Effect of acidic and sulfated environments on phase transformation, compressive strength and microstructure of natural rubber latex-modified cement pastes

Abstract

This study investigated the influence of aggressive acid and sulfate media on the phase transformation of cement materials to which natural rubber latex was added. After 28 days of curing underwater, all samples were subjected to sulfuric acid (H2SO4) and sodium sulfate (Na2SO4) solutions for 0, 7, 14, or 28 days. After that, X-ray diffraction (XRD) was used for phase identification. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to confirm the chemical functionally of the samples. The microstructure and elemental composition were also studied using scanning electron microscopy (SEM) and energy X-ray dispersive spectroscopy (EDS), respectively. XRD data showed no evidence of any clear relationship in rubber-modified cement pastes between any phase transformation and natural rubber content. FTIR results confirm the presence of portlandite, calcite, gypsum and C–S–H phases and indicate interaction between the rubber and cement phases. The inclusion of natural rubber latex in cement led to formation of a water channel structure of the bassanite phase (CaSO4 0.625H2O) after 14 and 28 days of exposure to sulfuric acid solutions. Bassanite (CaSO4 0.5H2O) and the water channel structures of bassanite were not found in the samples after sodium sulfate attack. Based on the results of compressive strength tests, it was suggested that an optimal ratio (rubber/cement = 11.11%) enhanced the stability of cement paste after acid and sulfate exposure. From SEM images, a major change in morphology was observed for samples exposed to H2SO4 compared to those subjected to Na2SO4.