Materials and Structures DOI 10.1617/s11527-014-0342-3
ORIGINAL ARTICLE
Mechanical and durability performance of concrete incorporating fine recycled concrete and glass aggregates Ali Mardani-Aghabaglou • Murat Tuyan Kambiz Ramyar
•
Received: 20 November 2012 / Accepted: 29 May 2014 Ó RILEM 2014
Abstract In this study, the effects of fine recycled concrete and glass aggregate on mechanical and durability performance of concrete were investigated. The waste concrete and glass were crushed, sieved and re-mixed to fulfill the same gradation as the available 0–4 mm crushed limestone aggregate size fraction. The recycled aggregates were substituted for fine aggregate as 0, 15, 30, 45 and 60 % by weight. 28-day mechanical and durability performance of the mixtures were determined. The maximum reduction in strength was observed in the specimens containing 60 % recycled glass aggregate. In addition, increasing the recycled concrete aggregate content caused decrease in UPV value and increase in water absorption, depth of penetration of water under pressure, chloride-ion penetration and water sorptivity of the concrete mixture. However, in recycled glass aggregate-containing mixture, UPV value increased and transport properties were improved with the increasing recycled glass aggregate content. Keywords Recycled concrete Recycled glass Mechanical properties Transport properties
A. Mardani-Aghabaglou (&) M. Tuyan K. Ramyar Department of Civil Engineering, Ege University, Bornova, Izmir, Turkey e-mail:
[email protected]
1 Introduction The construction industry is one of the most important activities affecting the environment negatively. The extraction, processing and transformation of raw materials during cement and aggregate production cause environmental and air pollution. For example, to produce 1 ton cement around 1.2 tons raw materials are necessary and 126 kWh energy is required. Meanwhile, about 1 ton CO2 is emitted. Beside, to produce 1 ton crushed limestone fine aggregate 1.1 tons raw materials and 2.6 kWh energy is required. The corresponding values for crushed limestone coarse aggregate are 1.05 tons and 2.4 kWh, respectively. Sustainability of aggregate used in concrete or asphalt is important for environmental, economical and social issues [1]. Wastes produced upon the demolition of the structures completing their service life result in environmental pollutions. In Europe, the annual production of waste demolition is around 180 million tons [2]. The waste is composed of various construction materials such as; concrete, ceramics, wood, metals and plastics. The percentage of concrete is approximately 40 % of the waste demolished [3]. One of the major difficulties in using recycled concrete (RC) aggregate is its high absorption capacity, which becomes prominent for the finer fractions [4]. Due to high absorption capacity of RC aggregate, workability of concrete is negatively affected. Poon et al. [5] investigated the influence of moisture states
Materials and Structures
of natural and recycled aggregates on the properties of fresh and hardened concretes. The test results indicated that the slump loss was significant when ovendried recycled aggregate was used. Utilization of the saturated surface dry recycled aggregate has largest negative effect on the concrete strength. The authors attributed this behavior to the bleeding of excess water in the prewetted aggregates in the fresh concrete. On the other hand, compressive strength of concretes containing air-dried or oven-dried recycled aggregate was higher than that of the concrete bearing saturated surface dry recycled aggregate. The authors indicated that in the former case mixing water may move from cement paste into recycled aggregate and this may result in strong bond between cement paste and recycled aggregate. The physical properties of recycled concrete also depend on original aggregate and adhered mortar characteristics. Type of the original aggregate, the adhered mortar quality and the amount of adhered mortar affect the properties of RC aggregate used in concrete [6]. Furthermore, the presence of unhydrated cement in RC aggregate improves the properties of concrete made with RC aggregate [7]. In most of the previous studies on RC aggregate, both coarse and fine aggregate were substituted for natural aggregate up to 100 % by weight in the concrete mixtures. Upon substitution of natural coarse or fine aggregate with RC aggregate, reduction in the compressive strength and increase in the permeability of concrete with an increase in RC aggregate content were reported. The fact was attributed to the porous structure of the RC aggregate [8–18]. Kikuchi et al. [19] suggested a maximum substitution level of 30 % for RC aggregate in structural concrete. Khatib [20] investigated the strength properties of recycled fine aggregate concrete up to 100 % substitution level. Test results indicated that the compressive strength decreased 30 % at a replacement level of 100 %. Kou and Pou [21] concluded that compressive strength of concrete decreased with increasing fine RC aggregate content up to 100 %. Drying shrinkage and chloride-ion penetration of concrete increased with increasing fine RC aggregate content. Evangelista and Brito [22] reported that, water absorption by immersion and capillarity increased 46 and 70 % with increasing fine RC aggregate content up to 100 %, respectively. In addition, the mixture containing 100 % RC aggregate showed 34 % higher chloride-ion
penetration compared to that of the control mixture. Moreover, carbonation resistance reduced with the addition of fine RC aggregate to the concrete. The increase in carbonation depth was attributed to the higher porosity of RC aggregate-bearing mixtures. Besides, the increase in paste content to provide acceptable workability and/or strength of recycled aggregate concrete may play an extra role in increasing the carbonation depth of these mixtures. Recycled glass (RG) has been used as an aggregate in concrete mixtures since 1960. Many researchers have investigated the use of RG as fine and coarse aggregate of the concrete in recent years [23–29]. Terro [30] showed that the compressive strength of concrete gradually decreased with increasing RG aggregate content up to 100 %. The effect was negligible up to 50 % replacement of the aggregate with glass. Topc¸u and Canbaz [31] investigated the effect of coarse RG aggregate on the mechanical properties of concrete. The mechanical properties of the mixture containing up to 60 % coarse RG aggregate decreased in the range of 49–60 % compared to that of the control mixture. Frost resistance of concrete, a major consideration in cold climate, is affected by its porosity, environmental conditions and aggregate characteristics. Recently, the frost resistance of concrete mixture containing recycled aggregate has been investigated by some researchers [32–35]. However, there is a lack of information about the frost resistance of concrete mixture containing fine RC and RG aggregate. A major concern regarding the use of glass aggregate in concrete is the alkali silica reaction (ASR). This reaction can be very detrimental to the stability of concrete, when coarse glass aggregate is used. It is reported that ASR, rather than occurring at the glass-paste interface, takes place in the microcracks generated inside the glass particles during the glass bottle crushing operation. Thus, owing to their larger and more active microcracks, larger glass particles show higher alkali-silica reactivity [36, 37]. Corinaldesi et al. [38] investigated the ASR of glass aggregate as fine aggregate in mortar and concrete. No detrimental effect was detected with the use of fine RG aggregate. Similarly, Zhu et al. [37] indicated that finely ground glass may show pozzolanic reaction and a reduction of ASR expansion when the glass particle size was\1.18 mm in ASTM C1260 test condition at 189 days.
Materials and Structures
Many researchers have investigated the effect of either glass or concrete recycled aggregate on the properties of concrete. In this study the effects of these recycled aggregates on the compressive and splitting tensile strength, ultrasonic pulse velocity, dynamic elastic modulus, water absorption, water sorptivity, depth of penetration of water under pressure and chloride-ion penetration were investigated comparatively. For this purpose, as a part of a more extensive study, two types of the fine recycled aggregate (concrete and glass) were used as a substitution for fine crushed limestone aggregate as 15, 30, 45 and 60 % by weight. In this way, nine different mixtures including control mixture were taken into consideration.
Table 1 Chemical composition and mechanical properties of cement Item
(%)
SiO2
20.06
Al2O3
5.68
Fe2O3
2.23
CaO
64.58
MgO
1.45
K2O
0.53
Na2O
0.20
SO3
3.09
Cl-
0.0064
Loss on ignition
1.74
Insoluble residue
0.30
Total
99.87
Major compounds
(%)
C3S
58.23
2 Experimental study
An ordinary portland cement (having a specific gravity of 3.11 and a Blaine specific surface of 3,362 cm2/g) was used. Chemical and mechanical properties of the cement provided from the manufacturer are given in Table 1. The major compounds of cement were calculated using Bogue’s equations. Two size fractions of a crushed coarse limestone aggregate (4–16 and 16–25 mm) were used in the concrete mixtures. A crushed fine limestone aggregate (0–4 mm size fraction) was used in the control mixture. In test mixtures, 15, 30, 45 and 60 % by weight of the fine aggregate was replaced with the RG or RC aggregate having the similar gradation as the fine limestone aggregate. The gradation curves of the fine aggregates and their conformations with ASTM C33 [39] limits for fine aggregates are shown in Fig. 1. Saturated surface dry specific gravity, water absorption capacity and loose bulk density of the aggregates are shown in Table 2. In addition, the abrasion and impact resistance of aggregates were determined in accordance with ASTM C131 [40] standard and the results are shown in Table 3. The RC aggregate was obtained from waste laboratory-made concrete and was crushed by a hammer crusher, sieved and remixed to have a gradation similar to that of the control fine aggregate. The waste flint glass was prepared in the similar manner in the laboratory.
C2S
13.90
C3A
11.28
C4AF
6.78
Mechanical properties
(MPa)
Compressive strength 2-day
25.4
7-day
37.2
28-day
44.6
Limestone
Recycled concrete
Recycled glass
100 90 80
Passing (%)
2.1 Materials
70 60 50 40 30 20 10 0
0.125
0.25
0.5
1
2
4
Sieve size (mm)
Fig. 1 Gradation curves of fine limestone, recycled concrete and recycled glass aggregate
2.2 Mixture proportions Concrete mixes having a cement content of 433 kg/m3 and water/cement ratio of 0.45 were prepared. The replacement levels of fine aggregate with both RG and
Materials and Structures Table 2 Physical properties of coarse and fine aggregates 0–4 mm limestone Saturated surface dry specific gravity
0–4 mm recycled glass
2.61
Water absorption capacity (%)
2.52
0.67
Loose unit weight (kg/m3)
Recycled aggregate Concrete
Glass
23
31
42
16–25 mm limestone
2.64
6.81
1,678
Crushed limestone aggregate
4–16 mm limestone
2.44
0.15
1,793
2.67
0.21
1,613
1,503
0.54 1,480
this purpose, RC aggregate was kept in water for 24 h and allowed to drying in the laboratory air on a dry cloth. The SSD condition of the aggregate was determined in accordance with EN 1097-6 [41]. The time required for wet aggregate to become SSD was recorded. The same regime was applied to the aggregate before introducing into the mixture. However, since RG aggregate has a low water absorption capacity, such a process was not applied to this aggregate. The cement, coarse and fine aggregate were placed into the mixer and mixed for about 2 min before adding the water. After 3 min of mixing followed by addition of water, the slump values were determined. Then, twelve 150 mm and three 100 mm cube specimens were prepared from each mixture. The specimens were demolded a day after casting and were cured in standard condition (20 ± 2 °C and 95 % relative humidity) up to 28 days.
Table 3 Los Angeles test result of crushed limestone and recycled aggregates
Loss on weight (%)
0–4 mm recycled concrete
RC aggregates were in the range of 0–60 wt%. The slump of the concrete mixtures was kept constant in the range of 100 ± 20 mm. The corrected proportions of the mixtures are summarized in Table 4. The mixtures were designated by their fine aggregate type following by the replacement level, e.g. the mixture containing 15 % recycled concrete aggregate was designated as RC-15. 2.3 Preparation of concrete mixtures
2.4 Test methods Owing to the high absorption capacity of the RC aggregate, it was brought into saturated surface dry condition before adding to the concrete mixtures. For
The 28-day compressive strength, splitting tensile strength and unit weight of hardened concrete mixtures
Table 4 Corrected proportions of the mixtures (kg/m3) Mix
Cement
Water
Aggregate 0–4 mm fine aggregate Limestone (L)
Recycled glass (RG)
Recycled concrete (RC)
4–16 mm
16–25 mm
Limestone (L)
Limestone (L)
Measured unit weight
Slump (mm)
Control
433
195
676
0
0
689
347
2,338
105
RG-15
432
195
574
101
0
687
346
2,334
110
RG-30
430
194
470
202
0
684
345
2,324
115
RG-45
427
193
367
300
0
680
343
2,310
120
RG-60
425
191
265
398
0
676
340
2,295
120
RC-15
431
194
573
0
101
686
346
2,330
100
RC-30
429
193
469
0
201
683
344
2,318
95
RC-45
425
191
365
0
298
676
340
2,296
90
RC-60
420
189
262
0
394
669
337
2,271
80
Materials and Structures
were determined on 150 mm cubic specimen in accordance with EN 12390-3 [42], EN 12390-6 [43] and EN 12390-7 [44], respectively. The UPV values of 28-day old concrete mixtures were determined on 150 mm cube specimens in accordance with ASTM C 597 [45] standard. The dynamic elastic modulus of concrete was calculated using Eq. (1) [46, 47]: Edh ¼ qc2
ð1 þ vÞð1 þ 2vÞ 1v
ð1Þ
where, Edn = dynamic elastic modulus of concrete (MPa), q = hardened concrete density (kg/m3), c = UPV (km/s) and m = Poisson’s ratio. Poisson’s ratio was assumed as 0.2 for all concrete mixtures. The 28-day water absorption of 150 mm cube specimens were obtained in accordance with ASTM C 642-82-97 [48] standard. Saturated surface dry specimens were weighed (b) and then kept in an oven at 100–110 °C until attaining a constant weight (a). Water absorption (m), was calculated according to Eq. (2): m ¼ ½ðb aÞ=a 100
ð2Þ
Sorptivity test was performed on 100 mm cube specimens in accordance with ASTM C1585 [49]. After 28 days, the specimens were dried at 105 °C until constant weight, and then the side surfaces of the cubes were sealed with an acrylic copolymer-based sealing material. Supporting rods were placed at the bottom of a pan and the pan was filled with tap water to provide 1–3 mm water level on the top of the supporting rods. At 0, 5, 10, 20, 30, 60, 120, 180, 240, 300, 360 min time intervals, the specimens were weighed. The sorptivity, I, was obtained from Eq. (3): mt I¼ Ad
ð3Þ
where, I = sorptivity in mm, mt = the change in weight in grams, at the time t, A = the exposed area of the specimen, in mm2, and d = the density of the water in g/mm3. The 28-day, depth of penetration of water under pressure of 150 mm cube specimens was obtained in accordance with EN 12390-8 [50] standard. Accordingly, the surface of the specimen to be exposed to water pressure was roughened with a wire brush. Then, the specimens were placed in the apparatus and water pressure of 5 bars was applied for 72 h. Afterwards,
the specimens were removed from the apparatus and were splitted perpendicularly to the face on which the water pressure was applied. The water front on the specimens was marked and the maximum depth of penetration of water was measured in millimeters. Chloride-ion penetration of concrete mixtures were determined on 100 mm in diameter and 50 mm length cylindrical specimen in accordance with ASTM C 1202 [51] at 28 day age. The amount of electrical current passed through the concrete was measured for 6 h. At the end of 6 h, the total charge passed, which is a measure of the concrete resistance to chloride ion penetration, was determined in coulombs. 3 Test results and discussion 3.1 Fresh concrete properties The slump values of concrete mixtures ranging from 80 to 120 mm are given in Table 4. Since the RC aggregate was used in saturated surface dry condition, there was not a significant change in the slump of the concrete upon increasing RC aggregate content. However, the small decrease in the slump of RC aggregate-bearing mixtures was attributed to the rougher texture of the RC aggregate compared to that of the limestone aggregate (Fig. 4). Moreover, due to smooth surface texture of RG aggregate a negligible increase in the slump of RG-bearing mixtures was observed upon increasing the substitution level of the recycled aggregate. 3.2 Compressive strength test results The compressive strength test results of the concrete mixtures are shown in Fig. 2. Each value presented is the average of three measurements. It is seen that the minimum strength values belong to the RG-60 mixture, were 60 wt% of the fine aggregate is replaced with RG aggregate. Compared to that of the control mixtures, the compressive strength of RG-15, RG-30, RG-45 and RG-60 mixtures were 1.6, 3.6, 6 and 10.6 % lower, respectively. Besides, the compressive strength of RC-15, RC-30, RC-45 and RC-60 mixtures were 0.6, 1.8, 4.2 and 7.6 % lower, than that of the control mixture, respectively. As it can be seen from the test results, substitution of the fine aggregate by the recycled ones, even up to 60 %, has not a significant
Materials and Structures 4.0
51
50.2
49.9
50
49.3
49
49.4
48.1 48.5
48
46.4
47
47.2
46 45 44.9
RG
44
RC
43
Splitting tensile strength (MPa)
Compressive strenght (MPa)
52
3.9
3.9
3.79
3.8 3.7
3.59
3.70
3.6 3.58
3.5
RG
3.4
RC
3.3
3.30
0 10
3.75
3.84
3.2
42 0
3.87
20
30
40
50
60
10
20
30
40
50
60
Replacement level (%)
Replacement level (%)
Fig. 3 Splitting tensile strength of concrete mixture Fig. 2 Compressive strength of concrete mixture, RG recycled glass aggregate was replaced with limestone aggregate up to 60 %, RC recycled concrete aggregate was replaced with limestone aggregate up to 60 %
effect on the compressive strength of the concrete. The major factor causing this slight reduction seems to be the weakness of the RC aggregate particles created during crushing of the old concrete [52, 53]. In addition, RG aggregate has lower density, more friability and higher surface smoothness compared to those of the limestone aggregate. Compressive strength of the RG aggregate-containing mixtures was slightly lower (3.2 %) than those of the RC aggregate-containing mixtures. This effect seems to be arisen in part from the higher friability of the glass aggregate, as can be seen from Los Angeles tests results given in Table 3, and in part, due to weaker ITZ in glass aggregate-bearing mixtures. The results of other studies where 100 % of the fine crushed limestone aggregate was replaced with either RC or RG aggregate indicate a decrease in compressive strength of concrete in the range of 8–40 % [20, 21, 33, 54].
3.3 Splitting tensile strength test results The 28-day splitting tensile strength test results of the concrete mixtures is given in Fig. 3. Each value presented is the average of three measurements. It was found that, the maximum strength values belong to the control mixture, containing no recycled aggregate. Compared to that of the control mixtures, the splitting tensile strength of RG-15, RG-30, RG-45 and RG-60 mixtures were 1.5, 5.0, 8.2 and 15.4 % lower, respectively. Besides, the splitting tensile strength of
RC-15, RC-30, RC-45 and RC-60 mixtures were 0.8, 2.8, 3.8 and 7.9 % lower than that of the control mixture, respectively. As it can be seen, even 45 % replacement of the aggregate with recycled ones caused a slight reduction in splitting tensile strength of the mixtures. However, in RG-60 mixture, there was a significant reduction (15.4 %) in splitting tensile strength. This may be due to weaker interfacial transition zone (ITZ) in RG aggregate-bearing mixtures compared to that of the control mixture. As it can be seen from Fig. 4, RG aggregate has a smoother surface than the limestone aggregate which decreases the bond between cement paste and aggregate. Besides, microcracks may occur in RC aggregate during crushing process; thus, the RC aggregate particles become more friable than limestone aggregate (Table 3). Therefore, concrete fracture seems to occur in sharp corners of the recycled aggregate phase in splitting tensile test. The splitting tensile strength of RC aggregate mixtures is slightly higher (8.1 %) than those of the RG aggregate mixtures. This fact, in part, is attributed to the rough surface of the RC aggregate (Fig. 4) and, in part, to the further hydration of unhydrated cement particles which may exist in these recycled aggregate. As shown in Fig. 5, a strong linear relationship between compressive and splitting tensile strength of the RG and RC-bearing mixtures were obtained. As it can be seen from the figure, the slight difference between the compressive strength-splitting tensile strength relationships of the mixtures containing two different types of recycled aggregate, once again, may be attributed to the difference between the ITZ characteristics of these mixtures.
Materials and Structures
Fig. 4 Microscopic image of the aggregates (910) a recycled glass aggregate, b crushed limestone aggregate, c recycled concrete aggregate
Compressive strength (MPa)
RG
RC
Linear (RG)
Linear (RC)
51 50
y = 8.4991x + 16.861 R = 0.9987
49 48 47 46
y = 12.885x + 0.1077 R = 0.9886
45 44 3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
Splitting tensile strength (MPa)
Fig. 5 Relationship between compressive and splitting tensile strength of RG and RC mixtures
3.4 Dynamic elastic modulus determined by ultrasonic pulse velocity (UPV) The UPV test results are shown in Fig. 6. Each value presented is the average of three measurements. The most important factors affecting UPV values of concrete are the concrete porosity, aggregate type and ITZ characteristics [55]. It can be seen that the
UPV values of the concrete mixtures were higher than 4.5 km/s, the limit specified for strong concrete by Whitehurst [56]. In the mixture containing RC aggregate, increasing the substitution level of the RC aggregate to 60 % caused a negligible reduction (0.5–4 %) in UPV compared to that of the control mixture. This may be arisen from higher porosity of RC aggregate compared to that of the crushed limestone aggregate. Similarly, Khatib [20] reported 8.8 % reduction in UPV values of the mixtures containing 100 % fine RC aggregate. In RG aggregate concrete, the UPV values increased slightly (0.4–7.4 %) with increasing RG aggregate content compared to that of the control mixture. This may be due to lower porosity of the glass aggregate compared to that of the limestone aggregate. In addition, as it can be seen from the microscopic image (Fig. 4), the surface of RG was smooth; thus, the ITZ of the mixture incorporating RG aggregate is expected to be somewhat weaker than that of the control mixture. In spite of having a weaker ITZ the higher UPV values of RG aggregate-bearing mixtures, compared to that of the control mixture, may be attributed to the difference between ultrasound
RG
5.2
RC
Whitehurst [56]: UPV >4.5 Strong, 3.5-4.5 Good, 3-3.5 Intermediate, 5% Poor.
Fig. 8 Water absorption test results of all concrete mixtures
15% Recycled aggregate 45% Recycled aggregate
30 25 20 15 10 5 0 Control
RG
RC
Fig. 10 Depth of penetration of water under pressure of all mixtures 15% Recycled aggregate 45% Recycled aggregate ASTMC1202[51]: Charge passed is >4000 High, 2000-4000 Moderate, 1000-2000 Low, 100-1000 Very Low,
