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Mechanical properties of recycled aggregate concrete proportioned with modified equivalent mortar volume method for paving applications
Construction and Building Materials 136 (2017) 9–17
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Mechanical properties of recycled aggregate concrete proportioned with modified equivalent mortar volume method for paving applications S. Yang a,⇑, H. Lee b a b
School of Architectural Engineering, Hongik University, South Korea Construction Safety Division, Korea Infrastructure Safety Corporation, South Korea
h i g h l i g h t s A modified equivalent mortar mix design is proposed for recycled aggregate concrete. Results show modulus of elasticity comparable or superior to those of similar mixes made with natural aggregates or conventional mixes with RCA. This modified recycling mix design may be performed well even for the paving concrete mix. This method applies to any recycled concrete aggregate regardless of poor absorption capacity.
a r t i c l e
i n f o
Article history: Received 29 February 2016 Received in revised form 1 September 2016 Accepted 8 January 2017
Keywords: Mixtures Recycled concrete aggregate Compressive strength Elastic modulus
a b s t r a c t The equivalent mortar volume (EMV) mix design method, which was originally proposed by Fathifazl et al., was successfully verified in their previous studies for concrete mixes containing coarse recycled concrete aggregate (RCA). However, especially for paving concrete mix, which is typically proportioned with a marginal amount of sand, the nature of the EMV mix proportions leads to a far lower amount of sand. Thus, a modified EMV proportioning method is proposed, assuming that the residual mortar in RCA concrete (RAC) can be represented as the sum of the volume fraction of mor(RM) volume V RAC RM RAC V RAC tar 1S V RM and the other volume fraction of coarse aggregate S1 RM , using scale factors S = 1, 2, and 3. S To verify this modified EMV method, four series of concrete mixes were made using the modified EMV mix design, along with the original EMV and the conventional mix designs, with various sources of RCAs. For each mix, the slump, air content, compressive strength and elastic modulus were measured. Test results show that the modified EMV method yields modulus properties comparable or superior to those of similar mixes made with natural coarse aggregates or those of conventional mixes with RCA. Furthermore, it is demonstrated that this modified method applies well to paving concrete mixes, regardless of the absorption capacity of RCA. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Since 2008, the government of South Korea has made it obligatory for public road agencies to use recycled concrete aggregate (RCA) [1–2]. From the year 2014 onwards, the mandatory usage of RCA was increased to be 30%, 40%, and 50% maximum replacement of total coarse aggregate in 2014, 2015, and 2016, respectively, for subgrade and subbase courses of road [1–2]. In the meantime, it has been reported that concrete airport pavements in S. Korea have been deteriorating. Several air bases have already been resurfaced; however, the RCAs produced on-site on air bases ⇑ Corresponding author at: School of Architectural Engineering, Hongik University, 2639 Sejong-ro, Jochiwon, Sejong 339-701, South Korea. E-mail address: [email protected] (S. Yang). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.029 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
have been used only for sub-base materials, regardless of the potentially good RCA quality. This is because of the strict RCA quality requirement for coarse RCA to have less than 3% of water absorption and above 2.5 of specific gravity for it to be used as structural or paving concrete [3–5]. In reality, 4–6 additional crushing process steps must be carried out at the recycling plant in order to satisfy the specifications, resulting in a loss of time and money [6–7]. In addition, for structural concrete, it is required that the compressive strength be within 27 MPa; it is also recommended that RCA be within 30% maximum replacement of NA, strongly limiting the use of this material [4]. Requirements for RCAs in other countries were well documented in reference [8]. A cost analysis of recycled aggregate production on airport pavement [6,9] came to the conclusion that excessive removal of RM using a great amount of energy or high cost to meet the RCA
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
quality requirement may not be the answer to the problem of procuring RCA concrete mixes that can be widely used in airport pavement. Rather, using RCA manufactured through 1–3 stage processing only, regardless of poor absorption capacity, the equivalent mortar volume method proposed by Fathifazl et al. [10] was considered to be one of the best resurfacing alternatives. Fathifazl and his colleagues [10–12] stated that recycled aggregate concrete (RAC) proportioned using the conventional mix proportioning method is inferior in material characteristics, such as the modulus of elasticity and drying shrinkage because of the increasing ratio of mortar in the total mixture. According to their theory, in fresh concrete before hardening, residual mortar (RM) attached to coarse RCA acts as coarse aggregate. After hardening, however, RM acts as mortar. In the case of the conventional mix design made with RAC, not only the newly made mortar but also the RM attached to the RCA is included in the total mortar (TM). The total mortar ratio of the RAC in the conventional mix design is greater than that in the natural aggregate concrete (NAC) mix. Fathifazl et al. explain that this mortar ratio difference causes a decrease in the modulus of elasticity and an increase in the drying shrinkage. Fathifazl [12] stated from 45 research results that the compressive strength of RAC is decreased by 0–42% due to changes in the mortar strength and the aggregate-mortar bond strength at the interfacial transition zone. In 17 articles, he states that the modulus of elasticity is decreased by 0–45% due to changes in the modulus of elasticity of natural coarse aggregate, the modulus of elasticity of the mortar, and the volume of the mortar. In 11 articles, he asserts that there is an increase of the drying shrinkage strain due to the change in the volume of the mortar. With these results, and considering RM, he came up with an equivalent mortar volume (EVM) mix design method and showed that the modulus of elasticity does not decrease. A number of beneficiation processes has been proposed to reduce the residual mortar content of RCA [13–17]. These techniques generally use mechanical, chemical, or thermal processing, or micro-assisted beneficiation [16,18] and various combinations of these methods [17]. The first attempt to measure RM goes back to Hansen [19] in 1986. The RM correlation trends of specific gravity as well as absorption capacity have been integrated comprehensively [19]. However no attempt has been made to systematically quantify the effect of RM in terms of its elastic modulus and volume fraction on RCA concrete properties [10]. The first study of this sort was performed by Abbas et al. [14], who attempted to measure the RM value and use it as an input variable in the EMV mix design for a series of experiments. It is known that the original EMV mix proportioning method is very proper for structural concrete mixes, which typically have about 800 kg/m3 of fine aggregate. However, especially for the concrete mix used in road pavement, which is typically proportioned with a marginal amount (usually less than 700 kg/m3) of fine aggregates, the nature of the EMV mix proportions leads to far lower amounts of fine aggregates, in some cases less than 600 kg/m3, leading to a harsh mix and slump loss. This will lead to a range of shortages in the amount of sand or fresh mortar. Thus, a modified EMV mix proportioning method is proposed; this method assumes that the volume fraction of the residual mortar (RM) may be mathematically treated as an original virgin aggregate (OVA), while the other fraction can be treated as part of the total mortar. This paper aims to assess the effect of different mix proportioning methods (the conventional ACI method/the original EMV method versus the modified EMV method) on the mechanical properties of RCA concrete. To verify this modified method, four series of mixes were made using the revised EMV mix design, along with the original EMV and the conventional mix design, with various types of coarse RCA.
2. Modified equivalent mortar volume mix method 2.1. Background and problem statements As previously mentioned, Faithifazl et al. [10] stated that material properties of RCA concrete become inferior because RM attached to RCA is not considered. To visually determine the volume fractions of the mortar and the original virgin aggregate of RCA, concrete was examined by making specimen with coarse RCA and white cement only. Fig. 1 illustrates polished section of a 150 mm 300 mm concrete cylindrical specimen. The white part of the section is mortar; the rest is RCA. The dark shaded parts of RCA are the original virgin aggregate, and the lighter part is RM. Fig. 2 shows the difference between the conventional mix design and the EMV mix design concepts proposed by Fathifazl et al. [10]. Figs. 2a and b show the volume composition of NAC and RAC, respectively, in the conventional mix design. Both mixes have a fixed volume ratio of coarse aggregate, fine aggregate, cement, water, and air. The difference between Fig. 2a and b is that the total mortar (TM) volume of RAC is larger than that of NAC. It is because of this discrepancy that the material properties of RAC become inferior. Fig. 2c shows the concept of the EMV mix design that Fathifazl et al. [10] originally proposed. This mix design method fixes the volume ratio of the total mortar equal to that shown in Fig. 2a. In the EMV mix design, the new mortar volume is reduced to the same degree as the reduction of RM attached to RCA. Especially for paving concrete mix, if RCA is used with more than a certain amount of or with more RMC content, the unit weight of the fine aggregate in the concrete mix according to the EMV concept itself leads to a value below 600 kg. Then, the shape or formability of the concrete may be a concern due to the lack of fillers. The decrease in flowable mortar affects not only the shape, but also, due to the slump decrease, the constructability. Table 1 shows the slump values of paving concretes measured during test series 2 in this study; these results will be discussed in more detail later, in section 3. The test results show that the slump of the 2C-N concrete mix (refer to Section 3.1.3 for notation), made with only natural aggregate, is 122 mm, while that of 2E-I1 concrete, made with the substitution of 50% RCA using the original EMV mix design, is 78 mm. In the case of concrete 2E-I2⁄, made with the substitution of 100% RCA and using the EMV mix design, a lack of workable new mortar or
Fig. 1. Polished concrete specimen mixed with white cement and coarse RCA only.
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
(a) Conventional mix (NAC)
(b) Conventional mix (RAC)
11
(c) EMV mix (RAC)
Fig. 2. Mix design concept.
Table 1 Slump in various trial mixes (Test series 2). Mix id
Fine agg. amount(kg/m3)
Slump(mm)
Mix design
2C-N 2E-I1 2E-I2* 2E-I2
757 655 496 633
122 78 10 87
Conventional EMV EMV Modified EMV
It was considered in the modified EMV model that the RM attached to RCA serves as aggregate in fresh concrete, and as mortar after it is hardened. Considering this treatment, the RM volume in RAC was represented as the sum of the volume fraction of the mortar
1 RAC V S RM
S1 RAC V RM , S
using the scale factor S as follows:
V RAC RM ¼ fine aggregate, as shown in Table 1, yields a large slump drop to 10 mm. This is the reason that this study proposes a modified EMV approach to paving concrete mix with greater RCA replacement or higher RMC value. Table 1 shows that, in the 2E-I2 mix proportioned using the preceding modified EMV approach, the slump value bounces back to the level of the 2E-I1 mix. It should be noted that, according to the original EMV method [10], this issue has also been considered by looking at the concept of the dry-rodded specific gravity of the aggregate. By enforcing either (1) minimum NA content (or minimum replacement ratio, Rmin), in case of high RM content in RCA, or (2) maximum RM content in RCA if one desires to use 100% RCA in RAC, one can come up with the upper bound values for maximum RCA content, or the maximum RM content in RAC. Fathifazl et al. [10] chose a replacement ratio (R) equal to the RM volume in RCA divided by the RCA volume in RAC. The physical interpretation of this specific R value is that it indicates the level of replacement of the RM volume in RCA with fresh NA in RAC. This in fact is equivalent to the concept of the modified EMV method, where S = 1.
by V NAC NA . Then, a companion mix, termed RAC, comprising a blend of NA and RCA is designed. The volume of fresh NA in the RAC is represented by V RAC NA . The NA content ratio was to be R in Fig. 3b, as originally defined by Fathifazl et al. [10], as
V NAC NA
ð2Þ
Therefore, the value of R was modified as follows:
R ¼1
V RAC RCA V NAC NA
1 SGRCA b 1 RMC OVA S SGb
ð3Þ
where the volume of fresh NA in the natural aggregate concrete (NAC) is represented by V NAC NA and the volume of RCA in RCA concrete RCA and SGOVA are the bulk specific gravities of RCA and of by V RAC b RCA ; SGb the original virgin aggregate (OVA), respectively. For the RAC and its associated NAC to have the same hardened properties, the revised method requires that the following two conditions be satisfied and modified
1 RAC NAC V RAC ¼ V RAC TM ¼ V M NM þ V RM S RAC RAC V RAC TNA ¼ V OVA þ V NA þ
S 1 RAC V RM S
ð4Þ
ð5Þ
concrete made entirely with coarse NA; V RAC TNA = total coarse natural
In order to explain the difference between the concepts of the original EMV mix design and the modified EMV mix design of this study, the previous Fig. 2 illustration was reconstructed into the following Fig. 3 as an 1/S-EMV mix proportioning model, where a scale factor, S, is introduced. In the original EMV design procedure [10], to design an RCA concrete (RAC) mix with the specified fresh and hardened properties, first, one proportions a concrete mix, called natural aggregate concrete (NAC). The volume of coarse NA in this mix is represented
V RAC NA
1 RAC S 1 RAC V V RM þ S RM S
NAC where V RAC = mortar in the companion TM = TM volume in RAC; V M
2.2. Model equation
R¼
and the other volume faction of the aggregate
ð1Þ
aggregate (TNA) volume in RAC; and V RAC OVA = OVA volume in RAC. Then, required volumes and weights of RCA and NA are subsequently determined, given by the example flowchart in Appendix I. Finally, the corresponding quantities of water, cement, and fine aggregate in RCA concrete can be determined. 3. Materials and mix design methods 3.1. Materials 3.1.1. Cement material and chemical admixture Type I Portland cement was used in this study. The cement specific gravity used in the mixture design was 3.15 and the specific surface area was 3200 cm2/g. The chemical admixture used for this study was a solution of air entraining and a water reducing agent.
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
(a) Conventional mix
(b) Original EMV mix
(c) 1/S-EMV mix
Fig. 3. Comparison of mix design concept between original EMV model and revised 1/S-EMV model.
3.1.2. Aggregates material properties Natural aggregate material properties [20] with standard deviations are tabulated in Table 2. Two similar fine aggregates were used in this experiment. Fine aggregate 1 is natural sand with specific gravity of 2.63 and absorption capacity of 0.58%, used in test series 1 (see Table 4); fine aggregate 2 has specific gravity of 2.55, and absorption capacity of 0.95% and is used in the other test series. For the coarse aggregate, natural crushed granite aggregate was used. The specific gravity was 2.64 and the absorption capacity was 0.77%. Four types of RCA were used in our study. Two of them were produced in the Daegil (D) and Insun (I) plants, and the rest were produced in the ‘C’ and ‘A’ airbase worksites in S. Korea. The maximum size of RCA 4 was 40 mm, while maximum size was 25 mm for the other RCAs. The specific gravity, absorption capacity, and residual mortar quantity of each of the four types of RCA, with standard deviations, are shown in Table 3. The RMC values of RCA 3 and RCA 4 were determined using the same method suggested by Abbas et al. [14]. Two samples were used to determine the RMC values in individual size fractions. For RCA 3, a weighted average RMC value was determined for the blended RCA (25 mm, 10 mm fraction sizes). For RCA 4, a weighted average RMC value was determined for the blended RCA (40 mm, 20 mm, and 10 mm fraction sizes). The amount of the sample was about 2000 g for the fraction sizes over 20 mm and 1000 g for the smaller fraction size. After drying the samples for 24 h at 105 °C, the oven dried samples were immersed for 24 h in a 26% by weight sodium sulfate solution. While still immersed in the sodium sulfate solution, RCA samples were subjected to five cycles of freezing and thawing, i.e., 16 h at 17 °C and 8 h at 80 °C. After the last freezing-thawing cycle, the solution was drained from the sample and the aggregate was washed with water over a No. 4 sieve. The washed aggregate was then placed in an oven for 24 h at 105 °C and its oven-dried weight was measured. The RMC value was then obtained using [10]:
RMCð%Þ ¼
W RCA W OVA 100 W RCA
ð5Þ
where WRCA = initial oven-dried weight (g) of the RCA sample before the test and WOVA = final oven-dried weight (g) of the OVA after removal of the residual mortar.
3.1.3. Mix design All four series of mixes were designed as shown in Table 4. The first series of mixes was designed for highway paving concrete, with maximum aggregate size of 25 mm. The second series of mixes was proportioned and based on a typical structural concrete mix design with a maximum aggregate size of 25 mm. The third and fourth series of mixes were designed for airport paving concrete with maximum aggregate size of 40 mm. The target air content for all mix designs was a minimum of 4.0%; the final mix design was determined after many trial batches. Due to the low slump requirement for road paving concrete, all mixes except for the second series of mixes were determined to have slump values under 50 mm. The target slump of structural concrete in test series 2 was provisionally 80–120 mm. Except for the first series of mixes proportioned with a 40% of w/c ratio, a w/c ratio of 38% of w/c ratio was chosen in the other series of mixes with the use of the water reducing agent. The example of mix identification in the second column of Table 4 can be explained as follows. There are three types of terms. The first number denotes the test series; the second term C denotes the conventional ACI mix design for normal concrete [21], while E denotes the EMV mix design. The third term designates the type of coarse aggregate: N indicates natural coarse aggregate; D and I are RCA produced from the Daegil and Insun plants in S. Korea, respectively; A and C are RCA from the ‘C’ and ‘A’ airbase jobsites in S. Korea, respectively. The number following the third term indicates the type of replacement amount of RCA in the total coarse aggregate. The S value in the fifth column of Table 4 indicates the scale factor applied in the 1/S-EMV model. For example, when applied to model 1/2-EMV, the S value becomes 2. The first series of mixes was designed to confirm how the conventional mix design with RCA leads to decreased material
Table 2 Natural aggregate material properties. Aggregates
Fine agg. 1a Fine agg. 2b Natural coarse agg.b a b
Determined from 3 test samples. Determined from 2 test samples.
Specific gravity
Absorption capacity(%)
Value
Standard deviation
Value
Standard deviation
2.63 2.55 2.64
0.002 0.099 0.007
0.58 0.95 0.77
0.092 0.028 0.134
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17 Table 3 RCA material properties. Aggregates
RCA RCA RCA RCA a b
1a 2a 3a 4a
RCA source
Maximum size(mm)
C airbase D plant I plant A airbase
25 25 25 40
Specific gravity
Absorption capacity(%)
RMC
Value
Standard deviation
Value
Standard deviation
Value
Standard deviation
2.42 2.37 2.54 2.35
0.021 0.028 n.ab n.ab
5.37 5.39 1.98 4.45
0.332 0.085 n.ab n.ab
n.ab n.ab 11.6 35.5
n.ab n.ab 0.283 1.768
Determined from 2 test samples. Not available.
Table 4 Concrete mixture designs and material quantities.
a b c
Test Series
Mix-id
w/c%
RCA content%a
S factor
Water kg
Cement kg
Sand kg
WRAb ml
AEc ml
NA kg
RCA, kg
1
1C-N 1C-C 1C-D
40.0 40.0 40.0
0 100 100
– – –
128 128 128
320 320 320
736 736 736
1157 0 0
0 1056 1038
0 0 0
64.0 38.4 38.4
2
2C-N 2C-I1 2C-I2 2E-I1 2E-I2
37.5 37.5 37.5 37.6 37.6
0 49.1 100 49.4 100
– – – 1 2
180 180 180 159 155
480 480 480 424 411
757 758 759 655 633
920 460 0 564 0
0 428 856 530 1102
1795 1795 1795 1586 1537
74.7 74.7 74.7 66.0 64.0
3
3C-N 3C-A 3E-A1 3E-A2 3E-A3
38.2 38.2 38.2 38.2 38.2
0 50.0 24.9 49.7 74.8
– – 1 2 3
140 140 126 121 117
366 366 329 318 305
675 675 606 585 563
1220 611 1025 708 366
0 543 303 623 969
4047 4047 4049 4051 4751
168.4 168.4 168.4 168.5 197.6
4
4C-N 4E-A1 4E-A2
38.2 38.2 38.2
0 24.9 49.7
– 1 2
140 126 121
366 329 318
675 606 585
1220 1025 708
0 303 623
2640 2211 2137
102.3 92.0 88.9
Coarse Aggregate
Ratio of RCA volumetric proportion to total coarse aggregates. Water reducing agent. Air entraining agent.
strength properties compared to the case of the companion concrete mix containing natural aggregate. The second series of mixes, before actual application to airbase paving concrete, was intended to validate the modified EMV mix design using structural concrete mix. Then the third series of mixes was designed to apply the modified EMV approach with scale factors, S = 1 (the original EMV mix proportion), 2, and 3 and those of companion mixes along with the conventional proportioning design. Finally, to verify the effect and repeatability of this modified EMV model, the fourth series of mixes was designed once more with the same mix design as that of the third series of mixes, except for the different amounts of admixture. It should be noted that the recycled concrete in each test series was produced by substituting 0, 25, 50, 75, or 100% levels of natural coarse aggregate with the RCA by volumetric proportion.
after batching, the fresh concrete properties such as air content [22] and slump [23] were tested. The hardened concrete property tests performed in this study included tests of compressive strength and modulus of elasticity. Specimens were prepared in plastic molds using the specified consolidation methods [24]. Then, the specimens were removed from the molds 24 h after casting. All specimens were moist cured at about 20 ± 2 °C from the time of molding until the moment of testing. Measurements of the compressive strength and modulus of elasticity of each mixture were carried out in accordance with ASTM C39 [25] and ASTM C469 [26], respectively. An average of three cylinders were tested at ages of different numbers of days, depending on the test groups. The cylinders were of the dimensions 100 mm 200 mm for test series 1 and 2 while cylinders were of dimensions of 150 mm 300 mm for test series 3 and 4. In test series 1, four specimens were tested, while three specimens were tested in test series 2–4.
3.2. Mixing process for making the concrete specimens 4. Experimental results A concrete pan mixer with a volume capacity of 60 L was used in the laboratory. Before the addition of water and the admixture solution, the admixture was thoroughly dispersed in the mixing water. Coarse aggregate and fine aggregate were added, and the mixer was given a few turns. Then cement was added and the mixer was started for about 90 s. Finally water was added while the mixer was running and the concrete was mixed for another 120 s. 3.3. Fresh and hardened concrete property testing The performances of the concrete mixtures were determined by testing the fresh and hardened concrete properties. Immediately
4.1. Slump and air content Generally, the target slump for road paving concrete is specified as being under 50 mm. In order to obtain excellent smoothness (or roughness), the slump value is required to be less than that of structural concrete. A slip-form paver vibrates, tamps, and shapes the rather harsh paving concrete mix to the desired surface configuration. All the slump test results are presented in Table 5 and Fig. 4. As can be seen in Fig. 4, compared to the conventional method, the EMV method in test series 2 resulted in lower slump probably due to the nature of the RM, which was treated as mortar in the
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
fresh concrete. When the replacement level of RCA in the EMV mixture was increased, from the level of the 2E-I1 mix, which has approximately 50% substitution to the level of the 2E-I2⁄ mix, which has 100% RCA substitution, the slump largely decreased due to the insufficiency of fine aggregates in the 2E-I2⁄ mix. This is probably because the required new mortar (NM), primarily comprised of sand, decreased by the amount of RM, causing the slump to decrease. As the 1/2-EMV mix design with S = 2 applies to the 2E-I2 mix with 100% RCA substitution, the slump value bounces back to the level of the 2E-I1 mix. In test series 3 and 4, slump tests were conducted on airport paving concrete. Here, it may be noticed with test series 3 in Fig. 4 that as the replacement level of RCA in the modified EMV mix increased, from the level of the 3E-A1 mix (S = 1) with 25% substitution to the level of the 3E-A2 mix (S = 2) with 50% substitution and to the level of the 3E-A3 mix (S = 3) with 75% substitution of RCA, the slump displays a decreasing tendency. Especially, compared to test series 3, test series 4 showed almost ‘zero slump’, because to induce better smoothness for airport concrete pavement, a reduced amount of water reducing agent was used in test series 4. Nevertheless, the problem of the decrease in slump can be solved by adjusting the vibration frequency because paving concrete is treated mechanically in slip form. In this study, the optimum mix design was determined in a range that satisfies the 4% of minimum air content. The air content value of each mix design is shown in Table 5. 4.2. Compressive strength The average laboratory target strength was 30 MPa at 28 days. Strength trends were compared only between the results of concrete specimens made from the conventional mix design and those from the EMV mix design for each test series. Fig. 5 uses error bars to illustrate the effect of the mix proportioning method on the compressive strength of the different mixes; the numbers above each bar represent the standard deviation. In test series 1, which only used the conventional mix design, the 1C-D mix, made by substituting 100% of the natural coarse aggregate with RCA produced at the D plant, showed decreases of 7.4%, 9.0%, and 12.6% at the ages of 7 days, 14 days, and 28 days, respectively. However, the 1C-C mix, made with 100% substitution of the RCA produced at the C airbase jobsite, showed a tendency similar to that of NA concrete. This may be ascribed to the high quality of the original virgin aggregate (river gravel) used at the airbase.
Table 5 Slump and air content test results. Test series
Mix-id
Slump, mm
Air contents,%
1
1C-N 1C-C 1C-D
40 20 29
5.0 5.5 5.3
2
2C-N 2C-I1 2C-I2 2E-I1 2E-I2
122 150 120 78 87
4.5 4.2 4.5 4.5 4.2
3
3C-N 3C-A 3E-A1 3E-A2 3E-A3
30 25 11 9 2
5.5 5.5 4.0 4.6 4.0
4
4C-N 4E-A1 4E-A2
1 0 2
3.9 4.0 3.8
The followings are the results of compressive strength tests of the structural concretes from test series 2, which was intended as a preliminary test before starting the paving concrete mix of the third and fourth test series. Values were only measured at the age of 7 days. The 2C-I1 mix with, approximately 50% substitution, resulted in a 2% lower compressive strength, while the 2C-I2 mix, with 100% substitution of RCA produced at the Insun plant, had a 7% higher compressive strength than that of the control 2C-N mix. It should be noted that these three mixes were based on the conventional mix design method. And, the 2E-I1 mix proportioned using the original EMV method (S = 1), with about 50% substitution, resulted in a 6% higher compressive strength, while the 2E-I2 mix proportioned using the modified EMV method (S = 2), with 100% substitution of RCA, had a 2% lower compressive strength than that of the control 2C-N mix. Test series 3 and 4 mixes were designed for airbase paving concrete. For reference, in airport construction specifications [8], the compressive strength values at both 28 days and 60 days of age are specified. In test series 3, the compressive strengths of the control mix had their lowest values. The 3C-A mix based on the conventional mix proportioning method, with 50% substitution of the RCA produced at ‘A’ airbase, unexpectedly yielded a compressive strength at the age of 60 days 17% higher than that of the control mix. And, the 3E-A1 mix (S = 1), 3E-A2 mix (S = 2), and 3E-A3 mix (S = 3) with substitutions of 25, 50, 75% of RCA resulted in compressive strength values that were 13%, 6%, and 16%, higher than those of the control mix. In test series 4, to reconfirm the effect and repeatability of the modified EMV mix design proposed in this study, the compressive strength tests of the control and the EMV mixes were conducted at the ages of 7 days and 28 days. The compressive strength values at 7 days and 28 days showed similar trends. From test series 3 and 4, it seems that the equal or somewhat higher strength of all the other mixes may be attributed to the higher quality of original virgin aggregate (crushed granite) used in the airbase compared to the natural aggregate of the control mix. Overall test results showed that the RCA concrete mixes proportioned using the (modified) EMV method do not yield compressive strength values that are consistently comparable to those of mixes that are similar but that are proportioned using the conventional mix design method. It should be noted that no consideration of an increase in compressive strength was intended for the mixes proportioned using the modified EMV method. 4.3. Modulus of elasticity Elastic modulus trends were compared only between the results of concrete specimens made from the conventional mix design and those from the EMV mix design for each test series. Fig. 6 uses error bars to illustrate the effect of the mix proportioning method on the elastic modulus of the different mixes, where the number above each bar represents the standard deviation. In test series 1, which only used the conventional mix design, the strong decrease of the modulus of elasticity of the RCA concrete can be seen in Fig. 6a. The 1C-C mix, made by substituting 100% of the RCA produced at the C airbase jobsite, had elastic modulus values 0.2%, 11%, and 12% lower than those of the 1C-N mix at the ages of 7, 14, and 28 days, respectively. Also, the 1C-D mix, made by substituting 100% of the RCA, resulted in elastic modulus values that were 10%, 20%, and 20% higher than those of the companion 1C-N mix at the ages of 7, 14, and 28 days, respectively. These results confirm that the conventional mix proportioning method results in low elastic modulus for RCA concrete mixes. Fig. 6b illustrates the effect of mix proportioning method on the elastic modulus of the structural concrete in test series 2. The 2C-I1 mix, with about 50% substitution, and the 2C-I2 mix, with 100%
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
15
Fig. 4. Slump test results.
Fig. 5. Compressive strength results with each series of mix.
substitution of the RCA produced at the Insun plant, both had 6% lower elastic modulus values than that of the control 2C-N mix. It should be noted that these the three mixes were based on the conventional mix proportioning method. However, the 2E-I1 mix, proportioned using the original EMV method (S = 1) with about 50% substitution of RCA, had the same value as that of the control mix, while the 2E-I2 mix proportioned using the modified EMV method (S = 2) with 100% substitution of RCA had a 3.7% lower elastic modulus than that of the control mix. In test series 3, the control mix 3C-N yielded a lower elastic modulus than that of the other mixes at the age of 7 days. How-
ever, at the age of 60 days, mix 3C-A, with 50% substitution of RCA, had an elastic modulus 10% lower than that of the control mix. However, the 3E-A1 mix (S = 1), and the 3E-A2 mix (S = 2) with substitutions of 25 and 50% of RCA, resulted in 3% and 6% higher elastic modulus values, than those values of the control mix. This result shows that the use of the modified EMV mixture proportioning method in this study will result in elastic modulus values, even for paving concrete, comparable or even superior to those of similar mixes made with natural aggregate. However, in the case of the 3E-A3 mix (S = 3) with substitution of 75% of RCA, the elastic modulus was 13% lower than that of the control mix.
16
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
Fig. 6. Modulus of elasticity results with each series of mix.
It should be noted in Table 3 that the 3E-A3 mix contains amounts of water, cement, and sand of 117 kg, 305 kg, and 563 kg, respectively. It may be possible to attribute the lower elastic modulus to the insufficient amount of fresh mortar or sand in the mix, which would cause lean mix. In test series 4, at the age of 7 days, the 4E-A1 mix (S = 1) and the 4E-A2 mix (S = 2), with substitutions of 25 and 50% of RCA, resulted in 2% and 4% higher values of elastic modulus compared to that of the control mix, 4C-N. However, at the age of 28 days, the 4E-A1 mix and the 4E-A2 mix resulted in 2% and 5% lower values of elastic modulus compared to that of the control mix. Overall, the elastic modulus for all mixes in test series 4 may be considered to yield similar values. Overall, these results confirm that, compared to the elastic modulus values of similar mixes made with natural aggregates, the use of the modified EMV mix proportioning method does not result in low elastic modulus of RCA concrete mixes for road paving.
5. Conclusions In this investigation a modified equivalent mortar volume mix design method is proposed and experimentally verified for concrete mixes made with coarse recycled concrete aggregate. From the results of this study, the following conclusions can be drawn.
1. Test results confirmed that the use of the EMV mix proportioning method originally proposed by Fathifazl et al. would not result in low elastic modulus of RCA concrete mixes. 2. However, for a typical concrete mix in road pavement containing less than 700 kg/m3 of sand, the original EMV mix design leads to a deficiency of the amount of sand or fresh mortar, causing large slump loss. 3. In compensation, a scale factor, S, and a 1/S-EMV mix proportioning approach were introduced and the original residual mortar was mathematically treated as a volume fraction of 1/ S, while the other fraction of (S-1)/S was treated as original virgin aggregate. 4. Test results showed that this modified EMV method yields modulus properties comparable or superior to those of similar concrete mixes made with natural coarse aggregates or conventional mixes with RCA. Acknowledgements This research was funded by the National Research Foundation, through a 2016 Korea Grant funded by the Korean Government in the project titled ‘‘Structural Performance of Reinforced Concrete Members made with Revised Equivalent Volume Mix Proportioning Method (2016R1A2B4007932)”; funds were partially provided by the 2015 Hongik University research fund in South Korea. Special thanks are given to Dr. G. Fathifazl at the National Research
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
Council of Canada for providing the original EMV mix design spreadsheet. Appendix I. Example: This example illustrates a sample mix proportioning for one of the mixes proportioned with the modified EMV method. It is helpful for reader to refer to Appendix I of the original EMV model [10]. 1. Proportioning 3C-N per m3 based on ACI mix proportioning method [21] Weight of water in NAC mix: W NAC ¼ 140 kg w ¼ 366 kg Weight of cement in NAC mix: W NAC c Oven-dry weight of NA in NAC mix: W NAC ODNA ¼ 1220 kg Oven-dry weight of fine aggregate in NAC mix: W NAC ODFA ¼ 675 kg 2. Checking whether R = 0 (100% RCA concrete) is feasible or not SGNA
2:64 b RMC Max ¼ 1 V NAC DRNA SGRCA ¼ 1 0:724 2:35 ¼ 0:187ð18:7%Þ b
Since the actual RMC content of RCA-S is 35.5%, it can be seen that it is not feasible to make a concrete mix comprising only RCA 4 as coarse aggregate. Thus, in the 3C-N mix for the S = 2 condition, RMC/S = 35.5/2 = 17.75 is used instead of 35.5%. 3. Calculating required volume of RCA and NA in RCA concrete W NAC
1;220 ODNA Volume of NA in NAC mix: V NAC NA ¼ SGNA 1;000 ¼ 2:641;000 ¼ 0:462 b
where SGNA b : bulk specific gravity of NA NAC Volume of NA in RAC mix: V RAC NA ¼ R V NA ¼ 0:58 0:462 ¼ 0:268 where R = 0.58 was used to make the RCA volumetric% in the fourth column in Table 4
Volume
of
RCA
in
RAC
mix:
V RAC RCA ¼
V NAC ð1RÞ NA
SGRCA
b ð1RMC1SÞSGOVA
¼
b
0:462ð10:58Þ
ð10:35512Þ2:35 2:64
¼ 0:266
SGRCA b :
bulk specific gravity of RCA, SGOVA where b : bulk specific gravity of OVA 4. Calculating required oven-dry weight of RCA and NA in RCA concrete Required oven-dry weight of RCA in RAC mix: RCA RAC W RAC 1000 ¼ 0:266 2:35 1000 ¼ 623 kg ODRCA ¼ V RCA SGb Required oven-dry weight of NA in RAC mix: NA RAC W RAC ODNA ¼ V NA SGb 1000 ¼ 0:268 2:64 1000 ¼ 708 kg 5. Calculating required fresh NM in RCA concrete, NAC V RAC Volume of NM in RAC mix: V RAC NM ¼ V M RM ¼ 0:538 0:071 ¼ 0:466
¼ 1 V NAC where volume of mortar in NAC mix: V NAC M NA ¼ 1 0:462 ¼ 0:538 6. Calculating required water, cement, and fine aggregate in RCA concrete, V RAC
NM ¼ W NAC V NAC ¼ Required weight of water in RAC mix: W RAC w w M
140 0:466 ¼ 121 kg 0:538 ¼ W NAC Required weight of cement in RAC mix: W RAC c c V RAC NM
V NAC M
¼ 366 0:466 ¼ 318 kg 0:538
Required oven-dry weight of fine aggregate in RAC mix: V RAC
NAC 0:466 NM W RAC ODFA ¼ W FA V NAC ¼ 675 0:538 ¼ 585 kg M
17
References [1] Ministry of Land, Transportation and Maritime Affairs, Regulations on the mandatory use of recycled aggregates for construction projects, 2009. [2] Ministry of Environment, Regulations on the mandatory use of recycled aggregates for construction projects, No. 2014-33, 2014. [3] Korea Expressway Corporation, Highway Construction Guide Specification, 2011. [4] Ministry of Land, Infrastructure and Transportation, Concrete structure specification, 2009. [5] Incheon International Airport Corporation, Concrete Construction Guidelines, 2012. [6] S. Kang, H. Lee, S. Yang, Cost analysis of recycled aggregate production on airport pavement, Int. J. Highway Eng. 16 (2014) 39–47. [7] S. Yang et al., Development of pavement reconstruction methodology for sustainable green airport, Research report, Korea Institute of Construction & Transportation Technology Evaluation and Planning, 2012. [8] J. Brito, N. Saikia, Recycled Aggregate in Concrete, Use of Industrial, Construction and Demolished Waste, Springer, 2013, pp. 379–426. [9] H. Lee, Structural Properties on Reinforced Concrete Beams Mixed With Recycled Concrete Aggregates (Master’s thesis), Hongik University, S. Korea, 2014. [10] G. Fathifazl, A. Abbas, A. Razaqpur, O. Isgor, B. Fournier, S. Foo, New mixture proportioning method for concrete made with coarse recycled concrete aggregate, J. Mater. Civ. Eng. 21 (2009) 601–611. [11] A. Abbas, Durability of green concrete as a structural material (Ph.D thesis), Carleton University, Canada, 2007. [12] G. Fathifazl, Structural performance of steel reinforced recycled concrete members (Ph.D thesis), Carleton University, Canada, 2008. [13] K. Kim, H. Cho, J. Ahn, Development of high quality recycled aggregate production process from waste concrete for resource circulation system, J. Korean Inst. Resour. Recycl. 18 (2009) 27–35. [14] A. Abbas, G. Fathifazl, O. Isgor, A. Razaqpur, B. Fournier, S. Foo, Proposed method for determining the residual mortar content of recycled concrete aggregates, J. ASTM Int. 5 (2008) 1–12. [15] A. Akbarnezhad, K. Ong, M. Zhang, C. Tam, Acid treatment technique for determining the mortar content of recycled concrete aggregates, J. Test. Eval. 41 (2013) 1–10. [16] A. Akbarnezhad, K. Ong, M. Zhang, C. Tam, T. Foo, Microwave-assisted beneficiation of recycled concrete aggregates, Constr. Build. Mater. 25 (2011) 3469–3479. [17] A. Akbarnezhad, K. Ong, Separation processes to improve the quality of recycled concrete aggregates (RCA), in: F. Pacheco-Torgal (Ed.), Handbook of Recycled Concrete and Demolition Waste, 2013, pp. 246–269. WP. [18] M. Byeon, Removal of adhered mortar from recycled aggregate using microwave irradiation and mixed solution of HCI and H2O2, Conference Proceedings, Kor. Soc. Waste Management, South Korea, 2015. [19] T. Hansen, Recycled aggregates and recycled aggregate concrete second stateof-the-art report developments 1945–1985, Mater. Struct. 19 (1986) 201–246. [20] ASTM C127, Standard test method for relative density (specific gravity) and absorption of coarse aggregate, ASTM International, West Conshohocken, PA, 2012. [21] ACI Committee 211, Standard practice for selecting proportions for normal, heavyweight and mass concrete, ACI 211.1-97, Farmington Hills, MI, 1997. [22] ASTM C231, Standard test method for air content of freshly mixed concrete by the pressure method, ASTM International, West Conshohocken, PA, 2009. [23] ASTM C143, Standard test method for slump of hydraulic-cement concrete, ASTM International, West Conshohocken, PA, 2012. [24] ASTM C192, Standard practice for making and curing concrete test specimens in the laboratory, ASTM International, West Conshohocken, PA, 2012. [25] ASTM C39, Standard test method for compressive strength of cylindrical concrete specimens, ASTM International, West Conshohocken, PA, 2014. [26] ASTM C469, Standard test method for static modulus of elasticity and Poisson’s ratio of concrete in compression, ASTM International, West Conshohocken, PA, 2014.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Mechanical properties of recycled aggregate concrete proportioned with modified equivalent mortar volume method for paving applications S. Yang a,⇑, H. Lee b a b
School of Architectural Engineering, Hongik University, South Korea Construction Safety Division, Korea Infrastructure Safety Corporation, South Korea
h i g h l i g h t s A modified equivalent mortar mix design is proposed for recycled aggregate concrete. Results show modulus of elasticity comparable or superior to those of similar mixes made with natural aggregates or conventional mixes with RCA. This modified recycling mix design may be performed well even for the paving concrete mix. This method applies to any recycled concrete aggregate regardless of poor absorption capacity.
a r t i c l e
i n f o
Article history: Received 29 February 2016 Received in revised form 1 September 2016 Accepted 8 January 2017
Keywords: Mixtures Recycled concrete aggregate Compressive strength Elastic modulus
a b s t r a c t The equivalent mortar volume (EMV) mix design method, which was originally proposed by Fathifazl et al., was successfully verified in their previous studies for concrete mixes containing coarse recycled concrete aggregate (RCA). However, especially for paving concrete mix, which is typically proportioned with a marginal amount of sand, the nature of the EMV mix proportions leads to a far lower amount of sand. Thus, a modified EMV proportioning method is proposed, assuming that the residual mortar in RCA concrete (RAC) can be represented as the sum of the volume fraction of mor(RM) volume V RAC RM RAC V RAC tar 1S V RM and the other volume fraction of coarse aggregate S1 RM , using scale factors S = 1, 2, and 3. S To verify this modified EMV method, four series of concrete mixes were made using the modified EMV mix design, along with the original EMV and the conventional mix designs, with various sources of RCAs. For each mix, the slump, air content, compressive strength and elastic modulus were measured. Test results show that the modified EMV method yields modulus properties comparable or superior to those of similar mixes made with natural coarse aggregates or those of conventional mixes with RCA. Furthermore, it is demonstrated that this modified method applies well to paving concrete mixes, regardless of the absorption capacity of RCA. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Since 2008, the government of South Korea has made it obligatory for public road agencies to use recycled concrete aggregate (RCA) [1–2]. From the year 2014 onwards, the mandatory usage of RCA was increased to be 30%, 40%, and 50% maximum replacement of total coarse aggregate in 2014, 2015, and 2016, respectively, for subgrade and subbase courses of road [1–2]. In the meantime, it has been reported that concrete airport pavements in S. Korea have been deteriorating. Several air bases have already been resurfaced; however, the RCAs produced on-site on air bases ⇑ Corresponding author at: School of Architectural Engineering, Hongik University, 2639 Sejong-ro, Jochiwon, Sejong 339-701, South Korea. E-mail address: [email protected] (S. Yang). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.029 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
have been used only for sub-base materials, regardless of the potentially good RCA quality. This is because of the strict RCA quality requirement for coarse RCA to have less than 3% of water absorption and above 2.5 of specific gravity for it to be used as structural or paving concrete [3–5]. In reality, 4–6 additional crushing process steps must be carried out at the recycling plant in order to satisfy the specifications, resulting in a loss of time and money [6–7]. In addition, for structural concrete, it is required that the compressive strength be within 27 MPa; it is also recommended that RCA be within 30% maximum replacement of NA, strongly limiting the use of this material [4]. Requirements for RCAs in other countries were well documented in reference [8]. A cost analysis of recycled aggregate production on airport pavement [6,9] came to the conclusion that excessive removal of RM using a great amount of energy or high cost to meet the RCA
10
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
quality requirement may not be the answer to the problem of procuring RCA concrete mixes that can be widely used in airport pavement. Rather, using RCA manufactured through 1–3 stage processing only, regardless of poor absorption capacity, the equivalent mortar volume method proposed by Fathifazl et al. [10] was considered to be one of the best resurfacing alternatives. Fathifazl and his colleagues [10–12] stated that recycled aggregate concrete (RAC) proportioned using the conventional mix proportioning method is inferior in material characteristics, such as the modulus of elasticity and drying shrinkage because of the increasing ratio of mortar in the total mixture. According to their theory, in fresh concrete before hardening, residual mortar (RM) attached to coarse RCA acts as coarse aggregate. After hardening, however, RM acts as mortar. In the case of the conventional mix design made with RAC, not only the newly made mortar but also the RM attached to the RCA is included in the total mortar (TM). The total mortar ratio of the RAC in the conventional mix design is greater than that in the natural aggregate concrete (NAC) mix. Fathifazl et al. explain that this mortar ratio difference causes a decrease in the modulus of elasticity and an increase in the drying shrinkage. Fathifazl [12] stated from 45 research results that the compressive strength of RAC is decreased by 0–42% due to changes in the mortar strength and the aggregate-mortar bond strength at the interfacial transition zone. In 17 articles, he states that the modulus of elasticity is decreased by 0–45% due to changes in the modulus of elasticity of natural coarse aggregate, the modulus of elasticity of the mortar, and the volume of the mortar. In 11 articles, he asserts that there is an increase of the drying shrinkage strain due to the change in the volume of the mortar. With these results, and considering RM, he came up with an equivalent mortar volume (EVM) mix design method and showed that the modulus of elasticity does not decrease. A number of beneficiation processes has been proposed to reduce the residual mortar content of RCA [13–17]. These techniques generally use mechanical, chemical, or thermal processing, or micro-assisted beneficiation [16,18] and various combinations of these methods [17]. The first attempt to measure RM goes back to Hansen [19] in 1986. The RM correlation trends of specific gravity as well as absorption capacity have been integrated comprehensively [19]. However no attempt has been made to systematically quantify the effect of RM in terms of its elastic modulus and volume fraction on RCA concrete properties [10]. The first study of this sort was performed by Abbas et al. [14], who attempted to measure the RM value and use it as an input variable in the EMV mix design for a series of experiments. It is known that the original EMV mix proportioning method is very proper for structural concrete mixes, which typically have about 800 kg/m3 of fine aggregate. However, especially for the concrete mix used in road pavement, which is typically proportioned with a marginal amount (usually less than 700 kg/m3) of fine aggregates, the nature of the EMV mix proportions leads to far lower amounts of fine aggregates, in some cases less than 600 kg/m3, leading to a harsh mix and slump loss. This will lead to a range of shortages in the amount of sand or fresh mortar. Thus, a modified EMV mix proportioning method is proposed; this method assumes that the volume fraction of the residual mortar (RM) may be mathematically treated as an original virgin aggregate (OVA), while the other fraction can be treated as part of the total mortar. This paper aims to assess the effect of different mix proportioning methods (the conventional ACI method/the original EMV method versus the modified EMV method) on the mechanical properties of RCA concrete. To verify this modified method, four series of mixes were made using the revised EMV mix design, along with the original EMV and the conventional mix design, with various types of coarse RCA.
2. Modified equivalent mortar volume mix method 2.1. Background and problem statements As previously mentioned, Faithifazl et al. [10] stated that material properties of RCA concrete become inferior because RM attached to RCA is not considered. To visually determine the volume fractions of the mortar and the original virgin aggregate of RCA, concrete was examined by making specimen with coarse RCA and white cement only. Fig. 1 illustrates polished section of a 150 mm 300 mm concrete cylindrical specimen. The white part of the section is mortar; the rest is RCA. The dark shaded parts of RCA are the original virgin aggregate, and the lighter part is RM. Fig. 2 shows the difference between the conventional mix design and the EMV mix design concepts proposed by Fathifazl et al. [10]. Figs. 2a and b show the volume composition of NAC and RAC, respectively, in the conventional mix design. Both mixes have a fixed volume ratio of coarse aggregate, fine aggregate, cement, water, and air. The difference between Fig. 2a and b is that the total mortar (TM) volume of RAC is larger than that of NAC. It is because of this discrepancy that the material properties of RAC become inferior. Fig. 2c shows the concept of the EMV mix design that Fathifazl et al. [10] originally proposed. This mix design method fixes the volume ratio of the total mortar equal to that shown in Fig. 2a. In the EMV mix design, the new mortar volume is reduced to the same degree as the reduction of RM attached to RCA. Especially for paving concrete mix, if RCA is used with more than a certain amount of or with more RMC content, the unit weight of the fine aggregate in the concrete mix according to the EMV concept itself leads to a value below 600 kg. Then, the shape or formability of the concrete may be a concern due to the lack of fillers. The decrease in flowable mortar affects not only the shape, but also, due to the slump decrease, the constructability. Table 1 shows the slump values of paving concretes measured during test series 2 in this study; these results will be discussed in more detail later, in section 3. The test results show that the slump of the 2C-N concrete mix (refer to Section 3.1.3 for notation), made with only natural aggregate, is 122 mm, while that of 2E-I1 concrete, made with the substitution of 50% RCA using the original EMV mix design, is 78 mm. In the case of concrete 2E-I2⁄, made with the substitution of 100% RCA and using the EMV mix design, a lack of workable new mortar or
Fig. 1. Polished concrete specimen mixed with white cement and coarse RCA only.
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
(a) Conventional mix (NAC)
(b) Conventional mix (RAC)
11
(c) EMV mix (RAC)
Fig. 2. Mix design concept.
Table 1 Slump in various trial mixes (Test series 2). Mix id
Fine agg. amount(kg/m3)
Slump(mm)
Mix design
2C-N 2E-I1 2E-I2* 2E-I2
757 655 496 633
122 78 10 87
Conventional EMV EMV Modified EMV
It was considered in the modified EMV model that the RM attached to RCA serves as aggregate in fresh concrete, and as mortar after it is hardened. Considering this treatment, the RM volume in RAC was represented as the sum of the volume fraction of the mortar
1 RAC V S RM
S1 RAC V RM , S
using the scale factor S as follows:
V RAC RM ¼ fine aggregate, as shown in Table 1, yields a large slump drop to 10 mm. This is the reason that this study proposes a modified EMV approach to paving concrete mix with greater RCA replacement or higher RMC value. Table 1 shows that, in the 2E-I2 mix proportioned using the preceding modified EMV approach, the slump value bounces back to the level of the 2E-I1 mix. It should be noted that, according to the original EMV method [10], this issue has also been considered by looking at the concept of the dry-rodded specific gravity of the aggregate. By enforcing either (1) minimum NA content (or minimum replacement ratio, Rmin), in case of high RM content in RCA, or (2) maximum RM content in RCA if one desires to use 100% RCA in RAC, one can come up with the upper bound values for maximum RCA content, or the maximum RM content in RAC. Fathifazl et al. [10] chose a replacement ratio (R) equal to the RM volume in RCA divided by the RCA volume in RAC. The physical interpretation of this specific R value is that it indicates the level of replacement of the RM volume in RCA with fresh NA in RAC. This in fact is equivalent to the concept of the modified EMV method, where S = 1.
by V NAC NA . Then, a companion mix, termed RAC, comprising a blend of NA and RCA is designed. The volume of fresh NA in the RAC is represented by V RAC NA . The NA content ratio was to be R in Fig. 3b, as originally defined by Fathifazl et al. [10], as
V NAC NA
ð2Þ
Therefore, the value of R was modified as follows:
R ¼1
V RAC RCA V NAC NA
1 SGRCA b 1 RMC OVA S SGb
ð3Þ
where the volume of fresh NA in the natural aggregate concrete (NAC) is represented by V NAC NA and the volume of RCA in RCA concrete RCA and SGOVA are the bulk specific gravities of RCA and of by V RAC b RCA ; SGb the original virgin aggregate (OVA), respectively. For the RAC and its associated NAC to have the same hardened properties, the revised method requires that the following two conditions be satisfied and modified
1 RAC NAC V RAC ¼ V RAC TM ¼ V M NM þ V RM S RAC RAC V RAC TNA ¼ V OVA þ V NA þ
S 1 RAC V RM S
ð4Þ
ð5Þ
concrete made entirely with coarse NA; V RAC TNA = total coarse natural
In order to explain the difference between the concepts of the original EMV mix design and the modified EMV mix design of this study, the previous Fig. 2 illustration was reconstructed into the following Fig. 3 as an 1/S-EMV mix proportioning model, where a scale factor, S, is introduced. In the original EMV design procedure [10], to design an RCA concrete (RAC) mix with the specified fresh and hardened properties, first, one proportions a concrete mix, called natural aggregate concrete (NAC). The volume of coarse NA in this mix is represented
V RAC NA
1 RAC S 1 RAC V V RM þ S RM S
NAC where V RAC = mortar in the companion TM = TM volume in RAC; V M
2.2. Model equation
R¼
and the other volume faction of the aggregate
ð1Þ
aggregate (TNA) volume in RAC; and V RAC OVA = OVA volume in RAC. Then, required volumes and weights of RCA and NA are subsequently determined, given by the example flowchart in Appendix I. Finally, the corresponding quantities of water, cement, and fine aggregate in RCA concrete can be determined. 3. Materials and mix design methods 3.1. Materials 3.1.1. Cement material and chemical admixture Type I Portland cement was used in this study. The cement specific gravity used in the mixture design was 3.15 and the specific surface area was 3200 cm2/g. The chemical admixture used for this study was a solution of air entraining and a water reducing agent.
12
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
(a) Conventional mix
(b) Original EMV mix
(c) 1/S-EMV mix
Fig. 3. Comparison of mix design concept between original EMV model and revised 1/S-EMV model.
3.1.2. Aggregates material properties Natural aggregate material properties [20] with standard deviations are tabulated in Table 2. Two similar fine aggregates were used in this experiment. Fine aggregate 1 is natural sand with specific gravity of 2.63 and absorption capacity of 0.58%, used in test series 1 (see Table 4); fine aggregate 2 has specific gravity of 2.55, and absorption capacity of 0.95% and is used in the other test series. For the coarse aggregate, natural crushed granite aggregate was used. The specific gravity was 2.64 and the absorption capacity was 0.77%. Four types of RCA were used in our study. Two of them were produced in the Daegil (D) and Insun (I) plants, and the rest were produced in the ‘C’ and ‘A’ airbase worksites in S. Korea. The maximum size of RCA 4 was 40 mm, while maximum size was 25 mm for the other RCAs. The specific gravity, absorption capacity, and residual mortar quantity of each of the four types of RCA, with standard deviations, are shown in Table 3. The RMC values of RCA 3 and RCA 4 were determined using the same method suggested by Abbas et al. [14]. Two samples were used to determine the RMC values in individual size fractions. For RCA 3, a weighted average RMC value was determined for the blended RCA (25 mm, 10 mm fraction sizes). For RCA 4, a weighted average RMC value was determined for the blended RCA (40 mm, 20 mm, and 10 mm fraction sizes). The amount of the sample was about 2000 g for the fraction sizes over 20 mm and 1000 g for the smaller fraction size. After drying the samples for 24 h at 105 °C, the oven dried samples were immersed for 24 h in a 26% by weight sodium sulfate solution. While still immersed in the sodium sulfate solution, RCA samples were subjected to five cycles of freezing and thawing, i.e., 16 h at 17 °C and 8 h at 80 °C. After the last freezing-thawing cycle, the solution was drained from the sample and the aggregate was washed with water over a No. 4 sieve. The washed aggregate was then placed in an oven for 24 h at 105 °C and its oven-dried weight was measured. The RMC value was then obtained using [10]:
RMCð%Þ ¼
W RCA W OVA 100 W RCA
ð5Þ
where WRCA = initial oven-dried weight (g) of the RCA sample before the test and WOVA = final oven-dried weight (g) of the OVA after removal of the residual mortar.
3.1.3. Mix design All four series of mixes were designed as shown in Table 4. The first series of mixes was designed for highway paving concrete, with maximum aggregate size of 25 mm. The second series of mixes was proportioned and based on a typical structural concrete mix design with a maximum aggregate size of 25 mm. The third and fourth series of mixes were designed for airport paving concrete with maximum aggregate size of 40 mm. The target air content for all mix designs was a minimum of 4.0%; the final mix design was determined after many trial batches. Due to the low slump requirement for road paving concrete, all mixes except for the second series of mixes were determined to have slump values under 50 mm. The target slump of structural concrete in test series 2 was provisionally 80–120 mm. Except for the first series of mixes proportioned with a 40% of w/c ratio, a w/c ratio of 38% of w/c ratio was chosen in the other series of mixes with the use of the water reducing agent. The example of mix identification in the second column of Table 4 can be explained as follows. There are three types of terms. The first number denotes the test series; the second term C denotes the conventional ACI mix design for normal concrete [21], while E denotes the EMV mix design. The third term designates the type of coarse aggregate: N indicates natural coarse aggregate; D and I are RCA produced from the Daegil and Insun plants in S. Korea, respectively; A and C are RCA from the ‘C’ and ‘A’ airbase jobsites in S. Korea, respectively. The number following the third term indicates the type of replacement amount of RCA in the total coarse aggregate. The S value in the fifth column of Table 4 indicates the scale factor applied in the 1/S-EMV model. For example, when applied to model 1/2-EMV, the S value becomes 2. The first series of mixes was designed to confirm how the conventional mix design with RCA leads to decreased material
Table 2 Natural aggregate material properties. Aggregates
Fine agg. 1a Fine agg. 2b Natural coarse agg.b a b
Determined from 3 test samples. Determined from 2 test samples.
Specific gravity
Absorption capacity(%)
Value
Standard deviation
Value
Standard deviation
2.63 2.55 2.64
0.002 0.099 0.007
0.58 0.95 0.77
0.092 0.028 0.134
13
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17 Table 3 RCA material properties. Aggregates
RCA RCA RCA RCA a b
1a 2a 3a 4a
RCA source
Maximum size(mm)
C airbase D plant I plant A airbase
25 25 25 40
Specific gravity
Absorption capacity(%)
RMC
Value
Standard deviation
Value
Standard deviation
Value
Standard deviation
2.42 2.37 2.54 2.35
0.021 0.028 n.ab n.ab
5.37 5.39 1.98 4.45
0.332 0.085 n.ab n.ab
n.ab n.ab 11.6 35.5
n.ab n.ab 0.283 1.768
Determined from 2 test samples. Not available.
Table 4 Concrete mixture designs and material quantities.
a b c
Test Series
Mix-id
w/c%
RCA content%a
S factor
Water kg
Cement kg
Sand kg
WRAb ml
AEc ml
NA kg
RCA, kg
1
1C-N 1C-C 1C-D
40.0 40.0 40.0
0 100 100
– – –
128 128 128
320 320 320
736 736 736
1157 0 0
0 1056 1038
0 0 0
64.0 38.4 38.4
2
2C-N 2C-I1 2C-I2 2E-I1 2E-I2
37.5 37.5 37.5 37.6 37.6
0 49.1 100 49.4 100
– – – 1 2
180 180 180 159 155
480 480 480 424 411
757 758 759 655 633
920 460 0 564 0
0 428 856 530 1102
1795 1795 1795 1586 1537
74.7 74.7 74.7 66.0 64.0
3
3C-N 3C-A 3E-A1 3E-A2 3E-A3
38.2 38.2 38.2 38.2 38.2
0 50.0 24.9 49.7 74.8
– – 1 2 3
140 140 126 121 117
366 366 329 318 305
675 675 606 585 563
1220 611 1025 708 366
0 543 303 623 969
4047 4047 4049 4051 4751
168.4 168.4 168.4 168.5 197.6
4
4C-N 4E-A1 4E-A2
38.2 38.2 38.2
0 24.9 49.7
– 1 2
140 126 121
366 329 318
675 606 585
1220 1025 708
0 303 623
2640 2211 2137
102.3 92.0 88.9
Coarse Aggregate
Ratio of RCA volumetric proportion to total coarse aggregates. Water reducing agent. Air entraining agent.
strength properties compared to the case of the companion concrete mix containing natural aggregate. The second series of mixes, before actual application to airbase paving concrete, was intended to validate the modified EMV mix design using structural concrete mix. Then the third series of mixes was designed to apply the modified EMV approach with scale factors, S = 1 (the original EMV mix proportion), 2, and 3 and those of companion mixes along with the conventional proportioning design. Finally, to verify the effect and repeatability of this modified EMV model, the fourth series of mixes was designed once more with the same mix design as that of the third series of mixes, except for the different amounts of admixture. It should be noted that the recycled concrete in each test series was produced by substituting 0, 25, 50, 75, or 100% levels of natural coarse aggregate with the RCA by volumetric proportion.
after batching, the fresh concrete properties such as air content [22] and slump [23] were tested. The hardened concrete property tests performed in this study included tests of compressive strength and modulus of elasticity. Specimens were prepared in plastic molds using the specified consolidation methods [24]. Then, the specimens were removed from the molds 24 h after casting. All specimens were moist cured at about 20 ± 2 °C from the time of molding until the moment of testing. Measurements of the compressive strength and modulus of elasticity of each mixture were carried out in accordance with ASTM C39 [25] and ASTM C469 [26], respectively. An average of three cylinders were tested at ages of different numbers of days, depending on the test groups. The cylinders were of the dimensions 100 mm 200 mm for test series 1 and 2 while cylinders were of dimensions of 150 mm 300 mm for test series 3 and 4. In test series 1, four specimens were tested, while three specimens were tested in test series 2–4.
3.2. Mixing process for making the concrete specimens 4. Experimental results A concrete pan mixer with a volume capacity of 60 L was used in the laboratory. Before the addition of water and the admixture solution, the admixture was thoroughly dispersed in the mixing water. Coarse aggregate and fine aggregate were added, and the mixer was given a few turns. Then cement was added and the mixer was started for about 90 s. Finally water was added while the mixer was running and the concrete was mixed for another 120 s. 3.3. Fresh and hardened concrete property testing The performances of the concrete mixtures were determined by testing the fresh and hardened concrete properties. Immediately
4.1. Slump and air content Generally, the target slump for road paving concrete is specified as being under 50 mm. In order to obtain excellent smoothness (or roughness), the slump value is required to be less than that of structural concrete. A slip-form paver vibrates, tamps, and shapes the rather harsh paving concrete mix to the desired surface configuration. All the slump test results are presented in Table 5 and Fig. 4. As can be seen in Fig. 4, compared to the conventional method, the EMV method in test series 2 resulted in lower slump probably due to the nature of the RM, which was treated as mortar in the
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
fresh concrete. When the replacement level of RCA in the EMV mixture was increased, from the level of the 2E-I1 mix, which has approximately 50% substitution to the level of the 2E-I2⁄ mix, which has 100% RCA substitution, the slump largely decreased due to the insufficiency of fine aggregates in the 2E-I2⁄ mix. This is probably because the required new mortar (NM), primarily comprised of sand, decreased by the amount of RM, causing the slump to decrease. As the 1/2-EMV mix design with S = 2 applies to the 2E-I2 mix with 100% RCA substitution, the slump value bounces back to the level of the 2E-I1 mix. In test series 3 and 4, slump tests were conducted on airport paving concrete. Here, it may be noticed with test series 3 in Fig. 4 that as the replacement level of RCA in the modified EMV mix increased, from the level of the 3E-A1 mix (S = 1) with 25% substitution to the level of the 3E-A2 mix (S = 2) with 50% substitution and to the level of the 3E-A3 mix (S = 3) with 75% substitution of RCA, the slump displays a decreasing tendency. Especially, compared to test series 3, test series 4 showed almost ‘zero slump’, because to induce better smoothness for airport concrete pavement, a reduced amount of water reducing agent was used in test series 4. Nevertheless, the problem of the decrease in slump can be solved by adjusting the vibration frequency because paving concrete is treated mechanically in slip form. In this study, the optimum mix design was determined in a range that satisfies the 4% of minimum air content. The air content value of each mix design is shown in Table 5. 4.2. Compressive strength The average laboratory target strength was 30 MPa at 28 days. Strength trends were compared only between the results of concrete specimens made from the conventional mix design and those from the EMV mix design for each test series. Fig. 5 uses error bars to illustrate the effect of the mix proportioning method on the compressive strength of the different mixes; the numbers above each bar represent the standard deviation. In test series 1, which only used the conventional mix design, the 1C-D mix, made by substituting 100% of the natural coarse aggregate with RCA produced at the D plant, showed decreases of 7.4%, 9.0%, and 12.6% at the ages of 7 days, 14 days, and 28 days, respectively. However, the 1C-C mix, made with 100% substitution of the RCA produced at the C airbase jobsite, showed a tendency similar to that of NA concrete. This may be ascribed to the high quality of the original virgin aggregate (river gravel) used at the airbase.
Table 5 Slump and air content test results. Test series
Mix-id
Slump, mm
Air contents,%
1
1C-N 1C-C 1C-D
40 20 29
5.0 5.5 5.3
2
2C-N 2C-I1 2C-I2 2E-I1 2E-I2
122 150 120 78 87
4.5 4.2 4.5 4.5 4.2
3
3C-N 3C-A 3E-A1 3E-A2 3E-A3
30 25 11 9 2
5.5 5.5 4.0 4.6 4.0
4
4C-N 4E-A1 4E-A2
1 0 2
3.9 4.0 3.8
The followings are the results of compressive strength tests of the structural concretes from test series 2, which was intended as a preliminary test before starting the paving concrete mix of the third and fourth test series. Values were only measured at the age of 7 days. The 2C-I1 mix with, approximately 50% substitution, resulted in a 2% lower compressive strength, while the 2C-I2 mix, with 100% substitution of RCA produced at the Insun plant, had a 7% higher compressive strength than that of the control 2C-N mix. It should be noted that these three mixes were based on the conventional mix design method. And, the 2E-I1 mix proportioned using the original EMV method (S = 1), with about 50% substitution, resulted in a 6% higher compressive strength, while the 2E-I2 mix proportioned using the modified EMV method (S = 2), with 100% substitution of RCA, had a 2% lower compressive strength than that of the control 2C-N mix. Test series 3 and 4 mixes were designed for airbase paving concrete. For reference, in airport construction specifications [8], the compressive strength values at both 28 days and 60 days of age are specified. In test series 3, the compressive strengths of the control mix had their lowest values. The 3C-A mix based on the conventional mix proportioning method, with 50% substitution of the RCA produced at ‘A’ airbase, unexpectedly yielded a compressive strength at the age of 60 days 17% higher than that of the control mix. And, the 3E-A1 mix (S = 1), 3E-A2 mix (S = 2), and 3E-A3 mix (S = 3) with substitutions of 25, 50, 75% of RCA resulted in compressive strength values that were 13%, 6%, and 16%, higher than those of the control mix. In test series 4, to reconfirm the effect and repeatability of the modified EMV mix design proposed in this study, the compressive strength tests of the control and the EMV mixes were conducted at the ages of 7 days and 28 days. The compressive strength values at 7 days and 28 days showed similar trends. From test series 3 and 4, it seems that the equal or somewhat higher strength of all the other mixes may be attributed to the higher quality of original virgin aggregate (crushed granite) used in the airbase compared to the natural aggregate of the control mix. Overall test results showed that the RCA concrete mixes proportioned using the (modified) EMV method do not yield compressive strength values that are consistently comparable to those of mixes that are similar but that are proportioned using the conventional mix design method. It should be noted that no consideration of an increase in compressive strength was intended for the mixes proportioned using the modified EMV method. 4.3. Modulus of elasticity Elastic modulus trends were compared only between the results of concrete specimens made from the conventional mix design and those from the EMV mix design for each test series. Fig. 6 uses error bars to illustrate the effect of the mix proportioning method on the elastic modulus of the different mixes, where the number above each bar represents the standard deviation. In test series 1, which only used the conventional mix design, the strong decrease of the modulus of elasticity of the RCA concrete can be seen in Fig. 6a. The 1C-C mix, made by substituting 100% of the RCA produced at the C airbase jobsite, had elastic modulus values 0.2%, 11%, and 12% lower than those of the 1C-N mix at the ages of 7, 14, and 28 days, respectively. Also, the 1C-D mix, made by substituting 100% of the RCA, resulted in elastic modulus values that were 10%, 20%, and 20% higher than those of the companion 1C-N mix at the ages of 7, 14, and 28 days, respectively. These results confirm that the conventional mix proportioning method results in low elastic modulus for RCA concrete mixes. Fig. 6b illustrates the effect of mix proportioning method on the elastic modulus of the structural concrete in test series 2. The 2C-I1 mix, with about 50% substitution, and the 2C-I2 mix, with 100%
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
15
Fig. 4. Slump test results.
Fig. 5. Compressive strength results with each series of mix.
substitution of the RCA produced at the Insun plant, both had 6% lower elastic modulus values than that of the control 2C-N mix. It should be noted that these the three mixes were based on the conventional mix proportioning method. However, the 2E-I1 mix, proportioned using the original EMV method (S = 1) with about 50% substitution of RCA, had the same value as that of the control mix, while the 2E-I2 mix proportioned using the modified EMV method (S = 2) with 100% substitution of RCA had a 3.7% lower elastic modulus than that of the control mix. In test series 3, the control mix 3C-N yielded a lower elastic modulus than that of the other mixes at the age of 7 days. How-
ever, at the age of 60 days, mix 3C-A, with 50% substitution of RCA, had an elastic modulus 10% lower than that of the control mix. However, the 3E-A1 mix (S = 1), and the 3E-A2 mix (S = 2) with substitutions of 25 and 50% of RCA, resulted in 3% and 6% higher elastic modulus values, than those values of the control mix. This result shows that the use of the modified EMV mixture proportioning method in this study will result in elastic modulus values, even for paving concrete, comparable or even superior to those of similar mixes made with natural aggregate. However, in the case of the 3E-A3 mix (S = 3) with substitution of 75% of RCA, the elastic modulus was 13% lower than that of the control mix.
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S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
Fig. 6. Modulus of elasticity results with each series of mix.
It should be noted in Table 3 that the 3E-A3 mix contains amounts of water, cement, and sand of 117 kg, 305 kg, and 563 kg, respectively. It may be possible to attribute the lower elastic modulus to the insufficient amount of fresh mortar or sand in the mix, which would cause lean mix. In test series 4, at the age of 7 days, the 4E-A1 mix (S = 1) and the 4E-A2 mix (S = 2), with substitutions of 25 and 50% of RCA, resulted in 2% and 4% higher values of elastic modulus compared to that of the control mix, 4C-N. However, at the age of 28 days, the 4E-A1 mix and the 4E-A2 mix resulted in 2% and 5% lower values of elastic modulus compared to that of the control mix. Overall, the elastic modulus for all mixes in test series 4 may be considered to yield similar values. Overall, these results confirm that, compared to the elastic modulus values of similar mixes made with natural aggregates, the use of the modified EMV mix proportioning method does not result in low elastic modulus of RCA concrete mixes for road paving.
5. Conclusions In this investigation a modified equivalent mortar volume mix design method is proposed and experimentally verified for concrete mixes made with coarse recycled concrete aggregate. From the results of this study, the following conclusions can be drawn.
1. Test results confirmed that the use of the EMV mix proportioning method originally proposed by Fathifazl et al. would not result in low elastic modulus of RCA concrete mixes. 2. However, for a typical concrete mix in road pavement containing less than 700 kg/m3 of sand, the original EMV mix design leads to a deficiency of the amount of sand or fresh mortar, causing large slump loss. 3. In compensation, a scale factor, S, and a 1/S-EMV mix proportioning approach were introduced and the original residual mortar was mathematically treated as a volume fraction of 1/ S, while the other fraction of (S-1)/S was treated as original virgin aggregate. 4. Test results showed that this modified EMV method yields modulus properties comparable or superior to those of similar concrete mixes made with natural coarse aggregates or conventional mixes with RCA. Acknowledgements This research was funded by the National Research Foundation, through a 2016 Korea Grant funded by the Korean Government in the project titled ‘‘Structural Performance of Reinforced Concrete Members made with Revised Equivalent Volume Mix Proportioning Method (2016R1A2B4007932)”; funds were partially provided by the 2015 Hongik University research fund in South Korea. Special thanks are given to Dr. G. Fathifazl at the National Research
S. Yang, H. Lee / Construction and Building Materials 136 (2017) 9–17
Council of Canada for providing the original EMV mix design spreadsheet. Appendix I. Example: This example illustrates a sample mix proportioning for one of the mixes proportioned with the modified EMV method. It is helpful for reader to refer to Appendix I of the original EMV model [10]. 1. Proportioning 3C-N per m3 based on ACI mix proportioning method [21] Weight of water in NAC mix: W NAC ¼ 140 kg w ¼ 366 kg Weight of cement in NAC mix: W NAC c Oven-dry weight of NA in NAC mix: W NAC ODNA ¼ 1220 kg Oven-dry weight of fine aggregate in NAC mix: W NAC ODFA ¼ 675 kg 2. Checking whether R = 0 (100% RCA concrete) is feasible or not SGNA
2:64 b RMC Max ¼ 1 V NAC DRNA SGRCA ¼ 1 0:724 2:35 ¼ 0:187ð18:7%Þ b
Since the actual RMC content of RCA-S is 35.5%, it can be seen that it is not feasible to make a concrete mix comprising only RCA 4 as coarse aggregate. Thus, in the 3C-N mix for the S = 2 condition, RMC/S = 35.5/2 = 17.75 is used instead of 35.5%. 3. Calculating required volume of RCA and NA in RCA concrete W NAC
1;220 ODNA Volume of NA in NAC mix: V NAC NA ¼ SGNA 1;000 ¼ 2:641;000 ¼ 0:462 b
where SGNA b : bulk specific gravity of NA NAC Volume of NA in RAC mix: V RAC NA ¼ R V NA ¼ 0:58 0:462 ¼ 0:268 where R = 0.58 was used to make the RCA volumetric% in the fourth column in Table 4
Volume
of
RCA
in
RAC
mix:
V RAC RCA ¼
V NAC ð1RÞ NA
SGRCA
b ð1RMC1SÞSGOVA
¼
b
0:462ð10:58Þ
ð10:35512Þ2:35 2:64
¼ 0:266
SGRCA b :
bulk specific gravity of RCA, SGOVA where b : bulk specific gravity of OVA 4. Calculating required oven-dry weight of RCA and NA in RCA concrete Required oven-dry weight of RCA in RAC mix: RCA RAC W RAC 1000 ¼ 0:266 2:35 1000 ¼ 623 kg ODRCA ¼ V RCA SGb Required oven-dry weight of NA in RAC mix: NA RAC W RAC ODNA ¼ V NA SGb 1000 ¼ 0:268 2:64 1000 ¼ 708 kg 5. Calculating required fresh NM in RCA concrete, NAC V RAC Volume of NM in RAC mix: V RAC NM ¼ V M RM ¼ 0:538 0:071 ¼ 0:466
¼ 1 V NAC where volume of mortar in NAC mix: V NAC M NA ¼ 1 0:462 ¼ 0:538 6. Calculating required water, cement, and fine aggregate in RCA concrete, V RAC
NM ¼ W NAC V NAC ¼ Required weight of water in RAC mix: W RAC w w M
140 0:466 ¼ 121 kg 0:538 ¼ W NAC Required weight of cement in RAC mix: W RAC c c V RAC NM
V NAC M
¼ 366 0:466 ¼ 318 kg 0:538
Required oven-dry weight of fine aggregate in RAC mix: V RAC
NAC 0:466 NM W RAC ODFA ¼ W FA V NAC ¼ 675 0:538 ¼ 585 kg M
17
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