Surface modification of crumb rubber and its influence on the mechanical properties of rubber-cement concrete

• Oxidation and sulphonation introduced strong polarity groups to crumb rubber surface.
• The surface modification generated a strong chemical bond between rubber and cement matrix.
• The mechanical properties of rubber concrete were improved due to the surface modification.

In this paper, a surface modification method was proposed to introduce strong polarity groups to rubber surface to generate a strong chemical bond between the rubber and the cement matrix. Rubber was first oxidized with KMnO4 solution and then sulphonated with NaHSO3 solution. The Fourier transform-infrared (FT-IR) spectra and contact angle measurement showed that the oxidation and sulphonation process introduced a large number of hydrophilic hydroxyl and sulfonate to crumb rubber and decreased the contact angle between rubber surface and water, thus greatly improved the interfacial bonding strength between crumb rubber and cement paste. After the rubber surface modification, the adhesion strength of the rubber and cement paste was increased by 41.1%. It was also found in the mechanical tests that the rubber surface modification was quite useful to enhance the compressive strength and impact strength of rubber-cement concrete. The compressive strength of the concrete with 4% modified rubber powder was 48.7% higher than that with ordinary rubber powder. Based on the results, it is concluded that the surface modification of crumb rubber with KMnO4 and NaHSO3 solutions is an effective method to improve the mechanical properties of rubber-cement concrete.