An approach to improve compressive strength of cement paste at low temperature by carbonation curing

Abstract

Portland cement showed a lower hydration rate and compressive strength development under lower temperature environment. In this paper, a novel approach to improve compressive strength of cement paste at low temperature by carbonation curing was put forwarded. The compressive strength of cement pastes under water-curing and CO2-cuirng at low temperature (5 °C) are both investigated. X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) were employed to analyze the phase changes in carbonated cement pastes. Scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) was adopted to examine the changes of morphologies and Mercury Intrusion Porosimeter (MIP) was used to analyze the pore structure of carbonated cement pastes. The results showed that the 1 d and 28 d compressive strength of carbonated samples was 18.2 % and 54.1 % higher than the values in hydrated samples at the corresponding ages. The 3 d compressive strength of carbonated sample was similar to the hydrated samples cured at 28 d. Calcium silicate hydrate (CSH), ettringite and portlandite (Ca(OH)2) were formed in hydrated sample, while calcium carbonate (CaCO3) and silica gel were generated in carbonated sample. The Ca(OH)2 was increased from 7.9 % (1 d) to 11.3 % (28 d) in hydrated samples, while the CaCO3 was increased from 20.9 % at 1 d to 37.7 % at 28 d in carbonated samples. The total porosity was reduced from 19.7 % in hydrated sample to 17.1 % in carbonated sample at 28 d. Furthermore, carbonation curing reduced the most probable pore diameters in comparison to hydrated samples. The needle-like ettringite was observed in hydrated sample, while typical prismatic calcite crystal was generated in carbonated samples. This paper confirmed that CO2 curing at low temperature could be an effective and promising way to obtain rapid compressive strength improvement.