The author would like to thank and express gratitude to Allah, the Almighty, for His blessings that made it possible to carry out the research as planned and achieve desirable results. Recycled concrete aggregate (RCA) can be an alternative to using natural aggregate (NA) in concrete production. The recycling of demolished concrete into aggregates for the production of Recycled Concrete (RAC) is environmentally beneficial by conserving natural resources, by reducing waste and by conserving landfill space.
Usually the mechanical properties and durability of recycled aggregate concrete are inferior to natural aggregate concrete (NAC) prepared with the same concrete mix design. This research presents the effect of superplasticizer on the mechanical properties and durability of recycled aggregate concrete. Two types of recycled aggregates, namely recycled stone aggregate (RSA) and recycled brick aggregate (RBA) were used in the research.
The test results obtained were encouraging to use superplasticizer for improving the mechanical and durability properties of recycled aggregate concrete. The durability property, assessed by the total charge passing through the samples in the RCPT test, decreases by 5-30% and 11-17%, respectively, for recycled stone and brick aggregate concrete for the considered aggregate replacement.
57 Figure 3.24 Static modulus of elasticity test setup in the laboratory 58 Figure 3.25 Schematic diagram of the ultrasonic pulse velocity (UPV) test. 59 Figure 3.26 Ultrasonic Pulse Velocity (UPV) Test Setup in Laboratory 60 Figure 3.27 Schematic Diagram Rapid Chloride Permeability Test Setup 61 Figure 3.28 Rapid Chloride Permeability Test Setup in Laboratory 62 Figure 4.1 Compressive strength of RSAC without superplasticizer at. 77 Figure 4.12 Effect of superplasticizer on the modulus of elasticity RSAC 79 Figure 4.13 Effect of superplasticizer on the modulus of elasticity RBAC 80 Figure 4.14 Relationship between compressive strength and modulus of elasticity.
LIST OF TABLES
LIST OF ABBREVIATIONS
INTRODUCTION
The lack of natural resources will push up the price of aggregates and concrete's reputation as an inexpensive building material will be at risk. The best alternative in this regard will be the recycling and reuse of waste concrete to produce recycled aggregate which in turn will be used for the production of recycled aggregate concrete (RAC). An experimental program will be conducted to determine the effect of superplasticizer on the mechanical properties and durability of recycled aggregate concrete (RAC).
A total of 224 cylinders and 42 cubes will be prepared by replacing natural aggregate with recycled stone aggregate and recycled brick aggregate at different percentages such as and 100%. Half of the prepared concrete samples will be mixed with superplasticizer with an assumption of 15% reduction of mixing water. Rapid Chloride Ion Penetration Test (RCPT) will be performed at 90 days to evaluate the durability of the prepared concrete samples.
Density, absorption and voids in hardened concrete will be determined at 90 days to establish a correlation with durability. In addition, a non-destructive test such as Ultrasound Pulse Velocity (UPV) will be used to evaluate the strength and quality of concrete.
LITERATURE REVIEW
Evaluation of source: The properties of recycled aggregate concrete largely depend on the properties of parent concrete. Consequently, one of the key factors controlling the quality of recycled concrete aggregates and, indeed, the performance of recycled concrete, is the quality and quantity of attached mortar (Pedro et al., 2014). This is due to the different qualities of the original waste (this property is influenced by initial aggregate density) as well as the number of crushing procedures that the concrete waste goes through.
Several studies have found that the resistance of recycled aggregates to crushing, impact and wear is lower than that of new aggregates, due to the separation and crushing of the porous mortar layer of the recycled aggregate during testing (Haitao and Shizhu, 2015). This is because the water/cement ratio of the original concrete is less essential than the wear loss value of the natural aggregate it contains (Zega et al., 2010). The grades and amount of recycled concrete aggregate can affect the compressive strength of recycled aggregate concrete.
For virtually every w/c ratio evaluated, the data for 30% RCA follows the data for 0% RCA, however, the data for 100% RCA lie at compressive strength levels around 5. The compressive strengths of RCA mixes differ from normal concrete at the lowest w/c ratios. According to Exteberria et al. 2007), the improvement can be attributed to greater absorption of the mortar associated with the recycled aggregate and an effective ITZ, indicating a solid bond between the aggregate. 2013) conducted an experimental study on recycled aggregate concrete (RAC) observing the effect on mechanical properties such as compressive strength and split tensile strength of concrete containing coarse aggregate recycled from waste concrete (in different percentages of 25%, 50% and 100%).
They made the concrete using recycled aggregate from existing masonry or concrete for and using 100% of the aggregate.
MATERIALS AND METHODS
Coarse aggregate is one of the essential components of concrete and occupies the largest volume in the mixture. The amount of superplasticizer used was 0.7% by weight of the cement content in the concrete mixes. Using the path length L (ie the distance between two probes) and the travel time T, the pulse velocity (V = L/T) is calculated.
RESULTS AND DISCUSSIONS
For recycled brick aggregate concrete without superplasticizer after 28 days the compressive strength has decreased and 33.04% corresponding to 25%, 50% and 100% replacements of natural stone aggregates with recycled brick aggregates. For natural aggregate concrete containing 100% natural stone aggregate, the compressive strength increases due to superplasticizer at different curing ages. The splitting tensile strength of natural aggregate concrete (NAC), recycled stone aggregate concrete (RSAC) and recycled brick aggregate concrete (RBAC) was investigated at 28 days of curing age according to ASTM C496.
Figures 4.6 and 4.7 graphically show the effect of superplasticizer on the splitting tensile strength of natural stone concrete, recycled stone concrete and recycled stone concrete at 28 days of curing age. For natural aggregate concrete containing 100% natural stone chips, splitting tensile strength increases by 15.38% due to superplasticizer at 28 days of curing age. For recycled stone aggregate concrete containing 25%, 50% and 100% recycled stone chips, the splitting tensile strength is correspondingly increased by 5.0% respectively due to superplasticizer.
And for recycled brick aggregate concrete containing 25%, 50% and 100% recycled brick chips, the corresponding tensile strength increases by and 5.88% respectively due to the superplasticizer at 28-day curing age. Figures 4.12 and 4.13 graphically present the effect of superplasticizer on the static modulus of elasticity of natural stone aggregate concrete, recycled stone aggregate concrete and recycled brick aggregate concrete at the age of 28 days. For natural aggregate concrete containing 100% natural stone chips, the static modulus of elasticity increases by 10.42% due to the superplasticizer at the 28-day curing age.
And for the recycled brick aggregate concrete containing 25%, 50% and 100% recycled brick chips, the corresponding modulus of elasticity increases by and 22.01%, respectively due to the inclusion of the superplasticizer at the 28-day curing age . For concrete with recycled stone aggregate with superplasticizer at 28 days, the pulse rate is reduced and 9.89% corresponding to 25%, 50% and 100% replacement of natural stone aggregate with recycled stone aggregate. The bulk and apparent density of recycled aggregate concrete were investigated at 90-day curing age.
For recycled stone aggregate concrete containing 25%, 50% and 100% recycled crushed stone, the corresponding water absorption after immersion decreases by 29.35% respectively due to the addition of superplasticizer. Figures 4.29 and 4.30 graphically illustrate the effect of superplasticizer on permeable voids of stone aggregate concrete, recycled stone aggregate concrete, and recycled brick aggregate concrete after a curing age of 90 days. For recycled stone aggregate concrete containing 25%, 50% and 100% recycled crushed stone, the corresponding volume of permeable voids decreases by 4.6% respectively due to the addition of superplasticizer.
And for recycled brick concrete containing 25%, 50% and 100% recycled stone chips, the corresponding amount of permeable voids decreases by 3.51%, respectively, due to the use of superplasticizer. Figures 4.35 and 4.36 graphically represent the effect of superplasticizer on the chloride ion permeability of natural stone aggregate concrete, reclaimed stone aggregate concrete and recycled brick aggregate concrete at 90 days curing age.
CONCLUSIONS AND RECOMMENDATIONS
Chloride ion permeability of recycled aggregate concrete was reduced due to the use of superplasticizer. The mechanical and durability properties of concrete from recycled aggregate largely depend on the properties of the base concrete. The effect of different types of superplasticizers on the mechanical and durability properties of recycled aggregate concrete should be studied to observe the variation in test results.
K., (2018) "Construction and demolition waste generation and properties of recycled aggregate concrete: a global perspective," Journal of Cleaner Production, vol. Corinaldesi, (2010) "Mechanical and elastic behavior of concrete made from recycled concrete coarse aggregates," Construction and Building Materials, vol. Q., (2006) "Test Study on the Resistance to Chloride Ion Penetration of Recycled Aggregate Concrete." Journal of Wuhan University of Technology, vol.
G., (2017) “Experimental study on the modification of recycled aggregate concrete by nano-SiO2”, Concrete, vol. 1977) “Concrete Waste as Aggregate for New Concrete”, ACI Journal, Vol. González-Taboada, I., González-Fonteboa, B., Martínez-Abella, F., Carro-López, D., (2016) "Study of the quality of recycled concrete aggregate and its relationship with the compressive strength of recycled concrete using database analysis," Materiales de Construccion, Vol.66 (323), e089. Jaturapitakkul, C., Somna, R., Rattanachu, P., and Chalee, W., (2012) "Effect of Ground Bagasse Ash on the Mechanical and Durability Properties of Recycled Aggregate Concrete," Material and Design, Vol.
Hirsch, (2007) "Impact of the zeta potential of early cement hydration phases on the adsorption of superplasticizers", Cement and Concrete Research, vol. 2004) “Sustainability of recycled concrete aggregate: a safe path to sustainable development”, Cement and Concrete Research, Vol. Pedro, D., de Brito, J., and Evangelista, L., (2014) “Influence of the use of recycled concrete aggregates from different sources on structural concrete”, Construction and Building Materials, vol. Padmini, A.K., Ramamurthy, K., and Mathews, M.S., (2009) "Influence of parent concrete on the properties of recycled aggregate concrete", Construction and Building Materials, vol.
Pavlu, T., Boehme, L., and Hajek, P., (2014) "Influence of recycled aggregate quality on the mechanical properties of concrete," Communications, vol. Experimental studies on high strength concrete using recycled coarse aggregate”, Research Inventory: International Journal of Engineering and Science, vol.4, issue 01, pp. Tavakoli, M., and Soroushian, P., (1996) “Strengths of aggregate concrete made using field-demolished concrete as aggregate,” ACI Materials Journal, vol. 2014) “Effects of Nanoreinforcement Technology on Durability of Recycled Concrete,” Concrete, vol.
