The research work presented in this contribution investigated the impact of Compression Casting Technique (CCT) on the compressive behavior of fully Recycled Aggregates Concrete (RAC). RAC mix containing 30% fine aggregates, 70% coarse aggregates and 15% cement by weight of total aggregates was prepared under two different casting pressures (i.e., 25 &amp; 35 MPa). For the purpose of comparison, Natural Aggregate Concrete (NAC) mix was also prepared under same casting pressures. Samples of RAC mix were also made by compaction through vibration. Recycled concrete aggregates required for this study were prepared by crushing of damaged concrete samples having compressive strength in the range of 21 to 28 MPa. Compressive response was evaluated in terms of compressive strength and modulus of elasticity (MOE). Ultrasonic pulse velocity test was employed to check the quality of internal matrix of concrete samples prepared by CCT and vibration. The results demonstrated positive effect of CCT on the properties of concrete resulting in higher compressive strength and MOE compared to properties of concrete prepared by compaction through vibration. With the increase in casting pressure from 25 to 35 MPa, compressive strength and MOE of RAC was increased by 21% and 29%, respectively. It was found that RAC mix exhibited inferior properties (i.e., compressive strength and MOE) compared with NAC mix

Hameed, Rashid

Nisa, Zaib un

Sohail, Muazzam Ghous

Tahir, Muhammad

English

Sustainable Structure and Material (E-Journal)

P a g e  | 111  Sustainable Structures and Materials, Vol. 6, No. 1, (2023) 111-115                                 DOI: https://doi.org/10.26392/SSM.2023.06.01.0111 Effect of Casting Technique on the Compressive Behaviour of Fully Recycled Aggregate Concrete Zaib un Nisa1, Rashid Hameed*1, Muhammad Tahir2, Muazzam Ghous Sohail3 1Department of Civil Engineering, University of Engineering & Technology Lahore, Pakistan 2Department of Civil Engineering, University of Engineering & Technology Lahore, Narowal Campus, Narowal Pakistan 3Department of Civil Engineering, Capital University of Science and Technology (CUST), Islamabad, Pakistan * Corresponding author/ E-mail: rashidmughal@uet.edu.pk,  (Received April 5, 2023, Revised April 29, 2023, Accepted June 4, 2023) ABSTRACT. The research work presented in this contribution investigated the impact of Compression Casting Technique (CCT) on the compressive behavior of fully Recycled Aggregates Concrete (RAC). RAC mix containing 30% fine aggregates, 70% coarse aggregates and 15% cement by weight of total aggregates was prepared under two different casting pressures (i.e., 25 & 35 MPa). For the purpose of comparison, Natural Aggregate Concrete (NAC) mix was also prepared under same casting pressures. Samples of RAC mix were also made by compaction through vibration. Recycled concrete aggregates required for this study were prepared by crushing of damaged concrete samples having compressive strength in the range of 21 to 28 MPa. Compressive response was evaluated in terms of compressive strength and modulus of elasticity (MOE). Ultrasonic pulse velocity test was employed to check the quality of internal matrix of concrete samples prepared by CCT and vibration. The results demonstrated positive effect of CCT on the properties of concrete resulting in higher compressive strength and MOE compared to properties of concrete prepared by compaction through vibration. With the increase in casting pressure from 25 to 35 MPa, compressive strength and MOE of RAC was increased by 21% and 29%, respectively. It was found that RAC mix exhibited inferior properties (i.e., compressive strength and MOE) compared with NAC mix.    Keywords:  Recycled aggregates concrete, Casting method, Compressive behavior, UPV  1. INTRODUCTION  Construction and Demolition (C&D) waste has been increasing rapidly in the recent years because of rapid urbanization process. In China, on average 200 million tonnes of C&D wastes are produced annually [1]. To avoid problem of environmental pollution due to C&D waste, exploring different methods for its effective management is presently a hot topic of research in different parts of the world. One of the best possible solutions is to recycle C&D waste and use it as recycled concrete aggregates in new concrete known as Recycled Aggregate Concrete (RAC). To fulfil the needs of ever-growing construction industry, it is observed that the annual consumption of natural concrete aggregates has increased significantly, and it has resulted in scarcity of their natural resources and a negative impact on our ecosystem. The use of RAC could also help to reduce burden on the natural resources required to produce concrete aggregates. Due to its high water absorption, low density, and complicated origin, which have been shown to impair the mechanical characteristics of the resulting concrete [2], RAC was first applied to non-structural application (such as landfills) due to its inferior mechanical and durability properties in comparison of NAC. However, many research works have been performed in the recent years to support the structural application of RAC, for instance [3].  Some studies such as [4,5] have demonstrated positive effect of CCT on the properties of RAC. To further strengthen the idea of employing compression casting to get improved properties of RAC, this study aimed to investigate the compressive strength and modulus of elasticity and to check the quality of RAC prepared by CCT through UPV test. The study parameter included casting technique (compression casting versus compaction through vibration) and casting pressure value (i.e., 25 and 35 MPa).  P a g e  | 112  2. MATERIALS AND METHODS 2.1 Materials To prepare concrete mixes, ordinary Portland cement was used. Table 1 and Table 2 provide the chemical composition and properties of cement, respectively. Laboratory-tested concrete specimens (cylinders and cubes) with compressive strengths of 21MPa (3000 psi) to 28MPa (4000 psi) were acquired and crushed with the help of jaw and roller crushers to get Recycled Coarse Aggregates (RCA) of maximum 12 mm particle size and Recycled Fine Aggregates (RFA). RCA were used in SSD conditions. For this purpose, the RCA were soaked in water for one day and before use, their surfaces were wiped off with a cloth to bring them in SSD condition. Locally available natural concrete aggregates were used to prepare NAC mix. Portable water was used for all concrete mixtures.  Table -1: Chemical composition of cement CaO SiO2 Al2O3 Fe2O3 MgO SO3 62.6 % 20.8 % 5.06 % 3.27 % 2.56 % 1.57 %  Table -2: Physical Properties of Cement Fineness Soundness Initial & final setting Standard consistency 8% 9mm 105 - 215 30%  2.2 Mix Proportions In this research investigation, total 5 concrete mixes were made and tested. These concrete mixes varied in terms of type of aggregates (NA & RA), methods of casting (CCT or vibration), and casting pressure (25 and 35 MPa). All RAC mixtures contained 100% recycled aggregates. Table 3 provides detail of all five concrete mixtures.  2.3 Test Specimen Preparations Cylindrical concrete specimens of 150 mm height and 75 mm diameter were prepared in this study using CCT and commonly employed casting method (i.e., through vibration). A customized metallic mold (shown in Figure 1) was designed and fabricated specifically to sustain the load for CCT. After preparation, the concrete mix was poured into the metallic mold in two layers by giving each layer 25 blows with a steel rod. The desired pressure was then applied on concrete through plunger with the help of machine and was maintained for 15 seconds. The sample was subsequently extruded. Additionally, samples were also cast using the conventional casting technique (i.e., through vibration). After air drying for 24 hours, all samples were water cured.  Table -3: Concrete Mix Proportions. Sr. # Designation Cement Content W/C Ratio Casting Pressure in MPa 1 RAC-30F70C 15% by Total weight of Aggregates w/c ratio = 0.5 (Coarse recycled aggregates used in SSD condition) 25 2 35 3 NAC-30F70C 25 4 35 5 RAC-30F70C-V Compaction by Vibration (Conventional method)  2.4 Testing Methods After 28 days of casting, displacement controlled compressive strength tests were performed on all samples. The tests were performed using Universal Testing Machine (UTM) with maximum loading capacity of 1000 kN and at loading rate of 0.5mm/min. Strain gauges were used to measure longitudinal deformation in compression of the test sample which was used to determine the static elastic modulus (E) of concrete in compression following the procedure described in ASTM standard C469. The ultrasonic pulse velocity test was carried out as per ASTM P a g e  | 113  C597. To determine the Ultrasonic Pulse Velocity (UPV) value of each test specimen, standard UPV apparatus as shown in Figure 2, was used. As per standard procedure, time to travel the wave between transmitter and receiver placed at the ends of specimen is measured using standard device and then based on length of each specimen, UPV is calculated. This value is then used to rate the quality of core concrete of test sample.   Fig -1: Metallic Mold   Fig -1: UPV Testing Device/ Apparatus  3. RESULTS AND DISCUSSIONS 3.1 Compressive Strength Chart 1 shows the compressive strength attained by test samples of RAC and NAC mixes prepared by CCT and of RAC mix prepared by conventional casting method. It was observed from these results that with the increase of casting pressure from 25 MPa to 35 MPa, the compressive strength of RAC as well as NAC was increased; an increase of 21% and 7% in compressive strength was observed for RAC and NAC, respectively. The compressive strength of NAC was found to be higher than RAC at both casting pressures. The results presented in Figure 3 also showed that the vibrated RAC samples were not able to achieve compressive strength equal to or greater than RAC samples prepared by CCT. This finding clearly demonstrated the beneficial effects of compression casting technique on the compressive strength. PlungerEnd BlockHollow CylinderP a g e  | 114   Chart -1: Compressive Strength 3.2 Modulus of Elasticity (E Value) Modulus of elasticity values exhibited by RAC and NAC are presented in Chart 2, where the results showed that the modulus of elasticity of concrete is improved with the increase of casting pressure from 25 MPa to 35 MPa; an increase of 29% and 5.5% in the E value was observed for RAC and NAC, respectively. As evident from the Figure 4 that the E value of NAC was significantly higher than RAC at both casting pressures. At 25 MPa casting pressure, E value of RAC prepared by CCT was similar to that of vibrated RAC, however, at 35 MPa casting pressure the E value exhibited by RAC prepared by CCT was 30% higher than the value attained by vibrated RAC. The E value results made it obvious that CCT has a favorable impact on the compressive response of RAC.  Chart -2: Modulus of Elasticity Values 3.3 Ultrasonic Pulse Velocity (UPV) Values of Ultrasonic Pulse Velocity (UPV) of RAC and NAC samples prepared by CCT, and vibrated RAC are presented in Table 4 and their qualitative assessment is done following the criteria suggested by [6,7] based on UPV value. As per this criterion, the quality of RAC mixes prepared by CCT and vibration in this study has been rated as good while the quality of NAC is rated as excellent. Future research may be carried out to develop relationship between UPV value and compressive strength of RAC prepared by CCT for field use. It is important to mention here that criteria for concrete quality based on UPV suggested by [6,7] is for vibrated concrete. The same has been employed here for the quality assessment of compressed concrete. It is suggested that in future comprehensive experimental study may be carried out to design criteria to access the quality of compressed recycled aggregate concrete based on UPV value. 051015202525 MPa (CCT) 35 MPa (CCT) VibratedCompressive Strength (MPa)Casting TechniqueRAC NAC05101520253025 MPa (CCT) 35 MPa (CCT) VibratedModulus of Elasticity (GPa)Casting TechniqueRAC NACP a g e  | 115  Table-4: Ultrasonic Pulse Velocity test results Sr. No Mix Designation Cement dosage Casting pressure, MPa UPV ((km/s) Quality 1 RAC-30F70C 15% by Total weight of Aggregates 25 4.053 Good 2 35 4.215 Good 3 NAC-30F70C 25 4.504 Excellent 4 35 4.626 Excellent 5 RAC-30F70C-V Vibrated Concrete 3.995 Good  4. CONCLUSIONS The study reported in this paper was carried out to investigate the effect of casting technique on the compressive strength and modulus of elasticity concrete made by 100% replacement natural aggregates with recycled aggregates. Ultrasonic pulse velocity test was employed to check the quality of RAC prepared by CCT and commonly employed casting method (i.e., through vibration). For comparison purpose, samples were also prepared using NAC and tested for the same properties. The experimental results obtained in this study made it possible to draw the following conclusions:  • The compressive strength of RAC is improved by compression casting. Increase in casting pressure from 25 to 35 MPa results in 21% enhancement in the compressive strength of RAC. • Positive impact of casting technique on the modulus of elasticity of RAC is linked with higher casting pressure. Compared to vibrated RAC, an improvement of 30% in the E value of RAC prepared by 35 MPa casting pressure, was attained.  • NAC mix exhibits higher compressive strength and modulus of elasticity than RAC mix. • Qualitative assessment of RAC and NAC prepared by CCT through UPV test was consistent with their compressive strength results.   ACKNOWLEDGEMENT The financial support to carry out this research study provided by the Higher Education Commission (HEC) of Pakistan under HEC-NRPU Project No. 9764 is highly acknowledged.  REFERENCES  [1] Yang H, Zhao H, Liu F. Residual cube strength of coarse RCA concrete after exposure to elevated temperatures. Fire Mater, 2018. 42(4): p. 424–35.  [2] Geng Y, Wang Q, Wang Y, Zhang H. Influence of service time of recycled coarse aggregate on the mechanical properties of recycled aggregate concrete. Material and Structures, 2019. 52, 97. [3] Zhihua, C., Jingxin, C., Yansheng, D., Yutong, Z., Zhilu, Z., Yongqi, L. & Linshan, Z. Seismic behaviors of tailings and recycled aggregate concrete-filled steel tube columns, Construction and Building Materials, 2023. Volume 365, 130115 [4] Hameed, R., Zaib-un-Nisa, Riaz, M. R. and Gillani, S.A.A. Effect of compression casting technique on the water absorption properties of concrete made using 100% recycled aggregates, 2022. Revista de la Construcción. Journal of Construction, 21(2), p. 387-407. [5] Yuva, S., Biruktawit, T., Tarekegne & Toshiharu, K. Recycling of hardened Cementitious Material by Pressure & Control of Volumetric Changes. Journal of Advanced Concrete Technology, 2016. Volume 14, p. 47-54.  [6] R.F. Feldman. Non-Destructive Testing of Concrete, 1977. CBD-187, National Research Council of Canada, Ottawa, Ontario [7] J.R. Leslie, W.J. Cheeseman. An ultrasonic method for studying deterioration and cracking in concrete structures, ACI Material Journal, 1949. 46 (2): p. 17–36. 

Effect of Casting Technique on the Compressive Behaviour of Fully Recycled Aggregate Concrete

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Effect of Casting Technique on the Compressive Behaviour of Fully Recycled Aggregate Concrete

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