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Case Study of Concrete Pedestrian Blocks with Crumb Rubber and Steel Fibres

Overview

• A study focused on the properties of rubberized concrete pedestrian blocks utilizing crumb rubber from recycled waste tyres, reinforced with steel fibres.

• Conducted by Chalermphol Chaikaewa, Piti Sukontasukkulb, Udomvit Chaisakulkieta, Vanchai Satac, and Prinya Chindaprasirtc associated with various engineering universities in Thailand.

• Aimed to address issues related to discarded tyres and enhance the mechanical properties of pedestrian blocks.

Key Terminology

• Crumb Rubber: Product derived from recycling old tyres, used to enhance concrete properties.

• Rubberized Concrete: Concrete that uses crumb rubber to improve certain performance metrics.

• Steel Fibres: Tungsten or steel strands added to the concrete matrix to improve strength and durability.

• Slip Resistance: The ability of a material to not slide when force is applied, important for safety in pedestrian areas.

Introduction

• Global usage of concrete pedestrian blocks manufactured through a pressing technique is discussed.

• Highlights the challenges of high rates of discarded tyres leading to environmental concerns in Thailand.

• Rubberized concrete blocks reportedly have good energy absorption but low load resistance, hence the need for enhancement through steel fibre incorporation.

• The study investigates the impact of adding short steel fibres at fractions of 0.5% and 1.0% on mechanical properties such as density, flexural strength, and slip resistance.

Research Context

• Thailand contributes significantly to rubber production worldwide, with about 85-90% of produced rubber being exported.

• An estimated 50 million tyres become waste annually due to regular tyre changes for registered vehicles in Thailand.

• Utilization of waste tyres presents opportunities for material recycling, including applications in construction materials.

Materials and Methodology

Materials Used

• Portland Cement Type I: Standard used for the concrete mixture.

• River Sand and Chipped Rock: Aggregates included in concrete composition.

• Commercial Grade Crumb Rubber: Specific properties carefully determined for testing.

• Steel Fibres: Two sizes (35 mm, 65 mm) utilized to assess performance at varied concentrations.

Mix Proportions

• Plain Concrete (PC):

  • Mix ratio: Cement : Fine Aggregate : Coarse Aggregate : Water = 1 : 1.5 : 1.5 : 0.35

• Rubberized Concrete (RC):

  • Crumb rubber replaces fine aggregates at 10% and 20% by volume.

• Steel Fibre Reinforced Rubberized Concrete (SFRRC):

  • Incorporates steel fibres at both 0.5% and 1.0% volume fractions.

Experimental Tests Conducted

• Specific Gravity and Absorption Tests: Conducted as per ASTM standards to measure density and pore absorption.

• Slip Resistance Tests: Performed using the BS7976 Pendulum slip testing method to determine slip potential under wet conditions.

• Flexural Tests: Utilized to measure flexural load capacity and behavior under stress using a standard UTM method.

• Field Abrasion Tests: Assessed the durability and resistance to wear of various block types under practical conditions.

Results and Discussion

Specific Gravity and Absorption

• The results indicated that specific gravity decreased and absorption increased with higher crumb rubber content, resulting in more porous material characteristics.

• The addition of steel fibres slightly increased the density but also enhanced absorption due to increased interfacial transition zones.

Slip Resistance

• All tested blocks maintained low to extremely low risk of slipping, with PTV values indicating safety levels. The crumb rubber contributed to a reduction in slip resistance with increasing content.

• The presence of steel fibres did not significantly alter slip resistance under the conditions tested.

Flexural Performance

• Traditional PC exhibited a brittle failure, whereas rubberized versions showed improved ductility owing to the presence of crumb rubber, allowing for crack bridging after peak load failure.

• SFRRC blocks displayed superior performance, with higher strength and improved toughness attributed to fibre reinforcement, with longer fibres providing the best results.

Abrasion Resistance

• PC blocks demonstrated lower weight loss than rubberized versions, indicating better abrasion resistance. SFRRC blocks exhibited improved resistance to wear with increasing fibre content. The steel fibres provided enhanced bonds at the micro-level due to their stronger properties compared to rubber.

Conclusion

• The study affirmed the effectiveness of incorporating steel fibres within rubberized concrete blocks for enhancing mechanical properties like flexural strength and toughness while improving their energy absorption characteristics.

• The applications of these findings underline a significant potential to reuse discarded tyres while simultaneously enhancing material properties suitable for construction applications.

• Future studies could explore optimizing the mix proportions and fibre orientations for further enhancements in the properties of rubberized concretes.