally forms tight transverse cracks to evenly transfer loads. The transverse cracks do not impair the structural integrity of the pavement. Initially, continuously reinforced designs generally cost more than jointed reinforced or jointed plain designs due to increased quantities of steel. However, CRCP can demonstrate superior long-term performance and cost-effectiveness. A number of agencies choose to use CRCP designs in their heavy urban traffic corridors. A couple advantages of concrete pavement are that they are typically stronger and more durable than asphalt roadways. They also can easily be grooved to provide a durable skid-resistant surface. Concrete reinforcing steel institute (CRSI) and the Federal Highway Administration (FHWA) have a joint venture project to provide recommended practices for the design, construction and repair of CRCP (USDOT-FHWA-HIF 12-039 2012, ACPA Bulletin EB 045 2009; USDOT-FHWA Technical Advisory T5040.37 2007).
The lack of landfill sites for waste disposal and the potential exhaustion of natural resources have led regulatory agencies and construction industry to consider the use of recycled wastes from old concrete structures and construction waste as a new source of construction materials (RCA). In order to successfully use the recycled materials in pavement construction, it is necessary to study the characteristics of concrete pavement incorporating RCA.
2. Materials and methods
Cement is a fine, grey powder. It is mixed with water and materials such as sand, gravel and crushed stone to make concrete. The cement and water form a paste that binds the other materials together as the concrete hardens. The cement used in this study conforms to the provisions of ASTM C150/C150M (2015) and WSDOT M41-10 (2016).
2.1.2. Aggregate properties
The fine aggregate, natural coarse aggregate and recycled coarse aggregate used in this study conform to the specifications of ASTM C33/C33M (2014), AASHTO M 80 (2013), AASHTO T 96-02 (2015), WSDOT M46-01 (2016) and USDOT-FHWA FP-14 (2014).
2.2.1. Mix design and slump test
Concrete mix was designed at a mix ratio of 1:2:3 of cement, fine aggregate and coarse aggregate and in accordance with the specifications of USDOT-FHWA FP-14 (2014) and WSDOT M46-01 (2016). All concrete mixtures were designed by keeping the water-cement ratio constant. The recycled coarse aggregate replacement percentage is defined as the weight ratio of recycled coarse aggregate to the total coarse aggregates in the concrete mixture and depending upon the selected replacement percentage, direct substitution of NCA with an equal weight of recycled coarse aggregate particles was carried out in this study.
According to USDOT-FHWA FP-14 (2014) and WSDOT M46-01 (2016), the slump test is a measure of the consistency of the concrete and a change in the slump test indicates that something in the manufacturing of the concrete has changed. In this study, slump test was conducted on the fresh concrete in accordance with WSDOT M41-10 (2016), WSDOT M46-01 (2016), and USDOT-FHWA FP-14 (2014).
2.2.2. Compressive strength test and split tensile strength
Compressive strength test and the split tensile test were performed on the hardened concrete in accordance with USDOT-FHWA FP-14 (2014), FDOT (2016), IDOT (2012), TXDOT (2014), WSDOT M41-10 (2016) and WSDOT M46-01 (2016). The cylindrical test specimens were of the size 150 mm diameter and 300 mm long and were cast as soon as practicable after mixing using standard moulds and compacted. The moulds were filled in three layers of 100 mm each and each layer was compacted. The samples were marked and cured in clean fresh water and were maintained at a room temperature of 25 [+ or -] 2 [degrees]C. The compressive strength machine used was power operated and load was applied continuously and without shock. The load was applied at a rate of movement corresponding to a stress rate on the specimen of 0.25 [+ or -] 0.05 N/[mm.sup.2] per seconds until the specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete. Six cubes from each of the seven different mixes were crushed at the 3rd, 7th, 14th, 28th and 56th days age, respectively, and the average were recorded as the compressive strength.
The split tensile strength for each mix was carried out at the 7th, 14th and 28th day of the 150 mm diameter and 300 mm long cylindrical concrete specimens. The compressive strength machine used was power operated and load was applied continuously and without shock, at a constant rate within the range of 0.689 to 1.38 N/[mm.sup.2] per minute splitting tensile stress until failure of the specimen. The splitting strength of the specimens was calculated.
3. Results and discussions
3.1. Aggregate properties
Table 1 shows the sieve analysis results of the fine aggregate and Table 2 shows the physical properties of fine aggregate, natural coarse aggregate and recycled concrete aggregate. Table 3 shows the sieve analysis results of the natural coarse aggregate (crushed granite from quarry site). Table 4 shows the sieve analysis results of the RCA used in this study.
For an aggregate to perform satisfactory in pavement, it must be sufficiently hard to resist the crushing, impact and abrasive effect of traffic over long period of time. The soft aggregates will be quickly ground to dust, whilst the hard aggregates are quite resistant to these effects and as such they are more durable.
The durability properties of RCA, which includes results from the aggregate crushing value, the aggregate impact value and the Los Angeles value tests were presented in Table 5. The ACV of NCA was 21.95 and that of RCA was 22.99. ASTM D5874-02 (2007) and AASHTO M 80 (2013) specification require that aggregates to be used in concrete pavement must have an aggregate crushing that is less than 30%. The aggregate impact value and the Los Angeles abrasion value of NCA are 20.81 and 26.40%, respectively, while those of RCA are 22.99 and 28.00%, respectively.
The WSDOT (2012), ASTM C131/C131M-14 (2006), AASHTO M 80 (2013) and AASHTO T 96-02 (2015) specification require that aggregate to be used in concrete pavements must have a Los Angeles wear loss that is not more than 40%. The RCA had a Los Angeles abrasion loss which is 28.00% which is greater than that of the NCA and less than 40% specified. Based on the ACV, AIV and Los Angeles abrasion loss results, the RCA used in this study meet relevant code requirements.
3.2. Mix design and slump values
A labelling system was developed to denote the six concrete mixes evaluated in this study. Table 5 shows the mix design used in this study. The mix design shows 400Kg/[m.sup.3] of cement which satisfied the minimum cement content of 300 to 360Kg/[m.sup.3] for standard and high performance concrete in accordance with the specifications of USDOT-FHWA FP-14 (2014), WSDOT M41-10 (2016), TXDOT (2014), FDOT (2016) and IDOT (2012). The fine aggregate to total aggregate ratio is 0.4 which satisfies the 0.35 to 0.45 specifications of USDOT-FHWA FP-14 (2014), TXDOT (2014), WSDOT M41-10 (2016), FDOT (2016) and IDOT (2012). The measured slump values for each of the six fresh concrete mixes were presented in Figure 1. The slump values were within the range of 50 to 120 mm as shown in Figure 1. The slump value decreases with increase in percentage replacement of natural coarse aggregate with RCA. This indicates poor workability in concrete containing higher percentage of RCA. This can be addressed by pre-wetting the RCA before batching.
3.3. Compressive strength and split tensile strength
The average compressive strength of the various mixtures of percentage replacement of NCA with RCA at an age of 3rd, 7th, 14th, 28th and 56th days are given in Table 6. Figure 2 shows the relationship between the compressive strength (N/[mm.sup.2]) and Curing age (days). From Table 6 and Figures 2 and 3, it can be seen that all the concrete mixtures show increase in strength with increase in the curing age and a decrease in compressive strength with increase in the percentage replacement of NCA with RCA. From the test results presented in Table 6 and in Figures 2, and 3, it can be observed the compressive strength of concrete mixtures containing 0 to 100% replacement of NCA with RCA satisfied the USDOT-FHWA FP-14 (2014), TXDOT (2014), WSDOT M41-10 (2016), FDOT (2016) and IDOT (2012) 28 days minimum compressive strength specification of 28 N/[mm.sup.2] to 31 N/[mm.sup.2] for standard and high performance concrete pavement. It is evident from the results presented that the compressive strength of all the mixtures continued to increase with the increase in age. However, maximum strength at all ages occurs with 0% natural coarse aggregate replacement and up to 60% replacement of NCA with RCA show no significant different in compressive strength value. The compressive strength values also reduce with increase in percentage replacement NCA with RCA. This may be due to attached mortar on the surface of the RCA, cracks in the aggregate itself (which could occur during the crushing) and weak aggregate-matrix interface bond. The results presented indicate that RCA used in this study were of good quality.
The split tensile strength of concrete mixtures incorporating RCA was evaluated at the age of 7th, 14th and 28th day age. Figure 2 shows the variation of percentage replacement of NCA with 7th, 14th and 28th day split tensile strength results. From Figure 4, it can be seen that there is increase in split tensile strength values with the increase in age. The maximum split tensile strength for all the mixtures under study occurs at 0% natural coarse aggregate replacement at all the ages.
Based on the results and performance of concrete incorporating RCA in this study, the following conclusions were drawn:
(1) The quality and properties of RCA are similar to the quality and properties of the natural coarse aggregate. As such choosing not to reuse high-quality RCA can be wasteful.
(2) The compressive strengths of new concrete pavement incorporating different percentages of RCA are in the order of 40.91 to 33.81 N/[mm.sup.2] at the 28 day age for 0 to 100% replacement of NCA with RCA.
(3) The 28 days compressive strength is in the range of 0.95 to 0.83 times that of natural coarse aggregate concrete (control mix). The 28 days compressive strengths obtained in this study for all the concrete mixtures satisfied the USDOT-FHWA FP-14 (2014), PCA EB 233 (2005), TXDOT (2014), WSDOT (2012), FDOT (2016) and IDOT (2012) 28 days minimum specified compressive strength of 28 to 31 N/[mm.sup.2] for standard and high strength CRCP.
(4) RCA produced from demolished and construction waste consisting high-quality original materials can be an acceptable source of aggregate for new concrete pavement at up to 100% replacement of natural coarse aggregate.
(5) The use of RCA in production of new concrete pavement should be encouraged with 60% maximum replacement of NCA.
(6) The use of RCA in concrete pavement addresses the problem of disposal cost, conservation of dwindling natural aggregates and construction cost.
No potential conflict of interest was reported by the author.
Notes on contributors
Alban Chidiebere Ogbonna is an academic staff/researcher, Department of Civil Engineering, College of Engineering, Waziri Umaru Federal Polytechnic, Birnin Kebbi, Kebbi State, Nigeria. The author's main research areas are Civil engineering, Civil engineering materials, Highway engineering, Pavement material engineering, Traffic engineering, Environmental engineering, and Transportation engineering.
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Alban Chidiebere Ogbonna
Department of Civil Engineering, Waziri Umaru Federal Polytechnic Birnin Kebbi, PMB 1034 Birnin Kebbi GPO, Birnin Kebbi, Kebbi, Nigeria
CONTACT Alban Chidiebere Ogbonna * firstname.lastname@example.org
Received 28 June 2017
Accepted 29 November 2017
Table 1. Sieve analysis of fine aggregate. S/N Sieve size (mm) Weight retained (g) Percentage retained (%) 1 10 0.00 0.00 2 6.25 0.00 0.00 3 4.75 17.70 1.77 4 2.36 58.80 5.88 5 1.18 129.50 12.95 6 0.60 148.50 14.85 7 0.30 324.50 32.45 8 0.15 308.00 30.80 9 0.075 13.00 1.30 Total 1000 100% Cumulative percentage retained S/N (%) Percentage passing (%) 1 0.00 100 2 0.00 100 3 1.77 98.23 4 7.65 92.35 5 20.26 79.74 6 35.45 64.55 7 67.90 32.10 8 98.70 1.30 9 99.70 0.30 Total 231.73 Table 2. Physical properties of fine aggregate, natural coarse aggregate and recycled concrete aggregate. Natural Recycled coarse concrete Fine aggregate aggregate S/N Characteristics aggregate (NCA) (RCA) 1 Type Natural Crushed Demolished river sand granite and crushed concrete 2 Fine modulus 2.32 2.15 1.98 3 Specific gravity 2.65 2.7 2.3 4 Water absorption (%) -- 1.1 4.9 -- 21.95 22.99 5 Aggregate crushing value (%) -- 20.81 22.99 6 Aggregate impact value (%) -- 26.40 28.00 7 Los Angeles abrasion value (%) Table 3. Gradation of natural coarse aggregate (NCA). S/N Sieve size (mm) Weight retained (g) Percentage passing (%) 1 20.00 0.00 0.00 2 16.00 108 10.80 3 12.50 190 19.00 4 10.00 380 38.00 5 6.50 203 20.30 6 4.75 85 8.50 Total 966 96.60 S/N Cumulative percentage retained (%) Percentage passing (%) 1 0.00 100 2 10.80 89.20 3 29.80 70.20 4 67.80 32.20 5 88.10 11.90 6 96.60 3.40 Total 214.5 Table 4. Gradation of recycled concrete aggregate (RCA). S/N Sieve size (mm) Weight retained (g) Percentage retained (%) 1 20.00 0.00 0.00 2 16.00 145 14.50 3 12.50 103 10.30 4 10.00 283 28.30 5 6.50 268 26.80 6 4.75 135 13.50 Total 934 93.40 Cumulative percentage retained S/N (%) Percentage passing (%) 1 0.00 100 2 14.50 85.50 3 24.80 75.20 4 53.10 46.90 5 79.90 20.10 6 93.40 6.60 Total 19.40 Table 5. Concrete mix design at 1:2:3. Water/Cement Cement (kg/[m.sup.3]) Cube mark ratio Water (kg/[m.sup.3]) A 0.55 220 400 B 0.55 220 400 C 0.55 220 400 D 0.55 220 400 E 0.55 220 400 F 0.55 220 400 Natural coarse Recycled Fine aggregate aggregate coarse aggregate Cube mark (kg/[m.sup.3]) (kg/[m.sup.3]) (kg/[m.sup.3]) A 800 1200 - B 800 960 240 C 800 720 480 D 800 480 720 E 800 240 960 F 800 -- 1200 Percentage replacement of Cube mark NCA with RCA (%) A 0 B 20 C 40 D 60 E 80 F 100 Table 6. Average compressive strength test results ([f.sub.ck]). Percentage replacement of NCA with RCA 3rd day (N/ 7th day (N/ Cube mark (%) Density kg/ [mm.sup.2]) [mm.sup.2]) [m.sup.3] A 0 2437 16.10 20.20 B 20 2437 14.60 18.60 C 40 2424 12.08 16.50 D 60 2421 10.80 14.80 E 80 2419 9.01 13.40 F 100 2415 8.66 11.70 14th day (N/ 28th day (N/ 56th day(N/ Cube mark [mm.sup.2]) [mm.sup.2]) [mm.sup.2]) A 29.58 40.91 43.88 B 28.00 38.82 42.61 C 27.30 37.08 40.92 D 26.60 36.37 38.86 E 23.90 34.68 36.48 F 21.70 33.81 35.66
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|Author:||Ogbonna, Alban Chidiebere|
|Publication:||Australian Journal of Civil Engineering|
|Date:||Apr 1, 2018|
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