Plain concrete cylinders and beams externally strengthened with natural flax fabric reinforced epoxy composites

The use of bio-composites as construction and building materials will be beneficial for the development of sustainable construction industry. This study evaluated the performance of natural flax fabric reinforced epoxy polymer (FFRP) composites as external strengthening materials for concrete elements. A total of 24 plain concrete cylinders and beams with and without FFRP reinforcement were tested under uni-axial compression and four-point bending. The considered FFRP thicknesses were 2, 4 and 6 layers of the fabric. Microstructures of flax/epoxy and FFRP/concrete interfaces were analysed by scanning electronic microscope (SEM). Test results indicate that in axial compression, FFRP as external strengthening material enhanced peak strength, strain, fracture energy and ductility of the concrete cylinders remarkably, i.e. the increase in strength and fracture energy by 6-layer FFRP is 134 and 2570 %, respectively. Experimental peak strength of the strengthened specimens were compared with the predictions by existing strength equations. A strength equation was proposed to predict the ultimate compressive strength accurately. In flexure, FFRP strengthening increased lateral load, deflection, flexural strength and fracture energy of the concrete beams significantly, i.e. the increase in peak load and fracture energy by 6-layer FFRP is 374 and 4660 %, respectively. SEM studies showed the good interfacial bond between FFRP and concrete because of the epoxy adhesive. The study therefore concluded that the woven FFRP composite is a suitable material for external strengthening of concrete structures.

[1]  H. Toutanji.  STRESS-STRAIN CHARACTERISTICS OF CONCRETE COLUMNS EXTERNALLY CONFINED WITH ADVANCED FIBER COMPOSITE SHEETS , 1999 .

[2]  It Meng Low,et al.  Microstructures and mechanical properties of hemp fabric reinforced organoclay–cement nanocomposites , 2013 .

[3]  L. C. Hollaway,et al.  Key issues in the use of fibre reinforced polymer (FRP) composites in the rehabilitation and retrofitting of concrete structures , 2011 .

[4]  L. Lorenzis,et al.  Bond of Fiber-Reinforced Polymer Laminates to Concrete , 2001 .

[5]  Arlindo Silva,et al.  Green composites: A review of adequate materials for automotive applications , 2013 .

[6]  Liang Huang,et al.  Compressive behavior of concrete confined by CFRP and transverse spiral reinforcement. Part A: experimental study , 2016 .

[7]  Libo Yan,et al.  Effect of alkali treatment on vibration characteristics and mechanical properties of natural fabric reinforced composites , 2012 .

[8]  Hota V. S. GangaRao,et al.  Critical review of recent publications on use of natural composites in infrastructure , 2012 .

[9]  Libo Yan,et al.  Effect of triggering and polyurethane foam-filler on axial crushing of natural flax/epoxy composite tubes , 2014 .

[10]  Libo Yan,et al.  Effect of column parameters on flax FRP confined coir fibre reinforced concrete , 2014 .

[11]  Nawawi Chouw,et al.  Effect of UV and water spraying on the mechanical properties of flax fabric reinforced polymer composites used for civil engineering applications , 2015 .

[12]  Nawawi Chouw,et al.  On energy absorption capacity, flexural and dynamic properties of flax/epoxy composite tubes , 2014, Fibers and Polymers.

[13]  L. Lorenzis,et al.  BOND OF FRP LAMINATES TO CONCRETE , 2001 .

[14]  Libo Yan,et al.  A comparative study of steel reinforced concrete and flax fibre reinforced polymer tube confined coconut fibre reinforced concrete beams , 2013 .

[15]  Faiz Shaikh,et al.  Characteristics of hemp fabric reinforced nanoclay–cement nanocomposites , 2014 .

[16]  R. Olivito,et al.  Development of durable cementitious composites using sisal and flax fabrics for reinforcement of masonry structures , 2014 .

[17]  Theodoros C. Rousakis.  Elastic Fiber Ropes of Ultrahigh-Extension Capacity in Strengthening of Concrete through Confinement , 2014 .

[18]  Yan Xiao,et al.  Compressive Behavior of Concrete Confined by Carbon Fiber Composite Jackets , 2000 .

[19]  Stephanie L. Walkup,et al.  Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (ACI 440.2R-02) , 2005 .

[20]  Libo Yan,et al.  Behavior and analytical modeling of natural flax fibre-reinforced polymer tube confined plain concrete and coir fibre-reinforced concrete , 2013 .

[21]  Renato S. Olivito,et al.  Flax and polyparaphenylene benzobisoxazole cementitious composites for the strengthening of masonry elements subjected to eccentric loading , 2015 .

[22]  Theodoros C. Rousakis,et al.  Hybrid Confinement of Concrete by Fiber-Reinforced Polymer Sheets and Fiber Ropes under Cyclic Axial Compressive Loading , 2013 .

[23]  Nawawi Chouw,et al.  Lateral crushing of empty and polyurethane-foam filled natural flax fabric reinforced epoxy composite tubes , 2014 .

[24]  Kypros Pilakoutas,et al.  Axial compressive behavior of concrete actively confined by metal strips; part A: experimental study , 2010 .

[25]  Nawawi Chouw,et al.  Crashworthiness characteristics of flax fibre reinforced epoxy tubes for energy absorption application , 2013 .

[26]  A. Machida,et al.  Fiber-Reinforced Polymer Composites for Construction—State-of-the-Art Review , 2002 .

[27]  T. Rousakis,et al.  Substandard reinforced concrete members subjected to compression: FRP confining effects , 2008 .

[28]  Libo Yan,et al.  Flax fibre and its composites – A review , 2014 .

[29]  Kent A. Harries,et al.  BEHAVIOR AND MODELING OF CONCRETE SUBJECT TO VARIABLE CONFINING PRESSURE , 2002 .

[30]  Xiaowen Yuan,et al.  Improving the mechanical properties of natural fibre fabric reinforced epoxy composites by alkali treatment , 2012 .

[31]  Nawawi Chouw,et al.  Natural FRP tube confined fibre reinforced concrete under pure axial compression: A comparison with glass/carbon FRP , 2014 .

[32]  Libo Yan,et al.  Dynamic and static properties of flax fibre reinforced polymer tube confined coir fibre reinforced concrete , 2014 .

[33]  M. Feng,et al.  Stress-strain model for concrete confined by FRP composites , 2007 .

[34]  J. Teng,et al.  Design-oriented stress–strain model for FRP-confined concrete , 2003 .

[35]  J. Teng,et al.  Intermediate Crack Debonding in FRP-Strengthened RC Beams: FE Analysis and Strength Model , 2007 .

[36]  Ralejs Tepfers,et al.  Behaviour and capacity of CFRP-confined concrete cylinders subjected to monotonic and cyclic axial compressive load , 2007 .

[37]  L. Lorenzis.  Some recent results and open issues on interface modeling in civil engineering structures , 2012 .

[38]  Amir Mirmiran,et al.  Model of Concrete Confined by Fiber Composites , 1998 .