Optimization of the formulation of micro-polymer concretes Murhaf Haidar a , Elhem Ghorbel a , Houssam Toutanji b,⇑ a University of Cergy Pontoise, 5 Mail Gay-Lussac, Neuville sur Oise, 95031 Cergy Pontoise Cedex, France b University of Alabama in Huntsville, Dept. of Civil and Environmental Eng., Huntsville, AL, USA article info Article history: Received 9 July 2010 Received in revised form 4 October 2010 Accepted 23 October 2010 Available online 24 November 2010 Keywords: Micro-polymer concrete Mechanical characteristics Porosity Formulations Microstructure Epoxy abstract This research investigates the optimization of micro-polymer concretes (MPC) formulations in order to produce a construction material that has excellent physical and mechanical properties, such as minimum void content, high Young’s modulus and excellent strength properties. An epoxy resin reinforced with a graded mixture of coarse and fine sands is used as a binder to design the micro-polymer concretes. Effects of curing time and binder contents were evaluated through ultrasonic wave propagation method and flexural, compressive, direct and tensile tests, performed at room temperature. The porosity of different MPC formulations as well as the distribution of the voids size is investigated as a function of curing time using mercury intrusion porosimeter (MIP). Results show that with increasing the binder content, the total pore volume and the maximum pore size are reduced significantly. The kinetics and the mechanisms of diffusion of water in MPC depend strongly on the mass fraction of resin. All the mechanical properties of MPC stabilize after 3 days curing at ambient temperatures. The micro-polymer concrete designed with a polymer content of 9% shows the highest physical and mechanical characteris- tics such as strengths, rigidity, the lower voids content and thus the best durability. The experimental results reveal that the mechanical behavior of MPC is time dependent. Scanning Electronic Microscopy (SEM) was applied to observe the microstructure and the porosity and to understand the failure mechanism of MPC. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The mechanical performance of polymer concretes strongly depends on the nature of the matrix (i.e. thermoplastic, thermoset- ting), the reinforcement (sand, gravel, fillers, fibers) and the quality of the adhesion between the components. Polymer concrete (PC) is made by replacing a part or all of the hydraulic cement binder of conventional mortar or concrete with polymers. If partial replace- ment is made, the replacement would be intended to strengthen the hydraulic cement binder with polymers [1]. This study focuses on concrete that is made with an epoxy resin. The epoxy resin was used as a substitute for the Portland cement binder. The initial applications of PC, in the late 1950s, were the production of build- ing cladding and cultured marble. However, its excellent properties such as bond with aggregates and steel reinforcement, high strength, excellent durability, fast curing time, and very low permeability made PC a very attractive material. Hence, polymer concrete has mainly been used for industrial flooring, retouching of damaged concrete structures, underground pipes [2] and for civil engineering applications where high strength, fast cure and durability are required [3]. Overlays in polymer concrete, for bridge surfaces and floors, have also become widely used to resist chem- ical and frost attacks. Precast components are another excellent use of the material. Polymer concrete is particularly attractive as a repair material because of its high strength, moldability and ability to form complex shape [4]. Several studies were carried out to optimize the formulations of PC to reduce the cost and to improve the mechanical properties. Most of them dealt with polymer mortar (PM). In the work of Gorninski et al. [5], polymer mortar was pro- duced using orthophtalic and isophtalic polyester mixed with river medium sand and fly ash. The concentrations of polymer used were 12% of orthophtalic polyester and 13% of isophtalic polyester by weight of the dry materials. The results demonstrated that the addition of fly ash to PM reduced voids and increased the packing of the aggregate–ash skeleton resulting in an increase in compres- sive strength of PM as the fly ash content increased. Moreover, it appears that PM produced with isophtalic polyester resulted in slightly higher mechanical properties. In a separate work Gorninski et al. [3] confirmed that the use of fly ash in polymer mortar pre- pared with the same concentration of orthophtalic and isophtalic resins improves the compressive and flexural strengths and the durability conducted under chemical attack. They showed that all the PM compositions exhibited higher strength values when 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.10.010 ⇑ Corresponding author. Fax: +1 2568246724. E-mail addresses: Haidar.Murhaf@u-cergy.fr (M. Haidar), elhem.ghorbel@ u-cergy.fr (E. Ghorbel), toutanji@cee.uah.edu (H. Toutanji). Construction and Building Materials 25 (2011) 1632–1644 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat