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Effect of using metakaolin as supplementary cementitious material and recycled CRT funnel glass as fine aggregate on the durability of green self-compacting concrete
Construction and Building Materials 235 (2020) 117802
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Effect of using metakaolin as supplementary cementitious material and recycled CRT funnel glass as fine aggregate on the durability of green self-compacting concrete Younes Ouldkhaoua a, Benchaa Benabed a,⇑, Rajab Abousnina b, El-Hadj Kadri c, Jamal Khatib d,e a
Civil Engineering Laboratory, University of Laghouat, 03000, Algeria Centre for Future Materials, School of Civil Engineering and Surveying, University of Southern Queensland, Toowoomba, Queensland 4350, Australia L2MGC Laboratory, University of Cergy-Pontoise, 95000, France d Faculty of Engineering, Beirut Arab University, Beirut, Lebanon e Faculty of Science and Engineering, University of Wolverhampton, Wolverhampton, UK b c
h i g h l i g h t s CRTG was used as fine aggregate and MK as partial cement replacement to produce a durable green SCC. Durability performance of green SCC has been evaluated. CRTG improves the fresh properties, strength and porosity of SCC incorporating MK. The use of MK and CRTG in SCC mixtures enhances the chloride-ions and gas permeability. The addition of MK also reduces the ASR expansion of SCC made with CRTG.
a r t i c l e
i n f o
Article history: Received 22 March 2019 Received in revised form 23 November 2019 Accepted 4 December 2019
Keywords: Cathode ray tube glass Metakaolin Green self-compacting concrete Strength Durability
a b s t r a c t This present work is a study of the durability of green self-compacting concrete (SCC) that incorporates recycled cathode ray tube glass (CRTG) and metakaolin (MK). In these SCC mixtures natural sand has been replaced with CRTG at levels of 0, 10, 20, 30, 40 and 50% by weight, and the cement has been partially replaced by MK at substitution ratios of 5, 10, and 15% by weight. The fresh properties of SCC mixtures were then evaluated by slump flow, V-funnel, L-Box tests and their resistance to segregation was measured by the sieve stability test. The strength and durability properties of hardened SCC mixtures was assessed according to the compressive strength, ultrasonic pulse velocity (UPV), porosity, ions chloride permeability, gas permeability, and Alkali-silica reaction (ASR) tests. A SEM analysis was also carried out to examine the developing microstructure of hardened SCC mixtures. This study revealed an improvement in the fresh properties of SCC mixtures with up to 50% CRTG replacement. At the hardened state, the compressive strength and UPV of the SCC mixtures (10MK + 50CRTG) improved by 16% and 3% respectively after 90 days of ageing compared to SCC control mixtures. Moreover, using MK in SCC mixtures with different amounts of CRTG resulted in the best durability, while 10% of MK enhanced the porosity, permeability of chloride and gas permeability in SCC. Results show also that, 10% and 15% of MK can be prescribed in 0.1% limit of ASR in SCC mixtures with CRTG. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Concrete industry achieved a milestone after the emergence of self-compacting concrete (SCC) [1]. SCC has proven several advantages and promised material in construction industry techniques such as pumpability, easy and speed of implementation [2]. The ⇑ Corresponding author. E-mail address: [email protected] (B. Benabed). https://doi.org/10.1016/j.conbuildmat.2019.117802 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
particularity of SCC appears in their fresh state properties, and it must be characterized by high workability and deformability while remaining stable [3], these properties contribute to ensure durable and resistant constructions [4]. To achieve these requirements, an SCC mix needs large amounts of Portland cement and superplasticizers (SP) [5], but high volumes of Portland cement increase the volume of cement consumed, lead to high heat of hydration that is associated with concrete cracking, have environmental impacts
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due to CO2 emissions, consume energy and natural resources and result in high production costs [6]. The world is facing many serious environmental challenges due to pollution and growing consumption, as well as an increase in solid wastes. Furthermore, the depletion of natural resources and the detrimental effect of CO2 emissions increase the environmental pressure to adopt environmentally friendly techniques for recycling and using these wastes in order to preserve more natural resources and reduce CO2 emissions [7]. The mineral additions have been used as supplementary cementitious materials (SCM) to reduce the high amounts of cement in SCC mixture, with positive effects on the performance of concrete, compaction, environmental and economic aspects [8]. The pozzolanic reaction due to the mineral additions takes effect during cement hydration improves the durability of concrete. The most commonly used SCM are silica fume (SF), fly ash, ground granulated blast furnace slag (GGBS), metakaolin (MK), and rice husk ash (RHA), etc. [9]. MK is a pozzolanic material that can be added as a cementitious material in concrete mixtures. Many investigators showed that MK improves the performance of concrete but it can have a negative effect on its rheological properties [10,11]. Sfikas et al. [12] studied the effect of MK on the composition of SCC, the results showed a reduction in the workability by inclusion of MK and a higher superplasticizers requirement in order to acquire a similar rheological behavior, but it increased the mechanical strength. Ghoddousi et al. [13] reported that the rheological properties of SCC mixes with partial replacement of MK reached a higher yield stress than with other mineral admixtures. Siddique et al. [14] researched the effect of MK as cement replacement in concrete; cement was partially replaced with MK at levels of 0%, 5%, 10%, and 15% by weight. The results showed at 15% MK replacement, compressive strength decreased and 10% MK content presented the optimum replacement level. Furthermore, several studies have shown that MK is the most effective material for reducing the negative effect of ASR. Lee et al. [15] studied the effect of pozzolanic materials on ASR of concrete blocks. The results indicated a decrease in the ASR expansion with an increase in MK content. Khatib al. [16] observed that early age concrete shrinkage can be reduced with MK replacement, while Singh, Mithulraj and Arya [17] concluded that concrete with MK has a lower depth of carbonation than those that control SCC. Cathode ray tube funnel glass (CRTG) was used for earlier generations for television and computer monitors [18]. This waste can pose serious environmental and health problems due to the toxicity of the lead content in the chemical composition of glass [19]. It is important to recycle these waste materials and be disposed to mitigate any harmful consequences [20]. Many researchers claim that the recycled CRTG can be used as substitution for natural sand in mortar and concrete, and it will also improve the fluidity and overcome the drawbacks of the mechanical properties as well as the performance of concrete. Poon et al. [21] treated this glass by immersing it in a bath of 5% nitric acid (HNO3) solution for 3 h, which will satisfied the limits of the toxicity characteristic leaching procedure (TCLP) test [22]. Hui and Sun [23] studied the use of CRTG on the workability of mortar and found that its slump diameter increased as the glass levels of CRT increased. Zhao et al. [24] investigated the effects of CRTG on alkali-silica reaction (ASR) on high-density concrete. They concluded that the increasing in CRTG content increased the ASR expansion of concrete. Saccani et al. [25] also reported an increase in glass proportions as fine aggregate resulted an increase in ASR expansion of concrete. The drying shrinkage may induce cracks which could result in debonding and reduce the durability of the concrete as reported by Mauroux et al. [26]. Ling and Poon [27] found a reduction in the drying shrinkage of concrete containing 100% CRT glass as a fine aggregate. Ling and Poon [28] studied the possible use of recycled CRT
funnel glass as heavyweight fine aggregate in barite concrete and found that its resistance to carbonation gradually decreased with an increasing use of CRT glass. In the other hand, Metalssi et al. [29] indicated in their study that the Carbonation improved the mechanical strengths and decrease the global porosity with modifying the pore size distribution. However, carbonation increases the shrinkage, and thus to a probable increase of cracking. From an ecological and economic perspective, the present research into the recycling and reuse of waste, particularly as aggregates and cement, will reduce the extraction of aggregates and CO2 emissions while prolonging the life of the landfills they are currently helping to saturate. This present work will study the rheological, mechanical and durability properties of the green self-compacting concrete that incorporates recycled CRT funnel glass (CRTG) as a partial substitution for fine aggregate and metakaolin (MK) as a partial replacement for cement. 2. Experimental program 2.1. Materials, mixture proportions and mixing procedure An ordinary Portland cement (CEMI 42.5) conforms to EN 197-1:2000 [30] was used in all SCC mixtures. MK used as a partial cement replacement was obtained from kaolin calcination at 850 °C for 3 h [31]. The XRD analysis of MK is shown in Fig. 1. The percentage of MK in the blended cement was 5, 10 and 15% by weight. The chemical and physical properties of both cement and MK are presented in Table 1. As chemical admixture, a superplasticiser polycarboxylic ether type (SP) was used with density of 1.07 and solid content of 30%. River sand with a maximum size of 5 mm was used as natural fine aggregate. Waste CRTG was used to replace river sand as fine aggregate of 0, 10, 20, 30, 40 and 50% by weight. In order to treat CRTG and remove the lead oxide; CRTG was treated with 5% of nitric acid solution (HNO3) for 3 h [21]. The result of TCLP test [21] of treated CRTG is given in Table 2. The particle size distribution of river sand and CRTG is presented in Fig. 2. Two classes of limestone gravel G 3/8 and G 8/15 were used for the coarse aggregate in proportions of 40% and 60% in SCC mixtures respectively. The physical properties of fine and coarse aggregates are given in Table 2. Nineteen mixtures were prepared to assess the effect of both MK and CRTG on the rheological, mechanical and durability properties of SCC. In order to determine the quantity required for each ingredients of concrete, the general method developed by Okamura and Ouchi [32] was used for this purpose, with some modifications regarding the quantity of sand in the mortar (sand/mortar ratio (S/M) was fixed at 0.5), the water/binder ratio (W/B = 0.4) and the dosage of superplasticizers (SP). The mixture proportions of the SCC mixes are given in Table 3. The mixing procedure for making SCC mixtures takes three steps. Firstly, the powder (cement, MK) and aggregates were mixed together for half minute, and then 70% of the mixing water was added and mixed for 1 min. The remaining 30% of water containing the superplasticizer was added and mixed for 1 min. This procedure continued for another 5 min and then stopped for 2 min. Finally, the SCC was mixed again for 30 s to ensure the homogeneity of SCC mixtures before discharging [33]. 2.2. Testing Several experiments were conducted following EFNARC [34] guidelines for selfcompacting concrete to assess the fresh properties of SCC. The filling, the passage ability and the resistance to segregation were determined by:
The The The The
slump flow diameter (EN 12350-8) [35]; V-funnel flow time (EN 12350-9) [36]; L-box height ration (EN 12350-10) [37]; sieve stability (EN 12350-11) [38].
The compressive strength was measured at 7, 28 and 90 days of curing, according to European Standard EN 196-1 [39]. All SCC specimens are subjected to ultrasonic pulse velocity (UPV) test, this test was performed in accordance with standard ASTM C597-16 [40]. It is a non-destructive test that, gives an idea of the homogeneity and porosity of the specimens. It consists in putting the two probes (transmitter and receiver) of ultrasound between the two ends of the prismatic specimens in order to measure the ultrasonic pulse velocity (UPV) using the following equation:
UPV ¼
L T
L : Distance between the two transducers in (m). T : Wave propagation time in (s).
ð1Þ
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Fig. 1. X-ray diffraction analysis of MK.
Table 1 Chemical composition and physical properties of cement and MK. Chemical composition (%)
Cement
MK
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O TiO2 Loss on ignition
20.83 4.13 5.58 62.19 1.42 2.30 0.38 0.028 2.04
50.30 41.81 1.5 0.08 0.4 0.81 0.09 0.024 5.77
Physical properties Specific gravity (kg/m3) Blaine fineness (m2/kg)
3120 330
2450 700
For the resistance of SCC to chloride-ions penetration, in accordance with ASTM C 1202 [43], the test was performed on a concrete disc (ɸ200 mm and h 50 mm) by calculating the amount of charge passed (Eq. (3)) into SCC specimens placed in cell subjected to 60 V for 6 h. Where one of the cell electrodes is immersed in a 3% sodium chloride solution (NaCl), and the other one in 0.3% sodium hydroxide solution (NaOH.)
Q ¼ 900ðI0 þ 2I30 þ2I60 þ þ 2I300 þ 2I330 þ I360 Þ
In terms of a porosity accessible to water test, three 100 50 mm discs cut from the 100 mm diameter by 200 mm high cylindrical specimens were used to evaluate their porosity in water up to 90 days, according to the NF P18-459 standard [41]. Gas permeability is one of the means that is generally used to characterize the porosity of concrete. The Nitrogen gas permeability test was performed using the CEMBUREAU method according to NF XP P18-463 [42]. The specimens used to achieve the gas permeability were cylindrical with a diameter of 150 and a height of 50 mm, then protected and confined laterally, which ensures unidirectional transfer of the gas. The apparent gas permeability Kapp was measured by applying relative pressures of gradient 1 bar and computed according to the following equation:
K app ¼
L : Thickness of the specimen in (m). A : Cross-sectional area of the specimen in (m2). Q : Gas flow in (m3 s1). l: Dynamic viscosity coefficient of nitrogen gas (17.5 106 Pa s). P i : Inlet pressure (Pa). P 0 : Atmospheric pressure (Pa).
2:Pi :Q :L:l
ð2Þ
AðP2i P20 Þ
ð3Þ
According to the standard ASTM C 1260 (2007) [44], an accelerated alkali-silica reaction (ASR) test was performed. Zero reading was taken after storage of the prism samples in distilled water at 80° C for 24 h. The samples were then transferred and immersed in 1 N sodium hydroxide solution (NaOH) at 80 °C until the time of the test. The measurement of ASR expansion was measured at 4, 7, 14 and 28 days. To understand the developing microstructure of some hardened SCC mixtures, a scanning electron microscopy analysis (SEM) was carried out using a VEGA3 – TESCAN SEM with 25 kV as the accelerating voltage.
3. Results and discussion 3.1. Fresh properties The slump flow of fresh SCC mixtures is shown in Fig. 3. As seen from this figure, the slump flow of all the SCC mixtures was
Table 2 Physical properties of fine and coarse aggregates. Physical properties
Water absorption (%) Specific density (kg/m3) Fineness modulus Sand equivalent (%) Los Angeles coefficient (%) TCLP (mg/L)
Fine aggregates
Coarse aggregates
Sand 0/5
CRTG
Gravel 3/8
Gravel 8/15
0.8 2700 2.44 81 – –
0 2750 2.16 – – 1.21
3.5 2690 – – 23 –
2.92 2640 – – 25 –
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Fig. 3. Slump flow of SCC mixtures.
Fig. 2. Particle size distribution of fine aggregates.
between 700 and 800 mm, which indicates good deformability and compliance with the EFNARC recommendations [34]. Mixtures with 15% of MK showed a remarkable reduction in the slump flow diameter, whereas mixtures with CTRG showed an increase in slump flow compared to mixtures with natural sand, particularly those with 50% of CRTG. This improvement in slump flow was due to the texture of the glass which filled the voids between the coarse aggregates better than natural sand; glass sand has a smooth surface and low water absorption [24,28,45]. As a result, the combinations of CRTG with MK have a beneficial effect on the slump spread. However, there was a slight decrease in the slump flow of SCC mixtures with 30% CRTG compared to those with 10% and 20% CRTG; this was due to the difference in SP dosage because it should be noted that every percentage of CRTG requires the necessary amount of SP to achieve the targeted flowability of SCC mixtures without segregation and bleeding. The flow times for the V-funnel test are given in Fig. 4. This figure shows that, the flow times of these SCC mixtures were very stable and less than recommended value by 12 s. The addition of MK increased the flow time and viscosity by up to 15%, but due to the high specific surface area of MK, the mixtures needed more
water and superplasticiser to have the desired self-compacting properties [46]. Madandoust and Mousavi [47] studied the fresh properties of SCC with MK and noted that the flow time increased as the amount of MK increased with a higher dose of SP. Moreover, substituting sand with CRTG reduced the flow time and it rapidly converged towards the lower yield stress. The best flow times occurred after adding 50% CRTG into all the group mixtures, with a lower dose of SP than the mixture that contains 20% CRTG aggregate. The dosage of SP for the 10MK + 20CRTG, 10MK + 50CRTG mixtures was 1.1 and 0.95 respectively; this reduced the SP dosage enough to achieve the same flow time. The risk of blocking estimated by the H2 / H1 ratio was measured by the L-box test; the results are shown in Fig. 5. From this figure, it can be noted that, all the SCC mixtures were in accordance with the EFNARC limitations (H2/H1 > 0.8) [34]. Fig. 5 shows that CRTG resulted in better mobility, a higher filling capacity, and the passage of SCC through heavily congested areas. Kou and Poon [48] found that the ability to fill in the L-box improved when the amount of recycled glass aggregate had increased in SCC. The results of sieve stability are presented in Fig. 6. The figure shows that all the SCC mixtures had the highest stability, whereas
Table 3 Mixture proportions of different SCC mixes. Mix. ID
Control MK5 + CRTG0 MK5 + CRTG10 MK5 + CRTG20 MK5 + CRTG30 MK5 + CRTG40 MK5 + CRTG50 MK10 + CRTG0 MK10 + CRTG10 MK10 + CRTG20 MK10 + CRTG30 MK10 + CRTG40 MK10 + CRTG50 MK15 + CRTG0 MK15 + CRTG10 MK15 + CRTG20 MK15 + CRTG30 MK15 + CRTG40 MK15 + CRTG50 *B: Binder = OPC + MK
Coarse aggregate (kg/m3)
Binder OPC (kg/m3)
MK (kg/m3)
469.59 446.11 446.11 446.11 446.11 446.11 446.11 422.63 422.63 422.63 422.63 422.63 422.63 399.15 399.15 399.15 399.15 399.15 399.15
0 18.68 18.68 18.68 18.68 18.68 18.68 37.35 37.35 37.35 37.35 37.35 37.35 56.03 56.03 56.03 56.03 56.03 56.03
823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24
Fine aggregate (kg/m3) Sand (kg/m3)
CRTG (kg/m3)
909.78 909.78 819 727.82 636.85 545.87 454.89 909.78 819 727.82 636.85 545.87 454.89 909.78 819 727.82 636.85 545.87 454.89
0 0 90.98 181.96 272.93 363.91 454.89 0 90.98 181.96 272.93 363.91 454.89 0 90.978 181.96 272.93 363.91 454.89
W/B*
SP (%)
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
0.8 0.85 0.85 0.85 0.83 0.83 0.8 1.1 1.1 1.1 1.05 1 0.95 1.2 1.2 1.2 1.15 1.15 1.1
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3.2. Hardened properties
Fig. 4. V-funnel time of SCC mixtures.
Fig. 5. Blocking ratio in L-box test of SCC mixtures.
Fig. 6. Sieve stability ratio of SCC mixtures.
the low limit was due to the paste that could not stick to the aggregates. However, beyond 50% of CRTG replacement, the stability of SCC mixtures decreased as the volume of CRTG increased because the less viscous the concrete, the easier it is to pass through the sieve.
3.2.1. Compressive strength Fig. 7 shows the variation in compressive strength of the different SCC mixtures at 7, 28 and 90 days of curing. As shown in this figure, a relative increase in compressive strength with the increase in percentage of MK. Beyond of 15% of MK content there was a loss in the strength at all ages of hardening compared with 5% and 10% of MK contents. The 7 days compressive strength of control SCC mixture without CRTG and MK (CRT0 + MK0) is 30 MPa, which improves to 36 MPa , 38 MPa and 33 MPa for SCC mixtures made with 5%, 10% and 15% MK without CRTG (5MK + 0CRTG, 10MK + 0CRTG and 15MK + 0CRTG) respectively. This may due to the hydration reaction progresses, consequently the strength of SCC begins to increase with the curing age. From the Fig. 7, a similar development of compressive strength at 28 days to that at 7 days, was observed for mixtures 5MK + 0CRTG, 10MK + 0CRTG and 15MK + 0CRTG. Similarly, the 90 days compressive strength of SCC mixtures increases from 60 MPa to 74 MPa, 77 MPa and 72 MPa, representing 23%, 28% and 20% rate increasing in strength compared to the control SCC. This improvement in strength with the introduction of MK at 90 days is explained by the pozzolanic reaction with Ca(OH)2 and the acceleration of the hydration of OPC [49,50]. De Silva and Glasser [51] reported hydration of metakaolin-based cements. The results showed that the removal of Ca (OH)2 and the addition of C-S-H by pozzolanic reaction are the keys to increasing the compressive strength of concrete. The results indicated that the optimum amount of strength developed with 10% of MK regardless of the curing ages, however, the compressive strength then decreased for mixtures with 15% MK, but it remained higher than that of mixtures without metakaolin. This decrease in compressive strength with 15% MK may attributed to the dilution of clinker, such that this reduction in cement due to the higher amount of MK affected the potential cementing material. The MK reaction improved the strength due to the pozzolanic and filling effect but increasing the level of substitution beyond 10% will reduce the strength due to clinker dilution. Furthermore, it is noticed in Fig. 7, that the addition of CRTG decreases compressive strength of SCC mixtures. But, the strength is still higher than the control SCC, this explained by the pozzolanic reaction of MK which can compensate the compressive strength at long-term. The 90 days compressive strength of SCC mixtures increases from 60 MPa to 62.31 MPa, 69.31 MPa and 61.8 MPa for mixtures 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG, which are 4%, 16%, and 3% higher than the SCC control mixture. This development of strength may be due to the presence of MK that enters and fills the pores, which helps to improve the interfacial transition zone between the aggregates and the cement paste [52]. 3.2.2. Ultrasonic pulse velocity (UPV) Fig. 8 represents the effect of MK and CRTG on UPV test of SCC mixtures at 7, 28 and 90 days of curing. The figure reveals that the UPV values reduce as the percentage of CRTG increases. A reduction in UPV values of 4810 m/s, 4840 m/s and 4805 m/s for mixtures 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG compared to mixtures without CRTG. This could be attributed to the increase in pores by increasing in CRTG which consequently reduces the UPV. However, the presence of MK gives an advantage in enhancing the UPV values of CRTG compared with control SCC (0MK + 0CRTG). It is observed that the UPV values of mixes with 50% CRTG are higher than control SCC by 2%, 3% and 2% with the inclusion of MK at 5, 10, and 15% respectively; this improvement is beneficial in terms of structural concrete. The highest improvement in UPV is recorded for mixtures with 10% MK. The linear relationship established between 90 day compressive strengths of all
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Fig. 8. UPV of SCC mixtures.
Fig. 7. Compressive strength of SCC mixtures.
the SCC mixtures and the UPV is shown in Fig. 9. This figure shows that the UPV is very dependent on the compressive strength. Furthermore, this increase in the compressive strength when the UPV increased indicated a strong relationship between the com-
pressive strength and UPV of all SCC, and with a good correlation coefficient (R2 > 0.9). 3.2.3. Porosity Fig. 10 shows the effect that MK and CRTG had on the porosity of all the SCC mixtures. The results show an increase in porosity as
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the percentage of CRTG increased; this porosity was very high compared to the reference concrete with MK added, this shows that MK positively reduces porosity. For the control SCC, the porosity was 13.05%, which decreased to 12.4%, 11.52 and 13.1% for SCC mixtures prepared with 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG, respectively. This reduction in porosity occurred because MK filled in the pores as additional C-S-H formed by pozzolanic reaction [53]. An inclusion of 15% MK led to an increase in porosity compared to the 5% and 10% MK groups due to the volume of water needed to complete the hydration process. The 90 days compressive strength and UPV test results are plotted against porosity in Fig. 11; this figure shows that the hardening properties of SCC containing MK and CRTG have a good relationship coefficient between them (R2 > 0.8). Finally, the trend in compressive strength and UPV was to increase as the porosity decreased. 3.3. Durability properties 3.3.1. Chloride-ions permeability The evolution of rapid chloride-ions penetration test at 90 days of mixtures made with MK and CRTG is shown in Fig. 12. The figure reveals the positive effect of adding MK with CRTG which can decreases the chloride penetrability. For control SCC the charge passed was 2200 C which decreases to 1702 C, 1500 C and 1821 C for SCC mixtures prepared with 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG respectively. The enhancement in chloride resistance is attributed to the fineness of MK which can fill the pores and compact the microstructure [54]. However, according to Peem et al. [55] the creates of pozzolanic reaction between MK and Ca(OH2) causes the formation of C-S-H gel which can give less porous concrete, and some chloride ions are absorbed onto the surface of the CASAH gel. The limitation presented by AASHTO T-277 specifications [56] is reported in Fig. 12. This classification shows that all SCC mixtures studied except the SCC control have been found to be in category of ‘low chloride permeability’ based on their range of charge passed (1000–2000 C) which can be adapted for a marine environment. The best performance has been obtained by SCC mixtures prepared with 10% MK groups. Kavitha et al. [57] reported that the use of 10% of MK had a positive effect in improving the chloride penetration of SCC. In addition, the same result reported by Navdeep et al. [17] concerning positive effect of the inclusion of MK to reduce the chloride-ions penetration. Fig. 13 shows the relationship between the charge passed and the total porosity of all the SCC mixtures at 90 days. From this figure, it is observed that, the increase in porosity is associated with an increase in the charge passed, with a good coefficient of correlation (R2 = 0.8).
Fig. 10. Porosity results of SCC mixtures.
Fig. 11. Correlation between porosity and compressive strength and UPV of SCC mixtures.
Compressive sterngth (MPa)
80
75
y = 0.0175x - 11.578 R² = 0.98
70
65
y = 0.1213x - 522.35 R² = 0.96
60
55 4750
4800
4850
4900
4950
5000
Fig. 12. Charge passed results of chloride penetration test of SCC mixtures.
5050
5100
5150
UPV (m/s) Fig. 9. Correlation between compressive strength and UPV of SCC mixtures.
3.3.2. Gas permeability Gas permeability is a transfer property which gives a good indicator of the durability of concrete. Permeability depends on many factors such as; the nature of the gas and the difference of flows are
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are 0.5 1016 m2, 0.41 1016 m2 and 0.53 1016 m2 respectively, which are 9%, 25% and 4% higher as compared to the control SCC. From the result, it can be concluded that 10% MK group has the lowest permeability. This indicates that the inclusion of MK is more efficient in reducing the permeability which can be explained by the hydration products resulted from pozzolanic reaction [58]. In addition, the high fineness of MK (7000 cm2/g) reduced the size of the pores due to the filling effect, which also reduced the permeability of SCC.
Fig. 13. Correlation between porosity and charge passed of SCC mixtures.
involved. The results of the apparent permeability coefficient Kapp obtained are shown in Fig. 14. It is observed that the permeability values of CRTG with MK mixtures are substantially higher than control SCC. The apparent permeability coefficients of 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG mixtures
Fig. 14. Apparent gas permeability coefficient Kapp of SCC mixtures.
Fig. 15. Correlation between porosity and apparent gas permeability of SCC mixtures.
Fig. 16. ASR expansion of SCC mixtures.
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Fig. 15 shows the correlation between gas permeability and porosity for all the SCC mixes. As shown, there is a good linear correlation (R2 = 0.94) between the two properties despite the tendency for the coefficient of gas permeability to increase with increasing total porosity. This could be explained by the fact that the diffusion of the gas depends on total porosity of material. 3.3.3. Alkali-silica reaction (ASR) Expansion due to ASR at 4, 7, 14 and 28 days of SCC mixtures containing different percentages of CRTG and MK is shown in Fig. 16. It is clear that expansion increased with an increasing CRTG, and the composition with 50% replacement had the highest expansion at 28 days. This increase in ASR expansion resulted from internal cracks due to the higher SiO2/CaO ratio [59]. These values were much lower than those obtained with higher amounts of MK. The inclusion of 10% and 15% MK was still within the prescribed limit of 0.1%, this might be due to the pozzolanic reaction which decreased the SiO2/CaO ratio. These observations imply that the infusion of MK entirely quashed the negative effect of CRTG, but the valuable effect of MK seemed to be evident for SCC containing higher amounts of CRTG (50%). Poon et al. [60] investigated the
9
effect of MK on ASR of architectural mortar; they found that 10% of MK mitigated the ASR expansion of mortar, and therefore concluded that expansion depends on the amount of reactive silica and alkali, as reflected in the percentage of CRTG replacement and the amount of cement clinker in the mixture. Several studies claimed that metakaolin is the best material for reducing the alkali-silica reaction phenomenon. 3.3.4. Microstructure analysis Fig. 17 shows the scanning electron microscopy (SEM) images of the 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG mixtures. It can be seen that mixtures with 5MK + 50CRTG, 10MK + 50CRTG have a uniform and a denser structure between the paste and aggregates than the 15MK + 50CRTG mixture with more pore areas and cracks, which can affect negatively the cohesion between the matrix and aggregates. This may explain the low compressive strength and micro-hardness. Moreover, the 10MK + 50CRTG mixture has smaller micro-pores than the other mixtures; this can be related to the very efficient pozzolanic reaction generated by (5% MK) and (10% MK). Consequently, this close network of hydration products has been produced with minor residues of CH, which would explain the pozzolanic reaction between MK and CH which helps to refine the binder capillary porosity [61]. These results are in good agreement with the porosity study. At high levels of cement substitution (15% MK), some pores were larger because the rate of pozzolanic reactions consumed all the portlandite, and some MK would be present in the cementitious mixtures as an inert material in the absence of CH hydrate; the result is that it will not contribute to the production of new CSH hydrates. 4. Conclusion The present study examined the use of MK as supplementary cementitious materials and CRTG as fine aggregates in SCC. These new green materials contribute to the sustainable management of solid waste, while saving landfills, conserving natural resources, and protecting the environment. It is therefore a good strategy for reducing CO2 emitted into the atmosphere and developing the performance of green SCC. Based on the tests results, the following conclusions may be drawn:
Fig. 17. SEM images of SCC mixtures.
Up to 50% of CRTG, there was an increase in the flowability of SCC mixtures, with low doses of SP due to low water absorption and smooth CRTG surfaces. This improvement compensated for the negative effect that MK had on the fresh properties of SCC. The compressive strength and UPV decreased as the quantity of CRTG increased in SCC for all curing ages. However, the presence of MK enhanced the compressive strength and UPV values of CRTG mixtures better than the control SCC. The substitution of cement with 10% MK and sand by 50% CRTG increased the compressive strength and UPV of the control SCC mixture by 16% and 3% at 90 days, respectively. For porosity and gas permeability, there was an approximately 46% decrease in porosity and 25% decrease in gas permeability for the mixture with 10MK and 50CRTG compared to the control SCC. The chloride-ions permeability resistance of mixtures made with MK and CRTG was much higher than the control SCC, which can be adapted for a marine environment. Thus, incorporating MK and CRTG proved to be beneficial for the durability properties. The use of MK in CRTG mixtures could reduce the expansion of SCC due to ASR. SCC mixtures with 10–15% MK had ASR values, which are below of 0.1% limit of ASR.
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The SEM analysis indicated that the use of MK in CRTG mixtures in an amount of up to 15% caused an increase in porosity because the pozzolanic effect of MK helped to develop the hydration process. Hence, a dense matrix of material was obtained which improved the performance of SCC in terms of its strength and durability.
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[22] W. Mcdonnel, Toxicity characteristic leaching procedure (TCLP), Amer Electroplaters Soc Inc 12644 Research PKWY, Orlando, FL 32826-3298, 1989. [23] Z. Hui, W. Sun, Study of properties of mortar containing cathode ray tubes (CRT) glass as replacement for river sand fine aggregate, Constr. Build. Mater. 25 (10) (2011) 4059–4064. [24] H. Zhao, C.S. Poon, T.C. Ling, Utilizing recycled cathode ray tube funnel glass sand as river sand replacement in the high-density concrete, J. Cleaner Prod. 51 (2013) 184–190. [25] A. Saccani, M.C. Bignozzi, ASR expansion behavior of recycled glass fine aggregates in concrete, Cem. Concr. Res. 40 (4) (2010) 531–536. [26] T. Mauroux, F. Benboudjema, P. Turcry, A. Aït-Mokhtar, O. Deves, Study of cracking due to drying in coating mortars by digital image correlation, Cem. Concr. Res. 42 (7) (2012) 1014–1023. [27] T.-C. Ling, C.-S. 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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of using metakaolin as supplementary cementitious material and recycled CRT funnel glass as fine aggregate on the durability of green self-compacting concrete Younes Ouldkhaoua a, Benchaa Benabed a,⇑, Rajab Abousnina b, El-Hadj Kadri c, Jamal Khatib d,e a
Civil Engineering Laboratory, University of Laghouat, 03000, Algeria Centre for Future Materials, School of Civil Engineering and Surveying, University of Southern Queensland, Toowoomba, Queensland 4350, Australia L2MGC Laboratory, University of Cergy-Pontoise, 95000, France d Faculty of Engineering, Beirut Arab University, Beirut, Lebanon e Faculty of Science and Engineering, University of Wolverhampton, Wolverhampton, UK b c
h i g h l i g h t s CRTG was used as fine aggregate and MK as partial cement replacement to produce a durable green SCC. Durability performance of green SCC has been evaluated. CRTG improves the fresh properties, strength and porosity of SCC incorporating MK. The use of MK and CRTG in SCC mixtures enhances the chloride-ions and gas permeability. The addition of MK also reduces the ASR expansion of SCC made with CRTG.
a r t i c l e
i n f o
Article history: Received 22 March 2019 Received in revised form 23 November 2019 Accepted 4 December 2019
Keywords: Cathode ray tube glass Metakaolin Green self-compacting concrete Strength Durability
a b s t r a c t This present work is a study of the durability of green self-compacting concrete (SCC) that incorporates recycled cathode ray tube glass (CRTG) and metakaolin (MK). In these SCC mixtures natural sand has been replaced with CRTG at levels of 0, 10, 20, 30, 40 and 50% by weight, and the cement has been partially replaced by MK at substitution ratios of 5, 10, and 15% by weight. The fresh properties of SCC mixtures were then evaluated by slump flow, V-funnel, L-Box tests and their resistance to segregation was measured by the sieve stability test. The strength and durability properties of hardened SCC mixtures was assessed according to the compressive strength, ultrasonic pulse velocity (UPV), porosity, ions chloride permeability, gas permeability, and Alkali-silica reaction (ASR) tests. A SEM analysis was also carried out to examine the developing microstructure of hardened SCC mixtures. This study revealed an improvement in the fresh properties of SCC mixtures with up to 50% CRTG replacement. At the hardened state, the compressive strength and UPV of the SCC mixtures (10MK + 50CRTG) improved by 16% and 3% respectively after 90 days of ageing compared to SCC control mixtures. Moreover, using MK in SCC mixtures with different amounts of CRTG resulted in the best durability, while 10% of MK enhanced the porosity, permeability of chloride and gas permeability in SCC. Results show also that, 10% and 15% of MK can be prescribed in 0.1% limit of ASR in SCC mixtures with CRTG. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Concrete industry achieved a milestone after the emergence of self-compacting concrete (SCC) [1]. SCC has proven several advantages and promised material in construction industry techniques such as pumpability, easy and speed of implementation [2]. The ⇑ Corresponding author. E-mail address: [email protected] (B. Benabed). https://doi.org/10.1016/j.conbuildmat.2019.117802 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
particularity of SCC appears in their fresh state properties, and it must be characterized by high workability and deformability while remaining stable [3], these properties contribute to ensure durable and resistant constructions [4]. To achieve these requirements, an SCC mix needs large amounts of Portland cement and superplasticizers (SP) [5], but high volumes of Portland cement increase the volume of cement consumed, lead to high heat of hydration that is associated with concrete cracking, have environmental impacts
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due to CO2 emissions, consume energy and natural resources and result in high production costs [6]. The world is facing many serious environmental challenges due to pollution and growing consumption, as well as an increase in solid wastes. Furthermore, the depletion of natural resources and the detrimental effect of CO2 emissions increase the environmental pressure to adopt environmentally friendly techniques for recycling and using these wastes in order to preserve more natural resources and reduce CO2 emissions [7]. The mineral additions have been used as supplementary cementitious materials (SCM) to reduce the high amounts of cement in SCC mixture, with positive effects on the performance of concrete, compaction, environmental and economic aspects [8]. The pozzolanic reaction due to the mineral additions takes effect during cement hydration improves the durability of concrete. The most commonly used SCM are silica fume (SF), fly ash, ground granulated blast furnace slag (GGBS), metakaolin (MK), and rice husk ash (RHA), etc. [9]. MK is a pozzolanic material that can be added as a cementitious material in concrete mixtures. Many investigators showed that MK improves the performance of concrete but it can have a negative effect on its rheological properties [10,11]. Sfikas et al. [12] studied the effect of MK on the composition of SCC, the results showed a reduction in the workability by inclusion of MK and a higher superplasticizers requirement in order to acquire a similar rheological behavior, but it increased the mechanical strength. Ghoddousi et al. [13] reported that the rheological properties of SCC mixes with partial replacement of MK reached a higher yield stress than with other mineral admixtures. Siddique et al. [14] researched the effect of MK as cement replacement in concrete; cement was partially replaced with MK at levels of 0%, 5%, 10%, and 15% by weight. The results showed at 15% MK replacement, compressive strength decreased and 10% MK content presented the optimum replacement level. Furthermore, several studies have shown that MK is the most effective material for reducing the negative effect of ASR. Lee et al. [15] studied the effect of pozzolanic materials on ASR of concrete blocks. The results indicated a decrease in the ASR expansion with an increase in MK content. Khatib al. [16] observed that early age concrete shrinkage can be reduced with MK replacement, while Singh, Mithulraj and Arya [17] concluded that concrete with MK has a lower depth of carbonation than those that control SCC. Cathode ray tube funnel glass (CRTG) was used for earlier generations for television and computer monitors [18]. This waste can pose serious environmental and health problems due to the toxicity of the lead content in the chemical composition of glass [19]. It is important to recycle these waste materials and be disposed to mitigate any harmful consequences [20]. Many researchers claim that the recycled CRTG can be used as substitution for natural sand in mortar and concrete, and it will also improve the fluidity and overcome the drawbacks of the mechanical properties as well as the performance of concrete. Poon et al. [21] treated this glass by immersing it in a bath of 5% nitric acid (HNO3) solution for 3 h, which will satisfied the limits of the toxicity characteristic leaching procedure (TCLP) test [22]. Hui and Sun [23] studied the use of CRTG on the workability of mortar and found that its slump diameter increased as the glass levels of CRT increased. Zhao et al. [24] investigated the effects of CRTG on alkali-silica reaction (ASR) on high-density concrete. They concluded that the increasing in CRTG content increased the ASR expansion of concrete. Saccani et al. [25] also reported an increase in glass proportions as fine aggregate resulted an increase in ASR expansion of concrete. The drying shrinkage may induce cracks which could result in debonding and reduce the durability of the concrete as reported by Mauroux et al. [26]. Ling and Poon [27] found a reduction in the drying shrinkage of concrete containing 100% CRT glass as a fine aggregate. Ling and Poon [28] studied the possible use of recycled CRT
funnel glass as heavyweight fine aggregate in barite concrete and found that its resistance to carbonation gradually decreased with an increasing use of CRT glass. In the other hand, Metalssi et al. [29] indicated in their study that the Carbonation improved the mechanical strengths and decrease the global porosity with modifying the pore size distribution. However, carbonation increases the shrinkage, and thus to a probable increase of cracking. From an ecological and economic perspective, the present research into the recycling and reuse of waste, particularly as aggregates and cement, will reduce the extraction of aggregates and CO2 emissions while prolonging the life of the landfills they are currently helping to saturate. This present work will study the rheological, mechanical and durability properties of the green self-compacting concrete that incorporates recycled CRT funnel glass (CRTG) as a partial substitution for fine aggregate and metakaolin (MK) as a partial replacement for cement. 2. Experimental program 2.1. Materials, mixture proportions and mixing procedure An ordinary Portland cement (CEMI 42.5) conforms to EN 197-1:2000 [30] was used in all SCC mixtures. MK used as a partial cement replacement was obtained from kaolin calcination at 850 °C for 3 h [31]. The XRD analysis of MK is shown in Fig. 1. The percentage of MK in the blended cement was 5, 10 and 15% by weight. The chemical and physical properties of both cement and MK are presented in Table 1. As chemical admixture, a superplasticiser polycarboxylic ether type (SP) was used with density of 1.07 and solid content of 30%. River sand with a maximum size of 5 mm was used as natural fine aggregate. Waste CRTG was used to replace river sand as fine aggregate of 0, 10, 20, 30, 40 and 50% by weight. In order to treat CRTG and remove the lead oxide; CRTG was treated with 5% of nitric acid solution (HNO3) for 3 h [21]. The result of TCLP test [21] of treated CRTG is given in Table 2. The particle size distribution of river sand and CRTG is presented in Fig. 2. Two classes of limestone gravel G 3/8 and G 8/15 were used for the coarse aggregate in proportions of 40% and 60% in SCC mixtures respectively. The physical properties of fine and coarse aggregates are given in Table 2. Nineteen mixtures were prepared to assess the effect of both MK and CRTG on the rheological, mechanical and durability properties of SCC. In order to determine the quantity required for each ingredients of concrete, the general method developed by Okamura and Ouchi [32] was used for this purpose, with some modifications regarding the quantity of sand in the mortar (sand/mortar ratio (S/M) was fixed at 0.5), the water/binder ratio (W/B = 0.4) and the dosage of superplasticizers (SP). The mixture proportions of the SCC mixes are given in Table 3. The mixing procedure for making SCC mixtures takes three steps. Firstly, the powder (cement, MK) and aggregates were mixed together for half minute, and then 70% of the mixing water was added and mixed for 1 min. The remaining 30% of water containing the superplasticizer was added and mixed for 1 min. This procedure continued for another 5 min and then stopped for 2 min. Finally, the SCC was mixed again for 30 s to ensure the homogeneity of SCC mixtures before discharging [33]. 2.2. Testing Several experiments were conducted following EFNARC [34] guidelines for selfcompacting concrete to assess the fresh properties of SCC. The filling, the passage ability and the resistance to segregation were determined by:
The The The The
slump flow diameter (EN 12350-8) [35]; V-funnel flow time (EN 12350-9) [36]; L-box height ration (EN 12350-10) [37]; sieve stability (EN 12350-11) [38].
The compressive strength was measured at 7, 28 and 90 days of curing, according to European Standard EN 196-1 [39]. All SCC specimens are subjected to ultrasonic pulse velocity (UPV) test, this test was performed in accordance with standard ASTM C597-16 [40]. It is a non-destructive test that, gives an idea of the homogeneity and porosity of the specimens. It consists in putting the two probes (transmitter and receiver) of ultrasound between the two ends of the prismatic specimens in order to measure the ultrasonic pulse velocity (UPV) using the following equation:
UPV ¼
L T
L : Distance between the two transducers in (m). T : Wave propagation time in (s).
ð1Þ
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Fig. 1. X-ray diffraction analysis of MK.
Table 1 Chemical composition and physical properties of cement and MK. Chemical composition (%)
Cement
MK
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O TiO2 Loss on ignition
20.83 4.13 5.58 62.19 1.42 2.30 0.38 0.028 2.04
50.30 41.81 1.5 0.08 0.4 0.81 0.09 0.024 5.77
Physical properties Specific gravity (kg/m3) Blaine fineness (m2/kg)
3120 330
2450 700
For the resistance of SCC to chloride-ions penetration, in accordance with ASTM C 1202 [43], the test was performed on a concrete disc (ɸ200 mm and h 50 mm) by calculating the amount of charge passed (Eq. (3)) into SCC specimens placed in cell subjected to 60 V for 6 h. Where one of the cell electrodes is immersed in a 3% sodium chloride solution (NaCl), and the other one in 0.3% sodium hydroxide solution (NaOH.)
Q ¼ 900ðI0 þ 2I30 þ2I60 þ þ 2I300 þ 2I330 þ I360 Þ
In terms of a porosity accessible to water test, three 100 50 mm discs cut from the 100 mm diameter by 200 mm high cylindrical specimens were used to evaluate their porosity in water up to 90 days, according to the NF P18-459 standard [41]. Gas permeability is one of the means that is generally used to characterize the porosity of concrete. The Nitrogen gas permeability test was performed using the CEMBUREAU method according to NF XP P18-463 [42]. The specimens used to achieve the gas permeability were cylindrical with a diameter of 150 and a height of 50 mm, then protected and confined laterally, which ensures unidirectional transfer of the gas. The apparent gas permeability Kapp was measured by applying relative pressures of gradient 1 bar and computed according to the following equation:
K app ¼
L : Thickness of the specimen in (m). A : Cross-sectional area of the specimen in (m2). Q : Gas flow in (m3 s1). l: Dynamic viscosity coefficient of nitrogen gas (17.5 106 Pa s). P i : Inlet pressure (Pa). P 0 : Atmospheric pressure (Pa).
2:Pi :Q :L:l
ð2Þ
AðP2i P20 Þ
ð3Þ
According to the standard ASTM C 1260 (2007) [44], an accelerated alkali-silica reaction (ASR) test was performed. Zero reading was taken after storage of the prism samples in distilled water at 80° C for 24 h. The samples were then transferred and immersed in 1 N sodium hydroxide solution (NaOH) at 80 °C until the time of the test. The measurement of ASR expansion was measured at 4, 7, 14 and 28 days. To understand the developing microstructure of some hardened SCC mixtures, a scanning electron microscopy analysis (SEM) was carried out using a VEGA3 – TESCAN SEM with 25 kV as the accelerating voltage.
3. Results and discussion 3.1. Fresh properties The slump flow of fresh SCC mixtures is shown in Fig. 3. As seen from this figure, the slump flow of all the SCC mixtures was
Table 2 Physical properties of fine and coarse aggregates. Physical properties
Water absorption (%) Specific density (kg/m3) Fineness modulus Sand equivalent (%) Los Angeles coefficient (%) TCLP (mg/L)
Fine aggregates
Coarse aggregates
Sand 0/5
CRTG
Gravel 3/8
Gravel 8/15
0.8 2700 2.44 81 – –
0 2750 2.16 – – 1.21
3.5 2690 – – 23 –
2.92 2640 – – 25 –
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Fig. 3. Slump flow of SCC mixtures.
Fig. 2. Particle size distribution of fine aggregates.
between 700 and 800 mm, which indicates good deformability and compliance with the EFNARC recommendations [34]. Mixtures with 15% of MK showed a remarkable reduction in the slump flow diameter, whereas mixtures with CTRG showed an increase in slump flow compared to mixtures with natural sand, particularly those with 50% of CRTG. This improvement in slump flow was due to the texture of the glass which filled the voids between the coarse aggregates better than natural sand; glass sand has a smooth surface and low water absorption [24,28,45]. As a result, the combinations of CRTG with MK have a beneficial effect on the slump spread. However, there was a slight decrease in the slump flow of SCC mixtures with 30% CRTG compared to those with 10% and 20% CRTG; this was due to the difference in SP dosage because it should be noted that every percentage of CRTG requires the necessary amount of SP to achieve the targeted flowability of SCC mixtures without segregation and bleeding. The flow times for the V-funnel test are given in Fig. 4. This figure shows that, the flow times of these SCC mixtures were very stable and less than recommended value by 12 s. The addition of MK increased the flow time and viscosity by up to 15%, but due to the high specific surface area of MK, the mixtures needed more
water and superplasticiser to have the desired self-compacting properties [46]. Madandoust and Mousavi [47] studied the fresh properties of SCC with MK and noted that the flow time increased as the amount of MK increased with a higher dose of SP. Moreover, substituting sand with CRTG reduced the flow time and it rapidly converged towards the lower yield stress. The best flow times occurred after adding 50% CRTG into all the group mixtures, with a lower dose of SP than the mixture that contains 20% CRTG aggregate. The dosage of SP for the 10MK + 20CRTG, 10MK + 50CRTG mixtures was 1.1 and 0.95 respectively; this reduced the SP dosage enough to achieve the same flow time. The risk of blocking estimated by the H2 / H1 ratio was measured by the L-box test; the results are shown in Fig. 5. From this figure, it can be noted that, all the SCC mixtures were in accordance with the EFNARC limitations (H2/H1 > 0.8) [34]. Fig. 5 shows that CRTG resulted in better mobility, a higher filling capacity, and the passage of SCC through heavily congested areas. Kou and Poon [48] found that the ability to fill in the L-box improved when the amount of recycled glass aggregate had increased in SCC. The results of sieve stability are presented in Fig. 6. The figure shows that all the SCC mixtures had the highest stability, whereas
Table 3 Mixture proportions of different SCC mixes. Mix. ID
Control MK5 + CRTG0 MK5 + CRTG10 MK5 + CRTG20 MK5 + CRTG30 MK5 + CRTG40 MK5 + CRTG50 MK10 + CRTG0 MK10 + CRTG10 MK10 + CRTG20 MK10 + CRTG30 MK10 + CRTG40 MK10 + CRTG50 MK15 + CRTG0 MK15 + CRTG10 MK15 + CRTG20 MK15 + CRTG30 MK15 + CRTG40 MK15 + CRTG50 *B: Binder = OPC + MK
Coarse aggregate (kg/m3)
Binder OPC (kg/m3)
MK (kg/m3)
469.59 446.11 446.11 446.11 446.11 446.11 446.11 422.63 422.63 422.63 422.63 422.63 422.63 399.15 399.15 399.15 399.15 399.15 399.15
0 18.68 18.68 18.68 18.68 18.68 18.68 37.35 37.35 37.35 37.35 37.35 37.35 56.03 56.03 56.03 56.03 56.03 56.03
823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24 823.24
Fine aggregate (kg/m3) Sand (kg/m3)
CRTG (kg/m3)
909.78 909.78 819 727.82 636.85 545.87 454.89 909.78 819 727.82 636.85 545.87 454.89 909.78 819 727.82 636.85 545.87 454.89
0 0 90.98 181.96 272.93 363.91 454.89 0 90.98 181.96 272.93 363.91 454.89 0 90.978 181.96 272.93 363.91 454.89
W/B*
SP (%)
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
0.8 0.85 0.85 0.85 0.83 0.83 0.8 1.1 1.1 1.1 1.05 1 0.95 1.2 1.2 1.2 1.15 1.15 1.1
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3.2. Hardened properties
Fig. 4. V-funnel time of SCC mixtures.
Fig. 5. Blocking ratio in L-box test of SCC mixtures.
Fig. 6. Sieve stability ratio of SCC mixtures.
the low limit was due to the paste that could not stick to the aggregates. However, beyond 50% of CRTG replacement, the stability of SCC mixtures decreased as the volume of CRTG increased because the less viscous the concrete, the easier it is to pass through the sieve.
3.2.1. Compressive strength Fig. 7 shows the variation in compressive strength of the different SCC mixtures at 7, 28 and 90 days of curing. As shown in this figure, a relative increase in compressive strength with the increase in percentage of MK. Beyond of 15% of MK content there was a loss in the strength at all ages of hardening compared with 5% and 10% of MK contents. The 7 days compressive strength of control SCC mixture without CRTG and MK (CRT0 + MK0) is 30 MPa, which improves to 36 MPa , 38 MPa and 33 MPa for SCC mixtures made with 5%, 10% and 15% MK without CRTG (5MK + 0CRTG, 10MK + 0CRTG and 15MK + 0CRTG) respectively. This may due to the hydration reaction progresses, consequently the strength of SCC begins to increase with the curing age. From the Fig. 7, a similar development of compressive strength at 28 days to that at 7 days, was observed for mixtures 5MK + 0CRTG, 10MK + 0CRTG and 15MK + 0CRTG. Similarly, the 90 days compressive strength of SCC mixtures increases from 60 MPa to 74 MPa, 77 MPa and 72 MPa, representing 23%, 28% and 20% rate increasing in strength compared to the control SCC. This improvement in strength with the introduction of MK at 90 days is explained by the pozzolanic reaction with Ca(OH)2 and the acceleration of the hydration of OPC [49,50]. De Silva and Glasser [51] reported hydration of metakaolin-based cements. The results showed that the removal of Ca (OH)2 and the addition of C-S-H by pozzolanic reaction are the keys to increasing the compressive strength of concrete. The results indicated that the optimum amount of strength developed with 10% of MK regardless of the curing ages, however, the compressive strength then decreased for mixtures with 15% MK, but it remained higher than that of mixtures without metakaolin. This decrease in compressive strength with 15% MK may attributed to the dilution of clinker, such that this reduction in cement due to the higher amount of MK affected the potential cementing material. The MK reaction improved the strength due to the pozzolanic and filling effect but increasing the level of substitution beyond 10% will reduce the strength due to clinker dilution. Furthermore, it is noticed in Fig. 7, that the addition of CRTG decreases compressive strength of SCC mixtures. But, the strength is still higher than the control SCC, this explained by the pozzolanic reaction of MK which can compensate the compressive strength at long-term. The 90 days compressive strength of SCC mixtures increases from 60 MPa to 62.31 MPa, 69.31 MPa and 61.8 MPa for mixtures 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG, which are 4%, 16%, and 3% higher than the SCC control mixture. This development of strength may be due to the presence of MK that enters and fills the pores, which helps to improve the interfacial transition zone between the aggregates and the cement paste [52]. 3.2.2. Ultrasonic pulse velocity (UPV) Fig. 8 represents the effect of MK and CRTG on UPV test of SCC mixtures at 7, 28 and 90 days of curing. The figure reveals that the UPV values reduce as the percentage of CRTG increases. A reduction in UPV values of 4810 m/s, 4840 m/s and 4805 m/s for mixtures 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG compared to mixtures without CRTG. This could be attributed to the increase in pores by increasing in CRTG which consequently reduces the UPV. However, the presence of MK gives an advantage in enhancing the UPV values of CRTG compared with control SCC (0MK + 0CRTG). It is observed that the UPV values of mixes with 50% CRTG are higher than control SCC by 2%, 3% and 2% with the inclusion of MK at 5, 10, and 15% respectively; this improvement is beneficial in terms of structural concrete. The highest improvement in UPV is recorded for mixtures with 10% MK. The linear relationship established between 90 day compressive strengths of all
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Fig. 8. UPV of SCC mixtures.
Fig. 7. Compressive strength of SCC mixtures.
the SCC mixtures and the UPV is shown in Fig. 9. This figure shows that the UPV is very dependent on the compressive strength. Furthermore, this increase in the compressive strength when the UPV increased indicated a strong relationship between the com-
pressive strength and UPV of all SCC, and with a good correlation coefficient (R2 > 0.9). 3.2.3. Porosity Fig. 10 shows the effect that MK and CRTG had on the porosity of all the SCC mixtures. The results show an increase in porosity as
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the percentage of CRTG increased; this porosity was very high compared to the reference concrete with MK added, this shows that MK positively reduces porosity. For the control SCC, the porosity was 13.05%, which decreased to 12.4%, 11.52 and 13.1% for SCC mixtures prepared with 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG, respectively. This reduction in porosity occurred because MK filled in the pores as additional C-S-H formed by pozzolanic reaction [53]. An inclusion of 15% MK led to an increase in porosity compared to the 5% and 10% MK groups due to the volume of water needed to complete the hydration process. The 90 days compressive strength and UPV test results are plotted against porosity in Fig. 11; this figure shows that the hardening properties of SCC containing MK and CRTG have a good relationship coefficient between them (R2 > 0.8). Finally, the trend in compressive strength and UPV was to increase as the porosity decreased. 3.3. Durability properties 3.3.1. Chloride-ions permeability The evolution of rapid chloride-ions penetration test at 90 days of mixtures made with MK and CRTG is shown in Fig. 12. The figure reveals the positive effect of adding MK with CRTG which can decreases the chloride penetrability. For control SCC the charge passed was 2200 C which decreases to 1702 C, 1500 C and 1821 C for SCC mixtures prepared with 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG respectively. The enhancement in chloride resistance is attributed to the fineness of MK which can fill the pores and compact the microstructure [54]. However, according to Peem et al. [55] the creates of pozzolanic reaction between MK and Ca(OH2) causes the formation of C-S-H gel which can give less porous concrete, and some chloride ions are absorbed onto the surface of the CASAH gel. The limitation presented by AASHTO T-277 specifications [56] is reported in Fig. 12. This classification shows that all SCC mixtures studied except the SCC control have been found to be in category of ‘low chloride permeability’ based on their range of charge passed (1000–2000 C) which can be adapted for a marine environment. The best performance has been obtained by SCC mixtures prepared with 10% MK groups. Kavitha et al. [57] reported that the use of 10% of MK had a positive effect in improving the chloride penetration of SCC. In addition, the same result reported by Navdeep et al. [17] concerning positive effect of the inclusion of MK to reduce the chloride-ions penetration. Fig. 13 shows the relationship between the charge passed and the total porosity of all the SCC mixtures at 90 days. From this figure, it is observed that, the increase in porosity is associated with an increase in the charge passed, with a good coefficient of correlation (R2 = 0.8).
Fig. 10. Porosity results of SCC mixtures.
Fig. 11. Correlation between porosity and compressive strength and UPV of SCC mixtures.
Compressive sterngth (MPa)
80
75
y = 0.0175x - 11.578 R² = 0.98
70
65
y = 0.1213x - 522.35 R² = 0.96
60
55 4750
4800
4850
4900
4950
5000
Fig. 12. Charge passed results of chloride penetration test of SCC mixtures.
5050
5100
5150
UPV (m/s) Fig. 9. Correlation between compressive strength and UPV of SCC mixtures.
3.3.2. Gas permeability Gas permeability is a transfer property which gives a good indicator of the durability of concrete. Permeability depends on many factors such as; the nature of the gas and the difference of flows are
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are 0.5 1016 m2, 0.41 1016 m2 and 0.53 1016 m2 respectively, which are 9%, 25% and 4% higher as compared to the control SCC. From the result, it can be concluded that 10% MK group has the lowest permeability. This indicates that the inclusion of MK is more efficient in reducing the permeability which can be explained by the hydration products resulted from pozzolanic reaction [58]. In addition, the high fineness of MK (7000 cm2/g) reduced the size of the pores due to the filling effect, which also reduced the permeability of SCC.
Fig. 13. Correlation between porosity and charge passed of SCC mixtures.
involved. The results of the apparent permeability coefficient Kapp obtained are shown in Fig. 14. It is observed that the permeability values of CRTG with MK mixtures are substantially higher than control SCC. The apparent permeability coefficients of 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG mixtures
Fig. 14. Apparent gas permeability coefficient Kapp of SCC mixtures.
Fig. 15. Correlation between porosity and apparent gas permeability of SCC mixtures.
Fig. 16. ASR expansion of SCC mixtures.
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Fig. 15 shows the correlation between gas permeability and porosity for all the SCC mixes. As shown, there is a good linear correlation (R2 = 0.94) between the two properties despite the tendency for the coefficient of gas permeability to increase with increasing total porosity. This could be explained by the fact that the diffusion of the gas depends on total porosity of material. 3.3.3. Alkali-silica reaction (ASR) Expansion due to ASR at 4, 7, 14 and 28 days of SCC mixtures containing different percentages of CRTG and MK is shown in Fig. 16. It is clear that expansion increased with an increasing CRTG, and the composition with 50% replacement had the highest expansion at 28 days. This increase in ASR expansion resulted from internal cracks due to the higher SiO2/CaO ratio [59]. These values were much lower than those obtained with higher amounts of MK. The inclusion of 10% and 15% MK was still within the prescribed limit of 0.1%, this might be due to the pozzolanic reaction which decreased the SiO2/CaO ratio. These observations imply that the infusion of MK entirely quashed the negative effect of CRTG, but the valuable effect of MK seemed to be evident for SCC containing higher amounts of CRTG (50%). Poon et al. [60] investigated the
9
effect of MK on ASR of architectural mortar; they found that 10% of MK mitigated the ASR expansion of mortar, and therefore concluded that expansion depends on the amount of reactive silica and alkali, as reflected in the percentage of CRTG replacement and the amount of cement clinker in the mixture. Several studies claimed that metakaolin is the best material for reducing the alkali-silica reaction phenomenon. 3.3.4. Microstructure analysis Fig. 17 shows the scanning electron microscopy (SEM) images of the 5MK + 50CRTG, 10MK + 50CRTG and 15MK + 50CRTG mixtures. It can be seen that mixtures with 5MK + 50CRTG, 10MK + 50CRTG have a uniform and a denser structure between the paste and aggregates than the 15MK + 50CRTG mixture with more pore areas and cracks, which can affect negatively the cohesion between the matrix and aggregates. This may explain the low compressive strength and micro-hardness. Moreover, the 10MK + 50CRTG mixture has smaller micro-pores than the other mixtures; this can be related to the very efficient pozzolanic reaction generated by (5% MK) and (10% MK). Consequently, this close network of hydration products has been produced with minor residues of CH, which would explain the pozzolanic reaction between MK and CH which helps to refine the binder capillary porosity [61]. These results are in good agreement with the porosity study. At high levels of cement substitution (15% MK), some pores were larger because the rate of pozzolanic reactions consumed all the portlandite, and some MK would be present in the cementitious mixtures as an inert material in the absence of CH hydrate; the result is that it will not contribute to the production of new CSH hydrates. 4. Conclusion The present study examined the use of MK as supplementary cementitious materials and CRTG as fine aggregates in SCC. These new green materials contribute to the sustainable management of solid waste, while saving landfills, conserving natural resources, and protecting the environment. It is therefore a good strategy for reducing CO2 emitted into the atmosphere and developing the performance of green SCC. Based on the tests results, the following conclusions may be drawn:
Fig. 17. SEM images of SCC mixtures.
Up to 50% of CRTG, there was an increase in the flowability of SCC mixtures, with low doses of SP due to low water absorption and smooth CRTG surfaces. This improvement compensated for the negative effect that MK had on the fresh properties of SCC. The compressive strength and UPV decreased as the quantity of CRTG increased in SCC for all curing ages. However, the presence of MK enhanced the compressive strength and UPV values of CRTG mixtures better than the control SCC. The substitution of cement with 10% MK and sand by 50% CRTG increased the compressive strength and UPV of the control SCC mixture by 16% and 3% at 90 days, respectively. For porosity and gas permeability, there was an approximately 46% decrease in porosity and 25% decrease in gas permeability for the mixture with 10MK and 50CRTG compared to the control SCC. The chloride-ions permeability resistance of mixtures made with MK and CRTG was much higher than the control SCC, which can be adapted for a marine environment. Thus, incorporating MK and CRTG proved to be beneficial for the durability properties. The use of MK in CRTG mixtures could reduce the expansion of SCC due to ASR. SCC mixtures with 10–15% MK had ASR values, which are below of 0.1% limit of ASR.
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The SEM analysis indicated that the use of MK in CRTG mixtures in an amount of up to 15% caused an increase in porosity because the pozzolanic effect of MK helped to develop the hydration process. Hence, a dense matrix of material was obtained which improved the performance of SCC in terms of its strength and durability.
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