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Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates
Construction and Building Materials 64 (2014) 172–183
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates Erhan Güneyisi a,⇑, Mehmet Gesog˘lu a, Zeynep Algın b, Halit Yazıcı c a
Department of Civil Engineering, Gaziantep University, 27310 Gaziantep, Turkey Department of Civil Engineering, Harran University, 63000 Sßanlıurfa, Turkey c _ Turkey Department of Civil Engineering, Dokuz Eylül University, 35160 Izmir, b
h i g h l i g h t s We studied use of recycled concrete aggregate (RCA) in self-compacting concrete (SCC). Treatment methods were applied on RCA used in SCC. Effect of treatment methods on engineering properties of SCC was investigated. Microstructures of treated RCA and produced SCC were examined. Treatment methods remarkably affect self-compactibility characteristics of concrete.
a r t i c l e
i n f o
Article history: Received 20 February 2014 Received in revised form 4 April 2014 Accepted 9 April 2014
Keywords: Fresh property Microstructure Recycled aggregate Self-compacting concrete Strength Treatment method
a b s t r a c t In this experimental study, the adverse effect of old cement-mortar composite on self-compacting concrete (SCC) containing recycled concrete aggregate (RCA) were investigated by means of potential aggregate treatment methods so as to promote the maximum RCA utilisation. Although the limited researches focus on the direct utilisation of untreated RCA in SCC, the hitherto unavailable results to the properties of SCCs containing treated RCAs are presented in this paper. Four alternative aggregate surface treatment methods introduced to RCAs are two-stage mixing approach, pre-soaking in HCl solution, water glass dispersion and cement–silica fume slurry. 100% coarse RCA replacement with the natural aggregate was used in SCC mixes having constant cement dosage, fly ash replacement and waterto-binder ratio. The slump flow and T500 time, V-funnel time, L-box height ratio, viscosity, compressive and splitting tensile strength, and freeze–thaw cycling tests were carried out to identify the effects of these aggregate treatment methods on the key properties of SCC. Test results reveals that selfcompactibility characteristics of the concretes are remarkably affected by surface treatment of RCAs. Moreover, the treatment methods of two stage mixing approach and water glass provide more dense and connected microstructures in SEM analysis leading to significant strength improvements compared to the control SCC. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Due to the changes in the requirements and planning of concrete structures, excessive amount of construction and demolition (C&D) waste is generated in urban areas worldwide. Annually, 900 million tonnes of C&D waste is estimated in Europe, USA and Japan [1]. The control and management on C&D waste is becoming a worldwide challenge, especially for the major urban centres. Considering the environmental pollution and the consumption of ⇑ Corresponding author. Tel.: +90 342 3172410; fax: +90 342 3601107. E-mail address: [email protected] (E. Güneyisi). http://dx.doi.org/10.1016/j.conbuildmat.2014.04.090 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
limited natural sources it is crucial to reuse and recycle C&D waste. The production of recycle concrete aggregate (RCA) from C&D waste is important issue since it provides an alternative mean to the dependence of construction industry on natural aggregates and the critical shortage problem of natural aggregate sources. This is a common practice for several European countries, USA, Australia, and Japan. For instance, according to 2010 annual reviews, Germany, UK, Netherland, France, and USA produce recycled aggregates approximately 60 Mt, 49 Mt, 20 Mt, 17 Mt, and 140 Mt, respectively [2,3]. RCA is produced by crushing the demolished concrete waste into smaller particles generally using two-stage crushing process.
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The targeted aggregate size from the utilised crushing process influences the quality of RCA [4–8]. The properties of RCA mainly differ from its natural counterpart by the remaining hardened cement mortar adhered to the original aggregate surface as shown in Fig. 1. The amount and quality of hardened old cement mortar in the aggregate directly affect the physical properties of RCA [4] because it is characterised as porous [9–13] and presents numerous microcracks [11]. Accordingly, RCA is specified as the type of aggregate having lower density, higher water absorption, and lower mechanical strength than the natural aggregates [9,14–17]. In the case of using RCA in new concrete production, it is generally expected that these characteristics of RCA cause the adverse effect on the interfacial bond between RCA and new cement paste. Subsequently, this may result a reduction in durability, strength and workability of concrete produced with RCA [18]. Generally, the water absorption capacity of RCA affects the workability of new concrete. Additionally, the shape and texture of aggregate depending mainly on the crusher type also affect the workability of concrete [19]. RCA tends to have more water absorption capacity compared to the natural aggregate because of the presence of old cement mortar’s porous microstructure [9,11,18,20–22]. The quality of interfacial transition zone (ITZ) between RCA and new cement mortar that is the connection between these two main components of new concrete poses considerable importance since it governs the mechanical strength properties of concrete [11,23]. Unlike the conventional concrete, new concrete produced with RCA has two ITZs which are new ITZ that is between RCA and new cement mortar and old ITZ that is between RCA and old adherent cement mortar. Accordingly, the structure of concrete produced with RCA demonstrates more complex material behaviour compared to the conventional concrete. Old cement mortar remaining in ITZ composes of microcracks and voids. This microstructure significantly affects the strength of concrete, leads to increase the water consumption and reduces the water required for hydration in ITZ [11]. Since RCA exhibits high water absorption capacity characteristics owing to the old cement mortar’s porous microstructure, RCA in new concrete leads to reduce the effective water content for the hydration process because the adhered mortar in the old ITZ tends to absorb a large amount of water during the initial mixing stage and subsequently creates loose ITZ in the hardened concrete [24,25]. Because of this adverse effect, the high percentage replacement of RCA with natural aggregate reduces the compressive strength of conventional concrete significantly [26– 28]. These drawbacks which are mainly caused by the weak and porous ITZ of old cement mortar adhered on RCA impose limitation on the widespread commercial use of RCA in structural concrete, especially in the production of self-compacting concrete (SCC).
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One of the promising methods to resolve the adverse effect of RCA to promote and encourage its maximum utilisation in the SCC production is to employ an effective aggregate treatment method. Hence, various techniques tend to enhance the physical properties of RCA by mainly attempting to remove the loose particles of old mortars have been investigated previously for conventional concrete production. The treatments are basically applied on RCA to attain the quality and improve the interfacial bond between RCA and new cement mortar compared to that of natural aggregate. Some of these methods improving the performance of conventional concrete (i.e. ultrasonic bath, thermal and heating methods) require the complicated mechanical equipments and utilises high energy consumption. The other potential treatment techniques that can be applied on RCA are two-stage mixing approach, pre-soaking in HCl solution, water glass dispersion, and cement– silica fume slurry. Unlike the complicated pre-treatment methods mentioned above, these techniques seemingly have potential because they are economical, effective and feasible. However, it is worthy to note that among these techniques two-stage mixing from industrial scale point of view appears to be more practical. In the current literature, to the best of the authors’ knowledge, none of these treatment methods is applied to RCA used in SCC and it has not been reported how these treatment methods affect the fresh and hardened properties of the SCC. The use of RCA in the SCC is a relatively new research area on which a very limited scientific research has been carried out [29–33]. This paper presents the hitherto unavailable results to some properties of the SCCs produced with treated RCAs. It investigates the potential use of high amount of RCA in the SCC production by employing the treatments on RCA. This paper also tends to overcome this short-coming in the current literature by assessing the influenced properties of treated RCA affecting the fresh and hardened states of the SCC at 100% replacement level for the coarse aggregates.
2. Experimental details and methodology 2.1. Materials In this study, the materials used are Type I ordinary Portland cement (OPC), fly ash (FA), fine aggregate, coarse RCA and superplasticizer. OPC (named as CEM I 42.5N) used in this study complies with TS EN 197-1 [34] (Turkish standard which is mainly based on EN 197-1 [35]). FA utilised in this research as cementitious material obtained from Yumurtalik-Sugozu thermal power plant is F type class according to ASTM C 618 [36]. The typical chemical compositions and some physical properties of OPC and FA are tabulated in Table 1. Commercially available polycarboxylic-ether type superplasticizer (SP) having specific gravity of 1.07 is used in this research. Natural river and crushed sands were utilised as fine aggregates with maximum size of 4 mm. The values of specific gravity and water absorption are 2.66% and 0.55% for the natural river sand and are 2.45% and 0.92% for the crushed sand, respectively. Particle size gradations and some physical properties of these aggregates are given in Table 2 and Fig. 2. RCA was used as coarse aggregate with two fractions that are in the range of 4– 8 mm and 8–16 mm in order to have more control over the aggregate combination to obtain the required gradation according with TS 802 [37]. The individual gradation curves of aggregates and the combined aggregate mixture obtained using the certain proportions of fine and coarse aggregates are shown in Fig. 2.
2.2. The production of RCA
Fig. 1. Coarse RCA.
The commercial crusher system which is generally included jaw, impact and cone types of crushers in the production of RCA directly affects the shape and texture of aggregates. Jaw crusher generally produces folieceous aggregate forms, whereas the cone and impact crushers generally provide cubical aggregate forms [38]. Some researchers in the literature demonstrate the advantages of using the two-stage crushing system to produce recycled aggregates [18,39–43]. They compare the properties such as water absorption, Los-Angeles abrasion, density and crushing values of RCA obtained from the jaw crusher with the integrated systems of jaw and impact crushers. It was concluded that the two-stage crushing system was more favourable and the characteristic properties were improved by this method [18].
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Table 1 Chemical composition and physical properties of cement and fly ash. Materials
Composition (%) CaO
SiO2
Al2O3
Fe2O3
MgO
SO3
K2O
Na2O
Cement Fly ash
64.35 4.24
20.08 56.2
4.63 20.17
2.84 6.69
2.07 1.92
2.85 0.49
– 1.89
– 0.58
Loss of ignition
Specific gravity
Blaine fineness (m2/kg)
2.56 1.78
3.18 2.25
318 287
Table 2 Physical properties and sieve analysis results of fine aggregates used. Fine aggregates
River sand Crushed sand
Sieve size (mm) 16 8 4 Percentage passing (%)
2
1
0.5
0.25
100 100
58.7 62.9
38.2 43.7
24.9 33.9
5.4 22.6
99.7 100
94.5 99.2
Fineness modulus
Specific gravity
Absorption (%)
2.79 2.38
2.66 2.45
0.55 0.92
In the implementation of two-stage mixing approach the certain amount of cement and water with fly ash is mixed for 1 min and then the aggregates are added to the mixture, and they are mixed further for 1 min. The remaining materials for the mix are then added and mixed further for another 2 min (see Fig. 4d and e). 2.4. Detail of mixes and preparation
Fig. 2. The gradation curves of aggregates.
Coarse RCAs used in this study were produced from the concrete samples having the dimensions of 150 150 150 mm by using the two-stage crushing system includes the integration of jaw and cone crushers. The strength of concrete samples was chosen as 20 MPa because the current Turkish Earthquake Regulation [44] disallows to use concrete having the strength less than that of C20. The primary crusher (jaw) and secondary crusher (cone) shown in Fig. 3(a and c) were used in the crushing process. In the first stage, as shown in Fig. 3(b) the concrete samples were crushed in the laboratory by the jaw crusher which led to produce folieceous-like aggregate shape using the effect of compression. In the following stage, the obtained aggregates were crushed further by the cone crusher (see Fig. 3d). The cone crusher contains a cone part rotates axially producing impact effects to obtain the required aggregate size and shape. In this stage, the folieceous aggregate shape is converted to the cubical aggregate shape using the effect of squashing and impact crushing. The recycled aggregates were graded in terms of the fractions of 4–8 and 8–16 mm to provide compatibility in the gradation curves provided by TS 802 [37] for natural aggregates (see Fig. 2). 2.3. The treatment methods for RCA In this study, the four potentially useful and practical treatment methods [11,21,45] were applied on the coarse RCA used. They are as follows. The aggregates were submerged in HCI (hydrochloric acid) solution at 0.1 molarity for 24 h at 20 °C. After then, they were submerged in distilled water in order to remove acidic solution (see Fig. 4a). The aggregates were submerged in water glass (Na2OnSiO2 sodium silicate) for 30 min. After then, they were held in suspension for 10 min to provide leakage of excess water glass from the aggregates which were taken out of the solution and then dried in oven for 1 h by preventing bonding the aggregate particles (see Fig. 4b). The aggregates were submerged in cement–silica fume slurry for 30 min, then taken out and spread over the wide sieves for 24 h. They were cured by submerging in water for 28 days (see Fig. 4c).
SCC mixes were produced with the water/binder ratio of 0.38 and the cement dosage of 550 kg/m3. In these mixes, 20% of cement was replaced with fly ash. In all mixes, treated and untreated RCAs were used as coarse aggregate with 100% replacement to the natural coarse aggregate originally designed in the mix. Table 3 shows the detail composition of five different concrete mixtures prepared in this study. The mix description of RCA (control) indicates the control mix, RCA–HCl, RCA–WG, RCA–CSF, and RCA–TSM mixes include RCAs introduced with the aforementioned treatment methods which are pre-soaking in HCl solution, water glass dispersion, cement–silica fume slurry, and two-stage mixing approach, respectively. In the process of preparing the mixes, the dry mix of RCA with cement and fly ash are mixed firstly, and then the natural sand is added. Afterwards, the water with superplasticizer is incorporated gradually to the mixtures and it is mixed for about 3 min and then left for 1 min to rest. Finally, the concretes are mixed for additional 1–2 min to complete the mixing process. The slump flow test, V-funnel test, L-box test, and viscosity tests are carried out to identify the required properties and the characteristics of the fresh SCC mixes. Thereafter, the fresh concrete is placed in the moulds. The test specimens are demoulded 24 h after casting and then water cure is applied until the time of testing. The compressive and splitting tensile strength tests at 28 and 90 days of curing are performed to establish the hardened properties of SCCs produced. Additionally, the deterioration of hardened SCCs during freeze–thaw cycles were assessed on the specimens from each SCC mixes. 2.5. Testing 2.5.1. The specific gravity and water absorption values of RCAs The specific gravity and water absorption values of treated and untreated coarse RCAs were determined with respect to the ASTM C127 [46]. The tests were conducted on particles of various sizes ranging from 4–8 mm to 8–16 mm. The water absorption was carried out by keeping a known quantity of dry aggregate in a pycnometer filled with water at room temperature for a certain period of time. The weight increase of aggregate was measured at 10, 30, 60, and 120 min, 24 h, 7 days and 15 days after submersion in water. 2.5.2. Examination of microstructure of treated RCAs and the produced SCCs The microstructure studies were conducted using a scanning electron microscope (SEM) on the microstructure surface of untreated and treated coarse RCAs as well as the samples from the produced SCC mixes. 2.5.3. Testing of the produced SCCs The testing programs were designed to determine how the considered aggregate treatment methods affect the properties of SCCs containing the high replacement level of RCAs, which determine flowability, filling ability, passing ability, viscosity, and strength results. The conducted tests on the fresh properties such as slump-flow, T500, V-funnel and L-box were complied with EFNARC [47]. Viscosity of the produced fresh SCC was measured by Rheometer testing device based on the Bingham model (see Fig. 5). The Bingham model that is represented by the following two-parameter relationship s ¼ s0 þ lc_ can be used to model the
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Fig. 3. The two-stage crushing system and the crushed concretes. (a) The primary crusher (jaw), (b) the crushed concretes obtained from the jaw crusher, (c) the secondary crusher (cone), and (d) the crushed concretes obtained from the cone crusher.
flow behaviour of concrete. s0 represents the yield stress indicating the shear stress required to initiate the flow. After the yield stress has been exceeded plastic viscosity denoted as l affects the resistance to flow. The flow curve that is defined by these two parameters represent the flow behaviour of concrete mixture [48]. The test setting consists of a 20 s pre-shear period at a constant speed of 0.50 rps followed by 8 flow curve points in descending order from 0.50 to 0.05 rps. The compressive strength measurement was applied on the cubical SCC samples of 150 150 mm complying with ASTM C 39 [49]. The test is conducted on three cube samples from each concrete mix at 28 and 90 days of curing. The compressive strength was computed by averaging the results from the three tested samples at each testing age. Splitting tensile strength of the concrete was measured on the cylindrical samples of 150 300 mm at 28 and 90 days of curing as it is recommended by ASTM C 496 [50]. The splitting tensile strength is obtained by averaging the results from the three tested cylindrical samples. SCC prisms having the size of 100 100 300 mm were prepared for the freeze–thaw cycling tests in accordance with ASTM C666 Procedure A [51]. 90 days cured specimens were moved into the freeze–thaw chamber and the programmable automated temperature controlled climatization device specifically designed for the freeze–thaw cycling test was used. After each 20 cycles the specimens were taken out of the device to measure the mass loss and the ultrasonic pulse velocity (UPV) variations at 3 points of the long side of each specimen. Three prisms from each SCC were tested repeatedly and the average value was used for each data presented.
3. Experimental results and discussion 3.1. Water absorption and specific gravity results The water absorption results of RCAs varying with time for the fractions of 4–8 mm and 8–16 mm are given in Figs. 6 and 7, respectively. Untreated (normal) RCA notated as RCA and treated RCAs are notated as RCA–CFS, RCA–HCI, and RCA–WG indicating
RCAs treated with cement–silica fume slurry, HCl solution and water glass, respectively. Since the treatment method of two stage mixing approach is a process based implementation and is conducted during the preparation of SCC, it is not included in Figs. 6 and 7. It is demonstrated that the water absorption capacity of recycled aggregates is increased with time for all aggregate types (see Figs. 6 and 7). It is clearly shown that the water glass treatment is the most effective enhancement method among others for the reduction of water absorption and drops the results approximately 67–77%, whereas HCI and cement–silica fume slurry treatments reduce the water absorption capacity about 20–11% and 6–4% for the fractions of 4–8 and 8–16 mm, respectively. As demonstrated in the microstructure images from SEM analysis in this paper, the pre-soaking treatment of water glass creates a aggregate surface with outer stronger coating which leads to decrease the water absorption of RCA to the value of 2%. This conclusion agrees with some researches [45,52] studied on lightweight aggregate in which it is stated that the water glass coatings substantially decrease the water absorption (i.e. reduces from 27% to 3%) and increase the wearing resistance by creating a smooth, dense and hard coating on aggregate surface. As previously demonstrated [21,24] that the pre-soaking treatment of HCl solution removes a great portion of weak cement mortar and certain loose substances attached on RCA surface and subsequently enhances the physical properties of RCA. The presence of residual old cement mortar obstructs the bond between RCA and new cement paste in SCC. The removal of loose particles from the surface of RCA leads stronger contact at the interfacial
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Fig. 4. (a) RCA treated with HCl solution, (b) RCA treated with water glass dispersion, (c) RCA treated with cement–silica fume slurry, (d) the first stage of two-stage mixing approach, and (e) the second stage of two-stage mixing approach.
Table 3 The proportions of concrete mixes (kg/m3). Mix description
RCA (control) RCA–HCl RCA–WG RCA–TSM RCA–CSF a
w/b
0.38 0.38 0.38 0.38 0.38
Cement
440 440 440 440 440
Fly ash
110 110 110 110 110
Water
209 209 209 209 209
SPa
9.35 9.35 7.7 9.35 9.35
Fine aggregate
Coarse RCA
River sand
Crushed sand
8–16 mm
4–8 mm
523.4 523.4 524.8 523.4 523.4
224.6 224.6 225.2 224.6 224.6
493.5 495.9 476.4 493.5 444.7
211.5 212.8 204.5 211.5 190.8
Superplasticizer.
zone between treated RCA and new cement paste in SCC. Since the interfacial bond between cement paste and aggregate is known to be critical in concrete structures and is a significant factor governing concrete strength development [24,53], the enhancement in the interfacial zone consequently reflects the improvement in concrete strength of SCC with treated RCA. This treatment decreases the water absorption of RCA with a reduction of 11–20%. This conclusion agrees with some researches [21,24] stating that the HCl treatment substantially decreases the water absorption between 1% and 28% and improves the compressive strength of normal concrete.
While the water absorption results of RCA treated with cement–silica fume slurry is a little lower than normal RCA, it is higher than that of the other surface treatment methods. Table 4 shows the results of water absorption in 24 h and the specific gravity results for untreated and treated RCAs. As shown in Figs. 6 and 7, and Table 4 that the water absorption values of treated RCAs are remarkably lower than that of normal RCA. As can be seen in Table 4 that the water absorption values of RCAs having the size of 4–8 mm and 8–16 mm in 24 h are 8.72% and 7.66%, respectively and the corresponding specific gravity results are 2.43 and 2.45. Accordingly, this shows that the water absorption values of RCAs
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E. Güneyisi et al. / Construction and Building Materials 64 (2014) 172–183 Table 4 The results of specific gravity and water absorption of the RCAs. Coarse aggregate
RCA RCA–HCl RCA–WG RCA–CFS
Specific gravity Fractions (mm)
Water absorption % (24 h)
4–8
8–16
4–8
8–16
2.43 2.45 2.34 2.20
2.45 2.46 2.36 2.21
8.72 6.99 2.85 8.24
7.66 6.84 1.77 7.35
this range. Therefore, it can be stated that the water absorption capacity increases and specific gravity decreases with a decrease in size of RCA. This is because the smaller size RCAs are having higher amount of adhered mortar and, accordingly, the absorption capacity of RCA is increased while the specific gravity is decreased with the amount of adhered mortar present. The previous studies [21,54] state that the pores structure of existing old cement mortar increases the porosity of RCA. This pores microstructure is also demonstrated in this paper using SEM image analysis. The obtained water absorption values of RCA indicate that the increase in porosity subsequently results an increase in water absorption values of RCA particles.
Fig. 5. Viscosity measurement by Rheometer.
Fig. 6. The water absorption results of RCAs having the fraction of 4–8 mm.
Fig. 7. The water absorption results of RCAs having the fraction of 8–16 mm.
having the size of 4–8 mm are higher than that of RCAs having the size of 8–16 mm, whereas the specific gravity results are lower for
3.2. Microstructures of RCAs and produced SCCs The differences between microstructures of untreated and treated RCAs, and produced SCCs were studied using the scanning electron microscope (SEM) images indicated in Figs. 8–13. Fig. 8(a–c) shows untreated RCA with old ITZ, the detailed view of untreated RCA with loose cement mortar, treated RCA with HCl solution, respectively. It is demonstrated that the surface of untreated RCA is considerably more porous containing certain amount of loose cement mortar and other small impurities, such as dust, which are loosely connected to their bulk aggregate particles. The comparison between Fig. 8(a–c) indicates that HCl solution treatment at 0.1 molarity significantly reduces the loose particles on RCA surface and, subsequently, makes the aggregate surface more cleaner and uniform. However, the increase in HCl molarities would possibly erode the surface more and cause more weaker and porous surface than the original RCA aggregate particles [24]. Therefore, as shown in Fig. 8(c) 0.1 HCl molarity produce sufficient results without the concerns of remaining acid solution within treated RCAs. Fig. 9(a and b) indicates treated RCAs having cement–silica fume and water glass coatings, respectively. Fig. 9(a and b) demonstrates that the treatments of water glass and cement–silica fume slurry produce the coatings allowing to cover RCAs containing voids. Fig. 10 shows control SCC with new ITZ. The comparison between Figs. 10 and 8(a and b) demonstrate that new ITZ is less porous compared to old ITZ owing to the recovery of microcracks and voids in RCA with new cement mortar from SCC. Fig. 11(a–d) indicates SCCs produced from treated RCAs implemented with two stage mixing approach, HCl solution, water glass, and cement–silica fume slurry, respectively. The improvement in the microstructure with more overlapping and intense ITZ is observed in Fig. 11(a–d) due to the implemented treatments on RCAs compared to control SCC shown in Fig. 10. The treatment methods of two stage mixing approach (see Fig. 11a) and HCl solution (see Fig. 11b) allow further penetration of new cement mortar from SCC into treated RCA. This penetration process subsequently results more dense and connected views especially in new ITZs (see Fig. 11a and b) compared to control SCC (see Fig. 10). The treatments of water glass and cement–silica fume produce a sort of protection coatings on RCAs by recovering the inner microcracks and voids (see Fig. 11c and d).
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Fig. 9. Surface microstructure views of treated RCAs having cement–silica fume and water glass coatings.
Fig. 8. Surface microstructure views of RCAs: (a) untreated RCA with old ITZ, (b) untreated RCA with loose cement mortar, and (c) treated RCA with HCl solution.
Fig. 12 indicates the cement mortar in control SCC. Since the water absorption characteristic of RCA differs in terms of the implemented treatment methods the new cement mortars among RCAs are accordingly affected and provided varying voids and loose mortar compositions. Due to the high water absorption characteristic of untreated RCA more voids and loosely connected mortars are observed in new cement mortar because RCA and the adhered old cement mortar consume some of the water present (see Fig. 12). Fig. 13(a–d) shows the cement mortars in SCCs produced from treated RCAs using two stage mixing approach, HCl solution, water glass and cement–silica fume slurry, respectively. The treatment process causes a decrease in water absorption and provides more dense and connected cement mortar compositions as demonstrated in Fig. 13(a–d). Considering the amount of voids and loose cement mortars, the treatment methods of two stage mixing approach and water glass are provided more dense and connected
Fig. 10. Surface microstructure view of control SCC with new ITZ.
mortar compositions compared to new cement mortar in control SCC (see Figs. 12 and 13a and c). Microstructure images from SEM analysis show that the interfacial zone between new cement paste and treated RCA exhibits less pores characteristics which are significantly different compared to those of SCC with untreated RCA. This demonstrates that the quality of interfacial zone depends on the surface characteristics of RCA particles and the implemented pre-treatments. Especially, two stage mixing approach, water glass and HCl treatments can significantly enhance the pores and weak characteristics of interfacial zone between RCA and new cement mortar of SCC. This enhancement improves the fresh properties of SCC and increases the paste–aggregate bond strength resulting a subsequent increase in the strength of SCC.
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Fig. 12. Surface microstructure view of cement mortar in control SCC.
Fig. 11. Surface microstructure views of SCCs produced from treated RCAs using (a) two stage mixing approach, (b) HCl solution, (c) water glass, and (d) cement–silica fume slurry.
3.3. Properties of SCCs with untreated and treated RCAs In order to specify the flowability, viscosity, and passing ability of the produced SCCs, slump flow diameter, T500 slump flow time,
V-funnel flow time, L-box height ratio, and viscosity were measured and the results are shown Table 5. The obtained results were compared with the SCC characteristic target values identified by class names provided by EFNARC [46]. As can be seen in Table 5 that the slump flow diameters of SCCs having coarse RCAs implemented with the pre-soaking treatment methods (i.e. HCI solution, water glass, and cement–silica fume slurry) are higher than the results from other SCC mixes. Table 5 shows that all of the slump flow diameters are in the range of 700–725 mm, these mixtures are classified as SF2 according to EFNARC [46]. Although the dosage of superplasticizer for SCC implemented with treated RCA using water glass was decreased in order to satisfy the EFNARC limitation [46], the high slump flow compared to control SCC is attributed to the weaker cohesion between the cement mortar and water glass treated RCAs due to the smooth and comparably impermeable surface of treated RCA. Table 5 shows that T500 slump flow time values for all of the produced SCC mixes are less than 4 s and SCC containing water glass treated RCA is the shortest compared to other mixes. Since the water absorption capacity is reduced for treated RCAs, more free water become present between the aggregate particles in SCC mixes resulting a reduction in the slump flow time (see Tables 4 and 5). All of the produced SCC mixes are having L-box height ratios in the range of 0.80–0.85 which satisfies the EFNARC limitation [46]. During the measurement of viscosity by Rheometer, approximately the yield stresses were obtained as 0.1 Pa for all produced mixes indicating the self-flow behaviour as the minimum stress to initiate flow. The viscosity results in Table 5 indicate that the viscosity is reduced for treated RCAs because the lower cohesion forces deriving from lower water absorption capacity generally cause lower flow viscosity. Similarly, V-funnel flow time results in Table 5 indicate that V-funnel flow time is reduced for treated RCAs. The compressive strength results of SCCs incorporating treated and untreated RCAs are determined at 28 and 90 days of curing, and presented in Fig. 14. It shows that due to the increased amount of hydration products produced on the prolonged curing age the compressive strength values on the age of 90 days are higher than the results obtained on the age of 28 days. These improvements are approximately in the range of 10–15% for SCCs produced with untreated RCA and treated RCAs. The comparison of compressive strength results between SCCs having untreated and treated RCAs indicates that all of the treatment methods except the cement– silica fume slurry treatment produce greater results than that of SCC containing untreated RCA. This lack of improvement in compressive strength from SCC containing cement–silica fume treatment is due to the weaker characteristics of new ITZ. The improvement of compressive strength on the age of 28 days
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Fig. 13. Surface microstructure views of the cement mortars in SCCs produced with treated RCAs using (a) two stage mixing approach, (b) HCl solution, (c) water glass, and (d) cement–silica fume slurry.
compared to that of the corresponding control mix is 4% for SCC with RCA treated using HCI solution and this improvement at 90 days of curing is 2%. The use of water glass treated RCAs causes an increase in compressive strength about 9% and 7% at 28 and 90 days of curing, respectively. The highest compressive strength
results on the ages of 28 and 90 days are obtained as 60 MPa and 67 MPa for SCCs containing RCAs treated with two stage mixing approach, corresponding 13% and 10% improvements compared to that of SCC with untreated RCA, respectively. These improvements in SCCs with RCAs treated using two stage mixing approach is owing to the achievement of forming a layer of cement slurry on the surface of RCA and leading to fill up the cracks and voids, and it subsequently improves ITZs at the pre-mix stage. This improvement in ITZs results an enhancement in compressive strength as demonstrated by previous research [11] on normal concrete. As shown in Figs. 11(a) and 13(a), the enhancement characteristics of two stage mixing approach provide more dense and connected microstructure compared to that of corresponding control mix. Fig. 15 shows the results from the splitting tensile strength tests on SCCs containing treated and untreated RCAs at 28 and 90 days of curing. As demonstrated for the compressive strength results in Fig. 14, the similar trend that is greater values for the age of 90 days is observed in Fig. 15 for this test compared to the results at 28 days of curing resulting from the increased amount of hydration products produced on the prolonged curing age. These strength improvements are approximately in the range of 13–21% for SCCs incorporating untreated RCA and treated RCAs. Apart from the cement–silica fume slurry treatment which produces lower splitting tensile strength compared to that of corresponding control SCC because of the its weaker bond new ITZ, all of the RCA treatment methods produce greater results than that of SCC with untreated RCA. Comparing with the corresponding control SCCs, the improvements in splitting tensile strength at 28 days of curing are 4%, 9% and 10% for SCCs containing treated RCAs with HCI solution, water glass and two stage mixing approach. These results on the age of 90 days are 3%, 4% and 6% respectively. The highest splitting tensile strength results at 28 and 90 days of curing are respectively 3.2 MPa and 3.7 MPa corresponding 10% and 6% improvements for SCCs containing RCAs treated with two stage mixing approach which significantly improves the governing ITZs by providing a layer of cement slurry on the surface of RCA and allowing to fill up the microcracks and voids as demonstrated in the aforementioned SEM analysis (see Figs. 11a and 13a). The characteristics of untreated RCA reduce the compressive strength of normal concrete [21]. The old cement mortar attached to RCA is the main reason that weakens the properties of SCC. Therefore, an effective pre-treatment of RCA is necessary to improve the properties of SCC. The implemented RCA treatments using HCI solution, water glass and two stage mixing approach contribute to the enhancement in compressive and splitting tensile strength of SCC. Especially, two stage mixing approach significantly improves the physical and mechanical properties of RCA by treating the weak and porous microstructure in the ITZs of produced SCC. Therefore, the variation in compressive and splitting tensile strength developments of SCC is significantly governed by RCA properties after the effective treatments such as the RCA treatments of two stage mixing approach or water glass demonstrated in this paper. The improvement in the properties of RCA using the treatments consequently reflects the improvement in the strength resulting from the stronger contact at the interfacial zone between the cement mortar and treated RCAs. This treatment mechanism in the interfacial bond between cement mortar and RCA is important for SCC incorporating high amount of RCA and governs the strength improvements disregarding to some extent the detrimental effects from the use of low-quality aggregate. Figs. 16 and 17 show the freeze–thaw cycle test results obtained from measuring UPV and mass loss after each 20 cycles, respectively. Fig. 16 indicates the deterioration of specimens by the reduction in UPV results during freeze–thaw cycles. The reduced UPV results at the end of 100 cycles are approximately 1.5%, 1.7%, 2.3%, 2.3% and 1.9% for SCCs produced with untreated RCA,
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E. Güneyisi et al. / Construction and Building Materials 64 (2014) 172–183 Table 5 Fresh properties of the SCCs. Mix description
T500 (s)
Slump-flow (mm)
V-funnel flow time (s)
RCA (control) RCA–HCl RCA–WG RCA–TSM RCA–CSF
3.9 3.81 1.59 2.5 1.65
700 725 720 700 715
23.62 19.31 17 22.73 21
L-box
Viscosity (Rheometer) (Pa s)
H2/H1
T20 (s)
T40 (s)
0.80 0.82 0.85 0.81 0.83
6.45 5.05 4.1 5.78 5.16
20.5 14.25 10.18 18.37 11.9
98.8 86.7 68.3 88.2 85.4
Fig. 14. Compressive strength results of SCCs containing RCAs. Fig. 17. Variation of mass loss during freeze–thaw cycles.
Fig. 15. Splitting tensile strength results of SCCs containing RCAs.
treated RCAs using HCI solution, water glass, two stage mixing approach and cement–silica fume slurry, respectively. The mass loss results during freeze–thaw cycles shown in Fig. 17 indicate approximately 0.2% reduction in mass at the end of 100 cycles for all of the specimens. The comparison of UPV results between SCCs having untreated and treated RCAs indicates that all of the treatment methods except the cement–silica fume slurry treatment produce greater results than that of SCC containing untreated RCA (see Fig. 16). This is attributed to the weaker and porous microstructure of SCCs containing RCAs treated with cement–silica fume slurry as demonstrated in Fig. 11(d). In the case of practicality and cost effectiveness of pretreatments are considered, the two stage mixing approach seems the most practical and cost effective treatment method among the other pre-treatments implemented. Although the pre-soaking treatments need investment to implement in practice, the water glass and HCl pre-soaking treatment approaches can be used as an alternative treatment method or they can be used when it is desired to strengthen the weak links of RCA directly and the remove old cement mortar attached. The overall quality for RCA is greatly improved by pre-treatments and therefore there is possibility that treated RCA can be used in practice as competitive as the normal aggregate in SCC production. 4. Conclusions The following conclusions are drawn from the test results and discussion:
Fig. 16. Variation of ultrasonic pulse velocity during freeze–thaw cycles.
The water absorption properties of RCAs have significantly improved after implementing the presented treatments as compared to untreated RCA. The water absorption capacity increases and specific gravity decreases with a decrease in size of RCAs due to higher amount of adhered mortar on smaller size
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RCAs. Water glass treated RCAs considerably reduce the water absorption providing the minimal value compared to the other treatments applied. The use of HCl concentration at 0.1 molarity has the potential to remove the loose adhered mortar and certain loose substances on RCA surface as demonstrated by the SEM analysis. The properties of RCA such as density and water absorption have improved after HCl treatment as compared to untreated RCA. The SEM analysis has demonstrated that new ITZs in SCCs containing RCAs treated using two stage mixing approach, water glass and HCI solution provide less porous, more dense and connected microstructure compared to untreated RCA owing to the recovery of microcracks and voids in RCAs with new cement mortar from SCCs. Cement–silica fume treatment causes porous microstructure and weaker bond in new ITZ. Especially, two stage mixing approach significantly improves ITZs by providing a layer of cement slurry on the surface of RCAs and allowing to fill up the microcracks and voids. The slump flow diameters of SCCs containing high amount of coarse RCAs implemented with the treatments of HCI solution, water glass and cement–silica fume slurry are higher than that of two stage mixing approach treatment and the control SCC. T500 slump flow time is the shortest for SCCs having water glass treated RCAs compared to other produced SCCs. All of the RCA treatment methods except the cement–silica fume slurry treatment produce the improved compressive and splitting tensile strength results than that of SCC with untreated RCA. The implemented RCA treatments using HCI solution, water glass and two stage mixing approach contribute to the enhancement in compressive and splitting tensile strength results of SCCs. The improvements of compressive strength results on the age of 28 and 90 days compared to that of the corresponding control mix are approximately in the range of 2– 13% for SCCs with RCAs treated using two stage mixing approach, water glass and HCI solution. The highest compressive strength results on the ages of 28 and 90 days are obtained in the range of 60–67 MPa for SCCs containing RCAs treated using two stage mixing approach. The deterioration of specimens is observed by the reduction in UPV results during freeze–thaw cycles. The reduced UPV results at the end of 100 cycles are approximately in the range of 1.5–2.3% for SCCs produced with untreated and treated RCAs.
Acknowledgements This project was supported by Gaziantep University Scientific Research Project Centre (GUBAP), Project no: MF.10.10. The authors gratefully acknowledge Ege Kimya and Harran Beton Limited companies for providing some of the materials used in this project.
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates Erhan Güneyisi a,⇑, Mehmet Gesog˘lu a, Zeynep Algın b, Halit Yazıcı c a
Department of Civil Engineering, Gaziantep University, 27310 Gaziantep, Turkey Department of Civil Engineering, Harran University, 63000 Sßanlıurfa, Turkey c _ Turkey Department of Civil Engineering, Dokuz Eylül University, 35160 Izmir, b
h i g h l i g h t s We studied use of recycled concrete aggregate (RCA) in self-compacting concrete (SCC). Treatment methods were applied on RCA used in SCC. Effect of treatment methods on engineering properties of SCC was investigated. Microstructures of treated RCA and produced SCC were examined. Treatment methods remarkably affect self-compactibility characteristics of concrete.
a r t i c l e
i n f o
Article history: Received 20 February 2014 Received in revised form 4 April 2014 Accepted 9 April 2014
Keywords: Fresh property Microstructure Recycled aggregate Self-compacting concrete Strength Treatment method
a b s t r a c t In this experimental study, the adverse effect of old cement-mortar composite on self-compacting concrete (SCC) containing recycled concrete aggregate (RCA) were investigated by means of potential aggregate treatment methods so as to promote the maximum RCA utilisation. Although the limited researches focus on the direct utilisation of untreated RCA in SCC, the hitherto unavailable results to the properties of SCCs containing treated RCAs are presented in this paper. Four alternative aggregate surface treatment methods introduced to RCAs are two-stage mixing approach, pre-soaking in HCl solution, water glass dispersion and cement–silica fume slurry. 100% coarse RCA replacement with the natural aggregate was used in SCC mixes having constant cement dosage, fly ash replacement and waterto-binder ratio. The slump flow and T500 time, V-funnel time, L-box height ratio, viscosity, compressive and splitting tensile strength, and freeze–thaw cycling tests were carried out to identify the effects of these aggregate treatment methods on the key properties of SCC. Test results reveals that selfcompactibility characteristics of the concretes are remarkably affected by surface treatment of RCAs. Moreover, the treatment methods of two stage mixing approach and water glass provide more dense and connected microstructures in SEM analysis leading to significant strength improvements compared to the control SCC. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Due to the changes in the requirements and planning of concrete structures, excessive amount of construction and demolition (C&D) waste is generated in urban areas worldwide. Annually, 900 million tonnes of C&D waste is estimated in Europe, USA and Japan [1]. The control and management on C&D waste is becoming a worldwide challenge, especially for the major urban centres. Considering the environmental pollution and the consumption of ⇑ Corresponding author. Tel.: +90 342 3172410; fax: +90 342 3601107. E-mail address: [email protected] (E. Güneyisi). http://dx.doi.org/10.1016/j.conbuildmat.2014.04.090 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
limited natural sources it is crucial to reuse and recycle C&D waste. The production of recycle concrete aggregate (RCA) from C&D waste is important issue since it provides an alternative mean to the dependence of construction industry on natural aggregates and the critical shortage problem of natural aggregate sources. This is a common practice for several European countries, USA, Australia, and Japan. For instance, according to 2010 annual reviews, Germany, UK, Netherland, France, and USA produce recycled aggregates approximately 60 Mt, 49 Mt, 20 Mt, 17 Mt, and 140 Mt, respectively [2,3]. RCA is produced by crushing the demolished concrete waste into smaller particles generally using two-stage crushing process.
E. Güneyisi et al. / Construction and Building Materials 64 (2014) 172–183
The targeted aggregate size from the utilised crushing process influences the quality of RCA [4–8]. The properties of RCA mainly differ from its natural counterpart by the remaining hardened cement mortar adhered to the original aggregate surface as shown in Fig. 1. The amount and quality of hardened old cement mortar in the aggregate directly affect the physical properties of RCA [4] because it is characterised as porous [9–13] and presents numerous microcracks [11]. Accordingly, RCA is specified as the type of aggregate having lower density, higher water absorption, and lower mechanical strength than the natural aggregates [9,14–17]. In the case of using RCA in new concrete production, it is generally expected that these characteristics of RCA cause the adverse effect on the interfacial bond between RCA and new cement paste. Subsequently, this may result a reduction in durability, strength and workability of concrete produced with RCA [18]. Generally, the water absorption capacity of RCA affects the workability of new concrete. Additionally, the shape and texture of aggregate depending mainly on the crusher type also affect the workability of concrete [19]. RCA tends to have more water absorption capacity compared to the natural aggregate because of the presence of old cement mortar’s porous microstructure [9,11,18,20–22]. The quality of interfacial transition zone (ITZ) between RCA and new cement mortar that is the connection between these two main components of new concrete poses considerable importance since it governs the mechanical strength properties of concrete [11,23]. Unlike the conventional concrete, new concrete produced with RCA has two ITZs which are new ITZ that is between RCA and new cement mortar and old ITZ that is between RCA and old adherent cement mortar. Accordingly, the structure of concrete produced with RCA demonstrates more complex material behaviour compared to the conventional concrete. Old cement mortar remaining in ITZ composes of microcracks and voids. This microstructure significantly affects the strength of concrete, leads to increase the water consumption and reduces the water required for hydration in ITZ [11]. Since RCA exhibits high water absorption capacity characteristics owing to the old cement mortar’s porous microstructure, RCA in new concrete leads to reduce the effective water content for the hydration process because the adhered mortar in the old ITZ tends to absorb a large amount of water during the initial mixing stage and subsequently creates loose ITZ in the hardened concrete [24,25]. Because of this adverse effect, the high percentage replacement of RCA with natural aggregate reduces the compressive strength of conventional concrete significantly [26– 28]. These drawbacks which are mainly caused by the weak and porous ITZ of old cement mortar adhered on RCA impose limitation on the widespread commercial use of RCA in structural concrete, especially in the production of self-compacting concrete (SCC).
173
One of the promising methods to resolve the adverse effect of RCA to promote and encourage its maximum utilisation in the SCC production is to employ an effective aggregate treatment method. Hence, various techniques tend to enhance the physical properties of RCA by mainly attempting to remove the loose particles of old mortars have been investigated previously for conventional concrete production. The treatments are basically applied on RCA to attain the quality and improve the interfacial bond between RCA and new cement mortar compared to that of natural aggregate. Some of these methods improving the performance of conventional concrete (i.e. ultrasonic bath, thermal and heating methods) require the complicated mechanical equipments and utilises high energy consumption. The other potential treatment techniques that can be applied on RCA are two-stage mixing approach, pre-soaking in HCl solution, water glass dispersion, and cement– silica fume slurry. Unlike the complicated pre-treatment methods mentioned above, these techniques seemingly have potential because they are economical, effective and feasible. However, it is worthy to note that among these techniques two-stage mixing from industrial scale point of view appears to be more practical. In the current literature, to the best of the authors’ knowledge, none of these treatment methods is applied to RCA used in SCC and it has not been reported how these treatment methods affect the fresh and hardened properties of the SCC. The use of RCA in the SCC is a relatively new research area on which a very limited scientific research has been carried out [29–33]. This paper presents the hitherto unavailable results to some properties of the SCCs produced with treated RCAs. It investigates the potential use of high amount of RCA in the SCC production by employing the treatments on RCA. This paper also tends to overcome this short-coming in the current literature by assessing the influenced properties of treated RCA affecting the fresh and hardened states of the SCC at 100% replacement level for the coarse aggregates.
2. Experimental details and methodology 2.1. Materials In this study, the materials used are Type I ordinary Portland cement (OPC), fly ash (FA), fine aggregate, coarse RCA and superplasticizer. OPC (named as CEM I 42.5N) used in this study complies with TS EN 197-1 [34] (Turkish standard which is mainly based on EN 197-1 [35]). FA utilised in this research as cementitious material obtained from Yumurtalik-Sugozu thermal power plant is F type class according to ASTM C 618 [36]. The typical chemical compositions and some physical properties of OPC and FA are tabulated in Table 1. Commercially available polycarboxylic-ether type superplasticizer (SP) having specific gravity of 1.07 is used in this research. Natural river and crushed sands were utilised as fine aggregates with maximum size of 4 mm. The values of specific gravity and water absorption are 2.66% and 0.55% for the natural river sand and are 2.45% and 0.92% for the crushed sand, respectively. Particle size gradations and some physical properties of these aggregates are given in Table 2 and Fig. 2. RCA was used as coarse aggregate with two fractions that are in the range of 4– 8 mm and 8–16 mm in order to have more control over the aggregate combination to obtain the required gradation according with TS 802 [37]. The individual gradation curves of aggregates and the combined aggregate mixture obtained using the certain proportions of fine and coarse aggregates are shown in Fig. 2.
2.2. The production of RCA
Fig. 1. Coarse RCA.
The commercial crusher system which is generally included jaw, impact and cone types of crushers in the production of RCA directly affects the shape and texture of aggregates. Jaw crusher generally produces folieceous aggregate forms, whereas the cone and impact crushers generally provide cubical aggregate forms [38]. Some researchers in the literature demonstrate the advantages of using the two-stage crushing system to produce recycled aggregates [18,39–43]. They compare the properties such as water absorption, Los-Angeles abrasion, density and crushing values of RCA obtained from the jaw crusher with the integrated systems of jaw and impact crushers. It was concluded that the two-stage crushing system was more favourable and the characteristic properties were improved by this method [18].
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Table 1 Chemical composition and physical properties of cement and fly ash. Materials
Composition (%) CaO
SiO2
Al2O3
Fe2O3
MgO
SO3
K2O
Na2O
Cement Fly ash
64.35 4.24
20.08 56.2
4.63 20.17
2.84 6.69
2.07 1.92
2.85 0.49
– 1.89
– 0.58
Loss of ignition
Specific gravity
Blaine fineness (m2/kg)
2.56 1.78
3.18 2.25
318 287
Table 2 Physical properties and sieve analysis results of fine aggregates used. Fine aggregates
River sand Crushed sand
Sieve size (mm) 16 8 4 Percentage passing (%)
2
1
0.5
0.25
100 100
58.7 62.9
38.2 43.7
24.9 33.9
5.4 22.6
99.7 100
94.5 99.2
Fineness modulus
Specific gravity
Absorption (%)
2.79 2.38
2.66 2.45
0.55 0.92
In the implementation of two-stage mixing approach the certain amount of cement and water with fly ash is mixed for 1 min and then the aggregates are added to the mixture, and they are mixed further for 1 min. The remaining materials for the mix are then added and mixed further for another 2 min (see Fig. 4d and e). 2.4. Detail of mixes and preparation
Fig. 2. The gradation curves of aggregates.
Coarse RCAs used in this study were produced from the concrete samples having the dimensions of 150 150 150 mm by using the two-stage crushing system includes the integration of jaw and cone crushers. The strength of concrete samples was chosen as 20 MPa because the current Turkish Earthquake Regulation [44] disallows to use concrete having the strength less than that of C20. The primary crusher (jaw) and secondary crusher (cone) shown in Fig. 3(a and c) were used in the crushing process. In the first stage, as shown in Fig. 3(b) the concrete samples were crushed in the laboratory by the jaw crusher which led to produce folieceous-like aggregate shape using the effect of compression. In the following stage, the obtained aggregates were crushed further by the cone crusher (see Fig. 3d). The cone crusher contains a cone part rotates axially producing impact effects to obtain the required aggregate size and shape. In this stage, the folieceous aggregate shape is converted to the cubical aggregate shape using the effect of squashing and impact crushing. The recycled aggregates were graded in terms of the fractions of 4–8 and 8–16 mm to provide compatibility in the gradation curves provided by TS 802 [37] for natural aggregates (see Fig. 2). 2.3. The treatment methods for RCA In this study, the four potentially useful and practical treatment methods [11,21,45] were applied on the coarse RCA used. They are as follows. The aggregates were submerged in HCI (hydrochloric acid) solution at 0.1 molarity for 24 h at 20 °C. After then, they were submerged in distilled water in order to remove acidic solution (see Fig. 4a). The aggregates were submerged in water glass (Na2OnSiO2 sodium silicate) for 30 min. After then, they were held in suspension for 10 min to provide leakage of excess water glass from the aggregates which were taken out of the solution and then dried in oven for 1 h by preventing bonding the aggregate particles (see Fig. 4b). The aggregates were submerged in cement–silica fume slurry for 30 min, then taken out and spread over the wide sieves for 24 h. They were cured by submerging in water for 28 days (see Fig. 4c).
SCC mixes were produced with the water/binder ratio of 0.38 and the cement dosage of 550 kg/m3. In these mixes, 20% of cement was replaced with fly ash. In all mixes, treated and untreated RCAs were used as coarse aggregate with 100% replacement to the natural coarse aggregate originally designed in the mix. Table 3 shows the detail composition of five different concrete mixtures prepared in this study. The mix description of RCA (control) indicates the control mix, RCA–HCl, RCA–WG, RCA–CSF, and RCA–TSM mixes include RCAs introduced with the aforementioned treatment methods which are pre-soaking in HCl solution, water glass dispersion, cement–silica fume slurry, and two-stage mixing approach, respectively. In the process of preparing the mixes, the dry mix of RCA with cement and fly ash are mixed firstly, and then the natural sand is added. Afterwards, the water with superplasticizer is incorporated gradually to the mixtures and it is mixed for about 3 min and then left for 1 min to rest. Finally, the concretes are mixed for additional 1–2 min to complete the mixing process. The slump flow test, V-funnel test, L-box test, and viscosity tests are carried out to identify the required properties and the characteristics of the fresh SCC mixes. Thereafter, the fresh concrete is placed in the moulds. The test specimens are demoulded 24 h after casting and then water cure is applied until the time of testing. The compressive and splitting tensile strength tests at 28 and 90 days of curing are performed to establish the hardened properties of SCCs produced. Additionally, the deterioration of hardened SCCs during freeze–thaw cycles were assessed on the specimens from each SCC mixes. 2.5. Testing 2.5.1. The specific gravity and water absorption values of RCAs The specific gravity and water absorption values of treated and untreated coarse RCAs were determined with respect to the ASTM C127 [46]. The tests were conducted on particles of various sizes ranging from 4–8 mm to 8–16 mm. The water absorption was carried out by keeping a known quantity of dry aggregate in a pycnometer filled with water at room temperature for a certain period of time. The weight increase of aggregate was measured at 10, 30, 60, and 120 min, 24 h, 7 days and 15 days after submersion in water. 2.5.2. Examination of microstructure of treated RCAs and the produced SCCs The microstructure studies were conducted using a scanning electron microscope (SEM) on the microstructure surface of untreated and treated coarse RCAs as well as the samples from the produced SCC mixes. 2.5.3. Testing of the produced SCCs The testing programs were designed to determine how the considered aggregate treatment methods affect the properties of SCCs containing the high replacement level of RCAs, which determine flowability, filling ability, passing ability, viscosity, and strength results. The conducted tests on the fresh properties such as slump-flow, T500, V-funnel and L-box were complied with EFNARC [47]. Viscosity of the produced fresh SCC was measured by Rheometer testing device based on the Bingham model (see Fig. 5). The Bingham model that is represented by the following two-parameter relationship s ¼ s0 þ lc_ can be used to model the
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Fig. 3. The two-stage crushing system and the crushed concretes. (a) The primary crusher (jaw), (b) the crushed concretes obtained from the jaw crusher, (c) the secondary crusher (cone), and (d) the crushed concretes obtained from the cone crusher.
flow behaviour of concrete. s0 represents the yield stress indicating the shear stress required to initiate the flow. After the yield stress has been exceeded plastic viscosity denoted as l affects the resistance to flow. The flow curve that is defined by these two parameters represent the flow behaviour of concrete mixture [48]. The test setting consists of a 20 s pre-shear period at a constant speed of 0.50 rps followed by 8 flow curve points in descending order from 0.50 to 0.05 rps. The compressive strength measurement was applied on the cubical SCC samples of 150 150 mm complying with ASTM C 39 [49]. The test is conducted on three cube samples from each concrete mix at 28 and 90 days of curing. The compressive strength was computed by averaging the results from the three tested samples at each testing age. Splitting tensile strength of the concrete was measured on the cylindrical samples of 150 300 mm at 28 and 90 days of curing as it is recommended by ASTM C 496 [50]. The splitting tensile strength is obtained by averaging the results from the three tested cylindrical samples. SCC prisms having the size of 100 100 300 mm were prepared for the freeze–thaw cycling tests in accordance with ASTM C666 Procedure A [51]. 90 days cured specimens were moved into the freeze–thaw chamber and the programmable automated temperature controlled climatization device specifically designed for the freeze–thaw cycling test was used. After each 20 cycles the specimens were taken out of the device to measure the mass loss and the ultrasonic pulse velocity (UPV) variations at 3 points of the long side of each specimen. Three prisms from each SCC were tested repeatedly and the average value was used for each data presented.
3. Experimental results and discussion 3.1. Water absorption and specific gravity results The water absorption results of RCAs varying with time for the fractions of 4–8 mm and 8–16 mm are given in Figs. 6 and 7, respectively. Untreated (normal) RCA notated as RCA and treated RCAs are notated as RCA–CFS, RCA–HCI, and RCA–WG indicating
RCAs treated with cement–silica fume slurry, HCl solution and water glass, respectively. Since the treatment method of two stage mixing approach is a process based implementation and is conducted during the preparation of SCC, it is not included in Figs. 6 and 7. It is demonstrated that the water absorption capacity of recycled aggregates is increased with time for all aggregate types (see Figs. 6 and 7). It is clearly shown that the water glass treatment is the most effective enhancement method among others for the reduction of water absorption and drops the results approximately 67–77%, whereas HCI and cement–silica fume slurry treatments reduce the water absorption capacity about 20–11% and 6–4% for the fractions of 4–8 and 8–16 mm, respectively. As demonstrated in the microstructure images from SEM analysis in this paper, the pre-soaking treatment of water glass creates a aggregate surface with outer stronger coating which leads to decrease the water absorption of RCA to the value of 2%. This conclusion agrees with some researches [45,52] studied on lightweight aggregate in which it is stated that the water glass coatings substantially decrease the water absorption (i.e. reduces from 27% to 3%) and increase the wearing resistance by creating a smooth, dense and hard coating on aggregate surface. As previously demonstrated [21,24] that the pre-soaking treatment of HCl solution removes a great portion of weak cement mortar and certain loose substances attached on RCA surface and subsequently enhances the physical properties of RCA. The presence of residual old cement mortar obstructs the bond between RCA and new cement paste in SCC. The removal of loose particles from the surface of RCA leads stronger contact at the interfacial
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Fig. 4. (a) RCA treated with HCl solution, (b) RCA treated with water glass dispersion, (c) RCA treated with cement–silica fume slurry, (d) the first stage of two-stage mixing approach, and (e) the second stage of two-stage mixing approach.
Table 3 The proportions of concrete mixes (kg/m3). Mix description
RCA (control) RCA–HCl RCA–WG RCA–TSM RCA–CSF a
w/b
0.38 0.38 0.38 0.38 0.38
Cement
440 440 440 440 440
Fly ash
110 110 110 110 110
Water
209 209 209 209 209
SPa
9.35 9.35 7.7 9.35 9.35
Fine aggregate
Coarse RCA
River sand
Crushed sand
8–16 mm
4–8 mm
523.4 523.4 524.8 523.4 523.4
224.6 224.6 225.2 224.6 224.6
493.5 495.9 476.4 493.5 444.7
211.5 212.8 204.5 211.5 190.8
Superplasticizer.
zone between treated RCA and new cement paste in SCC. Since the interfacial bond between cement paste and aggregate is known to be critical in concrete structures and is a significant factor governing concrete strength development [24,53], the enhancement in the interfacial zone consequently reflects the improvement in concrete strength of SCC with treated RCA. This treatment decreases the water absorption of RCA with a reduction of 11–20%. This conclusion agrees with some researches [21,24] stating that the HCl treatment substantially decreases the water absorption between 1% and 28% and improves the compressive strength of normal concrete.
While the water absorption results of RCA treated with cement–silica fume slurry is a little lower than normal RCA, it is higher than that of the other surface treatment methods. Table 4 shows the results of water absorption in 24 h and the specific gravity results for untreated and treated RCAs. As shown in Figs. 6 and 7, and Table 4 that the water absorption values of treated RCAs are remarkably lower than that of normal RCA. As can be seen in Table 4 that the water absorption values of RCAs having the size of 4–8 mm and 8–16 mm in 24 h are 8.72% and 7.66%, respectively and the corresponding specific gravity results are 2.43 and 2.45. Accordingly, this shows that the water absorption values of RCAs
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E. Güneyisi et al. / Construction and Building Materials 64 (2014) 172–183 Table 4 The results of specific gravity and water absorption of the RCAs. Coarse aggregate
RCA RCA–HCl RCA–WG RCA–CFS
Specific gravity Fractions (mm)
Water absorption % (24 h)
4–8
8–16
4–8
8–16
2.43 2.45 2.34 2.20
2.45 2.46 2.36 2.21
8.72 6.99 2.85 8.24
7.66 6.84 1.77 7.35
this range. Therefore, it can be stated that the water absorption capacity increases and specific gravity decreases with a decrease in size of RCA. This is because the smaller size RCAs are having higher amount of adhered mortar and, accordingly, the absorption capacity of RCA is increased while the specific gravity is decreased with the amount of adhered mortar present. The previous studies [21,54] state that the pores structure of existing old cement mortar increases the porosity of RCA. This pores microstructure is also demonstrated in this paper using SEM image analysis. The obtained water absorption values of RCA indicate that the increase in porosity subsequently results an increase in water absorption values of RCA particles.
Fig. 5. Viscosity measurement by Rheometer.
Fig. 6. The water absorption results of RCAs having the fraction of 4–8 mm.
Fig. 7. The water absorption results of RCAs having the fraction of 8–16 mm.
having the size of 4–8 mm are higher than that of RCAs having the size of 8–16 mm, whereas the specific gravity results are lower for
3.2. Microstructures of RCAs and produced SCCs The differences between microstructures of untreated and treated RCAs, and produced SCCs were studied using the scanning electron microscope (SEM) images indicated in Figs. 8–13. Fig. 8(a–c) shows untreated RCA with old ITZ, the detailed view of untreated RCA with loose cement mortar, treated RCA with HCl solution, respectively. It is demonstrated that the surface of untreated RCA is considerably more porous containing certain amount of loose cement mortar and other small impurities, such as dust, which are loosely connected to their bulk aggregate particles. The comparison between Fig. 8(a–c) indicates that HCl solution treatment at 0.1 molarity significantly reduces the loose particles on RCA surface and, subsequently, makes the aggregate surface more cleaner and uniform. However, the increase in HCl molarities would possibly erode the surface more and cause more weaker and porous surface than the original RCA aggregate particles [24]. Therefore, as shown in Fig. 8(c) 0.1 HCl molarity produce sufficient results without the concerns of remaining acid solution within treated RCAs. Fig. 9(a and b) indicates treated RCAs having cement–silica fume and water glass coatings, respectively. Fig. 9(a and b) demonstrates that the treatments of water glass and cement–silica fume slurry produce the coatings allowing to cover RCAs containing voids. Fig. 10 shows control SCC with new ITZ. The comparison between Figs. 10 and 8(a and b) demonstrate that new ITZ is less porous compared to old ITZ owing to the recovery of microcracks and voids in RCA with new cement mortar from SCC. Fig. 11(a–d) indicates SCCs produced from treated RCAs implemented with two stage mixing approach, HCl solution, water glass, and cement–silica fume slurry, respectively. The improvement in the microstructure with more overlapping and intense ITZ is observed in Fig. 11(a–d) due to the implemented treatments on RCAs compared to control SCC shown in Fig. 10. The treatment methods of two stage mixing approach (see Fig. 11a) and HCl solution (see Fig. 11b) allow further penetration of new cement mortar from SCC into treated RCA. This penetration process subsequently results more dense and connected views especially in new ITZs (see Fig. 11a and b) compared to control SCC (see Fig. 10). The treatments of water glass and cement–silica fume produce a sort of protection coatings on RCAs by recovering the inner microcracks and voids (see Fig. 11c and d).
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Fig. 9. Surface microstructure views of treated RCAs having cement–silica fume and water glass coatings.
Fig. 8. Surface microstructure views of RCAs: (a) untreated RCA with old ITZ, (b) untreated RCA with loose cement mortar, and (c) treated RCA with HCl solution.
Fig. 12 indicates the cement mortar in control SCC. Since the water absorption characteristic of RCA differs in terms of the implemented treatment methods the new cement mortars among RCAs are accordingly affected and provided varying voids and loose mortar compositions. Due to the high water absorption characteristic of untreated RCA more voids and loosely connected mortars are observed in new cement mortar because RCA and the adhered old cement mortar consume some of the water present (see Fig. 12). Fig. 13(a–d) shows the cement mortars in SCCs produced from treated RCAs using two stage mixing approach, HCl solution, water glass and cement–silica fume slurry, respectively. The treatment process causes a decrease in water absorption and provides more dense and connected cement mortar compositions as demonstrated in Fig. 13(a–d). Considering the amount of voids and loose cement mortars, the treatment methods of two stage mixing approach and water glass are provided more dense and connected
Fig. 10. Surface microstructure view of control SCC with new ITZ.
mortar compositions compared to new cement mortar in control SCC (see Figs. 12 and 13a and c). Microstructure images from SEM analysis show that the interfacial zone between new cement paste and treated RCA exhibits less pores characteristics which are significantly different compared to those of SCC with untreated RCA. This demonstrates that the quality of interfacial zone depends on the surface characteristics of RCA particles and the implemented pre-treatments. Especially, two stage mixing approach, water glass and HCl treatments can significantly enhance the pores and weak characteristics of interfacial zone between RCA and new cement mortar of SCC. This enhancement improves the fresh properties of SCC and increases the paste–aggregate bond strength resulting a subsequent increase in the strength of SCC.
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Fig. 12. Surface microstructure view of cement mortar in control SCC.
Fig. 11. Surface microstructure views of SCCs produced from treated RCAs using (a) two stage mixing approach, (b) HCl solution, (c) water glass, and (d) cement–silica fume slurry.
3.3. Properties of SCCs with untreated and treated RCAs In order to specify the flowability, viscosity, and passing ability of the produced SCCs, slump flow diameter, T500 slump flow time,
V-funnel flow time, L-box height ratio, and viscosity were measured and the results are shown Table 5. The obtained results were compared with the SCC characteristic target values identified by class names provided by EFNARC [46]. As can be seen in Table 5 that the slump flow diameters of SCCs having coarse RCAs implemented with the pre-soaking treatment methods (i.e. HCI solution, water glass, and cement–silica fume slurry) are higher than the results from other SCC mixes. Table 5 shows that all of the slump flow diameters are in the range of 700–725 mm, these mixtures are classified as SF2 according to EFNARC [46]. Although the dosage of superplasticizer for SCC implemented with treated RCA using water glass was decreased in order to satisfy the EFNARC limitation [46], the high slump flow compared to control SCC is attributed to the weaker cohesion between the cement mortar and water glass treated RCAs due to the smooth and comparably impermeable surface of treated RCA. Table 5 shows that T500 slump flow time values for all of the produced SCC mixes are less than 4 s and SCC containing water glass treated RCA is the shortest compared to other mixes. Since the water absorption capacity is reduced for treated RCAs, more free water become present between the aggregate particles in SCC mixes resulting a reduction in the slump flow time (see Tables 4 and 5). All of the produced SCC mixes are having L-box height ratios in the range of 0.80–0.85 which satisfies the EFNARC limitation [46]. During the measurement of viscosity by Rheometer, approximately the yield stresses were obtained as 0.1 Pa for all produced mixes indicating the self-flow behaviour as the minimum stress to initiate flow. The viscosity results in Table 5 indicate that the viscosity is reduced for treated RCAs because the lower cohesion forces deriving from lower water absorption capacity generally cause lower flow viscosity. Similarly, V-funnel flow time results in Table 5 indicate that V-funnel flow time is reduced for treated RCAs. The compressive strength results of SCCs incorporating treated and untreated RCAs are determined at 28 and 90 days of curing, and presented in Fig. 14. It shows that due to the increased amount of hydration products produced on the prolonged curing age the compressive strength values on the age of 90 days are higher than the results obtained on the age of 28 days. These improvements are approximately in the range of 10–15% for SCCs produced with untreated RCA and treated RCAs. The comparison of compressive strength results between SCCs having untreated and treated RCAs indicates that all of the treatment methods except the cement– silica fume slurry treatment produce greater results than that of SCC containing untreated RCA. This lack of improvement in compressive strength from SCC containing cement–silica fume treatment is due to the weaker characteristics of new ITZ. The improvement of compressive strength on the age of 28 days
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Fig. 13. Surface microstructure views of the cement mortars in SCCs produced with treated RCAs using (a) two stage mixing approach, (b) HCl solution, (c) water glass, and (d) cement–silica fume slurry.
compared to that of the corresponding control mix is 4% for SCC with RCA treated using HCI solution and this improvement at 90 days of curing is 2%. The use of water glass treated RCAs causes an increase in compressive strength about 9% and 7% at 28 and 90 days of curing, respectively. The highest compressive strength
results on the ages of 28 and 90 days are obtained as 60 MPa and 67 MPa for SCCs containing RCAs treated with two stage mixing approach, corresponding 13% and 10% improvements compared to that of SCC with untreated RCA, respectively. These improvements in SCCs with RCAs treated using two stage mixing approach is owing to the achievement of forming a layer of cement slurry on the surface of RCA and leading to fill up the cracks and voids, and it subsequently improves ITZs at the pre-mix stage. This improvement in ITZs results an enhancement in compressive strength as demonstrated by previous research [11] on normal concrete. As shown in Figs. 11(a) and 13(a), the enhancement characteristics of two stage mixing approach provide more dense and connected microstructure compared to that of corresponding control mix. Fig. 15 shows the results from the splitting tensile strength tests on SCCs containing treated and untreated RCAs at 28 and 90 days of curing. As demonstrated for the compressive strength results in Fig. 14, the similar trend that is greater values for the age of 90 days is observed in Fig. 15 for this test compared to the results at 28 days of curing resulting from the increased amount of hydration products produced on the prolonged curing age. These strength improvements are approximately in the range of 13–21% for SCCs incorporating untreated RCA and treated RCAs. Apart from the cement–silica fume slurry treatment which produces lower splitting tensile strength compared to that of corresponding control SCC because of the its weaker bond new ITZ, all of the RCA treatment methods produce greater results than that of SCC with untreated RCA. Comparing with the corresponding control SCCs, the improvements in splitting tensile strength at 28 days of curing are 4%, 9% and 10% for SCCs containing treated RCAs with HCI solution, water glass and two stage mixing approach. These results on the age of 90 days are 3%, 4% and 6% respectively. The highest splitting tensile strength results at 28 and 90 days of curing are respectively 3.2 MPa and 3.7 MPa corresponding 10% and 6% improvements for SCCs containing RCAs treated with two stage mixing approach which significantly improves the governing ITZs by providing a layer of cement slurry on the surface of RCA and allowing to fill up the microcracks and voids as demonstrated in the aforementioned SEM analysis (see Figs. 11a and 13a). The characteristics of untreated RCA reduce the compressive strength of normal concrete [21]. The old cement mortar attached to RCA is the main reason that weakens the properties of SCC. Therefore, an effective pre-treatment of RCA is necessary to improve the properties of SCC. The implemented RCA treatments using HCI solution, water glass and two stage mixing approach contribute to the enhancement in compressive and splitting tensile strength of SCC. Especially, two stage mixing approach significantly improves the physical and mechanical properties of RCA by treating the weak and porous microstructure in the ITZs of produced SCC. Therefore, the variation in compressive and splitting tensile strength developments of SCC is significantly governed by RCA properties after the effective treatments such as the RCA treatments of two stage mixing approach or water glass demonstrated in this paper. The improvement in the properties of RCA using the treatments consequently reflects the improvement in the strength resulting from the stronger contact at the interfacial zone between the cement mortar and treated RCAs. This treatment mechanism in the interfacial bond between cement mortar and RCA is important for SCC incorporating high amount of RCA and governs the strength improvements disregarding to some extent the detrimental effects from the use of low-quality aggregate. Figs. 16 and 17 show the freeze–thaw cycle test results obtained from measuring UPV and mass loss after each 20 cycles, respectively. Fig. 16 indicates the deterioration of specimens by the reduction in UPV results during freeze–thaw cycles. The reduced UPV results at the end of 100 cycles are approximately 1.5%, 1.7%, 2.3%, 2.3% and 1.9% for SCCs produced with untreated RCA,
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T500 (s)
Slump-flow (mm)
V-funnel flow time (s)
RCA (control) RCA–HCl RCA–WG RCA–TSM RCA–CSF
3.9 3.81 1.59 2.5 1.65
700 725 720 700 715
23.62 19.31 17 22.73 21
L-box
Viscosity (Rheometer) (Pa s)
H2/H1
T20 (s)
T40 (s)
0.80 0.82 0.85 0.81 0.83
6.45 5.05 4.1 5.78 5.16
20.5 14.25 10.18 18.37 11.9
98.8 86.7 68.3 88.2 85.4
Fig. 14. Compressive strength results of SCCs containing RCAs. Fig. 17. Variation of mass loss during freeze–thaw cycles.
Fig. 15. Splitting tensile strength results of SCCs containing RCAs.
treated RCAs using HCI solution, water glass, two stage mixing approach and cement–silica fume slurry, respectively. The mass loss results during freeze–thaw cycles shown in Fig. 17 indicate approximately 0.2% reduction in mass at the end of 100 cycles for all of the specimens. The comparison of UPV results between SCCs having untreated and treated RCAs indicates that all of the treatment methods except the cement–silica fume slurry treatment produce greater results than that of SCC containing untreated RCA (see Fig. 16). This is attributed to the weaker and porous microstructure of SCCs containing RCAs treated with cement–silica fume slurry as demonstrated in Fig. 11(d). In the case of practicality and cost effectiveness of pretreatments are considered, the two stage mixing approach seems the most practical and cost effective treatment method among the other pre-treatments implemented. Although the pre-soaking treatments need investment to implement in practice, the water glass and HCl pre-soaking treatment approaches can be used as an alternative treatment method or they can be used when it is desired to strengthen the weak links of RCA directly and the remove old cement mortar attached. The overall quality for RCA is greatly improved by pre-treatments and therefore there is possibility that treated RCA can be used in practice as competitive as the normal aggregate in SCC production. 4. Conclusions The following conclusions are drawn from the test results and discussion:
Fig. 16. Variation of ultrasonic pulse velocity during freeze–thaw cycles.
The water absorption properties of RCAs have significantly improved after implementing the presented treatments as compared to untreated RCA. The water absorption capacity increases and specific gravity decreases with a decrease in size of RCAs due to higher amount of adhered mortar on smaller size
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RCAs. Water glass treated RCAs considerably reduce the water absorption providing the minimal value compared to the other treatments applied. The use of HCl concentration at 0.1 molarity has the potential to remove the loose adhered mortar and certain loose substances on RCA surface as demonstrated by the SEM analysis. The properties of RCA such as density and water absorption have improved after HCl treatment as compared to untreated RCA. The SEM analysis has demonstrated that new ITZs in SCCs containing RCAs treated using two stage mixing approach, water glass and HCI solution provide less porous, more dense and connected microstructure compared to untreated RCA owing to the recovery of microcracks and voids in RCAs with new cement mortar from SCCs. Cement–silica fume treatment causes porous microstructure and weaker bond in new ITZ. Especially, two stage mixing approach significantly improves ITZs by providing a layer of cement slurry on the surface of RCAs and allowing to fill up the microcracks and voids. The slump flow diameters of SCCs containing high amount of coarse RCAs implemented with the treatments of HCI solution, water glass and cement–silica fume slurry are higher than that of two stage mixing approach treatment and the control SCC. T500 slump flow time is the shortest for SCCs having water glass treated RCAs compared to other produced SCCs. All of the RCA treatment methods except the cement–silica fume slurry treatment produce the improved compressive and splitting tensile strength results than that of SCC with untreated RCA. The implemented RCA treatments using HCI solution, water glass and two stage mixing approach contribute to the enhancement in compressive and splitting tensile strength results of SCCs. The improvements of compressive strength results on the age of 28 and 90 days compared to that of the corresponding control mix are approximately in the range of 2– 13% for SCCs with RCAs treated using two stage mixing approach, water glass and HCI solution. The highest compressive strength results on the ages of 28 and 90 days are obtained in the range of 60–67 MPa for SCCs containing RCAs treated using two stage mixing approach. The deterioration of specimens is observed by the reduction in UPV results during freeze–thaw cycles. The reduced UPV results at the end of 100 cycles are approximately in the range of 1.5–2.3% for SCCs produced with untreated and treated RCAs.
Acknowledgements This project was supported by Gaziantep University Scientific Research Project Centre (GUBAP), Project no: MF.10.10. The authors gratefully acknowledge Ege Kimya and Harran Beton Limited companies for providing some of the materials used in this project.
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